Foaming in submerged membrane bioreactors for municipal wastewater treatment

This thesis studied the foaming in two submerged membrane bioreactors (SMBR) operated in parallel for treating municipal wastewater. Foam formed in the pilot plants was collected daily to determine its mass and volume. The two key filamentous bacteria, Microthrix parvicella (M. parvicella) and Gordonia species (Gordonia spp.), were quantified simultaneously by using a newly proposed quantitative real-time PCR (qPCR) method. Mathematic models were compared from experimental data to help identify the possible mechanism of simultaneous growth of the two microbes in SMBR.;It was concluded that: 1) the high specificity of qPCR method were obtained to determine the concentration of M. pavicella and Gordonia spp. without pure cultures; 2) the mass of foam increased with the relative 16S rRNA gene copies of foaming bacteria to Eubacteria ; 3) 5MBR tended to have more sever foaming potential at a fairly low relative concentration of foaming bacteria to Eubacteria (<0.5%) as compared to CAS processes; 4) the amount of foam depended on both operating conditions and raw wastewater characteristics. Longer SRT produced more foam within the range of experimental conditions due to low F/M ratio; 5) the growth and distribution of the foaming bacteria experienced seasonal shift: M. parvicella was the dominant filamentous bacteria in spring while Gordonia spp. in summer; and 6) the preliminary simulation showed that the new food-web model were compatible with experimental data, suggesting that Gordonia spp. utilizes oils and fats as substrate while M. parvicella can use secondary substrates of floc-forming bacteria as substrate for growth in SMBR.