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Bioflocculation: Chemical free, pre-treatment technology for the desalination industry
Abstract
Rapid sand filtration (RSF), proceeded by chemical coagulation and flocculation, is a commonly used, effective pretreatment in the desalination industry. We designed and tested a novel, large pilot-scale, two-stage granular Rapid Bioflocculation Filter (RBF) based on a first-stage Bioflocculator (BF) unit followed by a mixed-media bed filter (MBF). The BF filter bed consisted of an extremely porous volcanic Tuff granular medium which provided an enlarged surface area for microbial development and biofilm proliferation. We compared the efficiency of the pilot RBF to that of a full-scale RSF, operating with upstream chemical coagulation, by measuring the removal from the same untreated seawater feed of key factors related to membrane clogging: SDI, turbidity, chlorophyll a (Chl a) and transparent exopolymer particles (TEP). After 2 weeks of operation, the Tuff grains were colonized extensively by coccoid bacteria that formed biofilm along the entire BF. With bacterial colonization and biofilm development, numerous aggregates of bacteria and some algal cells embedded in an amorphous organic matrix were formed on and within the Tuff grains. By 1-3 months, the biotic diversity within the Tuff filter bed had increased to include filamentous bacteria, cyanobacteria, fungi, protista and even crustaceans and marine worms. During and for ∼24 h after each cleaning cycle (carried out every5 to 7 days by upward flushing with air and water), large numbers of floc-like particles, from ∼15 μm to ∼ 2 mm in size were observed in the filtrate of the BF unit. Microscopic examination of these flocs (stained with Alcian Blue and SYTO(R) 9) showed that they were aggregates of many smaller particles with associated bacteria and algae within a polysaccharide gel-like matrix. These biogenic flocs (bioflocs) were observed to form during normal operation of the RBF, accumulating as aggregates of inorganic and organic material on the Tuff surfaces. With each flush cleaning cycle, these bioflocs were released into the BF effluent but were retained by the second phase MBF unit. No flocs were seen in the MBF filtrate. Over a year-long study, both the pilot RBF and the full-scale RSF showed similar filtration efficiencies, measured as the percentage removal of Chl a, TEP, turbidity and SDI from the same seawater feed. These results indicate the potential of the bioflocculation approach with no chemical additives as an alternative to conventional RSF pretreatment for large SWRO facilities.
... The large surface area and material porosity (internal porosity relative to the volume of~30%) enabled the tuff to harbor a greater microbial biomass (compared to SAT-sand), while the large grain size (3-5 mm) may have provided a higher water permeability. Additionally, previous studies have suggested that the iron-rich tuff (due to its volcanic origin) enhances the adhesion of negatively charged organic material (including bacteria) due to a net positive charge [35]. The tuff's high internal porosity may also increase the nutrient adsorption compared to the sand [36,37], thus supporting bacterial growth. ...
... The tuff's high internal porosity may also increase the nutrient adsorption compared to the sand [36,37], thus supporting bacterial growth. It was previously reported that bacteria colonized the tuff almost immediately after natural water passed through the media [35]. However, it should be stressed that it may take several months to establish a mature and diverse microbial community on the tuff grains. ...
... Differently than the redox potential [42,43], BP focuses specifically on the breakdown and anabolic assimilation of organic carbon into cell structures. The average assimilation rates measured from the bacteria associated with the tuff, compared to the sand, were most likely due to the enhanced buildup of bacterial biomass on and within the porous structure of the tuff, as previously shown for other biofilters [35,44,45]. The highest BP rates were measured from the bacteria associated with both the tuff and sand during May (2.11 and 0.37 µg C g −1 d −1 , respectively). ...
Soil aquifer treatment (SAT) is an established and sustainable wastewater treatment approach for water reuse that has been gaining increased attention in various countries around the world. Increasing volumes of domestic wastewater and escalating real estate prices around urban areas emphasize the urgent need to maximize the treatment efficiency by revisiting the SAT setup. In this study, a novel approach was examined to increase biodegradation rates and improve the quality of SAT topsoil effluent. Experiments with midscale, custom-made columns were carried out with sand collected from an operational SAT and a highly permeable natural material with high internal porosity, tuff, which was maturated (i.e., buried in the SAT infiltration basin) for 3 months. The filtration efficiency, biodegradation rates of organic material, microbial diversity, and outflow quality were compared between the operational SAT sand and the tuff using state-of-the-art approaches. The results of this study indicate that biodegradation rates (9.2 µg C g−1d−1) and filtration efficiency were up to 2.5-fold higher within the tuff than the SAT sand. Furthermore, the biofilm community was markedly different between the two media, giving additional insights into the bacterial phyla responsible for biodegradation. The results highlight the advantage of using highly porous material to enhance the SAT filtration efficiency without extending the topsoil volume. Hence, infusing a permeable medium, comprising highly porous material, into the SAT topsoil could offer a simple approach to upgrade an already advantageous SAT in both developed and developing countries.
... The removal efficiency of intracellular toxin was directly related to the removal of toxin producing algal cells during each pretreatment process. Algal cell removals through GMF systems were compiled based on pilot or full-scale SWRO studies reported in the literature (Table 2)[16,[35][36][37][38][39][40][41][42]. A pooled mean and standard deviation of algal cell removal for GMF systems with and without coagulation was calculated and fitted to a normal probability distribution (Table 2). ...
... Voutchkov[1]has stated that the removal of soluble organics in some second stage GMF systems can account to 20–40% by biological filtration processes alone. Biological treatment has the potential to remove dissolved organic carbon and TEP of the source water without requiring expensive cleaning/purchase of coagulants or cleaning chemicals, energy intensive backwashing (increase in filter run times), and can reduce the replacement frequency of membranes over the duration of operation[39,40,[66][67][68]. Other than pretreatment design and operation, the design of a proper seawater intake system represents a significant amendment for future SWRO facilities to mitigate the effects of HABs[12][13][14]. ...
The operation of seawater reverse osmosis (SWRO) desalination facilities has become challenged by the increasing frequency and severity of harmful algal blooms (HABs). The efficiency of algal toxins removal during SWRO and pretreatment processes has critical human health implications. Therefore, a probabilistic materials flow analysis (pMFA) was developed to predict the removal of algal toxins in source water by various pretreatment configurations and operations during SWRO desalination. The results demonstrated that an appreciable quantity of toxins exists in the SWRO permeate (ng/L–µg/L levels), the backwash of pretreatment, and final brine rejects (µg/L–mg/L levels). Varying the pretreatment train configuration resulted in statistically significant differences in toxin removals, where higher removal efficiencies were evidenced in systems employing microfiltration/ultrafiltration (MF/UF) over granular media filtration (GMF). However, this performance depended on operational practices including coagulant addition and transmembrane pressures of MF/UF systems. Acute human health risks during lifetime exposure to algal toxins from ingestion of desalinated water were benign, with margins of safety ranging from 100 to 4000. This study highlights the importance of pretreatment steps during SWRO operation in the removal of algal toxins for managing marine HABs.
... The biofilm microbial communities clustered mostly by surface type (media grains, filter or RO membrane) (Fig. 2). The seasonal stability demonstrated by the RSF microbial populations (in contrast to the variations in the feedwater that reached the RSF) emphasizes its potential to serve as a stable biological filter in addition to its particle and aggregate removal properties [15,55]. Seasonal differences observed in the CF biofilm communities were influenced primarily by the seasonal distribution of Planctomycetes whose relative abundance increased from winter (10% of total phyla) to summer, (28%). ...
... The seasonal variability in EMS surface water salinity ranges from 39.1 to 39.8 [57]. This change (0.7) is nearly negligible, even when doubled (1.4 or 0.14%) on the RO membrane surface [6,58], compared with the wide salinity growth range of Kangiella [55] and therefore cannot explain its seasonal abundance in the RO hypersaline biofilm environment. Alternatively, elevated temperatures from spring to summer may have promoted Kangiella growth with summer average temperatures (29.8°C) ( Table 1) consistent with the optimal growth temperature for Kangiella ranging from 30°C to 37°C [56]. ...
