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Nitrogen and Phosphorus Removal from Tertiary Wastewater in an Osmotic Membrane Photobioreactor
Abstract
An osmotic membrane photobioreactor (OMPBR) was designed and operated for 162 days for nitrogen and phosphorus removal from wastewater using Chlorella vulgaris. The removal efficiency for NH4+-N, NO3--N and PO43--P reached as high as 95%, 53% and 89%, whereas the maximum removal rates were 3.41 mg/L-day, 0.20 mg/L-day and 0.8 mg/l-day, respectively. The microalgae exhibited high tendency to aggregate and attached to the bioreactor and membrane surfaces, and total biomass accumulation in the OMPBR was over 5 g/L. Salt accumulation and biofouling had adverse effects on membrane filtration, but the performance could be recovered through periodic backwashing of the membranes. Extracellular polymeric substances characterization indicated higher fraction of polysaccharides as compared to proteins. The biomass in the OMPBR accumulated higher levels of carbohydrates and chlorophyll. These results indicate the suitability of OMPBR in wastewater treatment and in high-density microalgae cultivation.
... Phytoremediation, as the implementation of microalgae in the treatment of effluents, is used to remove nitrogen compounds and phosphorus that can cause eutrophication in receiving water bodies (Mohd-Sahib et al., 2017). Microalgae can remove more than 95% of nitrogen compounds and 90% of phosphorus in effluents (Praveen;Loh, 2016). The use of native algae, such as Chlorella vulgaris, in the phytoremediation of wastewater is very important because the species presents rapid cell growth, CO 2 removal, oxygen production, resistance to contamination, excellent biochemical composition and efficient nutrient absorption (Rodrigues-Sousa et al., 2021;Miao et al., 2016;Silva et al., 2015). ...
... Phytoremediation, as the implementation of microalgae in the treatment of effluents, is used to remove nitrogen compounds and phosphorus that can cause eutrophication in receiving water bodies (Mohd-Sahib et al., 2017). Microalgae can remove more than 95% of nitrogen compounds and 90% of phosphorus in effluents (Praveen;Loh, 2016). The use of native algae, such as Chlorella vulgaris, in the phytoremediation of wastewater is very important because the species presents rapid cell growth, CO 2 removal, oxygen production, resistance to contamination, excellent biochemical composition and efficient nutrient absorption (Rodrigues-Sousa et al., 2021;Miao et al., 2016;Silva et al., 2015). ...
... This result was similar to the present study, with capacity total nitrogen removal exceeding 80% and almost 70% phosphorus removal in effluents. Praveen and Loh (2016) used effluent from the tertiary wastewater and reported a high efficiency of C. vulgaris in the removal efficiency for ammonia, nitrate and phosphosrus reached as high as 95%, 53% and 89%, respectively. Different of present study, C. vulgaris prefered ammonia as a primary source of nitrogen, revealing that there are several factors that influence the growth and consequently the removal rate, since the microalgae incorporate nitrogen into the biomass for protein biosynthesis. ...
Phytoremediation, as the implementation of microalgae in the treatment of effluents, is used to remove nitrogen compounds and phosphorus that can cause eutrophication in receiving water bodies. The present study evaluated the phytoremediation of urban and fish farming wastewater and growth performance of Litopenaeus vannamei using microalgae Chlorella vulgaris. Microalgae were cultivated stationary with three treatments: T1 sewage treatment station effluent (STS), T2 fish farming effluent (FF) and T3 with standard medium (SM) Guillard f/2), conducted in quintuplicate for each culture medium, using a 20 L carboy for eight days. 5.0 L inoculum (25%) plus 15 L culture medium, T1 STS, T2 FF and T3 SM (75% of each) were used to start the experiment. The shrimp experiment was realized with three treatments in quintuplicates, completely randomized design, during 15 days. The animals were maintained in tanks of 100 L under constantly aerated, resulting in a concentration above 5.0 mg L− 1 of dissolved oxygen, in a density of 70 animals m-3, fed four times per day (8:00, 11:00, 14:00 and 16:00 h) offering to T1 commercial feed (C-Feed) with 35% crude protein, T2 and T3 with commercial feed plus addition of 5.0% dry biomass of C. vulgaris. The best result for algal perfomance, lipid biomass and nutrient removal was with Fish farm wastewater. The additive with the highest performance was FF-Feed. C. vulgaris has a high potential for removing nutrients from wastewater, producing biomass and lipids, in addition to increasing shrimp productivity.
... In Chlorella vulgaris (C. vulgaris) cultivated tertiary wastewater treatment, an OsMPBR achieved higher microalgal biomass productivity and nutrient removal than an MF-MPBR [25]. The possible reason is that the extracellular organic matter (EOM) concentration in an OsMPBR is higher than in an MF-MPBR due to the small pores in FO membranes. ...
... The main drawbacks are the low membrane permeance and low final microalgal concentration due to the mild driving force [31,93]. In addition, most reported FO filtration processes involve draw solute regeneration, resulting in high energy consumption [25]. ...
Although microalgal biomass and environmental benefits of microalgae surpass those of many other feedstocks, the costs associated with up- and downstream technologies still hinder their further development. Membrane technology is an emerging technology that has been applied in the microalgae industry for cultivation, harvesting, and biorefinery, and that has contributed to achieving the economic sustainability of microalgal cultivation and reducing energy input. In the most studied field (microalgae harvesting), the lowest energy consumption is currently 0.67 Wh/m³ when using vibrating, negatively charged, patterned PSf membranes with flocculation prior to filtration in an MMV system. However, the operational flux (95 L/m² h) is not the highest, leaving room for optimization. Cost calculations indicated that the total electrical cost is only a very small fraction (3.05%) of the total production cost (using the energy costs of that period, i.e., 0.1 €/kWh), with CO2 and labor suggested to be the key factors contributing to high production cost. Membrane-based microalgal biofilm systems recently gained a lot of attention as they offer a win-win strategy for low-cost simultaneous microalgae cultivation and harvesting. In addition, they can be used in other fields, such as wastewater treatment and the production of biochemicals. This review suggests that further studies should not only focus on developing new technologies but combine the existing technologies and find their synergistic effects to realize high performance and low costs.
... Using wastewater to grow microalgae is the most promising way to reduce production costs related to nutrition and water (Zhou et al., 2012). Some researchers have cultivated microalgae in membrane bioreactors to remove N and P from various sewage types Delgadillo-Mirquez et al., 2016;Praveen and Loh, 2016). For example, four microalgae species were cultivated in anaerobically digested wastewater using a membrane photobioreactor, and all removed NH 4 + -N and P, with Chlorella sorokiniana having the best removal effectiveness . ...
... For example, four microalgae species were cultivated in anaerobically digested wastewater using a membrane photobioreactor, and all removed NH 4 + -N and P, with Chlorella sorokiniana having the best removal effectiveness . Furthermore, Chlorella vulgaris that was cultured in an osmotic membrane photobioreactor can remove NH 4 + -N, NO 3 − -N, and PO 4 3− -P from tertiary wastewater with efficiencies of 95%, 53%, and 89%, respectively (Praveen and Loh, 2016). Chlorella vulgaris could also remove N and P from wastewater by mixed microalgae and bacteria culture, and the microalgae produced oxygen in situ for the bacteria to use. ...
Eutrophication has attracted extensive attention owing to its harmful effects to the organisms and aquatic environment. Studies on the functional microorganisms with the ability of simultaneously nitrogen (N) and phosphorus (P) removal is of great significance for alleviating eutrophication. Thus far, several strains from various genera have been reported to accomplish simultaneous N and P removal, which is primarily observed in Bacillus, Pseudomonas, Paracoccus, and Arthrobacter. The mechanism of N and P removal by denitrifying P accumulating organisms (DPAOs) is different from the traditional biological N and P removal. The denitrifying P removal (DPR) technology based on the metabolic function of DPAOs can overcome the problem of carbon source competition and sludge age contradiction in traditional biological N and P removal processes and can be applied to the treatment of urban sewage with low C/N ratio. This paper reviews the mechanism of N and P removal by DPAOs from the aspect of the metabolic pathways and enzymatic processes. The research progress on DPR processes is also summarized and elucidated. Further research should focus on the efficient removal of N and P by improving the performance of functional microorganisms and development of new coupling processes. This review can serve as a basis for screening DPAOs with high N and P removal efficiency and developing new DPR processes in the future.
... Low C/N ratio of the digestate can theoretically solved by the addition of CO 2 sourced from flue gas or other sources. The relatively low phosphorus to nitrogen (P/N) ratio is another disadvantage of the anaerobic digestate, which does not satisfy the stoichiometric phosphorus requirement of the microalgae (Praveen and Loh, 2016). Phosphate is known as the dominant component of total phosphorus (82-90%) in the digestate. ...
... This technique is very appropriate for digestate nutrient recovery (97% of the efficiency of nitrogen removal has been achieved), although it would require separating anaerobic bacteria from microalgae. By operating the MBR with aerobic heterotrophic micro-organisms in conjugation with a membrane photobioreactor (MPBR) under autotrophic conditions, the use of membrane bioreactors (MBR) will simplify these processes (Praveen and Loh, 2016). Membrane filtration will avoid microorganism mixing, thus enabling activity with high biomass retention at lower HRTs. ...
To suffice the escalating global energy demand, microalgae are deemed as high potential surrogate feedstocks for liquid fuels. The major encumbrance for the commercialization of microalgae cultivation is due to the high costs of nutrients such as carbon, phosphorous, and nitrogen. Meanwhile, the organic-rich anaerobic digestate which is difficult to be purified by conventional techniques is appropriate to be used as a low-cost nutrient source for the economic viability and sustainability of microalgae production. This option is also beneficial in terms of reutilize the organic fraction of solid waste instead of discarded as zero-value waste. Anaerobic digestate is the side product of biogas production during anaerobic digestion process, where optimum nutrients are needed to satisfy the physiological needs to grow microalgae. Besides, the turbidity, competing biological contaminants, ammonia and metal toxicity of the digestate are also potentially contributing to the inhibition of microalgae growth. Thus, this review is aimed to explicate the feasibility of utilizing the anaerobic digestate to cultivate microalgae by evaluating their potential challenges and solutions. The proposed potential solutions (digestate dilution and pre-treatment, microalgae strain selection, extra organics addition, nitrification and desulfurization) corresponding to the state-of-the-art challenges are applicable as future directions of the research.
... Thereafter, with the increase of microalgae biomass, the concentration of PO 4 3− -P in effluent was stable below 0.9 mg/L with a high removal efficiency. reported that in the continuous microalgae-membrane bioreactor to treat tertiary effluent, the removal amount of TN and TP were 3.6 mg/(L·d) and 0.8 mg/(L·d), respectively [23]. Gao et al. (2016) showed that in the continuous streamer-membrane bioreactor, the growth rate of microalgae was 42.6 mg/(L·d), and the removal amount of TN and TP was 5.85 mg/(L·d) and 0.42 mg/(L·d), respectively [24]. ...
