Comparison of PCDD and PCDF concentrations after aerobic and anaerobic digestion of sewage sludge.

The anaerobic stabilization of raw sludges of different origin was investigated. Precursors like chlorophenol and chlorobenzene isomers were added to some of the samples. The change of the PCDD/F concentrations as well as the change in the pattern of the isomers and congeners was independent of the type and amount of the added precursor. With respect to the change of the PCDD/F concentrations the digestion properties were typical in each digestion series but not applicable to other digestion processes. The quality of the digestion was characterized by measuring the change of pH, controlling the biogas flow rate and the determination of the mineralization degree. The added chlorobenzenes and chlorophenols were almost completely degraded. The aerobic digestion occurred in ventilated batch reactors leading to a significant degradation of all PCDD/F homologues. The degradation ratio depends on the origin of the sewage sludge. Independent of origin individual congeners were partially or completely degraded.