Peak flux performance and microbial removal by selected membrane bioreactor systems

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.

Interface behavior and removal mechanisms of human pathogenic viruses in anaerobic membrane bioreactor (AnMBR)

Effective removal of human pathogenic viruses is an indispensable yet rarely studied aspect for sustainable treatment of domestic wastewater by anaerobic membrane bioreactor (AnMBR). In this study, the interface behaviors and removal mechanisms of norovirus genogroup I (GI), genogroup II (GII), and rotavirus A from domestic wastewater was systematically investigated in a one-stage AnMBR. On average, norovirus GI, GII and rotavirus were reduced by 4.64, 5.00, and 2.31 logs, respectively. Viruses tended to be transferred to larger-sized suspended solids from sewage influent to the mixed liquor, and the weight-specific concentration of the virus in >100 μm particles of the mixed liquor was significantly higher than that of sewage, indicating a particle scale-dependent affinity with the virus. In-series membrane filtration test showed the main contribution of the membrane retention, which was dominated by the bio-cake layer and the pristine membrane, while the membrane and associated pore foulants can retain viruses in a filtration resistance-efficient way. An unsteady-state mass balance model revealed that free viruses in the bulk liquid of AnMBR were minimally attached to the cake layer but mainly retained by the membrane and pore foulants (>99%). In addition, despite the small virus decay rates in the mixed liquor, the associated contribution increased with run time due to the prolonged sludge retention time. These insights into virus behaviors and removal mechanisms may provide novel regulation strategies for enhanced virus removal by AnMBR.

A review of the potential of conventional and advanced membrane technology in the removal of pathogens from wastewater

Consumption of pathogenic contaminated water has claimed the lives of many people. Hence, this scenario has emphasized the urgent need for research methods to avoid, treat and eliminate harmful pathogens in wastewater. Therefore, effective water treatment has become a matter of utmost importance. Membrane technology offers purer, cleaner, and pathogen-free water through the water separation method via a permeable membrane. Advanced membrane technology such as nanocomposite membrane, membrane distillation, membrane bioreactor, and photocatalytic membrane reactor can offer synergistic effects in removing pathogen through the integration of additional functionality and filtration in a single chamber. This paper also comprehensively discussed the application, challenges, and future perspective of the advanced membrane technology as a promising alternative in battling pathogenic microbial contaminants, which will also be beneficial and valuable in managing pandemics in the future as well as protecting human health and the environment. In addition, the potential of membrane technology in battling the ongoing global pandemic of coronavirus disease 2019 (COVID-19) was also discussed briefly.

Virus removal during sewage treatment by anaerobic membrane bioreactor (AnMBR): The role of membrane fouling

Anaerobic membrane bioreactor (AnMBR) is a low-energy and promising solution for sewage treatment. During the treatment, the fouled membrane of AnMBR is recognized as an important barrier against pathogenic viruses. Here, the role of membrane fouling of an AnMBR at room temperature in the virus removal was investigated using MS2 bacteriophage as a virus surrogate. Results revealed that the virus removal efficiency of AnMBR was in the range of 0.2 to 3.6 logs, gradually increasing with the course of AnMBR operation. Virus removal efficiency was found to be significantly correlated with transmembrane pressure (R²=0.92, p<0.01), especially in the rapid fouling stage, indicating that membrane fouling was the key factor in the virus removal. The proportion of virus decreased from 52.03% to 15.04% in the membrane foulants when membrane fouling was aggravating rapidly, yet increased from 0.74% to 21.52% in the mixed liquor. Meanwhile, the permeate flux dramatically dropped. These imply that the primary rejection mechanism of virus by membrane in the slow fouling stage is the virus adsorption onto membrane, while the sieving effect is the main reason in the rapid fouling stage. Ex-situ virus rejection test unveiled that the cake layer was the main contributor to the overall virus rejection, while the greatest resistance-specific virus rejection was provided by the organic pore blocking. This paper provides operation strategies to balance enhanced virus removal and high permeate flux by regulating the membrane fouling process.

Comparative effectiveness of membrane technologies and disinfection methods for virus elimination in water: A review

The pandemic of the 2019 novel coronavirus disease (COVID-19) has brought viruses into the public horizon. Since viruses can pose a threat to human health in a low concentration range, seeking efficient virus removal methods has been the research hotspots in the past few years. Herein, a total of 1060 research papers were collected from the Web of Science database to identify technological trends as well as the research status. Based on the analysis results, this review elaborates on the state-of-the-art of membrane filtration and disinfection technologies for the treatment of virus-containing wastewater and drinking water. The results evince that membrane and disinfection methods achieve a broad range of virus removal efficiency (0.5-7 log reduction values (LRVs) and 0.09-8 LRVs, respectively) that is attributable to the various interactions between membranes or disinfectants and viruses having different susceptibility in viral capsid protein and nucleic acid. Moreover, this review discusses the related challenges and potential of membrane and disinfection technologies for customized virus removal in order to prevent the dissemination of the waterborne diseases.