... Overall, there was no obvious accumulation of NO 2 − -N during 40 days' operation.Most studies have shown that nitrate reductase and nitrite reductase successively transformed NO 3 − -N and NO 2 − -N to NH 4 + -N in algae cells, and finally assimilated to amino acids in the form of NH 4 + -N.Therefore, NO 2 − -N in effluent may be due to the transformation of NO 3 − -N. Praveen and Loh(2016)constructed a microalgae photobioreactor to treat tertiary effluent, and no NO 2 − -N was accumulated under HRT of 4 days[23]. Therefore, the longer HRT may help to alleviate the accumulation of NO 2 − -N. ...
A microalgae membrane bioreactor (MMBR) with internal circulating fluidized bed (ICFB) was constructed at room temperature to study the removal efficiency of marine aquaculture wastewater pollutants and continuously monitor the biomass of microalgae. Within 40 days of operation, the removal efficiency of NO3−–N and NH4+–N in the ICFB-MMBR reached 52% and 85%, respectively, and the removal amount of total nitrogen (TN) reached 16.2 mg/(L·d). In addition, the reactor demonstrated a strong phosphorus removal capacity. The removal efficiency of PO43−–P reached 80%. With the strengthening of internal circulation, the microalgae could be distributed evenly and enriched quickly. The maximum growth rate and biomass concentration reached 60 mg/(L·d) and 1.4 g/L, respectively. The harvesting of microalgae did not significantly affect the nitrogen and phosphorus removal efficiency of ICFB-MMBR. The membrane fouling of the reactor was investigated by monitoring transmembrane pressure difference (TMP). Overall, the membrane fouling cycle of ICFB-MMBR system was more than 40 days.
... FO relies on an osmotic gradient driving force across a semipermeable dense membrane to draw water (permeate) through the membrane while most salts, organics, and particles are concentrated in the feed solution (Cath et al. 2006). Due to this specific configuration (dense membrane with high rejection and no use of hydraulic pressure), the following advantages of FO separation of microalgae suspensions after wastewater treatment stage can be listed (Blandin et al. 2016a;Cath et al. 2006;Honda et al. 2015;Hoover et al. 2011;Larronde-Larretche and Jin 2017;Mazzuca Sobczuk et al. 2015;Novoveská et al. 2016;Praveen and Loh 2016;Sturm and Lamer 2011;Zou et al. 2013): ...
... Few additional bench-scale studies were published during 2013-2016 and were the first attempts to investigate the impacts of microalgae cell suspension specific properties and biofouling effects on FO process as an initial dewatering step in microalgae harvesting and for advanced wastewater treatment (Honda et al. 2015;Zou et al. 2013). Bench-scale comparative study of FO-based membrane photobioreactor operated with Chlorella vulgaris for continuous tertiary wastewater treatment revealed that for successful module operation factors pertaining to filtration, biofouling, concentration polarization, and salt accumulation must be addressed (Praveen and Loh 2016). Effects of hydraulic stress and exopolymeric substance (EPS) composition of cell wall of industrially promising species (Scenedesmus obliquus, Chlamydomonas reinhardtii, and C. vulgaris) were investigated in a comparative study; membrane fouling and algae dewatering efficiency were related to algae cell wall carbohydrate composition (Larronde-Larretche and Jin 2017), although in none of the previous FO studies the effect of environmental and operational culturing conditions were not really considered. ...
Forward osmosis is envisioned as a technology for microalgae concentration but fouling propensity during dewatering is currently a limiting factor that requires better understanding. The purpose of this study is to define the impact of microalgae culturing conditions on the downstream forward osmosis (FO) separation process—water recovery and microalgae harvesting. Chlorella vulgaris was cultivated in an outdoor lab-scale reactor fed with synthetic wastewater mimicking primary settled municipal influent under changing environmental conditions (temperature, solar radiation, nutrient balance) with varying hydraulic retention time. High efficiency of nutrient removal was achieved under all tested conditions but microalgae autoflocculation and lower rate of pollutant removal were observed with batches where culturing temperature (6.5–21 °C), solar irradiation rate (181 W/m²), and nitrogen/phosphorous ratio (2.9) were below the optimal range. Regarding FO concentration, high initial water fluxes (in the range of 18.2 to 19.5 L·m²·h⁻¹) and water extraction rate (60.1–83.9%) were observed in all subsequent FO concentration tests. Significant membrane fouling (microalgae deposition on surface) associated with poor biomass recovery from the FO cell was found to be dependent on exopolymeric substance accumulation, which was a response to non-optimal environmental culturing conditions.
... High concentrations of nitrogen and phosphorus in wastewater can disturb the balance of aquatic ecosystem through eutrophication [1,2]. On the other hand, wastewater is an inexpensive source of nutrients (nitrogen and phosphorus) for effective growth of microalgae. ...
... On the other hand, wastewater is an inexpensive source of nutrients (nitrogen and phosphorus) for effective growth of microalgae. Therefore, microalgae can play a beneficial role in removing nutrients from wastewater [1,2]. Over the last decade, open ponds and photobioreactor systems have been used for microalgal biomass production and nutrient removal [3]. ...
Abstract
The present study examined fouling in a microalgal membrane bioreactor under mixotrophic, heterotrophic and photoautotrophic conditions. N-enriched wastewater, containing nitrate source, was used as a nutrient source for cultivation of microalgae. The results confirmed that the membrane fouling rates increased under mixotrophic cultivation through enhanced production of carbohydrates in soluble microbial products (SMPc) and protein in extracellular polymeric substances (EPSp). The transmembrane pressure (TMP) jumping was observed under mixotrophic and photoautotrophic cultivation after 31 and 47 days of operation, respectively, while the TMP of heterotrophic cultivation did not exceed 10 kPa throughout 51 days. The highest EPSp was produced under mixotrophic condition due to high nitrogen removal rate. Also, the results of resistance analysis indicated that cake resistance was the main fouling resistance in all cultivation types and the latter result was confirmed by SEM analysis. In addition, higher protein fraction of cake layer on membrane foulants in comparison to carbohydrates fraction increased the hydrophobicity of membrane's surface in all cultivations (except heterotrophic culture). Compared to mixotrophic and photoautotrophic cultures, hydrophobic properties and cell size of heterotrophic microalgae increased and resulted in low membrane fouling rates.
... Biofilters using media variation to improve their performance is an emerging technique with growing popularity in the field of wastewater treatment [Praveen et al., 2016;Sekarani, et al., 2020;Son, et al., 2020] In the application of media variation, one of them uses serrated bio balls, which are hollow or protruding plastic balls like rambutan fruits with a complex structure, offering a large surface area for bacterial growth. Due to their lightweight and mobile shape, bio balls provide good circulation in the tank, ensuring maximum contact between bacteria and wastewater. ...
... Preveen and Loh operated an OMPBR for 162 days for a tertiary wastewater treatment and nutrient recovery scenario using Chlorella vulgaris [109]; Removal efficiencies of 93% 53% and 89% were achieved for NH 4 + -N, NO 3 − -N, and PO 4 3− -P at an HRT of 3 days. A high tendency of microalgae aggregation and attachment to the bioreactor and membrane surfaces was observed, resulting in the accumulated total biomass in the OMPBR being over 5 g/L. ...
The use of microalgae for wastewater remediation and nutrient recovery answers the call for a circular bioeconomy, which involves waste resource utilization and ecosystem protection. The integration of microalgae cultivation and wastewater treatment has been proposed as a promising strategy to tackle the issues of water and energy source depletions. Specifically, microalgae-enabled wastewater treatment offers an opportunity to simultaneously implement wastewater remediation and valuable biomass production. As a versatile technology, membrane-based processes have been increasingly explored for the integration of microalgae-based wastewater remediation. This review provides a literature survey and discussion of recent progressions and achievements made in the development of membrane photobioreactors (MPBRs) for wastewater treatment and nutrient recovery. The opportunities of using microalgae-based wastewater treatment as an interesting option to manage effluents that contain high levels of nutrients are explored. The innovations made in the design of membrane photobioreactors and their performances are evaluated. The achievements pave a way for the effective and practical implementation of membrane technology in large-scale microalgae-enabled wastewater remediation and nutrient recovery processes.
... Taken together, these works demonstrated that MPBRs could improve the effluent quality and achieve more biomass production. Previous studies showed that MPBRs might need aeration to provide carbon sources for microalgae growth, including air (Gao et al., 2014;Marbelia et al., 2014;Singh and Thomas, 2012;Xu et al., 2014) or pure or diluted CO 2 (Gao et al., 2015;Honda et al., 2012;Praveen and Loh, 2016). However, the aeration strategy is energy-intensive, which may promote more carbon emissions and thereby reduce the benefits of carbon utilization from MPBRs . ...
This study investigated the nutrients removal, decarbonization potentials, and bioenergy production (i.e., algal biomass and biogas) between a membrane photobioreactor (MPBR) and a sequencing photobioreactor (SPBR) as the post-treatment process of an anaerobic membrane bioreactor (AnMBR) for municipal wastewater treatment. All photobioreactors without aeration showed favourable performance on AnMBR effluent polishing and bioenergy production. In comparison, MPBRs achieved higher removal efficiencies with 98.4%-99.1% NH4-N and 74.8%-88.4% PO4-P removal compared to the SPBRs with 41.1%-82.0% NH4-N and 39.6%-72.9% PO4-P removal. MPBRs enhanced more nutrients utilization (24.9-49.3 g(N)/(m3·d) and 3.4-8.1 g(P)/(m3·d)) and CO2 assimilation (22.9-43.4 g(C)/(m3·d)), and concentrated more microalgae with 1.58-1.98 g/L higher than the SPBRs. Moreover, the MPBR effectively upgraded the biogas from AnMBR with superior methane percentage of 89.4%-93.4% due to its better CO2 biofixation. The MPBR, with better carbon, nitrogen and phosphorous removal and bioenergy production, following AnMBR is an attractive decarbonized technology for future sustainable wastewater treatment.
... Compared to Scenedesmus obliquus and Chlamydomonas reinhardtii, Chlorella vulgaris was the most suitable species to be harvested by FO with outstanding biomass recovery and negligible membrane fouling [15]. In 2016, Praveen and Loh [16] proposed to integrate FO and a photobioreactor (PBR) for continuous nutrient removal from wastewater using C. vulgaris. In this study, 95% NH 3 -N removal, 53% NO 2 -N removal and 89% PO 4 -P removal were achieved. ...
Microalgae have attracted great interest recently due to their potential for nutrients removal from wastewater, renewable biodiesel production and bioactive compounds extraction. However, one major challenge in microalgal bioremediation and the algal biofuel process is the high energy cost of separating microalgae from water. Our previous studies demonstrated that forward osmosis (FO) is a promising technology for microalgae harvesting and dewatering due to its low energy consumption and easy fouling control. In the present study, two FO module configurations (side-stream and submerged) were integrated with microalgae (C. vulgaris) photobioreactor (PBR) in order to evaluate the system performance, including nutrients removal, algae harvesting efficiency and membrane fouling. After 7 days of operation, both systems showed effective nutrients removal. A total of 92.9%, 100% and 98.7% of PO4-P, NH3-N and TN were removed in the PBR integrated with the submerged FO module, and 82%, 96% and 94.8% of PO4-P, NH3-N and TN were removed in the PBR integrated with the side-stream FO module. The better nutrients removal efficiency is attributed to the greater algae biomass in the submerged FO-PBR where in situ biomass dewatering was conducted. The side-stream FO module showed more severe permeate flux loss and biomass loss (less dewatering efficiency) due to algae deposition onto the membrane. This is likely caused by the higher initial water flux associated with the side-stream FO configuration, resulting in more foulants being transported to the membrane surface. However, the side-stream FO module showed better fouling mitigation by simple hydraulic flushing than the submerged FO module, which is not convenient for conducting cleaning without interrupting the PBR operation. Taken together, our results suggest that side-stream FO configuration may provide a viable way to integrate with PBR for a microalgae-based treatment. The present work provides novel insights into the efficient operation of a FO-PBR for more sustainable wastewater treatment and effective microalgae harvesting.
