Sustainable organic loading rate and energy recovery potential of mesophilic anaerobic membrane bioreactor for municipal wastewater treatment

Validation of LC-MS/MS method for opioid monitoring in Valencia City wastewater: Assessment of synthetic wastewater as potential aid

In this study, a comprehensive and sensitive method for the simultaneous detection of 17 opioids (OPs) and their human metabolites in wastewater using high-performance liquid chromatography coupled to tandem mass spectrometry was validated. The chromatographic separations of opioids were carried out on a Kinetex® Biphenyl column (1.7 μm, 100 Å, 50 × 2.1 mm). A synthetic wastewater approach was used for recovery studies to mimic a contaminant-free matrix. Two solid-phase extraction (SPE) sorbents (hydrophilic-lipophilic balance and mixed mode with the previous phase and a weak cationic exchange) were studied to optimize sample treatment and obtain higher recoveries. The mixed mode was chosen because the recoveries of 17 target analytes at three spiked concentrations (25, 50, and 100 ng mL-1) were > 80 % for 75 % of the analytes in a simulated wastewater. The intra- and inter-day relative standard deviations (RSDs) were between ±1 % and ±20 %. The method limits of quantification ranged from 5 to 25 ng L-1, the only exceptions being heroin (275 ng L-1) and morphine-3β-glucuronide (250 ng L-1). Suppression/enhancement is comparable between the synthetic and the influent wastewater. The analytical method was applied to the OPs analysis in twenty-one influent samples collected from the treatment plants treating the wastewater of Valencia City (Spain). Twelve OPs were detected with total daily concentrations ranging from 1 ng L-1 to 2135 ng L-1. The widespread presence of these compounds in water suggests potential widespread exposure, highlighting the need for increased environmental awareness. Furthermore, the estimated daily intake results raise concerns about opioid use as a potential future health and social issue.

A Review on Opportunities and Limitations of Membrane Bioreactor Configuration in Biofuel Production

Biofuels are a clean and renewable source of energy that has gained more attention in recent years; however, high energy input and processing cost during the production and recovery process restricted its progress. Membrane technology offers a range of energy-saving separation for product recovery and purification in biorefining along with biofuel production processes. Membrane separation techniques in combination with different biological processes increase cell concentration in the bioreactor, reduce product inhibition, decrease chemical consumption, reduce energy requirements, and further increase product concentration and productivity. Certain membrane bioreactors have evolved with the ability to deal with different biological production and separation processes to make them cost-effective, but there are certain limitations. The present review describes the advantages and limitations of membrane bioreactors to produce different biofuels with the ability to simplify upstream and downstream processes in terms of sustainability and economics.

Nitrification potential of daily-watered biofiltration designs for high ammonium wastewater treatment

The vegetated biofiltration systems (VBS), also known as bioretentions or rain gardens, are well-established technology for treatment of urban stormwater and recently greywater, offering multiple benefits to urban environments. However, the impact of high ammonium strength wastewater (60 mg/L) on the nitrification process in these systems is not well understood. Hence, a laboratory-based column study was conducted to uncover dominant nitrification mechanisms, based on the learnings from similar onsite wastewater treatment systems. The experimental columns tested the effect of contact time (filter media depth, 150 mm, 300 mm and 700 mm), media oxygenation (active and passive) and alkalinity/pH (marble chips 5 % weight), as well as optimal operational conditions (inflow loading, concentrations, and dissolved oxygen (DO)). All nitrogen species (NH₄⁺, NO₃^-, NO₂^-), chemical oxygen demand (COD) and physical parameters (DO, pH, electrical conductivity) were monitored across seven events over thirteen weeks. The results show that dosing with 30 and 60 mg/L of NH₄⁺ resulted in 700 mm sand column depth to perform almost complete nitrification of NH₄⁺ to NO₃^- (< 90 %), while 300 mm designs achieved partial nitrification of NH₄⁺ to NO₂^-, likely due to limited contact time and inefficient nitrite oxidizing bacteria activity. Nitrification potential of all designs further supported that appropriate aerobic contact time is necessary for effective nitrification. Inflow concentration of NH₄⁺ and DO did not significantly impact nitrification performance, while reducing daily volume loading reduced NO₃^- and NO₂^- leaching. Active and passive aeration and alkalinity buffering did not positively affect ammonium removal. While there is a potential to apply both nitrification-denitrification and anammox processes to future VBS design, further understanding of aeration and alkalinity on microbially driven nitrification processes is needed.

Metatranscriptional characterization of metabolic dynamics in anaerobic membrane bioreactor producing methane from low-strength wastewater

An anaerobic membrane bioreactor (AnMBR) with media is an emerging carbon-neutral biotechnology for low-strength wastewater (LSWW) treatment and methane recovery. Understanding metabolic dynamics among methanogens and syntrophic bacteria is important in optimizing the design and operation of AnMBR. However, little is known about it, especially in media-attached microbial communities. This study explored metabolic dynamics to compare media-attached and suspended conditions. Accordingly, metagenomes and metatranscriptomes from AnMBRs with polymeric media and fed with different influent concentrations (350 and 700 mg-COD/L) were analyzed. Metabolic dynamics were profoundly influenced by the different growth habitats and influent conditions, although the applied influent concentrations are within the range of typical LSWW. Metabolic dynamics prediction results suggest that media-attached-growth habitats may have provided a more favorable microenvironment for methanogens to grow and produce methane, especially under low influent conditions. These findings provide significant implications for optimizing floating media design and operation of AnMBR-producing methane from LSWW.