Physico-chemical and biological treatment strategies for converting municipal wastewater and its residue to resources

An increase in urbanization and industrialization has not only contributed to an improvement in the lifestyle of people, but it has also contributed to a surge in the generation of wastewater. To date, conventional physico-chemical and biological treatment methods are widely used for the treatment of wastewater. However, the efficient operation of these systems require substantial operation and maintenance costs, and the application of novel technologies for the treatment and disposal of sludge/residues. This review paper focuses on the application of different treatment options such as chemical, catalyst-based, thermochemical and biological processes for wastewater or sludge treatment and membrane-based technologies (i.e. pressure-driven and non-pressure driven) for the separation of the recovered products from wastewater and its residues. As evident from the literature, a wide variety of treatment and resource recovery options are possible, both from wastewater and its residues; however, the lack of planning and selecting the most appropriate design (treatment train) to scale up from pilot to the field scale has limited its practical application. The economic feasibility of the selected technologies was critically analyzed and the future research prospects of resource recovery from wastewater have been outlined in this review.

Reduction of antibiotic resistance determinants in urban wastewater by ozone: Emphasis on the impact of wastewater matrix towards the inactivation kinetics, toxicity and bacterial regrowth

This study investigated the impact of bench-scale ozonation on the inactivation of total cultivable and antibiotic-resistant bacteria (faecal coliforms, Escherichia coli, Pseudomonas aeruginosa, Enterococcus spp., and total heterotrophs), and the reduction of gene markers (16S rRNA and intl1) and antibiotic resistance genes (qacEΔ1, sul1, aadA1 and dfrA1) indigenously present in wastewater effluents treated by membrane bioreactor (MBR) or conventional activated sludge (CAS). The Chick-Watson model-predicted ozone exposure (CT) requirements, showed that higher CT values were needed for CAS- than MBR-treated effluents to achieve a 3-log reduction of each microbial group, i.e., ~30 and 10 gO₃ min gDOC^-1 respectively. Ozonation was efficient in inactivating the examined antibiotic-resistant bacteria, and no bacterial regrowth was observed after 72 h. The genes abundance decreased significantly by ozone, but an increase in their abundance was detected 72 h after storage of the treated samples. A very low removal of DOC was achieved and at the same time phyto- and eco-toxicity increased after the ozonation treatment in both wastewater matrices. The gene abundance, regrowth and toxicity results of this study may be of high environmental significance for comprehensive evaluation of ozone and may guide future studies in assessing these parameters for other oxidants/disinfectants.

Efficacy of electrochemical membrane bioreactor for virus removal from wastewater: Performance and mechanisms

Wastewater treatment facilities play pivotal roles in preventing the transmission of water-borne viruses and protecting human health. In this study, a new electrochemical membrane bioreactor (EMBR) was proposed to achieve a long-lasting and efficient removal of virus from wastewater. Results showed that applying a low electric field (2.0 V) in EMBR system could achieve ~100% removal efficiency at both batch tests and continuous flow experiments. In contrast, the control MBR, without the exertion of electric field, exhibited a very low removal efficiency (19.8% on average). Moreover, the fouling in EMBR was significantly mitigated, which enabled its operation duration almost 3 times longer than that of the control. Further explorations suggested that the reactive oxidants generated on electrodes in the EMBR system were mainly responsible for MS2 removal. This study demonstrated the potential of utilizing the EMBR process to achieve an enhanced virus disinfection efficiency during the wastewater treatment process.

Virus removal by membrane bioreactors: A review of mechanism investigation and modeling efforts

The increasing pressure on the global water supply calls for more advanced solutions with higher efficiency and better sustainability, leading to the promptly developing water reclamation and reuse schemes including treatment technologies and risk management strategies where microbial safety is becoming a crucial aspect in the interest of public health. Backed up by the development of membrane technology, membrane bioreactors (MBR) have received substantial attention for their superiority over conventional treatment methods in many ways and are considered promising in the water reclamation realm. This review paper provides an overview of the efforts made to manage and control the potential waterborne viral disease risks raised by the use of effluent from MBR treatment processes, including the mechanisms involved in the virus removal process and the attempts to model the dynamics of the removal process. In principle, generalized and integrated virus removal models that provide insight into real-time monitoring are urgently needed for advanced real-time control purpose. Future studies of approaches that can well handle the inherent uncertainty and nonlinearity of the complex removal process are crucial to the development and promotion of related technologies.

Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-Of-The-Art and Performance Analysis

Wastewater reuse as a sustainable, reliable and energy recovery concept is a promising approach to alleviate worldwide water scarcity. However, the water reuse market needs to be developed with long-term efforts because only less than 4% of the total wastewater worldwide has been treated for water reuse at present. In addition, the reclaimed water should fulfill the criteria of health safety, appearance, environmental acceptance and economic feasibility based on their local water reuse guidelines. Moreover, municipal wastewater as an alternative water resource for non-potable or potable reuse, has been widely treated by various membrane-based treatment processes for reuse applications. By collecting lab-scale and pilot-scale reuse cases as much as possible, this review aims to provide a comprehensive summary of the membrane-based treatment processes, mainly focused on the hydraulic filtration performance, contaminants removal capacity, reuse purpose, fouling resistance potential, resource recovery and energy consumption. The advances and limitations of different membrane-based processes alone or coupled with other possible processes such as disinfection processes and advanced oxidation processes, are also highlighted. Challenges still facing membrane-based technologies for water reuse applications, including institutional barriers, financial allocation and public perception, are stated as areas in need of further research and development.

Potential and limitation of fluorescence-based membrane integrity monitoring (FMIM) for reverse osmosis membranes

In wastewater recycle for potable purposes, virus removal is the most critical issue from the public health stand point. Therefore, the regulatory agency sets minimum virus removal efficiencies that must be met by combining multiple treatment processes. In most potable reuse processes, reverse osmosis (RO) plays a critical role by removing salts, viruses, dissolved organic matters, etc. It has been reported that RO removes viruses at over 6 log efficiencies, but it receives no more than 2 log credits from regulatory agencies due to the lack of sensitive integrity monitoring technologies better than conductivity-based technologies. In recent years, fluorescence-based membrane integrity monitoring (FMIM) has drawn special attention because of its simplicity, capability of continuous monitoring, and the high resolution. Lab and field studies have shown FMIM can provide around 4 log resolution for commercially available RO membranes. In this study, potential and limitation of current FMIM technology are reviewed. Further, ideas to improve the resolution beyond 4 log are suggested.

Removal of Antibiotic-Resistant Bacteria and Antibiotic Resistance Genes Affected by Varying Degrees of Fouling on Anaerobic Microfiltration Membranes

An anaerobic membrane bioreactor was retrofitted with polyvinylidene fluoride (PVDF) microfiltration membrane units, each of which was fouled to a different extent. The membranes with different degrees of fouling were evaluated for their efficiencies in removing three antibiotic-resistant bacteria (ARB), namely, bla_NDM-1-positive Escherichia coli PI-7, bla_CTX-M-15-positive Klebsiella pneumoniae L7, and bla_OXA-48-positive E. coli UPEC-RIY-4, as well as their associated plasmid-borne antibiotic resistance genes (ARGs). The results showed that the log removal values (LRVs) of ARGs correlated positively with the extent of membrane fouling and ranged from 1.9 to 3.9. New membranes with a minimal foulant layer could remove more than 5 log units of ARB. However, as the membranes progressed to subcritical fouling, the LRVs of ARB decreased at increasing operating transmembrane pressures (TMPs). The LRV recovered back to 5 when the membrane was critically fouled, and the achieved LRV remained stable at different operating TMPs. Furthermore, characterization of the surface attributed the removal of both the ARB and ARGs to adsorption, which was facilitated by an increasing hydrophobicity and a decreasing surface ζ potential as the membranes fouled. Our results indicate that both the TMP and the foulant layer synergistically affected ARB removal, but the foulant layer was the main factor that contributed to ARG removal.

Anaerobic Membrane Bioreactor Effluent Reuse: A Review of Microbial Safety Concerns

Broad and increasing interest in sustainable wastewater treatment has led a paradigm shift towards more efficient means of treatment system operation. A key aspect of improving overall sustainability is the potential for direct wastewater effluent reuse. Anaerobic membrane bioreactors (AnMBRs) have been identified as an attractive option for producing high quality and nutrient-rich effluents during the treatment of municipal wastewaters. The introduction of direct effluent reuse does, however, raise several safety concerns related to its application. Among those concerns are the microbial threats associated with pathogenic bacteria as well as the emerging issues associated with antibiotic-resistant bacteria and the potential for proliferation of antibiotic resistance genes. Although there is substantial research evaluating these topics from the perspectives of anaerobic digestion and membrane bioreactors separately, little is known regarding how AnMBR systems can contribute to pathogen and antibiotic resistance removal and propagation in wastewater effluents. The aim of this review is to provide a current assessment of existing literature on anaerobic and membrane-based treatment systems as they relate to these microbial safety issues and utilize this assessment to identify areas of potential future research to evaluate the suitability of AnMBRs for direct effluent reuse.

