Waste Management & Research (1989) 7, 277-290 COMPOST DETOXIFICATION OF VEGETABLE-TANNERY SLUDGE G. Vallini*, A. Pera*, F. Cecchit, Maria Briglia* and Franca Perghemt (Received March 1989, revised May 1989) The disposal problem represented by vegetable-tannery sludge is of great and ever- increasing concern in Italy. Such sludge is of a highly polluting nature and therefore, requires a reliable and safe treatment to make it harmless before release into the environment. Vegetable-tannery sludge contains some very toxic compounds, mainly polyphenols (i.e. tannins) and sulphides, that are hazardous to biological systems. This paper deals with experiments evaluating the feasibility of vegetable-tannery sludge management and recycling by an integrated cornposting process. Static windrow technique with forced air and temperature feedback has been adopted for composting a mixture of vegetable-tannery sludge and organic biodegradable frac- tion of municipal solid waste (MSW) as.bulking agent. Physico-chemical, microbiolo- gical and phytotoxicological aspects of this compost production from vegetable- tannery sludge are here emphasized along with some technological details. Key Words-Composting, tannery sludges, municipal solid waste (MSW), tempera- ture feedback control, forced air aeration, tannin reduction, sulphide removal. 1. Introduction The two main tanning methods, vegetable tannage and chemical tannage produce wastes which differ widely in physical, chemical, toxicological and microbiological characteris- tics. Tannage with natural vegetable bark extracts is the principal tanning method for the production of sole leather (hard leather) while tanning with chromium salts is used to obtain light, smooth and soft leather suitable for manufacturing goods such as shoe uppers, handbags, gloves and a variety of clothes. Although various treatment procedures for disposing tannery by-products have been suggested, sludge from tannery wastewater depuration is still an environmental problem. This paper explores the possibility of recycling vegetable-tannery sludge into a soil conditioner by using careful composting techniques. The objective of this process is to eliminate pollution, crop contamination and health hazards. The present study on this specific tannery waste arose from the fact that, until now, among all tannery by-products, sludges from tannery wastewater treatment have been considered as undesirable pollutants. See however Giugliano & Paggi (1985). The main concern of recycling vegetable-tannery sludge into an organic soil condi- tioner is its high concentration of toxic compounds. In particular, vegetable-tannery sludge derived from the physico-chemical treatment of process wastewaters is extremely * CNR, Soil Microbiology Center, Via de1 Borghetto 80, 56100 Pisa, Italy. TDepartment of Environmental Sciences, University of Venice, Venice, Italy. IDepartment of Chemistry, University of Florence, Florence, and Luigi Sacconi Center, Santa Croce sull’Arno. Italy. 0734242X/89/030277 + 14 $03.00/O 01989 ISWA