Factors governing the pre-concentration of wastewater using forward osmosis for subsequent resource recovery

Ultra-fast green hydrogen production from municipal wastewater by an integrated forward osmosis-alkaline water electrolysis system

Recent advancements in membrane-assisted seawater electrolysis powered by renewable energy offer a sustainable path to green hydrogen production. However, its large-scale implementation faces challenges due to slow power-to-hydrogen (P2H) conversion rates. Here we report a modular forward osmosis-water splitting (FOWS) system that integrates a thin-film composite FO membrane for water extraction with alkaline water electrolysis (AWE), denoted as FOWSAWE. This system generates high-purity hydrogen directly from wastewater at a rate of 448 Nm3 day-1 m-2 of membrane area, over 14 times faster than the state-of-the-art practice, with specific energy consumption as low as 3.96 kWh Nm-3. The rapid hydrogen production rate results from the utilisation of 1 M potassium hydroxide as a draw solution to extract water from wastewater, and as the electrolyte of AWE to split water and produce hydrogen. The current system enables this through the use of a potassium hydroxide-tolerant and hydrophilic FO membrane. The established water-hydrogen balance model can be applied to design modular FO and AWE units to meet demands at various scales, from households to cities, and from different water sources. The FOWSAWE system is a sustainable and an economical approach for producing hydrogen at a record-high rate directly from wastewater, marking a significant leap in P2H practice.

Integrating reverse osmosis and forward osmosis (RO-FO) for printing and dyeing wastewater treatment: impact of FO on water recovery

Reverse osmosis (RO) alone has low water recovery efficiency because of membrane fouling and limited operating pressure. In this study, a combined reverse osmosis-forward osmosis (RO-FO) process was used for the first time to improve the water recovery efficiency of secondary effluent in printing and dyeing wastewater. The effects of operating pressure and pH on water recovery and removal efficiency of RO-FO were investigated. The results showed that the optimum conditions were an operating pressure of 1.5 MPa and a feed solution pH of 9.0. Under optimal operating conditions, most of the organic and inorganic substances in the wastewater can be removed, and the rejection of total organic carbon (TOC), Sb, Ca, and K were 98.7, 99.3, 97.0, and 92.7%, respectively. Fluorescence excitation-emission matrices coupled with parallel factor (EEM-PARAFAC) analysis indicated that two components (tryptophan and tyrosine) in the influent were effectively rejected by the hybrid process. The maximum water recovery (Rw, max) could reach 95%, which was higher than the current single RO process (75%). This research provided a feasible strategy to effectively recover water from printing and dyeing wastewater.

Evaluation of Forward Osmosis and Low-Pressure Reverse Osmosis with a Tubular Membrane for the Concentration of Municipal Wastewater and the Production of Biogas

Currently, freshwater scarcity is one of the main issues that the world population has to face. To address this issue, new wastewater treatment technologies have been developed such as membrane processes. Among them, due to the energy disadvantages of pressure-driven membrane processes, Forward Osmosis (FO) and Low-Pressure Reverse Osmosis (LPRO) have been introduced as promising alternatives. In this study, the behavior of a 2.3 m² tubular membrane TFO-D90 when working with municipal wastewater has been studied. Its performances have been evaluated and compared in two operating modes such as FO and LPRO. Parameters such as fouling, flow rates, water flux, draw solution concentration, organic matter concentration, as well as its recovery have been studied. In addition, the biogas production capacity has been evaluated with the concentrated municipal wastewater obtained from each process. The results of this study indicate that the membrane can work in both processes (FO and LPRO) but, from the energy and productivity point of view, FO is considered more appropriate mainly due to its lower fouling level. This research may offer a new point of view on low-energy and energy recovery wastewater treatment and the applicability of FO and LPRO for wastewater concentration.