... Many species of microalgae have been reported to grow abundantly in polluted water systems (Molazadeh et al., 2019;Pittman et al., 2011). Among the microalgae, Chlorella species are well known for wastewater treatments and have been reported very efficient in the removal and recovery of nutrients such as nitrogen and phosphorus from wastewaters (Cai et al., 2013;Praveen and Loh, 2016). They are highly tolerant to CO2, pH, and salinity and proved to be highly industrially valuable for the production of lipids and biomass (Chou et al., 2019). ...
The microalgae are showing their future perspectives in the
phytoremediation technology to clean water, recapture waste nutrients,
degrade pollutants and convert them to economically valuable bio-based
products. Algae can produce high biomass by using the wastewater and
can be utilized to produce biofuels by using the existing technology. This
algal green technology has been accepted worldwide due to its vast
environmental benefits. Genetic engineering has an immense role in algal
bioremediation, such as it enables them to enhance their growth, and
helps to give resistance to harsh environments. This chapter is mainly
focusing on the advancements of genetic engineering improvement for
bioremediation along with the feasibility of low-cost technology for algal
biomass utilization. It also aims to improve the scientific attention to the future research perspectives in the field of engineered microalgae in
bioremediation for economic and environmental sustainability.
... Many species of microalgae have been reported to grow abundantly in polluted water systems (Molazadeh et al., 2019;Pittman et al., 2011). Among the microalgae, Chlorella species are well known for wastewater treatments and have been reported very efficient in the removal and recovery of nutrients such as nitrogen and phosphorus from wastewaters (Cai et al., 2013;Praveen and Loh, 2016). They are highly tolerant to CO2, pH, and salinity and proved to be highly industrially valuable for the production of lipids and biomass (Chou et al., 2019). ...
Humic substances (HS) improve soil fertility and structure, control nutrient uptake, and root architecture to increase plant growth and productivity. These modifications’ underlying biochemical and molecular mechanisms remain little understood. Colloidal dispersal systems have been discovered in HS, and although there is scant evidence to support this theory, it has been hypothesized that complex organic chemicals are already at work. In the book’s chapters, the authors give a summary of the findings that is currently available regarding the composition, biosynthesis, humification, and biological functions of humic compounds, with an emphasis on their surfaceactive characteristics. The biggest source of recalcitrant organic carbon in the terrestrial ecosystem, HS are an analytically defined percentage of soil organic matter. Where this book chapter explains the importance of humic substances as an essential environmental component for human life. They are very complex materials that need an explanation and simplification of how they are influencing the human life, so the reader will find in this book chapter a detailed explanation of how they are formed and structured in the soil. The authors explain the correction factors misconceptions about humic substances.
... These components influence the availability of nutrients, salinity, and pH (Chuka-ogwude et al., 2020) of the medium. In addition, appropriate nutrient concentration in AD has been proven to correlate with the enhancement of biomass production and lipid content of microalgae (Geider & La Roche, 2002;Praveen & Loh, 2016). Nevertheless, there is a concern when using anaerobic digestate directly for microalgal growth due to inappropriate nutrient concentrations, high toxicity, ammonia toxicity, turbidity, light penetration inhibition, contamination of unwanted microbes, and so on (Chuka-ogwude et al., 2020). ...
The book aims to analyse and discuss the conventional and emerging treatments of digestate generated in the anaerobic treatment of organic waste. Thus, in the circular economy framework, the book will address up-to-date strategies for the treatment and resource recovery from anaerobic digestate.
Anaerobic digestion is an expanding technology nowadays, especially when considering the thrust in ongoing research on the value-added products and energy recovery from biomass wastes, i.e., sludges, agro-industrial waste, animal waste, food waste and organic fraction of municipal solid waste, etc. Anaerobic digestate is a leftover and waste management authorities across the world do not have so many options for digestate management except using the digestate for land application as a fertilizer or composting. However, researchers and field engineers are still looking for robust options for digestate management. Thus, a timely book on digestate management will be an invaluable addition to this domain. The key features of the book include: the broad range of biomass waste covered, discussion of conventional to advanced technological options, and the inclusion of successful case studies.
ISBN: 9781789062748 (paperback)
ISBN: 9781789062755 (eBook)
ISBN: 9781789062762 (ePub)
... These waste substances can be developed to become important food sources for algae with high economic significance [29,30]. The removal efficiency of using Chlorella vulgaris for NH 3 -N, NO 3 − -N, and PO 4 3− -P reached as high as 95%, 53%, and 89%, whereas the maximum removal rates were 3.41 mg/L·day, 0.20 mg/L·day and 0.8 mg/L·day, respectively [31]. ...
The discharge of wastewater from aquaculture ponds causes a certain degree of damage to the environment. It is necessary to continuously improve the treatment efficiency of wastewater treatment devices. The purpose of this study is to obtain an optimal ratio of wastewater circulation devices in order to obtain the best operating parameters and to reduce the discharge of polluted water. We constructed an experimental wastewater circulation device consisting of three units. The primary unit contained modified attapulgite (Al@TCAP-N), volcanic stone, and activated carbon for precipitation. The secondary and tertiary units used biological methods to enhance removal rates of nitrogen and phosphorus. Water quality indicators of total phosphorus (TP), total nitrogen (TN), ammonia (NH3-N), permanganate (CODMn), and total suspended solids (TSS) were detected. Water quality was tested under different matching ratios for three units of different hydraulic retention time (HRT) and load Results showed that the removal rate of TP, TN, NH3-N, and TSS reached 20–60%, 20%, 30–70%, and 10–80%, respectively. The average reduction efficiencies of secondary module chlorella and filler on TP, TN, NH3-N, CODMn, and TSS were 56.88%, 30.09%, 0.43%, 46.15%, and 53.70%, respectively. The best removal rate can be achieved when the matching ratio of each unit becomes 2:1:1 and the hydraulic retention time is maintained within 2 h in the high-concentration load. Finally, the average removal rates of TP, TN, NH3-N, and TSS reached 58.87%, 15.96%, 33.99%, and 28.89%, respectively. The second unit obtained the enhanced removal effect in this wastewater treatment system when adding microorganisms and activated sludge.
... Nitrate removal efficiency differs with a different method of MPBR through the cultivation of Chlorella vulgaris such as algal biofilm membrane photo-bioreactor remove 64.9% of nitrogen (Gao et al., 2015). Osmotic membrane photobioreactor is designed by (Praveen et al., 2016) for wastewater by highdensity Chlorella vulgaris cultivation. With two and three days of hydraulic retention time, nitrate removal reached 53% and 66.5%, respectively, using the membrane photobioreactor for the secondary treatment of sewage effluent (Boonchai et al., 2015). ...
This study provides information on the occurrence of nitrogenous contamination in surface water, their sources and their negative effects. In addition, the study gives an overview of the possible technical, institutional and scientific methods of various biotechnological approaches of nitrogen removal and their limitations. Microalgae have a high capacity for converting CO2 from the atmosphere into beneficial products, including carbohydrates, lipids, and other bioactive compounds. Microalgae act as biofuels that are sustainable, renewable, and cost-effective. The impact of various environmental conditions on the efficiency of nitrogenous waste removal by microalgal species was studied. Literature related to microalgae-based bioremediation has a large research area with increasing trend. A bibliometric study was undertaken Based on the Science Citation Index Expanded of the Web of Science, to examine the body of knowledge on microalgae generated nitrate removal from wastewater from the year 2011. A global map based on co-authorship and co-occurrence analysis for countries, research areas, authors and institutions is presented based on the bibliometric analysis method.
... The influent phosphate concentration was 30 mg/L, but the phosphate concentration of the FS in the AnOMBR was increased from 30 mg/L to 74.3 mg/L after 10 days because of the concentrated ability of the FO technique and low phosphate requirement in anaerobic bacteria metabolism. However, the phosphorus accumulated in the bioreactor might cause eutrophication upon discharge; thus, the driving force of the OMBR system was reduced to hinder the growth of microorganisms in the bioreactor (Praveen and Loh, 2016;Wang et al., 2016). Thus, periodic MF extraction was performed every 10 days (other than the fourth MF extraction process was performed after 12 days because the water flux is still acceptable at 1.5 LMH) to withdraw excess phosphate from the FS. ...
Tetramethylammonium hydroxide (TMAH) is a toxic photoresist developer used in the photolithography process in thin-film transistor liquid crystal display (TFT-LCD) production, and it can be removed through anaerobic treatment. TMAH cannot be released into the environment because of its higher toxicity. A tight membrane, such as a forward osmosis (FO) membrane, together with an anaerobic biological process can ensure that no TMAH is released into the environment. Thus, for the first time, an anaerobic osmotic membrane bioreactor (AnOMBR) hybrid system was developed in this study to treat a low-strength TMAH wastewater and to simultaneously investigate its microbial community. Microfiltration extraction was used to mitigate the salinity accumulation, and a periodically physical water cleaning was utilized to mitigate the FO membrane fouling. The diluted draw solute (MgSO4) was reconcentrated and reused by a membrane distillation (MD) process in the AnOMBR to achieve 99.99% TMAH removal in this AnOMBR-MD hybrid system, thereby ensuring that no TMAH is released into the natural environment. Moreover, the membrane fouling in the feed and draw sides were analyzed through the fluorescence excitation-emission matrix (FEEM) spectrophotometry to confirm that the humic acid-like materials were the primary membrane fouling components in this AnOMBR. Additionally, 16 S rRNA metagenomics analysis indicated that Methanosaeta was the predominant contributor to methanogenesis and proliferated during the long-term operation. The methane yield was increased from 0.2 to 0.26 L CH4/g COD when the methanogen species acclimatized to the saline system.
... Positive correlation between P removal and pH [32] Polonit > Filtralite P > Top16 [33] Ion-exchange Maximum P sorption capacity: 66.22 mg/g [34] Hybrid ion exchange nanotechnology (HIX-Nano) resin adsorption capacity: 21.92 ± 4.13 mg PO 4 3--P/g [35] EPBR systems Membrane bioreactors TP: 87% at HRT 10 h from municipal wastewater [36] Biological phosphorus removal: 94.1% at HRT 7h from domestic wastewater [37] Granular sludge Phosphorus recovery from activated sludge: 51.3-56.1% [38] Sequencing bed reactor TP: 87.58% from mixed municipal wastewater [39] TP:85% [40] Algal systems Algal biofilm reactors TP:97% [41] Microalgal biofilm is recommended for tertiary treatment in the conventional treatment facility. [42] Immobilized/suspended algae bioreactors PO 4 3--P: 85% [43] TP: >75% [44] Membrane photo-film bioreactors PO 4 3--P: 89% at HRT 3d [45] Osmotic membrane bio-reactors PO 4 3--P: >96% [46] Forward osmosis membrane TP: 100% [47] Figure 2. Mechanism of P sorption. ...
