Thermophilic Anaerobic Digestion of Sugar Beet Tailings

摘要

Tailings from sugar beet processing are currently managed by landfilling or land application. As an alternate option, beet tailings were anaerobically digested at thermophilic temperatures. It was found that tailings contain a large fraction of water-soluble organic matter, approximately 0.6 g COD (chemical oxygen demand) per g VS (volatile solids), that inhibited initiation of methanogenesis. This work showed that methanogenesis can be initiated if the solubilized material is removed. By using a process that involves first leaching and removal of solubilized matter followed by flooding the bed with digested leachate containing acclimatized inoculum, anaerobic digestion of the tailings was successfully accomplished. Most of the methane potential remaining in solids was generated within a week. The methane yield of tailings was estimated to be 295 L at standard temperature and pressure (STP) per kg VS, of which 50% to 60% was from the readily solubilized organic matter. A volume reduction of 70% to 80% was achieved, and approximately 60% of dry matter and 75% of volatile solids were degraded. All the volatile organic acids (acetic, propionic, and butyric) after an initial accumulation were degraded to low levels in all experiments. Individually, 53.3% of crude protein, 88.3% of nonfibrous carbohydrates, 81% of hemicellulose, 31.5% of lignin, and 64.6% of cellulose were either degraded or solubilized. It was also shown that a robust inoculum for sustained thermophilic anaerobic digestion can be cultured by initially flooding a bed of tailings with a buffer solution. The inoculum thus developed was robust enough to carry out successive balanced digestion of several batches of tailings.