Do biological-based strategies hold promise to biofouling control in MBRs?

Abstract

Biofouling in membrane bioreactors (MBRs) remains a primary challenge for their wider application, despite the growing acceptance of MBRs worldwide. Research studies on membrane fouling are extensive in the literature, with more than 200 publications on MBR fouling in the last 3 years; yet, improvements in practice on biofouling control and management have been remarkably slow. Commonly applied cleaning methods are only partially effective and membrane replacement often becomes frequent. The reason for the slow advancement in successful control of biofouling is largely attributed to the complex interactions of involved biological compounds and the lack of representative-for-practice experimental approaches to evaluate potential effective control strategies. Biofouling is driven by microorganisms and their associated extra-cellular polymeric substances (EPS) and microbial products. Microorganisms and their products convene together to form matrices that are commonly treated as a black box in conventional control approaches. Biological-based antifouling strategies seem to be a promising constituent of an effective integrated control approach since they target the essence of biofouling problems. However, biological-based strategies are in their developmental phase and several questions should be addressed to set a roadmap for translating existing and new information into sustainable and effective control techniques. This paper investigates membrane biofouling in MBRs from the microbiological perspective to evaluate the potential of biological-based strategies in offering viable control alternatives. Limitations of available control methods highlight the importance of an integrated anti-fouling approach including biological strategies. Successful development of these strategies requires detailed characterization of microorganisms and EPS through the proper selection of analytical tools and assembly of results. Existing microbiological/EPS studies reveal a number of implications as well as knowledge gaps, warranting future targeted research. Systematic and representative microbiological studies, complementary utilization of molecular and biofilm characterization tools, standardized experimental methods and validation of successful biological-based antifouling strategies for MBR applications are needed. Specifically, in addition, linking these studies to relevant operational conditions in MBRs is an essential step to ultimately develop a better understanding and more effective and directed control strategy for biofouling.

Keywords: 2,4-dinitrophenol; 2D-PAGE; 3,3′,4′,5-tetrachlorosalicylanilide; AFM; AHL; AIP; ARDRA; ATP; Anti-biofouling; Biofilm; Biological-based; CCCP; CLSM; COD; CS; DGGE; DNP; DOC; ED; EEM; EPBR; EPS; EU; F/M; FISH; FTIR; Fourier transform infrared; Holistic control; MALDI-TOF; MBR; MF; MLSS; MS; Management; Membrane bioreactors; Membrane performance; Microbial community; NF; NMR; NO; NSM; PAOs; PFU; QQ; QS; RO; SEM; SIMS; SMP; SRT; STXM; T-RFLP; TEM; TOC; UF; acyl-homoserine lactone; adenosine triphosphate; amplified ribosomal deoxyribonucleic acid restriction analysis; atomic force microscopy; autoinducer peptide; carbonyl cyanide chlorophenylhydrazone; chemical oxygen demand; confocal laser scanning microscopy; denaturing gradient gel electrophoresis; dissolved organic carbon; energy uncoupling; enhanced biological phosphorous removal; enzymatic disruption; excitation emission matrix; extracellular polymers; fluorescent in situ hybridization; food to microorganisms ratio; mass spectrometry; matrix-assisted laser desorption/ionization -time of flight; membrane bioreactor; microfiltration; mixed liquor suspended solids; nanofiltration; natural small molecules; nitric oxide; nuclear magnetic resonance; plaque forming units; polyphosphate accumulating organisms; quorum quenching; quorum sensing; reverse osmosis; scanning electron microscopy; scanning transmission X-ray microscopy; secondary-ion mass spectrometry; sludge retention time; soluble microbial products; terminal restriction fragment length polymorphism; total organic carbon; transmission electron microscopy; two-dimensional polyacrylamide gel electrophoresis; ultrafiltration.