Anaerobic Membrane Bioreactor Research Articles

Effects of suspended titanium dioxide (TiO2) nanoparticles on cake layer formation in submerged anaerobic membrane bioreactor (AnMBR) for landfill leachate treatment (LFL)

In recent years, TiO2 NPs have attracted great attention among the semiconductors because of stability, commercial availability, and ease of preparation. For this reason, NPs are widely used in wastewater treatment and membrane bioreactor (MBRs) In this study, the effect of titanium dioxide (TiO2) nanoparticle material was investigated on both the landfill leachate (LFL) treatment and membrane fouling performance. The system performance was evaluated for under varying TiO2 concentrations (50–300 mg/L TiO2), constant HRT (24 h), and constant backwashing (5 min)-relaxing (0.5 min) in AnMBR. The optimum conditions were determined as 300 mg/L TiO2 and the corresponding to COD, Color, TOC and TN removal efficiencies were observed as 55 %, 23 %, 22 %, 30 %, respectively. The best membrane performance was observed at 300 mg/L TiO2 corresponding to membrane fouling rate as 0.01 mbar/min. TiO2 addition significantly mitigated membrane fouling (75 % decrease) for AnMBR. Bacteroidetes, Firmicutes and Proteobacteria have been observed to be the dominant species in LFL and MBRs. The bacterial species responsible for membrane fouling were determined as Alphaproteobacteria, Sphingobacteria and Flavobacteria. The addition of TiO2 was determined membrane fouling decreased in AnMBR. As a result of TiO2 NPs were observed to thin the cake layer and postpone membrane fouling and filtration.

Effect of powder activated carbon (PAC) addition on the performance of anaerobic dynamic membrane bioreactor (AnDMBR): Stratification analysis of dynamic membrane characteristics

Powdered activated carbon (PAC), proved to be an effective performance enhancer in membrane bioreactor studies, has yet been applied in anaerobic dynamic membrane bioreactors (AnDMBRs). A better understanding of dynamic membrane (DM) characteristics is important for optimizing AnDMBR performance. In this study, three AnDMBRs were operated for synthetic municipal wastewater treatment with PAC dosages of 0, 1, and 3 g/L. Particular efforts were devoted to understanding the DM characteristics in layers. It was found that PAC addition increased COD removal efficiency (10 %) and decreased DM filtration resistance (60 %). The extent of performance enhancement, particularly the decrease of DM filtration resistance, appears to be much more substantial in AnDMBR than aerobic DMBR. PAC addition significantly reduced the fouling potential of suspended sludge and consequently the filtration resistance of DM. Compared with inner DM layer, the outer DM layer exhibited relatively higher fouling characteristics, such as less porous structure, higher EPS content (mainly proteins), hydrophobicity, and relative abundance of biofouling-related bacteria. The positive effect of PAC addition on reducing DM fouling characteristics turned out to be more significant for outer DM layer, mainly because of its higher PAC content associated with the higher amount of small particles.

Improving organic and nutrient removal efficiencies in seafood processing wastewater using anaerobic membrane bioreactor (AnMBR) integrates with anoxic/oxic (AO) processes

Wastewater from seafood processing is a significant source of pollution, containing many harmful organic and inorganic compounds such as proteins, lipids, carbohydrates, nitrogen and phosphorus. This study investigated the enhancement of organic and nutrient removal efficiencies in seafood processing wastewater by integrating an Anaerobic Membrane Bioreactor (AnMBR) with an anoxic/oxic (AO) processes. A pilot-scale system was constructed with a capacity of 0.5 m3/day directly at the factory operated continuously, featuring an AnMBR process with a 24-hour hydraulic retention time (HRT) and an AO process with HRT values and internal recycle changes. The AnMBR system exhibited consistent and high-performance biochemical oxygen demand (COD) elimination, approximately 80 ± 5 %. However, this system demonstrated low-efficiency removal of total nitrogen (TN) at about 20 ± 5 %, and total phosphorus (TP) 15 ± 5 %, under organic loading rates (OLR) of 0.6 to 1.3 kg-COD/(L·d). The AO process was then continually employed to improve the treatment efficacy (at HRT, 5 h in the anoxic phase, and 8.3 h in the oxic phase, at a recycling rate of 300 %) resulting in the final post-treatment concentrations of COD 27–41 mg/L (removal 98.3 ± 0.3 %), TN 12–25 mg/L (90 ± 2 %), and TP 18 ± 2 mg/L (35 ± 5 %). The performance of the integrated AnMBR-AO system met the established Vietnamese discharge standards for seafood processing wastewater, as outlined in QCVN 11-MT: 2015/BTNMT.

