Methane from cattle waste: Effects of temperature, hydraulic retention time, and influent substrate concentration on kinetic parameter ( k )

The effects of temperature (35 and 55°C), influent volatile solids (VS) concentration ( S 0 = 43, 64, 82, 100, and 128 kg VS/m 3 ) and hydraulic retention time (HRT = 4, 5, 8, 10, 15, and 25 days) on methane (CH 4 ) production from cattle waste were evaluated using 3‐dm 3 laboratoryscale fermentors. The highest CH 4 production rate achieved was 6.11 m 3 CH 4 m −3 fermentor day −1 at 55°C, four days HRT, and S 0 = 100 kg VS/m 3 . Batch fermentations showed an ultimate CH 4 yield ( B 0 ) of 0.42 m 3 CH 4 /kg VS fed. The maximum loading rates for unstressed fermentation were 7 kg VS m −3 day −1 at 35°C and 20 kg VS m −3 day −1 at 55°C. The kinetic parameter ( K , an increasing K indicates inhibition of fermentation) increased exponentially as S 0 increased, and was described by: K = 0.8 + 0.0016 e   0.06 S   0. Temperature had no significant effect on K for S 0 between 40 and 100 kg VS/m 3 . The above equation predicted published K values for cattle waste within a mean standard error of 7%.