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Treatment of domestic wastewater can recover valuable resources, including clean water, energy, and ammonia. Important metrics for these systems are greenhouse gas (GHG) emissions and embodied energy, both of which are location- and technology-dependent. Here, we determine the embodied energy and GHG emissions resulting from a conventional process train, and we compare them to a nonconventional process train. The conventional train assumes freshwater conveyance from a pristine source that requires energy for pumping (US average of 0.29 kWh/m

Anaerobic membrane bioreactors can now produce effluent that meets regulatory standards for BOD, enabling energy recovery and use of the treated effluent for irrigation. RO treatment of this effluent can potentially enable recovery of potable water and total ammonia nitrogen (TAN). In this study, we optimized the removal of TAN from the effluent of a staged anaerobic membrane bioreactor (SAF-MBR), a system that consists of an anaerobic fluidized bed reactor and anaerobic membrane bioreactor. The SAF-MBR effluent was treated using an ESPA RO membrane. The result was a high-quality RO permeate that meets the typical potable water guidelines (≤1 mg N L−1). Hydraulic operating conditions (i.e., pressure and flux settings) did not affect TAN rejection efficiency, but pH had major impacts, due to changes in ammonium/ammonia speciation and membrane surface charge. At pH 6, the TAN rejection efficiency was optimal at 99.8%. For pH > 6, the passage of uncharged NH3 increased, decreasing TAN removal. For pH < 6, the membrane retained a progressively less negative (carboxylate) charge as the pH decreased, decreasing ammonium removal from the optimum and allowing increased passage of ammonium into the permeate. Our results suggest that an RO membrane having a lower isoelectric point (IEP) can enable higher TAN rejection efficiencies. A more concentrated RO retentate enables more efficient recovery of ammonia for reuse, and the energy required is less than the energy needed for biological removal of NH3 as N2 followed by synthesis of NH3 from N2 by the Haber–Bosch process. Further systems level research is needed to assess the energy intensity of different options for recovery and reuse of concentrated ammonia.

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

Conventional aerobic secondary treatment of domestic wastewater is energy intensive. Here we report net energy positive operation of a pilot-scale anaerobic secondary treatment system in a temperate climate, with low levels of volatile solids for disposal ( 0.15 mgVSS/mgCOD

This review presented the performances of the pilot-scale anaerobic membrane bioreactors (AnMBRs) treating domestic wastewater. High COD removal efficiencies and low biosolids productions were achieved at HRTs comparable to conventional aerobic processes under ambient temperatures. The energy demands for fouling control in the pilot-scale AnMBRs ranged from 0.04 to 1.35 kWh/m3, which is lower than those of lab-scale AnMBRs and aerobic MBRs. The energy demands for fouling control were in the order of gas sparging > particle sparging > rotating membrane AnMBR. Two major factors affecting the energy demand in gas sparging AnMBRs were specific gas demands (SGDm) and operating flux. The energy potentials in wastewater were significantly affected by the influent sulfate concentrations. Energy balances indicated that five out of nine pilot-scale AnMBRs was energy positive. However, further improvements of the AnMBRs are required to implement the energy positive wastewater treatment process.

An aluminum dioxide (Al2O3) ceramic membrane was used in a single-stage anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for low-strength wastewater treatment. The AFCMBR was operated continuously for 395days at 25°C using a synthetic wastewater having a chemical oxygen demand (COD) averaging 260mg/L. A membrane net flux as high as 14.5-17L/m2h was achieved with only periodic maintenance cleaning, obtained by adding 25mg/L of sodium hypochlorite solution. No adverse effect of the maintenance cleaning on organic removal was observed. An average SCOD in the membrane permeate of 23mg/L was achieved with a 1h hydraulic retention time (HRT). Biosolids production averaged 0.014±0.007gVSS/gCOD removed. The estimated electrical energy required to operate the AFCMBR system was 0.039kWh/m3, which is only about 17% of the electrical energy that could be generated with the methane produced.

A bench-scale short-term test, developed to predict the long-term integrity of membranes with potential for use in anaerobic fluidized-bed membrane bioreactors, was used to evaluate several commercial hollow-fiber membranes. It was found that membrane performance varied widely, some membranes failing much more rapidly than others. Also found was that larger sizes of the fluidized media, in this case granular activated carbon (GAC), severely affected membrane structural integrity more than did smaller sizes, as did the method used for membrane attachment. Within the limits studied, the GAC packing ratio had only a minor impact. A decrease in membrane permeability that sometimes resulted during the testing and was caused by the deposition of fine GAC particles could be eliminated without membrane damage through simultaneous chemical cleaning and sonication. This new testing procedure should be useful for selecting membranes and reactor operating conditions to better ensure long-term operating performance of anaerobic fluidized-bed membrane bioreactors.

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.

