| A new way of generating Class A sludge using microwaves was evaluated through a series of laboratory-scale experiments. Sludge was irradiated with 2,450 MHz microwaves and fecal coliforms, a pathogen indicator, were counted. For comparison, raw sludge and pre-treated sludge with conventional heating were also tested. The penetration depths of a 2,450 MHz microwave unit were 1.7 and 1.1 cm for primary and waste activated sludges, respectively.; Fecal coliforms were not detected at 65°C for primary sludge (PS) and anaerobic digester sludge (ADS) and 85°C for waste activated sludge (WAS) when sludge was pre-treated with microwaves. In batch tests, the relative cumulative biogas productions of ADS, PS, and WAS by microwave irradiation were approximately 13, 20, and 5% higher than external heating, and 54, 52, and 3% higher than the control, respectively.; During the bench scale anaerobic digester operation, the highest average log reduction of fecal coliforms was achieved by the anaerobic digester fed with microwave-pretreated sludge (2.66 log removal). From the paired t-test results, fecal coliform detection for pairs of digesters was statistically significantly different. The digester fed with microwave-irradiated sludges was more efficient in inactivation of fecal coliforms than the other two digesters fed with raw sludge and externally heated sludge, respectively.; Damages of fecal coliform cell membranes by microwave irradiation were observed using both SYTO 9 and propidium iodide stains. The genomic DNA bands extracted from the pure cultured fecal coliforms that had been irradiated with 1 kW microwaves were increasingly faint with the increase in irradiation time. This phenomenon was not observed in the externally heated samples.; Microwave technology appears to be an effective, economical, and clean method of generating environmentally safe sludge. A new microwave system was proposed to destruct pathogens in sludges generated from wastewater treatment plants. |
