Anaerobic Membrane Bioreactor Research Articles

Iron Recycle-Driven Organic Capture and Sidestream Anaerobic Membrane Bioreactor for Revolutionizing Bioenergy Generation in Municipal Wastewater Treatment.

The practicality of intensifying organic matter capture for bioenergy recovery to achieve energy-neutral municipal wastewater treatment is hindered by the lack of sustainable methods. This study developed innovative processes integrating iron recycle-driven organic capture with a sidestream anaerobic membrane bioreactor (AnMBR). Iron-assisted chemically enhanced primary treatment achieved elemental redirection with 75.2% of chemical oxygen demand (COD), 20.2% of nitrogen, and 97.4% of phosphorus captured into the sidestream process as iron-enhanced primary sludge (Fe-PS). A stable and efficient biomethanation of Fe-PS was obtained in AnMBR with a high methane yield of 224 mL/g COD. Consequently, 64.1% of the COD in Fe-PS and 48.2% of the COD in municipal wastewater were converted into bioenergy. The acidification of anaerobically digested sludge at pH = 2 achieved a high iron release efficiency of 96.1% and a sludge reduction of 29.3% in total suspended solids. Ultimately, 87.4% of iron was recycled for coagulant reuse, resulting in a theoretical 70% reduction in chemical costs. The novel system evaluation exhibited a 75.2% improvement in bioenergy recovery and an 83.3% enhancement in net energy compared to the conventional system (primary sedimentation and anaerobic digestion). This self-reliant and novel process can be applied in municipal wastewater treatment to advance energy neutrality at a lower cost.

Role of biochar addition to improve anaerobic membrane bioreactors to resist oil stress in synthetic food wastewater treatment

This study investigated biochar addition to improve the performance and stability of anaerobic membrane bioreactor (AnMBR) to resist different oil contents in food wastewater treatment. Results show that an increase in oil content in synthetic food wastewater from 2 to 4 g/L of oleate-Na aggravated AnMBR performance in terms of methane (CH4) production and membrane fouling as showed by an obvious increase in transmembrane pressure (TMP). The reduced performance was caused by the accumulation of volatile fatty acids (VFAs) to inhibit the growth and activity of Methanobacterium in response to increased oil content. Nevertheless, biochar addition improved AnMBR resistance to against oil increase. The dominance of Methanobacterium and their potential mutualism with genus T78 were enhanced by biochar to sustain CH4 yield. Moreover, biochar reduced the production of extracellular polymeric substance (EPS) to alleviate membrane fouling.

Investigating effective strategies for sustainable operation of a submerged anaerobic membrane bioreactor (SAnMBR) coupled with ceramic ultrafiltration membrane

This study presents a mechanistic approach to explore the key operational parameters governing the flux performance of an SAnMBR system coupled with a ceramic flat-sheet ultrafiltration membrane. Experiments were conducted at mixed liquor suspended solid (MLSS) concentrations of 12, 18, and 24 g/L using biogas sparging, backwashing, and a combination of both to investigate the most effective fouling mitigation strategy by exploring the fouling mechanism at a critical flux regime. To validate the experimental findings, a mathematical model was used to simulate the time-based variation of membrane effective pore radius (m), decrease in membrane porosity (%), thickness of cake layer (m), and membrane resistance (1/m). The study found that at a low biomass concentration, there was a sharp decline in the membrane pore radius leading to an increase in membrane resistance in the absence of any fouling mitigation strategies. However, by implementing these strategies individually and in combination, they maintained a higher pore radius and controlled the increase in membrane resistance even at high biomass concentrations. It was observed that biogas sparging outperformed the conventional backwashing strategy and the SAnMBR system exhibited superior performance attaining higher flux rates for prolonged duration. The advanced spectroscopic analysis confirmed the presence of a higher concentration of polysaccharides responsible for cake layer biofouling, and significant pore blocking due to inorganic foulants at high biomass concentrations. This suggests that the SAnMBR system must be operated at optimised biomass levels below the critical flux for sustained operation. Additionally, the key operational parameters identified using the mathematical model provide a precise assessment of SAnMBR performance, to improve its design efficiency for field applications.

