Impact on reactor configuration on the performance of anaerobic MBRs: treatment of settled sewage in temperate climates

Use of reclaimed municipal wastewater in agriculture: Comparison of present practice versus an emerging paradigm of anaerobic membrane bioreactor treatment coupled with hydroponic controlled environment agriculture

Advancements in anaerobic membrane bioreactor (AnMBR) technology have opened up exciting possibilities for sustaining precise water quality control in wastewater treatment and reuse. This approach not only presents an opportunity for energy generation and recovery but also produces an effluent that can serve as a valuable nutrient source for crop cultivation in hydroponic controlled environment agriculture (CEA). In this perspective article, we undertake a comparative analysis of two approaches to municipal wastewater utilization in agriculture. The conventional method, rooted in established practices of conventional activated sludge (CAS) wastewater treatment for soil/land-based agriculture, is contrasted with a new paradigm that integrates AnMBR technology with hydroponic (soilless) CEA. This work encompasses various facets, including wastewater treatment efficiency, effluent quality, resource recovery, and sustainability metrics. By juxtaposing the established methodologies with this emerging synergistic model, this work aims to shed light on the transformative potential of the integration of AnMBR and hydroponic-CEA for enhanced agricultural sustainability and resource utilization.

A Review on Opportunities and Limitations of Membrane Bioreactor Configuration in Biofuel Production

Biofuels are a clean and renewable source of energy that has gained more attention in recent years; however, high energy input and processing cost during the production and recovery process restricted its progress. Membrane technology offers a range of energy-saving separation for product recovery and purification in biorefining along with biofuel production processes. Membrane separation techniques in combination with different biological processes increase cell concentration in the bioreactor, reduce product inhibition, decrease chemical consumption, reduce energy requirements, and further increase product concentration and productivity. Certain membrane bioreactors have evolved with the ability to deal with different biological production and separation processes to make them cost-effective, but there are certain limitations. The present review describes the advantages and limitations of membrane bioreactors to produce different biofuels with the ability to simplify upstream and downstream processes in terms of sustainability and economics.

The third route: A techno-economic evaluation of extreme water and wastewater decentralization

Water systems need to become more locally robust and sustainable in view of increased population demands and supply uncertainties. Decentralized treatment is often assumed to have the potential to improve the technical, environmental, and economic performance of current technologies. The techno-economic feasibility of implementing independent building-scale decentralized systems combining rainwater harvesting, potable water production, and wastewater treatment and recycling was assessed for six main types of buildings ranging from single-family dwellings to high-rise buildings. Five different treatment layouts were evaluated under five different climatic conditions for each type of building. The layouts considered varying levels of source separation (i.e., black, grey, yellow, brown, and combined wastewater) using the corresponding toilet types (vacuum, urine-diverting, and conventional) and the appropriate pipes and pumping requirements. Our results indicate that the proposed layouts could satisfy 100% of the water demand for the three smallest buildings in all but the aridest climate conditions. For the three larger buildings, rainwater would offset annual water needs by approximately 74 to 100%. A comprehensive economic analysis considering CapEx and OpEx indicated that the cost of installing on-site water harvesting and recycling systems would increase the overall construction cost of multi-family buildings by around 6% and single-family dwellings by about 12%, with relatively low space requirements. For buildings or combined water systems with more than 300 people, the estimated total price of on-site water provision (including harvesting, treatment, recycling, and monitoring) ranged from $1.5/m³ to $2.7/m,³ which is considerably less than the typical tariffs collected by utilities in the United States and Western Europe. Where buildings can avoid the need to connect to centralized supplies for potable water and sewage disposal, water costs could be even lower. Urine-diversion has the potential to yield the least expensive solution but is the least well developed and had higher uncertainty in the cost analysis. More mature layouts (e.g., membrane bioreactors) exhibited less cost uncertainty and were economically competitive. Our analysis indicates that existing technologies can be used to create economically viable systems that greatly reduce demands on centralized utilities and, under some conditions, eliminate the need for centralized water supply or sewage collection.

