Kraft-Mill Biosolids Treatment by Conventional and Biphasic Fermentation

Abstract

Kraft primary and mixed primary-activated sludges were gasified by thermophilic (50 °C) high-rate and mesophilic two-phase digestion. Kraft sludges were deficient in nitrogen, phosphorus, and other unidentified nutrients. Municipal sludge proved to be a much better nutrient source than inorganic salts. Performance of the mesophilic (35°C), two-phase anaerobic digestion (TPAD) system was about the same as that of thermophilic single-stage, high-rate digestion at a 10-day HRT as judged in terms of methane yield (0.17 SCM/kg VS added) and VS reduction efficiency (43%). The mesophilic TPAD process yielded a higher methane-content (65%) fuel gas; it is capable of exhibiting higher net-energy recovery efficiency than thermophilic single-stage digestion.