Demo-scale up-flow anaerobic sludge blanket reactor coupled with hybrid constructed wetlands for energy-carbon efficient agricultural wastewater reuse in decentralized scenarios

The impact of climate change on water availability and quality has affected agricultural irrigation. The use of treated wastewater can alleviate water in agriculture. Nevertheless, it is imperative to ensure proper treatment of wastewater before reuse, in compliance with current regulations of this practice. In decentralized agricultural scenarios, the lack of adequate treatment facilities poses a challenge in providing treated wastewater for irrigation. Hence, there is a critical need to develop and implement innovative, feasible, and sustainable treatment solutions to secure the use of this alternative water source. This study proposes the integration of intensive treatment solutions and natural treatment systems, specifically, the combination of up-flow anaerobic sludge blanket reactor (UASB), anaerobic membrane bioreactor (AnMBR), constructed wetlands (CWs), and ultraviolet (UV) disinfection. For this purpose, a novel demo-scale plant was designed, constructed and implemented to test wastewater treatment and evaluate the capability of the proposed system to provide an effluent with a quality in compliance with the current European wastewater reuse regulatory framework. In addition, carbon-sequestration and energy analyses were conducted to assess the sustainability of the proposed treatment approach. This research confirmed that UASB rector can be employed for biogas production (2.5 L h−1) and energy recovery from organic matter degradation, but its effluent requires further treatment steps to be reused in agricultural irrigation. The AnMBR effluent complied with class A standards for E. coli, boasting a concentration of 0 CFU 100 mL−1, and nearly negligible TSS levels. However, further reduction of BOD5 (35 mg L−1) is required to reach water quality class A. CWs efficiently produced effluent with BOD5 below 10 mg L−1 and TSS close to 0 mg L−1, making it suitable for water reuse and meeting class A standards. Furthermore, CWs demonstrated significantly higher energy efficiency compared to intensive treatment systems. Nonetheless, the inclusion of a UV disinfection unit after CWs was required to attain water class B standards.

Application and effect evaluation of membrane bioreactor technology in municipal wastewater treatment

Due to the increasing amount of urban sewage and improved standards in sewage discharge, simple traditional biological sewage treatment fails to meet the needs of municipal sewage treatment. Therefore, to treat wastewater more efficiently, the process of combining biofilm technology with traditional biological wastewater treatment appeared. This paper analyzes the advantages and problems of the combined processes of membrane separation technology and traditional biological sewage treatment technology from and perspective of complementary processes, and puts forward relevant measures to alleviate membrane fouling. The study found that Membrane Bioreactor (MBR) technology occupies a small area, and has a better sewage effluent quality and strong stability, also the sludge output is low. Anaerobic Membrane Bioreactor (AnMBR) technology can increase the effectiveness of removing organic matter and enable resource reuse, which satisfies the demand for low energy consumption. Membrane Aeration Bioreactor (MABR) technology involves bubble-free aeration that greatly improves the quality of sewage effluent, and the production of sludge in MABR technology decreases. Anaerobic ammonium nitrogen membrane bioreactor technology can enhance the efficiency of Anammox bacteria, and the energy consumption and economic cost of this technology are low. Although these membrane combination processes can effectively treat sewage, they can easily be limited by factors such as temperature, microbial communities, and membrane fouling. This paper provides guiding opinions for decision makers in the field of urban sewage treatment so that they can apply appropriate sewage treatment technology to local municipal sewage treatment, promoting the sustainable development of sewage treatment.

