JOURNAL REVIEW Temperature Conversion (Mesophilic to Thermophilic) of Municipal Sludge Digestion

(kgVS/m 3 d and kgCOD/m 3 d), biogas and volumetric methane production rate (m 3 /m 3 d), pH, total acidity (mg acetic acid/L) and acidity/alkalinity relationship. The digester was initially operated with an organic loading rate (OLR) of 1.26 kgVS/m 3 d and a solids retention time (SRT) of 27 days under mesophilic conditions (35°C). The solids destruction efficiency was found to be 54.3%, while the volumetric biogas production in the digester reached 0.36 m 3 /m 3 d. The strategy selected for the conversion from mesophilic to thermophilic digestion involved slowly increasing the temperature of the digester (0.38° C/d) until it reached 43°C. In this way, the temperature of the digester was raised from 43 to 45°C and then operated at a constant 45°C. The performance parameters at this temperature indicated that the digester was unstable. For this reason the OLR was decreased until feeding was suppressed. The reactor operated at 45°C for 32 days, and the temperature of the digester was then raised from 45 to 50°C (without feeding). The temperature was subsequently raised to 50 – 52°C with the system operating at variable SRT (65-52 days), and finally, the temperature was increased at a rate of 0.13°C/d until it reached 55°C. At thermophilic conditions (55°C), the OLR studied was 1.48 kgVS/m 3 d (SRT: 27 days), and under these conditions the solids destruction efficiency was 53.3% VS, and the biogas produced in the digester reached 0.32 m 3 /m 3 d. © 2005 American Institute