Improving Anaerobic Digested Sludge Dewaterability through Gamma-Ray Irradiation and Struvite Precipitation

Abstract

Anaerobic digestion is a generally used microbial process in wastewater treatment plants, and anaerobic digestion sludge often possesses unacceptable characteristics including high resistance to solid-liquid separation and high concentration of nutrients, such as phosphorus and nitrogen. Gamma-ray irradiation was used to improve the dewaterability of anaerobic digestion sludge, and the struvite (magnesium ammonium phosphate) precipitation method was utilized to recover increased orthophosphate (PO43−-P) and ammonium nitrogen (NH4+-N) from the postirradiation liquor. An absorbed dose of 5–15 kGy would be potentially successful for dewaterability improvement, and the optimal dewaterability occurred at 10 kGy, which could reduce the water content of sludge cake from 80.08 to 73.46%. The mechanism for the enhanced dewaterability was also analyzed, and the lysis of extracelluar polymeric substances and reduction of particle surface charges were found to be the major reasons. Furthermore, the recovery rate of PO43−-P and NH4+-N were 86.07 and 15.08%, respectively, under the condition of Mg/P of 1.8 (molar ratio), pH 9.6, and reaction time of 30 min.