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ArticleLiterature Review
Algal biomass dehydration
Abstract
Biofuels are viewed as promising alternatives to conventional fossil fuels because they have the potential to eliminate major environmental problems created by fossil fuels. Among the still developing biofuel technologies, biodiesel production from algae offers a greater prospect for large-scale practical use, as algae are capable of producing much more yield than other biofuels. While research on algae-based biofuel is still in its developing stage, extensive work on laboratory- and pilot-scale algae harvesting systems with promising prospects has been reported. This paper presented a discussion of the literature review on recent advances in algae separation, harvesting and drying for biofuel production. The review and discussion focus on destabilization of algae, algae harvesting technologies and algae drying processes. Challenges and prospects of algae harvesting are also outlined.
... (d) Filtration: It is a process to isolate alga biomass from the liquid culture medium by using a porous membrane with various particle size ranges [22]. It can be implemented through three different ways: conventional, microfiltration and ultrafiltration (isolation of metabolites). ...
... Algae biomass is immediately processed to the following stage after being separated from the culture medium to prevent spoilage or to extend their shelf-life [22]. Three different types of drying or dehydration process that are normally used include sun-drying, spray-drying and freeze-drying. ...
... This technique is solely based on the solar energy which causes limitations in terms of weather condition, long drying period and the large drying area needed [24]. Since drying using sunlight is an uncontrollable process, the problem of overheating may occur, change of texture, colour and taste of the microalgae [22]. ...
Microalgae are known as a rich source of bioactive compounds which exhibit different biological activities. Increased demand for sustainable biomass for production of important bioactive components with various potential especially therapeutic applications has resulted in noticeable interest in algae. Utilisation of microalgae in multiple scopes has been growing in various industries ranging from harnessing renewable energy to exploitation of high-value products. The focuses of this review are on production and the use of value-added components obtained from microalgae with current and potential application in the pharmaceutical, nutraceutical, cosmeceutical, energy and agri-food industries, as well as for bioremediation. Moreover, this work discusses the advantage, potential new beneficial strains, applications, limitations, research gaps and future prospect of microalgae in industry.
... The perishable nature of microalgae makes it necessary to dry microalgae after harvest to prevent spoilage (Klein et al., 2018). After microalgae are harvested, the dewatered microalgae slurry is dried for end-use, stability, extraction and further processing (Show et al., 2013). The drying parameters affect the chemical properties of the biomass (Sahoo et al., 2017). ...
... Pyrolysis of microalgae with high moisture contents could yield bio-oil with high water contents, high concentrations of oxygenated compounds, and low viscosity, all of which can contribute to instability during storage (Lehto et al., 2013). (Chen et al., 2011;Show et al., 2015Show et al., , 2013 Rotary drying Slope rotating cylinder (movement of content by gravity) ...
... High cost of energy to operate dryer (Delrue et al., 2012;Show et al., 2013) Flash drying ...
Biofuels can be derived from waste biomass feedstocks, such as municipal, agricultural, forestry and industrial waste. There are several advantages in switching to microalgae for biofuel production. Microalgae has a rapid growth rate, so is more productive, so requires smaller areas for cultivation per unit of biomass produced. Microalgae can absorb “waste” CO2, does not compete with food crops (for land and freshwater), and can be cultivated in wastewater, doubling as a wastewater treatment. This paper gives an overview of microalgae cultivation, focusing on the early energy-intensive stages: growth, harvesting and drying. The harvesting and drying steps constitute a significant economic bottleneck, due to their high energy costs. This review also covers microalgal cultivation and its integration with wastewater treatment, carbon and energy sources, and the utilization of microalgal biofuel co-products from thermochemical conversion, as this route is the most likely to mitigate the techno-economic downsides of microalgal biofuel production.
... Additionally, filter press systems that utilize flocculants and other dewatering enhancing agents (polymers) also have worked well with algae and have been successfully used. 153,154 In either case, dewatering to levels between 15% to 30% solids is achieved using either of these systems. 155,156 Other harvesting processes have been used or are being studied 147,157,158 with none of these being proposed as often as centrifuges and filters. ...
... 105,155 A wide variety of commercial driers has been used or proposed for use in the drying of microalgae. 153,159,160 Some smaller operations have used simple air-drying, 161 but in most commercial-scale systems, this option is very land and processing time intensive. Depending on the lipid extraction system used, targeting of final solids levels for the final algae cakes at or above 90% is not uncommon. ...
... 162,163 Example systems include rotary dryers, 164 spray dryers, 165 freeze-dryers, 166 conveyor dryers, 159 drum dryers, 162 sun drying, 59 or even solar-powered dryers. 153 In essence, other than the capability to achieve targeted solids concentration (often being at or beyond 90% solids), costs are by far the most important parameter (of course, thermal breakdown of proteins is to be considered as well, but most economical systems do not heat to that level for economic reasons). In fact, drying costs can represent as much as 60% of total processing costs. ...
Microalgae is envisioned by many experts to be one of the key future feedstocks for producing transportation fuels and other chemical products. The concept has many positive aspects inclusive of being fully renewable, minimal carbon footprint, and able to be implemented in low value agricultural lands. There has been a tremendous amount of developmental work done to commercialize the concept since the mid-1900s; however, the reality is that the cost for a gallon of microalgae oil is still too expensive to be considered a viable option to produce bio-based diesels at this time. Expanding the production of more than one or two products from a microalgae biorefinery is an economic must. Products derived from the algal cake must be developed and commercialized to offset the high cost of oil production. This paper will investigate the status of the concept and provide insight into directions needed to improve economic viability.
... (d) Filtration: It is a process to isolate alga biomass from the liquid culture medium by using a porous membrane with various particle size ranges [22]. It can be implemented through three different ways: conventional, microfiltration and ultrafiltration (isolation of metabolites). ...
... Algae biomass is immediately processed to the following stage after being separated from the culture medium to prevent spoilage or to extend their shelf-life [22]. Three different types of drying or dehydration process that are normally used include sun-drying, spray-drying and freeze-drying. ...
... This technique is solely based on the solar energy which causes limitations in terms of weather condition, long drying period and the large drying area needed [24]. Since drying using sunlight is an uncontrollable process, the problem of overheating may occur, change of texture, colour and taste of the microalgae [22]. ...
Microalgae are known as a rich source of bioactive compounds which exhibit different biological activities. Increased demand for sustainable biomass for production of important bioactive components with various potential especially therapeutic applications has resulted in noticeable interest in algae. Utilization of microalgae in multiple scopes has been growing in various industries ranging from harnessing renewable energy to exploitation of high-value products. The focuses of this review are on the isolation of bioactive compounds from microalgae regarding different metabolites which are currently used and new possible applications of the compounds in industries and future prospects. Moreover, this work discusses the advantage, potential new beneficial strains, applications, limitations, research gaps and future prospect of microalgae in industry.
... The algal residue of Chlorella sp. was harvested by the centrifugation at 3000 rpm, and was washed three times to get dry biomass [204]. Different types of centrifuge are used such as nozzle type, solid-ejecting disc, solid-bowl-decanter and multi chamber centrifuges [201,205]. The choice of centrifugation process depends on cell size and harvesting efficiency [206]. ...
... EPS causes the fouling/clogging of filter/membrane depending on surface charge, cell size, cultural age and membrane type. Biofouling, energy requirement and high capital and operation costs challenge the feasibility of filtration process [205]. Membrane fouling can also resolved by using counter-current or turbulent flow, NaClO washing and other suitable flowing velocities [212]. ...
... There are different types of floatation based on bubble size such as dissolved air flotation, dispersed flotation, electro flotation and ozone flotation. Dissolved air flotation can be used for small sized and lighter algal cells harvesting [205]. Bubble size (10-100 µm) is desired in dissolved air flotation. ...
Conventional wastewater treatment technologies are energy-intensive and environmentally un-friendly due to the use of synthetic and expensive chemicals. This study investigates the potential of macroalgae and coal-based biochar (control) to remove methylene blue from simulated wastewater as well as real textile wastewater. The macroalgae and coal-based biochars adsorb more than 90% of methylene blue from simulated wastewater in only 10 min on their active surface sites. The distinct feature of the current study is that macroalgae-based biochar shows high dye removal efficiency (75%) even in real textile wastewater. Macroalgae-based biochar also shows 67% dye removal efficiency for second regeneration cycle. Langmuir isotherm (> R2 = 0.954) and pseudo-second-order models (R2 = 0.999) are well fitted to describe the monolayer homogenous biosorption and process kinetics, respectively. Thermodynamic analysis indicates that methylene blue biosorption on macroalgae and coal-based biochars is a spontaneous and endothermic process following physiosorption. The maximum biosorption capacity with macroalgae-based biochar is 353.9 mg g−1 at 303 K, which is approximately 27% higher than any previous biochar study on the treatment of methylene blue. It demonstrates that macroalgae-based biochars can be used as a promising alternative adsorbent to activated carbon for textile wastewater treatment.
Graphical abstract
... To avoid its decomposition and so that it can be stored, the biomass must be dried. Drying achieves to concentrate biomass up to 85% to 95% in dry solids [34,35]. Several drying techniques exist such as solar drying, spray, convection, and freeze-drying; however, the use of these techniques also depends on the final use of the biomass and some of them still have limitations to be used on a large scale. ...
... This can be achieved by drying in the sun, in a drum dryer, spray drying, freeze-drying, or any other technique that allows the removal of moisture in the biomass [11,29]. In this stage, two drying techniques were considered, spray drying and the drum dryer, since they are the two techniques with a large-scale application for drying a great variety of microalgae, Case E1 and E2, respectively [34,35]. In this stage, it was possible to concentrate the biomass up to 992.74 g/L and with a final humidity of approximately 5% (w/w), for both cases. ...
The cultivation of microalgae has become a viable option to mitigate increase in CO2 in the atmosphere generated by industrial activities since they can capture CO2 as a carbon source for growth. Besides, they produce significant amounts of oils, carbohydrates, proteins, and other compounds of economic interest. There are several investigations related to the process, however, there is still no optimal scenario, since may depend on the final use of the biomass. The objective of this work was to develop a techno-economic evaluation of various technologies in harvesting and drying stages. The techno-economic estimation of these technologies provides a variety of production scenarios. Photobioreactors were used considering 1 ha as a cultivation area and a biomass production of 22.66 g/m2/day and a CO2 capture of 148.4 tons/ha/year was estimated. The production scenarios considered in this study have high energy demand and high operating costs (12.09–12.51 kWh/kg and US $210.05–214.59/kg). These results are mainly a consequence of the use of tubular photobioreactors as a biomass culture system. However, the use of photobioreactors in the production of microalgal biomass allows it to be obtained in optimal conditions for its use in the food or pharmaceutical industry.
... In the production of microalgae biodiesel, it is necessary to first extract the oil from the dried biomass so that the transesterification reaction performs successfully later. The oil extraction rate of dried bio-feedstock is significantly higher than that of wet bio-feedstock [75]. ...
... Typical drying methods include rotary, spray, solar, freeze, cross-flow, vacuum, flashing, incinerator, and toroidal [75]. However, from an economic point of view, the huge energy demand in the drying process has brought great challenges to the feasibility of microalgae biofuel production [76][77][78]. ...
Microalgae biofuel is expected to be an ideal alternative to fossil fuels to mitigate the effects of climate change and the energy crisis. However, the production process of microalgae biofuel is sometimes considered to be energy intensive and uneconomical, which limits its large-scale production. Several cultivation systems are used to acquire feedstock for microalgal biofuels production. The energy consumption of different cultivation systems is different, and the concentration of culture medium (microalgae cells contained in the unit volume of medium) and other properties of microalgae vary with the culture methods, which affects the energy consumption of subsequent processes. This review compared the energy consumption of different cultivation systems, including the open pond system, four types of closed photobioreactor (PBR) systems, and the hybrid cultivation system, and the energy consumption of the subsequent harvesting process. The biomass concentration and areal biomass production of every cultivation system were also analyzed. The results show that the flat-panel PBRs and the column PBRs are both preferred for large-scale biofuel production for high biomass productivity.
... After recovery or collection, the dewatered slurry is dried for reuse, final usage, extraction, or further processing by separating the algae from the support product. Dry algae fed to the press will significantly promote the production of algae oil that could then be refined into biodiesel (Show et al., 2013). Also, the most practicable drying methods should be prepared to avoid the possible deterioration of the fragile nature of the algae resulting from the dehydration process. ...
