Fig. 5. Changes in TOC, VFAs, pH, gas evolution and H2S during the thermophilic methane fermentation of the stillage eluted from the ethanol producing process. (a) C/N ratio of 1100 and 100; (b) C/N ratio of 40. Crosses, TOC; circles, VFAs; triangles, pH; diamonds, gas evolution; and squares, H2S.