Seasonal variation in membrane fouling in membrane bioreactors (MBRs) treating municipal wastewater

Abstract

We investigated seasonal variation in membrane fouling in membrane bioreactors (MBRs) treating municipal wastewater regarding the difference between physically reversible and irreversible fouling. Two separate MBRs with different solid retention times (SRTs) operated in parallel for about 200 days including high-and low-temperature periods to evaluate the effect of operating conditions on seasonal variation of membrane fouling. Seasonal variations of both types of membrane fouling (i.e., physically reversible and irreversible fouling) were observed for the MBR with short SRT (13 days). However, in the MBR with long SRT (50 days), there were no significant seasonal variations in both types of membrane fouling. In the MBR with short SRT, the trends in the seasonal variation in the development rates of physically reversible and irreversible fouling were different. Physically reversible fouling was more significant in the low-temperature period, while physically irreversible fouling developed more rapidly in the high-temperature period. The development rates of physically reversible fouling can be related to the concentration of dissolved organic matter in the mixed liquor suspension of MBRs; whereas those of physically irreversible fouling could not be explained by the concentration of dissolved organic matter. The characteristics of dissolved organic matter differed depending on the temperature period, and the trends of dissolved organic matter variation in mixed liquor were similar with those of foulants that caused physically irreversible fouling. The results obtained in this study indicated that seasonal variation in physically reversible and irreversible fouling is related to changes in quantity and quality of organic matter, respectively.

Identification of proteins involved in membrane fouling in membrane bioreactors (MBRs) treating municipal wastewater

“…When membrane fouling became significant, the membrane modules were taken out from the reactor and were physically cleaned by spraying pressurized water on the membrane and surface wiping with a sponge. The physical membrane cleaning conducted in this study was efficient and almost all physically reversible fouling can be eliminated (Miyoshi et al 2009). …”

“…All three MBRs were fed with the same raw wastewater delivered from the inlet of the primary sedimentation basin of the facility. The characteristics of the raw wastewater of this plant can be found elsewhere (Miyoshi et al 2009). Two of the three MBRs (MBRs 1 and 2) were identical and operated in parallel (Miyoshi et al 2011).…”

“…In contrast, the development of both types of membrane fouling was insignificant in MBR 2 (long SRT). Many researches investigating membrane fouling in MBRs treating real wastewater also reported that membrane fouling became significant as SRT decreased (Kimura et al 2005;Ng et al 2006;Rosenberger et al 2006;Miyoshi et al 2009). Detailed information on characteristics of foulants that caused membrane fouling in these two MBRs is important for elucidating how the difference in SRT affected the development of membrane fouling.…”

“…In the early studies on membrane fouling in MBRs, the relationships between concentrations of such microbial products evaluated with conventional colorimetric methods (Lowry et al 1951;Dubois et al 1956) and fouling rate were intensively investigated. Although reasonable relationships between microbial products concentrations and fouling rates were seen in some studies (Ng et al 2006;Rosenberger et al 2006;Trussel et al 2006), other researchers reported that development of membrane fouling cannot be explained by concentrations of microbial products determined by the conventional analytical methods Kimura et al 2009;Miyoshi et al 2009). These discrepancies suggested that some fractions of organic matter contained in mixed liquor suspension contribute more to membrane fouling than the others (Drews 2010;Miyoshi et al 2010).…”

“…In a number of previous studies, together with polysaccharides, proteins were also identified as one of the major foulants in MBRs (Metzger et al 2007;Kimura et al 2008a;Miyoshi et al 2009;Tang et al 2010;Tian et al 2011). Identifying the major proteins causing membrane fouling will give us detailed information on the structures, the properties, and even the functions of the proteins that play important roles in developing membrane fouling.…”