Biofouling impacts seawater reverse osmosis (SWRO) desalination plants by hindering module performance, increasing energetic demands, and incurring further costs. Here we investigated the spatial-temporal dynamics of microbial communities along the feedwater, pretreatment, and reverse osmosis stages of a large-scale SWRO desalination facility. While the composition of water-based microbial communities varied seasonally, the composition of biofilm microbial communities clustered by locations. Proteobacteria dominated throughout the water and biofilm communities while other dominant phyla varied seasonally and spatially. The microbial community composition significantly differed along the pathway locations of feedwater, rapid sand filtration (RSF), cartridge filters (CF), and the reverse osmosis (RO) membranes. Biofilms on the RSF and CF were composed of more diverse microbial populations than RO biofilms as determined by the effective number of species. Biofilms that developed along the treatment pathway (CF) served as inocula enhancing biofouling downstream on the RO membranes. Subsequently, we believe that prior to the development of advanced antibiofouling treatments for the desalination industries, the site-specific microbial community of feedwater, pretreatment and RO biofouling should be characterized. Site specific identification of these communities will enable optimization of pretreatment and cleaning procedures and can ultimately reduce chemical usage and incurred costs.
... The biofilm microbial communities clustered mostly by surface type (media grains, filter or RO membrane) (Fig. 2). The seasonal stability demonstrated by the RSF microbial populations (in contrast to the variations in the feedwater that reached the RSF) emphasizes its potential to serve as a stable biological filter in addition to its particle and aggregate removal properties [15,55]. Seasonal differences observed in the CF biofilm communities were influenced primarily by the seasonal distribution of Planctomycetes whose relative abundance increased from winter (10% of total phyla) to summer, (28%). ...
... The seasonal variability in EMS surface water salinity ranges from 39.1 to 39.8 [57]. This change (0.7) is nearly negligible, even when doubled (1.4 or 0.14%) on the RO membrane surface [6,58] , compared with the wide salinity growth range of Kangiella [55] and therefore cannot explain its seasonal abundance in the RO hypersaline biofilm environment. Alternatively , elevated temperatures from spring to summer may have promoted Kangiella growth with summer average temperatures (29.8 °C) (Table 1) consistent with the optimal growth temperature for Kangiella ranging from 30 °C to 37 °C [56]. ...
Rapid sand filtration (RSF) is used today as an effective pretreatment procedure to enhance water quality prior to reverse osmosis (RO) membranes in desalination plants. RSF in newly operated desalination facilities requires a maturation period of about three months before the feedwater may be filtered efficiently. Up to date in the desalination industry RSF has been regarded mainly as a physical barrier effectively retaining particles larger than 0.35 mm.In this study we assessed the potential of RSF as a biological filter by following the dynamics of bacterial colonization and metabolic activity within the filter bed and determining filtration efficiency in respect to particulate and dissolved organic carbon, chlorophyll a and transparent exopolymeric particles (TEP). Bacterial abundance and diversity was shown by DGGE and SEM analysis to increase gradually over a three month sampling period. Bacterial metabolic activity within the filter bed interstitial water increased erratically with time. With the outgrowth of a microbial population and biofilm development on the filter bed medium, significant removal of organic carbon from the source water was always observed. Our results indicate that current RSF's function as biofilters with moderate efficiency. Innovative design is needed to maximize the biofiltration potential of these filters.
... High cost yet providing similar results to conventional rapid sand filtration used with a coagulant Pilot scale (Bar-Zeev et al., 2013) Air bubbling ...
... Several studies have examined the efficiency of DMF under various conditions in the literature [78][79][80][81][82]. Overall, the use of coagulation prior to DMF showed improved performance in terms of turbidity and organic removal compared to DMF alone, validating the need for some pretreatment steps for DMF unit stability. ...
High-energy consumption is a critical issue associated with seawater reverse osmosis (SWRO) desalination, although the SWRO has been regarded as one of the most energy-efficient processes for seawater desalination. This means that SWRO involves a larger amount of fossil fuel and other energy sources for water production, which imposes a negative impact on the environment such as greenhouse gas emission. Therefore, the high-energy consumption of SWRO should be addressed to minimize environmental impacts and to allow for sustainable exploitation of seawater. However, the recent trend of energy consumption in SWRO seems to have reached a saturation point, which is still higher than theoretical minimum energy. To find new and innovative strategies for lowering current energy consumption, a comprehensive understanding of energy use in SWRO plants from theoretical analysis to actual energy consumption in real SWRO plants is required. This book can provide readers with information about the current state of energy consumption in actual SWRO plants, the fundamental understanding of energy use of SWRO plants from theoretical point of view, and advanced technologies and processes that could be applied for future energy reduction. In addition, this book will offer a detailed methodology for analyzing energy issues in seawater desalination. Through this book, readers will obtain an insight into how to deal with and analyze the energy issues in SWRO desalination.
ISBN: 9781789061208 (paperback)
ISBN: 9781789061215 (eBook)
ISBN: 9781789061222 (ePub)
... Some novel techniques have been suggested including pretreatment with two-stage granular Rapid Bioflocculation Filter (RBF) [100], using CO 2 purging to lower the feed pH and boost the solubility of scale causing salts, using pulsed-electromagnetic field (PEMF) devices to monitor scaling [101], and utilizing ultrasound technology to disable about 1000 colony producing units of E. coli per milliliter [102]. Moreover, a new antiscalant, Genesys PHO manufactured by Genesys International Limited in United Kingdom, has been utilized that applies advanced threshold inhibiting mechanisms to increase the solubility of calcium phosphate 150 times. ...
Reverse osmosis (RO) membranes are widely employed due to their inherent advantage of achieving excellent water permeation rates and high salt rejection. However, fouling is a main issue in RO applications that leads to increasing the operational cost, reducing the lifespan of the membrane, decreasing the permeate flux, and increasing the energy demand. Therefore, many techniques have been developed and used in the industry to minimize and control fouling in RO membranes, such as feed pretreatment and membrane cleaning. In the context of fouling mitigation and control, the development of antifouling and self-cleaning RO membranes has gained significant attention. This review aims to discuss membranes fouling, its types, and mechanisms. Moreover, factors affecting the fouling process in RO have been highlighted. The article provides an overview of the novel techniques, such as physical and chemical surface modification and thin-film nanocomposite membrane synthesis for imparting antifouling/self-cleaning properties to RO membranes. Finally, some related challenges are discussed, and future recommendations are presented.
... Their study found that, over a year-long study, the pilot RBF and the conventional rapid sand filtration showed similar filtration efficiencies. TEP produced by microorganisms in RBF showed melancholy flocculation properties and if it can be used properly, the flocculation process does not require chemical additives [43,44]. ...
Transparent exopolymer particles (TEP) have been described as a class of particulate acidic polysaccharides, which are commonly found in various surface waters. Due to their unique physicochemical characteristics, they have recently been receiving increasing attention on their effects in water treatment. Currently, TEP are commonly known as clear, gel-like polysaccharides. This review first introduced the definition of TEP in water treatment and the relationship between TEP and algal organic matter (AOM). Further, in the review, the authors attempt to offer a holistic view and critical analysis concerning the research on TEPs in source water reservoirs, water plants and membrane treatment processes. It was clearly demonstrated in this review that the formation of TEP in source water reservoirs is largely related to water quality and phytoplankton, and the seasonal water stratification may indirectly affect the formation of TEP. In the waterworks, the relationship between TEP and water treatment process is mutual and there is limited research on this relationship. Finally, the mechanism of TEP-induced membrane fouling and the effect of alleviating TEP-induced membrane fouling is discussed in this review. The TEP removed by ultrafiltration can be recombined after membrane, and the recombination mechanism may be an important way to reduce reverse osmosis membrane contamination.