Effects of Different Draw Solutions on Biogas Slurry Concentration in Forward Osmosis Membrane: Performance and Membrane Fouling

Biogas slurry poses a severe challenge to the sustainable management of livestock farms. The technology of the forward osmosis (FO) membrane has a good application prospect in the field of biogas slurry concentration. Further research is needed to verify the effects of different draw solutions on FO membranes in biogas slurry treatment and the related membrane fouling characteristics. In this study, three different draw solutions were selected to evaluate the performance of FO membranes for biogas slurry concentration. Membrane fouling was investigated by characterization after FO membrane treatment to identify fouling contaminants. The result showed that FO membrane treatment can realize the concentration of biogas slurry and MgCl₂ as the draw solution has the best effect on the concentration of biogas slurry. The different draw solutions all contributed to the efficient retention of most organics and TP while each treatment was ineffective at retaining nitrogen. The cake layer that appeared after the biogas slurry was concentrated covered the surface of the FO membrane. Some functional groups were detected on the surface after membrane fouling, such as C–O and C=C. Moreover, the C element accounts for 57% of the main components of the cake layer after the membrane fouling. Membrane fouling is caused by both organic fouling and inorganic fouling, of which organic fouling is the main reason. This study provides a technical reference for the high-value utilization of biogas slurry.

Ecological Risk Evaluation and Removal of Emerging Pollutants in Urban Wastewater by a Hollow Fiber Forward Osmosis Membrane

Forward osmosis (FO) is a promising technology for the treatment of urban wastewater. FO can produce high-quality effluents and preconcentrate urban wastewater for subsequent anaerobic treatment. This membrane technology makes it possible to eliminate the pollutants present in urban wastewater, which can cause adverse effects in the ecosystem even at low concentrations. In this study, a 0.6 m2 hollow fiber aquaporin forward osmosis membrane was used for the treatment of urban wastewater from the Valladolid wastewater treatment plant (WWTP). A total of 51 Contaminants of Emerging Concern (CECs) were investigated, of which 18 were found in the target urban wastewater. They were quantified, and their ecotoxicological risk impact was evaluated. Different salts with different concentrations were tested as draw solutions to evaluate the membrane performances when working with pretreated urban wastewater. NaCl was found to be the most appropriate salt since it leads to higher permeate fluxes and lower reverse saline fluxes. The membrane can eliminate or significantly reduce the pollutants present in the studied urban wastewater, producing water without ecotoxicological risk or essentially free of pollutants. In all cases, good recovery was achieved, which increased with molecular weight, although chemical and electrostatic interactions also played a role.

Fouling and cleaning of thin film composite forward osmosis membrane treating municipal wastewater for resource recovery

Concentrating municipal wastewater by forward osmosis (FO) membrane to a high level of water recovery rate to facilitate downstream resource recovery might cause more serious membrane fouling. This study investigated the concentration of synthetic and real municipal wastewater to 90% water recovery rate by hollow fiber and flat-sheet thin film composite (TFC) FO membranes and their associated membrane fouling and cleaning. Results show that the FO membrane had high rejection rates of COD, phosphate, Ca²⁺ and Mg²⁺ with concentration factors at around 8 when achieving a 90% water recovery rate, which facilitated downstream phosphate recovery by precipitation and energy recovery by anaerobic digestion. Ca²⁺ concentration in municipal wastewater at 61 mg/L was found to be the main factor to cause inorganic scaling, and the fouling caused by calcium precipitates was harder to be cleaned by physical cleaning compared with suspended solids (SS) such as cellulose particles. In addition, the TFC FO membrane for treating real sewage with SS is not applicable for the hollow fiber configuration used in this study due to lumen clogging, while the TFC flat sheet configuration was able to achieve a 90% water recovery rate. The use of a spacer in the flat sheet configuration improved the efficiency of the following physical cleaning by around 15% although it did not alleviate membrane fouling during the membrane filtration process. This study highlighted the importance of the chemistry of FS and DS and FO membrane configuration on membrane fouling particularly at high water recovery rates and the necessity of pre-treatment of municipal wastewater by removing suspended solids.