Energy-Efficient AnMBRs Technology for Treatment of Wastewaters: A Review

In recent years, anaerobic membrane bioreactor (AnMBRs) technology, a combination of a biological reactor and a selective membrane process, has received increasing attention from both industrialists and researchers. Undoubtedly, this is due to the fact that AnMBRs demonstrate several unique advantages. Firstly, this paper addresses fundamentals of the AnMBRs technology and subsequently provides an overview of the current state-of-the art in the municipal and domestic wastewaters treatment by AnMBRs. Since the operating conditions play a key role in further AnMBRs development, the impact of temperature and hydraulic retention time (HRT) on the AnMBRs performance in terms of organic matters removal is presented in detail. Although membrane technologies for wastewaters treatment are known as costly in operation, it was clearly demonstrated that the energy demand of AnMBRs may be lower than that of typical wastewater treatment plants (WWTPs). Moreover, it was indicated that AnMBRs have the potential to be a net energy producer. Consequently, this work builds on a growing body of evidence linking wastewaters treatment with the energy-efficient AnMBRs technology. Finally, the challenges and perspectives related to the full-scale implementation of AnMBRs are highlighted.

Effects of Stepwise Temperature Shifts in Anaerobic Digestion for Treating Municipal Wastewater Sludge: A Genomic Study

In wastewater treatment plants (WWTP), anaerobic digester (AD) units are commonly operated under mesophilic and thermophilic conditions. In some cases, during the dry season, maintaining a stable temperature in the digester requires additional power to operate a conditioning system. Without proper conditioning systems, methanogens are vulnerable to temperature shifts. This study investigated the effects of temperature shifts on CH₄ gas production and microbial diversity during anaerobic digestion of anaerobic sewage sludge using a metagenomic approach. The research was conducted in lab-scale AD under stepwise upshifted temperature from 42 to 48 °C. The results showed that significant methanogen population reduction during the temperature shift affected the CH₄ production. With 70 days of incubation each, CH₄ production decreased from 4.55 L·g⁻¹-chemical oxygen demand (COD) at 42 °C with methanogen/total population (M·TP⁻¹) ratio of 0.041 to 1.52 L·g⁻¹ COD (M·TP⁻¹ ratio 0.027) and then to 0.94 L·g⁻¹ COD ( M·TP⁻¹ ratio 0.026) after the temperature was shifted to 45 °C and 48 °C, respectively. Methanosaeta was the most prevalent methanogen during the thermal change. This finding suggests that the Methanosaeta genus was a thermotolerant archaea. Anaerobaculum, Fervidobacterium, and Tepidanaerobacter were bacterial genera and grew well in shifted-up temperatures, implying heat-resistant characteristics.

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.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review

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

UV and bacteriophages as a chemical-free approach for cleaning membranes from anaerobic bioreactors

Anaerobic membrane bioreactor (AnMBR) for wastewater treatment has attracted much interest due to its efficacy in providing high-quality effluent with minimal energy costs. However, membrane biofouling represents the main bottleneck for AnMBR because it diminishes flux and necessitates frequent replacement of membranes. In this study, we assessed the feasibility of combining bacteriophages and UV-C irradiation to provide a chemical-free approach to remove biofoulants on the membrane. The combination of bacteriophage and UV-C resulted in better log cells removal and ca. 2× higher extracellular polymeric substance (EPS) concentration reduction in mature biofoulants compared to either UV-C or bacteriophage alone. The cleaning mechanism behind this combined approach is by 1) reducing the relative abundance of Acinetobacter spp. and selected bacteria (e.g., Paludibacter, Pseudomonas, Cloacibacterium, and gram-positive Firmicutes) associated with the membrane biofilm and 2) forming cavities in the biofilm to maintain water flux through the membrane. When the combined treatment was further compared with the common chemical cleaning procedure, a similar reduction on the cell numbers was observed (1.4 log). However, the combined treatment was less effective in removing EPS compared with chemical cleaning. These results suggest that the combination of UV-C and bacteriophage have an additive effect in biofouling reduction, representing a potential chemical-free method to remove reversible biofoulants on membrane fitted to an AnMBR.

