Submerged Anaerobic Membrane Bioreactor Research Articles

Landfill leachate treatment by means of anaerobic membrane bioreactor

The study was undertaken to examine feasibility of biological treating of landfill leachate in anaerobic submerged membrane bioreactor. The aim of the work was to estimate the optimal concentration of leachate in the reactor influent and process parameters on the base of anaerobic digestion efficiency. The treatment efficiency under different feeding condition of leachate dilution in the range of 5–75% (v/v) with a synthetic wastewater was studied. A higher COD removal over 95% was maintained with leachate addition of 10% and 20% (v/v). Gradual decrease in organic removals was observed as leachate percentage increase. At leachate addition of 25% the COD removal reached value of 80%. For leachate concentration in influent above 30% (v/v) significant decrease of anaerobic treatment efficiency due to inhibition of microbiological activity was observed. The influence of various hydraulic retention time (HRT) and organic loading rate (OLR) on pollutants removal efficiency and biogas production was also investigated. MBR reactor was operated at HRT in the range of 7–1 days and OLR in the range 0.7–4.9 kg COD/m 3 d. The best anaerobic digestion efficiency (COD removal 90%) was observed for HRT of 2 days and OLR of 2.5 kg COD/m 3 d.

Flux and performance improvement in a submerged anaerobic membrane bioreactor (SAMBR) using powdered activated carbon (PAC)

A three litre submerged anaerobic membrane bioreactor (SAMBR) was used to examine the effect of powdered activated carbon (PAC) on COD removal and flux. 98% COD removal efficiency was achieved at a high loading rate (16 gCOD l −1 d −1) and a low hydraulic retention time (HRT) of 6 h in the presence of 3.4 g l −1 of PAC. PAC addition improved start-up and performance during a hydraulic shock by buffering the volatile fatty acids (VFAs), however, a large amount of biomass was important in accommodating the higher loading rate in the SAMBR. Batch assays showed that PAC addition improved methane potential both in terms of amount and inoculation time. COD retention inside the SAMBR for three experiments was proportional to the soluble microbial products (SMPs) contribution to COD, as (VFAs) passed through the membrane at high sparging rates (5 litres per minute—LPM). Size exclusion chromatography showed that the membrane acted as an ultra-filter (<30 kDa) as the cake or gel layer significantly reduced the amount of organics passing through the membrane. PAC adsorbed slowly biodegradable low and high MW residual COD from the bulk liquid, and hence improved COD removal and flux. Particle size distributions demonstrated that PAC also adsorbs fine colloids, and flux data showed that only a thin biofilm was formed due to the high backtransport velocity of PAC. The combined effects of adsorption of fine colloids and dissolved organics, and the formation of a thin cake layer resulted in significant flux improvement from 2 to 9 litres per square metre per hour (LMH) in the presence of 1.67 g l −1 PAC. However, addition of 3.4 g l −1 PAC reduced the flux to 5 LMH by the combined effect of viscosity and its inability to completely adsorb the dissolved organics and fine colloids that resulted in high internal fouling. Under the given operating conditions, addition of 1.67 g l −1 PAC appears to be the optimum quantity in terms of cost, flux and soluble COD removal.

Submerged Anaerobic Membrane Bioreactors (SAMBR): Ready for the Big Ball?

Submerged Anaerobic Membrane Bioreactors (SAMBR): Ready for the Big Ball?

Thermophilic treatment of acidified and partially acidified wastewater using an anaerobic submerged MBR: Factors affecting long-term operational flux

The long-term operation of two thermophilic anaerobic submerged membrane bioreactors (AnSMBRs) was studied using acidified and partially acidified synthetic wastewaters. In both reactors, cake formation was identified as the key factor governing critical flux. Even though cake formation was observed to be mostly reversible, particle deposition proceeds fast once the critical flux is exceeded. Very little irreversible fouling was observed during long-term operation, irrespective of the substrate. Critical flux values at the end of the reactors operation were 7 and 3 L/m 2 h for the AnSMBRs fed with acidified and partially acidified wastewaters, respectively, at a gas superficial velocity of 70 m/h. Small particle size was identified as the responsible parameter for the low observed critical flux values. The degree of wastewater acidification significantly affected the physical properties of the sludge, determining the attainable flux. Based on the fluxes observed in this research, the membrane costs would be in the range of 0.5 €/m 3 of treated wastewater. Gas sparging was ineffective in increasing the critical flux values. However, preliminary tests showed that cross-flow operation may be a feasible alternative to reduce particle deposition.