Anaerobic dynamic membrane bioreactor treating sulfamethoxazole wastewater: advantages of dynamic membrane and its fouling mechanism

Discharge of improperly treated sulfamethoxazole (SMX) wastewater seriously threats environmental security and public health. Anaerobic dynamic membrane bioreactors (AnDMBRs) technology would be cost-effective for SMX wastewater treatment, considering its low cost and satisfactory treatment efficiency. The performance of AnDMBR, though demonstrated to be excellent in treating many types of wastewaters, was for the first time investigated for treating SMX wastewater. Particular efforts were devoted to elucidating the advantages of dynamic membrane (DM) and the governing mechanism responsible for DM fouling with the presence of SMX. The threshold SMX concentration for AnDMBR was found to be 90 mg/L and the AnDMBR exhibited excellent removal efficiency of COD (90.91 %) and SMX (88.95 %) as well as satisfactory acute toxicity reduction rate (88.84 %). It was noteworthy that the DM made indispensable contributions to the removal of COD (14.26 %) and SMX (22.20 %) as well as the acute reduction of toxicity (25.81 %). The presence of SMX significantly accelerated DM fouling mainly by increasing its specific resistance, which was attributed to the increased content of small particles, high-valence metal ions and EPS content (mainly hydrophobic proteins), resulting in a denser DM structure with lower porosity. Besides, the biofouling-related bacteria (Firmicutes) was found to be enriched in the DM with the presence of SMX.

Biohydrogen production from wastewater: Production technologies, environmental and economic aspects

Biohydrogen (bio-H2) production from wastewater can be a sustainable and innovative approach that uses biotechnological processes to convert organic waste into hydrogen, a clean energy source. Technologies such as dark fermentation, photo-fermentation, microbial electrolysis cells, and biophotolysis are widely utilized, with emerging technologies like anaerobic membrane bioreactors and microalgae processes also gaining prominence. Integration between these systems aims to enhance process efficiency. This study reviews the hydrogen production from wastewater, analyzing its potential as a source for bio-H2 production and evaluating environmental and economic issues. The performance of various processes in bio-H2 production from different wastewater sources is discussed, focusing on challenges, opportunities, and trends. Wastewater, including cassava (225.2 mL H2/gVS) and corn (265 mL H2/gVS) processing, dairy (54.5 mL H2/gVS), domestic (154–180 mL H2/gVS), fruit (104.9 mL H2/gVS) and starchy (153–200 mL H2/gVS), show promising potential for bio-H2 production. Economically, indirect biophotolysis is the most cost-effective technology per kg of bio-H2 produced, followed by microbial electrolysis cells, photo-fermentation, dark fermentation, and direct biophotolysis. Furthermore, from an environmental and sustainability perspective, bio-H2 production presents a strategic tool for global decarbonization efforts, reducing CO2 emissions and facilitating transformation towards clean energy solutions. Bio-H2 generation during wastewater treatment holds potential by concurrently producing clean fuel and enabling safe disposal of wastewater. Continued research and development efforts are essential to overcoming current challenges. Achieving this will require targeted investments, policy support, and technological innovations to make biohydrogen a viable and sustainable energy solution.

Optimizing mass flow and extracellular electron transfer to promote energy recovery during treating municipal wastewater in a biochar enhanced anaerobic membrane bioreactor (AnMBR)