Important effects of temperature on treating real municipal wastewater by a submerged anaerobic membrane bioreactor: Removal efficiency, biogas, and microbial community

A submerged anaerobic membrane bioreactor (SAnMBR) was used in the treatment of real municipal wastewater at operation temperatures ranging from 15 °C to 25 °C and hydraulic retention time (HRT) of 6 h. The treatment process was evaluated in terms of organic removal efficiency, biogas production, sludge growth and membrane filtration. During long-term operation, the SAnMBR achieved chemical oxygen demand removal efficiencies of about 90% with a low sludge yield (0.12-0.19 g-VSS/g-COD_rem) at 20-25 °C. Approximately 1.82-2.27 kWh/d of electric energy was generated during the wastewater treatment process at 20-25 °C, 0.67 kWh/d was generated at 15 °C. The microbial community analysis results showed that microbial community was dominated by aceticlastic methanogens, coupled by hydrogenotrophic methanogens and a very small quantity of methylotrophic methanogens. It was also shown that the stabilization of the microbial community could be attributed to the carbohydrate-protein degrading bacteria and the carbohydrate degrading bacteria.

One-year operation of a 20-L submerged anaerobic membrane bioreactor for real domestic wastewater treatment at room temperature: Pursuing the optimal HRT and sustainable flux

A 20 L hollow-fiber submerged anaerobic membrane bioreactor (SAnMBR) was used to treat real domestic wastewater at 25 °C with hydraulic retention times (HRTs) ranging from 4 to 12 h. The process performance was evaluated by organic removal efficiency, biogas production, sludge yield, and filtration behaviors during one-year's operation. For HRTs ranging between 6 and 12 h, the AnMBR showed good organic removal efficiency with chemical oxygen demand (COD) and biochemical oxygen demand (BOD) removal efficiencies of about 89% and 93%, respectively. The biogas yield was 0.26 L-gas/g-COD_fed, with approximately 80% methane content, and the sludge yield was 0.07-0.11 g-VSS/g-COD_rem. While at an HRT of 4 h, with the higher wastewater treatment capacity and organic loading rate (OLR), the biogas production was lower (0.17 L-gas/g-COD_fed), and the sludge production was higher (0.22 g-VSS/g-COD_rem). The organic removal performance (COD 84% and BOD 89%) at HRT of 4 h was acceptable due to the effective separation effect of the membrane filtration process. According to COD balance analysis, the low biogas yield and high sludge yield at HRT of 4 h were due to insufficient biodegradation under an OLR of 2.05 g-COD/L-reactor/d. Theoretical calculations based on Henry's law indicate that the ideal methane content in the biogas should be 82-85% when the operational temperature was 25 °C. To achieve a high flux and sustainable AnMBR operation, the impact of mixed liquor suspended solid (MLSS) and gas sparging velocity (GSV) on the filtration performance was analyzed. The critical flux increased with increase in the GSV from 24.2 to 174.3 m/h, but decreased with increase in the MLSS concentration from 8.2 to 20.2 g/L. Therefore, decreasing fouling rate to 0.8-1.2 kPa/d by efficiently controlling GSV and MLSS, sustainable operation could be achieved at a flux of 0.34 m/d.

Performance of AnMBR in Treatment of Post-consumer Food Waste: Effect of Hydraulic Retention Time and Organic Loading Rate on Biogas Production and Membrane Fouling

Anaerobic digestion of food waste (FW) is typically limited to large reactors due to high hydraulic retention times (HRTs). Technologies such as anaerobic membrane reactors (AnMBRs) can perform anaerobic digestion at lower HRTs while maintaining high chemical oxygen demand (COD) removal efficiencies. This study evaluated the effect of HRT and organic loading rate (OLR) on the stability and performance of a side-stream AnMBR in treating diluted fresh food waste (FW). The reactor was fed with synthetic FW at an influent concentration of 8.24 (± 0.12) g COD/L. The OLR was increased by reducing the HRT from 20 to 1 d. The AnMBR obtained an overall removal efficiency of >97 and >98% of the influent COD and total suspended solids (TSS), respectively, throughout the course of operation. The biological process was able to convert 76% of the influent COD into biogas with 70% methane content, while the cake layer formed on the membrane gave an additional COD removal of 7%. Total ammoniacal nitrogen (TAN) and total nitrogen (TN) concentrations were found to be higher in the bioreactor than in the influent, and average overall removal efficiencies of 17.3 (± 5) and 61.5 (± 3)% of TAN and TN, respectively, were observed with respect to the bioreactor concentrations after 2 weeks. Total phosphorus (TP) had an average removal efficiency of 40.39 (± 5)% with respect to the influent. Membrane fouling was observed when the HRT was decreased from 7 to 5 d and was alleviated through backwashing. This study suggests that the side-stream AnMBR can be used to successfully reduce the typical HRT of wet anaerobic food waste (solids content 7%) digesters from 20 days to 1 day, while maintaining a high COD removal efficiency and biogas production.

