Abstract
Biofilm formation is one of the main factors associated with membrane biofouling in membrane bioreactors (MBRs). As such, it is important to identify the responsible organisms to develop targeted strategies to control biofouling. This study investigated the composition and changes in the microbial communities fouling MBR membranes over time and correlated those changes with an increase in transmembrane pressure (TMP). Based on qPCR data, bacteria were the dominant taxa of the biofilm (92.9–98.4%) relative to fungi (1.5–6.9%) and archaea (0.03–0.07%). NMDS analysis indicated that during the initial stages of operation, the biofilm communities were indistinguishable from those found in the sludge. However, the biofilm community significantly diverged from the sludge over time and ultimately showed a unique biofilm profile. This suggested that there was strong selection for a group of organisms that were biofilm specialists. This pattern of succession and selection was correlated with the rapid increase in TMP, where bacteria including Rhodospirillales, Sphingomonadales and Rhizobiales dominated the biofilm at this time. While most of the identified fungal OTUs matched Candida sp., the majority of fungal communities were unclassified by 18S rRNA gene sequencing. Collectively, the data suggests that bacteria, primarily, along with fungi may play an important role in the rapid TMP increase and loss of system performance.
Highlights
In recent years, membrane bioreactors (MBRs), a water recycling technology integrating activated sludge mediated nutrient removal and membrane filtration in a single system, have attracted increased attention and have been widely applied in wastewater treatment plants [1,2]
For experiment-1 and 2, which were run at a constant flux of 13–15 Liters/m2 h (LMH), the system required 80–90 d for the transmembrane pressure (TMP) to increase from 3 kPa to 15 kPa
The microbial community was compared for both sludge and biofilm samples and the changes in community composition were related to changes in MBR performance, as determined by the change in TMP
Summary
Membrane bioreactors (MBRs), a water recycling technology integrating activated sludge mediated nutrient removal and membrane filtration in a single system, have attracted increased attention and have been widely applied in wastewater treatment plants [1,2]. Biofouling is caused by the deposition of microorganisms and microbial products, e.g. polysaccharides and proteins, on the membrane surface [5,6] In this process, the microbes attach and grow, forming a biofilm on the membrane, clogging the membrane pores and increasing the required applied pressure across the membrane, the transmembrane pressure (TMP), and affecting the MBR performance [7]. There is no consensus on the dominant bacteria in biofilms and whether there is a correlation between the increased TMP and specific microorganisms
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