... The goal is to produce the commodity at a reasonable cost and with ease of operation. This would render the development of biodiesel economically viable by extracting and cost-effectively drying large quantities of algae (Chen et al., 2011;Show et al., 2013). The following sections address various strategies of drying algae, such as rotary drying, spray drying, solar drying, cross-flow drying, vacuum drying, and flashing drying. ...
Research Article Abstract: Rapid human population growth has led to a rise in energy consumption, which is expected to increase by 50% or more by 2050. Natural oil cannot keep up with the existing usage rate, which has already been reported to be 100 times higher than nature can produce. Moreover, the use of fossil energy is devastating to our climate by greenhouse gas pollution and global warming. The quest for 'clean' energy has now become the biggest obstacle. A variety of solutions are currently being researched and introduced. Micro-Algae-based fuels are perceived to be the most sustainable, clean, reliable, and environmentally friendly solution to climate change and food protection, as well as the only renewable energy alternative capable of satisfying global demand for fuels in the long term. The goal of this analysis is therefore to recapitulate the existing work on the potential for micro-algal biofuel development and to explore alternative ways of bringing it into effect.
... Several centrifugal approaches such as a decanter, disc stack centrifuge, multichamber centrifuge, hydroclone, and the nozzle type centrifuge can be applied for microalgae separation. Among these types of centrifuges, some of them are carried out as a step separation process, while others need preconcentrated steps [65]. Disc stack centrifuge is suitable for separating material with 3-30 µm of particle sizes and can concentrate the suspensions from 2% to 25% solid content [2]. ...
... Membrane filtration is suitable for dewatering and harvesting of fragile cells. It has the ability to dewater microalgae at a very low cell density [65], whereas microfiltration and ultrafiltration are effective at dewatering smaller algae [59]. The dewatering of microalgae can be achieved by applying these membranes to the tangential flow filtration system (TFF). ...
Microalgae are an excellent source of bioactive compounds for the production of a wide range of vital consumer products in the biofuel, pharmaceutical, food, cosmetics, and agricultural industries, in addition to huge upstream benefits relating to carbon dioxide biosequestration and wastewater treatment. However, energy-efficient, cost-effective, and scalable microalgal technologies for commercial-scale applications are limited, and this has significantly impacted the full-scale implementation of microalgal biosystems for bioproduct development, phycoremediation, and biorefinery applications. Microalgae culture dewatering continues to be a major challenge to large-scale biomass generation, and this is primarily due to the low cell densities of microalgal cultures and the small hydrodynamic size of microalgal cells. With such biophysical characteristics, energy-intensive solid–liquid separation processes such as centrifugation and filtration are generally used for continuous generation of biomass in large-scale settings, making dewatering a major contributor to the microalgae bioprocess economics. This article analyzes the potential of electroflotation as a cost-effective dewatering process that can be integrated into microalgae bioprocesses for continuous biomass production. Electroflotation hinges on the generation of fine bubbles at the surface of an electrode system to entrain microalgal particulates to the surface. A modification of electroflotation, which combines electrocoagulation to catalyze the coalescence of microalgae cells before gaseous entrainment, is also discussed. A technoeconomic appraisal of the prospects of electroflotation compared with other dewatering technologies is presented.
... The final drying process used was determined by the size of the operating condition as well as the end use of the dried product. In a study comparing spray drying and drum drying methods for microalgae to produce bio-fuel (high lipid content), the latter was suggested due to greater digestibility, reduced energy consumption, and cheaper investment [44]. ...
... The stirring motor in a 2,500L PBR requires 4.65 kWh, while spray cleaning needs 7.35 kWh[30]. The system's power consumption for membrane filtration and rotary drum dryer was set at 2.23kWh/m 3[57] and 33.6kWh (evaporates 18.2 kg of water for every kilogram of dry algal product), respectively[44]. Secondly, the cultivation site was considered to be an indoor facility similar to the laboratory testing. ...
Scaling up algal cultures to large volumes for commercial production is a challenging task that involves high capital and operating cost. Hence, the feasibility of a laboratory scale culture process is important to be tested, before expanding the production. This study aims to investigate the scaling up of Chlorella vulgaris, FSP-E cultivation by discovering the best culture pathway using life cycle assessment, LCA. The study also emphasize on the techniques that can be used in large-scale algal operations, for photo-bioreactor cleaning and maintenance. Culture mediums plays a significant role in overall costing for microalgae growth processes, and their supply were addressed during the scaling up cultivation systems in terms of flow mixing, pipeline costing. Cradle to gate LCA technique was used in this study considering every phase in the lifecycle, starting from culture medium, carbon dioxide (CO2), air, and water supplies for microalgae growth till end-product dried biomass generation, including storage. Three growth media applications were compared between (1) BG-11, a chemical-based medium; (2) a combination of biscuit waste from a dairy processing facility with BG-11; and (3) re-cycling of Path 2's residual culture medium after harvesting. The results indicated that recycling of remaining culture water obtained from dried biomass back into the photo-bioreactor was identified to be the most sustainable Chlorella vulgaris production process that can be considered for a commercial facility for bio-fuel production.
... The choice of harvesting techniques primarily depends on the morphology and size of the strain, the density of the culture and the desire final product [27]. The most extended methods for harvesting are filtration, centrifugation, flocculation, flotation, and sedimentation [27,32]. Forthwith, the biomass needs to be dried to avoid degradation of algal quality [32]. ...
... The most extended methods for harvesting are filtration, centrifugation, flocculation, flotation, and sedimentation [27,32]. Forthwith, the biomass needs to be dried to avoid degradation of algal quality [32]. The technique applied varies according to the quality and quantity of the final product, the scale and the relation of the capital and production costs in terms of capital investment and the energy requirement. ...
Cyanobacteria, also called blue-green algae, are a group of prokaryotic microorganisms largely distributed in both terrestrial and aquatic environments. They produce a wide range of bioactive compounds that are mostly used in cosmetics, animal feed and human food, nutraceutical and pharmaceutical industries, and the production of biofuels. Nowadays, the research concerning the use of cyanobacteria in agriculture has pointed out their potential as biofertilizers and as a source of bioactive compounds, such as phycobiliproteins, for plant pathogen control and as inducers of plant systemic resistance. The use of alternative products in place of synthetic ones for plant disease control is also encouraged by European Directive 2009/128/EC. The present up-to-date review gives an overall view of the recent results on the use of cyanobacteria for both their bioprotective effect against fungal and oomycete phytopathogens and their plant biostimulant properties. We highlight the need for considering several factors for a proper and sustainable management of agricultural crops, ranging from the mechanisms by which cyanobacteria reduce plant diseases and modulate plant resistance to the enhancement of plant growth.
... The chemotrophic organisms can cultivate in phototrophic fermenters and obtain energy in the presence of sunlight. Phototrophic organisms generally cultivate in the closed photobioreactors as well as open pond system (Anto et al. 2020;Show et al. 2013). ...
... Microalgae and their role in various categories of biofuel production be digested anaerobically. Other methods are also available such as thermal degradation and gasification method (Show et al. 2013). ...
... In fact, there are many technologies for harvesting microalgae including filtration, flotation, flocculation, sedimentation, and centrifugation or any combination thereof [4,5]. But most of those harvesting technologies are not superior because they are either labor-intensive, energy-consuming or environmentally unfriendly [6][7][8][9][10]. ...
... While the fluid velocities induced by aeration could be expressed by the following equation: (12) where v y is the fluid velocity at the separation distance of y, v max is the maximum velocity in the middle between two membrane, b is the separation distance between two membrane and m is the exponent (4)(5)(6)(7)(8)(9). In this study m was arbitrarily set as 4. ...
Membrane fouling is a main problem in algae harvesting and retarding membrane fouling is significant to increase filtration efficiency and reduce harvesting cost. The aeration membrane system could mitigate membrane fouling by the coarse bubbles and the vibration membrane system could produce high shear by the vibration of membrane to mitigate fouling. In the critical flux experiment, the aeration membrane had a low critical flux of 34 L/(m²h) compared with the vibration membrane (49 L/(m²h)). After experiencing 12-h continuous filtration, the flux decline rates of vibration and aeration membrane were 3.6% and 46%, respectively. Based on the Extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory, the free energy of fouled vibration and aeration membranes were −53.76 and −62.51 mJ/m², respectively, indicating that vibration could better reduce the interaction of algae cells and membrane, compared with aeration. Moreover, vibration also had a better effect on the rejection of extracellular organic matter (EOM), which could reduce secondary pollution of the water body. The different working mechanism of vibration and aeration acting on membrane was draw, suggesting that the fluid velocity induced by vibration mainly acting on membrane surface could decrease membrane fouling, while the fluid velocity induced by aeration basically could not act on membrane.
... The process of filtration is made up of a porous medium that retains solid particles and allows the escape of liquids [11]. Filtration process can be categorized into different types of filtration (including magnetic, pressure, membrane, tangential flow, vacuum, and crossflow) that is applicable for microalgae harvesting [12]. Soomro et al. [13] highlighted yield and input in terms of the energy of various filtration types applied for microalgae dewatering from various studies. ...
... It is imperative to avoid the addition of the high concentrations of minerals during the harvesting process because they may cause toxicity in the harvested biomass. Moreover, they can interfere with subsequent downstream processes [12,32], as they should inevitably be removed from the biomass. ...
This chapter attempts to highlight and describe the
current technologies published in recent studies, aimed to cut down on the cost ofmicroalgae downstream process, which thus in return can lead to the price reduction of microalgae-derived products including bioenergy products. Downstream processes of microalgal biomass into bioproducts are subdivided into three parts: (1) harvesting and dewatering; (2) extraction; and (3) fractionation and conversion [4]. An overview of the microalgal products including biodiesel, biogas, hydrogen, pigments, and fatty acids, as end products of those downstream processes, is also highlighted in this chapter.
... The chemotrophic organisms can cultivate in phototrophic fermenters and obtain energy in the presence of sunlight. Phototrophic organisms generally cultivate in the closed photobioreactors as well as open pond system (Anto et al. 2020;Show et al. 2013). ...
... Biomass of microalgae and macroalgae can Microalgae and their role in various categories of biofuel production be digested anaerobically. Other methods are also available such as thermal degradation and gasification method (Show et al. 2013). ...
Biofuels are considered as alternative of fossil fuels. Nowadays, conventional fuels like as petrol, diesel, and liquid petroleum gas (LPG) are the major sources of energy. The sources of fossil fuels are limited on the Earth crust and will be finished after a certain period of time. Biofuels like bioethanol, biomethanol, biogas, biohydrogen, and biodiesel are derived from various types of biological sources (plant, algae, microbial biomass) and considered as renewable sources of energy. They are green energy sources and cost-effective and also considered as alternative of fossil fuel in the future. They can be classified into several categories such as first, second, third, and fourth generations based on the source of production. There are several methods that are currently used for the production of biofuels by utilization of several biomasses. The microorganisms such as microalgae, cyanobacteria, and fungi play an important role in the production of biofuels. These microorganisms provide suitable raw materials as well as involved bioconversion of biomass during production of biofuels. This chapter is focused on the brief introduction of biofuels and role of microorganism in the biofuel production.
... However, flotation can be more rapid and effective than sedimentation (Milledge and Heaven, 2013). Furthermore, this technique has relatively short operation times and requires low space equipment and lower initial equipment costs (Garg et al., 2012;Show et al., 2013). Although some microalgal strains naturally float to the surface when their lipid content increases, in most cases, flocculants need to be added to improve flotation efficiency (Gultom and Hu, 2013). ...
Microalgae and cyanobacteria have a wide range of applications, going from food industry to wastewater treatment. Although microalgal cultivation has been studied for more than half a century, their applicability in large scale is still prohibitive. Microalgal harvesting remains a critical point due to microalgae small size, high growth rates (which implies frequent harvesting), and the higher costs and energy consumption. In this sense, immobilization methods have been applied to microalgae to solve the problems associated to suspended growth systems. Accordingly, microalgal biofilms emerged as a cost-effective and ecologically safe solution, as they can remove nutrients and heavy metals from wastewaters and also produce biomass that can be used for the production of valuable compounds. A detailed description of microalgal applications, harvesting techniques, and biofilm formation is reviewed in this chapter. Additionally, the application of microalgal biofilms on wastewater treatment is discussed in more detail.
... The biomass collected (approximate concentration of biomass of 200 g/L and with an approximate content of 80% humidity) is perishable and must undergo additional processes for storage or convert it to other products immediately [32]. A drying or dehydration stage is necessary [33], which must reach a concentration of approximately 90% in dry solids of biomass, to increase the stability of the biomass and obtain greater efficiency in the extraction of oils (or any other use). The above can be achieved by drying in the sun, in a drum dryer, spray drying, freeze drying, or any other technique that allows for moisture to be removed from the biomass [6,28]. ...