Removal of RNA viruses from swine wastewater using anaerobic membrane bioreactor: Performance and mechanisms

The effective removal of viruses from swine wastewater using anaerobic membrane bioreactor (AnMBR) is vital to ecological safety. However, most studies have focused only on disinfectants, whereas the capabilities of the treatment process have not been investigated. In this study, the performance and mechanism of an AnMBR in the removal of porcine hepatitis E virus (HEV), porcine kobuvirus (PKoV), porcine epidemic diarrhea virus (PEDV), and transmissible gastroenteritis coronavirus (TGEV) are systematically investigated. The results show that the AnMBR effectively removes the four viruses, with average removal efficiencies of 1.62, 3.05, 2.41, and 1.34 log for HEV, PKoV, PEDV and TGEV, respectively. Biomass adsorption contributes primarily to the total virus removal in the initial stage of reactor operation, with contributions to HEV and PKoV removal exceeding 71.7 % and 68.2 %, respectively. When the membrane is fouled, membrane rejection dominated virus removal. The membrane rejection contribution test shows the significant contribution of membrane pore foulants (23–76 %). Correlation analysis shows that the surface characteristics and size differences of the four viruses contribute primarily to their different effects on biomass adsorption and membrane rejection. This study provides technical guidance for viral removal during the treatment of high-concentration swine wastewater using an AnMBR.

Phage phylogeny, molecular signaling, and auxiliary antimicrobial resistance in aerobic and anaerobic membrane bioreactors

Phage emit communication signals that inform their lytic and lysogenic life cycles. However, little is known regarding the abundance and diversity of the genes associated with phage communication systems in wastewater treatment microbial communities. This study focused on phage communities within two distinct biochemical wastewater environments, specifically aerobic membrane bioreactors (AeMBRs) and anaerobic membrane bioreactors (AnMBRs) exposed to varying antibiotic concentrations. Metagenomic data from the bench-scale systems were analyzed to explore phage phylogeny, life cycles, and genetic capacity for antimicrobial resistance and quorum sensing. Two dominant phage families, Schitoviridae and Peduoviridae, exhibited redox-dependent dynamics. Schitoviridae prevailed in anaerobic conditions, while Peduoviridae dominated in aerobic conditions. Notably, the abundance of lytic and lysogenic proteins varied across conditions, suggesting the coexistence of both life cycles. Furthermore, the presence of antibiotic resistance genes (ARGs) within viral contigs highlighted the potential for phage to transfer ARGs in AeMBRs. Finally, quorum sensing genes in the virome of AeMBRs indicated possible molecular signaling between phage and bacteria. Overall, this study provides insights into the dynamics of viral communities across varied redox conditions in MBRs. These findings shed light on phage life cycles, and auxiliary genetic capacity such as antibiotic resistance and bacterial quorum sensing within wastewater treatment microbial communities.

Understanding key factors determining the effect of particle scouring efficiency on membrane fouling mitigation in AnFMBRs: Correlation analysis via machine learning

Particle scouring methods offer several advantages, including low energy consumption, ease of operation, and effective fouling control. The anaerobic fluidized bed membrane bioreactor is considered to be the most efficient wastewater treatment method with zero energy consumption, as it produces bioenergy and has lower energy requirements compared to conventional processes. However, membrane fouling in AnFMBRs can be affected by various factors such as fluidized particle hydrodynamics, particle properties, and operating conditions. To identify the primary factors affecting membrane fouling control in AnFMBRs, machine learning methods were utilized. Analysis of datasets from previous studies revealed several key findings. The location of the membrane in the reactor, particle momentum, and particle size were identified as the major parameters that govern membrane fouling reduction. Additionally, the optimal condition for AnFMBRs was determined to involve a membrane height-to-reactor height ratio of ≤0.5 and the use of particles with diameters of 1.5–3.0 mm. Furthermore, the use of smaller fluidized particles was shown to decrease particle scouring efficacy, making it less cost-effective. Machine learning models were successfully established to predict fouling, thus providing a comprehensive understanding of the dominant factors influencing membrane fouling control in AnFMBRs and offering an efficient method for optimizing fouling mitigation.