... The disadvantages of SF are the difficulties associated with the filtration of appreciable turbid waters, the requirement for more space, and also the effects of algal blooms (Logsdon et al., 2002). In general, rapid filtration is preceded by a chemical pre-treatment of the water, generally coagulation-flocculation, decantation and a post-treatment (generally disinfection), together these processes are known as conventional treatment (Bar-Zeev et al., 2013;García-Ávila et al., 2021). ...
Safely managed drinking water for all is the United Nations Sustainable Development Goal 6.1. Achieving this goal is a challenge in rural areas. A strong partnership between users of a water treatment system was critical to the success of community-scale technological change. In this study, the efficiency of a water treatment system was evaluated after the implementation of a technological change in a rural area. This research was carried out in a community in Ecuador, which before the change in technology had a treatment system composed of gravel pre-filtration and slow filtration. This system did not guarantee adequate water quality, due to a notable increase in the color and turbidity levels of raw water; in addition to the growing demand for water in recent years. A new conventional treatment system was implemented consisting of: coagulation, flocculation, sedimentation, rapid filtration and disinfection. All the modernization works were carried out on the same infrastructure that had served as gravel pre-filters. Before modernization, samples of raw water and treated water were collected for six months. After the changes carried out, samples of raw and treated water were also collected for another six months. The parameters analyzed were: turbidity, color, pH, total dissolved solids, residual chlorine, nitrates, sulfates, phosphates, chlorides, alkalinity, total hardness and iron. The values of all the parameters analyzed improved after the modernization, indicating that the changes made in the treatment plant were successful. As a result, a conventional treatment to make water potable in rural areas has become a robust process that can operate within a wide range of water quality, improving the quality and quantity of drinking water.
... It is thought that combining RSF with biofiltration will eliminate the need for using coagulants that represent an environmental hazard. Zeev et al. (2013) investigated the effectiveness of a chemical-free, microbial-based pretreatment methodology based on bioflocculation. They utilized a novel RSF configuration with a highly porous filter media that provided a large surface area for bacterial growth and biofilm development. ...
Reverse Osmosis (RO) is becoming increasingly popular for seawater desalination and wastewater reclamation. However, fouling of the membranes adversely impacts the overall process efficiency and economics. To date, several strategies and approaches have been used in RO plants and investigated at the laboratory-scale for their effectiveness in the control of different fouling types. Amid growing concerns and stringent regulations for the conservation of environment, there is an increasing trend to identify technologies that are effective in fouling mitigation as well as friendly to the environment. The present review elaborates on the different types of environment-friendly technologies for membrane fouling control that are currently being used or under investigation. It commences with a brief introduction to the global water crisis and the potential of membrane-based processes in overcoming this problem. This is followed by a section on membrane fouling that briefly describes the major fouling types and their impact on the membrane performance. Section 3 discusses the predominant fouling control/prevention strategies including feedwater pretreatment, membrane and spacer surface modification and membrane cleaning. The currently employed techniques are discussed together with their drawbacks, with some light being shed on the emerging technologies that have the ability to overcome the current limitations. The penultimate section provides a detailed discussion on a variety of eco-friendly/chemical free techniques investigated to control different fouling types. These include both control and prevention strategies, for example, bioflocculation and electromagnetic fields, as well as remediation techniques such as osmotic backwashing and gas purging. In addition, quorum sensing has been specifically discussed for biofouling remediation. The promising findings from different studies are presented followed by a discussion on their drawbacks and limitations. The review concludes with a need for carrying out fundamental studies to develop better understanding of the eco-friendly processes discussed in the penultimate section and their optimization for possible integration into the RO plants.
... For open-channel discharges at the shoreline, dilution can be achieved by co-disposal, for example, with cooling waters from power plants. Alternative pretreatments for the desalination feed water, such as biofiltration and bioflocculation can be utilized instead of chemicals such iron hydroxide coagulants [72]. Other more environmentally friendly chemicals could replace more traditional antiscalants and coagulants. ...
Seawater desalination is now being widely regarded as the solution to the ever increasing need for potable water. However, in contrast to the rapid technological developments throughout the desalination process and expanding desalination facilities, not much is known on the environmental and ecological impacts on the marine ecosystem. Specifically, the effects of discharging brine and chemicals, used routinely in the desalination process, have been poorly documented. In this chapter, we summarize the available data examining the impacts of desalination brine and chemicals, such as iron-based coagulants and phosphonate antiscalants, on coastal seawater microbial communities. The data include results from controlled large-scale laboratory experiments and from in situ measurements around desalination plants outfalls. The observed effects could be immediate, on a time scale of several hours, affecting metabolic functions such as primary and bacterial productivity, and on longer temporal scales of days to weeks, influencing community composition and structure. The specific changes depend predominantly on plant location, capacity, chemical utilization, and discharge technologies (open versus submerged outfalls). We conclude with gaps in knowledge and recommendations for SWRO plant operations.
... Advances in desalination technology have already reduced the amount of chemicals used and the quantity of brine. Micro filtration (0.1-10 µm) and ultrafiltration (0.1-0.01 µm) may replace the pre-treatment through chemical coagulation (Fritzmann et al. 2007), biological pre-treatment, such as bioflocculation, may replace chemical coagulants (Bar-Zeev et al. 2013), and back wash from sand filters is dried and residuals disposed on land, where commercially important brine components can be isolated by new techniques (Macedonio et al. 2012;Pérez-González et al. 2012). ...
... Considering the carcinogenicity and biological incompatibility of the conventional inorganic and organic flocculants, the emerging bioflocculant attracts great interest currently because they are harmless, biodegradable and without the problem of producing secondary pollution to the environment [11]. Microbial bioflocculant (MBF), produced by microorganisms during their growth and cell lysis, is an environmental friendly material which can be utilized in water desalination [12], decoloration [13] and in the treatment of drinking water [14], sugarcane wastewater [15] and river water [16]. The Bacillus mucilaginosus [17] Serratia ficaria [18] and Aspergillus niger [19] have been proved as effective bioflocculant producing microorganism [6]. ...
A bioflocculant (MBFA18) was produced by Aspergillus niger (A18) using potato starch wastewater (PSW) as nutrients. The cultivation processes and flocculating treatment for PSW purification were systematically studied. The flocculating rate of the MBFA 18 achieved 90.06% (kaolin clay) under the optimal cultivation condition (PSW with 5950 mg/L COD, 20 g/L glucose, 0.2 g/L urea and without phosphorus source addition and pH adjustment). Furthermore, effects of flocculant dosage, initial pH, coagulant aid (CaCl2) addition and sedimentation time on the PSW treatment were discussed and studied in detail. The optimum flocculation treatment conditions were determined according to the treatment efficiency, cost and flocculation conditions. During the PSW treatment, 2 mL/L bioflocculant (1.89 g/L) dosage and 0.5 mol/L coagulant aid addition were applied without pH adjustment and 91.15% COD and 60.22% turbidity removal rate could be achieved within 20 min. The comparative study between the bioflocculant and conventional chemical flocculants showed excellent flocculating efficiency of MBFA 18 with lower cost (4.7 yuan/t), which indicated that the bioflocculant MBFA 18 produced in PSW substrate has a great potential to be an alternative flocculant in PSW treatment.
... + mixed bed filter 90 ± 8 27 ± 19 Bar-Zeev et al. [19] Coag. (1 mg Fe 2 (SO 4 ) 3 ) + RSF 79 ± 8 17 ± 28 Bar-Zeev et al. [17] Coag. + single media filter 32 Salinas-Rodriguez et al. [138] W. Mediterranean Sea Press. ...