Phosphorous (P) has been a component causing eutrophication of the water bodies. Adsorption has been broadly acknowledged as one of the best techniques for phosphate elimination and retrieval. Commonly used materials for adsorption of P have shown low removal capacity, creating the need to explore more efficient adsorbents. The present work aims to discuss recent developments and application of varied materials for adsorption of P. These materials (natural, artificial, and waste materials) have shown removal efficiencies ranging from 33% to 99.9% for P sorption. Some materials have shown adsorption greater than 90% like 99.9% (Zirconium-pillared bentonite clay), 96% (Iron scraps), 99% (Thermally treated Opoka), 90% (Biomass bottom ash), and 96.2% (Salted duck eggshells. The feasibility of recovery of P from saturated materials has been discussed along with the possibility of reuse of adsorbents after desorption, for alignment with the circular economy.
... The authors also declared that the membrane flux could be fully recovered by the backwashing method. In another research, Praveen and Loh [29] used Chlorella vulgaris in the osmotic membrane photobioreactor for investigating of nutrient removal from wastewater within 162 days. The authors reported the removal values of 95%, 53%, and 89% for ammonium, nitrate, and phosphate, respectively. ...
In this study, a novel reciprocal membrane photobioreactor (RMPBR) was designed. This system includes a PLC-programmed and a spongy blade that could clean the formed cake layer on the membrane surface. Moreover, various light-dark (L-D) cycles of 24-0, 16-8, and 12-12 for the Chlorella vulgaris cultivation were applied and the effects of these cycles on the membrane fouling time, transmembrane pressure (TMP), total extracellular polymeric substances (EPS) concentration, total soluble microbial product (SMP) concentration, the carbohydrate and protein contents through EPS (EPS c and EPS p), as well as the carbohydrate and protein contents through SMP (SMP c and SMP p) were evaluated. Obtained results revealed that this mechanical membrane revival method could reduce the total resistance at about 73-85%, without any cleaning/washing via chemical substances. Besides, the obtained results from microalgae cultures demonstrated that the contrary of the total concentration of EPS in 24-0 and 12-12, the total EPS contents for the 16-8 L/D regime did not change considerably. However, the total SMP for 16-8 L/D increased. Moreover, the SMP c and SMP p for all cycles depicted the rising trend. EPS p concentration gradually increased for 12-12 and 24-0 L/D cycles. These results could indicate that the EPS p was the main effective factor in TMP variations for 12-12 and 24-0 L/D regimes. However, the EPS p and EPS c in 16-8 L/D did not show any significant changes.
... Omics integration was addressed to promote sustainable microalgal cultivation system, wastewater treatment, and biofuel production. Praveen and Loh (2016) Diversity of microalgae and cyanobacteria Microalgae are classified under various phylogenetic lineages. Microalgae are photoautotrophs that carry photosynthesis in membrane-bound organelles (chloroplast) (Salama et al. 2013). ...
Emergence of pollutants in wastewater, expensive cultivation of microalgae, and difficulties in industrial scale production are the main challenges for successful coupling of microalgae with wastewater. Nitrogen, carbon, and phosphorus in wastewater are deliberately consumed by microalgae and cyanobacteria for their growth and could act as green technology for wastewater treatment. In this review, the role and mechanistic approaches of microalgae and cyanobacteria for removal of various (in)organic compounds from wastewater have been thoroughly addressed. Distinct pathways have been reported for improving wastewater treatment technologies through large-scale cultivation of microalgal. The techno-economic feasibility and major commercial production challenges along with genetic engineering research have been addressed. A biorefinery approach with integrated biology, ecology, and engineering would lead to a feasible microalgal-based technology for various applications.Graphic abstract
... When compared to other membranes (UF/MF), the benefits of FO are the higher selectivity and nutrient removal rate from the water [95,96]. FO can be implemented as a standalone concentration step for concentration or within a hybrid, also known as osmotic membrane photobioreactor [97]. Among the FO initiative, the OMEGA Project evaluated the possibility to concentrate microalgae and harvest nutrients from WW using FO bags placed in seawater; concentration by 4-to 6.6-times were achieved in the lab and full scale demonstration was realised in a real environment [88,98]. ...
In the past few years, osmotic membrane systems, such as forward osmosis (FO), have gained popularity as “soft” concentration processes. FO has unique properties by combining high rejection rate and low fouling propensity and can be operated without significant pressure or temperature gradient, and therefore can be considered as a potential candidate for a broad range of concentration applications where current technologies still suffer from critical limitations. This review extensively compiles and critically assesses recent considerations of FO as a concentration process for applications, including food and beverages, organics value added compounds, water reuse and nutrients recovery, treatment of waste streams and brine management. Specific requirements for the concentration process regarding the evaluation of concentration factor, modules and design and process operation, draw selection and fouling aspects are also described. Encouraging potential is demonstrated to concentrate streams more than 20-fold with high rejection rate of most compounds and preservation of added value products. For applications dealing with highly concentrated or complex streams, FO still features lower propensity to fouling compared to other membranes technologies along with good versatility and robustness. However, further assessments on lab and pilot scales are expected to better define the achievable concentration factor, rejection and effective concentration of valuable compounds and to clearly demonstrate process limitations (such as fouling or clogging) when reaching high concentration rate. Another important consideration is the draw solution selection and its recovery that should be in line with application needs (i.e., food compatible draw for food and beverage applications, high osmotic pressure for brine management, etc.) and be economically competitive.
... Thermodynamic parameters can give valuable information about the adsorption process [41,42]. The following equation used for the calculation of standard free energy: ...
The treatment of cyanide contaminated wastewater from a gold processing plant was performed by the synthesized nanostructured Layered Double Hydroxide (LDH) which has known as a Hydrotalcite-type anionic clay. LDH was synthesized by the co-precipitation process, characterized by X-ray fluorescence (XRF), X-ray powder diffraction (XRD), scanning electron microscope (SEM) Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy (FTIR) and Wavelength Dispersive X-ray analysis (WDX) and applied for removal of free cyanide from both synthetic solution and mining effluent. The maximum particle size of synthesized LDH was determined to be 4 nm based on the Scherrer’s equation. The maximum loading capacity of LDH, 60 mg/g, indicates that LDH is an interesting adsorbent for cyanide removal. The data modeling showed that the kinetic and equilibrium data best fitted by FPKM and RPIM, respectively, also, rate-controlling step in the adsorption process is intra-particle diffusion based on Weber–Morris plot, and the adsorption of CN− onto LDH is a two-step process. The thermodynamic studies confirm that the adsorption of free cyanide on Mg/Al LDH is a spontaneous and endothermic process. The energy of activation for adsorption of free cyanide on Mg/Al LDH was determined to be 6.14 kJ/mol, which is in the range physicochemical sorption. The mining wastewater treatment was performed by the synthesized LDH. The adsorption experiments showed that more than 90% of free cyanide was removed from the real solution during a short period of contact time, which confirms the ability of LDH for the treatment of industrial cyanide contaminated wastewater.
Graphical abstract
... .9% and 85.2% were achieved for nitrogen and phosphorus, respectively. Praveen and Loh [28] designed an osmotic membrane photobioreactor for nitrate and phosphate removal through wastewater by high-density Chlorella vulgaris cultivation. Consequently, the NO3removal was about 53%, and the PO4 3uptake was up to 89%, at three days HRT. ...
The membrane photobioreactor (MPBR) is a well‐operated system concerning microalgae cultivation and nutrients assimilation from wastewater effluent. In the present paper, a sample of pulp and paper wastewater was primarily treated by activated sludge system (ACS), and the concentration of nitrate and phosphate decreased as about 26 and 10%, respectively. Then, it was transferred into six flat plate MPBR systems with 5 L capacity and 0.45 μm membrane pore size for the secondary treatment process (nitrate and phosphate assimilation) by Chlorella vulgaris (green microalgae) species during six cultivation periods. In this section, the effects of different light intensities (100 and 300 μmol m⁻² s⁻¹) and light–dark cycles (24–0, 16–8, and 12–12) on nitrate and phosphate uptake through the treated pulp and paper wastewater effluent after 24 hr were investigated. The maximum photosynthetic productivity and nitrate‐phosphate removals after 24 hr (nitrate: 57% and phosphate: 43%) were recorded for the culture under 300 μmol m⁻² s⁻¹ and 24–0 light–dark regime within the MPBR system.
... galbana microalgae culture was used [41]. But in their study, Praveen and Loh [38] stated that pure C. vulgaris contained 8.95% protein in synthetic tertiary treatment water. When the obtained and literature values are examined together, it is obvious that the ratio of lipid and protein varies according to microalgae, quality of feed medium, and ambient conditions. ...
In this study, the effect of sludge retention time (SRT) on biomass production and nutrient removal was determined by constant hydraulic retention time (HRT) with mixed microalgae culture. The SRTs of 2, 3, 6, 12, and 24 days with constant 24 h HRT were studied in microalgae membrane photobioreactor (msMpBR) by using hollow fiber (HF) membranes with a pore diameter of 0.45 μm. According to the results, the best removal was achieved within 3 days of SRT. Chlorophyll-a/mixed liquor suspended solid (MLSS) ratios were found to be 0.033. Total nitrogen (TN) and phosphate phosphorus (PO4–P) removal rates were found to be 5.55 mg N/L day⁻¹, and 0.4 mg PO4–P/L day⁻¹, respectively. The volumetric microalgae production was found to be 0.118 g/L day⁻¹. Also, Chaetophora sp. and Navicula sp. cultures were found to be dominant in steady state. The percentage of lipid and protein in dry biomass was obtained to be 8.94% and 30.34%, respectively. It is advisable to use algal membrane photobioreactor, and mixed microalgae cultures instead of specific microalgae cultures, which could be readily affected by seasonal changes and outdoor conditions in wastewater treatment.
Phosphorus (P) discharge from anthropogenic sources, notably sewage effluent and agricultural runoff, significantly contributes to eutrophication in aquatic environments. Stringent regulations have heightened the need for effective P removal technologies in wastewater treatment processes. This paper provides a comprehensive review of current P removal methods, focusing on both biological and chemical approaches. Biological treatments discussed include enhanced biological P removal in activated sludge systems, biological trickling filters, biofilm reactors, and constructed wetlands. The efficiency of microbial absorption and novel biotechnological integrations, such as the use of microalgae and fungi, are also examined. Chemical treatments reviewed encompass the application of metal salts, advanced oxidation processes such as chlorination, ozonation, and the Fenton reaction, as well as emerging techniques including the Electro-Fenton process and photocatalysis. Analytical methods for P, including spectrophotometric techniques and fractionation analyses, are evaluated to understand the dynamics of P in wastewater. This review critically assesses the strengths and limitations of each method, aiming to identify the most effective and sustainable solutions for P management in wastewater treatment. The integration of innovative strategies and advanced technologies is emphasized as crucial for optimizing P removal and ensuring compliance with environmental regulations.