State-of-the-Art and Opportunities for Forward Osmosis in Sewage Concentration and Wastewater Treatment

The application of membrane technologies for wastewater treatment to recover water and nutrients from different types of wastewater can be an effective strategy to mitigate the water shortage and provide resource recovery for sustainable development of industrialisation and urbanisation. Forward osmosis (FO), driven by the osmotic pressure difference between solutions divided by a semi-permeable membrane, has been recognised as a potential energy-efficient filtration process with a low tendency for fouling and a strong ability to filtrate highly polluted wastewater. The application of FO for wastewater treatment has received significant attention in research and attracted technological effort in recent years. In this review, we review the state-of-the-art application of FO technology for sewage concentration and wastewater treatment both as an independent treatment process and in combination with other treatment processes. We also provide an outlook of the future prospects and recommendations for the improvement of membrane performance, fouling control and system optimisation from the perspectives of membrane materials, operating condition optimisation, draw solution selection, and multiple technologies combination.

Ammonium ultra-selective membranes for wastewater treatment and nutrient enrichment: Interplay of surface charge and hydrophilicity on fouling propensity and ammonium rejection

Membrane fouling and ammonium transmembrane diffusion simultaneously pose great challenges in membrane-based pre-concentration of domestic wastewater for efficient subsequent resources recovery (i.e., energy and nutrients). Herein, amine-functionalized osmotic membranes were fabricated by optimizing the grafting pathway of polyamidoamine (PAMAM) dendrimer to mitigate fouling and ammonium transmembrane diffusion. Compared to the control membrane, the PAMAM-grafted membranes with abundant primary amine groups possessed substantially increased hydrophilicity and positive charges (i.e., protonated primary amines) and thus exhibited superior anti-fouling capability and ammonium selectivity. With further increasing the PAMAM grafting ratio, the membrane exhibited a steady enhancement in ammonium selectivity and eventually achieved an ultra-high ammonium rejection of 99.4%. Nevertheless, the anti-fouling capability of such ammonium ultra-selective membrane was weakened due to the suppression of the adverse impact of excessive positive charges over the beneficial effect of increased surface hydrophilicity. This in turn leads to a drop of ammonium rejection below 90% during domestic wastewater concentration. This study demonstrates that the membrane with a moderate primary amine loading could achieve the highest anti-fouling capability with only less than 10% flux decline and meanwhile maintain an excellent ammonium rejection above 94% during raw domestic wastewater concentration. This work provides theoretical guidance for fabricating simultaneously enhanced anti-fouling and ammonia-rejecting membranes.

Achieving stable operation and shortcut nitrogen removal in a long-term operated aerobic forward osmosis membrane bioreactor (FOMBR) for treating municipal wastewater

Forward osmosis membrane bioreactor (FOMBR) is an integrated physical-biological treatment process that has received increased awareness in treating municipal wastewater for its potential to produce high effluent quality coupled with its low propensity for fouling formation. However, reverse salt diffusion (RSD) is a major issue and so far limited studies have reported long-term FOMBR operation under the elevated salinity conditions induced by RSD. This study investigated the performance of a FOMBR in treating municipal wastewater under a controlled saline environment (6-8 g L^-1 NaCl) using two separate sodium chloride draw solution (NaCl DS) concentrations (35 and 70 g L^-1) over 243 days. At 35 g L^-1 NaCl DS, the water flux performance dropped from 6.75 L m^-2 h^-1 (LMH) to 2.07 LMH after 72 days of operation in the first experimental stage, when no cleaning procedure was implemented. In the subsequent stage, the DS concentration was increased to 70 g L^-1 and a weekly physical cleaning regime introduced. Under stable operation, the water flux performance recovery was 67% after 21 cycles of physical cleaning. For the first time in FOMBR studies, a shortcut nitrogen removal via the nitrite pathway was also achieved under the elevated salinity conditions. At the end of operation (day 243), the ammonia-oxidising bacteria (Nitrosomonas sp.) was the only nitrifier species in the system and no nitrite oxidising bacteria was detected. The above study proves that a FOMBR system is a feasible process for treating municipal wastewater.