... For example, low TEP decreases across the MMF (37-38%) were observed in late November 2012 and early April 2013, whereas there was a decrease of >60% for the other sampling events, and in particular it exceeded 95% in mid July 2013 (Fig. 2). A high temporal variability in TEP removal from seawater has also been reported for rapid sand filtration [31,46,47]. Over the entire period of this study the concentration of TEP dropped (ρ = −0.54, ...
Seawater reverse osmosis desalination is affected greatly by membrane biofouling which reduces membrane lifetimes and increases cost of permeate production. This work reports on the analysis of pre-treated seawater from a small-scale desalination plant operating with a three-stage pre-treatment system namely, (1) medium-pressure ultraviolet (MP-UV) disinfection, (2) multimedia filtration (MMF), and then finally, (3) cartridge filtration. Transparent exopolymeric particles (TEPs), chlorophyll a, phytoplankton, bacteria and viruses were evaluated in the pre-treated seawater after each pre-treatment stage over a one-year period (July 2012–July 2013). The concentration of TEPs was found to occasionally increase after MP-UV disinfection. MP-UV disinfection had no effect on the phytoplankton, bacterial or viral cell counts. In contrast, MMF was shown to be the most efficient step in removing TEPs and micro-organisms from seawater, while this removal was less significant for viruses. Cartridge filters had limited efficiency. Phytoplankton was observed to be more efficiently removed compared to bacteria. Although phytoplankton removal rates varied over time and were dependent upon cell size and shape, most of the micro-organisms were removed from seawater throughout the period of study. Investigating the seawater pre-treatment system during different season provided, thus, useful insights on its efficiency.
Biofilms are the predominant mode of microbial life on Earth, and so a deep understanding of microbial communities─and their impacts on environmental processes─requires a firm understanding of biofilm properties. Because of the importance of biofilms to their microbial inhabitants, microbes have evolved different ways of engineering and reconfiguring the matrix of extracellular polymeric substances (EPS) that constitute the main non-living component of biofilms. This ability makes it difficult to distinguish between the biotic and abiotic origins of biofilm properties. An important route toward establishing this distinction has been the study of simplified models of the EPS matrix. This study builds on such efforts by using atomistic simulations to predict the nanoscale (≤10 nm scale) structure of a model EPS matrix and the sensitivity of this structure to interpolymer interactions and water content. To accomplish this, we use replica exchange molecular dynamics (REMD) simulations to generate all-atom configurations of ten 3.4 kDa alginate polymers at a range of water contents and Ca-Na ratios. Simulated systems are solvated with explicitly modeled water molecules, which allows us to capture the discrete structure of the hydrating water and to examine the thermodynamic stability of water in the gels as they are progressively dehydrated. Our primary findings are that (i) the structure of the hydrogels is highly sensitive to the identity of the charge-compensating cations, (ii) the thermodynamics of water within the gels (specific enthalpy and free energy) are, surprisingly, only weakly sensitive to cation identity, and (iii) predictions of the differential enthalpy and free energy of hydration include a short-ranged enthalpic term that promotes hydration and a longer-ranged (presumably entropic) term that promotes dehydration, where short and long ranges refer to distances shorter or longer than ∼0.6 nm between alginate strands.
Many desalination plants still struggle to control biological fouling in seawater reverse osmosis (SWRO) systems as there are no standard methods to monitor this type of fouling. Strategies to control biofouling in SWRO systems have been proposed such as antifouling coating and lowering biofouling potential in SWRO feedwater through pretreatment processes. Measuring biofouling potential in the pretreatment and SWRO feedwater has gained increased interest due to its direct link to biofouling. Moreover, this approach can be used as an early warning system allowing for taking corrective actions in the pretreatment processes to meet the required SWRO feedwater quality. This article presents the biofouling potential methods/tools developed for seawater, their applications to monitor and assess raw seawater, SWRO pretreatment and SWRO feedwater, and how these methods are employed to control SWRO biofouling membrane systems. The reported removal efficiency of biofouling potential during SWRO pretreatment processes was found to be low to moderate. Threshold values for biofouling limitation were then proposed based on several lab and plant studies. Research on biofouling potential has provided insight into SWRO pretreatment performance optimisation and biofouling control. Future research is anticipated to determine better pretreatment processes and to identify robust threshold values for mitigating biofouling in SWRO membranes.
Liquid waste with a high amount of total suspended solids (TSS) is one of the significant environmental issues from coal mining activities in Kalimantan island under high precipitation in of an extensive zone of coverage. The TSS concentration with Nano-sized particle in mine drainage is caused by clay minerals which are dominated by montmorillonite type. Therefore, a vast chemical agent is usually used to treat TSS concentrations of liquid waste less than 300 mg/L based on government regulation. However, in this case, the chemical flocculant triggers the onset of secondary pollutant because of carcinogenic and non-biodegradable conditions. This study aims to observe specific fungi, Marasmius sp, as bio-flocculant for the treatment of mine drainage with extra high TSS. The fungi can produce a biodegradable polymer that precipitate the montmorillonite with two-mode action, namely bio-flocculant polymerization and mycelial trapping. A role model was performed in a laboratory-scale less than 1 L in several graduated/measuring cylinders under 22-30 °C. The results of clarity and flocculation rate tests indicated that the minerals in the mine drainage samples from PT.BC mining excavation area, had been precipitated rapidly. The clarity test by using spectrophotometer indicated that eighty six percent (86%) clarity value averagely in one-hour treatment, while the TSS concentration amount decreased down to 110.1 mg/L from original measured at 11,000 mg/L based on the flocculation rate test.
Marine organic colloids (MOCs) cause serious membrane fouling in the process of seawater desalination. Hence, this study was designed to efficiently eliminate MOCs by biomineralization of forming calcium carbonate/phosphate precipitate. Results showed that crystal formed by calcium solution and carbonate dosage was calcite, while the precipitate of calcium solution with phosphate was similar to hydroxyapatite. MOCs in the solution were throughout involved in forming the calcite and hydroxyapatite precipitates. The removal rates of protein, acid polysaccharide and humic acid in the MOCs by forming hydroxyapatite approached 56.56%, 86.07% and 95.34%, extremely higher than that of calcite. Finally, MOCs removal mechanism by the biomineralization was proposed, where calcium ions were firstly absorbed by functional groups of organic macromolecules in the solution, then the added carbonate or phosphate anions were attracted by calcium ion, and finally the crystal growth occurred with macromolecules as templates. The present results might provide a new idea for the engineers to solve the problem of membrane fouling and thus present promising application in desalination process.
In this study, we investigated the organic matter responsible for reverse osmosis (RO) membrane fouling in seawater desalination. In addition, pretreatments by which fouling organic fractions causing severe membrane fouling can be removed effectively were investigated. The results from continuous operation of a pilot-scale sand filter indicated that the changes in the concentrations of specific organic fractions, such as transparent exopolymer particles (TEP) and biopolymers determined by liquid chromatography with organic carbon detection (LC-OCD), cannot be evaluated by comprehensive water quality indices (e.g., total organic carbon (TOC) or dissolved organic carbon (DOC) concentrations). In addition, the changes in the degree of membrane fouling cannot be explained by the comprehensive TOC and DOC concentrations. Among the water quality indices examined in this study, the concentration of TEP with relatively large particle size (i.e., >. 1.0 μm) and content of protein-like organic matter that can be detected by fluorescence excitation-emission matrix (EEM) spectral analysis were well correlated to RO membrane fouling levels. The results obtained in this study strongly suggest that developing a pretreatment method that can effectively eliminate TEP and proteinaceous compounds contained in seawater is important for the stable operation of a seawater desalination plant utilizing an RO membrane.