The anaerobic membrane bioreactor (AnMBR) is an alternative technology with energy neutrality potential when treating municipal wastewater (MWW). However, the poor bio-reaction kinetic conditions caused by low COD concentrations in MWW greatly limits the CH4 yield. In this study, the average methanogenesis rate was significantly increased from 164.8 to 275.5 mL/g COD with the two times biochar addition of 5 g/L. And following the second time addition of 5 g/L biochar, the CH4 component significantly increased to a high level of 89.0 ± 6.3 %. In addition, the rate for acetate converted into CH4 increased from 3.3 to 10.5 mmol/(g VS·d) with biochar addition of 10 g/L, indicating that acetotrophic methanogenesis route was significantly promoted by biochar. Bio-electrochemistry analysis showed that biochar accelerated 0.74 mol e-/g VS/min of electron transfer velocity in AD system. The addition of biochar enriched organic metabolism bacteria such as Ancinetobacter_lwoffii, Comamonas and Geobacter, and upregulated the expression of functional genes related to organics degradation such as lldD, sucD and fumC, facilitates the direct transfer of electrons and acetates produced by Comamonas and Geobacter to convert CO2 into CH4 through microbial mediation. Thus, the COD flow shifted significantly towards more CH4 production. The COD mass flow showed that biochar facilitated more bio-catabolism (up about 52.7 %) and less bio-anabolism (down about 92 %), and more COD in wastewater was converted to CH4, resulting a significant promoting of energy production. The energy balance analysis indicated that the net energy consumption was reduced by 15 % after two times addition of 5 g/L biochar, and the key to achieve the net energy output during treating MWW is the efficient operation of AnMBR at ambient temperature.

Synergic treatment of domestic wastewater and food waste in an anaerobic membrane bioreactor demo plant: Process performance, energy consumption, and greenhouse gas emissions

Ambient operation and large-scale demonstration have limited the implementation and evaluation of anaerobic membrane bioreactors (AnMBRs) for low-strength wastewater treatment. Here, we studied these issues at an AnMBR demo plant that treats domestic wastewater and food waste together at ambient temperatures (7–28 °C). At varied hydraulic retention times (HRTs, 8–42 h), the AnMBR achieved a COD removal efficiency and biogas production of 80.4% ± 3.9% and 66.5 ± 9.4 NL/m3-Influent, respectively. Moreover, a stable high membrane flux of 14.4 L/m2/h was reached. The electric energy consumption for the AnMBR operation was 0.269–0.433 kW·h/m3, and 49.4%–91.3% could be compensated by the electric energy produced from methane production. At an HRT of 10 h, the AnMBR system demonstrated an impressively low net electric energy consumption of merely 0.05 kW·h/m3, resulting in a net greenhouse gas emission of 0.015 CO2-eq/m3, cutting 85% compared to the conventional activated sludge process. Achievements in this study provide key parameters for the ambient operation of AnMBR and demonstrate that AnMBR is an energy-saving and low-carbon solution for low-strength wastewater treatment.

Synergetic association of hydroxyapatite-mediated biofilm and suspended sludge enhances resilience of partial nitrification/anammox (PN/A) system treating high-strength anaerobic membrane bioreactor (AnMBR) permeate

A single-stage partial nitrification/anammox (PN/A) system with biocarriers was used to treat the permeate from an anaerobic membrane reactor (AnMBR) processing organic fraction of municipal solid wastes. The suitable Ca/P ratio and high pH in the AnMBR permeate facilitated hydroxyapatite (HAP) formation, enhancing the biofilm attachment and the settleability of suspended sludge. This maintained sufficient biomass and a stable microbial structure after flushing to mitigate the free nitrous acid inhibition. Robust anammox bacteria in the biofilm and ammonia-oxidizing bacteria in the suspended sludge ensured that the PN/A system achieved an 87.3 % nitrogen removal efficiency at an influent NH4+-N concentration of 1802 mg/L. This study demonstrates that AnMBR permeate with high Ca, P and NH4+-N content is suitable for single-stage PN/A system with biocarriers due to the high resilience enhanced by HAP, offering a reference for the treatment of high-strength AnMBR permeate.

Enhancing sustainability: Upcycled membrane distillation for water and nutrient recovery from anaerobic membrane bioreactor effluent

