DEATH AND LYSIS DURING AEROBIC THERMOPHILIC SLUDGE TREATMENT - CHARACTERIZATION OF RECALCITRANT PRODUCTS

The nature and fate of the organic fraction released during the aerobi c thermophilic biodegradation of microbial cells were examined in a la boratory-scale treatment system. There was strong evidence for exoprot eolytic activity during the early phase of the biodegradation process. The lysis products could be separated into two broad fractions, a low molecular weight C-2-C-5 carboxylic acid fraction and a pooled fracti on of the remaining dissolved organic carbon (DOC). The former was pro duced as a result of fermentative metabolism of the aerobic thermophil ic process culture growing under oxygen limited conditions. The produc tion of these carboxylic acids occurred simultaneously with their util ization, as evidenced by the decrease in radioactivity in the DOC as a result of pulsing the culture with [C-14]acetate. However, a fraction of this [C-14]acetate pulse was metabolized into recalcitrant or slow ly biodegradable DOC. The non-carboxylic acid fraction of the DOC in t he lysis products was either slowly biodegradable or recalcitrant. The nature of the residual DOC in the supernatant after aerobic thermophi lic treatment could not be further characterized but is likely to repr esent humic substances.