Production of hydrogen and methane from potatoes by two-phase anaerobic fermentation.

A two-phase anaerobic process to produce hydrogen and methane from potatoes was investigated. In the first phase, hydrogen was produced using heat-shocked sludge. About 12h lag-phase vanished, hydrogen yield increased from 200.4 ml/g-TVS to 217.5 ml/g-TVS and the maximum specific hydrogen production rate also increased from 703.4 ml/g-VSS d to 800.5 ml/g-VSS d when improved substrate was used, in which Cl(-) was substituted for SO(4)(2-). Better performances of 271.2 ml-H(2)/g-TVS and 944.7 ml-H(2)/g-VSS d were achieved when potatoes were pretreated by alpha amylase and glucoamylase. In the second phase, methane was produced from the residual of the first phase using methanogens. The maximum additional methane yield was 157.9 ml/g-TVS and the maximum specific methane production rate was 102.7 ml/g-VSS d. The results showed that the energy efficiency increased from about 20% (hydrogen production process) to about 60%, which indicated the energy efficiency can be improved by combined hydrogen and methane production process.