Transparent exopolymer particles (TEP) are ubiquitous in marine and freshwater environments. For the last two decades, the distribution and ecological roles of these polysaccharide microgels in aquatic systems were extensively investigated. More recent studies have implicated TEP as an active agent in biofilm formation and membrane fouling. Since biofouling is one of the main hurdles for efficient operation of membrane-based technologies, there is a heightened interest in understanding the role of TEP in engineered water systems. In this review, we describe relevant TEP terminologies while critically discuss TEP biological origin, biochemical and physical characteristics, occurrence and distributions in aquatic systems. Moreover, we examine the contribution of TEP to biofouling of various membrane technologies used in the desalination and water/wastewater treatment industry. Emphasis is given to the link between TEP physicochemical and biological properties and the underlying biofouling mechanisms. We highlight that thorough understanding of TEP dynamics in feedwater sources, pretreatment challenges, and biofouling mechanisms will lead to better management of fouling/biofouling in membrane technologies.
Rapid sand filtration (RSF) is used today as an effective pretreatment procedure to enhance water quality prior to reverse osmosis (RO) membranes in desalination plants. RSF in newly operated desalination facilities requires a maturation period of about three months before the feedwater may be filtered efficiently. Up to date in the desalination industry RSF has been regarded mainly as a physical barrier effectively retaining particles larger than 0.35 mm.In this study we assessed the potential of RSF as a biological filter by following the dynamics of bacterial colonization and metabolic activity within the filter bed and determining filtration efficiency in respect to particulate and dissolved organic carbon, chlorophyll a and transparent exopolymeric particles (TEP). Bacterial abundance and diversity was shown by DGGE and SEM analysis to increase gradually over a three month sampling period. Bacterial metabolic activity within the filter bed interstitial water increased erratically with time. With the outgrowth of a microbial population and biofilm development on the filter bed medium, significant removal of organic carbon from the source water was always observed. Our results indicate that current RSF's function as biofilters with moderate efficiency. Innovative design is needed to maximize the biofiltration potential of these filters.
Transparent exopolymer particles (TEPs) are planktonic, organic microgels that are ubiquitous in aqueous environments. Increasing evidence indicates that TEPs play an active role in the process of aquatic biofilm formation. Frequently, TEPs are intensely colonized by bacteria and other microorganisms, thus serving as hot spots of intense microbial activity. We introduce the term "protobiofilm" to refer to TEPs with extensive microbial outgrowth and colonization. Such particles display most of the characteristics of developing biofilm, with the exception of being attached to a surface. In this study, coastal seawater was passed through custom-designed flow cells that enabled direct observation of TEPs and protobiofilm in the feedwater stream by bright-field and epifluorescence microscopy. Additionally, we could follow biofilm development on immersed surfaces inside the flow cells. Within minutes, we observed TEP and protobiofilm patches adhering to these surfaces. By 30 min, confocal laser-scanning microscopy (CLSM) revealed numerous patches of Con A and SYTO 9 staining structures covering the surfaces. Atomic force microscopy showed details of a thin, highly sticky, organic conditioning layer between these patches. Bright-field and epifluorescence microscopy and CLSM showed that biofilm development (observed until 24 h) was profoundly inhibited in flow cells with seawater prefiltered to remove most large TEPs and protobiofilm. We propose a revised paradigm for aquatic biofilm development that emphasizes the critical role of microgel particles such as TEPs and protobiofilm in facilitating this process. Recognition of the role of planktonic microgels in aquatic biofilm formation can have applied importance for the water industry.
Microorganisms can metabolize many aliphatic and aromatic organic contaminants, either to obtain carbon and/or energy for growth, or as co-substrates, thus converting them to products such as carbon dioxide, water, chloride and biomass. These biotransformations can be exploited for treatment of contaminated soils and ground water.
Prokaryotic biofilms that predominate in a diverse range of ecosystems are often composed of highly structured multispecies communities. Within these communities metabolic activities are integrated, and developmental sequences, not unlike those of multicellular organisms, can be detected. These structural adaptations and interrelationships are made possible by the expression of sets of genes that result in phenotypes that differ profoundly from those of planktonically grown cells of the same species. Molecular and microscopic evidence suggest the existence of a succession of de facto biofilm phenotypes. We submit that complex cell-cell interactions within prokaryotic communities are an ancient characteristic, the development of which was facilitated by the localization of cells at surfaces. In addition to spatial localization, surfaces may have provided the protective niche in which attached cells could create a localized homeostatic environment. In a holistic sense both biofilm and planktonic phenotypes may be viewed as integrated components of prokaryote life.
Despite the impressive advances that have been made in assessing the diversity of marine microorganisms, the mechanisms that underlie the participation of microorganisms in marine food webs and biogeochemical cycles are poorly understood. Here, we stress the need to examine the biochemical interactions of microorganisms with ocean systems at the nanometre to millimetre scale--a scale that is relevant to microbial activities. The local impact of microorganisms on biogeochemical cycles must then be scaled up to make useful predictions of how marine ecosystems in the whole ocean might respond to global change. This approach to microbial oceanography is not only helpful, but is in fact indispensable.
The paper is concerned principally with summarising the experience to-date of treating low alkalinity, low turbidity, humic-rich surface waters by the combination of ozone oxidation and biological filtration processes. In the UK, USA and other countries, upland coloured waters have often been treated by slow sand filtration in which only moderate removals of DOC have been achieved (< 20%). The presence of significant levels of humic matter in filtrate waters has led to difficulties in achieving compliance with the standards for colour and THMs, and concern about the stability of residual chlorine and potential biogrowth in water supply pipework. This has led to several investigations (eg. in the UK, Sweden and the USA) of the benefits of applying ozonation prior to slow sand filtration in view of its known capability to decolorise humic substances and enhance biodegradability of the organic fractions. This paper summarises the experience to-date and highlights the benefits and problems that have been identified. Some studies have attempted to compare the relative performances of slow sand filters and granular activated carbon (GAC) filters for the removal of BDOC and the paper reviews the principal findings of these studies in view of the growing worldwide interest in the application of ozone-GAC. One major limitation with the use of ozone-GAC is the need periodically to remove and regenerate the carbon, since bed lives for the removal of humic substances are typically short. An alternative approach is to use inorganic adsorbents instead of carbon which have the potential to be chemically regenerated in-situ. The paper refers to the results of laboratory tests that have been carried out on the potential use of pre-ozonation followed by inorganic adsorbents (eg. Activated alumina, bauxite) for the removal of humic substances.
Coagulation and flocculation are considered to be an essential part of drinking water treatment as well as wastewater treatment. A number of separate primary coagulant types, various combinations of coagulants, and mixing regimes should be studied over a range of imposed experimental conditions to optimize the treatment of water. The enhanced coagulation approach recognizes that the constituents of any given water govern the practical degree of treatment achievable. A chemical phosphorus removal is a common example of the practice of chemically enhancing primary treatment to reduce suspended solids and organic loads from primary classifiers. A book from IWA Publishing on coagulation and flocculation presents the properties of materials present in waters and wastewaters, details of experimental procedures for assessing primary coagulants and flocculant aids, sludge conditioners, and flocculation parameters.
The adhesion of bacteria to solid surfaces was studied using a physicochemical approach. Adhesion to negatively charged polystyrene was found to be reversible and could be described quantitatively using the DLVO theory for colloidal stability, i.e., in terms of Van der Waals and electrostatic interactions. The influence of the latter was assessed by varying the electrolyte strength. Adhesion increased with increasing electrolyte strength. The adhesion Gibbs energy for a bacterium and a negatively charged polystyrene surface was estimated from adhesion isotherms and was found to be 2-3 kT per cell. This low value corresponds to an adhesion in the secondary minimum of interaction as described by the DLVO theory. The consequences of these findings for adhesion in the natural environment are discussed.
