Figure 2. Variation of TVFA (■) and biogas production rate (♦) during operation of the thermophilic reactor at different temperatures. (a)decrease in OLR from 9.68 to 4.20 g[COD]/L/day; (b) increase in OLR from 4.20 to 9.68 g[COD]/L/day; (c) decrease in OLR from 9.68 to 4.20 g[COD]/L/day followed by a slow change from 4.20 to 9.68 g[COD]/L/day.