Cross-flow Membrane Bioreactor Research Articles

Fluorescence-assisted real-time study of magnetically immobilized enzyme stability in a crossflow membrane bioreactor

The detailed structures and distribution of enzymatically active magnetic-responsive dynamic layers (EnzSP) were investigated for the first time in a crossflow superparamagnetic biocatalytic membrane reactor (XF-BMRSP). The trade-off between a higher mass transfer rate, lower fouling tendency, and preventing washout of the dynamic layer, highly depends on the balance of the various forces that act on the EnzSP. The real-time visual inspection of the biointerface was realized through the design and fabrication of an adapted crossflow system, guided by computational fluid dynamics (CFD) simulations. Time-resolved images of the dynamic layer under a broad range of operational conditions was obtained using fluorescence microscopy.The deposition, dispersion and stability of the dynamic layer was mainly governed by the external magnetic force. The shear force did not cause significant particle washout when a buffer solution was recirculated without permeation even under a turbulent flow regime (6.4 cm/s ∼ Re = 5200). The removal of the external magnetic force after initial magnetic immobilization of the EnzSP, or the substitution of a smooth flow velocity by the propagation of an impulse flow, significantly affected the stability of the dynamic layer.Although membrane fouling occurs at the membrane-solution interface, where a laminar flow regime prevails, most membrane fouling models are based on turbulent flow. Therefore, the detailed, time-resolved images obtained here can provide solid foundation for the development of theoretical models that can describe the membrane fouling under the more representative laminar flow regime.

Biochemical Kinetics of Cross flow Membrane Bioreactor Processes in the Treatment of Refinery Wastewater

A lab-scale cross flow membrane bioreactor (CF-MBR) was operated to determine the biokinetic coefficients under MLSS concentrations of 5000 and 3000 mg/L. The investigation showed that the yield (Y), the endogenous decay coefficient (kd), the maximum specific growth rate (μm) and the saturation constant (KS) were 0.276 mg/mg, 0.07 /day, 0.653 /day, and 396.62 mg COD/L respectively for MLSS 5000 mg/L, and 0.222 mg/mg, 0.09 /day, 1.2 /day, and 659.45 mg COD/L for MLSS 3000 mg/L. The values of kinetic coefficients were within the normal range of the activated sludge process found in the literature, except the values of Y. However, value of Y increased with the increase of MLSS. Kinetic parameters determined from CF-MBR process were used to simulate the effluent COD. The simulation study showed good agreement between model prediction and experimental data. Sensitivity analysis was carried out to determine influence of biokinetic parameters on the effluent substrate concentration. From the analysis, it was evident that kd and KS were directly proportional to the effluent substrate concentration, while μm was inversely proportional.

Effect of cytostatic drugs on the sludge and on the mixed liquor characteristics of a cross-flow membrane bioreactor: Consequence on the process

The influence of cyclophosphamide and its principal metabolites (CPs) on the physicochemical properties of the mixed liquor of a cross-flow membrane bioreactor and the consequences for membrane fouling were investigated. The influence of CPs was determined by comparing the performance of two bioreactors running in parallel, MBR-CPs (with CPs) and MBR-control (without CPs). The physicochemical properties of the mixed liquor were characterized by soluble extracellular polymeric substances (soluble EPS content), particle size distribution and specific cake resistance. Results suggested that the CP toxicity altered the characteristics of the biological matrix of the activated sludge. Micro-organisms exposed to CPs showed higher endogenous respiration rates than MBR-control micro-organisms. The accumulation of soluble EPS and the formation of small particles (in MBR-CPs after cross-flow velocity was raised) increased the resistance to filtration. The fouling potential of the supernatant seemed to be linked more closely to the concentration of polysaccharides than of proteins and humic substances. Modifications of the membrane performance were observed. Under operating conditions, membrane fouling was faster in MBR-CPs than MBR-control. Moreover, the membrane played an important role in the permeate quality and the overall performance of the process, making possible the biological treatment of such an effluent.

Effect of oxygen concentration on biological nitrification and microbial kinetics in a cross-flow membrane bioreactor (MBR) and moving-bed biofilm reactor (MBBR) treating old landfill leachate

Ammonium nitrogen concentration in leachate from old Italian landfills ranges from 0.5 to as high as 3 g L −1. In this paper biological nitrogen removal from leachate has been achieved by partial nitrification to nitrite in a pure-oxygen membrane bioreactor (PO-MBR) and by subsequent denitrification in a moving-bed biofilm reactor (MBBR). When ammonium is biologically oxidized to nitrite, only 75% of the oxygen required for full nitrification is needed. Moreover, denitrification can be performed by saving 30–40% of the carbon required. The process was carried out by an MBR oxidation tank of 500 L equipped with an UF ceramic membrane followed by a 540-L post-denitrification tank filled with moving plastic support media. The best operational conditions to achieve partial nitrification were analyzed. TKN loading rate was variable from 50 to 120 g TKN (kg TSS day) −1 with an influent ammonia concentration between 1000 and 1500 mg L −1. When DO concentration in the MBR was kept in the range 0.2–0.5 mg L −1, 90% oxidation of ammonia to nitrite was achieved, with stable inhibition of nitrite-oxidizing bacteria even at sludge retention time higher than 45 days.

