Pilot-scale microwave treatment of wastewater slurries : assessment of a 915 MHz microwave generator and custom applicator

This study applied thermal-oxidative treatment to wastewater. It utilised a novel, pilot-scale microwave system with additions of hydrogen peroxide and acid. The system was instrumented to measure temperature, power and energy. This allowed aspects of process design, power draw and energy efficiency to be weighed against outcomes of treatment. Preliminary tests with salt water established procedures and expectations for the system, highlighting system sensitivity to variations in the target fluid. Primary tests treated manure and waste activated sludge, evaluating improvements in solids reduction, biogas production, dewaterability and nutrient recovery, each described by a suite of parameters, and referenced to power and energy consumed. Primary tests used various treatments, with some general trends observed. Acid solubilised inorganic constituents while fixing organics, improving settling and supernatant clarity. It had most acute effect on manure, achieving the majority of phosphorus released. Acid’s impact on phosphorus in sludge was less dramatic, though it produced a clear supernatant and good settling. For sludge, early addition of H₂O₂ and heat, or heat alone released most phosphorus and produced highest peaks in phosphate. However, results suggested that acid could be necessary to reduce suspended solids to a level required for struvite recovery. For both wastes, though especially dramatic for sludge, no acid, high heat and late addition of H₂O₂ proved best to disrupt organics and improve bulk parameters: dissolving most suspended solids; solubilising most carbon, volatile fatty acids and ammonia; and improving overall settling. This treatment indicated the most benefit for biogas production. This study shows some results similar to existing literature, though different processes may be used. This confirms a trend often noted in literature: that thermal treatments are largely reproducible, due to the dominant impact of heat. However, this study indicated that not all processes are equal in energy efficiency. Comparing continuous and semi-continuous operation, continuous runs showed slight detriment in treatment, but clear opportunity for improved energy efficiency. It increased stability in mechanical and chemical properties of target fluids, improving the stability and efficiency of microwave energy absorption.Applied Science, Faculty ofCivil Engineering, Department ofGraduat