An enhanced anaerobic membrane bioreactor treating bamboo industry wastewater by bamboo charcoal addition: Performance and microbial community analysis

Applicability analysis of algae biochar for anaerobic membrane bioreactors in wastewater treatment: A review from a sustainability assessment perspective

The incorporation of biochar can significantly enhance the performance of anaerobic membrane bioreactors (AnMBRs), achieving up to a 95 % increase in pollutant removal efficiency and an 86 % improvement in methane production. Algae biochar, in particular, shows great promise as an effective additive in AnMBR systems because of its low cost (approximately $0.470/kg) and the abundance of raw material sources. This paper presents a comprehensive applicability analysis of algae biochar-AnMBRs from a sustainability assessment perspective, addressing technical, environmental, economic, and social dimensions. Key technical benefits include a reduction in membrane fouling by 92.1 % and an enhancement of energy recovery by 58.7 % compared to conventional AnMBRs. Following this, the paper evaluates algae biochar-AnMBRs from environmental, economic, and social viewpoints to emphasize the practical applicability and potential of this process. Finally, this review addresses the limitations related to the full-scale implementation of this technology and proposes strategic approaches to overcome these challenges. Overall, the review provides valuable insights into the practical application of algae biochar-AnMBR systems, with a strong focus on sustainability.

Effect of magnetic field coupled magnetic biochar on membrane bioreactor efficiency, membrane fouling mitigation and microbial communities

The excitation by magnetic field was established to mitigate the membrane fouling of magnetic biochar (MB)-supplemented membrane bioreactor (MBR) in this study. The results showed that the transmembrane pressure (TMP) increase rates decreased by about 8 % after introducing the magnetic field compared with the magnetic biochar-MBR (MB-MBR). Membrane characterization suggested that the flocs in the magnetic field-magnetic biochar-MBR (MF-MB-MBR) formed a highly permeable developed cake layer, and a fluffier and more porous deposited layer on membrane surface, which minimized fouling clogging of the membrane pores. Further mechanistic investigation revealed that the decrease in contact angle of fouled membrane surface in MF-MB-MBR, i.e. an enhanced membrane hydrophilicity, is considered important for forming highly permeable layers. Additionally, the magnetic field was demonstrated to have a positive effect on the improvement of the magneto-biological effect, the enhancement of charge neutralization and adsorption bridging between sludge and magnetic biochar, and the reduction of formation of extracellular polymeric substances (EPSs), which all yielded sludge flocs with a large pore structure conducive to form a fluffy and porous deposited layer in the membrane surface. Furthermore, high-throughput sequencing analysis revealed that the magnetic field also led to a reduction in microbial diversity, and that it promoted the enrichment of specific functional microbial communities (e.g. Bacteroidetes and Firmicutes) playing an important role in mitigating membrane fouling. Taken together, this study of magnetic field-enhanced magnetic biochar for MBR membrane fouling mitigation provides insights important new ideas for more effective and sustainable operation strategies.

Biochar mediated high-rate anaerobic bioreactors: A critical review on high-strength wastewater treatment and management

Treatment of high-strength wastewater is critical for the aquatic environment and receiving water bodies around the globe. Untreated or partially treated high-strength wastewater may cause severe damage to the existing water bodies. Various high-rate anaerobic bioreactors have been developed in the last decades for treating high-strength wastewater. High-rate anaerobic bioreactors are effective in treating industrial wastewater and provide energy in the form of methane as well. However, the physical or chemical properties of high-strength industrial wastewater, sometimes, disrupt the functioning of a high-rate anaerobic bioreactor. For example, the disintegration of granular sludge in up flow anaerobic sludge blanket reactor or membrane blocking in an anaerobic membrane bioreactor are the results of a high-strength wastewater treatment which hamper the proper functioning and may harm the wastewater treatment plant economically. Biochar, if added to these bioreactors, may help to alleviate the ill-functioning of high-rate anaerobic bioreactors. The primary mechanisms by biochar work in these bioreactors are direct interspecies electron transfer, microbial immobilization, or gene level alternations in microbial structure. The present article explores and reviews the recent application of biochar in a high-rate anaerobic bioreactor treating high-strength industrial wastewater.

Biochar-assisted anaerobic membrane bioreactor towards high-efficient energy recovery from swine wastewater: Performances and the potential mechanisms

A high-efficient energy recovery system of biochar-assisted anaerobic membrane bioreactor (BC-AnMBR) was established for swine wastewater treatment. Comparing with a conventional AnMBR, biochar addition accelerated volatile fatty acids (VFA) degradation during start-up stage, thereby shortened start-up duration by 44.0 %. Under a high organic loading rate (OLR) of 21.1 gCOD/L/d, BC-AnMBR promoted COD removal efficiency from 90.1 % to 95.2 %, and maintained a high methane production rate of 4.8L CH₄/L/d. The relative abundance of Methanosaeta declined from 53.9 % in conventional AnMBR to 21.0 % in BC-AnMBR, whereas that of Methanobrevibacter dramatically increased from 10.3 % to 70.9 %, respectively. Metabolic pathway analysis revealed that biochar not only strengthened hydrogenotrophic methanogenesis pathway, but also upregulated the genes encoding electron transfer carriers and riboflavin metabolism, suggesting the role of biochar facilitating direct interspecies electron transfer for syntrophic methanogenesis. The excellent energy yield performances under high OLR confirmed BC-AnMBR as an advanced system for high-strength swine wastewater treatment.