To date, the field of microalgae has been slowly evolving and expanding to accommodate various industries from food and feed to biofuel production coupled with wastewater treatment which subsequently allowed greater access of water for daily usage. This technology is gradually proving its value, despite its limited use in the market. With the depletion of freshwater resources, conventional treatment methods are being replaced by microalgae-mediated wastewater treatment. This method not only has a lower environmental footprint and produces less chemical waste, but also captures nutrients more efficiently than conventional methods which would be subsequently consumed for the development of microalgal biomass. Several factors that influence the recovery of nutrients such as phosphorus and nitrogen that are crucial for algal growth are discussed accordingly in this chapter, including wastewater characteristics, turbidity, concentration of phosphorus and nitrogen as well a chemical oxygen demand and biological oxygen demand. Additionally, currently available microalgae-based wastewater technologies are introduced along with the respective advantages and disadvantages. Sustainability prospect of microalgae-based wastewater technologies is also examined. Lastly, this chapter also includes the potential challenges that hinder the development and commercialization of microalgae-based wastewater technologies and provides adequate future recommendations for resolving the current concerns.
With the focus on limiting greenhouse gas emissions, microalgae-based technology is a promising approach for wastewater treatment, combining cost-effective operation, nutrient recovery, and assimilation of CO2. In addition, membrane technology supports process intensification and wastewater reclamation. Based on a bibliometric analysis, this paper evaluated the literature on membrane photobioreactors to highlight promising areas for future research. Specifically, efforts should be made on advancing knowledge of interactions between algae and bacteria, analysing different strategies for membrane fouling control and determining the conditions for the most cost-effective operation. The Scopus® database was used to select documents from 2000 to 2022. A set of 126 documents were found. China is the country with the highest number of publications, whereas the most productive researchers belong to the Universitat Politècnica de València (Spain). The analysis of 50 selected articles provides a summary of the main parameters investigated, that focus in increasing the biomass productivity and nutrient removal. In addition, microalgal-bacterial membrane photobioreactor seems to have the greatest commercialisation potential. S-curve fitting confirms that this technology is still in its growth stage.
Chlorella vulgaris is a green unicellular microalgae species, which has the ability to be utilized as an effective agent in the secondary treatment of various wastewaters. Nitrate and phosphate ions are among hazardous materials within the wastewaters which can be assimilated by green microalgae species through various cultivation methods. In this study, three cultivation methods for Chlorella vulgaris cultivation were considered (autotrophic, heterotrophic, and mixotrophic), and the effect of these models in terms of nitrate and phosphate removal from municipal wastewater was investigated. The results revealed that the best pattern of microalgae growth is related to the mixotrophic culture method at about 2.3 grams on the ninth day. Besides, the highest rate of nitrate and phosphate removals were recorded through the mixotrophic model at 92.58% and 91.25%, respectively. According to the obtained results, mixotrophic cultivation had the greatest effect on the removal of nutrients from municipal wastewater compared to the other two cultivations.
The natural and anthropogenic sources of water bodies are contaminated with diverse categories of pollutants such as antibiotics, pharmaceuticals, pesticides, heavy metals, organic compounds, and other industrial chemicals. Depending on the type and the origin of the pollutants, the degree of contamination can be categorized into lower to higher concentrations. Therefore, the removal of hazardous chemicals from the environment is an important aspect. The physical, chemical and biological approaches have been developed and implemented to treat wastewaters. The microbial and algal treatment methods have emerged as a growing field due to their eco-friendly and sustainable approach. Particularly, microalgae emerged as a potential organism for the treatment of contaminated water bodies. The microalgae of the genera Chlorella, Anabaena, Ankistrodesmus, Aphanizomenon, Arthrospira, Botryococcus, Chlamydomonas, Chlorogloeopsis, Dunaliella, Haematococcus, Isochrysis, Nannochloropsis, Porphyridium, Synechococcus, Scenedesmus, and Spirulina reported for the wastewater treatment and biomass production. Microalgae have the potential for adsorption, bioaccumulation, and biodegradation. The microalgal strains can mitigate the hazardous chemicals via their diverse cellular mechanisms. Applications of the microalgae strains were found to be effective for sustainable developments and circular economy due to the production of biomass with the utilization of pollutants.
Pollutants, including dyes and heavy metals from textile industrial discharge, adversely affect the surface and groundwater resources, and pose a severe risk to the living organisms in the ecosystem. Phycoremediation of wastewater is now an emerging trend, as it is colossally available, inexpensive, eco-friendly, and has many other benefits, with high removal efficiency for undesirable substances, when compared to conventional treatment methods. Algae have a good binding affinity toward nutrients and toxic compounds because of various functional groups on its cell surface by following the mechanisms such as biosorption, bioaccumulation, or alternate biodegradation pathway. Algae-based treatments generate bioenergy feedstock as sludge, mitigate CO2, synthesize high-value-added products, and release oxygenated effluent. Algae when converted into activated carbon also show good potential against contaminants, because of its higher binding efficiency and surface area. This review provides an extensive analysis of different mechanisms involved in removal of undesirable and hazardous substances from textile wastewater using algae as green technology. It could be founded that both biosorption and biodegradation mechanisms were responsible for the removal of dye, organic, and inorganic pollutants. But for the heavy metals removal, biosorption results in higher removal efficiency. Overall, phycoremediation is a convenient technique for substantial conserving of energy demand, reducing greenhouse gas emissions, and removing pollutants.
Graphical abstract
It was found that immobilization of cells in poly(vinyl alcohol) (PVA) cryogel can be successfully applied for concurrent cryoimmobilization, cryoconservation and long-term storage of the cells of various phototrophic microorganisms (green and red microalgae, diatoms and cyanobacteria). For the first time, it was shown for 12 different immobilized microalgal cells that they can be stored frozen for at least 18 months while retaining a high level of viability (90%), and can further be used as an inoculum upon defrosting for cell-free biomass accumulation. Application of cryoimmobilized Chlorella vulgaris cells as inocula allowed the loading of a high concentration of the microalgal cells into the media for free biomass accumulation, thus increasing the rate of the process. It was shown that as minimum of 5 cycles of reuse of the same immobilized cells as inocula for cell accumulation could be realized when various real wastewater samples were applied as media for simultaneous microalgae cultivation and water purification.
The overconsumption of the non-renewable sources of energy has caused ecological imbalance and this has paved the way for the utilization of the renewable energy sources. Sustainable energy sources include solar energy, plant or forest biomass, tidal and wind energy. Renewable sources of energy are traditional, conventional, or new. Production of eco-friendly energy sources is now in high demand. The task for the production of sustainable energy can be overtook by a wide variety of microbes. A wide variety of microorganisms encompass the potential of biofuel production, for example, many bacteria can directly produce ethanol by sugar degradation. Microalgae and cyanobacteria can reduce CO2 to biofuels by photosynthesis. Methanotrophs can produce methanol by oxidizing methane. Geobacter sulfurreducens and Shewanella oneidensis can be used in the microbial fuel cells (MFCs) for bioelectricity and biohydrogen production. MFCs use catabolic function of microbes and generate electricity by using a wide variety of materials, for example, biomass. Recent research has shown that MFCs will be able to replace the non-renewable sources of energy and will produce electricity adequate for the consumption of human society.
Water is a basic need for the functioning of all life forms that exist on earth. However, current water resources are being polluted by anthropogenic sources, which include social unit, as well as agricultural and industrial waste. People all over the world have concerns about the impact of effluent pollution on the atmosphere, which is increasing day by day. It is hard to purify wastewater before it flows into water reservoirs. Hence, the treatment of wastewater remains an essential need before it is allowed to enter natural water streams. Wastewater treatment is relatively a modern practice. This review will particularly discuss the ways of heavy metal ion removal from wastewater. The ultimate purpose of wastewater management is to improve the health of human and environmental aspects.
The high levels of phosphorus (P) removal occurring through human activities contributes to Eutrophication. Therefore, it is important to understand the quantity of P flows of the different filter materials. This paper provides an overview on the different filter media used for P removal from wastewater also the conventional wastewater treatment system for phosphorus removal. The filter materials consist of natural materials, industrial by-products and man-made products. Most filters have been investigated in batch and column studies in laboratory. The results from these overview vary for every filters and recycled concrete aggregates (RCA) have demonstrated promising properties with regard to P removal capacity. The chemical composition of the adsorption media is a critical factor. Because phosphorus is removed via sorption and precipitation processes, Calcium (Ca), Iron (Fe) and Aluminium (Al) content is important in efficient P removal. Thus filter media should be selected very carefully. In such systems, appropriate pre-treatment will also allow for a longer lifetime of the filter media, by decreasing the risk of clogging and allowing one to use finer reactive filter media with higher sorption capacity. The usage of these alternatives filters materials will ease the environmental problems that are currently perceived globally.
In this study, the effect of hydraulic retention time (HRT) on the performance of microalgae membrane photobioreactor (MpBR) inoculate by mixed culture were with examined on biomass productivity and nutrient removal from synthetic secondary effluent. The optimization of HRT was aimed for the treatment of wastewater in MpBR operating at HRTs between 24 h and 72 h with at a fixed sludge retention times (SRT) of 3 d. The volumetric microalgae production rates were obtained to be from 0.118 g L⁻¹day⁻¹ to 0.064 g L⁻¹day⁻¹, respectively at increasing HRT from 24 h to 72 h at the stable conditions. The total nitrogen (TN) removal rate was calculated to be 5.55 mgL⁻¹day⁻¹ and the phosphate phosphorus (PO4–P) removal rate to 0.40 mgL⁻¹day⁻¹ where the highest biomass production rate was obtained at the HRT of 24 h. Although this work showed the potential use of mixed microalgae culture and membrane in both wastewater treatment and microalgae biomass production, it is looked that the treatment of the secondary effluent has not been able to meet the discharge standards according to EU and general directives unless optimization is made. But bioenergy power, namely lipid and protein ratios of dry biomass under the optimum conditions were also determined and lipid content was 8.94% and the protein content was 34%. Today, when there is a global food shortage, the oil and protein ratio in microalgae biomass obtained by treating wastewater is potentially competitive with traditional agricultural products.
Growing nutrient content of surface waters causes environmental concerns about eutrophication due to the immethodical release of nutrient containing effluent. The potential of microorganisms to decrease nitrogen and phosphorus concentration has drawn increasing attention. The present study is performed to evaluate the nutrient removal potential of cyanobacterium Synechococcus elongatus in different trophic cultivations. For this purpose, 15 experiments were designed by the Box-Behnken method using modified BG-11, including the initial concentrations of phosphorus, nitrogen, and glucose up to 10 mg L−1, 600 mg L−1, and 10 g L−1, respectively. Different trophic conditions were applied by changing carbon sources and light–dark cycles. The maximal removal of phosphorus and nitrogen were obtained in mixotrophic condition with 85.1% and 87.4%, respectively, and the specific growth rate of microalga was 0.99 day−1. Besides, its nutrient removal efficiency in dairy effluent was about 92% in mixotrophic culture, while the heterotrophic condition was not efficient. Based on the obtained results, mixotrophic cultivation of the cyanobacteria S. elongatus would be useful for application in N-riched and P-riched effluents.
