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

A novel Anaerobic Cathodic Dynamic Membrane Bioreactor (AnCDMBR) for efficient mitigating fouling and recovering bioenergy from municipal wastewater

Concerns regarding membrane fouling and suboptimal bioenergy recovery have constrained the implementation of anaerobic membrane bioreactor (AnMBR) for treating low-strength municipal wastewater. This study presents a novel anaerobic cathodic dynamic membrane bioreactor (AnCDMBR) designed to address these challenges. A self-formed cathodic dynamic membrane (CDM) on inexpensive carbon cloth was developed to function as both a membrane and biocathode to achieve dual-function effects of mitigating membrane fouling and accelerating organics conversion. Compared with common dynamic membrane (1.52 kPa/d) and commercial membranes (7.52 kPa/d), the developed CDM presented a significantly reduced fouling rate (1.02 kPa/d), exhibiting the potential as a substitute for high-cost conductive membranes. Furthermore, efficient and stable biomethanation occurred in AnCDMBR with a superior methane yield rate of 0.26 L-CH4/g-COD (CH4 content > 95 %), which was 1.42 times higher than the control, linked to the higher activities of microbial metabolism and methanogenic-related key enzymes. Further analysis revealed that electrostimulation-induced niche differentiation of microbiota regulated interspecies interactions between electroactive microorganisms and complex anaerobic digestion microbiomes, facilitating organic matter conversion to methane and leading to superior bioenergy recovery. This study offered a new strategy for effectively mitigating fouling and recovering bioenergy from low-strength wastewater, potentially expanding the application of AnMBRs.

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.

Mechanistic insights into different illumination positions control algae production in anaerobic dynamic membrane filtration (AnDM) during decentralized wastewater treatment

Sunlight illumination has the potential to control the stability and sustainability of dynamic membrane (DM) systems. In this study, an up-flow anaerobic sludge blanket (UASB) reactor was combined with DM under different illumination positions (direct, indirect and no illumination) to treat wastewater. Results indicated that the UASB achieved a COD removal up to 87.05 % with an average methane production of 0.28 L/d. Following treatment by the UASB, it was found that under illumination, the removal of organic substances by DM exhibited poor performance due to algal proliferation. However, the DM systems demonstrated efficient removal of ammonia nitrogen, ranging from 96.21 % to 97.67 % after stabilization. Total phosphorus removal was 45.72 %, and membrane flux remained stable when directly illuminated. Conversely, the DM system subjected to indirect illumination showed unstable membrane flux and severe fouling resistance. These findings offer valuable insights into optimizing illumination positions in DM systems under anaerobic conditions.

Identification of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification in the dynamic cake layer of a full-scale anoixc dynamic membrane bioreactor for treating hotel laundry wastewater

Identification of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification in the dynamic cake layer of a full-scale anoixc dynamic membrane bioreactor (AnDMBR) for treating hotel laundry wastewater was studied. A series of experiments were conducted to understand the contributions of DNRA and canonical denitrification activities in the dynamic cake layer of the AnDMBR. The dynamic cake layer developed included two phases - a steady transmembrane pressure (TMP) increase at 0.24 kPa/day followed by a sharp TMP jump at 1.26 kPa/day four to five days after the AnDMBR start-up. The nitrogen mass balance results showed that canonical denitrification was predominant during the development of the dynamic cake layer. However, DNRA activity and accumulation of bacteria equipped with a complete DNRA pathway showed a positive correlation to the development of the dynamic cake layer. Our metagenomic analysis identified an approximately 18% of the dynamic cake layer bacterial community has a complete DNRA pathway. Pannonibacter (1%), Thauera (0.8%) and Pseudomonas (3%) contained all genes encoding for funcional enzymes of both DNRA (nitrate reductase and DNRA nitrite reductase) and denitrification (nitrate reductase, nitrous oxide reductase and nitric oxide reductase). No other metagenome-assembled genomes (MAGs) possessed a complete cononical denitrification pathway, indicating food-chain-like interactions of denitrifiers in the dynamic cake layer. We found that COD loading rate could be used to control DNRA and canonical denitrification activities during the dynamic cake layer formation.