Fouling of reverse osmosis (RO) water filtration membranes is a common problem throughout the industry. Most membrane fouling has an organic component that is typically derived from planktonic transparent exopolymer particles (TEP). Polysaccharides are a major constituent of TEP that are produced both abiotically from organic colloid precursors and by a variety of organisms in marine and freshwaters. The microgel character of TEP makes them difficult to remove through conventional filtration other than by ultra filtration and RO membranes. However, removal of TEP by these membranes is also problematic. When the membrane surface is initially fouled with TEP, the TEP layer then acts as an attachment substrate for organism, colloids and other submicron particulates, further contributing to membrane clogging. We report on an innovative electroadsorptive, depth filter media that is shown to be effective in significantly reducing TEP from fresh water, sea water, and wastewater. This technology has significant potential to protect membranes from primary fouling due to both TEP and nanoparticle build-up. The electroadsorptive filter media removes TEP through a strong positive charge generated by nanofibers of the mineral boehmite and the torturous path created by the depth filter media itself. The filter media has a mean flow pore of about 0.7 microns and very high nanofiber surface area that produces a filter with low pressure drop but a high filtration efficiency and high loading capacity for TEP removal.
Transparent exopolymer particles (TEP), planktonic microgel particles that are ubiquitous and numerous in all waters, have been recently recognized as being involved in the formation of aquatic biofilm. Studies in several different environments (small scale experimental membrane arrays, pilot scale and full-sized, operational, sea water reverse osmosis, and water treatment plants) indicate that the extent of biofouling and clogging of filtration membranes is usually significantly correlated to the levels of TEP in the feedwater. Other studies have revealed that current pretreatment technology such as rapid sand filtration and microfiltration are only moderately effective in reducing the amounts of TEP in feedwater reaching reverse osmosis membranes. A revised paradigm has been proposed that takes into consideration the role of TEP microgels as important accelerators of aquatic biofilm formation. This model has applied implications for the desalination and water treatment industries. With the recognition of TEP as a critical “player” in aquatic biofilm formation, important aims for water industry R&D should be the design of improved pretreatment technologies to minimize the amounts of feedwater TEP reaching sensitive surfaces and the development of membranes that either impede surface adhesion or cause disintegration of microgels upon contact.
Appropriate devices for obtaining either interstitial water or grain particle samples or for measuring dissolved oxygen (DO) at depth within the interior of large-scale, industrial granular bed filters are currently lacking. We developed two innovative samplers for studying a Rapid Sand Filter (RSF) at an operational SWRO plant: the first for water and granular material, the second for DO measurements. 1. The particle and interstitial water sampler is based on a corer that retains grain particles inside a chamber using water suction created by an external peristaltic pump. 2. The DO sampler incorporates a temperature compensated oxygen measuring optode over which laminar water flow is maintained by an external peristaltic pump. To test these samplers, an operational, full-scale RSF at a SWRO plant was monitored at various depths within the filter bed over several months. Additionally, DO profiles within the filter bed were followed during and after a backwash cycle. These samplers enable efficient and precise collection of DO data, interstitial water, and granular material from previously inaccessible depth layers within the filter bed without interruption of the filter operation, providing information on microbiological processes such as biofilm development, microbial community structure and organic matter cycling.
Large transparent exopolymer particles (TEP) are found abundantly in the ocean and play an important role in many fields of marine ecology. Quantification of TEP by light microscopy, however, is labor-intensive and slow. Here we introduce a simple, semiquantitative method to determine the concentration of TEP colorimetrically. In this method TEP are first stained with alcian blue. The dye complexed with TEP is then redissolved and measured spectrophotometrically. Several independent tests of the method show that the concentration of TEP measured spectrophotometrically compares well with parallel light microscope counts. Fractionation experiments confirm that TEP are not generated as an artifact of filtration. Field data show that the concentration of TEP in different oceanic environments ranges from 10 to 500 μg liter -1 xanthan equivalent depending on season, depth, and plankton community composition.
The concentration of chlorophyll in laboratory grown cultures of marine phytoplankton and in oceanic samples has been determined
both by measurement of fluorescence and by measurement of light absorption. The lower limit for detection of chlorophyll by
fluorescence with the instrumentation described is about 0·01 μg chlorophyll a, which is about 5% that required for a spectro-photometric determination. Through choice of appropriate filters, the amount
of fluorescence reflects either the chlorophyll a concentration or the sum of chlorophylls a and c. By measurement of fluorescence before and after acidification, the ratio of chlorophyll to phaeophytin can be readily determined.
Dilute HCl is superior to oxalic acid for acidification of pigment extracts. As the fluorometric determination of chlorophyll
and phaeophytin is fast, reliable and sensitive, it will be very useful in field studies of productivity.
Biofouling is a major and very expensive problem for the water industry. An Amiad Automatic Microfiber Filter (AMF) was tested as a pretreatment for biofouling growth inhibition using a lake water source. The filtration efficiency of the AMF in reducing Transparent Exopolymer Particles (TEP) and chlorophyll (Chl) levels in the feedwater was measured in 24 experiments during 2010–2011. These experiments showed significant reductions in TEP (mean 47 ± 21%), Chl (mean 90 ± 6%), total suspended solids (67 ± 7%), NTU turbidity (89 ± 5%), and >3 μm particle count (93 ± 4%) concentrations in the AMF filtered water. In parallel, four tests were conducted over one year to compare details of biofilm development on the surfaces of Robbins devices exposed for 30 days to AMF filtered or unfiltered lake water. Confocal laser scanning microscopy (CLSM) showed that the volume and thickness of extracellular polymeric substances of the biofilm that formed on the surfaces was markedly inhibited when the feedwater was filtered through the AMF. Taken together, these results show that microfiber filtration has good potential as a pretreatment technology upstream of surfaces sensitive to biofouling.
The abundance of Transparent Exopolymer Particles (TEP) in surface waters has been unnoticed for many years until recently as a potential foulant in reverse osmosis systems. Recent studies indicate that TEP may cause organic and biological fouling and may enhance particulate/colloidal fouling in reverse osmosis membranes. The presence of TEP was measured in the raw water, the pre-treatment processes and reverse osmosis (RO) systems of 6 integrated membrane installations. A spectrophotometric method was used to measure TEP in the particulate size range (>0.40 um) and was extended to measure TEP in the colloidal size range (0.05–0.40 um). Ultrafiltration pre-treatment applied in 4 plants, totally removed particulate TEP while microfiltration systems (2 plants) and coagulation/ sedimentation/rapid sand filtration systems (3 plants) partially removed this fraction. None of the pre-treatment systems investigated totally removed colloidal TEP. Biopolymer analysis using LC–OCD showed consistency between colloidal TEP and polysaccharide removal by UF pre-treatment and further verified the presence of TEP in the RO feedwater. TEP deposition in the RO system was determined after measuring total TEP concentrations in the RO feed and concentrate. The TEP deposition factors and specific deposition rates indicate that TEP accumulation had occurred in all plants investigated. This observation was verified by an autopsy of RO modules from two RO plants. Further improvement and verification of the (modified) TEP method, in particular the calibration, is necessary so that it can be employed to investigate the role of TEP in the fouling of RO systems.
The mineralogical and chemical composition of three types (black, yellow and red) of tuffs from Mt. Peres in northern Israel, that differ in terms of degree of weathering were determined in order to understand the weathering sequence under Mediterranean or semi-arid conditions. The black tuff is very slightly weathered and contains 62% volcanic glass, 15% primary minerals, 12% titano-magnetite, 5% halloysite and 4.5% hydroxyapatite. The yellow tuff, considered to be the weathering product of the black tuff, contains only 4% volcanic glass and 21% primary minerals, 8% Fe-rich minerals, 51% amorphous material identified as halloysite-like allophane, 15% halloysite, and 5% hydroxyapatite. A different mineralogical composition from that of red tuff indicates that this material was formed during a different eruption. The red tuff consisted of 29% volcanic glass, 26% primary minerals (different from those of the black tuff), 11% iron-bearing minerals, 10% halloysite, 5% hydroxyapatite and 19% amorphous material. The specific surface area and cation exchange capacity of the black, red and yellow tuff (7, 28, 174 m2 g−1 and 107, 285, 601 mmolc, kg−1 at pH 7, respectively) were in accord with their amorphous material contents.
