Influence of lignin on the methanization of lignocellulosic wastes

The effect on anaerobic digestion of reducing the lignin content of vine shoots to 1% (w/w), by treatment with sodium chlorite in an acid medium at 80°C, is reported. The yields of methane obtained were 240 ml of CH₄ g⁻¹ of VS (volatile solids) fed for untreated vine shoots, and 370 ml of CH₄ g⁻¹ of VS fed for treated vine shoots. A mathematical model was used to calculate the kinetic parameters H and μ, and the increased biodegradability of the substrate in which lignin had been removed was confirmed. A study of the mass balances of the process under optimum conditions (temperature = 35°C; loading rate of 1 g litre⁻¹ digester day⁻¹) enabled the percentage of degraded cellulose to be calculated (35·5% for untreated vine shoots, 81·5% for the treated vine shoots), as were the volumes of biogas and methane produced per gram of VS introduced (VS₁) and degraded. The blocking effect of lignin on the methanization process was confirmed.