Pilot plant demonstration of temperature impacts on the methanogenic performance and membrane fouling control of the anaerobic membrane bioreactor in treating real municipal wastewater

A 5,000-L anaerobic membrane bioreactor (AnMBR) fed with actual municipal wastewater was employed to study the impact of temperature drops on methanogenic performance and membrane fouling. With temperature dropped from 25 °C to 15 °C, the methane yield decreased from 0.244 to 0.205 NL-CH₄/g-COD_removal and the dissolved methane increased from 29% to 43%, resulted in the methanogenic performance reduced by 25%. The membrane rejection offset the deteriorated anaerobic digestion at low temperatures and ensured the stable COD removal efficiency of 84.5%-90.0%. The synergistic effects of the increased microbial products and viscosity and the residual inorganic foulants aggravated the membrane fouling at lower temperatures. As the organic fouling was easily removed by NaClO, the inorganics related to the elements of S, Ca and Fe were the stubborn membrane foulants and required the enhanced acid membrane cleaning. These findings obtained under the quasi-practical condition are expected to promote the practical applications of mainstream AnMBR.

Role of microparticles in membrane fouling from acidogenesis to methanogenesis phases in an anaerobic baffled reactor

Microparticles (0.45-10 μm) have been recognized as key foulants in anaerobic membrane bioreactors (AnMBRs). However, their characteristics and fouling behaviors are often understood in single-stage and completely mixed reactors, failing to elucidate the occurrence of microparticles in the multi-stage anaerobic bioprocess. Here, a lab-scale anaerobic baffled reactor with four compartments (C1-C4) was employed to explore the composition and fouling potential of microparticles in different compartments. Photometric analysis showed that the microparticles had an increasing percentage in the total organics of the top supernatant but a decreasing concentration from C1 to C4. Long-term filtration and dead-end filtration tests revealed that the top supernatant in C1 had much higher fouling potential than those in C2-C4. The supernatant microparticles significantly accumulated in the cake layers for each compartment (68-95% of the total organics), particularly the fraction of 1-5 μm, and the fouling rate was positively correlated with the biomass accumulation rate. Based on reactor performance and 16S rRNA gene sequences, a significant bio-phase separation occurred between C1 (acidogenesis) and C2-C4 (methanogenesis). And hydrolytic and fermentative bacteria in the family Veillonellaceae, Streptococcaceae, and Enterobacteriaceae were dominant in the supernatant microparticles, particularly in C1, which had a positive correlation with the fouling rate and biomass accumulation rate. These above results all revealed that the microparticles in the acidogenesis phase had higher fouling potential. In summary, our results suggest that the tactic of pre-hydrolysis and acidification with feedstocks and constructing AnMBRs by coupling with multi-phase anaerobic bioprocesses and membrane units could be beneficial to fouling control.

Anaerobic membrane bioreactors (AnMBRs) for municipal wastewater treatment- potential benefits, constraints, and future perspectives: An updated review

The application of Anaerobic Membrane Bioreactors (AnMBRs) for municipal wastewater treatment has been made sufficiently sustainable for practical implementations. The potential benefits are significant as AnMBRs effectively remove a broad range of contaminants from wastewater for water reuse, degrade organics in wastewater to yield methane-rich biogas for resultant energy production, and concentrate nutrients for subsequent recovery for fertilizer production. However, there still exist some concerns requiring vigilant considerations to make AnMBRs economically and technically viable. This review paper briefly describes process fundamentals and the basic AnMBR configurations and highlights six major factors which obstruct the way to AnMBRs installations affecting their performance for municipal wastewater treatment: (i) organic strength, (ii) membrane fouling, (iii) salinity build-up, (iv) inhibitory substances, (v) temperature, and (vi) membrane stability. This review also covers the energy utilization and energy potential in AnMBRs aiming energy neutrality or positivity of the systems which entails the requirement to further determine the economics of AnMBRs. The implications and related discussions have also been made on future perspectives of the concurrent challenges being faced in AnMBRs operation.

