Abstract: A batch process for the conversion of organic solid waste material containing cellulose and lignin through liquid thermophilic aerobic digestion comprises comminuting the organic solid waste material, adjusting the moisture content of the comminuted material to at least 90% parts by weight of water, mixing the comminuted material with a thermophilic aerobic micro-organism, adjusting the pH of the mixture to 5.5-7.5 and supplying heat and oxygen to the mixture to effect thermophilic aerobic digestion of the mixture. The thermophilic aerobic digestion of the mixture is terminated after the mixture has stabilized as a low nitrogen material but prior to digestion of the cellulose and lignin in the mixture, and the stabilized mixture is separated into solid and liquid fractions. The process includes the monitoring of parameters for determining the termination of digestion.