Exploring the Function of Quorum Sensing Regulated Biofilms in Biological Wastewater Treatment: A Review

Quorum sensing (QS), a type of bacterial cell–cell communication, produces autoinducers which help in biofilm formation in response to cell population density. In this review, biofilm formation, the role of QS in biofilm formation and development with reference to biological wastewater treatment are discussed. Autoinducers, for example, acyl-homoserine lactones (AHLs), auto-inducing oligo-peptides (AIPs) and autoinducer 2, present in both Gram-negative and Gram-positive bacteria, with their mechanism, are also explained. Over the years, wastewater treatment (WWT) by QS-regulated biofilms and their optimization for WWT have gained much attention. This article gives a comprehensive review of QS regulation methods, QS enrichment methods and QS inhibition methods in biological waste treatment systems. Typical QS enrichment methods comprise adding QS molecules, adding QS accelerants and cultivating QS bacteria, while typical QS inhibition methods consist of additions of quorum quenching (QQ) bacteria, QS-degrading enzymes, QS-degrading oxidants, and QS inhibitors. Potential applications of QS regulated biofilms for WWT have also been summarized. At last, the knowledge gaps present in current researches are analyzed, and future study requirements are proposed.

Sodium hypochlorite induced inhibition in anaerobic digestion and possible approach to maintain methane fermentation performance

Since sodium hypochlorite (NaClO), a commonly used chemical to deal with membrane fouling, is toxic to microorganisms, it is a major concern in the membrane cleaning process. In this study, the concentration-dependent effects of NaClO (0-9 g/L) on the biodegradation performance and microbial activity were investigated via batch experiments. The methane production (obtained approximately 140 mL) and microbial community revealed by principal coordinates analysis were almost unaffected when the NaClO concentration ranged between 0 and 3 g/L. A follow-up batch experiment was conducted and revealed that the microbial products could help protect or recover the activity of anaerobic microorganisms at a high NaClO concentration of 10 g/L. Additionally, correlation analysis was used to investigate the associations between the 15 major bacterial genera. Moreover, the microbial analysis results indicated that the top 10 operational taxonomic units most affected by NaClO were primarily coryneform and filamentous bacteria.

Bamboo charcoal addition enhanced the nitrogen removal of anammox granular sludge with COD: Performance, physicochemical characteristics and microbial community

The effects of different chemical oxygen demand (COD) concentrations on the anammox granular sludge with Bamboo Charcoal (BC) addition were evaluated in UASB reactor. The results showed that the average total nitrogen (TN) removal efficiency was reduced from 85.9% to 81.4% when COD concentration was increased from 50 to 150 mg/L. However, the TN removal efficiency of BC addition reactors was dramatically 3.1%-6.4% higher than that without BC under different COD concentrations. The average diameter of granular sludge was 0.13 mm higher than that without BC. The settling velocity was increased by elevated COD concentration, while the EPS and VSS/SS were increased with BC addition. The high-throughput Miseq sequencing analyses revealed that the bacterial diversity and richness were decreased under COD addition, and the Planctomycetes related to anammox bacteria were Candidatus Brocadia and Candidatus Kuenenia. The Metagenomic sequencing indicated that the abundance of denitrification related functional genes all increased with elevated COD, while the abundance of anammox related functional genes of decreased. The functional genes related to anammox was hydrazine synthase encoding genes (hzsA, hzsB and hzsB). The average relative abundance of hzs genes in the reactor with BC addition was higher than the control at COD concentrations of 50 mg/L and 150 mg/L. The functional genes of denitrification mediated by BC were higher than those without BC throughout the operation phase. It is interesting to note that BC addition greatly enriched the related functional genes of denitrification and anammox.

Recent advances in attached growth membrane bioreactor systems for wastewater treatment

To tackle membrane fouling and limited removals of pollutants (nutrients and emerging pollutants) that hinder the wide applications of membrane bioreactor (MBR), attached growth MBR (AGMBR) combining MBR and attached growth process has been developed. This review comprehensively presents the up-to-date developments of media used in both aerobic and anaerobic AGMBRs for treating wastewaters containing conventional and emerging pollutants. It also elaborates the properties of different media, characteristics of attached biomass, and their contributions to AGMBR performance. Conventional media, such as biological activated carbon and polymeric carriers, induce formation of aerobic, anoxic and/or anaerobic microenvironment, increase specific surface area or porous space for biomass retention, improve microbial activities, and enrich diverse microorganisms, thereby enhancing pollutants removal. Meanwhile, new media (i.e. biochar, bioaugmented carriers with selected strain/mixed cultures) do not only eliminate conventional pollutants (i.e. high concentration of nitrogen, etc.), but also effectively remove emerging pollutants (i.e. micropollutants, nonylphenol, adsorbable organic halogens, etc.) by forming thick and dense biofilm, creating anoxic/anaerobic microenvironments inside the media, enriching special functional microorganisms and increasing activity of microorganisms. Additionally, media can improve sludge characteristics (i.e. less extracellular polymeric substances and soluble microbial products, larger floc size, better sludge settleability, etc.), alleviating membrane fouling. Future studies need to focus on the development and applications of more new functional media in removing wider spectrum of emerging pollutants and enhancing biogas generation, as well as scale-up of lab-scale AGMBRs to pilot or full-scale AGMBRs.

