Filamentous foaming problem control in activated sludge

Abstract

Filamentous foaming is a common problem happened in activated sludge treatment plants. It often deteriorates the quality of final effluent. It was previously identified as that the cause of foaming problem was the overgrowth of filamentous bacteria, like Microthrix parvicella. In this study, characteristics of filamentous and floc-forming bacteria were identified firstly. The maximum specific growth rate and the half-velocity constant(Ks) of the Monod kinetics model for filamentous and floc-forming bacteria, were obtained from the batch culture growth data, followed by processing with nonlinear regression method. It was discovered that the growth rate of Microthrix parvicella , under the condition of Food to Microorganism (F/M) ratio below 0.71 mg of BOD/(mg of MLSSd), was higher than non-filamentous bacteria like, like P.aeruginosa. Based on the theory of growth kinetics, "Revised Feast-Famine Operation (RFFO)" technology was developed in reducing the filamentous foaming problems. In the feast phase, with a high F/M ratio, activated sludge cultures consume nutrients and produce the stored polymers, like Polyhydroxyalkanoate (PHA), simultaneously. In the famine phase, with a low F/M ratio, activated sludge cultures consume stored polymers as a carbon and energy source. The sludge microbes underwent a repetitive switch between high and low F/M ratio during the course of wastewater treatment. In this dissertation, it will also discuss on the metabolic model for the activated sludge cultures. The experimental results revealed that FFO strategy effectively suppressed overgrowth of filamentous germs in keeping with high biological oxygen demand (BOD) removal efficiency. The overall performance of degree of foaming also indicated that the RFFO strategy effectively and rapidly restrained the overgrowth of filamentous bacteria in the reactor system. Finally, it was integrated with the mathematical modeling by evaluation of the experimental data. The model proves it is applicable to simulate the process of RFFO in controlling filamentous foaming problem. The technology introduced here is a contribution to a further development of activated sludge processes for filamentous foaming control.