Zero-valent iron addition in anaerobic dynamic membrane bioreactors for preconcentrated wastewater treatment: Performance and impact

Wastewater preconcentration to capture abundant organics is promising for facilitating subsequent anaerobic digestion (AD) to recover bioenergy, however research efforts are still needed to verify the effectiveness of such an emerging strategy as carbon capture plus AD. Therefore, lab-scale anaerobic dynamic membrane bioreactors (AnDMBRs) without and with the addition of zero-valent iron (ZVI) (i.e., AnDMBR1 versus AnDMBR2) were developed for preconcentrated domestic wastewater (PDW) treatment, and the impact of ZVI addition on process performance and associated mechanisms were investigated. The stepwise addition of ZVI from 2 to 4 to 6 g/L improved the treatment performance as COD removal slightly increased and TP removal and methane production were enhanced by 53.3%-62.9% and 22.6%-31.3%, respectively, in consecutive operational phases. However, the average increasing rate of the transmembrane pressure (TMP) in AnDMBR2 (0.18 kPa/d) was obviously higher than that in AnDMBR1 (0.05 kPa/d), indicating an unfavorable impact of dosing ZVI on the dynamic membrane (DM) filtration performance. ZVI that has transformed to iron ions (mainly Fe²⁺) can behave as a coagulant, electron donor or inorganic foulant, thus enabling the excellent removal of dissolved phosphorous, enhancing the enrichment and activities of specific methanogens and causing the formation of a compact DM layer. Morphological, componential, and microbial community analyses provided new insights into the functional mechanisms of ZVI added to membrane-assisted anaerobic digesters, indicating that ZVI has the potential to improve bioenergy production and resource recovery, while optimizing the ZVI dosage should be considered to alleviate membrane fouling.

Forward Osmosis as Concentration Process: Review of Opportunities and Challenges

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.

Improving wastewater management using free nitrous acid (FNA)

Free nitrous acid (FNA), the protonated form of nitrite, has historically been an unwanted substance in wastewater systems due to its inhibition on a wide range of microorganisms. However, in recent years, advanced understanding of FNA inhibitory and biocidal effects on microorganisms has led to the development of a series of FNA-based applications that improve wastewater management practices. FNA has been used in sewer systems to control sewer corrosion and odor; in wastewater treatment to achieve carbon and energy efficient nitrogen removal; in sludge management to improve the sludge reduction and energy recovery; in membrane systems to address membrane fouling; and in wastewater algae systems to facilitate algae harvesting. This paper aims to comprehensively and critically review the current status of FNA-based applications in improving wastewater management. The underlying mechanisms of FNA inhibitory and biocidal effects are also reviewed and discussed. Knowledge gaps and current limitations of the FNA-based applications are identified; and perspectives on the development of FNA-based applications are discussed. We conclude that the FNA-based technologies have great potential for enhancing the performance of wastewater systems; however, further development and demonstration at larger scales are still required for their wider applications.

Modeling and simulation of fertilizer drawn forward osmosis process using Aspen Plus-MATLAB model

Although experimental studies on the impact of feed (FS) and draw solutions (DS) on the forward osmosis (FO) applications are reported in literature, systematic mathematical modeling considering the dynamic change in solution properties is lacking. In this study, asymmetric FO membrane simulation model was established using Aspen Plus-MATLAB subroutines algorithm to account for the effect of concentration polarization (CP), types of FS and DS and in their properties on FO performance. The developed model was validated by comparing the simulation with experimental results. The model successfully predict the performance of FO process under wide varieties of operational conditions, FS and DS flow rates and concentrations. The model showed that the variation of MCFDS concentration had a marked effect on water flux (WF) in contrast to flow rate. The WFs obtained from seawater (SW) increased from 5.28 L/m².h to 42.08 L/m².h as MCFDS changes from 150 g/L to 300 g/L which corresponding to 11.66% to 45.33% of water recovery. As for synthetic aquaculture wastewater (SAWW), 9.70 L/m².h to 37.32 L/m².h of WFs were exhibited with the increase of MCFDS concentration from 50 g/L to 200 g/L, respectively. The effect of concentrated external CP (CECP) was found to be significant in case of SW and negligible with SAWW. Whereas, increasing MCFDS concentration increases the severity effect of dilutive internal CP (DICP). The degree of DICP depends on the solute resistivity (K_D) of porous layer, which were elevated (4.22-5.88 s/m) as MCFDS concentration increases (150-300 g/L). The study demonstrated the effectiveness and suitability of the developed Aspen Plus-MATLAB model simulating the FO process.