Hollow-Fiber Membrane Contactor for Biogas Recovery from Real Anaerobic Membrane Bioreactor Permeate

This study demonstrates the application of hollow-fiber membrane contactors (HFMCs) for the recovery of biogas from the ultrafiltration permeate of an anaerobic membrane bioreactor (AnMBR) and synthetic effluents of pure and mixed CH₄ and CO₂. The developed membrane degassing setup was coupled with a pilot-scale AnMBR fed with synthetic domestic effluent working at 25 °C. The membrane degassing unit was able to recover 93% of the total dissolved CH₄ and 83% of the dissolved CO₂ in the first two hours of permeate recirculation. The initial recovery rates were very high (0.21 mg CH₄ L⁻¹ min⁻¹ and 8.43 mg CO₂ L⁻¹ min⁻¹) and the membrane was able to achieve a degassing efficiency of 95.7% for CH₄ and 76.2% for CO₂, at a gas to liquid ratio of 1. A higher mass transfer coefficient of CH₄ was found in all experimental and theoretical evaluations compared to CO₂. This could also be confirmed from the higher transmembrane mass transport resistance to CO₂ rather than CH₄ found in this work. A strong dependency of the selective gas transport on the gas and liquid side hydrodynamics was observed. An increase in the liquid flow rate and gas flow rate favored CH₄ transport and CO₂ transport, respectively, over each component. The results confirmed the effectiveness of the collective AnMBR and membrane degassing setup for biogas recovery. Still, additional work is required to improve the membrane contactor’s performance for biogas recovery during long-term operation.

Insight into synergies between Acinetobacter sp. AL-6 and pomelo peel biochar in a hybrid process for highly efficient manganese removal

The manganese contamination of groundwater is a global issue that needs to be solved urgently. In this study, a hybrid process between pomelo peel biochar(BC) and Acinetobacter sp. AL-6 (strain AL-6) was established to remove manganese from water. The results showed that microbe-biochar composite had removed 98.19% of manganese (800 mg L^-1) within 48 h. Compared with two separate systems (biochar, strain AL-6), the co-system (strain AL-6 and BC composite) had an excellent synergy effect on manganese removal. The average removal rate of manganese in the synergistic system was 14.08 mg L^-1 h^-1, which was 6.41 times higher than strain AL-6, 3.45 times higher than biochar, and even at 2.24 times their sum. In addition, the scanning electron microscope (SEM) and the bioassay indicated that many strains were attached to biochar and had vigorous biological activity. The FTIR results showed that the functional groups of OH, CO, CO, CH₂, and CH played a vital role in removing manganese. And the correlation analysis shows that biochar with strains AL-6 has a highly synergistic effect on manganese removal. Meanwhile, the composite material can maintain excellent manganese removal efficiency under different pH conditions. Besides, in the sequence batch reactor (SBR) inoculating with the microbe-biochar composite, more than 96% of manganese was removed, which far exceeded the treatment efficiency of free bacteria in the SBR. Hence, biochar-immobilized AL-6 has great potential and can be applied to degrade manganese polluted wastewater.

Remediation of Chromium-Contaminated Soil Based on Bacillus cereus WHX-1 Immobilized on Biochar: Cr(VI) Transformation and Functional Microbial Enrichment

Microorganisms are applied to remediate chromium (Cr)-contaminated soil extensively. Nevertheless, the microbial loss and growth inhibition in the soil environment restrain the application of this technology. In this study, a Cr(VI)-reducing strain named Bacillus cereus WHX-1 was screened, and the microbial aggregates system was established via immobilizing the strain on Enteromorpha prolifera biochar to enhance the Cr(VI)-reducing activity of this strain. The mechanism of the system on Cr(VI) transformation in Cr-contaminated soil was illuminated. Pot experiments indicated that the microbial aggregates system improved the physicochemical characteristics of Cr-contaminated soil obviously by increasing organic carbon content and cation exchange capacity, as well as decreasing redox potential and bulk density of soil. Moreover, 94.22% of Cr(VI) was transformed into Cr(III) in the pot, and the content of residue fraction Cr increased by 63.38% compared with control check (CK). Correspondingly, the physiological property of Ryegrass planted on the Cr-contaminated soil was improved markedly and the main Cr(VI)-reducing microbes, Bacillus spp., were enriched in the soil with a relative abundance of 28.43% in the microbial aggregates system. Considering more active sites of biochar for microbial aggregation, it was inferred that B. cereus WHX-1 could be immobilized by E. prolifera biochar, and more Cr(VI) was transformed into residue fraction. Cr stress was decreased and the growth of plants was enhanced. This study would provide a new perspective for Cr-contaminated soil remediation.