Antifouling potential and microbial characterization of an electrochemical anaerobic membrane bioreactor utilizing membrane cathode and iron anode

Serious membrane fouling limits the application of anaerobic membrane bioreactors (AnMBRs) in sewage treatment. Herein, a novel electrochemical AnMBR (eAnMBR) was established by integrating electrocoagulation and a conductive membrane into an AnMBR. Compared with the traditional AnMBR, TP average removal rate increased by 24.97% and the membrane service cycle extended by 109.68% in the eAnMBR. Low extracellular polymeric substance concentration and large floc size were found in the mixed liquid of the eAnMBR due to the combined effect of coagulation and electric field, which induced a porous and hydrophilic cake layer, resulting in excellent water permeation capabilities. Additionally, the conductive membrane cathode effectively suppressed membrane fouling by the electrostatic repulsion and gas scouring. In the eAnMBR, the presence of an electric field and iron ions enriched the diversity of the microbial community, which may improve the adaptation of biochemical systems to environmental changes.

Considering the Prospect of Utilizing Anaerobic Membrane Biofouling Layers Advantageously for the Removal of Emerging Contaminants

Membrane biofilm formation has traditionally been perceived as a wholly negative occurrence in membrane filtration-based wastewater treatment systems due to its resultant effect on transmembrane pressure and energy expenditure. This is the case for both membrane bioreactor (MBR) systems, generally, and anaerobic membrane bioreactors (AnMBRs), specifically. Insight gained through recent research, however, has revealed a potentially positive aspect to biofouling in AnMBR systems—namely, the improved removal of certain emerging contaminants (both microbial and chemical) from wastewater that would not otherwise be retained by the microfiltration/ultrafiltration membranes that are commonly used. Although the exact reasons behind this are not yet understood, the biofilm-specific anaerobic microbial communities that develop on membrane surfaces may play a key role in the phenomenon. Mechanisms of biofouling development in AnMBRs have recently been proven distinctly different from those that govern fouling in aerobic MBR systems. Based on these differences, it may be possible to devise operational strategies that promote the development of anaerobic biofilms on membranes while also minimizing transmembrane pressure increases. If achievable, this would serve as a sustainable basis for reducing the release of emerging contaminants such as organic micropollutants (OMPs) and antibiotic resistance genes (ARGs) with treated wastewater effluents.

Robustness of granular activated carbon-synergized anaerobic membrane bioreactor for pilot-scale application over a wide seasonal temperature change

A novel granular activated carbon-synergized anaerobic membrane bioreactor (GAC-AnMBR), consisted of four expanded bed anaerobic bioreactors with GAC carriers and a membrane tank, was established in pilot scale (10 m³/d) to treat real municipal wastewater (MWW) at ambient temperature seasonally fluctuating from 35 to 5 °C. It showed sound organic removal over 86% with the permeate COD less than 50 mg/L even at extremely low temperatures below 10 °C. COD mass balance analysis revealed that membrane rejection (with a contribution rate of 10%-20%) guaranteed the stable organic removal, particularly at psychrophilic temperature. The methane yield was over 0.24 L CH_{4 (STP)}/g COD _removed at mesophilic temperature and 0.21 L CH_{4 (STP)}/g COD _removed at 5-15 °C. Pyrosequencing of microbial communities suggested that lower temperature reduced the abundance of the methane producing bacteria, but the methane production was enhanced by selectively enriched Methanosaeta, syntrophic Syntrophobacter and Smithella and exoelectrogenic Geobacter for direct interspecies electron transfer (DIET) on the additive GAC. Compared with previously reported pilot-scale AnMBRs, the GAC-AnMBR in this study showed better overall performance and higher stability in a wide temperature range of 5-35 °C. The synergistic effect of GAC on AnMBR guaranteed the robustness of GAC-AnMBR against temperature, which highlighted the applicational potential of GAC-AnMBR, especially in cold and temperate climate regions.