A current concern is the increase in greenhouse gas emissions, mainly CO2, with anthropogenic sources being the main contributors. Microalgae have greater capacity than terrestrial plants to capture CO2, with this being an attraction for using them as capture systems. This study aims at the techno-economic evaluation of microalgae biomass production, while only considering technologies with industrial scaling potential. Energy consumption and operating costs are considered as parameters for the evaluation. In addition, the capture of CO2 from a thermoelectric plant is analyzed, as a carbon source for the cultivation of microalgae. 24 scenarios were evaluated while using process simulation tools (SuperPro Designer), being generated by the combination of cultivations in raceway pond, primary harvest with three types of flocculants, secondary harvest with centrifugation and three filtering technologies, and finally the drying evaluated with Spray and Drum Dryer. Low biomass productivity, 12.7 g/m2/day, was considered, achieving a capture of 102.13 tons of CO2/year in 1 ha for the cultivation area. The scenarios that included centrifugation and vacuum filtration are the ones with the highest energy consumption. The operating costs range from US $ 4.75–6.55/kg of dry biomass. The choice of the best scenario depends on the final use of biomass.
... A significant barrier to the development of industry based around macroalgal production is the design of energy efficient and well-controlled drying systems that can transition freshly harvested biomass into a product suitable for storage and transport. The drying step of a process was recognised as the single biggest energy usage for the processing of algal biomass, due to the large amounts of moisture requiring removal [13]. The drying step can constitute up to 70-75% of processing costs in some cases. ...
Algae-based products have applications in the food and pharmaceutical industries, bioremediation of waste streams and biofuel production. Drying has been recognised to constitute the largest energy cost in algae processing, yet there is limited data or modelling characterising the drying kinetics of macroalgae. This research modelled the equilibrium moisture content of two macroalgae species, Ulva ohnoi, a saltwater alga and Oedogonium intermedium, a freshwater alga. The Guggenheim–Anderson–de Boer model was found to best represent experimental equilibrium moisture contents. Drying rate curves obtained under both convective and radiative conditions were fitted to an analytical solution of Fick’s second law, including the modelled equilibrium moisture values. Effective diffusivity values for the two species are presented.
... It has been reported that the autocoagulation of algal cell at high pH is induced more by the process of inorganic precipitates formation and not just by pH value alteration [6]. Therefore, the harvested biomass contains high concentrations of the specific inorganic precipitate [18], which often vitiates the application of the harvested biomass in other downstream operations. Thus far, no toxicity has been associated with calcium contamination. ...
Highly efficient and sustainable algae harvesting that produced biomass with enhanced characteristics and reusable culture medium were developed from the use of coagulant derived from the waste shell of Gastropod. Thermally treated Gastropod shell samples were screened for the algal cell harvesting efficiency (%) and the underlying mechanism was elucidated from the hydrodynamic equilibrium data and scanning electron microscopic analysis. The floc strength, settling rate parameters, settleability, and filterability were determined and compared with the flocs obtained from the pH induced autocoagulation system. The values of floc settling rate and the sludge volume index (mL/g) showed that the flocs obtained from the Gastropod shell system (rate constant = 1.945 L·mol⁻¹·s⁻¹) settled faster and more compacted than those from the pH induced system (rate constant = 0.2155 (L·mol⁻¹·s⁻¹). Both the growing and harvested flocs from the Gastropod shell system had better strength and breakage factors (>90%) than the pH induced system. The proximate and elemental compositions of the biomass from the Gastropod shell system were comparable with those from centrifugation and pH induced systems. Both the separated culture medium and the harvested algae biomass were successfully reused, in separate systems, to cultivate fresh algae. This indicated the non-toxic effects of the coagulants on both the culture medium and the algae harvested biomass.
... In most cases the main factors that influence this choice are energy efficiency and installation and operation costs. However, if the dried microalgal biomass is produced to human alimentation, the preservation of nutritional and functional components of the biomass must be also considered [22,23]. ...
... is value could be due to drying methods and drying time [49]. On the contrary, the packaging and the storage conditions might have an indirect influence on the humidity rate. ...
The present study aimed to characterize the nutraceutical properties and the antimicrobial effect of Moroccan Spirulina (Arthrospira platensis). The nutritional composition was evaluated, including water content, crude protein, total carbohydrates, lipids, phenolic composition, macro- and micromineral content, fiber content, and energy value. Then, the microbiological analysis and antioxidant activity were measured. The antimicrobial activity was evaluated using the minimum inhibitory concentration method on bacteria and fungi. Moroccan Spirulina contained a large amount of protein (76.65 ± 0.15%), followed by carbohydrates (6.46 ± 0.32%), minerals (20.91 ± 0.88%), crude fiber (4.07 ± 1.42%), lipids (2.45 ± 0.82%), ash (14.56 ± 0.74), and twenty phenolic acids being identified and quantified. Moreover, flavonoid and phenolic contents were present at 15.60 ± 2.74 mg RE/g dw and 4.19 ± 0.21 mg GAE/g dw, respectively. Microbiological risk assessment indicated that this product is safe to be consumed as a human food product. The antioxidant activity was higher in the methanolic fraction (23 mg TE/g dw) (DPPH).
... Biomass water content was below 10% for all Chlorella and Spirulina samples, which enables safe storage (Hosseinizand et al., 2017). Chlorella biomass originating from different producers presented on average a 36% lower water content (3.7%) compared to Spirulina (5.0%), which could be due to producer dependent drying methods and drying times (Show et al., 2013). As expected, the variability between producers was higher for both species compared to the variability between different production batches and within a batch (Figure 4.2 B, C). ...
We are, undeniably, in the midst of a food revolution, driven by necessity rather than societal trends. The global population and standard of living result in a protein demand that outstrips supply. In just over 30 years, we need to produce 50% more protein than is currently available, with increases of 82 and 102% for dairy and meat products, respectively. Yet our conventional food production system already trespassed the boundaries of sustainability and its inefficiency strongly contributes to climate change. Nutrient losses cause eutrophication, environmental pollution and biodiversity loss and the input of resources is already beyond the limits of sustainability. Additionally, phosphate fertilizers, which are essential for food production, are made from phosphate rock, of which the reserves will be depleted within 50 – 100 years if we continue business as usual. The decreasing quality of the remaining apatite will result in an increasing environmental impact of fertilizer production. Finally, our traditional food production model requires 30% of all ice-free land, 70% of all available freshwater and produces up to one third of the global greenhouse gas emission.
This PhD thesis aims to introduce and research microbial protein (MP) as novel hub in the classical food production chain. MP is the protein-rich biomass of microorganisms such as microalgae, bacteria and yeast, which can be applied as sustainable protein source in feed and food. MP are highly attractive for protein production due to their near perfect nutrient conversion efficiency, their high productivity in comparison with traditional crops and their extremely high true protein content (50-70% Dry Weight). They also offer additional functional benefits in terms of vitamins, pigments and potentially prebiotic compounds. The impact of MP introduction in the classical protein production chain can be maximized in two ways: one is the application of side and waste streams as direct or indirect substrate for MP production, researched in Chapter 2 and 3. The other way comprises the optimization of MP production parameters, to maximize biomass quality and productivity, researched in Chapter 3, 4 and 5. Throughout all chapters, biomass quality, productivity and safety for feed and food applications are the key elements of research.
In conclusion, this thesis aids to the development and introduction of MP as novel hub in the classical food production chain. Depending on the produced MP and the final application in animal feed or human food, direct and indirect nutrient recovery strategies were demonstrated to have potential. To improve biomass productivity and quality, process parameters present a wide range of useful tools; however, careful biomass post-processing is equally important to avoid a reduction in biomass quality. Further technological developments and the improvement of social awareness and acceptance, should facilitate the introduction of novel MP in feed and food markets. Here it can represent an important part of the solution in sustainably feeding the growing world population.
... The electro and flotation techniques are not very energy efficient as compared to the sedimentation techniques. Centrifugation and filtration methods can effectively dewater the algal biomass up to 20% (w/w) (Show et al. 2013). These techniques are highly efficient but are energy-intensive and require maintenance, thus make the overall harvesting costly. ...
Establishing cost-effective algal biorefineries is a cornerstone research to enhance the process value by exploiting the full potential of microalgae and utilizing each component (protein, carbohydrates, lipids, and pigments) for biofuel and myriad industrial applications. Additionally, algal biorefineries offer environmental sustainability by reducing atmospheric CO2, greenhouse gases, heavy metals, toxic compounds, and nutrients by utilizing flue gas as carbon source and wastewater as low-cost cultivation media. However, industrial applications of such biorefineries are still at infancy due to various challenges encountered during cultivation, harvesting, downstream processing, incomplete biomass utilization, uncertain nature of adopted technologies, and reduced economic viability. This chapter highlights the key challenges and opportunities to configure optimal algal biorefineries. A combination of integrated-biorefinery and cascading approaches is evaluated to systematically address the challenges. It emphasizes to consider the environmental, technical, and economic aspects to enhance the sustainability of algal biorefinery. Analysis and assessment of current frameworks in terms of raw biomass (especially indigenous algae), cultivation conditions (seasonal influx and wastewater sources), harvesting approaches (chemical and biological), processing technologies, and product-based biorefinery schemes are discussed to design a self-sustainable multiproduct algal biorefinery to achieve commercial robustness.
... Therefore, the selection of harvesting methods is key for the economics of biofuel production [4] . Gravity sedimentation, filtration, centrifugation, flotation, flocculation, and electrolytic methods are currently widely used in microalgae harvesting and recovery [5] . Of all the harvesting methods, flocculation was shown to be most efficient for large-scale harvesting of microalgae [6] . ...
Microalgae are potential candidates for the production of third-generation biofuels, but the high-energy consumption of harvesting biomass makes current commercial microalgal biodiesel production economically unfeasible. Self-flocculation is regarded as a cost-efficient strategy for harvesting microalgae. In this work, a coculture system was developed by the mixotrophic cultivation of two poorly flocculating microalgae, Desmodesmus sp. ZFY and Monoraphidium sp. QLY-1, for self-flocculation of microalgal cells. The flocculation efficiency for harvesting was enhanced to 85.33% with settling for 4 h in coculture, which was better than that in mono-culture (57.98% and 32.45%). Coculture resulted in changes in both the concentration and composition of extracellular polymeric substances (EPS) in the culture, which partially contributed to cell aggregation. The concentration of polysaccharides in LB-EPS ranged from 27.01% and 27.35% in mono-culture to 46.53% in coculture. Moreover, the fine properties of lipid productivity (93.99 mg L ⁻¹ d ⁻¹ ) and fatty acid composition in coculture indicated the potential to produce biodiesel within most biodiesel standards.
... Despite their efficiency, coagulation-occulation techniques, with the use of chemical products, contribute to the increase in environmental impacts. According to Jorquera et al. (2010) and Show et al. (2013), the coagulation-occulation process helps in the separation of microalgae, increasing the efficiency of gravitational sedimentation 30 to 50x and reducing energy consumption in drying. In the present study, there were no environmental impacts from the harvesting stage, but the efficiency of suspended microalgae separation was reduced. ...