A general concern that anaerobic treatment of dilute wastewaters is limited by the inability of methanogenic and related syntrophic organisms to reduce substrate concentrations adequately was evaluated using a 35 °C granular activated carbon-containing laboratory-scale fluidized bed reactor fed an acetate-propionate equal chemical oxygen demand (COD) mixture synthetic wastewater. Contrary to general expectations, effluent acetate and propionate concentrations remained near or below their detection limits of 0.4 mg COD/L with influent COD of 200 mg/L, 17 min hydraulic retention time, and organic loading as high as 17 kg COD/m 3 d, or with influent COD values ranging from 45 to 2010 mg COD/L and organic loadings of 4.2–4.5 kg COD/m 3 d. The effluent acetate concentrations in these well-fed systems were at or much below reported threshold limits for starving non-fed cultures, suggesting that a better understanding of threshold values and factors affecting treatment efficiency with anaerobic treatment of dilute wastewaters is needed.

Anaerobic membrane bioreactors have potential for energy-efficient treatment of domestic and other wastewaters, membrane fouling being a major hurdle to application. It was found that fouling can be controlled if membranes are placed directly in contact with the granular activated carbon (GAC) in an anaerobic fluidized bed bioreactor (AFMBR) used here for post-treatment of effluent from another anaerobic reactor treating dilute wastewater. A 120-d continuous-feed evaluation was conducted using this two-stage anaerobic treatment system operated at 35 °C and fed a synthetic wastewater with chemical oxygen demand (COD) averaging 513 mg/L. The first-stage was a similar fluidized-bed bioreactor without membranes (AFBR), operated at 2.0-2.8 h hydraulic retention time (HRT), and was followed by the above AFMBR, operating at 2.2 h HRT. Successful membrane cleaning was practiced twice. After the second cleaning and membrane flux set at 10 L/m(2)/h, transmembrane pressure increased linearly from 0.075 to only 0.1 bar during the final 40 d of operation. COD removals were 88% and 87% in the respective reactors and 99% overall, with permeate COD of 7 ± 4 mg/L. Total energy required for fluidization for both reactors combined was 0.058 kWh/m(3), which could be satisfied by using only 30% of the gaseous methane energy produced. That of the AFMBR alone was 0.028 kWh/m(3), which is significantly less than reported for other submerged membrane bioreactors with gas sparging for fouling control.

A pilot-scale staged anaerobic fluidized membrane bioreactor (SAF-MBR) was operated continuously for 485 days, without chemical cleaning of membranes, treating primary-settled domestic wastewater with wastewater temperature between 8 and 30 °C and total hydraulic retention time (HRT) between 4.6 and 6.8 h. Average chemical oxygen demand (COD) and biochemical oxygen demand (BOD 5 ) removals averaged 81% and 85%, respectively, during the first winter at 8–15 °C before full acclimation had occurred. However, subsequently when fully acclimated, summer and winter COD removals of 94% and 90% and BOD 5 removals of 98% and 90%, respectively, were obtained with average effluent COD never higher than 23 mg/L nor BOD 5 higher than 9 mg/L. Operational energy requirement of 0.23 kW h/m 3 could be met with primary and secondary methane production, and could be reduced further through hydraulic change. Biosolids production in all seasons averaged 0.051 g volatile suspended solids per g COD removed.

Performance of a single anaerobic fluidized membrane bioreactor (AFMBR) was compared with that of a staged anaerobic fluidized membrane bioreactor system (SAF-MBR) that consisted of an anaerobic fluidized bed bioreactor (AFBR) followed by an AFMBR. Both systems were fed with an equal COD mixture (200 mg/L) of acetate and propionate at 25 °C. COD removals of 93–96% were obtained by both systems, independent of the hydraulic retention times (HRT) of 2–4 h. Over more than 200 d of continuous operation, trans-membrane pressure (TMP) in both systems was less than 0.2 bar without significant membrane fouling as a result of the scouring of membrane surfaces by the moving granular activated carbon particles. Results of bulk liquid suspended solids, extracellular polymeric substances (EPS), and soluble microbial products (SMP) analyses also revealed no significant differences between the two systems, indicating the single AFMBR is an effective alternative to the SAF-MBR system.

The effect of influent DO/COD (dissolved oxygen/chemical oxygen demand) ratio on the performance of an anaerobic fluidized bed reactor (AFBR) containing GAC was studied. A high influent DO concentration was found to have adverse impacts on organic removal efficiency, methane production, and effluent suspended solids (SS) concentration. These problems resulted with a DO/COD ratio of 0.12, but not at a lower ratio of 0.05. At first organic removal appeared satisfactory at the higher DO/COD ratio at a hydraulic retention time of 0.30 h, but soon a rapid growth of oxygen-consuming zoogloeal-like organisms resulted, eventually causing high effluent SS concentrations. The influent DO also had an inhibitory effect, resulting in a long recovery time for adequate methanogenic activity to return after influent DO removal began. With the growing interest in anaerobic treatment of low COD wastewaters, the increased possibility of similar adverse DO effects occurring needs consideration.