Addressing the critical issue of recycling end-of-life membranes, this study focuses on the meticulous process of removing contaminants and rejuvenating deteriorated polyvinylidene difluoride (PVDF) membranes for secondary applications. We unveil a successful upcycling approach wherein these membranes are effectively cleaned and recoated, transforming them for utilization in the membrane distillation (MD) process. Citric acid proved to be the most effective cleaning agent, efficiently removing foulants and restoring the membranes’ original color, surface composition, and hydrophobicity. Surface analyses confirmed the removal of metallic foulants, with significant improvements in pore structure and contact angle, indicating effective property restoration. Further analyses revealed that coating PVDF membranes with 5 % carnauba wax and 0.1 % polysulfone resulted in the most hydrophobic surface, characterized by increased prominence of carnauba wax peaks, decreased PVDF peaks, and reduced O 1s peak, enhancing hydrophobicity. Optimal hydrophobicity suitable for MD was achieved with minimal polysulfone addition, producing near-superhydrophobic characteristics with a water contact angle of ∼150° and peak surface roughness of 287 nm. Higher polysulfone content reduced hydrophobicity and surface roughness. The upcycled membrane significantly decreased the crossover of ionic species to the permeate with minimal reduction in water flux, demonstrating superior retention of nutrients as eco-friendly fertilizers from anaerobic digestate. Additionally, acidifying the digestate to pH 5 minimizes NH3 emissions, and MD treatment at 70 °C inactivates pathogens, making the process suitable for water and nutrient recovery, thereby supporting zero liquid discharge and the transition to a circular economy.

Enhancing seafood processing wastewater treatment efficiency of an Anaerobic Membrane Bioreactor (AnMBR) system: a comparison of post-treatment methods

<p class="Paragraph"><span lang="EN-US">An Anaerobic membrane bioreactor (AnMBR) was applied for treating wastewater of a seafood processing factory in Vietnam. However, Chemical Oxygen Demand (COD), Total Phosphorus (TP), and Total Nitrogen (TN) values </span><a name="_Hlk163246539"><span lang="EN-US">of the AnMBR effluent were 250.43 mg/l, 19.96 mg/l, and 62.65 mg/l, respectively, and were about two times higher than the technical regulation for seafood processing wastewater in Vietnam. AnMBR </span></a><span lang="EN-US">needs to be combined with other post-treatment processes to ensure that treated water can meet the technical regulation. Therefore, current research has tested various advanced post-treatment methods for AnMBR effluent including chlorine, poly aluminum chloride (PAC) combined with anionic polymer, and granular activated carbon (GAC). Different concentrations of the above chemicals and reaction times were tested to select the appropriate post-treatment method. The results showed that chlorine had the lowest treatment efficiency for all four parameters (Total suspended solids – TSS, COD, TP, and TN). GAC was more effective than PAC in treatment of TN and TSS. Besides, GAC with a concentration of 5000 mg/L and a reaction time of 60 minutes brought the highest TSS, COD, TP, and TN treatment efficiency with </span><span lang="DE">94.04, 79.11; 86.19, and 71.23%. </span><span lang="EN-US">This implies that GAC is the suitable method for the post-treatment of AnMBR seafood processing effluent.</span></p>

A comparative study on UASB MF-OMBR and AnMF-OMBR treating slaughterhouse wastewater: Process performance, struvite precipitation, and economic evaluation

Up-flow anaerobic sludge blanket microfiltration osmotic membrane bioreactor (UASB MF-OMBR) is a cutting-edge technology derived from the anaerobic osmotic membrane bioreactor (AnOMBR). This study investigated long-term performance of an UASB MF-OMBR and an anaerobic microfiltration osmotic membrane bioreactor (AnMF-OMBR) comparatively focusing on process performance, membrane fouling, microbial community shift, struvite precipitation, and economic evaluation for the treatment of synthetic and real slaughterhouse wastewater (SSW and RSW). The UASB MF-OMBR achieved higher process performance regarding chemical oxygen demand (COD) removal (70 ± 1 %), methane yield (0.24 ± 0.03 L CH4 g−1 CODremoved) and NH4+-N rejection (85 ± 3 %). On the other hand, high COD and PO43−-P rejections were observed in both systems (>92 % and ∼98 %, respectively). The impact of the salinity build-up in the UASB MF-OMBR was the lower due to the bioreactor configuration. In addition, compared to the AnMF-OMBR, the better water fluxes were obtained in the UASB MF-OMBR, which can be attributed to the less membrane fouling. The results of precipitation modelling and Mg2+ measurement in the sludge of both bioreactors demonstrated that the struvite precipitation occurred during the forward osmosis (FO) operation was more often and in higher amounts in the AnMF-OMBR. The economic evaluation indicated that the specific produced permeate cost (SPC) with revenue was slightly lower for the UASB MF-OMBR than that of the AnMF-OMBR.

