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Enhanced Anaerobic Biodegradability and Inactivation of Fecal Coliforms and Salmonella spp. in Wastewater Sludge by Using Microwaves

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During continuous operation of three mesophilic-anaerobic digesters, the effect of microwave irradiation, as sludge thermal pretreatment (60 to 65°C), was studied. The fecal coliforms log inactivation for microwaved/digested sludge was 4.2 ± 0.4, whereas for conventionally heated/digested sludge and control were 2.9 ± 0.5 and 1.5 ± 0.5, respectively. In the case of Salmonella spp., no colonies were detected in 85% of the microwaved/digested samples. Considering the detection limit, the log inactivation of these samples was greater than 2.0 ± 0.3. The conventionally heated/digested sludge and control showed log inactivations of 1.9 ± 0.2 and 1.1 ± 0.3, respectively.

At the 95% confidence level, microwaved/digested sludge increased the biogas production by 16.4 ± 5.6% and 6.3 ± 2.4%, as compared to control and conventionally heated/digested sludge, respectively. When thermally treated sludge was analyzed for soluble chemical oxygen demand, microwaved waste-activated sludge showed considerable solubilization between 37 and 60°C.

Microwaved/digested sludge showed a reduction of capillary suction times by 11.1 ± 5.9% and 10.7 ± 5.6%, as compared to control and conventionally heated/digested sludge, respectively.

Keywords: anaerobic digestion; biosolids; microwaves; pathogen inactivation

Document Type: Research Article


Publication date: February 1, 2006

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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