Anaerobic membrane bioreactor performance at different wastewater pre-concentration factors: An experimental and economic study

This research evaluated the performance of a lab-scale anaerobic membrane bioreactor (AnMBR) treating municipal sewage pre-concentrated by forward osmosis (FO). The organic loading rate (OLR) and sodium concentrations of the synthetic sewage stepwise increased from 0.3 to 2.0 g COD L^-1 d^-1 and from 0.28 to 2.30 g Na⁺ L^-1 to simulate pre-concentration factors of 1, 2, 5 and 10. No major operational problems were observed during AnMBR operation, with COD removal efficiencies ranging between 90 and 96%. The methane yield progressively increased from 214 ± 79 to 322 ± 60 mL CH₄ g^-1 COD as the pre-concentration factor increased from 1 to 10. This was mainly attributed to the lower fraction of methane dissolved lost in the permeate at higher OLRs. Interestingly, at the highest pre-concentration factor (2.30 g Na⁺ L^-1) the difference between the permeate and the digester soluble COD indicated that membrane biofilm also played a role in COD removal. Finally, a preliminary energy and economic analysis showed that, at a pre-concentration factor of 10, the AnMBR temperature could be increased 10 °C and achieve a positive net present value (NPV) of 4 M€ for a newly constructed AnMBR treating 10,000 m³ d^-1 of pre-concentrated sewage with an AnMBR lifetime of 20 years.

Impact of decreasing hydraulic retention times on the specific affinity of methanogens and their community structures in an anaerobic membrane bioreactor process treating low strength wastewater

Maximum specific growth rate (μ_max) and substrate saturation constant (K_s) are widely used in determining the growth of microorganisms. The ratio (μ_max/K_s), also referred to as specific affinity, a_A⁰, is a better parameter to assess the advantage in competition for substrates by bridging microbial growth and the kinetics of enzymatic substrate uptake, but is not well studied. This study investigated the effect of hydraulic retention time (HRT) on the a_A⁰ of anaerobic sludge from an anaerobic membrane bioreactor (AnMBR), associated microbial communities and the overall wastewater treatment performance. The AnMBR was fed with acetate wastewater (~500 mg COD/L) and operated at fixed solids retention time (45 d) while HRT continued to decrease. There was no significant difference in K_s (ranging from 170 to 243 mg COD/L) at different HRTs. However, a_A⁰ increased from (4.0 ± 0.2) × 10^-4 to (4.9 ± 0.2) × 10^-4 and to (6.5 ± 0.1) × 10^-4 L/mg COD/d as HRT decreased from 24 h to 12 h and further to 6 h, respectively. This was accompanied by the increase in acetoclastic methanogens (mainly Methanosaeta) from 3.85 × 10¹⁰, 8.82 × 10¹⁰ to 1.05 × 10¹¹ cells/L, respectively. The fraction of Methanosaeta in the anaerobic biomass increased from 33.67% to 61.08% as HRT decreased from 24 h to 6 h. Correspondingly, effluent quality was improved, as evidenced from the COD concentrations of 32 ± 6, 21 ± 4, and 13 ± 5 mg/L at the HRTs of 24 h, 12 h, and 6 h, respectively. The results confirm that microorganisms are able to adapt to growth conditions by adjusting their kinetic properties and suggest that short HRTs in the AnMBR favor the growth and accumulation of Methanosaeta with high specific affinity likely because they can compete for acetate at low concentrations by increasing substrate uptake rate and thus specific microbial growth rate.

Different fouling propensities of loosely and tightly bound extracellular polymeric substances (EPSs) and the related fouling mechanisms in a membrane bioreactor

In this study, fouling propensities of loosely bound extracellular polymeric substances (LB-EPSs) and tightly bound EPSs (TB-EPSs) in a membrane bioreactor (MBR) were investigated. It was found that, both the LB-EPSs and TB-EPSs possessed rather high specific filtration resistance (SFR), and LB-EPSs possessed about three times higher SFR but a lower adhesion ability than the TB-EPSs. A series of characterizations demonstrated that LB-EPSs had higher ratio of proteins to polysaccharides (PN/PS ratio), lower CO bonds content, higher hydrophilicity, higher deformation or mixing ability and more abundant high molecular weight (MW) substances than TB-EPSs. Thermodynamic analyzes revealed that the total interaction energy between the TB-EPSs and membrane was always attractive and strengthened, well explaining the higher adhesion ability of the TB-EPSs than the LB-EPSs. Meanwhile, the filtration process was found to be associated with gel layer formation, and the high SFR of EPSs was caused by the chemical potential change in gel layer filtration. According to the Flory-Huggins lattice theory, LB-EPSs tended to form a gel layer with higher cross-linking and/or polymer entanglement level because they contained more abundant high molecular weight (MW) substance, corresponding to higher SFR than that of the TB-EPSs. The proposed thermodynamic mechanisms well interpreted the different fouling propensities of LB-EPSs and TB-EPSs in MBRs.