In the first of a series of articles, Graeme Pearce looks at the issues involved in the selection of pre-treatment technology in seawater reverse osmosis applications.
The paper is concerned principally with summarising the experience to-date of treating low alkalinity, low turbidity, humic-rich surface waters by the combination of ozone oxidation and biological filtration processes. In the UK, USA and other countries, upland coloured waters have often been treated by slow sand filtration in which only moderate removals of DOC have been achieved (< 20%). The presence of significant levels of humic matter in filtrate waters has led to difficulties in achieving compliance with the standards for colour and THMs, and concern about the stability of residual chlorine and potential biogrowth in water supply pipework. This has led to several investigations (eg. in the UK, Sweden and the USA) of the benefits of applying ozonation prior to slow sand filtration in view of its known capability to decolorise humic substances and enhance biodegradability of the organic fractions. This paper summarises the experience to-date and highlights the benefits and problems that have been identified. Some studies have attempted to compare the relative performances of slow sand filters and granular activated carbon (GAC) filters for the removal of BDOC and the paper reviews the principal findings of these studies in view of the growing worldwide interest in the application of ozone-GAC. One major limitation with the use of ozone-GAC is the need periodically to remove and regenerate the carbon, since bed lives for the removal of humic substances are typically short. An alternative approach is to use inorganic adsorbents instead of carbon which have the potential to be chemically regenerated in-situ. The paper refers to the results of laboratory tests that have been carried out on the potential use of pre-ozonation followed by inorganic adsorbents (eg. Activated alumina, bauxite) for the removal of humic substances.
Transparent exopolymer particles (TEP) are sticky organic microgels, ubiquitous in natural waters, which have been implicated as a potentially important factor in the development of aquatic biofilm. An experimental cross-flow membrane array was used to investigate the relationship between the rate of membrane clogging and levels of TEP and other water quality variables in a lake water source. In three experimental series, feedwater TEP concentrations correlated significantly with membrane fouling rate. To check whether feedwater TEP could be a source for extracellular polymeric substances (EPS) of early biofilm, 5 experiments were run with either untreated (active bacteria) or chlorinated (inactivated bacteria) feedwater. Confocal scanning laser microscopy and image analysis of biofilm on membranes after 50 h showed similar EPS in the biofilm, irrespective of whether the bacteria were ~ 98% inactivated or fully active. This would indicate that most of the EPS appearing at early stages of biofilm on membranes originated from TEP in the feedwater rather than from metabolizing bacteria adhering to the surface. Taken together, these experiments support the premise that TEP in source waters play a significant role in the early stages of aquatic biofilm formation and are an important causative factor in membrane fouling.Research Highlights► Are Transparent exopolymer particles (TEP) important in aquatic biofilm formation? ► Experimental cross-flow membrane array used to study TEP role in biofilm formation. ► Rate of membrane fouling correlated significantly with TEP levels in feedwater. ► EPS in early biofilm derives mainly from TEP, not from adhering bacteria.
Recent discoveries reveal that polymer gel particles are abundant and important in the microbial loop, sedimentation processes, biogeochemical cycling, marine carbohydrate chemistry, and particle dynamics in the ocean. The novelty of these discoveries elicited an interdisciplinary discussion among investigators working in marine geochemistry, microbiology, and polymer physics on the significance of gels in the functioning of marine ecosystems. Marine gels are three-dimensional networks of biopolymers imbedded in seawater. They range in size from single macromolecules entwined, forming single-chain colloidal networks, to assembled polymer networks several hundreds of microns or larger. Gels can form in minutes to hours from dissolved organic matter or polymer chains released by phytoplankton or bacteria. They enclose nanoscale microenvironments that exhibit emerging physical, chemical, and biological properties that are drastically different from those of the DOM polymers that make them. Previous studies show that ∼10% of surface DOM could be assembled as gels, yielding estimates of ∼70×1015 g of organic carbon. This figure exceeds the global biomass of marine organisms by a factor of 50. The potential huge magnitude of the oceanic gel organic matter (GOM) pool suggests a need to develop reliable quantitative methods to systematically investigate the budget of marine gels and their role in biogeochemical cycling. Gels are particularly important for carbon cycling in that they provide an abiotic mechanism to move organic molecules up the particle size spectrum to sizes capable of sedimentation and eventual sequestration in the deep sea. Macrogels such as transparent exopolymer particles (TEP) are especially significant in sedimentation processes because they appear to be critical for the formation of marine snow and the aggregation of diatom blooms. The discovery of highly abundant gels in seawater also fundamentally changes how we think about the physical nature and microscale structure of the fluid and organic matter field encountered by bacteria, protists, and viruses in the sea. Gels may serve as nutrients and/or attachment surfaces for microbes, as refuges from predation, and as hot spots of high substrate concentration.Investigation of gels in the ocean represents an important new area of research ripe for exciting discovery. Areas where future research should be focused include the following: (1) determination of the budgets and pool sizes of gels, (2) investigation of the role of gels in biogeochemical cycling, (3) reconciliation of polymer physics and aggregation theory as explanations for macrogel formation, (4) quantification of the role of gels in sedimentation processes and particle dynamics and, (5) assessment of the role of gels as microhabitats, food sources, and attachment surfaces for marine organisms.
A good quality pre-treatment process is instrumental to the successful operation of a seawater reverse osmosis (SWRO) plant. The compounds that are susceptible to foul the reverse osmosis (RO) membranes are inorganic suspended solids, sand, oil, clays, bacteria, and dissolved organic matters. In order to prevent the fouling, a pre-treatment of the raw water needs to be conducted. The pre-treatment technologies to prevent membrane fouling and to extend the lifetime of the RO membrane are commonly grouped into two categories, conventional and non-conventional. Both of these treatments are currently applied in SWRO plants in the world. The pre-treatment system applied is highly site specific and depending on the type of the feed water. This paper reviews the recent representative researches that are related to SWRO antifouling strategies and answers the most crucial questions about design and operating parameters of SWRO and its pre-treatment process. Also the economic evaluation of the SWRO system in regards to antifouling strategies' experience is discussed.
Throughout the world, water scarcity is being recognised as a present or future threat to human activity and as a consequence, a definite trend to develop alternative water resources such as desalination can be observed. The most commonly used desalination technologies are reverse osmosis (RO) and thermal processes such as multi-stage flash (MSF) and multi-effect distillation (MED). In Europe, reverse osmosis, due to its lower energy consumption has gained much wider acceptance than its thermal alternatives. This review summarises the current state-of-the art of reverse osmosis desalination, dealing not only with the reverse osmosis stage, but with the entire process from raw water intake to post treatment of product water. The discussion of process fundamentals, membranes and membrane modules and of current and future developments in membrane technology is accompanied by an analysis of operational issues as fouling and scaling and of measures for their prevention such as adequate cleaning procedures and antiscalant use. Special focus is placed on pre-treatment of raw water and post-treatment of brine as well as of product water to meet drinking and irrigation water standards, including evaluation of current boron removal options. Energy requirements of reverse osmosis plants as well as currently applied energy recovery systems for reduction of energy consumption are described and cost and cost structure of reverse osmosis desalination are outlined. Finally, current practices of waste management and disposal as well as new trends such as the use of hybrid plants, i.e. combining reverse osmosis with thermal processes and/or power generation are addressed.