Enhanced methane recovery from anaerobic membrane bioreactor coupled with cold plasma pretreatment for rapid hydrolysis and nitrogen removal

Research to increase biomethane recovery efficiency from thickened sewage sludge (TSWS) using sustainable anaerobic digestion (AD) in municipal wastewater treatment plants is ongoing. Pretreating substrates is known to increase organic biodegradation and biomethane conversion rates in AD. Cold plasma (CP), a recently adopted advanced oxidation processes (AOP) has emerged as an alternative to accelerate pretreatment times under different operation variables. This study assessed raw and CP-pretreated TSWS in an anaerobic sequencing batch reactor (ASBR) and anaerobic membrane bioreactor (AnMBR). The effects of incremental organic loading rates (OLR) and nitrogenous compounds concentration on enhanced CH4 bioconversion efficiency were evaluated. We found that the AnMBR outperformed the ASBR, with an overall chemical oxygen demand (COD) conversion rate of 67%, lower total nitrogen (T–N) accumulation (594 mg L−1), and an overall methane yield of 0.24 L CH4 g−1 COD. CP pretreatment improved TSWS AD, resulting in more efficient COD removal and methane recovery. This study suggests that CP technology is a promising pretreatment to improve AD when treating TSWS.

Biogas upgrading and membrane anti-fouling mechanisms in electrochemical anaerobic membrane bioreactor (EC-AnMBR): Focusing on spatio-temporal distribution of metabolic functionality of microorganisms

Electrochemical anaerobic membrane bioreactor (EC-AnMBR) by integrating a composite anodic membrane (CAM), represents an effective method for promoting methanogenic performance and mitigating membrane fouling. However, the development and formation of electroactive biofilm on CAM, and the spatio-temporal distribution of key functional microorganisms, especially the degradation mechanism of organic pollutants in metabolic pathways were not well documented. In this work, two AnMBR systems (EC-AnMBR and traditional AnMBR) were constructed and operated to identify the role of CAM in metabolic pathway on biogas upgrading and mitigation of membrane fouling. The methane yield of EC-AnMBR at HRT of 20 days was 217.1 ± 25.6 mL-CH4/g COD, about 32.1 % higher compared to the traditional AnMBR. The 16S rRNA analysis revealed that the EC-AnMBR significantly promoted the growth of hydrolysis bacteria (Lactobacillus and SJA-15) and methanogenic archaea (Methanosaeta and Methanobacterium). Metagenomic analysis revealed that the EC-AnMBR promotes the upregulation of functional genes involved in carbohydrate metabolism (gap and kor) and methane metabolism (mtr, mcr, and hdr), improving the degradation of soluble microbial products (SMPs)/extracellular polymeric substances (EPS) on the CAM and enhancing the methanogens activity on the cathode. Moreover, CAM biofilm exhibits heterogeneity in the degradation of organic pollutants along its vertical depth. The bacteria with high hydrolyzing ability accumulated in the upper part, driving the feedstock degradation for higher starch, sucrose and galactose metabolism. A three-dimensional mesh-like cake structure with larger pores was formed as a biofilter in the middle and lower part of CAM, where the electroactive Geobacter sulfurreducens had high capabilities to directly store and transfer electrons for the degradation of organic pollutants. This outcome will further contribute to the comprehension of the metabolic mechanisms of CAM module on membrane fouling control and organic solid waste treatment and disposal.

Anaerobic acidification membrane bioreactor operating at acidic condition for treating concentrated municipal wastewater: Performance and implication

To address the low-carbon treatment requirements for municipal wastewater, a novel anaerobic acidification membrane bioreactor (AAMBR) was developed for recovering organic matter in terms of volatile fatty acids (VFAs). While the AAMBR successfully generated VFAs from municipal wastewater through forward osmosis (FO) membrane concentration, its operation was limited to a single pH value of 10.0. Here, performance of the AAMBR operating at acidic condition was evaluated and compared with that at alkaline condition. The findings revealed that the AAMBR with pH 5.0 efficiently transformed organic matter into acetic acid, propionic acid, and butyric acid, resulting in a VFAs yield of 0.48 g/g-CODfeed. In comparison with the AAMBR at pH 10.0, this study achieved a similar VFAs yield, a lower fouling tendency, a lower loss of nutrients and a lower controlling cost. In conclusion, this study demonstrated that a pH of 5.0 is optimal for the AAMBR treating municipal wastewater.