Wastewater utilization as a medium for microalgal cultivation have copious simultaneous perquisites such as removal of nutrients (80–100%), heavy metal removal, carbon dioxide (CO2) sequestration from atmosphere (1.83 kg CO2 kg−1 biomass), and high biomass production for biofuel generation (40–50% higher than crops feedstock). Municipal, industrial, domestic, agro-industrial, and several other types of wastewater treatment by coupling microalgal cultivation require two sorts of systems: open pond systems (OPs) and closed photobioreactors (PBRs). Many studies have focused on the utilization of OPs and closed PBRs for microalgal cultivation; however, comprehensive information in context of nutrient removal efficiency and biomass productivity with updated data is not fully addressed. In this review, wastewater treatment coupled microalgal cultivation for biofuel generation is emphasized in OPs and closed PBRs. The limitations of both systems, implementation of different approaches to enhance the biomass productivity, and economic feasibility are also highlighted. Based on the literature analysis, PBRs are more effective in wastewater treatment and biomass/biofuel generation due to contamination control and management of major parameters affecting microalgal growth. However, the implementation of various techniques to reduce the capital investment in PBR reactor designs is required for further use on commercial scale.
Graphical abstract
Gravity settler was integrated into an algal membrane photobioreactor (MPBR) for in situ biomass concentration and harvesting of Graesiella emersonii. By continuous circulation of suspended biomass between MPBR and settler, biomass was sedimented in the settler and harvested. MPBR-Settler operations at different recirculation rates (0.15-2.4 L/d) and settler volumes (250-1000 mL) affected both suspended (0.4-3.4 g/L) and settled (16.1-31.1 g/L) biomass concentrations. Maximum biomass productivity of 0.26 ± 0.06 g/L/d was achieved in the 1000 mL settler operating at 0.6 L/d recirculation rate, which also yielded 9-131 times concentrated biomass (31.1 g/L) compared to the baseline MPBR (0.2-3.4 g/L). This novel design also facilitated MPBR operation at low solids retention times (6-8 d) without incurring large outflow of unfiltered effluent, while alleviating light limitation via biomass dilution. These results demonstrated that the MPBR-Settler system can provide an excellent way to mitigate light limitation, enhance biomass productivity, and simplify biomass harvesting.
Forward osmosis (FO) has great potential for low energy consumption wastewater reuse provided there is no requirement for draw solutes (DS) regeneration. Reverse solute flux (RSF) can lead to DS build-up in the feed solution. This remains a key challenge because it can cause significant water flux reduction and lead to additional water quality problems. Herein, an osmotic photobioreactor (OsPBR) system was developed to employ fast-growing microalgae to consume the RSF nutrients. Diammonium phosphate (DAP) was used as a fertilizer DS, and algal biomass was a byproduct. The addition of microalgae into the OsPBR proved to maintain water flux while reducing the concentrations of NH4⁺-N, PO4³⁻-P and chemical oxygen demand (COD) in the OsPBR feed solution by 44.4%, 85.6%, and 77.5%. Due to the forward cation flux and precipitation, intermittent supplements of K⁺, Mg²⁺, Ca²⁺, and SO4²⁻ salts further stimulated algal growth and culture densities by 58.7%. With an optimal hydraulic retention time (HRT) of 3.33 d, the OsPBR overcame NH4⁺-N overloading and stabilized key nutrients NH4⁺-N at ∼ 2.0 mg L⁻¹, PO4³⁻-P < 0.6 mg L⁻¹, and COD < 30 mg L⁻¹. A moderate nitrogen reduction stress resulted in a high carbohydrate content (51.3 ± 0.1%) among microalgal cells. A solids retention time (SRT) of 17.82 d was found to increase high-density microalgae by 3-fold with a high yield of both lipids (9.07 g m⁻³ d⁻¹) and carbohydrates (16.66 g m⁻³ d⁻¹). This study encourages further exploration of the OsPBR technology for simultaneous recovery of high-quality water and production of algal biomass for value-added products.
Coupling algal biomass growth to wastewater treatment is a promising alternative for the simultaneous removal and recovery of nutrients. This study aims to evaluate the effects of the Hydraulic Retention Time (HRT) on the fouling behavior and biomass characteristics of C. Vulgaris in a Membrane Photobioreactor (MPBR), fed with a secondary synthetic wastewater effluent. The changes in the algal cell characteristics and in their metabolic products were assessed at three different HRTs (12 h, 24 h and 36 h). Experimental results showed that higher loading rates led to a broader Particle Size Distribution (PSD) resulting from looser and less stable algal flocs. In contrast, bigger and homogeneously distributed particles observed at lower loading rates, led to a porous layer with lower fouling rates and organic removal. The presence of smaller particles and dissolved organics resulted in a more compact and less porous layer that increased the removal of small-MW organics.
In this study, a pilot-scale anoxic/aerobic biofilter system combined with chemical precipitation was devised and applied for the tertiary treatment of nitrogen, and post-treatment of phosphorus and residual organics in effluent from existing wastewater treatment facilities. When the system operated under a system hydraulic retention time (HRT) of 5.98 h, nitrified effluent recirculation ratio of 0.5, average methanol-supplement concentration of 23.2 mg/L, and average aluminum-sulfate concentration of 2.37 mg/L, the average concentration of BOD5, COD, SS, TN, and TP in the system effluent were 3.3, 10.4, 4.2, 6.1, and 0.43 mg/L, respectively. Despite the shorter HRT of 1.35 h in the anoxic filter packed with media, noticeable denitrification was achieved rapidly. A perfect nitrification rate was achieved and no clear deterioration in performance by chemical addition was observed. Thus, the system achieved not only outstanding nitrogen-removal performance, but also the additional removal of residual organics and phosphorus.
Many rural areas of Latin America and the Caribbean region (LAC) are economically depressed. Rural sewage treatment in most areas of LAC is deficient or non-existent. Consequently, the possibility of generating economic revenue from treated sewage is an attractive option for deprived areas of developing countries. Given its peculiar characteristics, rural sewage may be coupled with biological systems such as algae for nutrient cycling. Acceptable algae growth and nutrient elimination were obtained from rural sewage whose treatment may have fallen short of current disposal standards. In this study, aerobic systems working on an 8-month cycle at three different volumetric loading rates (Bv) were assessed in relation to the lifetime growth of three algae strains native to Ecuador. Results indicate Chlorella sp. M2 as the optimal algal strain, with the highest growth rate at Bv of 1 g COD L−1 d−1 and a removal of organic-N (30%), PO43–-P (87%) and NH4+-N (95%). Concomitantly, the kinetic constants of the sewage resulted in a low biomass yield coefficient, making the proposed system highly suitable for developing countries. Finally, the proposed partial recovery stream method, combining nutrient recovery with economic resource generation, appears to contain great potential.
A detailed and systematic study was conducted to investigate the role of sludge retention time (SRT) on biomass production in an algal membrane photobioreactor (MPBR) treating synthetic tertiary wastewater. At 10–350 days SRT, biomass accumulation was independent of SRT and steady state biomass concentration was stable at about 1.9 g/L. At lower SRTs of 2–10 days, biomass concentration in MPBR decreased proportionately, and reached a minimum of 0.54 g/L at 2 days SRT. On the other hand, biomass productivity increased monotonically from 5.9 mg/L-day at 350 days SRT to 318 mg/L-day at 2.5 days SRT, although these changes had little influence on nutrients removal in the MPBR. In contrast, biomass production in the MPBR was independent of hydraulic retention time (HRT), although nutrient removal decreased at lower HRTs. Changes in light intensity affected both biomass accumulation and nutrients removal. By operating the MPBR at high light intensity, 95% NO3⁻-N and 73% PO4³⁻-P removal were obtained even at a shorter HRT of 0.5 days, while biomass concentration and productivity were 3.13 g/L and 313 mg/L-h, respectively. Statistical analysis indicated that the influence of SRT and light intensity on biomass productivity in the MPBR were comparable. These results indicate that SRT is not merely an operating parameter to control biomass removal rate, but it can serve as a tool to alleviate light limitation and enhance biomass production in MPBRs.
Graesiella emersonii was cultivated in an osmotic membrane photobioreactor (OMPBR) for nutrients removal from synthetic wastewater in continuous mode. At 1.5 days of hydraulic retention time and under continuous illumination, the microalgae removed nitrogen (N) completely at influent NH4⁺-N concentrations of 4–16 mg/L, with removal rates of 3.03–12.1 mg/L-day. Phosphorus (P) removal in the OMPBR was through biological assimilation as well as membrane rejection, but PO4³⁻-P assimilation by microalgae could be improved at higher NH4⁺-N concentrations. Microalgae biomass composition was affected by N/P ratio in wastewater, and a higher N/P ratio resulted in higher P accumulation in the biomass. The OMPBR accumulated about 0.35 g/L biomass after 12 days of operation under continuous illumination. However, OMPBR operation under 12 h light/12 h dark cycle lowered biomass productivity by 60%, which resulted in 20% decrease in NH4⁺-N removal and nearly threefold increase in PO4³⁻-P accumulation in the OMPBR. Prolonged dark phase also affected carbohydrate accumulation in biomass, although its effects on lipid and protein accumulation were negligible. The microalgae also exhibited high tendency to aggregate and settle, which could be attributed to reduction in cell surface charge and enrichment of soluble algal products in the OMPBR. Due to a relatively shorter operating period, membrane biofouling and salt accumulation did not influence the permeate flux significantly. These results improve the understanding of the effects of N/P ratio and light/dark cycle on biomass accumulation and nutrients removal in the OMPBR.
Forward osmosis membranes are less prone to fouling with high rejection of salts, and the osmotic membrane bioreactor (OMBR) can be considered as an innovative membrane technology for wastewater treatment. In this study, a submerged OMBR having a cellulose triacetate membrane, with the active layer facing the feed solution configuration, was operated at different organic loading rates (OLRs), i.e., 0.4, 1.2 and 2.0 kg-COD/(m(3)·d) with chemical oxygen demand (COD) concentrations of 200 mg/L, 600 mg/L and 1,000 mg/L, respectively, to evaluate the performance on varying wastewater strengths. High organic content with sufficient amount of nutrients enhanced the biomass growth. High OLR caused more extrapolymeric substances production and less dewaterability. However, no significant differences in fouling trends and flux rates were observed among different OLR operational conditions.
In the view of limited phosphorous resources and tightened discharge regulations, the recovery of phosphate and nitrate from wastewater is of great interest. Here, the integration of microalgae into wastewater treatment processes is a promising approach. A prototype-scale Twin-Layer photobioreactor immobilizing the green alga Halochlorella rubescens on vertical sheet-like surfaces was constructed and operated using primary and secondary municipal wastewater. The process was not impaired by suspended solids, bacteria or loss of algal biomass by leaching. The average areal microalgal growth was 6.3gm(-2) d(-1). After treatment, P and N concentrations in the effluents could efficiently be reduced by 70-99%, depending on element and type of wastewater. Mean effluent values of ⩽1.0mg L(-1)P and 1.3mgL(-1)N met the legal discharge limits of the European Water Framework Directive and show a potential to comply with upcoming, more stringent legislation.