Anaerobic membrane bioreactors for treatment of emerging contaminants: A review

Emerging contaminants (ECs) are synthetic organic chemicals that released into the environment, which pose a serious threat to the ecosystem and human health. Due to the high costs of physicochemical methods and the possibility of secondary pollution, and conventional biological treatment techniques are not efficient to remove ECs. Thus, there is a need to develop novel technologies to treat ECs. Anaerobic digestion (AD) is reported to degrade most ECs. Anaerobic membrane bioreactor (AnMBR) is an upgraded AD technology that has high system stability and microbial community abundance. The biogas production and EC biodegradation efficiency in the AnMBR system are markedly higher than those in the traditional AD system. In recent years, AnMBR is widely used to remove environmental ECs. This review analyzes the feasibility and challenges of AnMBR in the treatment of ECs and provides useful insights for improving the performance and efficiency of AnMBR to treat ECs.

Microbial community in an anaerobic membrane bioreactor and its performance in treating organic solid waste under controlled and deteriorated conditions

The adoption of anaerobic membrane bioreactors (AnMBRs) for organic solid waste management is important for the recovery of energy and high-quality treated water. However, few studies have focused on AnMBR treatment of high-strength organic solid waste and the microorganisms involved under deteriorated operating conditions. In the present study, a 15-L bench-scale AnMBR was operated using a model slurry of high-strength organic solid waste with the organic loading rate (OLR) increasing from 2.3 g chemical oxygen demand (COD) L^-1 day^-1 (represented as a controlled condition) to 11.6 g COD L^-1 day^-1 (represented as a deteriorated condition), and microbial community dynamics over 120 days of operation were analyzed. The abundances of methanogens and bacteria that were dominant under the controlled condition decreased as a result of both high organic loading and sludge withdrawal under the deteriorated condition and did not recover thereafter. Instead, numbers of putative volatile fatty acid (VFA)-producing bacterial operational taxonomic units (OTUs) related to the genus Prevotella increased rapidly, reaching a relative abundance of 43.2%, leading to the deterioration of methanogenic AnMBR operation. Considering that the sequences of these OTUs exhibited relatively low sequence identity (91-95%) to those of identified Prevotella species, the results strongly suggest that the accumulation of VFAs by novel VFA-producing bacteria in the digestion sludge promotes the disruption of the methanogen community under deteriorated conditions.

Effects of Solids Retention Time on the Anaerobic Membrane Bioreactor with Yttria-Based Ceramic Membrane Treating Domestic Wastewater at Ambient Temperature

The effects of solid retention times (SRTs) (100 days, 50 days, 25 days) on the performance, microbial community, and membrane fouling of a lab-scale anaerobic yttria-based ceramic membrane bioreactor (AnCMBR) treating synthetic domestic wastewater at ambient temperature (31.2 ± 2.7 °C) were examined. The soluble chemical oxygen demand (SCOD) removal was higher (89.6%) at 25 days SRT compared with 50 days (39.61%) and 100 days (34.3%) SRT. At 100 days SRT, more Bacteroidetes, Firmicutes, and Proteobacteria were present in the microbial community. At 25 days SRT, more Chloroflexi, Synergistetes, and Pastescibacteria emerged, contributing to the stable performance. The SRT of 25 days has resulted in a more stable microbial community compared with 50 days and 100 days SRT. Both bacterial and archaeal community diversities were higher at 25 days SRT, and the specific production of soluble microbial by-products (SMPs) and extracellular polymeric substances (EPSs) were higher at 25 days SRT as well. Consequently, the membrane flux was lower at 25 days SRT with the increased particle size and the enhanced SMPs and EPSs production. Fourier transform infrared spectroscopy analysis (FTIR) and three-dimensional excitation and emission matrix (3D-EEM) analysis showed that protein and SMPs were the major membrane foulants at all SRT stages. In this study, SRT at 25 days was favorable for the stable operation of an AnCMBR treating domestic wastewater at ambient temperature.