Performance evaluation and microbial community analysis of a continuous stirred tank reactor–anaerobic ceramic membrane bioreactor system for practical swine wastewater treatment

To treat swine wastewater from a practical piggery, a continuous stirred tank reactor (CSTR)–anaerobic ceramic membrane bioreactor (AnCMBR) was operated for 201 days. A high chemical oxygen demand (COD) removal efficiency of 95 % and biogas production rate of 0.31 L/L·d were achieved at an organic loading rate (OLR) of 1.19 g-COD/L·d. Although the free ammonia concentration reached a maximum of 200 mg/L during the last operational phase, no evident inhibitory effect on AnCMBR performance was observed. Microbial community analyses indicated that six bacterial phyla were responsible for the hydrolysis, acidification, and fermentation of organics and environmental stabilization. Hydrotrophic methanogenic archaea were dominant, indicating that the main methane production pathway involved the use of H2 and CO2 as substrates. The results demonstrated that CSTR–AnCMBR systems exhibit excellent organics removal performance and energy recovery at high organic concentrations and possess strong anti-shock ability. Thus, they represent alternative green and sustainable anaerobic technologies for practical swine wastewater treatment.

Recommendation on the selection of powdered activated carbon as carrier to enhance performance of polymeric UF membrane

The addition of powdered activated carbon (PAC) has been widely accepted as a solution to alleviate membrane fouling and maintain a sustainable flux in membrane bioreactor (MBR) and anaerobic membrane bioreactor (AnMBR). This is due to PAC's unique characteristics, such as serving as a supportive medium for bacterial attachment and growth, achieving adsorption of organic foulants and providing abrasion effect that minimizes the formation of cake layers on membrane surfaces. While majority of ultrafiltration (UF) membranes used in MBR and AnMBR application are polymeric, no study has yet investigated the integrity of polymeric UF membranes with the addition of PAC adsorbents. The abrasive effects of PAC on membrane surfaces under gas sparging in AnMBR or air scouring in MBR have not been studied, and no guidelines have been established for selecting a reliable PAC for such purposes. To address these concerns, this study systemically investigated the integrity of polymeric UF membranes with five different types of PACs to establish recommendations for PAC selection. Based on the integrity testing of polymeric UF membranes, a recommendation for PAC selection was formulated, highlighting bulk density and Gold Number (GN) as pivotal criteria. Five distinct types of PACs were studied to determine the optimal characteristics for polymeric UF membranes, considering variations in raw materials (coal-based and wood-based), activation methods (chemical and steam), particle morphology (sharp and granular), bulk densities (ranging from 0.23 to 0.6 kg/L) and GNs (spanning from 0.1 to > 6.0). The investigation extended beyond 100 d or until irreversible defects were observed in the UF membranes. This study provides guidelines for selecting PACs to be used with polymeric UF membranes, aiming to improve membrane performance while minimising their impact on membrane surfaces.

Sludge bound-EPS solubilization enhance CH4 bioconversion and membrane fouling mitigation in electrochemical anaerobic membrane bioreactor: Insights from continuous operation and interpretable machine learning algorithms

