Life cycle assessment and economic analysis of anaerobic membrane bioreactor whole-plant configurations for resource recovery from domestic wastewater.

The use of the anaerobic membrane bioreactor (AnMBR) process for domestic wastewater treatment presents an opportunity to mitigate environmental, social, and economic impacts currently incurred from energy-intensive conventional aerobic activated sludge processes. Previous studies have performed detailed evaluations on improving AnMBR process subcomponents to maximize energy recovery and dissolved methane recovery. Few studies have broadly evaluated the role of chemical use, membrane fouling management, and dissolved methane removal technologies. A life cycle assessment was conducted to holistically compare multiple AnMBR-based domestic wastewater treatment trains to conventional activated sludge (CAS) treatment. These treatment trains included different scouring methods to mitigate membrane fouling (gas-sparging and granular activated carbon-fluidizing) with consideration of upstream treatment (primary sedimentation vs. screening only), downstream treatment (dissolved methane removal and nutrient removal) and sludge management (anaerobic digestion and lime stabilization). This study determined two process subcomponents (sulfide and phosphorus removal and sludge management) that drove chemical use and residuals generation, and in turn the environmental and cost impacts. Furthermore, integrating primary sedimentation and a vacuum degassing tank for dissolved methane removal maximized net energy recovery. Sustainability impacts were further mitigated by operating at a higher flux and temperature, as well as by substituting biological sulfide removal for chemical coagulation.

Discriminating activated sludge flocs from biofilm microbial communities in a novel pilot-scale reciprocation MBR using high-throughput 16S rRNA gene sequencing.

Membrane bioreactors (MBRs) are a well-established filtration technology that has become a popular solution for treating wastewater. One of the drawbacks of MBRs, however, is the formation of biofilm on the surface of membrane modules. The occurrence of biofilms leads to biofouling, which eventually compromises water quality and damages the membranes. To prevent this, it is vital to understand the mechanism of biofilm formation on membrane surfaces. In this pilot-scale study, a novel reciprocation membrane bioreactor was operated for a period of 8 months and fed with domestic wastewater from an aerobic tank of a local WWTP. Water quality parameters were monitored and the microbial composition of the attached biofilm and suspended aggregates was evaluated in this reciprocating MBR configuration. The abundance of nitrifiers and composition of microbial communities from biofilm and suspended solids samples were investigated using qPCR and high throughput 16S amplicon sequencing. Removal efficiencies of 29%, 16%, and 15% of chemical oxygen demand, total phosphorus and total nitrogen from the influent were observed after the MBR process with average effluent concentrations of 16 mg/L, 4.6 mg/L, and 5.8 mg/L respectively. This suggests that the energy-efficient MBR, apart from reducing the total energy consumption, was able to maintain effluent concentrations that are within regulatory standards for discharge. Molecular analysis showed the presence of amoA Bacteria and 16S Nitrospira genes with the occurrence of nitrification. Candidatus Accumulibacter, a genus with organisms that can accumulate phosphorus, was found to be present in both groups which explains why phosphorus removal was observed in the system. High-throughput 16S rRNA amplicon sequencing revealed the genus Saprospira to be the most abundant species from the total OTUs of both the membrane tank and biofilm samples.

Pilot demonstration of energy-efficient membrane bioreactor (MBR) using reciprocating submerged membrane.

Membrane bioreactor (MBR) is becoming popular for advanced wastewater treatment and water reuse. Air scouring to "shake" the membrane fibers is most suitable and applicable to maintain filtration without severe and rapidfouling. However, membrane fouling mitigating technologies are energy intensive. The goal of this research is to develop an alternative energy-saving MBR system to reduce energy consumption; a revolutionary system that will directly compete with air scouring technologies currently in the membrane water reuse market. The innovative MBR system, called reciprocation MBR (rMBR), prevents membrane fouling without the use of air scouring blowers. The mechanism featured is a mechanical reciprocating membrane frame that uses inertia to prevent fouling. Direct strong agitation of the fiber is also beneficial for the constant removal of solids built up on the membrane surface. The rMBR pilot consumes less energy than conventional coarse air scouring MBR systems. Specific energy consumption for membrane reciprocation for the pilot rMBR system was 0.072 kWh/m3 permeate produced at 40 LMH, which is 75% less than the conventional air scouring in an MBR system (0.29 kWh/m3). Reciprocation of the hollow-fiber membrane can overcome the hydrodynamic limitations of air scouring or cross-flow membrane systems with less energy consumption and/or higher energy efficiency.

Performance evaluation of a novel reciprocation membrane bioreactor (rMBR) for enhanced nutrient removal in wastewater treatment: a comparative study.