Cake formation and consolidation: Main factors governing the applicable flux in anaerobic submerged membrane bioreactors (AnSMBR) treating acidified wastewaters

A laboratory scale anaerobic submerged membrane bioreactor (AnSMBR) was operated for over 200 days, with a volatile fatty acid mixture as substrate. Gas sparging was used for mixing and to provide membrane surface shear. Results show that cake formation was entirely governing the applicable flux. Cake formation showed to be mainly reversible on a short-term basis, however cake consolidation was observed when a long-term operation was performed at a flux close to the critical flux. Consolidated cake could not be removed by the back-flush cycles, and required an external physical cleaning procedure. Surprisingly, low levels of internal pore fouling were observed, significantly decreasing the need for chemical cleaning. The critical flux towards the end of the operation period reached 20 L/m 2 h, at a solids concentration of 40 g/L and a gas superficial velocity of 57 m/h. Further increases in gas superficial velocity were ineffective in achieving a substantially higher critical flux.

Hydrogen-dependent denitrification of water in an anaerobic submerged membrane bioreactor coupled with a novel hydrogen delivery system

Hydrogen-dependent denitrification has gained significant attention due to its potential economic advantage over heterotrophic denitrification. However, effective hydrogen delivery and biomass retention under anaerobic conditions are significant challenges to implementation of this process. An innovative hydrogenotrophic denitrification system, that addresses these challenges, consisting of an anaerobic submerged membrane bioreactor (MBR) and a novel hydrogen delivery unit, was evaluated for removal of nitrate from a synthetic groundwater feed. The hydrogen delivery unit was designed to release hydrogen-supersaturated water to the reactor and was efficient in hydrogen delivery, providing complete mass transfer. The anaerobic submerged MBR was successful in both reducing nitrate from 25 mg NO 3–N l −1 to below detection and separating biomass from treated water to produce effluent free of suspended solids. Nitrogen gas produced during denitrification was internally recycled to effectively achieve membrane scouring and reactor mixing. The total organic carbon was similar to that of the incoming feed water, averaging approximately 6 mg l −1.

Activated Carbon Addition to a Submerged Anaerobic Membrane Bioreactor: Effect on Performance, Transmembrane Pressure, and Flux

This study examined the effect of the addition of activated carbon to three, 3 L submerged anaerobic membrane bioreactors (SAMBRs) in terms of chemical oxygen demand (COD) removal, flux, and transmembrane pressure (TMP). The feed was a synthetic substrate with a COD of 460mgL−1, with one reactor run as a control, one with 1.7gL−1 of powdered activated carbon (PAC), and the third with 1.7gL−1 of granular activated carbon (GAC). While COD removal was high in all reactors (>90%), in comparison to the control (SAMBR1), the average COD removal in SAMBR2 (PAC) increased by 22.4%, while SAMBR3 with GAC was not significantly better. Because PAC has a significantly greater surface area per mass than GAC, it is probable that this difference was primarily due to the greater absorbance of fine colloidal particles and high molecular weight organics onto the carbon surface. These effects manifested themselves by SAMBR2 having lower TMPs and higher fluxes than both SAMBR3 and SAMBR1. Volatile fatty acids in the effluent from all three SAMBRs were extremely low (<18mgL−1), even during step changes in hydraulic retention tune, and most of the soluble COD in the effluent was soluble microbial products. Biochemical methane potential assays showed that biomass in the SAMBRs was less active than the seed sludge, and it appears that the addition of activated carbon to Reactors SAMBR2 and SAMBR3 provided a solid support for growth, and hence reduced floc breakage.

Hydrogen-driven denitrification of wastewater in an anaerobic submerged membrane bioreactor: potential for water reuse

An anaerobic submerged membrane bioreactor was coupled with a novel hydrogen delivery system for hydrogenotrophic denitrification of municipal final effluent containing nitrate. The biological treatment unit and hydrogen delivery unit were proven successful in removing nitrate and delivering hydrogen, respectively. Complete hydrogen transfer resulted in reducing nitrate below detectable levels at a loading of 0.14 kg Nm(-3) d(-1). The produced water met all drinking water guidelines except for color and organic carbon. However, the organic carbon was removed by 72% mostly by membrane rejection. To reduce the organic carbon and color of the effluent, post treatment of the produced water is required.

