Neue Techniken zur Kompostierung. Teilvorhaben 11/3: Eliminierung von chlorierten Verbindungen aus Klaerschlaemmen durch anaerobe Behandlung Abschlussbericht

Polychlorinated biphenyls (PCB) and dioxins/furans (PCDD/F) are frequent contaminants of sewage sludges. They are resistant against aerobic microbial processes. However, it was reported that they are subject to reductive dechlorination by anaerobic bacteria. The objective of this project was (i) the enrichment of microbial mixed cultures capable of dechlorination of xenobiotics relevant to sewage sludges (chlorophenols, chlorocatechols, PCDD), (ii) the characterisation of the process and the products of dechlorination and (iii) the establishment of principles for growth and application of dechlorinating bacteria. Methods and results: The occurrence of dechlorinating bacteria in natural and technical habitats was analyzed by MPN-studies. The studies revealed high numbers of dechlorinating bacteria in river sediments and low numbers in sewage sludges. Therefore, dechlorinating mixed cultures were enriched from sediment samples. The degree of chlorination of chlorophenols, chlorocatechols and tetra- (TCDD) and trichlorinated dibenzo-p-dioxins was reduced by different cultures to a level, that allowed the attack of aerobic bacteria. One of the mixed cultures dechlorinated 12 different chlorophenols in the ortho- and partly in the metaposition. High dechlorination rates (about 0.5 g 2,4,6-trichlorophenol/l-d) were obtained by continuous cultivation. A model for the generation of inocula was established by combining chemostat and fed-batch cultures. Immobilised coils were used as inoculum in sewage sludge and exhibited high dechlorinating activity. Conclusions: The regionspecific dechlorination of TCDD observed in the lateral position is an important property of the culture investigated. This kind of attack leads to products with reduced toxicity. Approaches for cultivation and growth and methods for the immobilisation of dechlorinating bacteria were presented. (orig.)SIGLEAvailable from TIB Hannover: F97B62+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman