(412c) Microwave Irradiation as an Alternative Pretreatment Method for Sludge Stabilization

Conventional secondary wastewater treatments plants produce primary sludge and secondary waste activated sludge (WAS) that are usually stabilized via anaerobic digestion. Both sludge's have different physical and biological properties that impact on mesophilic digestion. WAS is the most problematic since it is mostly composed of microbial cells. Cell walls and membranes act as chemical and physical barriers for cell lyses that limit the extent of digestion and for the most part hydrolysis becomes rate limiting. Many pretreatment methods (thermal, mechanical, chemical and combinations) have been investigated and shown to improve WAS hydrolysis and to increase biogas production. This paper reports on Microwave (MW) irradiation as an effective alternative method to conventional heating. Results indicate that MW irradiation to high temperatures and pressures increase WAS disintegration with concomitant increase in volatile solid destruction, pathogen removal and biogas production. Mesophilic Biological Methane Production (BMP) assays performed on WAS subjected to various MW intensities, pretreatment temperature (110 to 175ºC) and WAS concentrations (5.5 and 12% total solid) increased WAS hydrolysis as well as cumulative biogas production. Results of WAS solubilization (up to 6 fold improvement) and BMP assays in terms of total and soluble chemical oxygen demand (COD), ammonia, soluble protein, reducing sugar as well as volatile and total solids concentration changes as they pertain to enhanced biogas production with MW pretreatment will be presented. Based on pathogen reductions due to the high temperatures studied it is concluded that microwave pretreatment can enhance the degree of mesophilic anaerobic sludge stabilization and produce stabilized sludge for disposal.