Architecture, component, and microbiome of biofilm involved in the fouling of membrane bioreactors

Tomohiro Inaba,Atsushi Ogata,Hiroshi Habe,Tomoyuki Hori,Hidenobu Aizawa

doi:10.1038/s41522-016-0010-1

Abstract

Biofilm formation on the filtration membrane and the subsequent clogging of membrane pores (called biofouling) is one of the most persistent problems in membrane bioreactors for wastewater treatment and reclamation. Here, we investigated the structure and microbiome of fouling-related biofilms in the membrane bioreactor using non-destructive confocal reflection microscopy and high-throughput Illumina sequencing of 16S rRNA genes. Direct confocal reflection microscopy indicated that the thin biofilms were formed and maintained regardless of the increasing transmembrane pressure, which is a common indicator of membrane fouling, at low organic-loading rates. Their solid components were primarily extracellular polysaccharides and microbial cells. In contrast, high organic-loading rates resulted in a rapid increase in the transmembrane pressure and the development of the thick biofilms mainly composed of extracellular lipids. High-throughput sequencing revealed that the biofilm microbiomes, including major and minor microorganisms, substantially changed in response to the organic-loading rates and biofilm development. These results demonstrated for the first time that the architectures, chemical components, and microbiomes of the biofilms on fouled membranes were tightly associated with one another and differed considerably depending on the organic-loading conditions in the membrane bioreactor, emphasizing the significance of alternative indicators other than the transmembrane pressure for membrane biofouling.

Highlights

Membrane bioreactors (MBRs) have been broadly exploited for the treatment of municipal and industrial wastewaters
Dently operated at low and high organicloading rates (OLRs) for 13 and 15 days, Under the low OLR conditions, the fouled membranes were respectively, before collecting the fouled membrane samples obtained at two different transmembrane pressure (TMP) (10 and 31 kPa) and thereafter (Supplementary Fig. S1)
The direct confocal reflection microscopy (CRM) showed that the under the low OLR conditions (Supplementary Fig. S1A), with the total organic carbon (TOC) of the treated effluent kept below 35 average thickness of the biofilms was approximately 150 μm at both TMPs, indicating that the biofilm thickness was not in mg/L (TOC removal rates: 97.8 ± 0.4%)

Summary

INTRODUCTION

Membrane bioreactors (MBRs) have been broadly exploited for the treatment of municipal and industrial wastewaters. The advent of highthroughput DNA sequencers has opened a new era of microbiome studies and has generated metagenomic and gene-amplicon libraries at multimillion-sequence scales.[11, 12] A combination of direct CRM and a comprehensive phylogenetic analysis of biofilm microbiomes should be powerful to clarify the main solid-phase components and the key microbial species involved in the fouling of MBRs, in which an enormous number of microorganism types coexist by interacting with one another. The objective in this study was to investigate the architectures, chemical components, and microbiomes of biofilms developed on filtration membranes during the actual biofouling induced at low and high organicloading rates (OLRs) in the MBR. A virgin polyacrylonitrile (PAN) membrane treated with SYTO9 and propidium iodide (PI) was visualized as the

RESULTS AND DISCUSSION

CONCLUSION

MATERIALS AND METHODS