Microalgae biomass (MB) is a promising source of renewable energy, especially when the cultivation is associated with wastewater treatment. However, microalgae wastewater technologies still have much to improve. Additionally, microalgae biomass valorization routes need to be optimized to be a sustainable and feasible source of green bioenergy. Thus, this paper aimed to evaluate the environmental impacts of the production of briquettes from MB, cultivated during domestic wastewater treatment. Also, it was evaluated how much the drying of the MB affected the life cycle and the environment. Improvements in the life cycle to mitigate the environmental impacts of this energy route were proposed. Cradle-to-gate modeling was applied to obtain a life cycle assessment (LCA) from cultivation to the valorization of MB, through its transformation into a solid biofuel. With LCA, it was possible to identify which technical aspect of the process needs to be optimized so that environmental sustainability can be achieved. Two scenarios were compared, one with the microalgae growth in a high-rate algal pond (HRAP) (scenario 1) and the other in a hybrid reactor, formed by a HRAP and a biofilm reactor (BR) (scenario 2). LCA highlighted the electric power mix, representing, on average, 60% of the total environmental impacts in both scenarios. The valorization of MB in briquettes needs to consume less energy to offset its yield. The environment suffered pressure in freshwater eutrophication, due to the release of 3.1E-05 and 3.9E-05 kg of phosphorus equivalent; in fossil resources scarcity, with the extraction of 1.4E-02 and 4.5E-02 kg of oil equivalent; and in climate change, by the emission of 1.0E-01 and 1.9E-01 kg of carbon dioxide (CO2) equivalent, in scenarios 1 and 2, respectively. Scenario 1 was highly damaging to terrestrial ecotoxicity, with the release of 3.5E-01 kg of 1,4 Dichlorobenzene, coming from the CO2 used in MB growth. This category was the one that most negatively pressured the environment, differing from scenario 2, in which this input was not required. This was the only impact category in which scenario 2 had a better environmental performance when compared to scenario 1. Cotton, required in scenario 2, represented up to 87% of emissions in some of the evaluated categories. Despite the impacts that occurred in the two modeled scenarios, the environmental gains due to the use of wastewater for microalgae growth, replacing the synthetic cultivation medium, stood out. In the sensitivity analysis, two alternative scenarios were proposed: (i) electricity consumption for drying has been reduced, due to the natural decrease of MB humidity, and (ii) MB briquettes were considered a substitute for coal briquettes. Results indicated that pressures on climate change and fossil resource scarcity were eliminated in both scenarios and this also occurred for freshwater eutrophication in scenario 2. This paper contributes to the improvement and development of converting MB routes into more sustainable products, causing less pressure on the environment. Also, the study contributes to filling a gap in the literature, discussing methods and technologies to be improved, and consequently making microalgae biotechnology environmentally feasible and a potential renewable energy alternative.
... Freeze-drying involves freezing of algal biomass before lowering the temperature to dry up the product. Substances which are heat-labile such as pigments can be dehydrated efficiently with freezedrying than spray-drying method [190][191][192][193]. ...
Microalgae and cyanobacteria (blue‐green algae) are used as food by humans.
They have gained a lot of attention in recent years because of their potential
applications in biotechnology. Microalgae and cyanobacteria are good sources
of many valuable compounds, including important biologically active compounds
with antiviral, antibacterial, antifungal, and anticancer activities.
Under optimal growth condition and stress factors, algal biomass produce
varieties of potential bioactive compounds. In the current review, bioactive
compounds production and their remarkable applications such as pharmaceutical
and nutraceutical applications along with processes involved in
identification and characterization of the novel bioactive compounds are
discussed. Comprehensive knowledge about the exploration, extraction,
screening, and trading of bioactive products from microalgae and cyanobacteria
and their pharmaceutical and other applications will open up new
avenues for drug discovery and bioprospecting.
... Conversely, water-soluble EPS may neutralize cationic flocculants applied to microalgae suspensions. For instance, negatively charged carboxyl groups on polysaccharide chains interact with functional groups on cationic polyelectrolytes, thereby interfering with the microalgae-polymeric flocculant interactions that induce flocculation [58,59]. A few studies have established adverse effects of EPS on polymeric flocculation that surpass the impact of high ionic strength [37,59]. ...
Microalgae biomass is touted as a highly promising source of renewable third-generation biofuels that could enable a lucrative transition from conventional fossil fuels to more sustainable and environment-friendly energy alternatives. A significant limiting step for large-scale microalgae production and utilization is harvesting and dewatering the cultivated biomass, which comprise 20-30% of the total production expenses. Compared to traditional physical harvesting methods, coagulation-flocculation techniques using polyacrylamide-based flocculants have garnered attention as promising alternatives due to their high harvesting efficiencies, cost-effectiveness, convenience, and scalability. This paper delivers an up-to-date progress in the harvesting of microalgae suspensions using various polyacrylamide flocculants. For the first time, a comprehensive evaluation of existing harvesting studies for freshwater and marine microalgae species using polyacrylamide-based flocculants was conducted. The impact of polyacrylamide-based flocculant characteristics (e.g., charge type, charge density, polymer architecture, molecular weight) on flocculation efficiencies was examined. The effect of the culture medium properties (e.g., pH, salinity, microalgae species, microalgae growth phase, cell density, flocculation aids) on polyacrylamide-induced flocculation was also evaluated. Existing pilot-scale and large-scale polyacrylamide-based flocculation studies were explored. The review further identifies the research gaps, key challenges and future prospects for optimizing microalgae flocculation studies.
... There are a variety of centrifugation equipment available on the market, including hydro cyclones, tubular centrifuges, solid-bowl decanter centrifuges, nozzle-type centrifuges, and solids-ejecting disc centrifuges of varied sizes and capacities. However, these were used for microalgae separation from the dilute culture medium (Show et al. 2013). ...
Carotenoids are pigments having a proven role as food colorants, antioxidants, health-promoting substances, food additives, feed additives, vitamins, pharmaceuticals, etc. After experiencing the hazard of synthetic entities in human life, people are again trying to “go natural.” Being natural and part of a healthy ecosystem, microalgae may have immense potential to provide many such entities. In the present scenario, microalgal systems are among the top-ranked bioresources to meet the demands of the fast-growing world population. In addition, being grown in natural water resources provides opportunities to socially backward classes to manage their lifestyle for economic upliftment and nutritional well-being. Carotenoids may be divided into primary and secondary groups. The secondary carotenoids are present in the lipid vesicles in the cytosol or plastids. Also, phycobiliproteins, phycocyanin, phycoerythrins, β-carotenes, lutins, and astaxanthins are the pigments which are commonly produced by microalgae. Many microalgal systems have been investigated so far to produce different pigments, for instance, diatoms and members of Phaeophyceae for fucoxanthins, dinoflagellates for peridinin, cryptophytes for alloxanthins, Porphyridium spp. for β-carotenes, Tetraselmis spp. for lutein, and so on. This chapter aims to provide an overview of the potential of microalgal systems to generate valuable carotenoids and pigments.
... To limit this competition with the food chain, there is a second generation of biofuel (generated from agricultural waste, forest residues, and lignocellulosic biomass, etc.) that is set up [36][37][38][39]. Currently, researchers are studying a third generation of biofuel based on microorganisms or microalgae that are capable of producing biofuels [40][41][42][43][44][45][46]. Coming back to the problem of the phenomenon of cavitation in injectors, biofuels present an additional advantage compared to standard fuels: they are more viscous [47][48][49][50]. ...
Concerning the problem of wanting the performance of heat engines used in the automotive, aeronautics, and aerospace industries, researchers and engineers are working on various possibilities for improving combustion efficiency, including the reduction of gases such as CO, NOx, and SOx. Such improvements would also help reduce greenhouse gases. For this, research and development has focused on one factor that has a significant impact on the performance of these engines: the phenomenon of cavitation. In fact, most high-performance heat engines are fitted with a high-speed fuel supply system. These high speeds lead to the formation of the phenomenon of cavitation generating instabilities in the flow and subsequently causing disturbances in the combustion process and in the efficiency of the engine. In this review article, it is a question of making a state-of-the-art review on the various studies which have dealt with the characterization of the phenomenon of cavitation and addressing the possible means that can be put in place to reduce its effects. The bibliographic study was carried out based on five editors who are very involved in this theme. From the census carried out, it has been shown that there are many works which deal with the means of optimization that must be implemented in order to fight against the phenomenon of cavitation. Among these solutions, there is the optimization of the geometry of the injector in which the fuel flows and there is the type of fuel used. Indeed, it is shown that the use of a biofuel, which, by its higher viscosity, decreases the effects of cavitation. Most of these jobs are performed under cold fluidic conditions; however, there is little or no work that directly addresses the effect of cavitation on the combustion process. Consequently, this review article highlights the importance of carrying out research work, with the objective of characterizing the effect of cavitation on the combustion process and the need to use a biofuel as an inhibitor solution on the cavitation phenomenon and as a means of energy transition.
... Several separation techniques are applied to dewater a microalgal soup. These comprise vacuum separation, magnetic filtration, cross-flow filtration, and pressure filtration (Show et al. 2013). Cells, for instance, typically produce compressible cakes that enhance fluid flow resistance as the differential pressure from across the cake rises. ...
... It greatly prevents the decomposition of compounds that degrade product quality (de Farias Neves et al., 2019). In addition to the aforementioned drying methods, drum drying, roller drying, fluidized bed drying (Fasaei et al., 2018), incinerator drying, flash drying, cross-flow air drying (Show et al., 2015), vortex flashing drying (Show et al., 2013), and infrared drying (Mnasri-Ghnimi & Frini-Srasra, 2019) can be used to dry microalgal slurry. ...
Microalgal research has made significant progress in terms of the high-value-added industrial application of microalgal biomass and its derivatives. However, cost-effective techniques for producing, harvesting, and processing microalgal biomass on a large scale still need to be fully explored in order to optimize their performance and achieve commercial robustness. In particular, technologies for harvesting microalgae are critical in the practical process as they require excessive energy and equipment costs. This review focuses on microalgal flocculation, dewatering, and drying techniques and specifically covers the traditional approaches and recent technological progress in harvesting microalgal biomass. Several aspects, including the characteristics of the target microalgae and the type of final value-added products, must be considered when selecting the appropriate harvesting technique. Furthermore, considerable aspects and possible future directions in flocculation, dewatering, and drying steps are proposed to develop scalable and low-cost microalgal harvesting systems.
... These electrons transfer to PSI, FDX1 and finally hydrogenase enzyme (K.-Y. Y. Show et al., 2013). The procedure is not continuous; as soon as mild length resumes, photosynthetic oxygen is released and prohibited hydrogenase. ...
Hydrogen is a promising future fuel with high energy content for both heat and electrical energy without emission of any hazardous gases such as carbon dioxide or ozone-harming substances. Bio-hydrogen driven from microalgae has recently gained considerable attention. As it is more sustainable than other sources, further developments in such systems are still in their early stages and require improving efficiency and achieving a real-world application on a large scale. This chapter focuses on assessing the potential of microalgae applied sciences for the industrial manufacturing of hydrogen from algae using solar energy. It summarizes the principle key of hydrogen production, the viable and theoretical limits of microalga hydrogen manufacturing systems, and the rising techniques to engineer next-generation structures and how these fitting into a developing hydrogen economy. In addition, it discusses the utilization of a solar collector system for long-range storage of thermal solar energy in dark conditions or winter.
... Freeze-drying involves freezing of algal biomass before lowering the temperature to dry up the product. Substances which are heat-labile such as pigments can be dehydrated efficiently with freezedrying than spray-drying method [190][191][192][193]. ...
Microalgae and cyanobacteria (blue-green algae) are used as food by humans. They have gained a lot of attention in recent years because of their potential applications in biotechnology. Microalgae and cyanobacteria are good sources of many valuable compounds, including important biologically active compounds with antiviral, antibacterial, antifungal, and anticancer activities. Under optimal growth condition and stress factors, algal biomass produce varieties of potential bioactive compounds. In the current review, bioactive compounds production and their remarkable applications such as pharmaceutical and nutraceutical applications along with processes involved in identification and characterization of the novel bioactive compounds are discussed. Comprehensive knowledge about the exploration, extraction, screening, and trading of bioactive products from microalgae and cyanobacteria and their pharmaceutical and other applications will open up new avenues for drug discovery and bioprospecting.
... Lower ash content is indicative of a good quality final product because the ash component may interfere with further biomass processing (e.g., damage to processing equipment) or the final applications of the biomass (e.g., high salt content or impurities for food or feed products) [9]. A previous study also found the biomass obtained from high pH-induced flocculation contained a high concentration of minerals [7,35]. Under a high pH environment, inorganic ions, such as Mg 2+ and Ca 2+ , were also precipitated with flocculant and became a part of the harvested algal paste. ...
Using a commercially scalable system designed for processing thousands of liters a day, here we evaluated the factors that affected the performance, energy consumption and capital/operating costs of both flocculation-based and filtration-based algal harvesting systems over a 16 month period. Coagulation efficiency was the primary driver of harvest efficiency in the flocculation-based method, while cell lysis was important for the filtration-based method. Culture (algae) age differentially influenced harvest efficiency through changes in cell fragility and stickiness. The average energy consumption of the flocculation-based method was 0.389 kWh/m³, while that for the filtration-based method was 4.343 kWh/m³. The average harvesting cost of the filtration-based method was 5.35 $/m³, while for flocculation-based method it was 4.52 $/m³. The concentration factor of filtration-based and flocculation-based method were 770–1086 and 407–448, respectively. For both harvesting methods, labor costs dominated and ranged from 55.84%–67.94% of total cost. Further system automation is a potential method to lower the harvesting cost. The filtration-based harvesting method could produce a better quality of algal biomass with higher concentration factors and less ash content, but needed more energy input, as compared with a flocculation-based method. This study highlights the importance of algal culture status to successful harvesting, and it also provides insight into developing more efficient harvesting technology with lower energy and capital cost.