An algae-based membrane bioreactor (A-MBR) was evaluated for high-density algae cultivation and phosphorus (P) removal. The A-MBR was seeded with Chlorella emersonii and operated at a hydraulic retention time of 1day with minimal biomass wastage for about 150days. The algae concentration increased from initially 385mg/L (or 315mg biomass COD/L) to a final of 4840mg/L (or 1664mg COD/L), yielding an average solids (algae biomass+minerals) production rate of 32.5gm(-3)d(-1) or 6.2gm(-2)d(-1). The A-MBR was able to remove 66±9% of the total P from the water while the algal biomass had an average of 7.5±0.2% extracellular P and 0.4% of intracellular P. The results suggest that algae-induced phosphate precipitation by algae is key to P removal and high-density algae cultivation produces P-rich algal biomass with excellent settling properties.
The marine diatom Chaetoceros cf. wighamii has been investigated for its potential use as food in mariculture. In this work, we investigated temperature (20, 25, and 30 °C), salinity (25 and 35) and carbon dioxide addition (air and air+CO2) effects on growth and biochemical composition of C. cf. wighamii, under laboratory conditions. C. cf. wighamii growth and biomass was primarily affected by carbon dioxide addition and to a lesser extent by temperature and salinity. In general, lipid and carbohydrate content were higher at lower temperatures (20 and 25 °C) while protein was unaffected. Carbon dioxide addition increased protein and lowered carbohydrates, but had no effect on lipid content. Carbohydrates were enhanced while lipids and protein decreased at the highest salinity (35). These results should be taken into consideration when evaluating the nutritional value of this microalga for marine invertebrate larvae.
Although adhesion of bacteria and yeast have been extensively studied by a wide range of experimental and theoretical approaches, significantly less attention has been focused on microalgae adhesion to solid materials. This work is focused on physicochemical aspects of microalgae adhesion. The results are based on experimental characterization of surface properties of both microalgae and solids by contact angle and zeta potential measurements. These data are used in modeling the surface interactions (thermodynamic and colloidal models) resulting in quantitative prediction of the interaction intensities. Finally, the model predictions are compared with experimental adhesion tests of microalgae onto model solids in order to identify the physicochemical forces governing the microalgae–solid interaction. The model solids were prepared in order to cover a wide range of properties (hydrophobicity and surface charge). The results revealed that, in low ionic strength environment, the adhesion was influenced mostly by electrostatic attraction/repulsion between surfaces, while with increasing ionic strength grew the importance of apolar (hydrophobic) interactions. The impact of solid surface properties on the degree of colonization by microlagae was statistically more significant than the influence of medium composition on cell surface of Chlorella vulgaris.
The recently resurgent forward osmosis (FO) membrane process has the potential to become a sustainable alternative to conventional membrane processes. However, the fouling and cleaning behavior of FO membranes remains largely unknown. There is a need to fully understand the fouling phenomena in FO in order to take advantage of this emerging technology. In this study, we used alginate as a model organic foulant to examine FO membrane fouling and cleaning behavior with the ultimate goal of determining the underlying FO fouling/cleaning mechanisms. Results showed that alginate fouling in FO is almost fully reversible, with more than 98% recovery of permeate water flux possible after a simple water rinse without any chemical cleaning reagents. We also studied the role of applied hydraulic pressure in membrane fouling and cleaning by performing fouling tests in FO (without hydraulic pressure) and RO (with hydraulic pressure) modes. Flux recovery in the FO mode was much higher than that in the RO mode under similar cleaning conditions, although the rate of membrane flux decline was similar in the two modes. The fouling reversibility of FO was attributed to the less compact organic fouling layer formed in FO mode due to the lack of hydraulic pressure. Our results suggest that operating in FO mode may offer an unprecedented advantage in reducing or even eliminating the need for chemical cleaning. AFM force measurements were used to elucidate the impact of membrane materials (cellulose acetate versus polyamide) on membrane fouling and cleaning behavior. Adhesion force data revealed that a small percentage of relatively adhesive sites on the membrane surface play an important role in increasing membrane fouling potential and decreasing cleaning efficiency. This finding implies that using average adhesion force to predict membrane fouling potential is inadequate. Extensive long-range adhesion forces are observed for the polyamide membrane in the presence of alginate and calcium ions. The long-range interactions are attributed to calcium bridging of alginate molecules between the AFM probe and the adhesive sites on the polyamide membrane surface.
Batch experiments were carried out to investigate the effect of the initial nitrogen and phosphorus concentrations on nutrient removal performance of microalgae Chlorella vulgaris and to determine biokinetic coefficients such as k; reaction rate constant, Km, half saturation constant, and Y, yield coefficient by using Michaelis–Menten rate expression. The NH4-N concentration was varied between 13.2–410 mg l−1 while PO4-P concentration was between 7.7–199 mg l−1 by keeping N/P ratio around 2/1 in the synthetic wastewater. The experiments were performed at pH 7.0 and at room temperature (20 ± 2 °C) with artificial illumination (4100 lux). Experimental results indicated that effluent water quality decreases with increasing nutrient concentrations and algae culture can remove nitrogen more effectively compared to phosphorus. Biokinetic coefficients were determined as k = 1.5 mg NH4-N mg−1 chl a d−1, Km = 31.5 mg l−1, YN = 0.15 mg chl a mg−1 NH4-N for nitrogen and k = 0.5 mg PO4-P mg−1 chl a d−1, Km = 10.5 mg l−1, YP = 0.14 mg chl a mg−1 PO4-P for phosphorus.
Continuous phenol biodegradation was accomplished in a two-phase partitioning osmotic membrane bioreactor (TPPOMBR) system, using extractant impregnated membranes (EIM) as the partitioning phase. The EIMs alleviated substrate inhibition during prolonged operation at influent phenol concentrations of 600-2000mg/L, and also at spiked concentrations of 2500mg/L phenol restricted to 2 days. Filtration of the effluent through forward osmosis maintained high biomass concentration in the bioreactor and improved effluent quality. Steady state was reached in 5-6 days at removal rates varying between 2000 and 5500mg/L-day under various conditions. Due to biofouling and salt accumulation, the permeate flux varied from 1.2-7.2 LMH during 54 days of operation, while maintaining an average hydraulic retention time of 7.4h. A washing cycle, comprising 1h osmotic backwashing using 0.5M NaCl and 2h washing with water, facilitated biofilm removal from the membranes. Characterization of the extracellular polymeric substances (EPS) through FTIR showed peaks between 1700 and 1500cm(-1), 1450-1450cm(-1) and 1200-1000cm(-1), indicating the presence of proteins, phenols and polysaccharides, respectively. The carbohydrate to protein ratio in the EPS was estimated to be 0.3. These results indicate that TPPOMBR can be promising in continuous treatment of phenolic wastewater.
Chlorella vulgaris encapsulated in alginate beads were added into a bioreactor treating synthetic wastewater using Pseudomonas putida. A symbiotic CO2/O2 gas exchange was established between the two microorganisms for photosynthetic aeration of wastewater. During batch operation, glucose removal efficiency in the bioreactor improved from 50 % in 12 h without aeration to 100 % in 6 h, when the bioreactor was aerated photosynthetically. During continuous operation, the bioreactor was operated at a low hydraulic retention time of 3.3 h at feed concentrations of 250 and 500 mg/L glucose. The removal efficiency at 500 mg/L increased from 73 % without aeration to 100 % in the presence of immobilized microalgae. The initial microalgae concentration was critical to achieve adequate aeration, and the removal rate increased with increasing microalgae concentration. The highest removal rate of 142 mg/L-h glucose was achieved at an initial microalgae concentration of 190 mg/L. Quantification of microalgae growth in the alginate beads indicated an exponential growth during symbiosis, indicating that the bioreactor performance was limited by oxygen production rates. Under symbiotic conditions, the chlorophyll content of the immobilized microalgae increased by more than 30 %. These results indicate that immobilized microalgae in symbiosis with heterotrophic bacteria are promising in wastewater aeration.
Membrane bioreactor (MBR) has been widely applied worldwide in full scale. Recent research and development trends of MBR technology has been shifted from process optimization and economic evaluation to installation of new process architecture to enrich functional strains like nitrifiers or providing assisted field for performance enhancement, to incorporation of affordable adsorbents or scouring agent for membrane fouling mitigation, and to applying MBR hybrid systems for achieving simultaneous removals of nutrients and other pollutants. This mini-review summarized the recent works, principally in 2014-2015, on the above aspects, and provided a discussion on the osmotic MBR based on forward osmosis on its use of high-osmotic-pressure draw solution and the pre-treatment needed, and the reverse solute leakage that affects the MBR efficiency.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Biofilm-based algal cultivation has received increased attention as a potential platform for algal production and other applications such as wastewater treatment. Algal biofilm cultivation systems represent an alternative to the suspension-based systems that have yet to become economically viable. One major advantage of algal biofilm systems is that algae can be simply harvested through scraping and thus avoid the expensive harvesting procedures used in suspension-based harvesting such as flocculation and centrifugation. In recent years, an assortment of algal biofilm systems have been developed with various design configurations and biomass production capacities. This review summarizes the state of the art of different algal biofilm systems in terms of their design and operation. Perspectives for future research needs are also discussed to provide guidance for further development of these unique cultivation systems.
A chemostat was coupled with a forward osmotic hollow fiber membrane bioreactor (FOHFMB) for treatment of high strength saline phenolic wastewater using Pseudomonas putida ATCC 11,172. The microorganisms were protected from the inhibitory effects of phenol and sodium chloride through dilution of the feed wastewater. This resulted in high cell growth and biodegradation rates during transient operation and steady state was achieved within 20 h. Effluent from the chemostat was desalinated in the FOHFMB through forward osmosis (FO) using magnesium chloride as the draw solute (DS). Permeate flux during FO remained stable for over 70 h in the orientation with DS facing the porous side of the membranes (PRO mode of operation). Water used for dilution could be recovered using 0.8 M DS when the wastewater did not contain any sodium chloride, whereas, 1.5 M DS was required to recover water from the wastewater containing 0.6 M sodium chloride. Biomass attachment on the membranes during FO operation was visualized using SEM, which showed that FO membranes was susceptible to fouling propensity and biomass deposition on the membranes was directly associated with permeate flux. Nevertheless, biofouling of membranes was reversible and membrane performance was recovered by osmotic backwashing.
Eutrophication of surface water has been an important environmental issue for nearly half a century. High concentrations of phosphorus contribute to the process of eutrophication, resulting in the demand for effective and economic methods of phosphorus removal from treated water. The aim of this study was to evaluate the capacity for phosphorus removal of a microalgal biofilm during different light regimes. The photobioreactor was operated for nine months each year over a two-year period without interruption and without any need of re-inoculation. The algal biofilm was able to remove 97 ± 1% of total phosphorus from wastewater during 24 h of continuous artificial illumination. The average TP uptake rate in our experiments was 0.16 ± 0.008 g m(-2) d(-1). Phosphorus removal values ranged from 36 to 41% when the algal biofilm was illuminated by natural light (12 h sunlight-12 h night). The biomass production rate was 12.21 ± 10 g dry weight m(-2) d(-1) in experiments with continuous artificial light and 5.6 ± 1 g dry weight (DW) m(-2) d(-1) in experiments with natural light. These results indicate the great potential of microalgal biofilms in the tertiary treatment of wastewater.