Characterization of dissolved compounds in submerged anaerobic membrane bioreactors (SAMBRs)

AbstractTwo submerged anaerobic membrane bioreactors (SAMBRs) with essentially 100% cell recycle (150 days retention time, SRT), one with powdered activated carbon addition (PAC 1.7 g L−1) and one without, were continuously fed a low‐strength feed (450 mg COD L−1) in order to investigate membrane fouling and to characterize the foulants. The SAMBR which did not receive PAC experienced more fouling, and the molecular weight (MW) distribution showed that there was a greater amount of high‐MW compounds in this reactor when compared with the reactor with PAC. Size exclusion chromatography showed that although extracellular polymeric substances (EPS) seemed to contribute to the soluble chemical oxygen demand (COD) inside the reactor, it was mainly rejected by the membrane. High‐MW protein and carbohydrate material originating mainly from cell lysis and EPS seemed to be the main organics that contributed to the internal fouling of the membrane. Copyright © 2006 Society of Chemical Industry

Cake layer formation in anaerobic submerged membrane bioreactors (AnSMBR) for wastewater treatment

Cake layer formation in anaerobic gas-sparged submerged membrane bioreactors was studied using the critical flux concept, at 30 and 55 °C. The impact of biomass concentration, from 25 to 50 g TSS/L, and superficial gas velocity, up to 70 m/h, of over cake layer formation was studied, using response surface methodology. Under mesophilic conditions, assessed critical flux values were in the range 5–21 L/m 2 h, while a first order relation between critical flux and both biomass concentration and gas flow rate was observed. Within studied range of experimentation, at 30 °C, effect of biomass concentration on critical flux was three times higher than the effect of gas superficial velocity. Under thermophilic conditions, critical flux values were in the range 16–23 L/m 2 h, even though gas superficial velocities were about 50% lower than in the mesophilic reactor. At 55 °C, both biomass concentration and gas superficial velocity presented a value, below and over which no further effect on critical flux was observed. On a short-term basis (minutes or hours), cake layer formation was mainly reversible. However, cake layer formation proceeds fast once critical flux has been exceeded, restricting feasible operational flux to the range of the critical flux. Better performance of thermophilic reactor opens interesting perspectives for the application of membrane anaerobic bioreactors at high temperatures, condition where biomass aggregation is difficult to achieve.

High rate sulfate reduction in a submerged anaerobic membrane bioreactor (SAMBaR) at high salinity

Sulfate reduction in salt rich wastewaters (50 g NaCl L −1 and 1 g MgCl 2·6H 2O L −1; conductivity 60–70 mS cm −1) was investigated in a 6 L submerged anaerobic membrane bioreactor (SAMBaR) and inoculated solely with the halotolerant sulfate reducing bacterium Desulfobacter halotolerans. The SAMBaR was fed with acetate and ethanol at organic loading rates up to 14 g COD L −1 day −1 in excess of sulfate (COD/SO 4 2− of 0.5) and operated at pH 7.2 ± 0.2 and a hydraulic retention time (HRT) from 8 to 36 h. A sulfate reduction rate up to 6.6 g SO 4 2− L −1 day −1 was achieved in the SAMBaR operating at a flux of 17.1 L m −2 h −1, which resulted in a HRT of 9 h including the backflow of permeate used for backflushing. The fairly constant very high specific sulfate reduction rate of 5.5 g SO 4 2− g VSS −1 day −1 showed that the performance of the SAMBaR was limited by the low amount of biomass (0.85 g VSS L −1) present in the reactor at the end of the experiment. It was shown that sulfate reducing submerged anaerobic membrane bioreactors can be operated over extended periods of time without chemical cleaning of the membranes at a certain fixed flux if this flux is substantially below the nominal critical flux determined experimentally (18–21 L m −2 h −1). Intermittent operation as well as backflush of the membranes were shown to slow the fouling in the membranes. Frequent backflush (e.g. 1 min each 10 min) is the suggested operational strategy to minimize fouling in anaerobic MBRs.