Generation of Class A Sewage Sludges Using 2,450 MHz Microwave Irradiation
Abstract:A new way of generating Class A sludge using microwaves was evaluated through a series of laboratory-scale experiments. Microwaves provide rapid and uniform heating throughout the material, instant and accurate control, and selective and concentrated heating on the material that has a high dielectric loss factor. Sludge was irradiated with 2,450 MHz microwaves and fecal coliforms, a pathogen indicator, were counted. 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 irradiated with 2,450 MHz microwaves. 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). A statistical analysis was performed to evaluate the difference of three bench-scale anaerobic digesters. From the paired t-test results at the 95% confidence interval, the results of fecal coliform detection for pairs of digesters were 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. Class A sludge can be produced consistently if sludge is irradiated with microwaves to reach 65 C before fed to anaerobic digester. It will take more than three hydraulic retention times (HRTs) to meet Class A sludge after microwave irradiation of sludge.
Document Type: Research Article
Publication date: January 1, 2002
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