Anaerobic membrane bioreactor coupled with polyaluminum chloride for high-strength phenolic wastewater treatment: Robust performance and potential mechanisms

Anaerobic digestion of phenolic wastewater by anaerobic membrane bioreactor (AnMBR) has revealed increasing attractiveness, but the application of AnMBRs for treating high-strength phenolic wastewater faces challenges related to elevated phenol stress and membrane fouling. In this study, the coupling of AnMBR and polyaluminum chloride (PAC) was developed for efficient treatment of high-strength phenolic wastewater. The system achieved robust removal efficiencies of phenol (99%) and quinoline (98%) at a gradual increase of phenol concentration from 1000 to 5000 mg/L and a constant quinoline concentration of 100 mg/L. The dosing of PAC could effectively control the membrane fouling rate with the transmembrane pressure (TMP) increasing rate as low as 0.17 kPa/d. The robust performances were mainly attributed to the favorable retention of functional microbes through membrane interception, while pulse cross flow buffered against phenol stress and facilitated cake layer removal. Meanwhile, the enriched core functional microbes, such as Syntrophorhabdus, Syntrophus, Mesotoga and Methanolinea, played a crucial role in further reduction of phenol stress. Notably, the significant presence of biomacromolecule degrader, such as Levilinea, contributed to membrane fouling mitigation through extracellular polymer degradation. Moreover, the enlargement of particle size distribution (PSD) by PAC was expected to mitigate membrane fouling. This study provided a promising avenue for sustainable treatment of high-strength phenolic wastewater.

UV/TiO2 photocatalysis as post-treatment of anaerobic membrane bioreactor effluent for reuse

Advanced oxidation processes have been widely applied as a post-treatment solution to remove residual organic compounds in water reuse schemes. However, UV/TiO2 photocatalysis, which provides a sustainable option with no continuous chemical addition, has very rarely been studied to treat anaerobically treated effluents. In the current study, the removal of organics and nutrients from an anaerobic membrane bioreactor (AnMBR) effluent is evaluated during adsorption and photocatalysis processes under various conditions of TiO2 dose and UV intensity and compared to the effluent from an aerobic membrane bioreactor (AeMBR). The sequence for preferential adsorption on TiO2 was found to be phosphorus, inorganic carbon and then ammonia/organic carbon were found. The competing effect between the organics and nutrients, along with the low UV transmission efficiency caused by the need for high doses of TiO2, ultimately compromise the organic removal efficiency in the AnMBR permeate. TiO2 dosage was found to have a greater impact than UV intensity on improving the overall removal performance as nutrients are competing for the adsorption site but are not photodegraded. Under the same operational condition, the UV/TiO2 photocatalysis displayed a higher removal efficiency of organic matter and phosphorus in the AeMBR effluent due to a lower initial organics concentration and absence of ammonia as compared to the AnMBR effluent.

Synergistic effects of biochar addition and filtration mode optimization on mitigating membrane fouling in high-solid anaerobic membrane bioreactors

In this study, a high-solid anaerobic membrane bioreactor was established for treating food waste, and membrane fouling rates were regulated through multivariate modulation. The anaerobic membrane bioreactor operated stably at a high organic loading rate of 28.75 gCOD/L/d achieved a methane production rate of 8.03 ± 0.61 L/L/d. Experimental findings revealed that the most effective control of membrane fouling was achieved at a filtration– relaxation ratio (F/R) of 10/90 s. This indicates that a higher relaxation frequency provided improved the mitigation of membrane fouling. Compared with single F/R modulation, the combined modulation of biochar and F/R provided enhanced control over membrane fouling. Moreover, the addition of biochar altered the sludge properties of the reactor, thereby preventing the formation of a dense cake layer. Additionally, biochar enhanced the sheer force of the fluid on the membrane surface and facilitated the separation of pollutants during the relaxation stage, thereby contributing to improved control of membrane fouling.

Coupling a Simple and Generic Membrane Fouling Model with Biological Dynamics: Application to the Modeling of an Anaerobic Membrane BioReactor (AnMBR).

