Two-stage anaerobic digestion of the organic fraction of municipal solid waste - Effects of process conditions during batch tests

Results showed that both initial pH and F/M ratio had an impact on hydrogen yield, hydrogen production rate and duration of lag phase. The highest hydrogen yield of 29.8 mLH2/gVS was obtained at initial pH of 5.5 and F/M ratio of 6. However, the highest hydrogen production rate (65 mLH2/gVS/d) was recorded at pH of 9 and F/M ratio of 6. Increasing the initial pH from 5.5 to 9, led to shorter lag phases for all F/M ratios. Methane production from second phase was not significantly influenced by the F/M ratios tested in the first digestion phase. When compared to single-phase AD, two-stage AD tests resulted in enhanced methane production rates from 37.3 to 68.5 mLCH4/gVS/d, reducing by half both the lag phase and the time required to reach maximum methane production.