Discharge or reuse? Comparative sustainability assessment of anaerobic and aerobic membrane bioreactors

Water reuse is believed to be a sustainable solution to overcome the scarcity of freshwater. Aerobic and anaerobic membrane bioreactors are becoming an effective technology for wastewater treatment and reuse. Aerobic membrane bioreactors show good nutrient removal, whereas those that are anaerobic have nutrient-rich effluent, enabling the direct agricultural use of the effluent. As a result, the end use will dictate the potential environmental impacts of the bioreactor's application. Therefore, with the consideration of the end use (i.e., discharge or reuse) of the effluent, this study aimed to compare the environmental and economic impacts associated with full-scale aerobic and anaerobic membrane bioreactors for municipal wastewater treatment under different end use scenarios using life cycle assessment and cost analysis. The results of these analyses show that anaerobic bioreactors have greater environmental impacts and life cycle cost than aerobic bioreactors in the discharge scenario due to the incorporation of a biological nutrient removal system. In the reuse scenario, anaerobic membrane bioreactors have lower impacts that are attributable to the offset of the nutrients required for crops, and the potential benefits vary depending on the types of crops receiving the reclaimed water. Integrating anaerobic membrane bioreactors with agricultural fertigation resulted in effluent water nitrate concentrations (after crop uptake and soil treatment) of <2 mg L^-1 in most U.S. states. This indicated that the use of the anaerobic membrane bioreactors effluent for fertigation could be a win-win solution to both irrigation water shortage and high environmental impact associated with nutrient removal.

Anaerobic hybrid membrane bioreactor for treatment of synthetic leachate: Impact of organic loading rate and sludge fractions on membrane fouling

In the present study, the treatment of synthetic landfill leachate was carried out using a lab-scale anaerobic hybrid membrane bioreactor (An-HMBR). The reactor was operated for 250 days at two days of hydraulic retention time (HRT). Average chemical oxygen demand (COD) removal efficiency was ≥ 88% at steady-state conditions at 100% raw leachate. As organic loading rate (OLR) increased from 1.6 to 13.9 Kg COD m^-3 d^-1, flux gradually declined from 70 to 52 L/m² h (LMH) within 250 days. Chemical membrane cleaning enhanced the flux up to 75% of the initial flux at the final stage of the reactor. Reversible fouling (>90%) dominated over irreversible fouling (<8%). Membrane fouling was mainly caused by extracellular polymeric substances (EPS) fraction, which resulted in cake layer formation on the ceramic membrane used in the An-HMBR system. Membrane resistance increased with variables in the following order OLR > MLSS (mixed liquor suspended solids) > EPS > SMP (soluble microbial products). A nonlinear regression model developed for prediction of membrane resistance at different OLR can predict with an error of ±7%.

Removal and biotransformation pathway of antibiotic sulfamethoxazole from municipal wastewater treatment by anaerobic membrane bioreactor

A lab-scale mesophilic anaerobic membrane bioreactor (AnMBR) was used to treat synthetic municipal wastewater with variable concentrations of antibiotic Sulfamethoxazole (SMX) and bulk organics in this study. The removal and biotransformation pathway of SMX in the AnMBR were systematically investigated during a 170 d of operation under hydraulic retention time of 1 d. Average SMX removal was 97.1% under feed SMX of 10-1000 μg/L, decreasing to 91.6 and 88.0% under feed SMX of 10,000 and 100,000 μg/L due to the inhibition effects of high SMX loading rate on anaerobic microorganisms. SMX biotransformation followed pseudo-first order reaction kinetics based on SMX removal independent of feed SMX of 10-1000 μg/L during continuous operation and also in a batch test under initial SMX of 100,000 μg/L. According to the identified 7 transformation products (TPs) by gas chromatography-mass spectrometry, the biotransformation pathway of SMX from municipal wastewater treatment via AnMBR was first proposed to consist of 2 primary routes: 1) Butylbenzenesulfonamide without antibiotic toxicity dominated under feed SMX of 10-100 μg/L; 2) Sulfanilamide with much lower antibiotic toxicity than SMX dominated under feed SMX of 1000-100000 μg/L, further transforming to secondary TPs (4-Aminothiophenol, Aniline, Acetylsulfanilamide) and tertiary TPs (4-Acetylaminothiophenol, Acetylaniline).

Identification and characterization of core sludge and biofilm microbiota in anaerobic membrane bioreactors

An analysis of sludge (i.e., 63 samples) and biofilm (i.e., 79 samples) sampled from 13 anaerobic membrane bioreactors (AnMBR) was conducted. Predominant microbial community identification and multivariate analysis indicate that these reactors showed different microbial community structure, but these differences had no impact on the overall AnMBR performance. Instead, core microbial genera which occurred in ≥90% of sludge (20 genera) and biofilm (12 genera) samples could potentially account for the AnMBR performance. A further calculation on net growth rate (NGR) of core genera in sludge suggested distribution into two main groups (i.e., I: low relative abundance and NGR, II: high relative abundance or high NGR). Consistent positive correlations between bacterial genera were observed among those that exhibited either high relative abundance or high NGR. The anaerobic microbial consortium in both sludge and biofilm were largely affected by stochastic dispersal and migration processes (i.e., neutral assembly). However, Acinetobacter spp. and Methanobacterium spp. occurred consistently in higher frequency in the biofilm but in lower occurrence frequency in the AnMBR permeate. Findings from this study suggest first, specific core microorganisms exist in the sludge regardless of the operating conditions of the AnMBRs, and second, prevention of biofoulant layer on anaerobic membranes can be devised by minimizing attachment of microbes on surfaces in a non-selective manner.