Treatment of municipal wastewater in AnMBRs with powdered activated carbon addition under psychrophilic temperatures

The performance of anaerobic membrane bioreactors (AnMBRs) at psychrophilic temperatures commonly observed in temperate climates (10-24°C) was assessed. A unique aspect of the research was operation at controlled SRT with regular membrane cleaning. COD removal and permeate VFA concentrations were similar at 15 and 24°C and deteriorated at 10°C. As temperature decreased, the COD mass flow to methane decreased and COD mass flows in the permeate and waste sludge increased. At 24°C, rapid membrane TMP increases were not observed while at 15 and 10°C rapid increases occurred at 11.7 ± 0.46 and 7.6 ± 0.45 days, respectively, indicating a greater fouling propensity of the mixed liquor at lower temperatures. When the temperature was reduced from 15°C to 10°C in a transient test, CH₄ production was reduced and VFA concentrations increased. A 2-3 SRT lag in the responses suggested that the delayed response was due to long-term changes in microbial population. The permeate VFA content in a PAC-dosed reactor was lower than that without PAC dosing, and PAC addition increased the time to rapid TMP development to 11.3 ± 0.46 days from 7.4 ± 0.49 days. The primary benefit of PAC addition at low temperatures is enhanced membrane performance. PRACTITIONER POINTS: AnMBRs can produce high-quality effluents at temperatures of 15°C Membrane fouling increases as temperature decreases Bioreactor performance was sustained for 2-3 SRTs after temperature decrease PAC addition reduced the permeate VFA concentrations Membrane fouling at 10°C was reduced through PAC addition.

Anaerobic membrane bioreactor performance at different wastewater pre-concentration factors: An experimental and economic study

This research evaluated the performance of a lab-scale anaerobic membrane bioreactor (AnMBR) treating municipal sewage pre-concentrated by forward osmosis (FO). The organic loading rate (OLR) and sodium concentrations of the synthetic sewage stepwise increased from 0.3 to 2.0 g COD L^-1 d^-1 and from 0.28 to 2.30 g Na⁺ L^-1 to simulate pre-concentration factors of 1, 2, 5 and 10. No major operational problems were observed during AnMBR operation, with COD removal efficiencies ranging between 90 and 96%. The methane yield progressively increased from 214 ± 79 to 322 ± 60 mL CH₄ g^-1 COD as the pre-concentration factor increased from 1 to 10. This was mainly attributed to the lower fraction of methane dissolved lost in the permeate at higher OLRs. Interestingly, at the highest pre-concentration factor (2.30 g Na⁺ L^-1) the difference between the permeate and the digester soluble COD indicated that membrane biofilm also played a role in COD removal. Finally, a preliminary energy and economic analysis showed that, at a pre-concentration factor of 10, the AnMBR temperature could be increased 10 °C and achieve a positive net present value (NPV) of 4 M€ for a newly constructed AnMBR treating 10,000 m³ d^-1 of pre-concentrated sewage with an AnMBR lifetime of 20 years.

Hydrolysis and Methanogenesis in UASB-AnMBR Treating Municipal Wastewater Under Psychrophilic Conditions: Importance of Reactor Configuration and Inoculum

Three upflow anaerobic sludge blanket (UASB) pilot scale reactors with different configurations and inocula: flocculent biomass (F-UASB), flocculent biomass and membrane solids separation (F-AnMBR) and granular biomass and membrane solids separation (G-AnMBR) were operated to compare start-up, solids hydrolysis and effluent quality. The parallel operation of UASBs with these different configurations at low temperatures (9.7 ± 2.4°C) and the low COD content (sCOD 54.1 ± 10.3 mg/L and pCOD 84.1 ± 48.5 mg/L), was novel and not previously reported. A quick start-up was observed for the three reactors and could be attributed to the previous acclimation of the seed sludge to the settled wastewater and to low temperatures. The results obtained for the first 45 days of operation showed that solids management was critical to reach a high effluent quality. Overall, the F-AnMBR showed higher rates of hydrolysis per solid removed (38%) among the three different UASB configurations tested. Flocculent biomass promoted slightly higher hydrolysis than granular biomass. The effluent quality obtained in the F-AnMBR was 38.0 ± 5.9 mg pCOD/L, 0.4 ± 0.9 mg sCOD/L, 9.9 ± 1.3 mg BOD₅/L and <1 mg TSS/L. The microbial diversity of the biomass was also assessed. Bacteroidales and Clostridiales were the major bacterial fermenter orders detected and a relative high abundance of syntrophic bacteria was also detected. Additionally, an elevated abundance of sulfate reducing bacteria (SRB) was also identified and was attributed to the low COD/SO₄ ^2- ratio of the wastewater (0.5). Also, the coexistence of acetoclastic and hydrogenotrophic methanogenesis was suggested. Overall this study demonstrates the suitability of UASB reactors coupled with membrane can achieve a high effluent quality when treating municipal wastewater under psychrophilic temperatures with F-AnMBR promoting slightly higher hydrolysis rates.