Dominance of candidate Saccharibacteria in a membrane bioreactor treating medium age landfill leachate: Effects of organic load on microbial communities, hydrolytic potential and extracellular polymeric substances

A membrane bioreactor (MBR), accomplishing high nitrogen removal efficiencies, was evaluated under various landfill leachate concentrations (50, 75 and 100% v/v). Proteinous and carbohydrate extracellular polymeric substances (EPS) and soluble microbial product (SMP) were strongly correlated (p<0.01) with organic load, salinity and NH₄⁺-N. Exceptionally high β-glucosidase activities (6700-10,100Ug^-1) were determined during MBR operation with 50% v/v leachate, as a result of the low organic carbon availability that extendedly induced β-glucosidases to breakdown the least biodegradable organic fraction. Illumina sequencing revealed that candidate Saccharibacteria were dominant, independently of the leachate concentration applied, whereas other microbiota (21.2% of total reads) disappeared when undiluted leachate was used. Fungal taxa shifted from a Saccharomyces- to a newly-described Cryptomycota-based community with increasing leachate concentration. Indeed, this is the first report on the dominance of candidate Saccharibacteria and on the examination of their metabolic behavior in a bioreactor treating real wastewater.

Molecular-based detection of potentially pathogenic bacteria in membrane bioreactor (MBR) systems treating municipal wastewater: a case study

Although membrane bioreactor (MBR) systems provide better removal of pathogens compared to conventional activated sludge processes, they do not achieve total log removal. The present study examines two MBR systems treating municipal wastewater, one a full-scale MBR plant and the other a lab-scale anaerobic MBR. Both of these systems were operated using microfiltration (MF) polymeric membranes. High-throughput sequencing and digital PCR quantification were utilized to monitor the log removal values (LRVs) of associated pathogenic species and their abundance in the MBR effluents. Results showed that specific removal rates vary widely regardless of the system employed. Each of the two MBR effluents' microbial communities contained genera associated with opportunistic pathogens (e.g., Pseudomonas, Acinetobacter) with a wide range of log reduction values (< 2 to >5.5). Digital PCR further confirmed that these bacterial groups included pathogenic species, in several instances at LRVs different than those for their respective genera. These results were used to evaluate the potential risks associated both with the reuse of the MBR effluents for irrigation purposes and with land application of the activated sludge from the full-scale MBR system.

Characteristics and trihalomethane formation reactivity of dissolved organic matter in effluents from membrane bioreactors with and without filamentous bulking

In this study, synthetic wastewater was treated by two identical membrane bioreactors (MBRs): the normal sludge MBR (NS-MBR) and the bulking sludge MBR (BS-MBR). Effects of filamentous bulking on the characteristics and trihalomethane (THM) formation reactivity of MBR effluent dissolved organic matter (EfOM) were investigated. Filamentous sludge bulking had no significant influence on the regulated MBR effluent water quality except NO2-N and NO3-N. NS-MBR effluent had more low molecular weight (LMW) (<5kDa) EfOM (92.43%) than BS-MBR (75.18%). About two-thirds of EfOM from BS-MBR were hydrophilic substances. On the contrary, EfOM from NS-MBR exhibited higher hydrophobicity. The ratio of polysaccharides and proteins in MBR effluents increased after filamentous bulking. There were more protein-like materials, fulvic acid-like and humic acid-like in BS-MBR EfOM. The THM formation reactivity of BS-MBR EfOM was 30.15% of NS-MBR EfOM, whereas BS-MBR EfOM exhibited higher formation reactivity of bromine containing species.

Effect of pressure relaxation and membrane backwash on adenovirus removal in a membrane bioreactor

Pressure relaxation and permeate backwash are two commonly used physical methods for membrane fouling mitigation in membrane bioreactor (MBR) systems. In order to assess the impact of these methods on virus removal by MBRs, experiments were conducted in a bench-scale submerged MBR treating synthetic wastewater. The membranes employed were hollow fibers with the nominal pore size of 0.45 μm. The experimental variables included durations of the filtration (tTMP>0), pressure relaxation (tTMP=0) and backwash (tTMP<0) steps. Both pressure relaxation and permeate backwash led to significant reductions in removal of human adenovirus (HAdV). For the same value of tTMP>0/tTMP=0, longer filtration/relaxation cycles (i.e. larger tTMP+tTMP=0) led to higher transmembrane pressure (TMP) but did not have a significant impact on HAdV removal. A shorter backwash (tTMP<0 = 10 min) at a higher flow rate (Q = 40 mL/min) resulted in more substantial decreases in TMP and HAdV removal than a longer backwash (tTMP<0 = 20 min) at a lower flow rate (Q = 20 mL/min) even though the backwash volume (QtTMP<0) was the same. HAdV removal returned to pre-cleaning levels within 16 h after backwash was applied. Moderate to strong correlations (R(2) = 0.63 to 0.94) were found between TMP and HAdV removal.

