Chiang Mai Journal of Science

 Domestic waste activated sludge (WAS) produced from wastewater treatment process, non hazardous organic waste can reach up to 550,000 ton/y by 2012. For instance, poultry slaughter house and food processing plant generates lots of sludge waste 20,000 ton per year. To minimize the sludge waste disposal and to further transform organic matter into biogas, sludge anaerobic digestion is one of the most potential treatment processes. This study aimed to accelerate hydrolysis period by microwave-assisted pretreatment for improvement of biogas production from the WAS.  Effect of mixing ratios between primary and anaerobic sludge, temperature and vacuum degree using microwave (MW) irradiation on biogas production improvement were studied in anaerobic batch reactors under mesophilic condition for 25 days. Experimental results showed that vacuum MW pretreatment at 65^oC and sludge mixture ratio of primary to secondary sludge at 60:40 was the most suitable condition for biogas production. The average methane yield was achieved 5,256 g CH₄/kg dried solid and 91% CH₄ content which was about 1.3-fold higher than non-MW pretreatment. The accelerated hydrolysis of organic matters in WAS was hydrolyzed 3-fold faster than non-MW pretreatment. In comparisons between MW and non- MW pretreating experiments, average %COD removal, %glucose consumption and %VS production rate during hydrolysis period were decreased by 25.6%, 47.5% and 82.27%, respectively. A vacuum degree of MW thermal pretreatment had a direct effect on the mesophilic anaerobic biodegradability of WAS by damaging activated sludge floc structures and cell membranes as indicated by the solubilization of particulate CODs, glucose concentration and volatile solid amount.