Anaerobic membrane bioreactors (AnMBR) treating urban wastewater in mild climates

Feasibility of an AnMBR demonstration plant treating urban wastewater (UWW) at temperatures around 25-30 °C was assessed during a 350-day experimental period. The plant was fed with the effluent from the pre-treatment of a full-scale municipal WWTP, characterized by high COD and sulfate concentrations. Biodegradability of the UWW reached values up to 87%, although a portion of the biodegradable COD was consumed by sulfate reducing organisms. Effluent COD remained below effluent discharge limits, achieving COD removals above 90%. System operation resulted in a reduction of sludge production of 36-58% compared to theoretical aerobic sludge productions. The membranes were operated at gross transmembrane fluxes above 20 LMH maintaining low membrane fouling propensities for more than 250 days without chemical cleaning requirements. Thus, the system resulted in net positive energy productions and GHG emissions around zero. The results obtained confirm the feasibility of UWW treatment in AnMBR under mild and warm climates.

Establishing the mechanisms underpinning solids breakthrough in UASB configured anaerobic membrane bioreactors to mitigate fouling

In this study, the mechanisms for solids breakthrough in upflow anaerobic sludge blanket (UASB) configured anaerobic membrane bioreactors (AnMBRs) have been described to establish design parameters to limit membrane fouling. As the sludge blanket develops, two periods can be identified: (i) an initial progressive enhancement in solids separation provided through sludge blanket clarification, via depth filtration, which sustains downstream membrane permeability; and (ii) sludge blanket destabilisation, which imposed solids breakthrough resulting in a loss in membrane permeability. The onset of sludge blanket destabilisation was identified earlier in the flocculent AnMBR, which was ascribed to an increased gas production, caused by hydrolysis within the sludge blanket at extended solids residence time. Whilst hydrolysis also induced higher gas productivity within the granular AnMBR, solids breakthrough was not evidently observed during this period, and was instead only observed as the sludge blanket approached the UASB overflow. However, solids breakthrough was observed earlier for both reactors when treating wastewater with lower temperatures. This was explained through characterisation of the settling velocity of discrete particles from the sludge blanket of both MBRs; solids washout was evidenced to be induced by the increase in fluid viscosity with a reduction in temperature, which lowered terminal particle settling velocity. Nevertheless, particle settling velocity was comparable for particles from both sludge blankets. We therefore propose that the enhanced stability imparted by the granular AnMBR is due to the higher inertial force of the dense granular sludge. From this study, we suggest that similarly low levels of membrane fouling can be achieved within flocculent AnMBR by managing solids retention time to constrain sludge bed height and excess hydrolysis, together with adopting an upflow velocity based on particle buoyancy at the lowest expected operating temperature.

Enhanced performance and hindered membrane fouling for the treatment of coal chemical industry wastewater using a novel membrane electro-bioreactor with intermittent direct current

A membrane electro-bioreactor (MEBR) embracing biological treatment, electrokinetic phenomena and membrane filtration was established by applying intermittent direct current (DC) to MBR. MEBR exhibited significant improvement of treatment performance and reduction of membrane fouling. COD and total phenols removal efficiencies increased to 83.53% and 93.28% at an exposure mode of 24'-OFF/6'-ON, compared to 71.24% and 82.43% in MBR. Trans-membrane pressure increment rate declined dramatically in MEBR, which was mainly attributed to the increase of sludge floc size and decrease of zeta potential, soluble microbial products and specific resistance to filtration, resulted from electrokinetic effects such as electrocoagulation, electrophoresis, electroosmosis and electromigration of ions. It was notable that DC exposure exerted distinct evolution on microbial community, with the improvement of microbial community richness and diversity. The relative abundances of functional genera were promoted noticeably in MEBR. An interactive relevance existed among microbial community structure, mixed liquor properties and operational parameters.