Removal properties of human enteric viruses in a pilot-scale membrane bioreactor (MBR) process

In order to evaluate removal properties of human enteric viruses from wastewater by a membrane bioreactor (MBR), influent, anoxic and oxic mixed liquor, and membrane effluent samples were collected in a pilot-scale anoxic-oxic MBR process for 16 months, and concentrations of enteroviruses, norovirus GII, and sapoviruses were determined by real-time PCR using murine norovirus as a process control. Mixed liquor samples were separated into liquid and solid phases by centrifugation, and viruses in the bulk solution and those associated with mixed liquor suspended solids (MLSS) were quantified. Enteroviruses, norovirus GII, and sapoviruses were detected in the influent throughout the sampling period (geometrical mean, 4.0, 3.1, and 4.4 log copies/mL, respectively). Enterovirus concentrations in the solid phase of mixed liquor were generally lower than those in the liquid phase, and the mean log reduction value between influent and anoxic mixed liquor was 0.40 log units. In contrast, norovirus GII and sapovirus concentrations in the solid phase were equal to or higher than those in the liquid phase, and higher log reduction values (1.3 and 1.1 log units, respectively) were observed between influent and anoxic mixed liquor. This suggested that enteroviruses were less associated with MLSS than norovirus GII and sapoviruses, resulting in lower enterovirus removal in the activated sludge process. Enteroviruses and norovirus GII were detected in the MBR effluent but sapoviruses were not in any effluent samples. When MLSS concentration was reduced to 50-60% of a normal operation level, passages of enteroviruses and norovirus GII through a PVDF microfiltration membrane were observed. Since rejection of viruses by the membrane was not related to trans-membrane pressure which was monitored as a parameter of membrane fouling, the results indicated that adsorption to MLSS plays an important role in virus removal by an MBR, and removal properties vary by viruses reflecting different adsorptive behavior to MLSS. Our observations suggested that sapoviruses are more associated with MLSS and removed more efficiently than enteroviruses and norovirus GII.

Bacteriophage removal in a full-scale membrane bioreactor (MBR) - Implications for wastewater reuse

The aim of this study was to assess the potential removal efficacy of viruses in a full-scale membrane bioreactor (MBR) wastewater reuse system, using a range of indigenous and 'spiked' bacteriophages (phages) of known size and morphology. Samples were taken each week for three months from nine locations at each treatment stage of the water recycling plant (WRP) and tested for a range of microbiological parameters (n = 135). Mean levels of faecal coliforms were reduced to 0.3 CFU/100 ml in the MBR product and were undetected in samples taken after the chlorination stage. A relatively large reduction (5.3 log) in somatic coliphages was also observed following MBR treatment. However, F-specific and human-specific (GB124) phages were less abundant at all stages, and demonstrated log reductions post-MBR of 3.5 and 3.8, respectively. In 'spiking' experiments, suspended 'spiked' phages (MS2 and B-14) displayed post-MBR log reductions of 2.25 and 2.30, respectively. The removal of these suspended phages, which are smaller than the membrane pore size (0.04 μm), also highlights the possible role of the membrane biofilm as an effective additional barrier to virus transmission. The findings from this study of a full-scale MBR system demonstrate that the enumeration of several phage groups may offer a practical and conservative way of assessing the ability of MBR to remove enteric viruses of human health significance. They also suggest that phage removal in MBR systems may be highly variable and may be closely related on the one hand to both the size and morphology of the viruses and, on the other, to whether or not they are attached to solids.

Risk assessment of Giardia from a full scale MBR sewage treatment plant caused by membrane integrity failure

Membrane bioreactors (MBR) are highly efficient at intercepting particles and microbes and have become an important technology for wastewater reclamation. However, many pathogens can accumulate in activated sludge due to the long residence time usually adopted in MBR, and thus may pose health risks when membrane integrity problems occur. This study presents data from a survey on the occurrence of water-borne Giardia pathogens in reclaimed water from a full-scale wastewater treatment plant with MBR experiencing membrane integrity failure, and assessed the associated risk for green space irrigation. Due to membrane integrity failure, the MBR effluent turbidity varied between 0.23 and 1.90 NTU over a period of eight months. Though this turbidity level still met reclaimed water quality standards (≤5 NTU), Giardia were detected at concentrations of 0.3 to 95 cysts/10 L, with a close correlation between effluent turbidity and Giardia concentration. All β-giardin gene sequences of Giardia in the WWTP influents were genotyped as Assemblages A and B, both of which are known to infect humans. An exponential dose-response model was applied to assess the risk of infection by Giardia. The risk in the MBR effluent with chlorination was 9.83×10(-3), higher than the acceptable annual risk of 1.0×10(-4). This study suggested that membrane integrity is very important for keeping a low pathogen level, and multiple barriers are needed to ensure the biological safety of MBR effluent.