Performance of a crossflow membrane bioreactor (CF–MBR) when treating refinery wastewater

The use of a crossflow membrane bioreactor (CF–MBR) in treating wastewater discharged by a petroleum refinery was investigated. The performance of the CF–MBR process was evaluated at MLSS concentrations of 5000 and 3000 mg/l. The process performance was measured in terms of the hydraulic efficiency as well as the COD removal efficiency. A laboratory-scale experimental set-up comprised mainly of tubular ceramic membranes, aeration tank, and circulation pump was used throughout the investigation. The results of the investigation showed that a COD removal efficiency of more than 93% was obtained at both MLSS values. The study also showed that hydraulic retention time did not have a significant effect on the system’s performance. The relationship between permeate flux and crossflow velocity was found to be best described by a power relationship (J = kV n ) where constants k and n were affected by MLSS concentration. The cleaning mechanism investigation showed that cleaning the membrane with an acidic detergent, Superclean, with a pH value of about 1.5, produced the best results.

Experimental Study of Mass Transfer Phenomena in a Cross Flow Membrane Bioreactor: Aeration and Membrane Separation

Experimental work carried out on wastewater from a wastewater treatment plant (WWTP) showed that in a cross flow membrane bioreactor the gas/liquid transfer is highly dependent on the biomass concentration. In new biological wastewater membrane treatment processes (mostly using deep end membranes), the biomass concentration is usually about 15 g/L, which entails a decrease in the bioreactor aeration capacity by a factor of approximately four compared with clean water. The gas/liquid transfer may therefore become a limiting step in this type of process. To prevent the operating costs of the biological treatment from increasing, it is imperative that the oxygen transfer be optimized. Membrane experiments showed that the permeate flux is highly dependent on the biomass concentration and the tangential velocity in the membrane module.

Immobilization of cross-linked lipase aggregates within microporous polymeric membranes

A new approach is proposed to immobilize lipase into microporous polymeric membrane via embedding cross-linked enzyme aggregates (CLEA) within membrane pores. Preparation of biocatalytic membranes was implemented with hydrophilic cellulose and hydrophobic PTFE membranes. Formation of lipase CLEAs is initiated by solvent exchange between aqueous solution of the enzyme filling membrane pores and organic media containing cross-linking agent. The influence of organic media composition and matrix hydrophilicity/hydrophobicity on membrane biocatalytic properties has been studied. Highly effective biocatalytic membranes with embedded lipase CLEA have been obtained on the base of both hydrophilic and hydrophobic membranes by varying the content of glutaric dialdehyde used as a cross-linking agent. Bio-imprinting has been tested as a mean to improve efficiency of the biocatalytic membranes. Biocatalytic esterification of oleic acid with n-butanol has been studied in cross-flow membrane bioreactor with membrane-supported lipase CLEA using hexane and iso-octane as reaction solvents of different hydrophobicity.

Anaerobic treatment of wastewater with high organic content using a stirred tank reactor coupled with a membrane filtration unit

Using a cross-flow membrane bioreactor, high anaerobic conversion rates of three different types of wastewater with varying organic content were achieved. Loading rates obtained were as follows: 20 g COD L −1 d −1 for artificial wastewater, approximately 8 g COD L −1 d −1 from vegetable processing industry (sauerkraut brine) and 6–8 g COD L −1 d −1 for wastewater from an animal slaughterhouse. At stable conditions, COD-removal rates in all three wastewaters were higher than 90%. Methane yields from the treatment of artificial wastewater, sauerkraut brine, and animal slaughterhouse wastewater were in the range of 0.17–0.30, 0.20–0.34, and 0.12–0.32 L n g −1 COD −1 fed, respectively. The complete retention of biomass and suspended solids is a unique feature of this treatment process, which combines a high loading capacity and at the same time, high COD removal rates even for complex wastewater containing high concentrations of particulate matter.

The behavior of membrane fouling initiation on the crossflow membrane bioreactor system

A membrane bioreactor (MBR) system (i.e. an activated sludge system where the clarifier has been replaced with membrane filtration) has many advantages compared with the conventional activated sludge process. However a serious problems that has prevented this technology from reaching its potential is membrane fouling. In this study, the biomass was cultivated under three conditions: normal (high dissolved oxygen, DO); bulking; and normal conditions with low DO concentration. Membrane filtration tests were performed with cellulose acetate (CA), sulfonated polyethersulfone (SPES) and polyethersulfone (PES) membranes, respectively. Relatively hydrophobic PES membranes fouled more seriously than hydrophilic CA membranes. This phenomenon was especially significant under bulking conditions. Ultimate flux was almost equal for all three membrane types however, since the PES and SPES started with higher initial fluxes. Effluent quality was not affected by membrane fouling/flux but did deteriorate at low DOs.