Psychrophilic anaerobic dynamic membrane bioreactor for domestic wastewater treatment: Effects of organic loading and sludge recycling

Two upflow anaerobic dynamic membrane bioreactors (AnDMBRs) with and without sludge recycling were operated in parallel at varied organic loadings and psychrophilic temperature for domestic wastewater treatment. A 75 μm nylon mesh, used as a supporting material, enabled quick and stable dynamic membrane formation. The AnDMBRs could operate continuously without relaxation at a high flux rate of 22.5 L/m²h; however, high organic loading accelerated the increasing rate of trans-membrane pressure (TMP). High chemical oxygen demand removal was achieved in both AnDMBRs with removal efficiencies of 70-90%. Sludge recycling enhanced the cross-flow velocity but negatively affected the effluent turbidity, sludge properties (particle size reduction and biopolymer release) and dynamic membrane filterability. Although increased organic loading enhanced biogas yield, the low biogas production was related to the dissolved methane loss in the effluent. Easy-operation, minimal maintenance and low-energy consumption makes the AnDMBR process cost-effective for practical wastewater treatment in temperate areas.

Effects of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor for municipal wastewater treatment

This study aimed to evaluate the impact of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor (SAAMB-AnGMBR) in municipal wastewater treatment. The results showed that organic removal efficiencies were above 94% at all C/N conditions. Nutrient removal was over 91% at C/N ratio of 100/5 but was negatively affected when decreasing C/N ratio to 100/10. At lower C/N ratio (100/10), more noticeable membrane fouling was caused by aggravated cake formation and pore clogging, and accumulation of extracellular polymeric substances (EPS) in the mixed liquor and sludge cake as a result of deteriorated granular quality. Foulant analysis suggested significant difference existed in the foulant organic compositions under different C/N ratios, and humic substances were dominant when the fastest fouling rate was observed. The performance of the hybrid system was found to recover when gradually increasing C/N ratio from 100/10 to 100/5.

Investigation on the response of anaerobic membrane bioreactor to temperature decrease from 25°C to 10°C in sewage treatment

Anaerobic membrane bioreactor (AnMBR) for sewage treatment was operated for 650days with the decrease of temperature from 25°C to 10°C. At higher temperature >15°C, COD removal was above 94% while sewage treatment efficiency and relevant CH₄ production decreased below 15°C. The effluent COD at 10°C was 134mg/L at HRT of 16h. Moreover, low temperature can result in a higher membrane fouling rate due to the microbial self-protection behavior in coping with the temperature decrease by releasing soluble microbial products (SMP) and extracellular polymeric substances (EPS). The contribution of pore blocking to membrane fouling caused by protein from SMP and EPS increased from 17% to 45% and that of cake layer decreased from 81% to 53% at 25°C and 15°C respectively. The inhibition to hydrolysis and acidification process was responsible to the decrease of sewage treatment at lower temperature.

Developing cold-adapted biomass for the anaerobic treatment of domestic wastewater at low temperatures (4, 8 and 15 °C) with inocula from cold environments