Mechanisms of pathogenic virus removal in a full-scale membrane bioreactor

Four pathogenic virus removal mechanisms were investigated in a full-scale membrane bioreactor (MBR; nominal pore size 0.04 μm): (i) attachment of virus to mixed liquor solids; (ii) virus retention by a just backwashed membrane; (iii) virus retention by the membrane cake layer; and (iv) inactivation. We quantified adenovirus, norovirus genogroup II (GII), and F+ coliphage in the influent wastewater, the solid and liquid fractions of the mixed liquor, return flow, and permeate using quantitative PCR (adenovirus and norovirus GII) and infectivity assays (F+ coliphage). Permeate samples were collected 4-5 days, 1 day, 3 h, and immediately after chlorine enhanced backwashes. The MBR achieved high log removals for adenovirus (3.9 to 5.5), norovirus GII (4.6 to 5.7), and F+ coliphage (5.4 to 7.1). The greatest contribution to total removal was provided by the backwashed membrane, followed by inactivation, the cake layer, and attachment to solids. Increases in turbidity and particle counts after backwashes indicated potential breakthrough of particles, but virus removal following backwashes was still high. This study demonstrates the ability of the MBR process to provide over 4 logs of removal for adenovirus and norovirus GII, even after a partial loss of the cake layer, and provides evidence for assigning virus disinfection credit to similar MBRs used to reclaim wastewater for reuse.

Impacts of powdered activated carbon addition on trihalomethane formation reactivity of dissolved organic matter in membrane bioreactor effluent

Characteristics and trihalomethane (THM) formation reactivity of dissolved organic matter (DOM) in effluents from two membrane bioreactors (MBRs) with and without powdered activated carbon (PAC) addition (referred to as PAC/MBR and MBR, respectively) were examined to investigate the effects of PAC addition on THM formation of MBR effluent during chlorination. PAC addition increased the specific UV absorbance. Hydrophobic DOM especially hydrophobic acids in PAC/MBR effluent (50%) were more than MBR effluent (42%). DOM with molecular weight <1 kDa constituted 12% of PAC/MBR effluent DOM, which was less than that of MBR effluent (16%). Data obtained from excitation and emission matrix fluorescence spectroscopy revealed that PAC/MBR effluent DOM contained more simple aromatic protein, but had less fulvic acid-like and soluble microbial by-product-like. PAC addition reduced the formation of bromine-containing THMs during chlorination of effluents, but increased THM formation reactivity of effluent DOM.

Influences of dissolved organic matter characteristics on trihalomethanes formation during chlorine disinfection of membrane bioreactor effluents

Dissolved organic matter (DOM) in MBR-treated municipal wastewater intended for reuse was fractionated through ultrafiltration and XAD-8 resin adsorption and characterized by fluorescence spectroscopy. To probe the influences of DOM characteristics on trihalomethanes (THMs) formation reactivity during chlorination, THMs yield and speciation of DOM fractions was investigated. It was found that chlorine reactivity of DOM decreased with the decrease of molecular weight (MW), and MW>30kDa fractions produced over 55% of total THMs in chlorinated MBR effluent. Hydrophobic organics had much higher THMs formation reactivity than hydrophilic substances. Particularly, hydrophobic acids exhibited the highest chlorine reactivity and contributed up to 71% of total THMs formation. Meanwhile, low-MW and hydrophilic DOM were susceptible to produce bromine-containing THMs. Of the fluorescent DOM in MBR effluent, aromatic moieties and humic acid-like had higher chlorine reactivity. Conclusively, macromolecular and hydrophobic organics containing aromatic moieties and humic acid-like must be removed to reduce THMs formation.

Impact of MBR cleaning and breaching on passage of selected microorganisms and subsequent inactivation by free chlorine

Membrane bioreactors (MBRs) produce better quality effluent compared to conventional treatment processes but they are still subjected to the same disinfection requirements as conventional processes by many regulatory agencies. A research study consisting of bench-, pilot- and full-scale studies was conducted to characterize effluents produced from an MBR system operating under routine and challenged conditions and to assess the disinfection requirements for these effluents. Membrane cleaning did not seem to pose a substantial risk with respect to passage of target microorganisms; however, the membrane under breached conditions (turbidity > 0.5 NTU) resulted in an increase in a total coliform bacterial concentration up to 8500 CFU/100 mL. Adenoviruses were always detected in MBR filtrate samples by PCR (method detection limit of 10(3) genome copies per 25 μL reaction) irrespective of the membrane cleaning or breaching status. Passage of MS-2 bacteriophage through a breached membrane was lower compared to total coliform bacteria potentially due to their lower densities in the mixed liquor. Despite an increase in microbial concentration, a free chlorine CT of 30 mg-min/L was sufficient to achieve greater than 5-log removal of seeded MS-2 bacteriophage and removal of total coliform bacteria at or below the method detection limit (2 CFU/100 mL) for samples with a filtrate turbidity of 1.0 NTU. If such lower CT were to be employed, a significant decrease in plant footprint and operational costs could be realized.