Process characteristics and energy self-sufficient operation of a low-fouling anaerobic dynamic membrane bioreactor for up-concentrated municipal wastewater treatment

Up-concentration of municipal wastewater using physico-chemical methods can effectively enrich organic matter, facilitating subsequent anaerobic digestion of up-concentrated wastewater for enhanced methanogenesis at reduced energy consumption. An anaerobic dynamic membrane bioreactor (AnDMBR) assisted with biogas-sparging was developed to treat up-concentrated municipal wastewater, focusing on the effects of operating temperature and hydraulic retention time (HRT) as well as COD mass balance and energy balance. The COD removal stabilized at about 98 % over the experimental period, while gaseous and dissolved methane contributed 43-49 % and 2-3 % to the influent COD reducing greenhouse gas emissions. The formed dynamic membrane exists mainly as a heterogeneous cake layer with a uneven distribution feature, ensuring the stable effluent quality. Without adopting any physico-chemical cleaning, the transmembrane pressure (TMP) maintained at a low range (2.7 to 14.67 kPa) with the average TMP increasing rate of 0.089 kPa/d showing a long-term low-fouling operation. Increasing the concentration ratio, the methane production rate decreased from 0.18 to 0.15 L CH₄/gCOD likely due to the accumulation of particulate organics. Microbial community analysis indicated the predominant methanogenic pathway shifted from hydrogenotrophic to acetoclastic methanogenesis in response to the temperature change. Net energy balance (0.003-0.600 kWh/m³) can be achieved only under room temperature (25 °C) rather than mesophilic conditions (36 °C).

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.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review

Currently, there is growing scientific interest in the development of more economic, efficient and environmentally friendly municipal wastewater treatment technologies. Laboratory and pilot-scale surveys have revealed that the anaerobic membrane bioreactor (AnMBR) is a promising alternative for municipal wastewater treatment. Anaerobic membrane bioreactor technology combines the advantages of anaerobic processes and membrane technology. Membranes retain colloidal and suspended solids and provide complete solid–liquid separation. The slow-growing anaerobic microorganisms in the bioreactor degrade the soluble organic matter, producing biogas. The low amount of produced sludge and the production of biogas makes AnMBRs favorable over conventional biological treatment technologies. However, the AnMBR is not yet fully mature and challenging issues remain. This work focuses on fundamental aspects of AnMBRs in the treatment of municipal wastewater. The important parameters for AnMBR operation, such as pH, temperature, alkalinity, volatile fatty acids, organic loading rate, hydraulic retention time and solids retention time, are discussed. Moreover, through a comprehensive literature survey of recent applications from 2009 to 2021, the current state of AnMBR technology is assessed and its limitations are highlighted. Finally, the need for further laboratory, pilot- and full-scale research is addressed.

Critical insights into psychrophilic anaerobic digestion: Novel strategies for improving biogas production

Anaerobic digestion (AD) under psychrophilic temperature has only recently garnered deserved attention. In major parts of Europe, USA, Canada and Australia, climatic conditions are more suited for psychrophilic (<20 ℃) rather than mesophilic (35 - 37 ℃) and thermophilic (55 - 60 ℃) AD. Low temperature has adverse effects on important cellular processes which may render the cell biology inactive. Moreover, cold climate can also alter the physical and chemical properties of wastewater, thereby reducing the availability of substrate to microbes. Hence, the use of low temperature acclimated microbial biomass could overcome thermodynamic constraints and carry out flexible structural and conformational changes to proteins, membrane lipid composition, expression of cold-adapted enzymes through genotypic and phenotypic variations. Reduction in organic loading rate is beneficial to methane production under low temperatures. Moreover, modification in the design of existing reactors and the use of hybrid reactors have already demonstrated improved methane generation in the lab-scale. This review also discusses some novel strategies such as direct interspecies electron transfer (DIET), co-digestion of substrate, bioaugmentation, and bioelectrochemical system assisted AD which present promising prospects. While DIET can facilitate syntrophic electron exchange in diverse microbes, the addition of organic-rich co-substrate can help in maintaining suitable C/N ratio in the anaerobic digester which subsequently can enhance methane generation. Bioaugmentation with psychrophilic strains could reduce start-up time and ensure daily stable performance for wastewater treatment facilities at low temperatures. In addition to the technical discussion, the economic assessment and future outlook on psychrophilic AD are also highlighted.

