AEROBIC THERMOPHILIC WASTE SLUDGE BIOTREATMENT - CARBOXYLIC-ACID PRODUCTION AND UTILIZATION DURING BIODEGRADATION OF BACTERIAL-CELLS UNDER OXYGEN LIMITATION

The production and utilization of carboxylic acids during aerobic ther mophilic treatment of a model sludge composed of bacterial cells were examined in a laboratory treatment system. Operation under a limited s upply of O-2, typical for such treatment systems, resulted in a distin ct pattern of production and simultaneous utilization of low molecular weight carboxylic acids. Pulse-addition of a mixture of carboxylic ac ids at the end of a fed-batch cycle indicated that simultaneous utiliz ation of acetate, propionate, isobutyrate, n-butyrate and isovalerate could occur, but only after a lag phase during which only acetate was utilized. In an attempt to differentiate between production and utiliz ation of the carboxylic acids, a series of pulse experiments were perf ormed using C-14-labelled acetate. The results indicated that producti on continued late into the fed-batch cycle whereas utilization could o ccur during the entire cycle. When acetate was pulsed to the process, only 11% of the acetate carbon was incorporated into new biomass, wher eas 75% was converted into CO2. However, 14% of the original radioacti vity persisted in the supernatant despite complete acetate utilization . This suggested that some of the acetate was metabolized into more sl owly biodegradable products.