A comparative long-term operation using up-flow anaerobic sludge blanket (UASB) and anaerobic membrane bioreactor (AnMBR) for the upgrading of anaerobic treatment of N, N-dimethylformamide-containing wastewater

Synthetic industrial wastewater containing approximately 2000 mg/L N, N-dimethylformamide (DMF) was treated using a lab-scale anaerobic sludge blanket (UASB) and an anaerobic membrane bioreactor (AnMBR) in this study. The inoculum consisted of two sources of sludge: Co-culture of anaerobic digested sludge (ADS) with DMF-hydrolyzing activated sludge (DAS) for the AnMBR, and co-culture of anaerobic granular sludge (AGS) with DAS for the UASB. Effective DMF methanogenic degradation of nearly 100% removal was achieved in both reactors on the first day. Both reactors obtained excellent DMF removal efficiency and high methane production under a low organic loading rate (OLR) of around 3-4 g COD/L/d. However, excessive elevation of OLR significantly limited DMF hydrolysis. When OLR exceeded 6 g COD/L/d, the removal efficiency and methane production in both reactors dramatically dropped. Despite their different forms and shapes, the ADS and AGS both provide methanogens which are responsible for methanogenesis. The UASB tolerated a higher OLR while the AnMBR was limited by membrane fouling due to the increased sludge concentration. However, the AnMBR obtained high-quality effluent without suspended solid. Whether DMF can be effectively degraded depends on DAS, in which abundant DMF-hydrolyzing bacteria (DHB) provide sufficient quantities of the hydrolytic enzyme for effective hydrolysis of DMF. However, these DHB were facultative and were also identified as denitrifying bacteria which require nitrate as the electron acceptor or otherwise survive under the aerobic condition. They gradually decayed rather than proliferated and were outcompeted by methanogens. Therefore, it is conceivable that a slight dosage of nitrate would enrich the abundance of DHB in both the UASB and the AnMBR, and provide a sufficient quantity of enzymes for the DMF hydrolysis. The cultivation of the anaerobic DMF-degrading granular sludge using the UASB is considered an upgraded solution to the effective treatment of DMF-containing wastewater.

Treatment of anthraquinone dye textile wastewater using anaerobic dynamic membrane bioreactor: Performance and microbial dynamics

The performance and microbial community structure of anaerobic dynamic membrane bioreactor (AnDMBR) treating textile wastewater was investigated. The reactor showed excellent soluble COD and color removal of 98.5% and >97.5%, respectively. Dynamic membrane layer grown over the 3D printed dynamic membrane support showed decent rejection for high molecular weight compounds (>20 kDa); and the total suspended solid rejection by the dynamic layer was >98.8%. Gel permeation chromatography analysis of extracellular polymeric substance (EPS) and effluent samples revealed EPS accounted for more than 76.7% of low molecular weight fractions (<20 kDa) that end up in the effluent. Higher applied flux facilitated the rapid formation dynamic layer which enabled a satisfactory effluent quality. Microbial community analysis revealed that during the operation the archaeal community was relatively stable while obvious changes took place in the bacterial community. Introduction of dye Remazol Brilliant Blue R (RBBR) to the AnDMBR increased the abundances of phyla of Proteobacteria and Spirochaetae whereas fractions of Firmicutes and Euryarchaeota decreased obviously. Furthermore, relative stable abundances of phyla Aminicenantes, Bacteroidetes, Thermotogae and Chloroflexi among the top six phyla detected in the system ensured a healthy anaerobic degradation environment for RBBR wastewater treatment.

Microbial community succession and its correlation with reactor performance in a sponge membrane bioreactor coupled with fiber-bundle anoxic bio-filter for treating saline mariculture wastewater

The application of MBR in high saline wastewater treatment is mainly constrained by poor nitrogen removal and severe membrane fouling caused by high salinity stress. A novel carriers-enhanced MBR system was successfully developed for treating saline mariculture wastewater, which showed efficient TN removal (93.2%) and fouling control. High-throughput sequencing revealed the enhancement mechanism of bio-carriers under high saline condition. Bio-carriers substantially improved the community structure, representatively, nitrifiers abundance (Nitrosomonas, Nitrospira) increased from 2.18% to 9.57%, abundance of denitrifiers (Sulfurimonas, Thermogutta, etc.) also rose from 3.81% to 14.82%. Thereby, the nitrogen removal process was enhanced. Noteworthy, ammonia oxidizer (Nitrosomonas, 8.26%) was the absolute dominant nitrifiers compared with nitrite oxidizer (Nitrospira, 1.13%). This supported the finding of shortcut nitrification-denitrification process in hybrid system. Moreover, a series of biomacromolecule degraders (Lutibacterium, Cycloclasticus, etc.) were detected in bio-carriers, which could account for the mitigation of membrane fouling as result of EPS and SMP degradation.

Comparing powdered and granular activated carbon addition on membrane fouling control through evaluating the impacts on mixed liquor and cake layer properties in anaerobic membrane bioreactors

Concerning the lack of comprehensive study on the impact of powdered and granular activated carbon (PAC and GAC) on AnMBR, their impact on treatment performance, mixed liquor and cake layer properties and membrane fouling behaviors were further investigated. High COD removal efficiencies (>90%) and COD converting to CH₄ rates (>70%) were achieved. GAC greatly increased extracellular polymeric substances (EPS) production in mixed liquor, but significantly reduced biosolids deposited on membrane surface; while PAC largely increased proteins and polysaccharides on membrane surface. In addition, PAC decreased, whereas GAC increased particle sizes. Fouling rates showed PAC and GAC addition effectively alleviated membrane fouling at HRT 8 h, and GAC remarkably postponed the occurrence of the transmembrane pressure jump and extended membrane service time. This study clarified the roles of GAC and PAC on membrane fouling control over long-term operation, which provides the basis for decision-making in practical application.

