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Microwave enhanced advanced oxidation treatment of sludge from a municipal wastewater treatment plant Tan, Hanji


It has been proven that microwave enhanced advanced oxidation process (MW-AOP) has an outstanding treatment efficiency on the organic slurries, such as sewage sludge and dairy manure (liquid portion), yet the treatment efficiencies on different substrates remain unknown. This study was carried out to: 1) identify the effects of MW-AOP on different types of sludge, 2) evaluate the effects of flowrates and solids concentrations on the heating profile, 3) evaluate the MW-AOP treatment efficiencies of secondary sludge at 90 and 110 ºC, and 4) examine the treatment efficiencies of MW-AOP of dairy manure (liquid portion). The study on the sludge was to evaluate treatment efficiencies of different sludge (primary sludge, secondary sludge, and anaerobic digested sludge) and the centrate by the MW-AOP. The results indicated that the secondary sludge was most suitable for the MW-AOP treatment. This is because secondary sludge had the highest number of solids and phosphorus contents, but also yielded the highest soluble materials. The pilot-scale 915 MHz MW-AOP system was used to treat the secondary sludge at 90 and 110ºC, which suggested that higher temperature would favor nutrients release. The dewaterability of treated sludge improved significantly at both temperatures. The pilot-scale 915 MHz continuous flow MW-AOP system was also tested with salt water at different flowrates and salt concentrations to understand the heating and power consumption profile of the system. Among the flowrates (6, 7.5, 9 L/min) and salt concentrations (10 mg/L to 120 mg/L) examined, the total energy consumption increased with an increase of salt concentration, while flowrates had lesser effect. In contrast, the temperature rise was more rapid with lower salt concentrations. The overall heating rate was similar for different flowrates. Similar to secondary sludge, the pilot-scale 915 MHz continuous flow MW-AOP system was used to treat dairy manure (liquid portion). The results suggested a sound treatment efficiency, with an increase from 3% to up to 90% of soluble TP/TP, which enhances subsequent struvite recovery. Both the ratios of soluble TP/TP and of ortho-P/soluble TP were favored by higher temperatures.

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