Alkaline pretreatment of sorghum and wheat straw for increasing methane production

The aim of this study was to determine the effect of alkaline pretreatment on fiber composition,biodegradability and methane production rate of sorghum forage and wheat straw. Samples were treated at 40 °C for 24 h with a sodium hydroxide solution. The specific dosages were 1, 3 and 10gNaOH/100gTS. By increasing the alkaline dosage, a reduction in the total fiber content and an increase in COD solubilization is observed. Total sugars content increased up to five times at the highest alkaline dosage with respect to control samples, proving that alkali pretreatment improves substrate swelling and hydrolysis of hemicellulose. Biochemical methane production tests showed that the chemical pretreatment increased both the ultimate anaerobic biodegradability and the methanization rate. The ultimate biodegradability was increased from 66 to 86% for sorghum and from 56 to 72% for wheat straw. The first order kinetic constant for methane production was increased by 33% (from 0.21 to 0.28 d-1) for sorghum and by 170% (from 0.10 to 0.27 d-1) for wheat straw.