Linking process performances and core microbial community structures in anaerobic membrane bioreactor with rotatory disk (ARMBR) system fed with high-strength food waste recycling wastewater

This study first evaluated the process performances and microbial community structures of anaerobic rotary membrane bioreactor (ARMBR) fed with food waste recycling wastewater (FRW). Three identical ARMBRs were operated under different organic loading rate (OLR) conditions (1.5, 3.0, and 6.0 kg COD m^-3 d^-1) after the same start-up periods. The start-up performances and archaeal community structures differed among the ARMBRs, probably due to the sudden OLR shock. After the start-up, bio-methane was stably produced until the end of the operational period, with all of the ARMBRs showing >95% COD removal efficiency. Methanosaeta spp. was the predominant methanogen; diverse hydrogenotrophic methanogens co-existed. Bacteroidetes-like bacteria and Candidatus Cloacamonas acted as major fermentative bacteria producing acetate or hydrogen for the growth of methanogens. The results suggest that our ARMBR system can be a promising option to manage high-strength organic wastewater such as FRW.

Effects of sodium hypochlorite concentration on the methanogenic activity in an anaerobic fluidized membrane bioreactor

The effect of membrane cleaning chemical, NaOCl on specific acetoclastic methanogenic activity (SAMA) of biomass in the anaerobic fluidized membrane bioreactors (AFMBRs) was assessed. Granular activated carbon (GAC) was used as a fluidizing media in the AFMBR to provide membrane scouring effect and surface for biofilm attachment. Effect of NaOCl on methane production was negligible for GAC with biofilm (bGAC) samples up to 150 mg NaOCl/g VSS, but was significant for the bulk liquid samples with noticeable lag period over 300 h even at the dosage of 50 mg NaOCl/g VSS. The toxicity of NaOCl on methane production was reduced in samples with virgin GAC (vGAC) by allowing 14 days of biomass buildup period prior to NaOCl addition, although the vGAC alone did not alleviate the toxicity. The results revealed that NaOCl concentrations beyond 100 mg/L within the reactor inhibited methanogenic activity and the effects were more pronounced on suspended biomass than the immobilized biomass on GAC.

Highly synergistic effects on ammonium removal by the co-system of Pseudomonas stutzeri XL-2 and modified walnut shell biochar

Pseudomonas stutzeri strain XL-2 presented efficient ammonium removal due to heterotrophic nitrification-aerobic denitrification. The modified walnut shell biochar also showed ammonium adsorption due to chemical interaction. The complex of modified biochar and strain XL-2 exhibited excellent synergistic effects on ammonium removal, especially in unfavorable environment. The maximum average ammonium removal rate of the complex was 4.40 mg·L^-1·h^-1, which was 3.01 times higher than that of pure bacteria and 5.57 times higher than that of biochar. A large number of irregular pores and hydrophilic functional groups promoted the immobilization of strain XL-2 on biochar. Adsorption of ammonium, high specific surface area and release of Mg²⁺ by biochar enhanced biodegradation of strain XL-2. Approximately 96.34%-98.73% of ammonium was removed in a sequencing batch reactor (SBR) inoculating with the complex of strain XL-2 and biochar, which was much higher than the treatment efficiency of free bacteria in SBR.

Anaerobic treatment of N,N-dimethylformamide-containing high-strength wastewater by submerged anaerobic membrane bioreactor with a co-cultured inoculum

The anaerobic treatment of wastewater containing approximately 2000 mg L^-1N,N-dimethylformamide (DMF) was conducted by a lab-scale submerged anaerobic membrane bioreactor (SAnMBR). The inoculum consisted of aerobic DMF-hydrolyzing activated sludge (DAS) and anaerobic digested sludge (ADS). A rapid start-up was achieved with thorough DMF methanogenic degradation on the first day. The results of a 250-day long-term experiment demonstrated that under a low organic loading rate (OLR) of 3.14-4.16 g COD L^-1 d^-1, SAnMBR maintained excellent DMF removal efficiency along with high methane conversion. However, the elevation of OLR significantly limited DMF hydrolysis. When OLR exceeded 6.54 g COD L^-1 d^-1, both removal efficiency and methane production dramatically dropped. The DMF-hydrolyzing bacteria originating from the DAS gradually decayed under the anaerobic condition, resulting in the weak hydrolysis of DMF. The shortening of hydraulic retention time (HRT) is not recommended for the SAnMBR because severe membrane fouling occurred when HRT was shortened to 8 h. To handle high OLRs, an appropriate solution is to maintain a low F/M ratio by increasing both the influent DMF concentration and sludge concentration. The high CH₄ content in the biogas, exceeding 85%, was shown to be the reason for the suitability of anaerobic treatment to DMF. Some improvements which would help to maintain the effective hydrolysis are proposed: a side-stream system to replenish DAS to the SAnMBR is helpful; slight dosage of nitrate could also help to enrich the DMF-hydrolyzing bacteria; and the co-digestion of DMF and other organics might be convenient to establish a stable DMF-degrading consortium.