Treatment of low strength wastewater using compact submerged aerobic fixed film (SAFF) reactor filled with high specific surface area synthetic media

Studies on laboratory-scale submerged aerobic fixed film reactor (SAFF) packed with synthetic media having specific surface area of 165 m²/m³ with a void volume of 89% were carried out to assess its performance under various organic loading rates (OLR) and hydraulic retention times (HRT). Synthetic wastewater having chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of 400 ± 10% and 210 ± 10% mg/L respectively was fed and the reactor was subjected to OLRs ranging from 0.37 to 1.26 kg COD/m³.d. It was observed that steady sloughing of biofilm occurs within the SAFF reactor all the times and average concentration of sloughed biomass in the effluent was 26 mg/L. The COD and BOD removal efficiencies varied between 85 and 89% and 86 to 94%, respectively. The kinetic studies demonstrated that SAFF reactor followed Stover-Kincannon and Grau models, with high correlation coefficients (R²) of 0.9977 and 0.9916, respectively. Thus, the values of kinetic coefficients such as maximum substrate utilization rate, U_max = 64.1 g/(L^.d); saturation value constant, K_B = 72.31 g/(L.d) and Grau second-order substrate removal rate constant, Ks = 2.44 day^-1 can be useful to develop and design large scale SAFF reactors. Finally, the study reveals that the optimum range for OLR can vary within 0.68-0.94 kg COD/m³.d.

Organic micropollutants removal in sequential batch reactor followed by nanofiltration from municipal wastewater treatment

The removal of 26 organic micropollutants (OMPs) in synthetic municipal wastewater was investigated via the process of aerobic sequential batch reactor (SBR) alone and SBR followed by nanofiltration (NF). SBR-NF performed better than SBR alone, ascribed to the contribution of NF: 1) complete biomass rejection resulted in diverse microbial community and much less fluctuated performance than SBR alone, and 2) direct OMPs rejection (74-98%) increased their retention time in SBR and thus overall removal via biodegradation/transformation and accumulation in SBR. Nine OMPs showed high biological removal (over 60%), 6 OMPs showed moderate biological removal (30-70%) and 10 OMPs showed low biological removal (below 40%). Most readily and moderately biodegradable OMPs contained strong electron donating group. Most refractory OMPs contained strong electron withdrawing group and/or halogen substitute. The batch addition of powdered activated carbon (100 mg/L) into SBR showed short term sorption performance for both OMPs and bulk organics.

Polishing of anaerobic secondary effluent by Chlorella vulgaris under low light intensity

To investigate anaerobic secondary effluent polishing by microalgae (Chlorella vulgaris) under low light intensity (14μmol/m²/s), bubbling column reactors were operated in batches of 8 d with initial ammonium nitrogen 10-50mg/L, initial phosphate phosphorus 2-10mg/L and microalgal seed 40mg/L. Maximum microalgal biomass and minimum generation time were 370.9mg/L and 2.5d, respectively. Nitrogen removal (maximum 99.6%) was mainly attributed to microalgal growth rate, while phosphorus removal (maximum 49.8%) was related to microalgal growth rate, cell phosphorus content (maximum 1.5%) and initial nutrients ratio. Dissolved microalgal organics release in terms of chemical oxygen demand (maximum 63.2mg/L) and hexane extractable material (i.e., oil and grease, maximum 8.5mg/L) was firstly reported and mainly affected by nitrogen deficiency and deteriorated effluent quality. Ultrafiltration critical flux (16.6-39.5L/m²/h) showed negative linear correlation to microalgal biomass. Anaerobic membrane bioreactor effluent polishing showed similar results with slight inhibition to synthetic effluent.

Methane production in an anaerobic osmotic membrane bioreactor using forward osmosis: Effect of reverse salt flux

This study investigated the impact of reverse salt flux (RSF) on microbe community and bio-methane production in a simulated fertilizer driven FO-AnMBR system using KCl, KNO₃ and KH₂PO₄ as draw solutes. Results showed that KH₂PO₄ exhibited the lowest RSF in terms of molar concentration 19.1mM/(m².h), while for KCl and KNO₃ it was 32.2 and 120.8mM/(m².h), respectively. Interestingly, bio-methane production displayed an opposite order with KH₂PO₄, followed by KCl and KNO₃. Pyrosequencing results revealed the presence of different bacterial communities among the tested fertilizers. Bacterial community of sludge exposed to KH₂PO₄ was very similar to that of DI-water and KCl. However, results with KNO₃ were different since the denitrifying bacteria were found to have a higher percentage than the sludge with other fertilizers. This study demonstrated that RSF has a negative effect on bio-methane production, probably by influencing the sludge bacterial community via environment modification.