This study compared and evaluated the performance of a conventional membrane bioreactor (MBR) and a novel reciprocation MBR (rMBR) which used mechanical membrane reciprocation in place of membrane air scouring in pilot-scale tests. Each system was independently operated for 280 days at a local wastewater treatment plant for a parallel assessment of operating performance. The rMBR was found to be more effective than the MBR with regard to operating performance and energy consumption. Inertial forces created by the reciprocating motion shook foulants from the membrane surface. In addition, because of the looseness of the fibers, they moved relative to each other during reciprocation thus preventing sludge clogging inside the fiber bundle. Because the rMBR does not use aeration for membrane cleaning, the membrane tank in the rMBR maintained anoxic conditions, allowing endogenous denitrification in the membrane tank. The rMBR permeate contained an average of 1.7 mg/L total nitrogen (TN) with less than 1 mg/L NO(3)-N, while the TN concentration in the MBR permeate averaged 5 mg/L with 3.5 mg/L NO(3)-N. The specific energy consumption for membrane reciprocation in the rMBR was 0.064 kWh/m(3), while that for air scouring in the MBR was 0.19 kWh/m(3).

Anaerobic membrane bioreactor treatment of synthetic municipal wastewater at ambient temperature.

The performance of a crossflow anaerobic membrane bioreactor (AnMBR) to treat synthetic municipal wastewater was investigated at different hydraulic retention times (HRTs). The AnMBR was operated at chemical oxygen demand (COD) loading rates of 1 to 2 kg COD/m3 x d for 280 days. The permeate COD concentration was always lower than 40 mg/L, and no noticeable volatile fatty acids were detected, regardless of HRT variations, while soluble COD (SCOD) was accumulated in the reactor with decreases in HRT. The particle size reduction was relatively lower than other studies reported, even after a long operation time resulting from the low operation crossflow velocity. Approximately 30% of COD was not available for methane recovery, irrespective of applied HRTs, as a result of the COD loss by dissolved methane, sulfate reduction, and untreated COD in the permeate. The fraction of methane recovered from the synthetic municipal wastewater decreased from 48 to 35%, with the decrease of HRT from 12 to 6 hours, as a result of the increase of mixed-liquor SCOD, which was rejected and accumulated in the AnMBR. Therefore, AnMBR operation with relatively long HRTs and SRTs may be favorable, to enhance methane recovery and reduce or eliminate sludge production.

A comparative pilot-scale evaluation of gas-sparged and granular activated carbon-fluidized anaerobic membrane bioreactors for domestic wastewater treatment.

Two significantly different pilot-scale AnMBRs were used to treat screened domestic wastewater for over one year. Both systems similarly reduced BOD5 and COD by 86-90% within a 13-32 °C temperature range and at comparable COD loading rates of 1.3-1.4 kg-COD m-3 d-1 and membrane fluxes of 7.6-7.9 L m-2 h-1 (LMH). However, the GAC-fluidized AnMBR achieved these results at a 65% shorter hydraulic retention time than the gas-sparged AnMBR. The gas-sparged AnMBR was able to operate at a similar operating permeability with greater reactor concentrations of suspended solids and colloidal organics than the GAC-fluidized AnMBR. Also, the membranes were damaged more in the GAC-fluidized system. To better capture the relative advantages of each system a hybrid AnMBR comprised of a GAC-fluidized bioreactor connected to a separate gas-sparged ultrafiltration membrane system is proposed. This will likely be more effective, efficient, robust, resilient, and cost-effective.

Methanogenic activities in anaerobic membrane bioreactors (AnMBR) treating synthetic municipal wastewater.

Two laboratory-scale anaerobic membrane bioreactors, AnMBR 1 and AnMBR 2, were run in parallel at 25 and 15 degrees C, respectively. Total chemical oxygen demand (COD) removal efficiency was more than 95% and 85% for AnMBR 1 and 2, respectively. The COD removal of AnMBR 1 was mostly carried out biologically. However, the physical removal on the membrane surface compensated for the decreased biological removal rate in AnMBR 2. The membrane in AnMBR systems is likely not only to retain all biomass in the reactor, but also complement decreased biological removal efficiency at low temperature by rejecting soluble organics. Specific methanogenic activity (SMA) test was used to investigate the methanogenic activity profiles of suspended and attached sludge in AnMBRs treating synthetic municipal wastewater at 25 and 15 degrees C. The methanogenic activity was 51.8 ml CH(4)/g VSSd on day 1 and eventually increased 27% and reached 65.7 ml CH(4)/g VSSd on day 75 for AnMBR 1. However, the methanogenic activity of AnMBR 2 sludge was lower than that of AnMBR 1. The microbial activity of suspended sludge continuously increased, while that of attached sludge gradually decreased in this study. The methanogenic activity of attached sludge was far lower than that of suspended sludge. The role of attached sludge on the membrane in AnMBRs as a biofilm for biological organic removal was minimal compared to suspended sludge.