Anaerobic self-forming dynamic membrane bioreactors (AnSFDMBRs) for wastewater treatment - Recent advances, process optimization and perspectives

Recently, anaerobic self-forming dynamic membrane bioreactors (AnSFDMBRs) have attracted increasing attention, and are considered as an alternative to conventional anaerobic membrane bioreactors (AnMBRs). The key advantages of AnSFDMBRs include high flux, low propensity towards fouling, and low capital and operational costs. Although there have been several reviews on AnMBRs, very few reviews on AnSFDMBR system. Previous AnSFDMBR studies have focused on lab-scale to investigate the long-term flux, methods to improve performance and the associated mechanisms. Microbial analysis showed that the phyla namely Proteobacteria, Bacteroidetes and Firmicutes are dominant in both bulk sludge and cake biofilm, but their abundance is low in biocake. This review critically examines the fundamentals of AnSFDMBRs, operational conditions, process optimization and applications. Moreover, the current knowledge gaps (e.g., dynamic membrane module optimization, membrane surface modification and functional microbes enrichment) that should be studied in future to design an efficient AnSFDMBR system for treatment of diverse wastewaters.

Characterization of preconcentrated domestic wastewater toward efficient bioenergy recovery: Applying size fractionation, chemical composition and biomethane potential assay

Domestic wastewater (DWW) can be preconcentrated to facilitate energy recovery via anaerobic digestion (AD), following the concept of "carbon capture-anaerobic conversion-bioenergy utilization." Herein, real DWW and preconcentrated domestic wastewater (PDWW) were both subject to particle size fractionation (0.45-2000 μm). DWW is a type of low-strength wastewater (average COD of 440.26 mg/L), wherein 60% of the COD is attributed to the substances with particle size greater than 0.45 μm. Proteins, polysaccharides, and lipids are the major DWW components. PDWW with a high COD concentration of 2125.89 ± 273.71 mg/L was obtained by the dynamic membrane filtration (DMF) process. PDWW shows larger proportions of settleable and suspended fractions, and accounted for 63.4% and 33.8% of the particle size distribution, and 52.4% and 32.2% of the COD, respectively. The acceptable biomethane potential of 262.52 ± 11.86 mL CH₄/g COD of PDWW indicates bioenergy recovery is feasible based on DWW preconcentration and AD.

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.

Insights into fouling behavior in a novel anammox self-forming dynamic membrane bioreactor by the fluorescence EEM-PARAFAC analysis

Fouling behavior of the novel anaerobic ammonium oxidation (anammox) self-forming dynamic membrane bioreactor (SFDMBR) was elucidated, which is using nylon mesh as the filter with controlled fouling and successful anammox process. Properties of anammox sludge and foulants in the anammox SFDMBR and MBR (using PVDF microfiltration membrane) were compared to analyze the alleviated fouling in the SFDMBR, of which transmembrane pressure could be kept below 10 kPa for 50 days in one filtration cycle of 82 days with flux of 12 L m^-2 h^-1. Colorimetrical determination and excitation emission matrices-parallel factor (EEM-PARAFAC) analysis of the foulants showed that humic acid content in foulants on nylon mesh was obviously lower than that on PVDF membrane. Considering that the small-sized and flexible humic acids prefer to plug into membrane pores, the alleviated irreversible fouling in the SFDMBR could be attributed to the less microbial humic acid content of foulants (8.8 ± 1.0%) compared with the MBR (20.7 ± 2.9%). The adequate efflux of humic-like substances in the operation with nylon mesh was speculated to be the main mechanism of fouling control in the SFDMBR. These findings highlighted the potential of anammox SFDMBR in practical applications, because of the high humic acid contents in real ammonium-laden wastewater. Our study highlights the important role of humic acids in fouling behavior of the novel anammox SFDMBR to provide guidance for fouling control strategies. Graphical abstract.

Investigation of the short-term effects of extracellular polymeric substance accumulation with different backwashing strategies in an anaerobic self-forming dynamic membrane bioreactor