Fate and Persistence of a Pathogenic NDM-1-Positive Escherichia coli Strain in Anaerobic and Aerobic Sludge Microcosms

The presence of emerging biological pollutants in treated wastewater effluents has gained attention due to increased interest in water reuse. To evaluate the effectiveness of the removal of such contaminants by the conventional wastewater treatment process, the fate and decay kinetics of NDM-1-positive Escherichia coli strain PI7 and its plasmid-encoded antibiotic resistance genes (ARGs) were assessed in microcosms of anaerobic and aerobic sludge. Results showed that E. coli PI7 decayed at a significantly lower rate under anaerobic conditions. Approximate half-lives were 32.4 ± 1.4 h and 5.9 ± 0.9 h in the anaerobic and aerobic microcosms, respectively. In the aerobic microcosms, after 72 h of operation, E. coli PI7 remained detectable, but no further decay was observed. Instead, 1 in every 10,000 E. coli cells was identified to be recalcitrant to decay and persist indefinitely in the sludge. ARGs associated with the E. coli PI7 strain were detected to have transferred to other native microorganisms in the sludge or were released to the liquid fraction upon host decay. Extracellular DNA quickly degraded in the liquid fraction of the aerobic sludge. In contrast, no DNA decay was detected in the anaerobic sludge water matrix throughout the 24-h sampling period. This study suggests an increased likelihood of environmental dispersion of ARGs associated with anaerobically treated wastewater effluents and highlights the potential importance of persister cells in the dissemination of E. coli in the environment during reuse events of treated wastewater.

IMPORTANCE This study examines the decay kinetics of a pathogenic and antibiotic resistant strain of Escherichia coli in microcosms simulating biological treatment units of aerobic and anaerobic sludge. The results of this study point at a significantly prolonged persistence of the E. coli and the associated antibiotic resistance gene in the anaerobic sludge. However, horizontal transfer of the plasmid encoding the antibiotic resistance gene was detected in the aerobic sludge by a cultivation method. A subpopulation of persister E. coli cells was also detected in the aerobic sludge. The findings of this study suggest potential areas of concern arising from pathogenic and antibiotic-resistant E. coli during both anaerobic and aerobic sludge treatment processes.

Performance and microbial community variations of anaerobic digesters under increasing tetracycline concentrations

The impact of different concentrations of tetracycline on the performance of anaerobic treatment was evaluated. Results revealed that for all of the tested tetracycline concentrations, no major sustained impact on methane production was observed. Instead, a significant increase in propionic acid was observed in the reactor subjected to the highest concentration of tetracycline (20 mg/L). Microbial community analyses suggest that an alternative methanogenic pathway, specifically that of methanol-utilizing methanogens, may be important for ensuring the stability of methane production in the presence of high tetracycline concentrations. In addition, the accumulation of propionate was due to an increase in volatile fatty acids (VFA)-producing bacteria coupled with a reduction in propionate utilizers. An increase in the abundance of tetracycline resistance genes associated with ribosomal protection proteins was observed after 30 days of exposure to high concentrations of tetracycline, while other targeted resistance genes showed no significant changes. These findings suggest that anaerobic treatment processes can robustly treat wastewater with varying concentrations of antibiotics while also deriving value-added products and minimizing the dissemination of associated antibiotic resistance genes.

Time-resolved monitoring of biofouling development on a flat sheet membrane using optical coherence tomography

Biofouling on a membrane leads to significant performance decrease in filtration processes. In this study, an optical coherence tomography (OCT) was used to perform a time-resolved analysis of dynamic biofouling development on a submerged membrane under continuous operation. A real-time change in the biofouling morphology was calculated through the image analysis of OCT scans. Three videos were generated through the acquisition of serial static images. This is the first study that displays the dynamic biofouling formation process as a video. The acquisition of OCT cross-sectional scans of the biofouling allowed to evaluate the time-lapsed evolution for three different time periods (early stage, double layers and long-term). Firstly, at the early filtration stage, membrane coverage and average biofouling layer thickness were found to be linearly correlated with the permeate flux pattern. Secondly, after 3 d of operation, an anomalous morphology was observed, constituted by a double-layered biofouling structure: denser on the bottom and looser on the top. In a long-term operation, the biofouling structure underwent a dynamic evolution over time, resulting in a multi-layered structure. The biofouling formation information was closely associated with filtration performance (i.e. flux) indicating the suitability of OCT as real-time and in-situ biofouling monitoring technique.

Integrated approach to characterize fouling on a flat sheet membrane gravity driven submerged membrane bioreactor

Fouling in membrane bioreactors (MBR) is acknowledged to be complex and unclear. An integrated characterization methodology was employed in this study to understand the fouling on a gravity-driven submerged MBR (GD-SMBR). It involved the use of different analytical tools, including optical coherence tomography (OCT), liquid chromatography with organic carbon detection (LC-OCD), total organic carbon (TOC), flow cytometer (FCM), adenosine triphosphate analysis (ATP) and scanning electron microscopy (SEM). The three-dimensional (3D) biomass morphology was acquired in a real-time through non-destructive and in situ OCT scanning of 75% of the total membrane surface directly in the tank. Results showed that the biomass layer was homogeneously distributed on the membrane surface. The amount of biomass was selectively linked with final destructive autopsy techniques. The LC-OCD analysis indicated the abundance of low molecular weight (LMW) organics in the fouling composition. Three different SEM techniques were applied to investigate the detailed fouling morphology on the membrane.

