Enhancement of microwave effect with addition of chemical agents in solubilization of waste activated sludge

Microwave (MW) is a promising method for solubilization of wasted activated sludge (WAS) due to the accelerated reaction rates, environmental friendliness and low overall cost compared to conventional heating. In this study, to enhance the MW effect on solubilization of WAS, several chemical agents were applied including H2SO4 as the acidic material and NaCl and CaCl2 as ionic materials. In the experiment of salt-assisted MW pretreatment, CaCl2 turned out to be ineffective on WAS solubilization, whereas NaCl had a positive effect on WAS solubilization compared to that of MW only assisted pretreatment. Thus, NaCl was considered to be appropriate salt to assist MW pretreatment for WAS solubilization. In the chemically assisted MW pretreatments, H2SO4 assisted MW pretreatment was the most effective for WAS solubilization. However, the application of H2SO4 to MW pretreatment has the drawbacks of reuse, which may increase the operating costs. Thus, food wastewater was used for enhancement of MW efficiency on WAS solubilization due to its high NaCl and acidity. As a result, the application of food wastewater to WAS afforded the solubilization efficiency higher than that of MW-H2SO4 pretreatment. (C) 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.