Performance Evaluation of a Thermophilic Anaerobic Membrane Bioreactor for Palm Oil Wastewater Treatment

Anaerobic treatment processes have achieved popularity in treating palm oil mill effluent due to its high treatability and biogas generation. The use of externally submerged membranes with anaerobic reactors promotes the retention of the biomass in the reactor. This study was conducted in thermophilic conditions with the Polytetrafluoroethylene hollow fiber (PTFE-HF) membrane which was operated at 55 °C. The reactor was operated at Organic Loading Rates (OLR) of 2, 3, 4, 6, 8, and 10 kg Chemical Oxygen Demand (COD)/m³·d to investigate the treatment performance and the membrane operation. The efficiency of the COD removal achieved by the system was between 93-98%. The highest methane yield achieved was 0.56 m³ CH₄/kg COD_r. The reactor mixed liquor volatile suspended solids (MLVSS) was maintained between 11.1 g/L to 20.9 g/L. A dead-end mode PTFE hollow fiber microfiltration was operated with the constant flux of 3 LMH (L/m²·h) in permeate recirculation mode to separate the clear final effluent and retain the biomass in the reactor. Membrane fouling was one of the limiting factors in the membrane bioreactor application. In this study, organic fouling was observed to be 93% of the total membrane fouling.

An overview of the recent trends on the waste valorization techniques for food wastes

A critical and up-to-date review has been conducted on the latest individual valorization technologies aimed at the generation of value-added by-products from food wastes in the form of bio-fuels, bio-materials, value added components and bio-based adsorbents. The aim is to examine the associated advantages and drawbacks of each technique separately along with the assessment of process parameters affecting the efficiency of the generation of the bio-based products. Challenges faced during the processing of the wastes to each of the bio-products have been explained and future scopes stated. Among the many hurdles encountered in the successful and high yield generation of the bio-products is the complexity and variability in the composition of the food wastes along with the high inherent moisture content. Also, individual technologies have their own process configurations and operating parameters which may affect the yield and composition of the desired end product. All these require extensive study of the composition of the food wastes followed by their effective pre-treatments, judicial selection of the technological parameters and finally optimization of not only the process configurations but also in relation to the input food waste material. Attempt has also been made to address the hurdles faced during the implementation of such technologies on an industrial scale.

Volatile fatty acids and biogas recovery using thermophilic anaerobic membrane distillation bioreactor for wastewater reclamation

The effects of bioreactor temperatures and salinities of an anaerobic membrane distillation bioreactor (anMDBR) on the permeation performance and their potential recovery of bioresources were fully examined in this study. To the best of our knowledge, this is the first study of a lab-scale anMDBR process utilizing sub-merged hollow fiber membranes. The hybrid system utilizing both membrane distillation (MD) and anaerobic bioreactors achieved 99.99% inorganic salt rejection regardless the operation temperatures and high initial flux from (2-4 L m^-2 h^-1) at 45-65 °C. However, after 7-day operation, the flux dropped by 16-50% proportional to the bioreactor temperatures. It was found that the effects of bioreactor temperatures had strong impacts on both the permeation performance and fouling behavior while salinity had insignificant effect. A compact non-porous fouling layer was observed on the membrane surface from the bioreactor operated at 65 °C while only a few depositions was found on the membrane from 45 °C bioreactor. In the present study, the optimal anMDBR temperature was found to be 45 °C, showing a balanced biogas production and membrane permeation performance including less fouling formation. At this bioreactor temperature (45 °C), the biogas yield was 0.14 L/g COD_removal, while maintaining a methane recovery of 42% in the biogas, similar recovery to those at bioreactor temperatures of 55 and 65 °C. The potential recovery of volatile fatty acids made anMDBR a more economically efficient system, in addition to its lower operation cost and smaller footprint compared with most other technologies for on-site wastewater treatment.

Polytetrafluoroethylene (PTFE) hollow fiber AnMBR performance in the treatment of organic wastewater with varying salinity and membrane cleaning behavior

PTFE hollow fiber anaerobic membrane bio-reactor (AnMBR) performance was investigated in the treatment of organic wastewater, with varying salinity and PTFE membrane cleaning behavior. The AnMBR was operated for 226 days, with a total and biological COD removal efficiency of 97.2% and 89.9% respectively, at a NaCl concentration of 35 g L^-1. A high number of Proteobacteria (38.2%) and Bacteroidetes (25.9%) were present in the system, with an increase in membrane fouling rate from 1.88 × 10¹¹ to 2.63 × 10¹¹ m^-1 d^-1 with higher salinity. The effects of soluble microbial products (SMP), extracellular polymeric substances (EPS), low molecular-weight (LMW) carbohydrates, sludge particle size and inorganic element accumulation, were evaluated on membrane fouling. Flux recovery of fouled PTFE membranes reached 91.6% with offline cleaning. Overall, results indicate that PTFE hollow fiber AnMBR provides a promising method for the treatment of saline organic wastewater.

