Effects of ammoniation pretreatment on anaerobic digestion performance of rice straw

In order to provide N for the growth of microorganisms, reduce operating costs, and maintain efficiency gas production, ammonic pretreatments of straw were used. Effects of ammonic pretreatment on anaerobic digestion performance of rice straw were investigated. Four NH3 doses (0%, 2%, 4%, and 6%), and three loading rates (50, 65 and 80?g/L) were used. The rice straw was first pretreated by different doses of NH3. The results showed that pretreated rice straw achieved the best pretreatment results with the dose of 4%NH3. At the dose of 4% NH3 and loading rate of 65 g/L，the total biogas productions was 37010 mL on anaerobic digestion for 70 d, 33920 mL yielded at the technical digestion time 90 d, which were 38.3%, 14.6% and 8.2% respectively more than the untreated, 2% NH3 and 6% NH3 pretreated rice straw at the same standard, and total methane production increased by 34.8%, 15.1% and 9.6%, respectively. Total biogas and total methane were 60.8% and 60.3% more than the untreated at the same time (45 d). Anaerobic digestion time was decreased by 10 days. Accordingly the reductions in total solids and volatile solids were increased from 41.6% and 46.6% to 46.4% and 58.6%, respectively. Compared to untreated rice straw, hemicellulose and lignin of NH3 pretreated rice straw were decreased from 27.7% and 6.9% to 20.8% and 5.2%, the crude protein of rice straw was significantly improved from 4.0% to 10.1%. This experimental study can provide an effective way to improve gas production, and provide guideline for designing straw biogas plant.