Factors governing the pre-concentration of wastewater using forward osmosis for subsequent resource recovery

This study demonstrated a technique using forward osmosis (FO) to pre-concentrate the organic matter in raw wastewater, thereby transforming low strength wastewater into an anaerobically digestible solution. The chemical oxygen demand (COD) of raw wastewater was concentrated up to approximately eightfold at a water recovery of 90%. Thus, even low strength wastewater could be pre-concentrated by FO to the range suitable for biogas production via anaerobic treatment. Excessive salinity accumulation in pre-concentrated wastewater was successfully mitigated by adopting ionic organic draw solutes, namely, sodium acetate, and EDTA-2Na. These two draw solutes are also expected to benefit the digestibility of the pre-concentrated wastewater compared to the commonly used draw solute sodium chloride. Significant membrane fouling was observed when operating at 90% water recovery using raw wastewater. Nevertheless, membrane fouling was reversible and was effectively controlled by optimising the hydrodynamic conditions of the cross-flow FO system.

Life cycle cost of a hybrid forward osmosis - low pressure reverse osmosis system for seawater desalination and wastewater recovery

In recent years, forward osmosis (FO) hybrid membrane systems have been investigated as an alternative to conventional high-pressure membrane processes (i.e. reverse osmosis (RO)) for seawater desalination and wastewater treatment and recovery. Nevertheless, their economic advantage in comparison to conventional processes for seawater desalination and municipal wastewater treatment has not been clearly addressed. This work presents a detailed economic analysis on capital and operational expenses (CAPEX and OPEX) for: i) a hybrid forward osmosis - low-pressure reverse osmosis (FO-LPRO) process, ii) a conventional seawater reverse osmosis (SWRO) desalination process, and iii) a membrane bioreactor - reverse osmosis - advanced oxidation process (MBR-RO-AOP) for wastewater treatment and reuse. The most important variables affecting economic feasibility are obtained through a sensitivity analysis of a hybrid FO-LPRO system. The main parameters taken into account for the life cycle costs are the water quality characteristics (similar feed water and similar water produced), production capacity of 100,000 m(3) d(-1) of potable water, energy consumption, materials, maintenance, operation, RO and FO module costs, and chemicals. Compared to SWRO, the FO-LPRO systems have a 21% higher CAPEX and a 56% lower OPEX due to savings in energy consumption and fouling control. In terms of the total water cost per cubic meter of water produced, the hybrid FO-LPRO desalination system has a 16% cost reduction compared to the benchmark for desalination, mainly SWRO. Compared to the MBR-RO-AOP, the FO-LPRO systems have a 7% lower CAPEX and 9% higher OPEX, resulting in no significant cost reduction per m(3) produced by FO-LPRO. Hybrid FO-LPRO membrane systems are shown to have an economic advantage compared to current available technology for desalination, and comparable costs with a wastewater treatment and recovery system. Based on development on FO membrane modules, packing density, and water permeability, the total water cost could be further reduced.

A novel configuration for an anaerobic submerged membrane bioreactor (AnSMBR). Long-term treatment of municipal wastewater under psychrophilic conditions

A novel design for a pilot scale anaerobic submerged membrane bioreactor (AnSMBR) equipped with an ultrafiltration unit, treating municipal wastewater at 18 ± 2°C, and inoculated with a mesophilic inoculum without acclimation, was implemented and evaluated over 3 years of stable operation. The AnSMBR operated with a volumetric loading rate between 1.6 to 2.0 kg COD/m(3)UASBd, 12.8 to 14.2h hydraulic retention time, and reached a tCOD removal efficiency of around 90%. Biosolid production was between 0.05 and 0.083 g VS/g CODremoved. Dissolved methane oversaturation in the effluent was observed, reaching average values of 19.1 ± 0.84 mg CH4/L. The permeate flow rate ranged from 10 to 14L/m(2)h with trans-membrane pressure (TMP) values of 400-550 mbar, using cycles of 30s backwash, 7.5 min filtration, and continuous biogas sparging (9-16 m/h). During the three years of continuous operation, the membrane was not physically or chemically cleaned.

Membrane fouling control using a rotary disk in a submerged anaerobic membrane sponge bioreactor

Despite significant research efforts over the last few decades, membrane fouling in anaerobic membrane bioreactors (AnMBRs) remains an unsolved problem that increases the overall operational costs and obstructs the industrial applications. Herein, we developed a method for effectively controlling the membrane fouling in a sponge-submerged AnMBRs using an anaerobic rotary disk MBR (ARMBR). The disk rotation led the effective collision between the sponge and membrane surface; thus successfully enhanced the membrane permeability in the ARMBR. The effect of the disk rotational speed and sponge volume fraction on the membrane permeability and the relationship between the water flow direction and membrane permeability were investigated. The long-term feasibility was tested over 100days of synthetic wastewater treatment. As a result, stable and economical performance was observed without membrane replacement and washing. The proposed integrated rotary disk-supporting media appears to be a feasible and even beneficial option in the AnMBR technology.