Global desalination quadrupled in the last 15 years and the relative importance of seawater desalination by reverse osmosis (SWRO) increased as well. While the technological aspects of SWRO plants are extensively described, studies on the environmental impact of brine discharge are lacking, in particular in situ marine environmental studies. The Ashqelon SWRO plant (333,000 m(3) d(-1) freshwater) discharges brine and backwash of the pretreatment filters (containing ferric hydroxide coagulant) at the seashore, next to the cooling waters of a power plant. At the time of this study brine and cooling waters were discharged continuously and the backwash discharge was pulsed, with a frequency dependent on water quality at the intake. The effects of the discharges on water quality and neritic microbial community were identified, quantified and attributed to the different discharges. The mixed brine-cooling waters discharge increased salinity and temperature at the outfall, were positively buoyant, and dispersed at the surface up to 1340 m south of the outfall. Nutrient concentrations were higher at the outfall while phytoplankton densities were lower. Chlorophyll-a and picophytoplankton cell numbers were negatively correlated with salinity, but more significantly with temperature probably as a result of thermal pollution. The discharge of the pulsed backwash increased turbidity, suspended particulate matter and particulate iron and decreased phytoplankton growth efficiency at the outfall, effects that declined with distance from the outfall. The discharges clearly reduced primary production but we could not attribute the effect to a specific component of the discharge. Bacterial production was also affected but differently in the three surveys. The combined and possible synergistic effects of SWRO desalination along the Israeli shoreline should be taken into account when the three existing plants and additional ones are expected to produce 2 Mm(3) d(-1) freshwater by 2020.
Reverse osmosis membrane technology has developed over the past 40 years to a 44% share in world desalting production capacity, and an 80% share in the total number of desalination plants installed worldwide. The use of membrane desalination has increased as materials have improved and costs have decreased. Today, reverse osmosis membranes are the leading technology for new desalination installations, and they are applied to a variety of salt water resources using tailored pretreatment and membrane system design. Two distinct branches of reverse osmosis desalination have emerged: seawater reverse osmosis and brackish water reverse osmosis. Differences between the two water sources, including foulants, salinity, waste brine (concentrate) disposal options, and plant location, have created significant differences in process development, implementation, and key technical problems. Pretreatment options are similar for both types of reverse osmosis and depend on the specific components of the water source. Both brackish water and seawater reverse osmosis (RO) will continue to be used worldwide; new technology in energy recovery and renewable energy, as well as innovative plant design, will allow greater use of desalination for inland and rural communities, while providing more affordable water for large coastal cities. A wide variety of research and general information on RO desalination is available; however, a direct comparison of seawater and brackish water RO systems is necessary to highlight similarities and differences in process development. This article brings to light key parameters of an RO process and process modifications due to feed water characteristics.
This paper focuses on the concept that traditional SEM artifacts, encountered in soft biological specimens, may be overcome by improving the physico-chemical properties of these samples rather than by applying sophisticated drying procedures. Emphasis is placed upon fixation strategies minimizing these artifacts and allowing the air drying of various specimens, even those showing very delicate surface microprojections. This attitude is illustrated by a variety of cells and tissues prepared for SEM by both conservative (i.e., critical point drying of samples treated with glutaraldehyde and/or osmium tetroxide) and reformative procedures, i.e., air drying of samples treated with glutaraldehyde, tannic acid, guanidine-HCl, and osmium tetroxide (GTGO-AD). The results clearly indicate that samples which were prepared by the GTGO procedure displayed very well preserved surface features with minimum shrinkage, even after being air dried.
Biogranulation technology developed for wastewater treatment includes anaerobic and aerobic granulation processes. Anaerobic granulation is relatively well known, but research on aerobic granulation commenced only recently. Many full-scale anaerobic granular sludge units have been operated worldwide, but no report exists of similar units for aerobic granulation. This paper reviews the fundamentals and applications of biogranulation technology in wastewater treatment. Aspects discussed include the models of biogranulation, major factors influencing biogranulation, characteristics of biogranules, and their industrial applications. This review hopes to provide a platform for developing novel granules-based bioreactors and devising a unified interpretation of the formation of anaerobic and aerobic granules under various operation conditions.
Understanding the interaction between bacterial cells and solid surfaces is essential to our attempts to quantify and predict the transport of microbes in groundwater aquifers, whether from the point of view of contamination or from that of bioremediation. The sorption of bacterial cells suspended in groundwater to porous medium grains was examined in batch studies. Bacterial sorption to clean quartz sand yielded equilibrium, linear, adsorption isotherms that varied with the bacterial strain used and the ionic strength of the aqueous solution. Values of K(d) (the slope of the linear sorption isotherm) ranged from 0.55 to 6.11 ml g, with the greatest sorption observed for the highest groundwater ionic strength. These findings are consistent with the interpretation that an increasingly compressed electrical double layer results in stronger adsorption between the like-charged mineral surface and the bacterial cells. When iron-oxyhydroxide-coated sand was used, however, all of the added bacteria were adsorbed up to a threshold of 6.93 x 10 cells g of coated sand, beyond which no further adsorption occurred. The irreversible, threshold adsorption is the result of a strong electrostatic attraction between the sesquioxide coating and the bacterial cells. Experimental results of adsorption in mixtures of quartz and Fe(III)-coated sand were successfully predicted by a simple additive model for sorption by the two substrate phases. Even small amounts of Fe(III)-coated sand in a mixture influenced the extent of adsorption of bacterial cells. A quantitative description of adsorption in the mixtures can be realized by using a linear isotherm for reversible adsorption to the quartz grains with a y intercept that represents the number of cells irreversibly adsorbed to the Fe(III)-coated sand.
Two landfill bioreactors were operated under aerobic and anaerobic conditions in a thermo-insulated room at a constant temperature of 32 degrees C. Reactors were filled with 19.5 kg of shredded synthetic solid waste prepared according to the average municipal solid waste compositions determined in Istanbul and operated under wet-tomb management strategy by using leachate recirculation. Aerobic conditions in the reactor were developed by using an air compressor. The results of experiments indicated that aerobic reactor had higher organic, nitrogen, phosphorus and alkali metal removal efficiencies than the anaerobic one. Furthermore, stabilization time considerably decreased when using aerobic processes with leachate recirculation compared to the anaerobic system with the same recirculation scheme.
Properly designed biological filters or infiltration systems have the capacity to significantly reduce effluent concentrations of pathogenic microorganisms in wastewater. The retention and elimination of microbial cells in biological wastewater filter systems is influenced by several factors. In this review, these factors are discussed. Immobilization of microbial cells moving through a porous media is influenced by mechanisms such as physical straining as well as adsorption to porous media. The grain size of porous media and bacterial cell size are important factors affecting the straining of bacteria, as are the hydraulic loading rate or the extent of clogging layer development in the filter. Adsorption of cells to the porous media is influenced by the content of organic matter, degree of biofilm development, and electrostatic attraction due to ion strength of the solution or electrostatic charges of cell- and particle surfaces. The rate of inactivation of pathogenic microorganisms, in adsorbed or liquid phases, has been shown to be affected by abiotic and biotic factors such as moisture content, pH, temperature, organic matter, bacterial species, predation, and antagonistic symbiosis between microorganisms in the system.
The oceanic gel phase: a bridge in the DOM-POM continuum The fate of transparent exopolymer particles (TEP) in integrated membrane systems: removal through pretreatment processes and deposition on reverse osmosis membranes
- P Verdugo
- A L Alldredge
- F Azam
- D L Kirchman
- U Passow
- P H Santschi
Verdugo, P., Alldredge, A.L., Azam, F., Kirchman, D.L., Passow, U., Santschi, P.H., 2004. The oceanic gel phase: a bridge in the DOM-POM continuum. Marine Chemistry 92, 65e66. Villacorte, L.O., Kennedy, M.D., Amy, G.L., Schippers, J.C., 2009. The fate of transparent exopolymer particles (TEP) in integrated membrane systems: removal through pretreatment processes and deposition on reverse osmosis membranes. Water Research 43, 5039e5052.
Mineralogical and chemical composition of three tuffs from northern Israel Retention and removal of pathogenic bacteria in wastewater percolating through porous media: a review Biofilms as complex differentiated communities
- A Silber
- B Bar-Yosef
- A Singer
- Y Chen
- e
- K T Stevik
- A Kari
- G Ausland
- F J Hanssen
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