Foam Formation in Submerged Membrane Bioreactors for Municipal Wastewater Treatment

Excessive foaming formed in submerged membrane bioreactors (SMBR) causes serious operational problems. Pilot tests were conducted to examine the mass and volume of foam collected daily from two SMBR pilot plants operated at different sludge retention times (SRTs) to treat municipal wastewater. The effects of wastewater characteristics and sludge properties on foam production were evaluated. Two key foaming microorganisms, M. parvicella and Gordonia spp. in the bioreactors were further quantified using quantitative real-time PCR (qPCR).The results showed that foaming and the density of the scum layer were greater at longer SRTs, and the longer SRTs also facilitated the growth of filamentous bacteria and caused their enrichment in the scum layer due to the low F/M ratio. Foam production in the SMBR was sensitive to the variation in influent temperature while being less impacted by influent COD and floc size. Foaming experienced a seasonal shift because the growth rates of M. parvicella and Gordonia spp. varied with temperature differently: M. parvicella was the dominant filamentous bacteria in spring while Gordonia spp. predominated during summer.