Comparison of the degree of fouling at various flux rates and modes of operation using forward osmosis for remediation of produced water from unconventional oil and gas development

Driven by increased energy demands and technological advancements, the energy landscape of the United States has been changed by the expansion of unconventional oil and gas extraction. Unconventional development requires well stimulation, which uses millions of gallons of water per well and generates billions of gallons of wastewater annually. The waste matrix, referred to as produced water, has proven to be challenging to treat due to the complex physical, chemical, and biological composition, which can change over the lifetime of a production well. Here, forward osmosis was used as a remediation technique to extract fresh water from produced water procured from the Permian Basin region of west Texas. These data examine the durability of thin-film hollow-fiber membranes by determining how quickly the membranes irreversibly fouled at various flux rates during two modes of operation: a) active layer in contact with the draw solution (AL-DS); and b) active layer in contact with the feed solution (AL-FS). Membranes used in AL-DS mode fouled faster than their counterparts used in AL-FS mode. Additionally, membranes used with higher flux rates fouled more quickly than those used under low flux conditions. Ultimately, it was determined that produced water will require pretreatment prior to being concentrated using forward osmosis.

Pretreatment Techniques for Produced Water with Subsequent Forward Osmosis Remediation

Unconventional oil and gas extraction is on the rise across the United States and comprises an integral component in meeting the nation’s energy needs. The primary by-product of this industrious process is produced water, which is a challenging matrix to remediate because of its complex physical and chemical composition. Forward osmosis is a viable option to treat high-salinity produced water; however, fouling has been an issue. This study aimed to treat produced water before using forward osmosis as a remediation option. Trials consisted of a series of five experiments in order to evaluate the performance of the membrane. Samples were treated by centrifugation, activated carbon, filtration, ferric chloride, as well as coagulants and a polymer. It can be concluded that forward osmosis can be used to extract water from high-salinity oil field brines and produced water, and that pretreating the produced water decreased the tendency for fouling. The pretreatment with the overall best performance was activated carbon, which also yielded the lowest total organic carbon concentrations of 1.9 mg/L. During remediation trials using produced water pretreated with activated carbon as the feed solution, there was a 14% decrease in flux over the course of the 7 h trials. The membrane performance was restored after washing.

Anaerobic membrane bioreactor for biogas production from concentrated sewage produced during sewer mining

A laboratory scale anaerobic membrane bioreactor was operated for 11 months treating synthetic wastewater that mimicked the concentrate from a forward osmosis process treating municipal wastewater with 80% water recovery. The effect of temperature variation on reactor performance was assessed. The reactor operated during 4 months at 34 °C and then temperature was decreased to 23 °C, 17 °C and 15 °C mimicking the typical temperature seasonal variations of the sewage. Average COD removal efficiencies were 95, 87, 76 and 67% at 34, 23, 17 and 15 °C respectively, obtaining lower biogas production and lower COD removal at lower temperatures. Dissolved methane in the permeate averaged 8.2 mg CH₄/L and did not significantly change with temperature. After 2 months operating at 15 °C, temperature was progressively increased, resulting in an immediate increase of methane production and COD removal efficiencies. Microbial analysis showed important changes in the archaeal community when temperature was changed from 34 to 23 °C.

Nutrient removal in an algal membrane photobioreactor: effects of wastewater composition and light/dark cycle

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 PO₄^3--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 PO₄^3--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.

