Fate of 1,2,3,4,6,7,8-heptachlorodibenzofuran and pentachlorophenol during laboratory-scale anaerobic mesophilic sewage sludge digestion Joanna L. Stevens, Nicholas J.L. Green, Kevin C. Jones * Department of Environmental Science, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster, LA1 4YQ, UK Received 31 January 2002; received in revised form 4 October 2002; accepted 21 October 2002 Abstract The possibility of the formation of PCDDs and dechlorination of PCDFs during the anaerobic digestion of sewage sludge in laboratory scale digesters was investigated. Digesters were spiked with 1,2,3,4,6,7,8-HpCDF– 13 C 6 (240 ng/g organic matter (OM)) and pentachlorophenol (PeCP)– 13 C 6 (24 lg/g OM) and the output sludge monitored for 60 days. No dechlorination or formation of the labelled or native PCDD/Fs was observed. The detectable 1,2,3,4,6,7,8-HpCDF– 13 C 6 dechlorination yield was 0.0008–1% depending on homologue group and the detectable formation of OCDD yield was 0.00042% PeCP– 13 C 6 . Preferential respiration of other, more bioavailable, substrates is suggested as the most plausible explanation for the lack of dechlorination. Formation of PCDDs from PeCP has been observed in aerobic environments but this study provides further evidence that it is not a precursor for formation during anaerobic di- gestion. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: PCDD/Fs; Dioxins; Wastewater treatment; Dechlorination; Formation 1. Introduction Anaerobic, mesophilic digestion is presently the most common method of sewage sludge treatment in the UK. Approximately 50% of the sewage sludge produced in the UK is applied to agricultural land. PCDD/Fs are present at trace levels (pg–ng/g dry weight) in almost all sewage sludge and it has been shown that sludge appli- cation to agricultural land may increase levels in soils and, under certain circumstances, residues in human foodstuffs (McLachlan et al., 1994, 1996; Wild et al., 1994). It is therefore important to investigate the effect of anaerobic digestion on the levels of these compounds. Formation from precursors or dechlorination to more toxic congeners could increase the TEQ value of the PCDD/F mixture. Although PCDD/Fs are thought to be resistant to abiotic and biochemical degradation in soil there is evidence of dechlorination in anaerobic sediment. Experiments on both spiked and native PCDD/Fs in freshwater and estuarine sediments have shown dechlorination can begin after less than 1 month of incubation (Barkovskii and Adriaens, 1996). Studies on sediment, sewage sludge and soil spiked with 1,2,3,4- TCDD incubated for 13 months observed dechlorina- tion to DiCDDs in the sediments but no dechlorination in the soil or sludge (Ballerstedt et al., 1997). However, 1,2,3,4-TCDD is not a useful compound with which to investigate dechlorination. PCDD/F mixtures in sedi- ments and in sewage sludge are dominated by the higher chlorinated congeners, therefore, the dechlori- nation pathway of concern is from the higher chlori- nated 2,3,7,8-substituted PCDD/Fs to lower chlorinated congeners with a higher TEF rating which may increase Chemosphere 50 (2003) 1227–1233 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +44-1524-593972; fax: +44- 1524-843854/593985. E-mail address: k.c.jones@lancaster.ac.uk (K.C. Jones). 0045-6535/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. PII:S0045-6535(02)00703-8