Bound extracellular polymeric substances (EPS) are complex, high-molecular-weight polymer mixtures that play a critical role in pore clogging, foulants adhesion, and fouling layer formation during membrane filtration, owing to their adhesive properties and gelation tendencies. In this study, a novel electrochemical anaerobic membrane bioreactor (EC-AnMBR) was constructed to investigate the effect of sludge bound-EPS solubilization on methane bioconversion and membrane fouling mitigation. During the 150-days’ operation, the EC-AnMBR demonstrated remarkable performance, characterized by an exceptionally low fouling rate (transmembrane pressure (TMP) < 4.0 kPa) and high-quality effluent (COD removal > 98.2 %, protein removal > 97.7 %, and polysaccharide removal > 98.5 %). The highest methane productivity was up to 38.0 ± 3.1 mL/Lreactor/d at the applied voltage of 0.8 V with bound-EPS solubilization, 107.6 % higher than that of the control stage (18.3 ± 2.4 mL/Lreactor/d). Morphological and multiplex fluorescence labeling analyses revealed higher fluorescence intensities of proteins, polysaccharides, total cells and lipids on the surface of the fouling layer. In contrast, the interior exhibited increased compression density and reduced activity, likely attributable to compression effect. Under the synergistic influence of the electric field and bound-EPS solubilization, biomass characteristics exhibited a reduced propensity for membrane fouling. Furthermore, the bio-electrochemical regulation enhanced the electroactivity of microbial aggregates and enriched functional microorganisms, thereby promoting biofilm growth and direct interspecies electron transfer. Additionally, the potential hydrogenotrophic and methylotrophic methanogenesis pathways were enhanced at the cathode and anode surfaces, thereby increasing CH₄ productivity. The random forest-based machine learning model analyzed the nonlinear contributions of EPS characteristics on methane productivity and TMP values, achieving R² values of 0.879 and 0.848, respectively. Shapley additive explanations (SHAP) analysis indicated that S-EPSPS and S-EPSPN were the most critical factors affecting CH₄ productivity and membrane fouling, respectively. Partial dependence plot analysis further verified the marginal and interaction effects of different EPS layers on these outcomes. By combining continuous operation with interpretable machine learning algorithms, this study unveils the intricate impacts of EPS characteristics on methane productivity and membrane fouling behaviors, and provides new insights into sludge bound-EPS solubilization in EC-AnMBR.

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.

Biokinetic and microbial insights into regulatory mechanisms of long-chain fatty acid degradation during food waste-lipid co-digestion within anaerobic membrane bioreactor

This study investigated the effects of varying lipid ratios on the anaerobic co-digestion of high-lipid food waste (FW) in a mesophilic anaerobic membrane bioreactor (AnMBR). At a lipid concentration of 5 %, optimal biogas production (3.84 L/L/d) and lipid removal efficiency (78 %) were achieved; however, increasing lipid concentrations resulted in significant accumulations of long-chain fatty acids (LCFAs) and volatile fatty acids (VFAs). Batch tests further demonstrated the impact of various types of LCFAs, with stearic acid showing the slowest microbial growth rate (0.033d-1), confirming its role in the accumulation of acetate-dominated VFAs, potentially limiting the methanogenesis process at elevated lipid levels. Furthermore, at 8 % lipid content, the downregulation of key LCFA degradation enzymes and dominance of hydrogenotrophic methanogens indicated adverse conditions. The importance of the intricate interplay between LCFA degradation kinetics and microbial community for the system efficiency was evidenced, offering insights for optimizing and managing high-lipidic wastes.

Enhancement of membrane filtration performance and mitigation of sludge calcification in an intermittent anaerobic membrane bioreactor treating high-calcium wastewater

Anaerobic membrane bioreactors (AnMBRs) can alleviate the inhibitory effect of sludge calcification on anaerobic process when treating high-calcium wastewater. However, sludge calcification induced by high-calcium wastewater and flocculated sludge formation under reactor aeration shear will inhibit membrane filtration performance. In this study, an intermittently operated AnMBR (A2) was used to treat high-calcium wastewater, and continuously operated AnMBR (A1) was used as the parallel control. When treating 200–1000 mg/L calcium ion wastewater, A2 achieved a stable chemical oxygen demand removal efficiency of 91.8±3.9 %. The methane production of A2 was 188.2±22.5 mL/(gVSS⋅d), which was marginally higher than the continuous AnMBR (A1) methane production of 174.7±11.7 mL/(gVSS⋅d). Analysis of the microbial community demonstrated significant enrichment in hydrolyzing acidifying bacteria and archaea in A2, compared to A1, which played a crucial role in improving the performance of anaerobic process. A1 exhibited a maximum transmembrane pressure (TMP) of 19.6 kPa, and scanning electron microscopy (SEM) analysis revealed the deterioration of membrane fouling due to sludge calcification on the membrane surface. Surprisingly, the maximum TMP of A2 was just 3.6 kPa during the study. When treating 1000 mg/L of high calcium wastewater, the average effluent calcium concentration in A2 was 650 mg/L, which indicated that A2 effectively retained calcium ions. SEM analysis revealed that anaerobic sludge had a tendency to agglomerate, which slowed down membrane fouling in A2. Sludge agglomeration was due to intermittent operation effectively increasing the contact time of sludge with calcium ions, thereby stimulating the protein secretion of extracellular polymers. These results showed that the intermittent operation effectively mitigated membrane fouling. This work provides a new strategy for comprehensively addressing the challenges of high-calcium wastewater and achieving the stable performance of anaerobic reactors.

Study on membrane fouling mechanisms and mitigation strategies in a pilot-scale anaerobic membrane bioreactor (P-AnMBR) treating digestate

Anaerobic Membrane Bioreactor (AnMBR) are employed for solid-liquid separation in wastewater treatment, enhancing process efficiency of digestion systems treating digestate. However, membrane fouling remains a primary challenge. This study operated a pilot-scale AnMBR (P-AnMBR) to treat high-concentration organic digestate, investigating system performance and fouling mechanisms. P-AnMBR operation reduced acid-producing bacteria and increased methane-producing bacteria on the membrane, preventing acid accumulation and ensuring stable operation. The P-AnMBR effectively removed COD and VFA, achieving removal rates of 82.3 % and 92.0 %, respectively. Higher retention of organic nitrogen and lower retention of ammonia nitrogen were observed. The membrane fouling consisted of organic substances (20.3 %), predominantly polysaccharides, and inorganic substances (79.7 %), primarily Mg ions (10.1 %) and Ca ions (4.5 %). To reduce the increased transmembrane pressure (TMP) caused by fouling (a 10.6-fold increase in filtration resistance), backwash frequency experiment was conducted. It revealed a 30-min backwash frequency minimized membrane flux decline, facilitating recovery to higher flux levels. The water produced amounted to 70.3 m³ over 52 days. The research provided theoretical guidance and practical support for engineering applications, offering practical insights for scaling up P-AnMBR.

Boosting nutrient recovery from AnMBR effluent by means of electrodialysis technology: Operating parameters assessing

This work describes a comprehensive assessment of operating parameters of a bench-scale electrodialysis (ED) plant for nutrient concentration from an Anaerobic Membrane BioReactor (AnMBR) effluent. The ED bench-scale plant serves a dual purpose. Firstly, to generate a concentrated stream with a high nutrient content, and secondly, to produce high-quality reclaimed water in the diluted stream, both sourced from real wastewater coming from the effluent of an AnMBR. Two sets of experiments were conducted: 1) short-term experiments to study the effect of some parameters such as the applied current and the type of anionic exchange membrane (AEM), among others, and 2) a long-term experiment to verify the feasibility of the process using the selected parameters. The results showed that ED produced concentrated ammonium and phosphate streams using a 10-cell pair stack with 64 cm2 of unitary effective membrane area, working in galvanostatic mode at 0.24 A, and operating with an Acid-100-OT anionic exchange membrane. Concentrations up to 740 mg/L and 50 mg/L for NH4–N and PO4–P, respectively, were achieved in the concentrated stream along with removal efficiencies of 70% for ammonium and 60% for phosphate in the diluted stream. The average energy consumption was around 0.47 kWh·m−3.

Impact of feeding regimes on the performance of anaerobic sequencing batch membrane bioreactor treating wastewater from an urban drain

ABSTRACT This work evaluated an anaerobic sequencing batch membrane bioreactor (AnSBR-MBR) equipped with waste-based ceramic membranes for treating low-strength real drain wastewater. Two feeding regimes, viz. settled feed (Phase 1) and mixed feed (Phase 2) were compared. The biological performance (chemical oxygen demand (COD) and phosphate (PO43-) removal) and filtration performance (total suspended solids (TSS) removal and membrane fouling) were investigated. The reactor characteristics in terms of solids content, sludge settling behaviour, and extracellular polymeric substances (EPS) were also assessed. In Phase 1, the settled feed (with the absence of particulate organic matter) resulted in low volatile suspended solids (VSS; 0.23 ± 0.15 g/L), causing low COD removal (28.38 ± 8.14%). In the mixed feed regime in Phase 2, VSS increased (1.82 ± 0.60 g/L) due to the organic content in the particulate matter, which gave microorganisms additional food, resulting in increased COD removal (47.42 ± 2.81%); this phase was also characterised by lower membrane fouling because of the lower EPS content. Marginally higher TSS removal was obtained as well in Phase 2 (96.72 ± 3.26%) than in Phase 1 (90.48 ± 8.14%). This work demonstrates that AnSBR-MBR performance is superior with mixed drain wastewater containing suspended solids and thus pre-settling is not recommended.