Resource recovery from wastewater by anaerobic membrane bioreactors: Opportunities and challenges

This review examines the potential of anaerobic membrane bioreactor (AnMBR) to serve as the core technology for simultaneous recovery of clean water, energy, and nutrient from wastewater. The potential is significant as AnMBR treatment can remove a board range of trace organic contaminants relevant to water reuse, convert organics in wastewater to biogas for subsequent energy production, and liberate nutrients to soluble forms (e.g. ammonia and phosphorus) for subsequent recovery for fertilizer production. Yet, there remain several significant challenges to the further development of AnMBR. These challenges evolve around the dilute nature of municipal wastewater, which entails the need for pre-concentrating wastewater prior to AnMBR, and hence, issues related to salinity build-up, accumulation of substances, membrane fouling, and membrane stability. Strategies to address these challenges are proposed and discussed. A road map for further research is also provided to guide future AnMBR development toward resource recovery.

Biofouling Mitigation by Chloramination during Forward Osmosis Filtration of Wastewater

Pre-concentration is essential for energy and resource recovery from municipal wastewater. The potential of forward osmosis (FO) membranes to pre-concentrate wastewater for subsequent biogas production has been demonstrated, although biofouling has also emerged as a prominent challenge. This study, using a cellulose triacetate FO membrane, shows that chloramination of wastewater in the feed solution at 3⁻8 mg/L residual monochloramine significantly reduces membrane biofouling. During a 96-h pre-concentration, flux in the chloraminated FO system decreased by only 6% and this flux decline is mostly attributed to the increase in salinity (or osmotic pressure) of the feed due to pre-concentration. In contrast, flux in the non-chloraminated FO system dropped by 35% under the same experimental conditions. When the feed was chloraminated, the number of bacterial particles deposited on the membrane surface was significantly lower compared to a non-chloraminated wastewater feed. This study demonstrated, for the first time, the potential of chloramination to inhibit bacteria growth and consequently biofouling during pre-concentration of wastewater using a FO membrane.

Treatment of Palm Oil Mill Effluent Using Membrane Bioreactor: Novel Processes and Their Major Drawbacks

Over the years, different types of alternative technologies have been developed and used for palm oil mill effluent (POME) treatment. Specifically, membrane bioreactor (MBR) has been employed to relegate pollutants contained in POME under different operating conditions, and the technology was found to be promising. The major challenge impeding the wider application of this technology is membrane fouling, which usually attracts high operating energy and running cost. In this regard, novel methods of mitigating membrane fouling through the treatment processes have been developed. Therefore, this review article specifically focuses on the recent treatment processes of POME using MBR, with particular emphasis on innovative processes conditions such as aerobic, anaerobic, and hybrid processing as well as their performance in relation to fouling minimization. Furthermore, the effects of sonication and thermophilic and mesophilic conditions on membrane blockage were critically reviewed. The types of foulants and fouling mechanism as influenced by different operating conditions were also analyzed censoriously.

Recovery of organic matters in wastewater by self-forming dynamic membrane bioreactor: Performance and membrane fouling

Formation process and fouling characteristics of the dynamic membrane were studied in a modified self-forming dynamic membrane bioreactor (SF-DMBR) for recovering the organic matters in wastewater, and the performance of this SF-DMBR was investigated. Results indicated that 80% of the organic matters in wastewater could be quickly recovered under continuous operation. Furthermore, the evolutions of the fouling components were determined during the formation and development processes of dynamic membrane. After the long-term operation, the decreases of protein concentration, accompanying with the increases of polysaccharides and microorganisms contents due to special operating conditions, were interestingly observed in the sludge of membrane surface. This could explain why membrane fouling was much weak. Therefore, though high membrane fluxes at 50-150 L/(m²·h) were adopted in this study, the reactor can still obtain a long-term stable operation and the operating cycle reached as long as 8 days. Finally, membrane fouling process was described by combined models.

