Biohydrogen production by dark fermentation of wheat powder solution: Effects of C/N and C/P ratio on hydrogen yield and formation rate

The effects of C/N and C/P ratio on hydrogen yield and specific production rate were investigated in dark fermentation of wheat powder solution (WPS) by external addition of N and P since the wheat powder was N and P deficient. A Box–Wilson statistical experiment design approach was used. C/N ratio was varied between 20 and 200 while C/P ratio was between 50 and 1000. A quadratic response function was used to correlate the objective functions with the independent variables and the response function coefficients were determined by regression analysis. Hydrogen yield increased with increasing C/N and C/P ratios. Low nitrogen concentrations required low phosphorous contents for high hydrogen yields. A C/N ratio of 200 and C/P ratio of 1000 yielded the highest H2H2 yield of 281mlH2g-1starch at STP. SHPR also increased with increasing C/N and C/P ratios. Again the highest SHPR (98mlH2g-1biomassh-1 at STP) was obtained at C/N and C/P ratios of 200 and 1000, respectively. The C/N/P ratio maximizing the yield and formation rate of hydrogen was 100/0.5/0.1 (ww-1w-1).