Energy Recovery and Treatment of Winery Wastes by a Compact Anaerobic Digester

Abstract

The objective of this study was to examine the process of aqueous extraction of organics and phenolics from winery wastes (grape marc and wine lees) and the anaerobic digestion of the extracts using a pilot-scale anaerobic digester. Samples of grape marc and wine lees were extracted with tap water under controlled laboratory conditions at different solid/liquid ratios 1:3, 1:5 and 1:10 (w/w). The extracts were characterized in terms of organic matter composition, and phenolic content. Following this, a 3 m3 stirred tank digester, inoculated with anaerobic granular sludge, was installed and operated at the premises of a winery using original grape marc and wine lees extracts. The recovered extracts were characterized by a high chemical oxygen demand (COD = 20–30 kg m3) and low concentration of phenolics (<100 mg L−1). They displayed high anaerobic degradability with a biogas yield of 0.50 m3 kg−1 COD, a methane content of 72 % and an effluent COD concentration between 0.6 and 1.6 g L−1. Based on a preliminary design and cost analysis it was demonstrated that for a medium sized winery (1000 tn grapes per season) a 40 m3 compact anaerobic digester suffices, while the payback period is around 6–7 years. Aqueous extraction of organics from winery wastes enables the recovery of readily degradable COD with low phenolic content. Generation of biogas from the recovered extracts was highly efficient using a compact anaerobic digester.