AGRICULTURAL WASTE CHEMICAL PRETREATMENT WITH SODIUM HYDROXIDE AND UREA FOR THE OPTIMIZATION OF METHANE YIELD IN TWO-STAGE ANAEROBIC CODIGESTION

This study addresses the valorization of organic agricultural waste for the energy generation.To this end, we evaluated the efficiency of chemical pretreatment of a mixture of straw (sugarcane, wheat, corn and soybean) with alkaline reagents on methane yield in anaerobic biodigestion processes.The pretreatment step was performed with two solutions, 3% sodium hydroxide and 2% sodium hydroxide/5% urea, with different contact times between substrate and reagent (24 and 48 h), compared to the sample without pretreatment (untreated wastes -UTW).In the subsequent anaerobic biodigestion step, the straw mixture was inoculated with animal manure (horse, swine and equine) and was performed under mesophilic conditions at 37C for 37 days, in batch biodigesters (BMP -biochemical methane potential).The methane yield results indicated that the two systems with only sodium hydroxide (without addition of urea) resulted in greater methane accumulation per mass of volatile solids of residue (1.46 and 1.31 mL CH4 /g VS for the systems pretreated only with NaOH for 24 and 48 hours, respectively).The results of low methane generation (compared to other similar studies reported in the technical literature) showed the need to optimize the biodigestion system for these substrates and inocula, especially with regard to parameters such as retention time of the biodigestion phases and nutrient content of the residue mixture.