Drying of Biomass, Biosolids, and Coal: For Efficient Energy Supply and Environmental Benefits provides insight into advanced technologies and knowledge of the drying of biomass, biosolids, and coal in terms of improved efficiency, economics, and environmental impact. It comprehensively covers all the important aspects of drying for a variety of biomass, biosolids and coal resources. This book covers the drying of biomass, bio-solids and coal while also providing integration of the drying process with the energy system. Important issues in the commercial drying operations are tackled, including energy and exergy efficiencies, environmental impact, and potential safety concerns. It also assesses the performance of energy production plants in integration with biomass/coal drying to provide information for plant optimization. It offers in-depth analysis and data for process understanding and design, and analyzes the drying process’s effect on economics and the environment. This book is aimed at drying professionals and researchers, chemical engineers, industrial engineers, and manufacturing engineers. It will also be of use to anyone who is interested in the utilization of biomass, organic solid wastes, algae and low-rank coals for energy.
Macroalgae have many potential applications and can make important contributions to sustainability and circular economy objectives. Macroalgae are degradable high-moisture biomaterials and drying is a necessary step, but drying is an energy and capital-intensive part of their production process. This study presents convective drying curves for commercially promising fresh and saltwater species (U. ohnoi and O. intermedium), obtained over a range of industry-relevant drying gas velocities (0.3–2 m/s) and material bulk densities (33–100 kg/m3). Pragmatic diffusion-based drying models that account for the influence of drying gas velocity, material bulk density, and material shrinkage are presented. Results provide critical insights into the validity of diffusion model assumptions for compressible biomaterials and new mechanisms describing gas penetration into such materials are proposed. The drying models provided in this work demonstrate a high degree of accuracy for both species.
RESUMO: O desenvolvimento de equipamentos eficientes e específicos para a secagem de microalgas é essencial para a exploração comercial destes microrganismos que apresentam alta taxa de crescimento e grande potencial biotecnológico. Os custos de secagem da biomassa de microalgas ainda são elevados e precisam ser reduzidos para a produção de compostos com baixo valor agregado. Portanto, realizou-se o estudo da secagem da microalga Scenedesmus obliquus BR003 utilizando baixas temperaturas. S. obliquus BR003 é uma microalga robusta que apresenta alta produtividade de lipídeos. Em escala laboratorial, observou-se que a biomassa de S. obliquus BR003 foi rapidamente seca em baixas temperaturas entre 50 e 60 ºC. Um secador a gás foi utilizado para avaliar a secagem da biomassa de S. obliquus BR003 em escala piloto. A biomassa foi seca em menos de 24 h utilizando o secador a gás, entretanto, a elevada umidade da biomassa da microalga requereu uma maior renovação de ar na câmara do secador. A análise de fluidodinâmica computacional do secador a gás mostrou dois parâmetros importantes para se obter uma maior efetividade de transferência de calor e massa durante o processo de secagem da biomassa de microalga. Concluiu-se que um secador a gás adequado, para a biomassa de microalgas, deve possuir múltiplos pontos de injeção de ar, e um eficiente sistema de circulação e renovação de ar no interior da câmara de secagem.
The adverse impacts of fossil fuels on the environment, specifically climate change, have intensified the need for finding a sustainable alternative source of energy. Numerous studies have postulated that biotechnology development, focusing on biofuel production processes, could be a suitable solution for sustainable energy production. The utilization of microorganisms, such as microalgae, is one of the basic strategies to produce biodiesel, pharmaceuticals, and nutraceuticals. Co-cultivation has overtaken mono-cultivation to improve the production of microalgae due to its endurance, foreseeability, and stability. However, further development of the co-cultivation process requires elaborate efforts to make it safe, practical, and optimal. Some dominant factors affecting the co-culture system control are the diversity of the cell groups, mass transfer, scale-up, population ratio, and time. In this review article, we will discuss some critical topics related to the co-cultivation process, such as data collection, modelling, cultivation methods, and interaction varieties. An overview of the quantification techniques for biomass concentration and lipid content is also provided. Moreover, the utilization of microalgal co-cultures will be analyzed, depicting the difficulties associated with their efficient control. As knowledge of the reactions and their entailing kinetics is elemental for analyzing the microalgal systems, which are used to synthesize intermediate products and chemicals, some studies focusing on the kinetics of microalgal biomass conversion into biofuels are presented. Since the microbial fuel cells (MFCs), as a new bioelectrochemical process, are utilized in the mixed-culture systems to treat wastewater and produce biofuels and other valuable by-products, a summary of the microalgal MFCs is also provided. Finally, arguments about the challenges and advantages of the co-cultivation systems are presented.
The search for biodegradable plastics has become the focus in combating the global plastic pollution crisis. Polyhydroxyalkanoates (PHAs) are renewable substitutes to petroleum-based plastics with the ability to completely mineralize in soil, compost, and marine environments. The preferred choice of PHA synthesis is from bacteria or archaea. However, microbial production of PHAs faces a major drawback due to high production costs attributed to the high price of organic substrates as compared to synthetic plastics. As such, microalgal biomass presents a low-cost solution as feedstock for PHA synthesis. Photoautotrophic microalgae are ubiquitous in our ecosystem and thrive from utilizing easily accessible light, carbon dioxide and inorganic nutrients. Biomass production from microalgae offers advantages that include high yields, effective carbon dioxide capture, efficient treatment of effluents and the usage of infertile land. Nevertheless, the success of large-scale PHA synthesis using microalgal biomass faces constraints that encompass the entire flow of the microalgal biomass production, i.e., from molecular aspects of the microalgae to cultivation conditions to harvesting and drying microalgal biomass along with the conversion of the biomass into PHA. This review discusses approaches such as optimization of growth conditions, improvement of the microalgal biomass manufacturing technologies as well as the genetic engineering of both microalgae and PHA-producing bacteria with the purpose of refining PHA production from microalgal biomass.
Microalgae have been largely used as a source of human and animal food, essential fatty acids for the treatment and prevention of diseases, and as a source of pigments for natural colorants. They have also been considered a promising feedstock for the production of liquid biofuels, as they can achieve oil yields considerably higher than oilseed crops. However, microalgae-based biofuels are not yet economically feasible due to high operating costs and large energy demands, which result in poor net energy returns and unattractive internal rates of return. Biomass cultivation, nutrient recycling, water usage, and biomass harvesting are critical process issues. Refining the biomass in its various constituents presents an opportunity for making microalgal lipids economically viable for bioenergy production, supported on high added-value co-products. Hence, this review aims to consolidate the public information on microalgal biomass processing and to present an analysis of the best options for integrating individually studied processes in an energy-driven biorefinery. From this analysis, a preliminary proposal of a biorefinery flow diagram is presented, along with recommendations for further research and technology development in the critical areas for accelerating the development of microalgae biorefineries.
Fukushima, northeastern Japan, was damaged by a tsunami and nuclear incident following the March 2011 earthquake. To make effective use of non-arable lands, an examination of biofuel production from native microalgal communities was carried out in Minamisoma city, Japan. After cultivation in open-air raceway ponds, the concentration of suspended solids (SS) of microalgae culture reaches 0.03 wt%. Efficient dehydration of microalgae is, therefore, essential. This study examined a bench-scale dehydration process composed of centrifugation, flocculation and filtration. A continuous centrifuge was used for primary concentration, and 14,600 kg of algal culture was dehydrated. After centrifugation, a cationic trimethylamine-type polymer as flocculant was added to the primary concentrate, and mixed. The mixture was processed by a continuous vacuum filtration and compression, and 12.9 kg of concentrate was obtained with 82.7% recovery. Through this process, SS concentration reached a satisfactory value of 24.6 wt% with the high throughput of 5920 kg/h.
Microalgae have attracted the attention of several researchers, due to the undeniable potential of these microorganisms in several applications. Microalgae can be used in environmental applications, such as CO2 capture from the atmosphere or flue gas emissions, and in the removal of nutrients and pollutants from different wastewaters. They can also be used in the energetic sector, as a renewable energy source. Due to their very rich composition in terms of proteins, vitamins, lipids, polyunsaturated fatty acids, and other valuable compounds, microalgae can be used as raw material for several industries, such as food and feed, pharmaceuticals, and cosmetics.
Despite the advantages of microalgal culturing, commercialization of microalgal biomass and products is still not economically feasible, particularly due to the costs associated to microalgal recovery/harvesting (which typically account for 20%–30% of overall production costs). Microalgal growth in dilute suspensions (0.02%–0.05% dry solids), similar densities between microalgal cells and the culture medium, and small-sized (< 20 μm) negatively charged microalgal cells are among the factors that contribute to a time-consuming and energy-demanding recovery process. Taking into account these challenges, several research studies have focused on the development of effective harvesting techniques for microalgal recovery. Currently, these techniques include gravity sedimentation, flocculation, flotation, centrifugation, membrane separation, or a combination of these. However, the selection of a unique method for microalgal harvesting is a difficult task because it must take into account microalgal cells’ properties, such as morphology, density, and size, and final product specifications. Accordingly, this chapter presents an overview of currently applied techniques for microalgal harvesting, trying to elucidate the advantages and disadvantages of each, and their feasibility according to the target product/market.
Microalgae are currently subject to worldwide investigation as a promising ecological and renewable energy source to meet future energy demand. Microalgae can store lipids up to 75% (w/w) under certain stressed conditions, and the lipid productivity is many folds higher compared to other crop plants used as biofuel feedstocks. However, the production of biofuels from microalgae is still not economical. The upstream process of biofuel production from microalgae involves a number of steps such as strain selection, media formulation, cultivation, harvesting, and drying of algal biomass. Among them, the harvest of microalgal biomass from dilute microalgae culture broth is a very difficult task because of low concentration and small cell size (<20 µm). In addition, the water content in the harvested biomass could cause problems in downstream processes such as oil extraction and transesterification of algal oil to bio-diesel. Therefore, the drying of harvested biomass to reduce moisture content up to a certain extent is necessary to obtain the target product efficiently, enhance oil yield, and reduce production cost. This eventually leads to long time storage and easy transportation of algal biomass. It has been documented that no single method of harvesting can be applicable for all algal species. The choice of technology depends on the physicochemical properties of the algal suspension, process design and fate of end products. Hence, efficient and cost-effective harvesting methods for microalgae heavily affect the overall energy consumption and production cost of microalgal products. In this chapter, we discuss the various techniques used for harvesting, their critical evaluation, and feasibility for algal biomass.
Keywords: Microalgae, Biomass, Biofuel, Harvesting.
Carbon capture and sequestration technologies are used to reduce carbon emissions. Membranes, solvents, and adsorbents are the three major methods of CO2 capture. One of the promising methods is the use of algae to absorb CO2 from flue gases and convert it into biomass. Algae have great potential as renewable fuel sources and CO2 capture using photosynthesis for carbon fixation has also attracted much attention. This paper presents an extensive and in-depth report on the utilization of algae for carbon capture and accumulation. This is done in conjunction with cultivating the algae for the production of biomass for biodiesel production. Different systems are investigated for algae cultivation as well as carbon capture to effectively mitigate carbon emissions. The performance and productivity of these biosystems depend on various conditions including algae type, light sources, nutrients, pH, temperature, and mass transfer. Macroalgae and microalgae species were explored to determine their suitability for carbon capture and sequestration, along with the production of biodiesel. The steps for producing biodiesel were comprehensively reviewed, which are harvesting, dehydrating, oil extraction, oil refining, and transesterification. This technology combines active carbon capture with the potential of biodiesel production.
Membrane fouling caused by the deposition of algae cells and extracellular organic matter (EOM) is a major challenge for algae filtration. To find a suitable membrane pore size for microalgae harvesting, membranes with different pore sizes (0.03, 0.05 and 0.1 μm) were utilized in algae filtration in this study. The 0.1-μm membrane had the highest reversible fouling and the lowest irreversible fouling, in comparison with 0.03- and 0.05-μm membranes; thus, the 0.1-μm membrane was more suitable for algae harvesting than the 0.03-μm and 0.05-μm membranes. The molecular weight distribution of reversible EOM was primarily under 1 kDa whether irreversible EOM was over 100 kDa. Moreover, the larger the pore size, the more likely it was fouled by low molecular weight organics, regardless of reversible fouling or irreversible fouling. Fluorescence excitation-emission matrix spectra analysis showed that for protein-like and humic/fulvic acid-like substances, protein-like substances were more likely to cause reversible fouling while fulvic acid-like substances were more apt to cause irreversible fouling. The 0.1-μm membrane had better repulsion to fulvic acid-like substances than the 0.03- and 0.05-μm membranes, leading to less irreversible fouling. The results obtained from this study have many microalgae applications. For example, employing membrane technology in microalgae harvesting can help treat rivers and promote ecological restoration. In addition, applying this technique in sewage treatment plants will not only lead to wastewater treatment, but it will also acquire biomass resources.