Effect of pump shear on the performance of a crossflow membrane bioreactor

The influences of pumping shear on the performance of a crossflow membrane bioreactor (MBR) were investigated. To compare the intensity of pumping shear, two types of pumps (a centrifugal pump and a rotary one) were used in turn to recirculate mixed liquor. Rotary pump system imposed much stronger shear to microbial floc than centrifugal one and resulted in severe floc breakage. Colloidal particles and organics were liberated from microbial floc by shear and caused rapid loss of membrane permeability by the formation of dense cake layers on the surface of membrane. Recirculation of mixed liquor with a rotary pump gradually increased the soluble COD in the bioreactor and deteriorated microbial activity. After 7 days’ operation, specific oxygen uptake rate (SOUR) of microorganisms in rotary pump system reduced to 78% of initial condition. With a centrifugal pump, however, buildup of soluble COD was not observed and change in microbial activity was negligible. Sludge yield in MBR process was lower than that (0.4–0.5 g MLVSS gCOD −1) reported in a conventional activated sludge process: 0.3 g MLVSS gCOD −1 for the centrifugal pump system and 0.2 g MLVSS gCOD −1 for the rotary pump system.

Ultrafiltration of activated sludge with ceramic membranes in a cross-flow membrane bioreactor process

A cross-flow membrane bioreactor (MBR) for raw municipal wastewater treatment, consisting of a suspended growth bioreactor and a ceramic membrane ultrafiltration unit, was run over a period of more than 300 days in a wastewater treatment plant (WWTP). Sludge Retention Times (SRT) of 20, 10 and 5 days, respectively, and Hydraulic Retention Times (HRT) of 15 and 7.5 hours were tested. Membrane fouling was found to be a function of SRT and permeate flux. Under an SRT of 20 days and flux of 71 l/m2\ · h at 30°C, the MBR was successfully run over 70 days without the need for chemical cleaning. However chemical cleaning had to be undertaken every 3–5 days at shorter sludge retention times (typically an SRT of five days and a flux of 143 l/m2\ · h at 30°C). In this study, fouling materials were removed efficiently through chemical cleaning, with an average permeablity recovery of 87±11%.

Retrofitting municipal sewage treatment plants using an innovative membrane-bioreactor system

Most of the municipal sewage treatment plants (MSTPs) being operated in Korea were designed for wastewater with average concentrations of municipal sewage. However, they are in fact being operated at low organic loading. Thus, most of the secondary small-scale sewage treatment plant cannot satisfy the effluent standard. An innovative ultrafiltration membrane-bioreactor (MBR) system was proposed to retrofit the existing MSTP. The objective of this study was to investigate the feasibility of applying ultrafiltration MBR to the conventional activated sludge process in order to improve the treatment efficiency of the plant. The tested membrane was a UF of 50 kDa and an effective surface area per module was 8.4m 2. The UF was operated with about 2m/s of the crossflow velocity. In preliminary experiments, the MBR was more effective than the direct ultrafiltration of sewage for the enhancement of effluent quality and the preventing fouling. In the crossflow membrane-bioreactor (CFMBR) system, the COD concentration of the effluent was maintained at less than 10 mg/L, regardless of the influent COD concentration. The total nitrogen and total phosphorus of the effluent were 5 mg/L and 1 mg/L, respectively. The CFMBR system could completely remove pin-flocs which occurred in the sedimentation tank due to the low organic loading. The water qualities of the effluent obtained from all the experiments in this study were satisfied to the guidelines for the effluent discharge. Stable operation of a CFMBR, as judged by the effluent COD, SS and T-N concentrations, was achieved with low organic wastewater for 40 days without chemical washing.

Experimental analysis of a cross-flow membrane bioreactor with entrapped whole cells: influence of transmembrane pressure and substrate feed concentration on reactor performance

In a previous paper the authors gave a detailed description of the process for the production of capillary ultrafiltration bioactive membranes. Whole cells of Sulfolobus solfataricus were entrapped within the polymeric matrix of asymmetric polysulphone membranes. In this paper the kinetic behaviour of a cross-flow bioreactor equipped with such membranes is discussed with reference to hydrolysis of lactose to glucose and galactose, catalyzed by a cytoplasmic β-galactosidase. An experimental investigation is presented of the effects of transmembrane pressure and substrate feed concentration on reactor performance, based on substrate conversion in the permeate. Long-term operation and storage indicate a remarkable kinetic stability of the immobilized cells.