One and two-stage digestion of solid organic waste

• Published in: Water research (Oxford) 1999, Vol.33 (3), p.854-860
• Main Authors: Schober, Gabriele, Schäfer, Joachim, Schmid-Staiger, Ulrike, Trösch, Walter
• Format: Article
• Language: English
• Subjects: anaerobic digestion; Applied sciences; biogas; Biological and medical sciences; Biological treatment of sewage sludges and wastes; Biotechnology; digestion; Environment and pollution; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; gas production (biological); Industrial applications and implications. Economical aspects; kitchen waste; mathematical models; mesophilic conditions; modelling; MSW; municipal solid waste; organic waste; organic wastes; Pollution; temperature; thermophilic conditions; two stage process; Urban and domestic wastes; Wastes
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/S0043-1354(98)00254-1

Digestion of municipal solid organic waste (MSW), particularly of kitchen refuse with a total solid concentration of 7–8% VS (volatile solids) was investigated. Experiments at mesophilic (37°C) and thermophilic (55°C) conditions were carried out comparatively in continuously stirred digesters with 30 l volume. Increasing the organic loading rate (OLR) by reducing the hydraulic retention time (HRT), the maximum capacity of the biological process was assessed. With OLR=6.0 g VS l −1 d −1 and HRT=11 d, the maximum VS reduction under steady state conditions reached 72% at mesophilic and 80% at thermophilic conditions. At 55°C, the yield of gas, Y gas, reached about 830 l gas kg VS −1, whereas at mesophilic conditions only about 800 l gas kg VS −1 were generated. A simple mathematical model was set up to describe digestion performance adequately designating the process conditions for most effective turnover. This model was based on kinetic data of a one stage digester. With the assistance of the model and the data of digestion experiments the process conditions could be optimized. The main result was that the digestion of MSW should be performed in a two stage plant with a concentration unit between the two stages. Under these optimized process conditions a turnover of the organic matter of 90% with low retention time could be realized.