Algal biomass is a versatile raw material for a variety of products such as biofuel, nutraceuticals pharmaceuticals, cosmetics, nutritional and health supplements, and animal feeds. Production of these value‐added products requires algal cultivation and harvesting, followed by drying and disruption of the algal cells for subsequent extraction and processing of the intended products. A major hurdle to engaging algal biomass for large‐scale commercial applications is the high processing costs. Increasing the recovery of intracellular substances from algal cells could result in greater product yields and lower production costs. Drying and milling are two integral processes for effective production of value‐added products from algae. This chapter presents a review on recent advancements in algal cell drying and milling technologies. Technology development, energy requirements, and comparisons of the processing methods are discussed. Challenges and prospects of algae drying and milling for sustainable and viable algal biorefineries are also outlined.
The decline in reserves of fossil fuels has shifted the world towards renewable and sustainable alternatives of fuels. Microalgae a rich source of triacylglycerol are potential candidate for biodiesel production. The rising industrial uses of algae led to the development of different unit operations. Unraveling the biochemistry of compounds present in algae to produce biofuels and byproducts, biomass productivity and efficient extraction of bioactive compounds remains key hurdles. This review brings into light the different cell disruption methodologies, with reduced environmental hazards as caused by conventional methods. The production of lipids for biofuel like biodiesel cannot alone sustain the algae-based economy. Therefore, use of lipid extracted biomass for various other purposes serves it a solution. Lipid Extracted Biomass has numerous applications including production of biofuels like biohydrogen and biogas, biochar, bio-composites, carbon quantum dots, bio-polythene of different densities. It can also be used as animal feed, manure to improve soil fertility and to treat wastewater. The present article discusses the state-of-the-art technologies developed for algal biomass cultivation, harvesting and drying. This comparative discussion on different algal biofuels’ unit operations will help in revelation of associated technological challenges arising during various unit operations; starting from cultivation to lipid extraction and its conversion to biodiesel. This study presents a sustainable solution for extraction of lipids from microalgae by utilizing its byproducts for several different commercial purposes. The study concludes that modifications are required in the conventional approaches of harvesting, drying along with cultivation to improve the bioeconomic potential of algae
Microalgae are being developed as a source of fuels and/or chemicals. A processing challenge is dewatering the algae. Electrical approaches to dewatering include exploiting electrophoresis or electroflocculation. The reported experiments show that electrophoresis does occur but is complicated by the effects of the fluid motion. It appears that the coupling of the algal cell and the fluid can be sufficiently strong such that fluid motion effects can influence or dominate behavior. Electroflocculation appears to be a robust process. It does, however, inherently leave electrically induced trace metal flocculants in the dewatered algae.
Following scrutiny of present biofuels, algae are seriously considered as feedstocks for next-generation biofuels production. Their high productivity and the associated high lipid yields make them attractive options. In this review, we analyse a number aspects of large-scale lipid and overall algal biomass production from a biochemical and energetic standpoint. We illustrate that the maximum conversion efficiency of total solar energy into primary photosynthetic organic products falls in the region of 10%. Biomass biochemical composition further conditions this yield: 30 and 50% of the primary product mass is lost on producing cellprotein and lipid. Obtained yields are one third to one tenth of the theoretical ones. Wasted energy from captured photons is a major loss term and a major challenge in maximising mass algal production. Using irradiance data and kinetic parameters derived from reported field studies, we produce a simple model of algal biomass production and its variation with latitude and lipid content. An economic analysis of algal biomass production considers a number of scenarios and the effect of changing individual parameters. Our main conclusions are that: (i) the biochemical composition of the biomass influences the economics, in particular, increased lipid content reduces other valuable compounds in the biomass; (ii) the “biofuel only” option is unlikely to be economically viable; and (iii) among the hardest problems in assessing the economics are the cost of the CO2 supply and uncertain nature of downstream processing. We conclude by considering the pressing research and development needs.
Background: Although stabilization ponds and lagoons are suitable treatment processes due to simplicity of operation and low per capital costs, the effluents of these systems have too high of a total suspended solids concentration to be discharged into receiving waters. This problem is mainly caused by algae. In this study, an electro-coagulation reactor was examined to remove algae from the final effluent of the wastewater treatment plant belong to Bu-Ali Industrial Estates (Hamadan City). Methods: For the continuous flow electro-coagulation reactor used in these experiments three aluminum anodes were util-ized. This type of metal was selected because it could introduce the flocculation agent into the effluent, thereby algae could be removed by both mechanisms of electro-flotation and electro-flocculation. Results: The results of treatment were remarkably good and the efficiencies of total suspended solids (TSS) and chlorophyll a removal reached to as high as 99.5% and about 100% by applying a power input of about 550 W. In fact, this level of power input was needed for complete removal of algae in a low retention time of 15 minutes. Meanwhile, by applying less power input of about 100Wdm -3 , the required time for a relatively same treatment was reached to 30 minutes. Conclusion: It is expected that this method which is also known as a multiple contaminants removal process will be consid-ered as a suitable alternative for final polishing of effluents from lagoons and similar treatment systems.
In this article it is proven that ultrasound can be used to harvest microalgae. The separation process is based on gentle acoustically induced aggregation followed by enhanced sedimentation. In this paper, the efficiency of harvesting and the concentration factor of the ingoing biomass concentration are optimized and the relevance of this process compared to other harvesting processes is determined. For the optimisation, five parameters were modeled simultaneously by the use of an experimental design. An experimental design was chosen, because of possible interaction effects between the different parameters. The efficiency of the process was modeled with a R-squared of 0.88. The ingoing flow rate and the biomass concentration had a lot of influence on the efficiency of the process. Efficiencies higher than 90% were reached at high biomass concentrations and flow rates of 4–6 L day–1. At most, 92% of the organisms could be harvested and a concentration factor of 11 could be achieved at these settings. It was not possible to harvest this microalga with higher efficiencies due to its small size and its small density difference with water. The concentration factor of the process was modeled with a R-squared of 0.75. The ingoing flow rate, biomass concentration and ratio between harvest flow and ingoing flow rate had a significant effect on the concentration factor. Highest concentration factors, up to 20, could be reached at low biomass concentrations and low harvest flows. On industrial scale, centrifuges can better be used to harvest microalgae, because of lower power consumption, better efficiencies and higher concentration factors. On lab- or pilot-plant scale, an ultrasonic harvesting process has the advantages that it can be operated continuously, it evokes no shear stress and the occupation space is very small. Also, when the algae excrete a soluble high valued product this system can be used as a biofilter.
An analysis of the energy life-cycle for production of biomass using the oil-rich microalgae Nannochloropsis sp. was performed, which included both raceway ponds, tubular and flat-plate photobioreactors for algal cultivation. The net energy ratio (NER) for each process was calculated. The results showed that the use of horizontal tubular photobioreactors (PBRs) is not economically feasible ([NER]<1) and that the estimated NERs for flat-plate PBRs and raceway ponds is >1. The NER for ponds and flat-plate PBRs could be raised to significantly higher values if the lipid content of the biomass were increased to 60% dw/cwd. Although neither system is currently competitive with petroleum, the threshold oil cost at which this would occur was also estimated.
This article, the second in a three-part series, continues the update of the rapidly evolving technology of soliduliquid separation. Throughout the chemical process industries (CPI), separations play a major role in the recovery of product from process streams and in the purification of liquids. In this part, the author focuses on techniques that take advantage of density differences between the solid and the liquid. The driving force in such separations is generally the result of gravity, centrifugal action, or buoyancy. Discussed here are the theory, design and selection of equipment used to carry out these separations. (A)
Froth flotation separation was used to remove Scenedesmus quadricauda, an algae species which is commonly found in lakes and reservoirs, from an aqueous suspension as a function of several variables. The removal efficiencies of both live and dead algae (thermally terminated) using the froth flotation method as a function of the introduction of two types of surfactant, aeration rates, pH and temperature of operation are compared. The characteristics of the algal suspension such as the zeta potential of the algae and the surface tension measurements are also reported. Cetyltrimethylammonium bromide (CTAB), a cationic surfactant species, gave a comparatively good algal removal efficiency while sodium dodecylsulphate (SDS), an anionic surfactant species, gave, in comparison, a relatively poor removal efficiency. By decreasing the ambient pH values of the algal suspensions, the SDS gave an increasingly better extent of separation. As the aeration rates were increased, the removal efficiencies of both the live and the dead algae were increased slightly whereas when the temperature increased from 20 to 40°C, the removal rates were, more or less, unchanged. In most cases, the removal of the dead algae was greater than that of the live algae. The surface tension of the dead algal suspensions with CTAB was slightly lower than that of the live algal suspensions with CTAB at comparable concentrations, which may facilitate the removal of the dead algae.
It is now known that since cyanobacteria (blue-green algae) occur in both swimming and drinking water supplies, and lakes and rivers, they represent an increasing hazard to animal life and human population. Moreover, high algal contents pose also a number of operation problems for water purification plants. The objective of the work is to study the elimination of a Microcystis strain of cyanobacteria by the use of an ozoflotation process which associates the oxidizing properties of ozone and the physical aspects of flotation. The functioning and the efficiency of a pilot unit is presented according to such parameters as: ozone dose, flow rate, coagulants and raw water quality. The use of ozone in pretreatment leads to an inactivation of the algal cells. Experiments let us calculate the specific ozone utilisation rate of Microcystis and the [C.t] (ozone concentration, contact time) curve is determined versus algal removal. Under real conditions, a previous coagulation stage is necessary; best results are obtained with ferric chloride. Preozonation is also of influence on the enhancement of the coagulation efficiency. Association of the ozoflotation process and bilayer filtration can solve the algae problems of waters presenting low turbidity and low organic content, and improve water quality.
The effects of ozone and chlorine on algae were examined with respect to cell surface characteristics, lysis and coagulation ability. Two algae were studied: a green alga (Scenedesmus quadricauda) and a diatom (Cyclotella sp.). Cell properties were characterized using scanning electron micrographs, particle size distributions and electrophoretic mobility measurements. Jar tests were used to evaluate the coagulation of the algal suspensions with a polyaluminium chloride (PACl). The results showed that changes in the characteristics of the algal cells from ozone or chlorine yielded an improvement in removal of Scenedesmus through a combination of lysis and improved coagulation ability with PACl. Cyclotella removal was not enhanced by preoxidation. Additionally, preoxidation increased the organic carbon concentration of the settled water, which could lead to increased tastes and odours and production of disinfection by-products.
Oxidation pond effluents have proved unsatisfactory in recent years because of the presence of algae in lagoon effluents. Data from this study indicate an average of 1.19 mg chemical oxygen demand per mg of both laboratory and wastewater grown algae (dry weight basis). This paper reports the effects of lime, alum, magnesium salts, and several organic polymers on algae removal. The primary benefit of lime addition was pH adjustment while small dosages of Mg ++ (about 10 mg/l) were found to be very effective coagulants at pH 11. Alum was found to be an effective coagulant in the 5 to 9 pH range. None of the organic polymers proved to be cost effective for the conditions tested. Based on 90 day studies, in pond separation with fill and draw techniques appears feasible for small communities and industries.
This paper like Ken Ives' PhD research comments upon algae and their removal from drinking water. Specifically, algal properties, difficulties in removing algae by conventional treatment, and dissolved air flotation (DAF) as a treatment method are emphasized. The stability of algal suspensions may be due to surface charge, hydrophilic effects, or steric effects. Coagulation is required as a pretreatment step in DAF to destabilize algal particles relative to the microbubbles, and thus ensure particle-bubble attachment. The air supplied in DAF may be expressed fundamentally as mass, volume, and number concentrations of air bubbles. Calculations show high bubble volume concentrations compared to suspended particle volumes. The effectiveness of flotation is examined in terms of dimensionless products and compared to other particle processes. DAF is compared to settling for algal separation in experiments with DAF operating at higher overflow rates and smaller flocculation times. DAF produced clarified waters with lower turbidities and algal counts.