Copyright © 2015 Elsevier Ltd. All rights reserved.
The influence of extracellular organic matter (EOM) on membrane fouling is important for algae cultivation and harvest. Therefore, a deep understanding of EOM and a systematic extraction process are necessary. In this study, EOM from Chlorella pyrenoidosa was thoroughly studied by using different methods to stratify it into dEOM and bEOM. Among these methods, the centrifugation method was optimized for dEOM extraction, and the heating and NaOH methods were optimized for bEOM extraction. In addition, dEOM and bEOM were compared by using analytical methods to obtain their protein and polysaccharide contents, dissolved organic carbon (DOC) contents, specific UV absorbances (SUVA), zeta potentials, FTIR spectra, EEM fluorescence spectra, hydrophobicities and molecular weights. The dEOM and bEOM both primarily consisted of proteins and polysaccharides and carried negative charges with relatively low SUVAs. The protein/polysaccharide ratios in the bEOM were 6.35 (control), 12.54 (heating) and 7.54 (NaOH)mgmg(-1), which were greater than the ratio of the dEOM (2.93mgmg(-1)). Furthermore, the hydrophobicity analysis indicated that the bEOM had higher hydrophobic fraction content than the dEOM. However, both types of EOM were more hydrophilic in terms of the DOC. Finally, size fraction analysis indicated that high-MW (>100kDa) and low-MW fractions (<1kDa) were the primary components in EOMs. Specifically, a greater high-MW fraction was observed in the bEOM, which primarily consisted of DOC and proteins. In contrast with the proteins, the polysaccharides of the dEOM and bEOM were primarily distributed in the hydrophilic and low-MW fractions. Using comparative analysis, centrifugation at 10,000×g for 10min was chosen as the best method for extracting dEOM. In contrast, heating at 70°C for 20min was the best method for extracting bEOM.
Copyright © 2014 Elsevier B.V. All rights reserved.
In present research, a microalgae membrane bioreactor (MMBR) was constructed by combining the optical panel photobioreactor (OPPBR) and membrane bioreactor (MBR). Experiments were conducted in MMBR pilot-plant configuration for 150 days. A biomass productivity of 2.53 g/l/day with light transmittance of 94 % at a 300-mm depth in the OPPBR was achieved. The total reduction of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in the MMBR were found to be 96.99 and 97.09 %, respectively. Additionally, the removal of total nitrogen (TN), NH4-N, NO3-N, total phosphorus (TP), and PO4-P were 96.38, 99.80, 97.62, 92.75, and 90.84 % in MMBR, respectively. These results indicated that the MMBR process was highly effective for COD, BOD, and nutrient removal when compared to the OPPBR or MBR process.
Microalgae in three submerged ceramic membrane photobioreactors (SCMPBRs) with different hydraulic retention times (HRTs) were fed with permeate of a submerged ceramic membrane bioreactor for a period of 3 months to investigate the lipid content and also the biodiesel quality produced at different HRTs. The lipid content, lipid productivity and fatty acid compositions for all three SCMPBRs were not significantly different at the 95% confidence level. These results suggested that insignificant change in the amount of fatty acids was observed at different HRTs that supplied varying concentration of nitrate in the medium. Among the fatty acids, palmitic acid, palmitoleic acid, oleic acid and linoleic acid were the main components, whereas stearic acid was a minor fatty acid. Since there was insignificant effect of HRT on lipid content, lipid productivity and fatty acid compositions, the optimum HRT for SCMPBRs can then be designed based on optimum nutrient removal performance and low membrane fouling propensity.
Chlorella vulgaris was used for the removal of residual ammonia/ammonium ion (NH3/NH4+) and orthophosphate ion (PO43-) from secondary wastewater effluent collected from a municipal wastewater treatment plant. The uptake rates for nitrogen and phosphorus were studied with different initial algal cell densities and the addition of CO2 gas for pH control and supply of inorganic carbon. Our result showed that typical NH3/NH4+ and PO43- concentrations could be readily removed within 48 h. It was found that the culture with an initial algal cell density of similar to 350 mg/L and CO2 gas supply could significantly enhance both the rates of cell growth and nutrient uptake. The Monod equation well described the algal cell growth under substrate-limiting conditions, and could be used for the design and operation of photobioreactors for potential tertiary wastewater treatment.
Scenedesmus obliquus, Chlorella vulgaris, Chlorella kessleri and a natural Bloom were cultivated in batch experiments, under controlled conditions, in urban wastewater (WW) and synthetic wastewater (SW) under 5% CO2 in air, with the object of estimating their capacity for nutrient removal, carbon dioxide biofixation, and generation of valuable biomass. In both culture media, the Bloom (Bl) and Scenedesmus (Sc) showed higher final biomass concentration (dried weight, dw) than the other species; the maximum yield obtained was 1950 ± 243 mg L(-1) for Bl and the minimum 821 ± 88 mg L(-1) for Cv, both in synthetic wastewater. Maximum specific growth rate values do not show significant differences between any of the 4 strains tested (p ≤ 0.05), nor between the 2 culture media. A new homogeneous method of calculating productivities has been proposed. Nitrogen removal in all the reactors was higher than 90%, except for BlSW (79%), and for phosphorus, the removal was higher than 98% in all trials. Maximum CO2 consumption rates reached were 424.4 and 436.7 mg L(-1) d(-1) for ScSW and ScWW respectively.
Carbon dioxide (CO2) is one of the most important contributors for the increase of the greenhouse effect. CO2 concentrations are increasing in the last decades mainly due to the increase of anthropogenic emissions. To reduce the effects caused by this environmental problem, several technologies were studied to capture CO2 from large emission source points: (i) absorption; (ii) adsorption; (iii) gas-separation membranes; and (iv) cryogenic distillation. The resulting streams with high CO2 concentrations are transported and stored in geological formations. However, these methodologies, known as carbon capture and storage (CCS) technologies, are considered as short-term solutions, as there are still concerns about the environmental sustainability of these processes.A promising technology is the biological capture of CO2 using microalgae. These microorganisms can fix CO2 using solar energy with efficiency ten times greater than terrestrial plants. Moreover, the capture process using microalgae has the following advantages: (i) being an environmental sustainable method; (ii) using directly the solar energy; and (iii) co-producing high added value materials based on biomass, such as human food, animal feed mainly for aquaculture, cosmetics, medical drugs, fertilizers, biomolecules for specific applications and biofuels. Approaches for making CO2 fixation by microalgae economically competitive in comparison with CCS methodologies are discussed, which includes the type of bioreactors, the key process parameters, the gaseous effluents and wastewater treatment, the harvesting methods and the products extracted by microalgal biomass.
This paper explores the use of a novel microalgae membrane photoreactor (mMR) to polish the effluent from an aerobic membrane bioreactor (MBR) fed with domestic wastewater. Four microalgae species Chlorella (Chlorella sp.), Chlorella vulgaris (C. vulgaris), Scenedesmus quadricauda (S. quadricauda) and Scenedesmus dimorphus (S. dimorphus) were isolated from the environment and tested in batch reactors fed with permeate from the aerobic MBR to evaluate the nutrient removal rates for each species. All four microalgae species were able to completely remove NH4 in the reactor within 3 days. The removal rates of NO3, NO2 and PO4 were between 43-54%, 83-95% and 70-92%, respectively after 3 days in the batch reactor. Subsequently, an MBR-mMR system was operated for 23 days. The mMR was able to remove on average 50% of NH4, 75% of NO2, 35% of NO3 and 60% of PO4 consistently from the MBR effluent under the conditions tested.
A novel osmotic membrane bioreactor (OsMBR) is presented. The system utilizes a submerged forward osmosis (FO) membrane module inside a bioreactor. Through osmosis, water is transported from the mixed liquor across a semi-permeable membrane, and into a draw solution (DS) with a higher osmotic pressure. To produce potable water, the diluted DS is treated in a reverse osmosis (RO) unit; the by-product is a reconcentrated DS for reuse in the FO process. Preliminary results from experiments conducted with a flat-sheet cellulose triacetate FO membrane demonstrated high sustainable flux and relatively low reverse transport of solutes from the DS into the mixed liquor. Membrane fouling was controlled with osmotic backwashing. The FO membrane was found to reject 98% of organic carbon and 90% of ammonium-nitrogen; the OsMBR process (bioreactor and FO membrane) was found to remove greater than 99% of organic carbon and 98% of ammonium-nitrogen, respectively; suggesting a better compatibility of the OsMBR with downstream RO systems than conventional membrane bioreactors.
Results reported here highlight the potential and several challenges in the development of a novel osmotic membrane bioreactor (OMBR) process for the treatment of municipal wastewater. Following the initial gradual decline, a stable permeate flux value was obtained after approximately four days of continuous operation. There was evidence of continuous deterioration of biological activity of the OMBR system, possibly due to the build-up of salinity in the reactor. The removal of 25 out of 27 trace organic compounds with molecular weight higher than 266 g/mol was above 80% and was possibly governed by the interplay between physical separation of the FO membrane and biodegradation. In contrast, the removal efficiency values of the other 23 trace organic compounds with molecular weight less than 266 g/mol were very scattered. The removal efficiency of these low molecular weight compounds by OMBR treatment appears to depend mostly on biological degradation.
The composition of extracellular polymeric substances (EPS) from Shewanella sp. HRCR-1 biofilms was investigated using infrared spectroscopy and proteomics to provide insight into potential ecophysiological functions and redox activity of the EPS. Both bound and loosely associated EPS were extracted from Shewanella sp. HRCR-1 biofilms prepared using a hollow-fibre membrane biofilm reactor. Fourier transform infrared spectra revealed the presence of proteins, polysaccharides, nucleic acids, membrane lipids and fatty acids in the EPS fractions. Using a global proteomic approach, a total of 58 extracellular and outer membrane proteins were identified in the EPS. These included homologues of multiple Shewanella oneidensis MR-1 proteins that potentially contribute to key physiological biofilm processes, such as biofilm-promoting protein BpfA, surface-associated serine protease, nucleotidases (CpdB and UshA), an extracellular lipase, and oligopeptidases (PtrB and a M13 family oligopeptidase lipoprotein). In addition, 20 redox proteins were found in extracted EPS. Among the detected redox proteins were the homologues of two S. oneidensis MR-1 c-type cytochromes, MtrC and OmcA, which have been implicated in extracellular electron transfer. Given their detection in the EPS of Shewanella sp. HRCR-1 biofilms, c-type cytochromes may contribute to the possible redox activity of the biofilm matrix and play important roles in extracellular electron transfer reactions.
Standard Methods for the Examination of Water and Wastewater
- Awwa Apha
- Wef
APHA, AWWA, WEF, 2012. Standard Methods for the Examination of Water and
Wastewater, 22 ed. American Public Health Association.