The optimum operation strategy for a side-stream external anaerobic self-forming dynamic membrane bioreactor (AnSFDMBR) was investigated by coupling such a system with an up-flow anaerobic sludge blanket reactor. Time-based backwashing with different intervals and transmembrane pressure (TMP)-based backwashing were compared as the operation strategies of the AnSFDMBR. The system performance, extracellular polymeric substance (EPS) accumulation in the dynamic layer and on the membrane mesh of the AnSFDMBR, and the physical properties of the dynamic layer were closely monitored. Both operation strategies achieved stable operation with effluent turbidity less than 5 nephelometric turbidity units with a slowly increasing TMP. However, with the time-based backwashing strategy, the EPS accumulation rate in the dynamic layer was more than 20 times higher than that on the mesh, indicating that frequent backwashing might have a negative impact on the AnSFDMBR. The impacts of EPS accumulation on the membrane mesh were negligible considering the small amount of EPS residual and the large pore size of the mesh. On the contrary, the EPS accumulation in the dynamic layer changed the layer's physical properties and further impacted on the performance of the AnSFDMBR. The accumulation of polysaccharides in the dynamic layer was the main reason for the layer's compactness, which was negatively correlated with the specific surface area and further led to the TMP increase. The polysaccharides in the dynamic layer-to-sludge ratio increased to around 1.6 with only 5 days of time-base operation. With TMP-based operation, it took more than 10 days for polysaccharides in the dynamic layer-to-sludge ratio reaching 1.6. The low TMP increase rate, high effluent quality, and slow EPS accumulation with TMP-based backwashing indicated TMP-based operation is applicable in the studied AnSFDMBR. Nevertheless, the correlation between TMP and the accumulation of polysaccharides should be further investigated to find the optimum TMP for backwashing.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Submerged anaerobic membrane bioreactor for low-concentration domestic sewage treatment: performance and membrane fouling

A submerged anaerobic membrane bioreactor (SAnMBR) was used to treat low-concentration domestic sewage. The effects of hydraulic retention time (HRT) and organic load (OLR) on chemical oxygen demand (COD) removal, methanogenesis, and membrane fouling of the system were investigated. The SAnMBR achieved good COD removal efficiency as well as stable methane production, which were significantly affected by both OLR and HRT. The influent dissolved organic matter (DOM) was decomposed and transformed over time, and DOM concentration was gradually reduced. It can be inferred that the SAnMBR can effectively intercept the production of extracellular polymeric substances and improve effluent quality. The phenomenon of membrane fouling was investigated using various analytical tools. Results demonstrated that the SAnMBR was achieved good transmembrane pressures (TMP) (10-15 kPa), and the hydraulic force generated by the stirring device has a dynamic physical shearing action on the surface of the membrane, which can partly alleviate membrane fouling.

Carbon cloth enhances treatment of high-strength brewery wastewater in anaerobic dynamic membrane bioreactors

Anaerobic dynamic membrane bioreactors (AnDMBRs) can improve the efficiency of organic matter removal during wastewater treatment at a low cost. However, application of AnDMBRs for treatment of high-strength wastewater is usually unsuccessful. This study investigated whether use of conductive carbon cloth as the supporting material in an AnDMBR permits higher organic loading rates for treatment of brewery wastewater than non-conductive polyester cloth. The AnDMBR with carbon cloth operated stably with a COD removal efficiency of 98% even when high concentrations of influent COD (10,000 mg/L) were provided, while the polyester cloth reactor deteriorated when reactors were fed only 5000 mg/L influent COD. Microorganisms capable of direct interspecies electron transfer (DIET), including Geobacter and Methanothrix species, dominated the surface of the carbon cloth. These results demonstrate that carbon cloth provides an excellent supporting material for AnDMBRs by stimulating growth of microorganisms that can directly transport electrons to and from conductive materials.

Characteristics of a Self-Forming Dynamic Membrane Coupled with a Bioreactor in Application of Anammox Processes

A novel anammox self-forming dynamic membrane bioreactor (SFDMBR) was proposed to achieve an efficient anammox process with high biomass retention and cost-effective operation. The cake layer formed on nylon mesh (pore size, 20-25 μm) was referred to as a dynamic membrane (DM). The high permeability of the DM layer contributed to low transmembrane pressure (TMP), which kept below 10 kPa for 50 days in one filtration cycle of 82 days. Compared to the high TMP (mainly > 20 kPa) in the MBR using polyvinylidene fluoride (PVDF) microfiltration membrane, energy can be significantly conserved in the SFDMBR. Besides, the mature DM layer achieved efficient biomass retention comparable to that of PVDF membrane, which favored anammox bacteria enrichment. Concomitantly, an appropriate microenvironment for autotrophic anammox bacterial growth with well-controlled extracellular polymeric substances (EPS) concentration (33.22 mg·g^-1 VSS) was achieved in SFDMBR. According to specific filtration resistance (SFR) analysis, reducing the EPS concentration in the bulk sludge improves sludge filterability and alleviate fouling, which was achieved in the SFDMBR system with a low SFR of 1.47 × 10¹² m^-1·kg^-1. Our results show that the cost-effective operations and technical merits make anammox SFDMBRs promising for practical applications.

