The effects of pretreatment on biogas production from maize straw and cattle manure

The main aim of this study was to determine the effects of physical and chemical pretreatments on biogas production from two agricultural wastes (maize straw and cattle manure). The total solids (TS) were 86.1% and 41.2% for the cattle manure and maize straw respectively while the volatile solids (VS) were 82.0% for cattle manure and 51.6% for maize straw (both interms of total biomass). 5% TS was used for both biomasses in the measurement of reducing sugars and the Biochemical methane potential (BMP) test. Solubility was determined by measuring the reducing sugar concentration using the Miller method (Miller 1959). Biomass samples were seeded with sludge seed on a 50:50 biomass to sludge ratio. The pH of the mixture was regulated to between 7.0 and 7.5 and placed in an incubator at 37oC (mesophilic temperature range). Biogas measurements were done daily and carbon dioxide was measured once in a week. Two chemical pretreatment methods were applied on both biomasses; acid and alkaline pretreatments assisted with heat. The most effective pretreatment method for maize straw was alkaline pretreatment producing the highest concentrations of daily and cumulative biogas with an average increase of 163%. Acid pretreatment of maize straw lasted between 24 to 27 (the fewest number of days) compared to all other pretreatments applied. Physical pertreatment methods applied on maize straw include; comminution, microwave and liquid hot water pretreatment. The Microwave pretreated samples produced the highest increase in biogas production of about 3 folds. Cattle manure was pretreated with H2SO4, NaOH, microwave and liquid hot water (LHW). Acid pretreatment was more effective for cattle manure than maize straw with both acid concentrations increasing biogas production. Cattle manure samples treated at LHW 135oC produced the highest cumulative amount of biogas resulting in a 103% increase. Microwave pretreatment was also very effective resulting in 97% increase in methane production which lasted for 32 days. Keywords: Biogas, pretreatment, lignocellulose, methane, maize straw, cattle manure.