Short communication Improvement of biogas production from vinasse via covalently immobilized methanogens Ivo G. Lalov a , Milka A. Krysteva a, * , Jean-Louis Phelouzat b a University of Chemical Technology and Metallurgy, Department of Biotechnology, 8, blvd. K1 Okhridski, 1756 So®a, Bulgaria b Ecole Nationale Sup erieure d'Arts et M etiers, Laboratoire de Turbomachines et de Conversion d'  Energie, 151, boulevard de l'H^ opital, 75013 Paris, France Received 9 November 2000; received in revised form 2 February 2001; accepted 19 February 2001 Abstract Improvement of biogas production was realized by covalent immobilization of a methanogenic consortium onto a granulated polymeric support [polyacrylonitrile-acrylamide)]. The growth kinetics of the immobilized consortium was investigated during a process of vinasse methanation, and a cell concentration increase from 12:3 mg g 1 support to 52:1 mg g 1 support was established. The methane yield reached 0:33 m 3 kg 1 COD r , the maximum yield on chemical oxygen demand COD) removal being 92%. The inhibitory eect of oxygen was reduced by immobilizing the methanogenic consortium. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cell immobilization; Vinasse; Biomethanation; Fixed-®lm anaerobic reactor 1. Introduction The by-product remaining after distillation during the production of wine brandies is characterized by a high concentration of organic acids and polyphenols. This determines the relatively high values of chemical oxygen demand COD) typical of this kind of liquid waste called ``vinasse''. The classical way of vinasse treatment is one-stage biomethanation Peres et al., 1998) or a two-stage process Shin et al., 1992). Since the growth rate of methanogenic bacteria is very low, the desirable de- gree of organic matter degradation is achieved after a long residence time in the anaerobic reactor. For that reason, many investigations deal with the development of techniques aimed at maintaining high biomass concentrations in the anaerobic reactors. The most used method in this respect consists in sedimentation of the microbial cells onto various supports as well as gel entrapment of the biomass. The aim of the present investigation was to immobi- lize a methanogenic consortium covalently to a synthetic polymer in order to improve the process of biogas production. 2. Methods 2.1. Vinasse The substrate used for methanation was industrial vinasse derived from the distillation of red wines, which was supplied by the National Wine Research and Con- trol Institute in So®a, Bulgaria. 2.2. Isolation and cultivation of a methanogenic consor- tium The mixed methanogenic culture labelled as culture 1) used in the experiments was isolated from anaerobic digester sludge supplied by an oil re®nery. It was en- riched and maintained in a fresh anaerobic mineral medium according to Shelton and Tiedje 1984) for 3 months. The enriched culture was labelled as culture 2. The methanogenic culture 2 was adapted to the vinasse substrate in a continuously-stirred reactor under strict anaerobic conditions at 37°C for 90 days. This adapted culture was labelled as culture 3. Bioresource Technology 79 2001) 83±85 * Corresponding author. Tel.: +359-2-625-4532; fax: +359-2-683-460. E-mail address: m.krysteva@mbox.cit.bg M.A. Krysteva). 0960-8524/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0960-852401)00045-1