Prof. HONDA Ryo
Faculty of Geosciences and civil Engineering, Kanazawa University
Mechanism of fouling mitigation by vanillin in MBR revealed by size-polarity profiling of EPS
Extracellular polymeric substances (EPS) are expected to be primary foulant of membrane filtration process in membrane bioreactor (MBR) processes (Shi et al., 2017) and biofilm formation on membrane surface to cause fouling expectedly is natural behaviour of microbes in MBR sludge (Nguyen et al., 2012). Therefore, inhibiting biofilm formation and EPS production is a promising approach to mitigate membrane fouling.
Recently vanillin - an inhibiting agent of various biological activity is found to effectively to mitigate fouling in a membrane bioreactor process. Vanillin addition is hypothesized to inhibit quorum sensing and subsequent EPS production; however, effect of vanillin on biological activity in sludge was still veiled. In this study, mechanism of fouling mitigation by vanillin was investigated with lab-scale MBR experiments.
EPS in the bulk and cake sludge was extracted and fractionated as soluble microbial products (SMP) by centrifuge, loosely-bound EPS (LB-EPS) by sonication, and tightly-bound EPS (TB-EPS) by alkaline extraction, according to Hong et al. (2017). Each EPS extract was first fractioned by polarity, using reverse-phase HPLC-ELSD equipped with a fraction collector. Collected polarity fraction was subsequently analyzed with size-exclusion HPLC-ELSD. The EPS components were mapped on a 2D chart according to retention time and peak area of the two chromatogram (Hong et al. 2018). Microbial community targeting V3-V4 regions of 16S rRNA gene was analyzed by a high-throughput sequencing system (MiSeq, Illumina).
Size vs. polarity profiling of EPS and microbial community analysis suggested that addition of vanillin reduced fragmentation of EPS by inhibiting EPS degrading bacteria. From these results, vanillin mitigated fouling by the following mechanism: (i) vanillin inhibited EPS degrading bacteria, (ii) by inhibition of EPS degradation, fragmentation of EPS was suppressed and large EPS fraction became dominant, (iii) by lacking small EPS fractions, cake layer became less dense and could maintain better water permeability.