Validation of a full-scale membrane bioreactor and the impact of membrane cleaning on the removal of microbial indicators

The removal of microbial indicators through a full-scale membrane bioreactor (MBR) was characterised. The overall log reduction of Escherichia coli and total coliforms were in the range of 5.0-5.9log10 units, while the reduction of clostridia was marginally less at 4.9log10 units. Removal of bacteriophage was in excess of 4.6log10 units. The impact of membrane cleaning on the elimination of microbial indicators was also assessed since this had been identified by pilot-scale studies as a potential hazardous event. Membrane cleaning temporarily reduced the log removal values of E. coli and total coliforms each by 1log10 unit, but did not affect the removal of bacteriophage or clostridia. Very little research has previously examined the consequences of hazardous events on the performance of full-scale MBRs, and thus the findings presented here will facilitate improvements for the risk assessment and management of MBRs used in water recycling schemes.

Pseudomonas putida response in membrane bioreactors under salicylic acid-induced stress conditions

Starvation and changing feeding conditions are frequently characteristics of wastewater treatment plants. They are typical causes of unsteady-state operation of biological systems and provoke cellular stress. The response of a membrane bioreactor functioning under feed-induced stress conditions is studied here. In order to simplify and considerably amplify the response to stress and to obtain a reference model, a pure culture of Pseudomonas putida was selected instead of an activated sludge and a sole substrate (salicylic acid) was employed. The system degraded salicylic acid at 100-1100mg/L with a high level of efficiency, showed rapid acclimation without substrate or product inhibition phenomena and good stability in response to unsteady states caused by feed variations. Under starvation conditions, specific degradation rates of around 15mg/gh were achieved during the adaptation of the biomass to the new conditions and no biofilm formation was observed during the first days of experimentation using an initial substrate to microorganisms ratio lower than 0.1. When substrate was added to the reactor as pulses resulting in rapidly changing concentrations, P. putida growth was observed only for substrate to microorganism ratios higher than 0.6, with a maximum YX/S of 0.5g/g. Biofilm development under changing feeding conditions was fast, biomass detachment only being significant for biomass concentrations on the membrane surface that were higher than 16g/m(2).

Mechanisms of MS2 bacteriophage removal by fouled ultrafiltration membrane subjected to different cleaning methods

An ultrafiltration unit with a polyvinylidene fluoride (PVDF) membrane of 40 nm nominal pore size was used to study bacteriophage MS2 removal under different membrane conditions: pristine membrane, membrane fouled by soluble microbial product (SMP) extracted from membrane bioreactor (MBR) feedwater, backwashed membrane, and chemically cleaned membrane. The order of MS2 removal by these membranes was as follows: fouled membrane > backwashed membrane > chemically cleaned membrane ≈ pristine membrane. A linear correlation between membrane relative permeability and MS2 removal was found. Mass balance analysis showed a high percentage of MS2 in the concentrate for the fouled membrane as compared with the pristine membrane. Quartz crystal microbalance (QCM) results showed faster kinetics of MS2 adhesion to the pristine membrane than to the SMP-fouled membrane. In agreement with QCM results, an attractive force between MS2 and the pristine membrane was detected using an atomic force microscope (AFM), whereas a repulsive force was detected for the interaction between MS2 and the fouled membrane. The presence of SMP on the membrane surface led to higher rejection of MS2 due to both pore blocking and repulsion between MS2 and the SMP layer. Chemical cleaning removed most of the SMP foulant and as a result led to a lower MS2 removal.

A hybrid microbial fuel cell membrane bioreactor with a conductive ultrafiltration membrane biocathode for wastewater treatment

A new hybrid, air-biocathode microbial fuel cell-membrane bioreactor (MFC-MBR) system was developed to achieve simultaneous wastewater treatment and ultrafiltration to produce water for direct reclamation. The combined advantages of this system were achieved by using an electrically conductive ultrafiltration membrane as both the cathode and the membrane for wastewater filtration. The MFC-MBR used an air-biocathode, and it was shown to have good performance relative to an otherwise identical cathode containing a platinum catalyst. With 0.1 mm prefiltered domestic wastewater as the feed, the maximum power density was 0.38 W/m(2) (6.8 W/m(3)) with the biocathode, compared to 0.82 W/m(2) (14.5 W/m(3)) using the platinum cathode. The permeate quality from the biocathode reactor was comparable to that of a conventional MBR, with removals of 97% of the soluble chemical oxygen demand, 97% NH3-N, and 91% of total bacteria (based on flow cytometry). The permeate turbidity was <0.1 nephelometric turbidity units. These results show that a biocathode MFC-MBR system can achieve high levels of wastewater treatment with a low energy input due to the lack of a need for wastewater aeration.

