A novel biphasic extractive membrane bioreactor for minimization of membrane‐attached biofilms

Abstract

Extractive membrane bioreactor (EMB) systems offer a means of biologically treating wastewaters, but, like other membrane processes, are constrained by their tendency to be fouled by membrane-attached biofilms (MABs). This study describes a new approach to eradicate MAB formation and accumulation in EMB systems. To this end, an innovative EMB configuration, the biphasic extractive membrane bioreactor (BEMB), has been developed. In BEMB systems, the two main constituents of the EMB process, membrane and bacteria, are kept separated and interact via a suitable recirculating solvent. Nineteen candidate solvents were tested to assess their suitability for BEMB application. Based on the results of the solvent selection, guidelines are provided to screen solvents for BEMB application. BEMB and EMB runs were carried out to demonstrate the effectiveness of BEMB technology in avoiding MAB accumulation and to compare BEMB and EMB performance. A synthetic wastewater containing monochlorobenzene (MCB) was used as a model system. Abiotic BEMB and EMB runs were carried out and used as comparative references for estimating the effect of MAB accumulation on system performance. MAB thickness in the BEMB systems was controlled at 18 microm during 1 month of operation, whereas, in the EMB systems, MAB thickness reached 1250 microm. Analysis of mass transport in EMB and BEMB systems revealed that the high affinity of the permeating molecules for the solvent may contribute to a reduction in shell-side mass transfer resistance. This reduction of shell-side mass transfer resistance and the absence of MAB accumulation led to overall mass transfer coefficients of about sevenfold greater (4.5 x 10(-5) m s(-1)) in the BEMB system than in the EMB system (0.6 x 10(-5) m s(-1)).

Control of membrane‐attached biofilms using surfactants

“…Formation of membraneattached biofilms (MABs) results in a host of undesirable effects, including reduced flux of permeating molecules and increased module pressure drop (Flemming et al, 1994). These effects demand countermeasures (such as expensive membrane pre-treatments), downtime for membrane cleaning or replacement (Flemming et al, 1994), or complex process design (Splendiani et al, 2003).…”

Biocatalytic membrane reactors (BMR)

“…The organic solvent must not be toxic for bacteria or inhibit the pollutant metabolization; it must not be utilized by bacteria as a source of carbon and energy -it must exhibit low microbial adhesivity, low membrane swelling and emulsionforming tendency. According to Splendiani et al [78], the solvent that best satisfies these requirements is perfluoromethyldecalin (PFMD). They tested the BEMBR system with PFMD as a solvent for degradation of monochlorobenzene using a synthetic wastewater.…”

“…Splendiani et al [78] have developed the biphasic extractive membrane bioreactor (BEMBR) in which biofilm accumulation was controlled by preventing direct contact between microorganisms and the membrane. In BEMBR systems, the two main constituents of the process, membrane and bacteria, are kept separated and interact via a suitable recirculating solvent, as shown in Fig.…”

“…Consequently, an inverse relationship between the organic flux and biofilm thickness was observed. Several modifications have been attempted to suppress the metabolism of the biofilmforming bacteria, such as addition of sodium chloride [76], increasing the shear stress on the membrane surface [77], using a biphasic system [78] and the addition of nitrate as an electron acceptor instead of oxygen [79]. Nitrate is highly soluble in water and therefore, the nitrate concentration in the biomedium can be sufficiently high to fully penetrate the biofilm, ensuring that nitrate is present at the biofilm/membrane interface.…”

Treatment of phenol in synthetic saline wastewater by solvent extraction and two-phase membrane biodegradation

“…This may make phase separation and subsequent treatment (e.g., solvent recovery) more difficult. On the other hand, an extractive membrane bioreactor (EMBR) has been proposed to solve the problems outlined above [1,10,11], which uses a dense membrane that is virtually permeable to organic compounds but non-permeable to water or ionic species. The membrane separates wastewater from cell medium where biodegradation occurs under controlled conditions, making it useful for the treatment of saline effluents.…”