Treatment of synthetic wastewater and cheese whey by the anaerobic dynamic membrane bioreactor

The aim of this study was to develop a laboratory-scale anaerobic dynamic membrane bioreactor (AnDMBR) for the treatment of high-strength synthetic and real cheese whey wastewater. We determined the appropriate pore size for a convenient type of support material (nylon mesh) to optimize cake layer formation. The performance of the AnDMBRs was measured in terms of chemical oxygen demand (COD) and solids removal efficiencies. During high-strength synthetic wastewater treatment, the 70-μm pore size AnDMBR achieved COD removal efficiencies of 78% and 96% with COD loading rates of 4.03 and 2.34 kg m^-3 day^-1, respectively, while the 10-μm pore size AnDMBR achieved 66% and 92% COD removal efficiencies at COD loading rates of 5.02 and 3.16 kg m^-3 day^-1. The 10 μm pore size AnDMBR was operated in two periods: first period and second period (before and after physical cleaning) during high-strength synthetic wastewater treatment. The 10-μm pore size AnDMBR removed 83% and 88% of suspended solids during period 1 and period 2, respectively. Furthermore, using a pore size of 10 μm retained 72% of solids (973 mg L^-1) in the reactor outlet. The 10-μm pore size AnDMBR performed better than the 70-μm pore size AnDMBR in terms of cake layer formation. The 10-μm pore size AnDMBR was used to treat real cheese whey wastewater, resulting in COD removal efficiencies ranging from 59% (4.32 kg m^-3 day^-1) to 97% (5.22 kg m^-3 day^-1). In addition, 85% of suspended solids were removed from real cheese whey wastewater after treatment. The results show that dynamic membrane technology using a pore size of 10 μm can be used to treat real industrial wastewater.

Impact of sludge recirculation ratios on the performance of anaerobic membrane bioreactor for wastewater treatment

The performance of a lab scale anaerobic membrane bioreactor (AnMBR) was evaluated for wastewater treatment. The efficacy of the system was determined at different operating conditions in terms of fluxes and recirculation ratios (R); 10.28 L/m² h (R = 1, Phase I), 8.8 L/m² h (R = 2, Phase II and R = 3, Phase III) and 6 L/m² h (R = 2, Phase IV and R = 3, Phase V), respectively. In comparison with all the operating conditions tested, optimum efficacy of the system was found at flux of 6 L/m² h and R of 3 in terms of highest COD removal (96.7%), and maximum biogas yield (0.44 L/g COD_removed). The MLSS and MLVSS concentrations under optimum phase were 6.23 and 4.83 g/L, respectively at OLR of 0.46 kg COD/m³ day. The system also exhibited significant reduction of foulants i.e. extracellular polymeric substances (EPS) and soluble microbial products (SMP) resulting in longer membrane runs in optimized phase.

Applying a dynamic membrane filtration (DMF) process for domestic wastewater preconcentration: Organics recovery and bioenergy production potential analysis

Wastewater is increasingly recognized as a valuable resource rather than as a waste, motivating a shift in the perspective of wastewater treatment from pollution control to resource recovery. This study proposes the recovery of organic matter from domestic wastewater for the production of bioenergy through a novel process of wastewater preconcentration based on dynamic membrane filtration (DMF). The selection of a dynamic membrane (DM) supporting material, the preconcentration performance of organics, and the biomethane production potential (BMP) of the organic concentrate were investigated. The process optimization results indicated that a DM module with a supporting material of a 25 μm stainless steel mesh with a three-layer structure, assisted by internal suspended particles derived from raw wastewater, enabled the rapid DM layer formation within 1 h. The DMF process operated under a constant high flux of 30-60 L/m² h at a trans-membrane pressure (TMP) of less than 40 kPa. During the continuous DMF operation, the average chemical oxygen demand (COD) of the influent, effluent and concentrate was 305, 113 and 2000-2500 mg/L, respectively, while the removal performance of other pollutants(such as nitrogen and phosphorus) varied, indicating differential retention effects for the various pollutants by the DM layer. Air back-flushing can effectively regenerate the DM layer and maintain long-term stable operation, but higher rates of TMP increase were observed for later filtration cycles, probably due to the accumulation of physically irremovable fouling. The BMP of the DMF concentrate was 0.20 L CH₄/g COD, which was comparable to the ordinary biogas yield from municipal wastewater by anaerobic digestion. The DMF process integrated with anaerobic digestion can be a promising alternative for energy-sufficient wastewater treatment.