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UBC Theses and Dissertations

Applications of microwave technology to wastewater treatment Yin, Guiqing

Abstract

A microwave enhanced advanced oxidation process using hydrogen peroxide (MW/H₂O₂-AOP) was used for the release of nutrients and the destruction of solids from secondary municipal sewage sludge. The significant factors affecting the MW/H₂O₂-AOP that would yield maximum soluble substrates were studied. Using a computer statistical software package for experimental design and data analysis, four factors including microwave heating temperature, heating time, hydrogen peroxide dosage, and sludge solids content, were selected and examined. The initial sludge TS content and hydrogen peroxide dosage were the most significant factors for the solubilization of COD and nutrients release under the experimental conditions selected in this study. Overall, the maximum solubilization of nutrients was obtained at 2.5 % of total solids content, 2% of hydrogen peroxide by weight, 5 min. of microwave heating and 120 ºC. The effects of combination of microwave treatment and oxidative reagents on solids destruction and nutrients release were also investigated. Microwave enhanced advanced oxidation processes (MW-AOP), such as MW/O₃, MW/H₂O₂ and MW/H₂O₂/O₃, were conducted at 100 °C. In terms of nutrients release and solids reduction, the MW/H₂O₂/O₃-AOP yielded the best result. Subsequently, three factors including microwave heating temperature, hydrogen peroxide dosage, and ozone dosage, were investigated. The best result, in terms of the release of phosphate and ammonia, and solids reduction, was obtained with additions of 2 % hydrogen peroxide by weight and ozone dosage of 5.09 mg/ml, and operating at 120ºC. About 95%, 32% and 78% of TP, TKN and COD were released into the solution, respectively. The microwave enhanced advanced oxidation processes, with and without an addition of ferrous sulfate (MW/H₂O₂-AOP and MW/H₂O₂/Fe+²-AOP), were also studied for reducing solids, and solubilizing nutrients from the secondary sewage sludge. For the MW/H₂O₂/Fe+²-AOP, the best results of solubilization, in terms of orthophosphate, ammonia and soluble chemical oxygen demand, were obtained at treatment temperatures of 40 ºC, the yields decreased as the temperature was increased. The highest yields of solubilization were obtained at 60 ºC for orthophosphate, and at 80 ºC for both ammonia and soluble chemical oxygen demand.

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