Magnetic filtration was used for the removal of phosphate from natural water in the presence of magnetite, alum and montmorillonite. This process, which allowed a rapid and efficient removal of phosphate, could be used as an alternative to settling tanks in the tertiary treatment of wastes.
Separation of algae from oxidation pond effluents was tested in a bench scale flotation column using ozone-enriched oxygen. Experimental results indicated that the process could produce a clear, colorless liquid, over 98% removal of suspended solids, and up to three orders of magnitude reduction in fecal coliforms. Ozone dosage ranged from 15 to 50 mgl−1. The collapsed froth thickens to produce a pure algal mass of up to 8.5% solids. It was hypothesized and supported by experimental results that ozone reaction with algal cells results in the formation of a hydrophobic surface amenable to separation by rising bubbles. The high quality products, both liquid and solid, make the combination of stabilization ponds with ozone flotation very attractive for wastewater treatment under certain conditions.
Experiments with a patented modification of an electroflotation cell showed that the power requirements for the treatment of pond effluents were less than for other electroflotation methods. The relationship between current densities and removal efficiencies of algae in suspension was found in laboratory and pilot-scale experiments. It was found that simultaneous flocculation-electroflotation gives better results than consecutive operation. The results obtained with electroflotation even with low current densities were almost equal to dissolved air flotation. It is believed that better adherence of electrolytically produced gases to the floc is responsible for the superiority of electroflotation.
El crecimiento de microorganismos a partir de cultivos ha sido siempre un problema para la obtencion de grandes cantidades de biomasa. Describe un metodo electrolitico altamente eficiente para la floculacion de microorganismos. Se utilizo una celda electrolica; con electrodos de carbon separados por placas de asbesto. El voltaje e intensidad utilizados dependio de la concentracion salina del medio
This paper investigates the potential for using surface modified bubbles in the treatment of algae using dissolved air flotation (DAF) instead of upstream coagulation and flocculation. Bubble modification is attempted by adding either metal coagulant, surfactant or polymers direct to the saturator. In this way, the chemical characteristics most suitable for removing small algae cells using this technique are examined. Optimum removal using metal coagulant, aluminium sulphate, was 60%; however, both a decrease in the magnitude of the zeta potential and microfloc generation occurred concurrently, thus accounting for the improved removal. In contrast, there was no change in system zeta potential and no microfloc generation when using cationic surfactant cetyltrimethyl-ammonium bromide (CTAB), for which 63% removal was achieved. An average of 95% removal was achieved using the cationic polymer, PolyDADMAC, with no change to system zeta potential. The results therefore confirm that there is a potential for adapting the conventional DAF process to operate without upstream coagulation and flocculation. A chemical with both a hydrophobic component in addition to a high molecular weight, hydrophilic, highly charge component is advised for the process.
Marine microalgae are still an important larval feeding source. One of the most promising harvesting techniques of the algae produced appears to be chemical flocculation. We report results obtained with chitosan flocculation of five marine species of microalgae of importance to mariculture (Skeletonema costatum, Dunaliella tertiolecta, Thalassiosira nordenskoldii, Chlorella sp. and Thalassionema sp.). The algae were grown in the laboratory in 20-liter batch cultures under normal conditions in artificial seawater. Without pH control, a 100% flocculation efficiency was reached at fairly high chitosan concentrations (above 40 mg liter−1). When the final pH was adjusted to around 7·8–8·0, a 100% flocculation efficiency was obtained with chitosan concentrations of 40 mg liter−1 or more. However, when pH was adjusted to around 7 or less, prior to chitosan addition for S. costatum and Chlorella sp., the concentration of chitosan required to obtain a 95–100% flocculation efficiency was reduced to 20 mg liter−1 for Chlorella and 2 mg liter−1 for S. costatum. The results are discussed in the light of the currently accepted theories on flocculation.
Cross-flow microfiltration and ultrafiltration techniques have become a suitable process for the separation of micro-organisms in a variety of biotechnical applications. In this paper, eight commercial membranes (IRIS, Orelis, Miribel, France) were evaluated for the harvest-ing of two marine microalgae: Haslea ostrearia and Skeletonema costatum, both widely cultivated in western France (Région des Pays de Loire). The effects of cross-flow velocity, transmembrane pressure, concentration and the characteristics of suspensions are discussed. The ultrafiltration membrane (polyacrylonitrile, 40 kDa) proves to be the most efficient in the peculiar conditions of low pressure and low tangential velocity for a long-term operation. © 1999 Elsevier Science B.V. All rights reserved.
The phenomenon of ozone-induced particle destabilization was studied employing a colloidal suspension of 150 mg/L sodium montmorillonite (Na-M) suspended in river water containing 3.1 mg/L natural organic matter(NOM). The suspension was treated with high (approximately 105 muM) and low (approximately 10 muM) ozone doses. Extended DLVO theory was utilized to investigate the surface thermodynamics of unozonated and ozonated Na-M coated with NOM (cNa-M). Ozonation decreased the surface charge and the Lewis base parameter, and increased the Lewis acid parameter and Lifshitz-van der Waals component of the surface energy. The overall result of these changes was a decrease in the change in the total free energy of interaction and hence a decrease in the stability of cNa-M with increasing ozonation. Modification in the surface thermodynamics responsible for destabilization could possibly be attributed to partial dealuminization of Na-M and associated NOM transformations, increasing the autophilicity of the colloids.
A parametric method was used to study the removal efficiency of both laboratory and high-rate oxidation pondgrown Scenedesmus obliquas from dilute solutions by use of high gradient magnetic filtration. The removal was accomplished by coadsorbing the algae and magnetite in the presence of ferric chloride and by placing the mixture for a given residence time in a magnetic filter. Both for the laboratory and pond-grown algae, excellent chlorophyll removals (>90%) were observed for small residence times, low magnetic fields, and reasonable flocculant dosages.
An account is given of the development of the utilization of microalgae for food and feed with special emphasis on the advantages of algal technologies for tropical and subtropical countries. The present status of microalgae mass production is characterized with respect to technology, product properties, yields, nutrition, toxicology and economics. As a multipurpose operation, the treatment of liquid wastes with algae-bacteria systems is the most promising microalgal technology. It yields proteinaceous microbial biomass as a comparatively inexpensive by-product of the operation of high-rate algal ponds, either at the simplified rural level or at the technically more elaborate industrial level. The aspect of hard-currency saving by employing algae-bacteria systems in sewage treatment for animal feed production is stressed.
The effect of the released polysaccharide (RPS) of the cyanobacterium Aphanothece halophytica GR02 on the recovery of the alga by flocculation with ferric chloride was studied. With increasing RPS concentration in algal
cultures from 0 to 68mg L−1 the flocculation efficiency at the same dosage of ferric chloride decreased, and higher dosages of ferric chloride were required
to attain the same flocculation efficiency. It is demonstrated that RPS could form complexes with ferrum during flocculation.
In conclusion, RPS of A. halophytica GR02 had a significant inhibitory effect on flocculation of the alga with ferric chloride. The inhibitory mechanism of A. halophytica GR02 RPS allows the RPS to compete for ferrum by forming complexes with ferrum, thus leading to the consumption of ferrum
in ferric chloride.
A novel fungi pelletization-assisted bioflocculation technology was developed for efficient algae harvesting and wastewater treatment. Microalga Chlorella vulgaris UMN235 and two locally isolated fungal species Aspergillus sp. UMN F01 and UMN F02 were used to study the effect of various cultural conditions on pelletization process for fungi-algae complex. The results showed that pH was the key factor affecting formation of fungi-algae pellet, and pH could be controlled by adjusting glucose concentration and fungal spore number added. The best pelletization happened when adding 20 g/L glucose and approximately 1.2E8/L spores in BG-11 medium, under which almost 100% of algal cells were captured onto the pellets with shorter retention time. The fungi-algae pellets can be easily harvested by simple filtration due to its large size (2-5 mm). The filtered fungi-algae pellets were reused as immobilized cells for treatment wastewaters and the nutrient removal rates of 100, 58.85, 89.83, and 62.53 % (for centrate) and 23.23, 44.68, 84.70, and 70.34% (for diluted swine manure wastewater) for ammonium, total nitrogen, total phosphorus, and chemical oxygen demand, respectively, under both 1- and 2-day cultivations. The novel technology developed is highly promising compared with current algae harvesting and biological wastewater treatment technologies in the literature.
A sodium montmorillonite (NaM) suspension (150 mg/liter) was treated with various ozone doses up to 97 μM (0.65 μmol O3/mg NaM). Suspension stability increased with increasing levels of ozonation as evidenced by increases in critical coagulation concentration (CCC) values of Na+, Ca2+, and La3+. The increase in induced stability of NaM was found to be most pronounced with Na+ as an indifferent electrolyte and least noticeable when La3+ was used. The enhanced stability of NaM can in large measure be attributed to an increase in the surface charge as a result of ozone-induced transformations. The conductivity of the suspending medium (water) was found to increase with ozonation indicating a leaching of ions from the crystal structure. DLVO theory was utilized to interpret the stability behavior of NaM suspensions; however, it underestimated CCC values. This discrepancy was attributed to an additional force resulting from hydrogen-bonding interactions. These interactions were found to be repulsive (hydration pressure) in nature. Hydration pressure increased with ozonation while Liftshitz—van der Waal forces remained largely unaffected. Electrostatic forces were found to be the major component responsible for increased stability of NaM as a result of ozonation, supporting a crystal dissolution hypothesis.
Using a number of commercial and natural water humic substances, the positive effect of preozonation as an aid to coagulation-flocculation of these compounds was confirmed by a 13–30% decrease in alum consumption. Experiments were conducted at a pH of 5.5 and humic substance concentrations of 20 mg/l (total organic carbon concentrations of approx. 10 mg/l). Standard jar test procedures were used to evaluate alum dosage requirements and the primary water quality parameters monitored were turbidity, u.v., TOC and color. In addition to decreased alum consumption the existence of an optimum preozonation dose (OPD) was also confirmed. For ozone dosages beyond the OPD, the benefit is reduced, then eliminated and further ozonation becomes detrimental to the coagulation-flocculation removal process. The OPD was found to be a function of the initial colloidal charge density (CCD) of the humic substances. The strong correlation of initial CCD to the OPD identified the major mechanism for preozonation to be effective as a reduction in CCD due to mild ozonation. Preozonation did not show a positive effect on a system with very low molecular weight (noncolloidal) humic substances.
Autoflotation of algae by photosynthetically produced dissolved oxygen was shown to be a rapid and effective harvesting technique. When used in conjunction with chemical flocculation by alum or C-31 polymer, removal of 80–90% of algal cells was achieved at overflow rates in the flotation basin of up to 2m per hour with algal float concentrations averaging more than 6% solids. Optimum ratios of flocculant to recovered air-dried solids were 1·09 for alum and 0·37 for the polymer. The corresponding chemical costs of alum-flocculated and polymer-flocculated solids containing 11–14% moisture were 18 cents per kilogram and 72 cents per kilogram, respectively. Major problems encountered with the autoflotation process were undersaturated hypolimnetic dissolved oxygen concentration, partial sedimentation and ephemeral periods of poor flocculation with C-31 polymer.
The dispersed air flotation process was utilized to remove algae (Scenedesmus quadricauda) from water. Three types of collector, cationic N-Cetyl-N-N-N-trimethylammonium bromide (CTAB), anionic sodium dodecylsulfate (SDS), and the nonionic Triton X-100 were used and compared. It was observed that ca. 10% of algae removal was achieved when SDS and Triton X-100 were used, respectively; and ca. 90% algae was removed when CTAB was used. Upon the addition of 10 mg l−1 of chitosan, over 90% algae was removed when SDS was used as the collector. The electrostatic interactions between collector and algae surface plays a critical role in the removal. Effects of pH, ionic strength, air flow rate, and alkalinity on flotation efficiency were also investigated.
Flocculation of three freshwater algae, Spirulina,Oscillatoria and Chlorella, and onebrackish alga, Synechocystis, using chitosan was studiedinthe pH range 4 to 9, and chlorophyll-a concentrations inthe range 80 to 800 mg m–3, which produces aturbidity of 10 to 100 nephelometric turbidity units (NTU) in water. Chitosanreduced the algal content effectively by flocculation and settling. Theflocculation efficiency is very sensitive to pH, and reached a maximum at pH7.0for the freshwater species, but lower for the marine species. The optimalchitosan concentration that is required to effect maximum flocculation dependedon the concentration of alga. Flocculation and settling were faster whenconcentrations of chitosan higher than optimal are used. The settled algalcellsare intact and live, but will not be redispersed by mechanical agitation. Thede-algated water may be reused to produce fresh cultures of algae.