Temperature is the bottleneck for the anaerobic treatment of domestic wastewater in temperate climates. Most previous attempts to achieve anaerobic treatment at low temperatures have attempted to acclimatize mesophilic sludge and have failed at temperatures below 10-13 °C. We describe an alternative approach using communities from environments that have been exposed to low temperatures over evolutionary time-scales as seed for such reactors. Batch reactors were inoculated with a mixture of soils and sediments from the high Arctic and an Alpine lake to treat UV-sterilized raw domestic wastewater at 4, 8 and 15 °C. To evaluate the intrinsic treatment capacity of the bacteria the specific rates of methanogenesis and hydrolysis were evaluated. Specific methanogenic activity at 4, 8 and 15 °C was 6.3, 7.6 and 10.3 fmol CH₄ cell^-1day^-1 respectively. Specific putative hydrolysis rates were 76.2, 186.6 and 251.9 fgrams COD cell^-1day^-1. Hydrolysis was twice as temperature sensitive as methanogenesis (Q₁₀: 4.62 and 1.57 respectively). The specific rates are over ten times higher than we have previously observed in microcosms fed with settled wastewater at the same temperatures. The results imply that inoculating reactors with cold-adapted communities is a promising way to develop biomass capable of treating anaerobic wastewater treatment at low temperatures whilst achieving an effluent that conforms to the EC Directive COD standards. Large-scale reactors are feasible if satisfactory cell concentrations can be achieved.

Anaerobic treatment of low-strength wastewater: a comparison between single and staged anaerobic fluidized bed membrane bioreactors

Performance of a single anaerobic fluidized membrane bioreactor (AFMBR) was compared with that of a staged anaerobic fluidized membrane bioreactor system (SAF-MBR) that consisted of an anaerobic fluidized bed bioreactor (AFBR) followed by an AFMBR. Both systems were fed with an equal COD mixture (200mg/L) of acetate and propionate at 25°C. COD removals of 93-96% were obtained by both systems, independent of the hydraulic retention times (HRT) of 2-4h. Over more than 200d of continuous operation, trans-membrane pressure (TMP) in both systems was less than 0.2bar without significant membrane fouling as a result of the scouring of membrane surfaces by the moving granular activated carbon particles. Results of bulk liquid suspended solids, extracellular polymeric substances (EPS), and soluble microbial products (SMP) analyses also revealed no significant differences between the two systems, indicating the single AFMBR is an effective alternative to the SAF-MBR system.

Treatment of domestic wastewater by an integrated anaerobic fluidized-bed membrane bioreactor under moderate to low temperature conditions

The performance of a novel integrated anaerobic fluidized-bed membrane bioreactor (IAFMBR) for treating practical domestic wastewater was investigated at a step dropped temperature from 35, 25, to 15°C. The COD removal was 74.0 ± 3.7%, 67.1 ± 2.9% and 51.1 ± 2.6% at 35, 25 and 15°C, respectively. The COD removal depended both on influent strength and operational temperature. The accumulation of VFAs (Volatile Fatty Acids) was affected by temperature, and acetic acid was the most sensitive one to the decrease of temperature. The methanogenic activity of the sludge decreased eventually and the methane yield was dropped from 0.17 ± 0.03, 0.15 ± 0.02 to 0.10 ± 0.01 L/Ld. And as compared with a mesophilic temperature, a low temperature can accelerate membrane biofouling. Proteins were the dominant matters causing membrane fouling at low temperature and membrane fouling can be mitigated by granular active carbon (GAC) through protein absorption.

Pilot-scale temperate-climate treatment of domestic wastewater with a staged anaerobic fluidized membrane bioreactor (SAF-MBR)

A pilot-scale staged anaerobic fluidized membrane bioreactor (SAF-MBR) was operated continuously for 485 days, without chemical cleaning of membranes, treating primary-settled domestic wastewater with wastewater temperature between 8 and 30°C and total hydraulic retention time (HRT) between 4.6 and 6.8h. Average chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) removals averaged 81% and 85%, respectively, during the first winter at 8-15°C before full acclimation had occurred. However, subsequently when fully acclimated, summer and winter COD removals of 94% and 90% and BOD5 removals of 98% and 90%, respectively, were obtained with average effluent COD never higher than 23 mg/L nor BOD5 higher than 9 mg/L. Operational energy requirement of 0.23 kW h/m(3) could be met with primary and secondary methane production, and could be reduced further through hydraulic change. Biosolids production in all seasons averaged 0.051 g volatile suspended solids per g COD removed.