Investigation of pretreatment methods to improve biogas yield of agricultural wastes

In this study alkali and acidic pre-treatments were applied to evaluate methane production potential from agricultural wastes. Banana peel, corn stalk and grass were used as agricultural wastes due to their high lignodellulosic content. The studies were carried out with 2,5 L biorector equipped with gas collection and feeding tubes on the top. The pH was automatically measured and controlled. The system was heated to 35oC by the water jacket around the reactor. The contents were mixed by a propeller type of mixer to obtain a homogeneous content and to provide gas release. The retention times for each reactor were 42 days. The solids content of agricultural wastes was respectively %6, % 8 and %10. NaOH (w/w %3,%6 and %8) and H2SO4 (w/w %1,%2 and %3) were chhosen as alkali and acidic pretratment method respectively. NaOH doses were optimized according to biogas fermentation performance, and the best doses were 3% and 6% (by weight) based on the total solid content (TS) of wastes. After digestion, TS and volatile solid (VS) reductions of the codigestion were 45-50% and 60-65 %, respectively. The highest methane yield of banana peel, corn stalk and grass wastes were 201 mLCH4/g Vs, 208 mLCH4/g Vs and 181 mLCH4/g Vs respectively, %10-40 higher than the control. The best H2SO4 doses were 1% and 2% (by weight). After biogas digestion, TS and volatile solid (VS) reductions of the codigestion were 45-55% and 55-60 %, respectively. The highest methane yield of banana peel, corn stalk and grass wates were 233 mLCH4/g Vs, 213 mLCH4/g Vs and 185 mLCH4/g VS respectively, %20-30 greater than the control. Results indicated that low doses of alkali and acidic process could be an effective method for using agricultural to produce biogas.