Low-voltage electric fields (3–9 V cm−1) and certain chemical factors known to influence the stability of colloids in suspension were applied to culture suspensions of the unicellular green alga Chlorella vulgaris Beijerinck. Passage of an electric current through the algal suspension caused formation of buoyant algal flocs, with the degree of flocculation being a function of the duration of the electric treatment under a set of conditions. Both the rate and the degree of algal flocculation depended on pH of the medium, electric field, cell density, and various counterionic additives. At pH of ca. 7.0, up to 90% of algal cells could be separated within 30 min by application of a 3 V cm−1 electric field. A natural population of Chlorella and Scenedesmus showed an almost similar extent of flocculation after passage of electric current.
Filtration-based separation of Chlorella vulgaris, a species with excellent potential for CO(2) capture and lipid production, was investigated using a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane. Coagulation using polyaluminum chloride (PACl) attained maximum turbidity removal at 200 mg L(-1) as Al(2)O(3). The membrane filtration flux at 1 bar increased as the PACl dose increased, regardless of overdosing in the coagulation stage. The filtered cake at the end of filtration tests peaked in solid content at 10 mg L(-1) as Al(2)O(3), reaching 34% w/w, roughly two times that of the original suspension. Differential scanning calorimetry (DSC) tests demonstrate that the cake with minimum water-solid binding strength produced the driest filter cake. Coagulation using 10 mg L(-1) PACl as Al(2)O(3), followed by PTFE membrane filtration at 1 bar, is an effective process for harvesting C. vulgaris from algal froth.
In an effort to search for an efficient and environmentally friendly harvesting method, a commercially available microbial flocculant poly (γ-glutamic acid) (γ-PGA) was used to harvest oleaginous microalgae. Conditions for flocculation of marine Chlorella vulgaris and freshwater Chlorella protothecoides were optimized by response surface methodology (RSM) and determined to be 22.03 mg L(-1) γ-PGA, 0.57 g L(-1) biomass, and 11.56 g L(-1) salinity, and 19.82 mg L(-1) γ-PGA and 0.60 g L(-1) biomass, respectively. Application of the two optimized flocculation methods to Nannochloropsis oculata LICME 002, Phaeodactylum tricornutum, C. vulgaris LICME 001, and Botryococcus braunii LICME 003 gave no less than 90% flocculation efficiency and a concentration factor greater than 20. Micrographs of the harvested microalgal cells showed no damage to cell integrity, and hence no lipid loss during the process. The results show that flocculation with γ-PGA is feasible for harvesting microalgae for biodiesel production.
Microalgae hold great potential as a feedstock for biofuels or bulk protein or treatment of wastewater or flue gas. Realising these applications will require the development of a cost-efficient harvesting technology. Here, we explore the potential of flocculation induced by high pH for harvesting Chlorella vulgaris. Our results demonstrate that flocculation can be induced by increasing medium pH to 11. Although both calcium and magnesium precipitated when pH was increased, only magnesium (≥0.15 mM) proved to be essential to induce flocculation. The costs of four different bases (sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and sodium carbonate) were calculated and evaluated and the use of lime appeared to be the most cost-efficient. Flocculation induced by high pH is therefore a potentially useful method to preconcentrate freshwater microalgal biomass during harvesting.
A meta-analysis of several published life cycle assessments of algae-to-energy systems was developed to better understand the environmental implications of deploying this technology at large scales. Taken together, results from these six studies seemed largely inconclusive because of differences in modeling assumptions and system boundaries. To overcome this, the models were normalized using a generic pathway for cultivating algae in open ponds, converting it into biodiesel, and processing the nonlipid fraction using anaerobic digestion. Meta-analysis results suggest that algae-based biodiesel would result in energy consumption and greenhouse gas emissions on par with terrestrial alternatives such as corn ethanol and soy biodiesel. Net energy ratio and normalized greenhouse gas emissions were 1.4 MJ produced/MJ consumed and 0.19 kg CO(2)-equivalent/km traveled, respectively. A scenario analysis underscores the extent to which breakthroughs in key technologies are needed before algae-derived fuels become an attractive alternative to conventional biofuels.
Flotation separation of Chlorella vulgaris, a species with excellent potential for CO(2) capture and lipid production, was studied using dispersed ozone gas. Pure oxygen aeration did not yield flotation. Conversely, applying ozone effectively separation algae from broth through flotation. The ozone dose applied for sufficient algal flotation is <0.05 mg/g biomass, much lower than those used in practical drinking waterworks (0.1-0.3 mg/g suspended solids). Main products, lipid C16:0, was effectively collected in the flotage phase. The algae removal rate, surface charge, and hydrophobicity of algal cells, and proteins and polysaccharides contents of algogenic organic matter (AOM) were determined. Certain quantities of proteins were present in the cultivated algal suspension, hence, minimal quantity of ozone was required to release intracellular proteins as surfactants to lead to effective flotation.
Microalgae have the ability to mitigate CO(2) emission and produce oil with a high productivity, thereby having the potential for applications in producing the third-generation of biofuels. The key technologies for producing microalgal biofuels include identification of preferable culture conditions for high oil productivity, development of effective and economical microalgae cultivation systems, as well as separation and harvesting of microalgal biomass and oil. This review presents recent advances in microalgal cultivation, photobioreactor design, and harvesting technologies with a focus on microalgal oil (mainly triglycerides) production. The effects of different microalgal metabolisms (i.e., phototrophic, heterotrophic, mixotrophic, and photoheterotrophic growth), cultivation systems (emphasizing the effect of light sources), and biomass harvesting methods (chemical/physical methods) on microalgal biomass and oil production are compared and critically discussed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.
The Scenedesmus obliquus FSP-3, a species with excellent potential for CO(2) capture and lipid production, was harvested using dispersed ozone flotation. While air aeration does not, ozone produces effective solid-liquid separation through flotation. Ozone dose applied for sufficient algal flotation is similar to those used in practical drinking waterworks. The algae removal rate, surface charge, and hydrophobicity of algal cells, and fluorescence characteristics and proteins and polysaccharides contents of algogenic organic matter (AOM) were determined during ozonation. Proteins released from tightly bound AOM are essential to modifying the hydrophobicity of bubble surfaces for easy cell attachment and to forming a top froth layer for collecting floating cells. Humic substances in the suspension scavenge dosed ozone that adversely affects ozone flotation efficiency of algal cells.
This paper analyses the potential environmental impacts and economic viability of producing biodiesel from microalgae grown in ponds. A comparative Life Cycle Assessment (LCA) study of a notional production system designed for Australian conditions was conducted to compare biodiesel production from algae (with three different scenarios for carbon dioxide supplementation and two different production rates) with canola and ULS (ultra-low sulfur) diesel. Comparisons of GHG (greenhouse gas) emissions (g CO(2)-e/tkm) and costs (¢/tkm) are given. Algae GHG emissions (-27.6 to 18.2) compare very favourably with canola (35.9) and ULS diesel (81.2). Costs are not so favourable, with algae ranging from 2.2 to 4.8, compared with canola (4.2) and ULS diesel (3.8). This highlights the need for a high production rate to make algal biodiesel economically attractive.
This paper provides an analysis of the potential environmental impacts of biodiesel production from microalgae. High production yields of microalgae have called forth interest of economic and scientific actors but it is still unclear whether the production of biodiesel is environmentally interesting and which transformation steps need further adjustment and optimization. A comparative LCA study of a virtual facility has been undertaken to assessthe energetic balance and the potential environmental impacts of the whole process chain, from the biomass production to the biodiesel combustion. Two different culture conditions, nominal fertilizing or nitrogen starvation, as well as two different extraction options, dry or wet extraction, have been tested. The best scenario has been compared to first generation biodiesel and oil diesel. The outcome confirms the potential of microalgae as an energy source but highlights the imperative necessity of decreasing the energy and fertilizer consumption. Therefore control of nitrogen stress during the culture and optimization of wet extraction seem to be valuable options. This study also emphasizes the potential of anaerobic digestion of oilcakes as a way to reduce external energy demand and to recycle a part of the mineral fertilizers.
Source water eutrophication has caused serious problems in drinking water supplies, with enhanced coagulation widely used to remove the resulting algae. This paper investigates the use of sonication to improve the removal by coagulation of Microcystis aeruginosa, a common species of toxic algae. The results show that sonication significantly enhances the reduction of algae cells, solution UV254, and chlorophyll a without increasing the concentration of aqueous microcystins. The main mechanism involved the destruction during ultrasonic irradiation of gas vacuoles inside algae cells that acted as 'nuclei' for acoustic cavitation and collapse during the "bubble crush" period, resulting in the settlement of cyanobacteria. Coagulation efficiency depended strongly on the coagulant dose and sonication conditions. When the coagulant dose was 0.5mg/l, 5s of ultrasonic irradiation increased algae removal efficiency from 35% to 67%. As further sonication enhanced the coagulation efficiency only slightly due to better mixing, optimal sonication time was 5s. The most effective sonication intensity was 47.2W/cm2, and the highest removal ratio of M. aeruginosa was 93.5% by the sonication-coagulation method. Experiments with reservoir water showed that this method could be successfully applied to natural water containing multiple species of algae.
This study evaluates the effectiveness and costs of using dissolved air flotation to remove algae from wastewater stabilization pond effluents. Batch tests, in which algal concentration, coagulant dosage, and recycle rates were varied, were conducted on cultures of laboratory grown algae. Pilot plant studies were performed on the effluent from a wastewater stabilization pond lagoon. Using an initial algal concentration of 100 mg/l, it required 75 mg/l of alum to achieve 90% removal of the suspended solids in the batch tests. However, in the pilot plant studies, 175 mg/l of alum was needed to obtain the same degree of removal only a slightly greater initial concentration of algae (125 mg/l). In both tests, the use of pressurized recycle greatly improved the solids removal efficiencies of both naturally and chemically flocculated algae.
A continuous flow kinetic model was developed to describe and predict the effects of temperature on the toxicity of a specific oil refinery waste to the green alga, Selenastrum capricornutum. The model is based on Michaelis Menten enzyme inhibition kinetics, with ammonium nitrogen limited, continuous flow algal cultures between 20° and 28°C. Phenol is the controlling inhibitor. The model was applied to continuous flow algal cultures exposed to an actual oil refinery waste. The phenol and oil refinery waste studied exerted competitive inhibition of Selenastrum capricornutum. Phenol was more toxic at 24°C than at either 20° or 28°C. The particular oil refinery waste used was approximately 10 times more toxic than pure phenol to Selenastrum capricornutum.
The feasibility of removing algae from water and wastewater by chemical flocculation techniques was investigated. Mixed cultures of algae were obtained from both continuous- and batch-fed laboratory reactors. Representative cationic, anionic, and nonionic synthetic organic polyelectrolytes were used as flocculants. Under the experimental conditions, chemically induced algal flocculation occurred with the addition of cationic polyelectrolyte, but not with anionic or nonionic polymers, although attachment of all polyelectrolyte species to the algal surface is shown. The mechanism of chemically induced algal flocculation is interpreted in terms of bridging phenomena between the discrete algal cells and the linearly extended polymer chains, forming a three-dimensional matrix that is capable of subsiding under quiescent conditions. The degree of flocculation is shown to be a direct function of the extent of polymer coverage of the active sites on the algal surface, although to induce flocculation by this method requires that the algal surface charge must concurrently be reduced to a level at which the extended polymers can bridge the minimal distance of separation imposed by electrostatic repulsion. The influence of pH, algal concentration, and algal growth phase on the requisite cationic flocculant dose is also reported.
This paper describes the removal of algae and attached water using a froth flotation method as a function of the collector type, aeration rates, the pH of the algal suspension and temperature of operation. Dispersed air flotation was used in this study to remove Scenedesmus quadricaudo. The addition of surfactants such as cetyltrimethylammonium bromide and sodium dodecylsulfate increased the aeration rates and reduced the size of air bubbles. Only cetyltrimethylammonium bromide gave high algal removal (90%) whereas sodium dodecylsulfate gave poor algal removal (16%). However, by decreasing the pH values of the algal suspension, it was possible to increase the algal removal efficiency up to 80%. Low temperature operation had an important effect on reducing the rate of algal removal but when the temperature was 20 degrees C or higher there was little change with further temperature rises. The amount of water removed with the algal phase was reduced by using a two-stage flotation process.