Diverse and Distinct Bacterial Communities Induced Biofilm Fouling in Membrane Bioreactors Operated under Different Conditions

Abstract

We conducted a laboratory-scale experiment using real municipal wastewater with identical submerged membrane bioreactors (MBR) operated under different conditions (sludge retention time (SRT) and membrane flux) for nearly 6 months. Membrane biofilm samples were periodically retrieved, and cultivation-independent molecular approaches were used to systematically elucidate the community composition and diversity of microorganisms responsible for biofilm formation in the MBRs. Membrane fouling occurred earlier and faster in the low-SRT reactors which had more active mixed liquor biomasses and higher concentrations of dissolved organic matters. Denaturing gradient gel electrophoresis (DGGE) analysis and comparative rRNA sequencing revealed that diverse and distinct bacterial communities significantly differing from those in the planktonic biomass developed on the microfiltration membrane surfaces, with phylotypes from the Proteobacteria (particularly the alpha and beta subdivisions) and Bacteroidetes dominating the 16S rRNA gene libraries. This indicated that specific groups of bacteria were preferentially growing in the membrane habitats. Membrane flux had great impact on the predominant populations selected in the fouling biofilms. At lower fluxes, biofilm community composition was quite similar independent of sludge ages and biofilm formation seemed to be the result of a more natural process of colonization and biofilm development. In contrast, distinct biofilm communities developed on membrane surfaces at high fluxes. Despite the high convective forces, the biofilm composition was significantly different from the planktonic biomass, and selective enrichments of certain species were observed. Our study suggests that the microbial communities responsible for membrane biofouling in MBRs are far more complex and variable than expected and thus could be challenging to control.

A sequencing approach targeting the 16S rRNA gene unravels the biofilm composition of spiral-wound membranes used in the dairy industry

“…The short read lengths (400-440 bp) enabled a thorough taxonomic assignment for all samples at the genus level, with an overall low abundance of 1% of unclassified phyla. In comparison to many studies previously conducted on biofouling in water treatment plants (including desalination and waste water treatment plants), biofilm composition in the dairy industry is different, most notably because of the high proportion of Firmicutes, which are absent from water treatment plants (Chen et al 2004;Ivnitsky et al 2007;Huang et al 2008;Matin et al 2011;Khan et al 2013;Levi et al 2016).…”

Ecological succession in long-term experimentally evolved biofilms produces synergistic communities

“…As examples, the complex microbial communities found in reef ecosystems (Nocker et al, 2004), on river bottoms (Lyautey et al, 2005) or in sewage pipes (Huang et al, 2008) are likely to be many years old and reflect many of the developments in community composition associated with classical ecological succession (Odum, 1975;Connell and Slatyer, 1977). The same mechanisms that cause species turnover in the plant communities that exemplify succession are also likely to operate in microbial biofilms, with at least the same level of uncertainty about the relative role of neutral, antagonistic or facilitative processes (Connell and Slatyer, 1977).…”

Nitric Oxide Treatment for the Control of Reverse Osmosis Membrane Biofouling

“…Biofilm formation on membrane surfaces results in a severe decline in flux, or an increase in transmembrane pressure (TMP; defined as the pressure gradient of the membrane, or the average feed pressure minus the permeate pressure) to maintain flux, higher energy consumption, and a deterioration of system performance and product water production (3,8,9). As the adhesive and cohesive matrix of biofilms, EPS has been suggested to be the predominant culprit for biofouling of water treatment membranes (1,10,11).…”