Chungheon Shin

Anaerobic Fluidized Bed Membrane Bioreactor for Wastewater Treatment

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.

Pilot-scale temperate-climate treatment of domestic wastewater with a staged anaerobic fluidized membrane bioreactor (SAF-MBR).

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 6.8h. Average chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) 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 BOD5 removals of 98% and 90%, respectively, were obtained with average effluent COD never higher than 23 mg/L nor BOD5 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.

Anaerobic treatment of low-strength wastewater: A comparison between single and staged anaerobic fluidized bed membrane bioreactors

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 (200mg/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 2-4h. Over more than 200d of continuous operation, trans-membrane pressure (TMP) in both systems was less than 0.2bar 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.

Low energy single-staged anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for wastewater treatment

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.

Effects of influent DO/COD ratio on the performance of an anaerobic fluidized bed reactor fed low-strength synthetic wastewater.

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.

Current status of the pilot-scale anaerobic membrane bioreactor treatments of domestic wastewaters: A critical review

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 1.35kWh/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.

Lower operational limits to volatile fatty acid degradation with dilute wastewaters in an anaerobic fluidized bed reactor.

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 200mg/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.

Development and application of a procedure for evaluating the long-term integrity of membranes for the anaerobic fluidized membrane bioreactor (AFMBR)

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.