Abstract
Reverse osmosis (RO) system at a stage after membrane bioreactor (MBR) is used for the wastewater treatment and reclamation. One of the most serious problems in this system is membrane fouling caused by biofilm formation. Here, microbiomes and chemical components of the feed water and membrane-attached biofilm of RO system to treat MBR effluents were investigated by non-destructive confocal reflection microscopy, excitation-emission fluorescence spectroscopy and high-throughput sequencing of 16S rRNA genes. The microscopic visualization indicated that the biofilm contained large amounts of microbial cells (0.5 ± 0.3~3.9 ± 2.3 µm3/µm2) and the extracellular polysaccharides (3.3 ± 1.7~9.4 ± 5.1 µm3/µm2) and proteins (1.0 ± 0.2~1.3 ± 0.1 µm3/µm2). The spectroscopic analysis identified the humic and/or fulvic acid-like substances and protein-like substances as the main membrane foulants. High-throughput sequencing showed that Pseudomonas spp. and other heterotrophic bacteria dominated the feed water microbiomes. Meanwhile, the biofilm microbiomes were composed of diverse bacteria, among which operational taxonomic units related to the autotrophic Hydrogenophaga pseudoflava and Blastochloris viridis were abundant, accounting for up to 22.9 ± 4.1% and 3.1 ± 0.4% of the total, respectively. These results demonstrated that the minor autotrophic bacteria in the feed water played pivotal roles in the formation of polysaccharide- and protein-rich biofilm on RO membrane, thereby causing membrane fouling of RO system.
Highlights
Wastewater reclamation is one of the most common and serious issues in the world
Before the Reverse osmosis (RO) membrane treatment, the synthesized wastewater (SWW) and heavy oil-containing SWW were treated by membrane bioreactor (MBR) and the resultant effluents served as the feed water of RO system
Physicochemical profiles of the feed water and RO membrane-treated water are shown in Supplementary Figs S2 and S3
Summary
Wastewater reclamation is one of the most common and serious issues in the world. A dual-membrane treatment system combining the microfiltration (MF) or ultrafiltration (UF) membrane and the reverse osmosis (RO) membrane is a wastewater reclamation technology that attracts attention due to its high treatment efficiency and high economic benefit[1,2]. When the MBR effluent of SWW was used as the feed water, the SYTO9 and PI staining and quantitative image analysis indicated that most of microbial cells on RO membrane were alive (living cell rate; 81.6 ± 11.7%), but the major part of the biofilm was non-cell region (Fig. 1A–D and Table 1).
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