An anaerobic membrane bioreactor - membrane distillation hybrid system for energy recovery and water reuse: Removal performance of organic carbon, nutrients, and trace organic contaminants

In this study, a direct contact membrane distillation (MD) unit was integrated with an anaerobic membrane bioreactor (AnMBR) to simultaneously recover energy and produce high quality water for reuse from wastewater. Results show that AnMBR could produce 0.3-0.5L/g COD_added biogas with a stable methane content of approximately 65%. By integrating MD with AnMBR, bulk organic matter and phosphate were almost completely removed. The removal of the 26 selected trace organic contaminants by AnMBR was compound specific, but the MD process could complement AnMBR removal, leading to an overall efficiency from 76% to complete removal by the integrated system. The results also show that, due to complete retention, organic matter (such as humic-like and protein-like substances) and inorganic salts accumulated in the MD feed solution and therefore resulted in significant fouling of the MD unit. As a result, the water flux of the MD process decreased continuously. Nevertheless, membrane pore wetting was not observed throughout the operation.

Assessing the integration of forward osmosis and anaerobic digestion for simultaneous wastewater treatment and resource recovery

This study assessed the performance and key challenges associated with the integration of forward osmosis (FO) and anaerobic digestion for wastewater treatment and resource recovery. Using a thin film composite polyamide FO membrane, maximising the pre-concentration factor (i.e. system water recovery) resulted in the enrichment of organics and salinity in wastewater. Biomethane potential evaluation indicated that methane production increased correspondingly with the FO pre-concentration factor due to the organic retention in the feed solution. At 90% water recovery, about 10% more methane was produced when using NaOAc compared with NaCl because of the contribution of biodegradable reverse NaOAc flux. No negative impact on anaerobic digestion was observed when wastewater was pre-concentrated ten-fold (90% water recovery) for both draw solutes. Interestingly, the unit cost of methane production using NaOAc was slightly lower than NaCl due to the lower reverse solute flux of NaOAc, although NaCl is a much cheaper chemical.

Effects of sulphur on the performance of an anaerobic membrane bioreactor: Biological stability, trace organic contaminant removal, and membrane fouling

This study investigated the impact of sulphur content on the performance of an anaerobic membrane bioreactor (AnMBR) with an emphasis on the biological stability, contaminant removal, and membrane fouling. Removal of 38 trace organic contaminants (TrOCs) that are ubiquitously present in municipal wastewater by AnMBR was evaluated. Results show that basic biological performance of AnMBR regarding biomass growth and the removal of chemical oxygen demand (COD) was not affected by sulphur addition when the influent COD/SO₄^2- ratio was maintained higher than 10. Nevertheless, the content of hydrogen sulphate in the produced biogas increased significantly and membrane fouling was exacerbated with sulphur addition. Moreover, the increase in sulphur content considerably affected the removal of some hydrophilic TrOCs and their residuals in the sludge phase during AnMBR operation. By contrast, no significant impact on the removal of hydrophobic TrOCs was noted with sulphur addition to AnMBR.

Insight into chemical phosphate recovery from municipal wastewater

Phosphate plays an irreplaceable role in the production of fertilizers. However, its finite availability may not be enough to satisfy increasing demands for the fertilizer production worldwide. In this scenario, phosphate recovery can effectively alleviate this problem. Municipal wastewater has received high priority to recover phosphate because its quantity is considerable. Therefore, phosphate recovery from municipal wastewater can bring many benefits such as relieving the burden of increasing production of fertilizers and reduction in occurrence of eutrophication caused by the excessive concentration of phosphate in the released effluent. The chemical processes are the most widely applied in phosphate recovery in municipal wastewater treatment because they are highly stable and efficient, and simple to operate. This paper compares chemical technologies for phosphate recovery from municipal wastewater. As phosphate in the influent is transferred to the liquid and sludge phases, a technical overview of chemical phosphate recovery in both phases is presented with reference to mechanism, efficiency and the main governing parameters. Moreover, an analysis on their applications at plant-scale is also presented. The properties of recovered phosphate and its impact on crops and plants are also assessed with a discussion on the economic feasibility of the technologies.

Exploration of polyepoxysuccinic acid as a novel draw solution in the forward osmosis process

Polyepoxysuccinic acid (PESA) is a green corrosion scale inhibitor.