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UBC Theses and Dissertations

An effective microwave system to achieve solid disintegration and nutrient release of sewage sludge Ning, Ruihuan


In order to achieve solid disintegration and nutrient recovery from sewage sludge, research on the microwave/hydrogen peroxide advanced oxidation process (MW/H₂O₂-AOP) has been underway within the research group led by Dr. Victor Lo since 2004. In an effort to promote the commercialization of the technology, a series of sludge experiments, salt water experiments, simplification of the system and a comparison study of different total phosphorus determination methods were conducted to further understand, simplify, and standardize the treatment process. The sludge experiments were carried out to test the impact of temperature and hydrogen peroxide dosage on the treatment efficiency of the custom-designed 915MHz continuous-flow pilot scale system. The microwave system, designed to withstand high temperature and pressure, delivered energy effectively into the reaction vessel. High temperature and/or high H₂O₂ dosage implemented in this system yielded high treatment efficiency in terms of solid disintegration, nutrient release, and altering of physical properties. The inter-relationship between chemical changes and physical transformation was also documented. The clear solution after the treatment was ideal for struvite crystallization and anaerobic digestion processes. The results would provide the basic knowledge for designing an industrial-scale MW/H₂O₂-AOP system. A comparison study among different phosphorus determination methods suggested alternatives to currently used phosphorus determination methods. It was discovered that microwave digestion at both 95 and 120 ⁰C resulted in comparable measurements as the wet digestion followed by ICP, indicating the possibility of shortening digestion time from 2 hours to 10 min using microwave digestion. Simplification to the feed line of the microwave system offered operational advantage because it separated the feed line from the recirculation line, reducing confusions and complications in operation. It also minimized the chance of a two-stage cavity pump running dry. The salt water experiments were designed to characterize the system after it was modified to withstand higher temperature above 110 ⁰C. It was discovered that changing flow influenced temperature rise per pass. Ion concentration of the substrate influenced heating rate by influencing reflected power from the substrate.

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