A simple model is developed for membrane fouling, taking into account two main fouling phenomena: cake formation, due to attached solids on the membrane surface, and pore clogging, due to retained compounds inside the pores. The model is coupled with a simple anaerobic digestion model for describing the dynamics of an anaerobic membrane bioreactor (AnMBR). In simulations, we investigate its qualitative behavior: it is shown that the model exhibits satisfying properties in terms of a flux decrease due to membrane fouling. Comparing simulation and experimental data, the model is shown to predict quite well the dynamics of an AnMBR. The simulated flux best fits the experimental flux with a correlation coefficient r2=0.968 for the calibration data set and r2=0.938 for the validation data set. General discussions are given on possible control strategies to limit fouling and optimize the flux production. We show in simulations that these strategies allow one to increase the mean production flux to 33 L/(h·m2),whereas without control, it was 18 L/(h·m2).

Comparison of Trace Organic Chemical Removal Efficiencies between Aerobic and Anaerobic Membrane Bioreactors Treating Municipal Wastewater.

Evaluating persistent trace organic chemicals (TOrCs) and transformation products (TPs) in membrane bioreactors (MBRs) is essential, given that MBRs are now widely implemented for wastewater treatment and water reuse. This research applied comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC/TOF-MS)-based nontargeted analysis to compare the effectiveness of parallel aerobic and anaerobic MBRs (AeMBRs and AnMBRs, respectively), treating the same municipal wastewater. The average total chromatographic feature peak area abundances were significantly reduced by 84% and 72% from influent to membrane permeate in both the AeMBR and AnMBR (p < 0.05), respectively. However, the reduction of the average number of chromatographic features was significant for only AeMBR treatment (p = 0.006). A similar number of TPs were generated during both AeMBR and AnMBR treatments (165 vs 171 compounds, respectively). The overall results suggest that the AeMBR was more effective for reducing the diversity of TOrCs than the AnMBR, but both aerobic and anaerobic processes had a similar reduction of TOrC abundance. Suspect screening analysis using GC×GC/TOF-MS, which resulted in the tentative identification of 351 TOrCs, proved to be a powerful approach for uncovering compounds previously unreported in wastewater, including many fragrances and personal care products.

Study on the mechanism of mitigating membrane fouling in MFC-AnMBR coupling system treating sodium and magnesium ion-containing wastewater

ABSTRACT Anaerobic Membrane Bioreactors (AnMBR) offer numerous advantages in wastewater treatment, yet they are prone to membrane fouling after extended operation, impeding their long-term efficiency and stability. In this study, a coupled system was developed using modified conductive membranes as the filtration membrane for the AnMBR and as the anodic conductive membrane in the microbial electrochemical system, with a total volume of approximately 2.57 L. The research focused on understanding the membrane fouling characteristics of the AnMBR when treating wastewater containing sodium ion (Na+) and magnesium ion (Mg2+). When the system was treating wastewater containing Na+, organic pollutants such as proteins and polysaccharides were identified as the primary causes of membrane fouling. Three experimental groups generating different electric currents exhibited extended operational times compared to the open-circuit control group, with extensions of 30, 24, and 15 days, respectively. Conversely, when treating wastewater with Mg2+, organic–inorganic composite fouling, primarily driven by Mg2+ bridging, emerged as the key challenge, with the experimental groups showing operational extensions of 5, 8, and 23 days, respectively, in comparison to the control group. Analysis of proteins and polysaccharides indicated that electric current played a crucial role in reducing organic fouling in the sludge cake layer. When treating wastewater containing Na+, the effectiveness of membrane fouling control was directly proportional to the electric current, while when treating wastewater containing Mg2+, it was directly proportional to the voltage.

