Behavior of PCDD/Fs and PCBs from Wastewater Treatment Plants during Sewage Sludge Composting: Study of Semi-Anaerobic Conditions and Different Stages of the Process

Author:

Gomez-Rico Maria Francisca1ORCID,Hernandez Teresa1,Garrido Maria Angeles1,Font Rafael1

Affiliation:

1. Department of Chemical Engineering, University of Alicante, P.O. Box 99, E-03080 Alicante, Spain

Abstract

Composting is a common treatment for the high amounts of sewage sludge produced in wastewater treatment plants, and the product is used in agriculture. Composting reduces the levels of biodegradable organic pollutants, although other compounds present in wastewater and not eliminated previously by conventional physical–chemical and chemical treatments, such as polychorodibenzo-p-dioxins/furans (PCDD/Fs) and polychlorinated biphenyls (PCBs), have been found in the final compost at higher levels than those observed in the initial sludge. Their formation was studied during composting under unfavorable aeration conditions and paying attention to different stages of the process. Experiments were carried out in small vessels inside a controlled oven for three types of sewage sludge. Pentachlorophenol was previously added as a dioxin precursor. A clear formation of PCDD/Fs was found, especially during the maturation stage for two experiments. Mainly octachlorodibenzo-p-dioxin (OCDD) and 1234678-heptachlorodibenzo-p-dioxin (1234678-HpCDD) to a lesser extent were formed. OCDD levels in the final samples were around 10 times higher than those of the initial mixture after removing the concentration effect. No clear formation nor degradation of PCBs was observed. The toxicity values due to PCDD/Fs and PCBs found in the initial mixtures were 1.20–2.46 ng WHO-TEQ/kg, and those from the final samples were 2.30–7.86 ng WHO-TEQ/kg. Although the toxicity values are below the most restrictive limits found in Europe in this case, toxicity could increase considerably with the presence and concentration of other precursors. Compost from sewage sludge is an ecological product, but the operating conditions must be controlled to avoid PCDD/F formation and facilitate degradation of persistent organic pollutants.

Funder

Generalitat Valenciana

Ministry of Economy, Industry and Competitiveness

Publisher

MDPI AG

Reference46 articles.

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2. European Commission Commision Staff Working Document Evaluation (2023, October 30). Council Directive 86/278/EEC of 12 June 1986 on the Protection of the Environment, and in Particular of the Soil, When Sewage Sludge Is Used in Agriculture. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52023SC0157.

3. Huygens, D., Garcia-Gutierrez, P., Orveillon, G., Schillaci, C., Delre, A., Orgiazzi, A., Wojda, P., Tonini, D., Jones, A., and Pistocchi, A. (2022). Screening Risk Assessment of Organic Pollutants and Environmental Impacts from Sewage Sludge Management, Publications Office of the European Union.

4. Transfer of Polychlorinated, Polybrominated and Mixed-Halogenated Dioxins, Furans and Biphenyls, Polychlorinated Naphthalenes and Alkanes, Polycyclic Aromatic Hydrocarbons and Chlorobenzenes to the Milk of Dairy Cattle from Controlled Ingestion of Industrial and Municipal Bioresources Recycled to Agricultural Land;Rigby;Sci. Total Environ.,2023

5. (2023, October 30). EUR-Lex Council Directive of 12 June 1986 on the Protection of the Environment, and in Particular of the Soil, When Sewage Sludge Is Used in Agriculture. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:31986L0278.

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