The effects of an advanced oxidation process combining microwave, hydrogen peroxide and acid hydrolysis in a single stage (MW/H2O2/H+-AOP) on the process efficiency of sewage sludge treatment and nutrient recovery were investigated. At lower temperature regimes (60–80°C), the soluble phosphate was substantially higher in a two-stage process than in a single stage MW/H2O2/H+-AOP process. However, higher soluble phosphate concentration was obtained for single-stage treatment at the higher operating temperature regimes (100–120°C). With the addition of an inorganic acid, a very high yield of soluble phosphate was obtained in the solution at 120°C. In tests with acid addition, soluble ammonia increased as temperature increased. For single stage MW/H2O2/H+-AOP, maximum soluble ammonia was obtained at 120°C. Significant concentrations of soluble COD were also obtained in this treatment. A threshold temperature of 80°C was observed, at which all of the COD could be solubilized. However, at higher temperatures (100–120°C), further oxidation processes occurred to form carbon dioxide, resulting in decreased amounts of soluble COD in the solution.
Acknowledgments
The authors wish to acknowledge the research funding, in the form of a Discovery Grant, provided by the Natural Science and Engineering Research Council, Canada.