Volatile fatty acids production from kitchen waste slurry using anaerobic membrane bioreactor via alkaline fermentation with high salinity: Evaluation on process performance and microbial succession

In this study, a pilot-scale anaerobic membrane bioreactor (AnMBR) was developed to continuously produce volatile fatty acids (VFAs) from kitchen waste slurry under an alkaline condition. The alkaline fermentation effectively suppressed methanogenesis, thus achieving high VFAs production of 60.3 g/L. Acetic acid, propionic acid, and butyric acid accounted for over 95.0 % of the total VFAs. The VFAs yield, productivity, and chemical oxygen demand (COD) recovery efficiency reached 0.5 g/g-CODinfluent, 6.0 kg/m3/d, and 62.8 %, respectively. Moreover, the CODVFAs/CODeffluent ratio exceeded 96.0 %, and the CODVFAs/NH3-N ratio through ammonia distillation reached up to 192.5. The microbial community was reshaped during the alkaline fermentation with increasing salinity. The membrane fouling of the AnMBR was alleviated by chemical cleaning and sludge discharge, and membrane modules displayed a sustained filtration performance. In conclusion, this study demonstrated that high-quality VFAs could be efficiently produced from kitchen waste slurry using an AnMBR process via alkaline fermentation.

Dual-chamber up-flow fluidized hollow-fiber anaerobic membrane bioreactor (UF-HF-AnMBR) treating synthetic purified terephthalic acid wastewater: Granular sludge regranulation and methane production

Up-flow anaerobic sludge blanket is a representative way to treat high-strength industrial wastewater, but suffers from granule collapse and poor long-term performance. In this study, a dual-chamber up-flow fluidized hollow-fiber anaerobic membrane bioreactor (UF-HF-AnMBR) was constructed to enhance sludge regranulation and process stability for purified terephthalic acid (PTA) wastewater treatment. A stable and satisfactory aromatic compound removal (>99 %) was achieved at the organic loading rate of 7.15 ± 0.21 g-COD·Lreactor−1·d−1, with the methane yield of 0.345 ± 0.028 L·g-CODremoved−1. Although the granular sludge collapsed initially induced the pore blocking and membrane fouling, membrane separation promoted the agglomeration of small particles, sludge regranulation and biomass retention. Parallel factor analysis identified that the amino acid tryptophan in extracellular polymeric substances exerted a more critical effect on membrane fouling. The 16S rRNA and network analysis revealed the robust proliferation/enrichment of Methanosaeta, Pelotomaculum, etc., as well as the establishment of mutualistic symbiotic relationship among different species, ensured a stable microbial community and created a favorable circumstance for highly effective anaerobic treatment of PTA wastewater. This study proves that UF-HF-AnMBR can be an efficient and promising technique for sludge regranulation and microbe enrichment, advancing its application in PTA wastewater treatment and bioenergy recovery.

Efficient sulfide and methane removal in anaerobic secondary effluent using a pilot-scale membrane-aerated biofilm reactor

Anaerobic secondary treatment can enable energy-efficient removal of organic matter but may produce effluent containing dissolved methane and sulfide that must be managed before discharge or reuse. In this study, we operated a Membrane-aerated Biofilm Reactor (MABR) to achieve reliable removal of dissolved sulfide and methane from anaerobic secondary effluent at pilot-scale. The pilot-scale MABR was equipped with gas permeable polymethyl pentene (PMP) membranes, promoting surface growth of aerobic biofilm via diffusion-based aeration (lumen-to-surface diffusion). The system treated anaerobic secondary effluent from a demonstration-scale anaerobic membrane bioreactor (AnMBR) processing 90 m3/d primary effluent. MABR influent flow rate was increased from 8.2 to 32.7 m3/d to elevate substrate loading rates to the biofilm. The MABR consistently achieved >99 % removal of sulfide and dissolved methane, even at the maximum substrate loading rate: 2.3 g-S/m2/d for sulfide and 2.5 g-CH4/m2/d for dissolved methane. Despite effective sulfide and methane removal, incomplete nitrification (<25 % ammonia removal) occurred, with a portion of ammonia converted into nitrous oxide (N2O), a greenhouse gas 298 times more potent than CO2. Operating the MABR incurred low energy costs: 0.01 to 0.05 kWh/m3 for the compressor supplying air to the membrane lumen and 0.01 kWh/m3 for the influent pump. An in-depth mass balance of N2O emissions from the MABR revealed that N2O was subject to counter-diffusion (surface-to-lumen diffusion) in which >99 % of the N2O produced within the biofilm was recovered in off-gas from the gas permeable membranes (hollow fibers).