Characterization of effluent water qualities from satellite membrane bioreactor facilities

Membrane bioreactors (MBRs) are often a preferred treatment technology for satellite water recycling facilities since they produce consistent effluent water quality with a small footprint and require little or no supervision. While the water quality produced from centralized MBRs has been widely reported, there is no study in the literature addressing the effluent quality from a broad range of satellite facilities. Thus, a study was conducted to characterize effluent water qualities produced by satellite MBRs with respect to organic, inorganic, physical and microbial parameters. Results from sampling 38 satellite MBR facilities across the U.S. demonstrated that 90% of these facilities produced nitrified (NH4-N <0.4 mg/L-N) effluents that have low organic carbon (TOC <8.1 mg/L), turbidities of <0.7 NTU, total coliform bacterial concentrations <100 CFU/100 mL and indigenous MS-2 bacteriophage concentrations <21 PFU/100 mL. Multiple sampling events from selected satellite facilities demonstrated process capability to consistently produce effluent with low concentrations of ammonia, TOC and turbidity. UV-254 transmittance values varied substantially during multiple sampling events indicating a need for attention in designing downstream UV disinfection systems. Although enteroviruses, rotaviruses and hepatitis A viruses (HAV) were absent in all samples, adenoviruses were detected in effluents of all nine MBR facilities sampled. The presence of Giardia cysts in filtrate samples of two of nine MBR facilities sampled demonstrated the need for an appropriate disinfection process at these facilities.

Performance of a submerged membrane bioreactor for the aerobic treatment of abattoir wastewater

The performance of a submerged membrane bioreactor (SMBR) has been investigated for abattoir wastewater (AW) treatment. The chemical oxygen demand (COD) of permeate has not exceeded 25 mg L(-1) providing an average COD removal of 98%. Microbiological analysis showed that the SMBR has allowed a complete removal of fecal coliforms, Listeria and Salmonella. A significant reduction in the excess biomass production was also observed. In fact, the yield of biomass production (Yobs) ranged between 0 and 0.106 g suspended solids/g COD removed. The study of the dynamic of bacterial communities using the single strand conformation polymorphism (SSCP) method showed a significant change in the population structure and revealed a correlation between the sludge production yield and the bacterial communities.

Scientific Opinion on an update on the present knowledge on the occurrence and control of foodborne viruses

A review of the biology, epidemiology, diagnosis and public health importance of foodborne viruses was performed. Data needs to support a risk assessment were also identified. In addition possible control options and their anticipated impact to prevent or reduce the number of foodborne viral human infections were identified, including the scientific reasons for and against the establishment of food safety criteria and process hygiene criteria for viruses for certain food categories. Food may be contaminated by virus during all stages of the food supply chain, and transmission can occur by consumption of food contaminated during the production process (primary production, or during further processing), or contaminated by infected food handlers. Transmission of zoonotic viruses (e.g. HEV) can also occur by consumption of products of animal origin. Viruses do not multiply in foods, but may persist for extended periods of time as infectious particles in the environment, or in foods. At the EU-level it is unknown how much viral disease can be attributed to foodborne spread. The relative contribution of different sources (shellfish, fresh produce, food handler including asymptomatic shedders, food handling environment) to foodborne illness has not been determined. The Panel recommends focusing controls on preventive measures to avoid viral contamination rather than trying to remove/inactivate these viruses from food. Also, it is recommended to introduce a microbiological criteria for viruses in bivalve molluscs, unless they are labelled "to be cooked before consumption". The criteria could be used by food business operators to validate their control options. Furthermore, it is recommended to refine the regulatory standards and monitoring approaches in order to improve public health protection. Introduction of virus microbiological criteria for classification of bivalve molluscs production areas should be considered. A virus monitoring programme for compliance with these criteria should be risk based according to the findings of a sanitary survey.

Removal of microbial indicators from municipal wastewater by a membrane bioreactor (MBR)

The impact of removable and irremovable fouling on the retention of viral and bacterial indicators by the submerged microfiltration membrane in an MBR pilot plant was evaluated. Escherichia coli, sulphite-reducing Clostridium spores, somatic coliphages and F-specific RNA bacteriophages were used as indicators. The membrane demonstrated almost complete removal of E. coli and sulphite-reducing Clostridium spores. However, there was no correlation with membrane fouling. The phage removal varied in accordance with the irremovable fouling, rising from 2.6 to 5.6 log(10) units as the irremovable fouling increased (measured by the change in the transmembrane pressure). In contrast, removable fouling did not have any effect on the retention of viruses by the membrane. These results indicate that irremovable membrane fouling may affect the removal efficiency of MBRs and, therefore, their capacity to ensure the required microbiological standards for the permeate achieved.