Effect of magnetic powder on membrane fouling mitigation and microbial community/composition in membrane bioreactors (MBRs) for municipal wastewater treatment

This study aims to investigate the usefulness of magnetic powder addition in membrane bioreactors (MBRs) for membrane fouling mitigation and its effect on microbial community and composition. The comparison between the two MBRs (one with magnetic powder (MAS-MBR) and one without magnetic powder (C-MBR)) was carried out to treat synthetic municipal wastewater. Results showed that bioflocculation and adsorption of magnetic powder contributed only minimally to membrane fouling mitigation while the slower fouling rate might be ascribed to magnetic bio-effect. The macromolecules (larger than 500 kDa and 300-500 kDa) of soluble microbial product from the MAS-MBR were reduced by 24.06% and 11.11%, respectively. High-throughput sequencing demonstrated the most abundant genera of biofilm sludge indicated lower abundance in bulk sludge from the MAS-MBR compared to the C-MBR. It is possible that less membrane fouling is connected to reductions in large molecules and pioneer bacteria from bulk sludge.

A modelling approach to study the fouling of an anaerobic membrane bioreactor for industrial wastewater treatment

An Anaerobic Membrane BioReactors (AnMBR) model is presented in this paper based on the combination of a simple fouling model and the Anaerobic Model 2b (AM2b) to describe biological and membrane dynamic responses in an AnMBR. In order to enhance the model calibration and validation, Trans-Membrane Pressure (TMP), Total Suspended Solid (TSS), COD, Volatile Fatty Acid (VFA) and methane production were measured. The model shows a satisfactory description of the experimental data with R²≈0.9 for TMP data and R²≈0.99 for biological parameters. This new model is also proposed as a numerical tool to predict the deposit mass composition of suspended solid and Soluble Microbial Products (SMP) on the membrane surface. The effect of SMP deposit on the TMP jump phenomenon is highlighted. This new approach offers interesting perspectives for fouling prediction and the on-line control of an AnMBR process.

Effects of bamboo charcoal on fouling and microbial diversity in a flat-sheet ceramic membrane bioreactor

Membrane fouling is a problem in full-scale membrane bioreactors. In this study, bamboo charcoal (BC) was evaluated for its efficacy in alleviating membrane fouling in flat-sheet membrane bioreactors treating municipal wastewater. The results showed that BC addition markedly improved treatment performance based on COD, NH₄⁺-N, total nitrogen, and total phosphorus levels. Adding BC slowed the increase in the trans-membrane pressure rate and resulted in lower levels of soluble microbial products and extracellular polymeric substances detected in the flat-sheet membrane bioreactor. BC has a porous structure, and a large quantity of biomass was detected using scanning electron microscopy. The microbial community analysis results indicated that BC increased the microbial diversity and Aminomonas, Anaerofustis, uncultured Anaerolineaceae, Anaerolinea, and Anaerotruncus were found in higher abundances in the reactor with BC. BC addition is an effective method for reducing membrane fouling, and can be applied to full-scale flat-sheet membrane bioreactors to improve their function.

Microbial community composition and function in a pilot-scale anaerobic-anoxic-aerobic combined process for the treatment of traditional Chinese medicine wastewater

Biodegradation of traditional Chinese medicine (TCM) wastewater was investigated in a pilot-scale anaerobic-anoxic-aerobic combined process, which was composed of an expanded granular sludge blanket (EGSB) reactor, a hydrolysis acidification (HA) reactor and a biological contact oxidation (BCO) reactor. In stable stage, the average values of COD and color in the combined process effluent were 45.7mgL^-1 and 13 times, respectively. Excellent linear relations (R²>0.915) were achieved between color and UV₂₅₄ at three color levels. Comprehensive community structures of the combined process were analysed by Illumina MiSeq Sequencing, which revealed that microbial community in the aerobic reactor had the greatest diversity and richness. Bacteroidetes, Firmicutes and Proteobacteria were dominant phyla in the three reactors, and Bacteroidales, Geobacter, ZB2 were the predominant functional microorganisms in the anaerobic, anoxic and aerobic reactors, respectively. Good removal efficiencies and presence of core microorganisms confirmed that the combined process was feasible for treating TCM wastewater.

Effect of bioflocculation on fouling-related biofoulants in a membrane bioreactor during saline wastewater treatments

A membrane bioreactor (MBR) was operated in two modes; with and without the inoculation of marine Arthrobacter cells, to investigate the effect of bioflocculation on membrane biofouling during saline wastewater treatments. The MBR-Arthrobacter system showed a higher resistance to membrane fouling than the normal MBR system. Lower concentrations of the fouling-related components and higher removal efficiencies of COD and NH₃-N were observed in the MBR-Arthrobacter system. The bioflocculation of Arthrobacter preferred to settle down the humic acid-like, fulvic acid-like and aromatic proteins components (larger biomolecules) rather than the soluble microbial by-product-like components (smaller biomolecules).