Minimization of activated sludge production by chemicallly stimulated energy spilling

Minimization of excess sludge production in activated sludge processes has been pursued around the world in order to meet stringent environmental regu lations on sludge treatment and disposal. To achieve this goal, physical, c hemical, and biological approaches have been proposed. In this paper, a che mical compound, 3,3',4',5-tetrachlorosalicylanilide (TCS) was tested for en hancing microbial energy spilling of the sludge so as to minimize its growt h. In order to examine this, an exploratory study was conducted using both batch and continuous activated sludge cultures. Batch experiments with thes e two cultures were carried out at different initial concentrations of TCS. It has been confirmed that an addition of TCS is affective in reducing the production of both the sludge cultures, particularly the continuous cultur e where the observed growth yield was reduced by around 70%,when the initia l TCS concentration was 0.8 ppm. Meanwhile, the substrate removal activity of this culture was found not to be affected at this TCS concentration. To further evaluate the TCS effect, a pure microbial culture of E, coli was em ployed. Batch experiment results with this culture implied that TCS might b e able to reduce the cell density of E. coli drastically when an initial TC S concentration was greater than 0.12 ppm. it was also found that TCS was n ot toxic to this type of bacteria. Microscopic examinations with a 4',6-dia midino-2-phenylindole (DAPI) staining technique revealed that TCS neither a ffected the cell division nor altered the cell size of E.coli. However, bot h the cell ATP content and the cell dry weight were reduced significantly w ith the addition of TCS.