Microwave enhanced advanced oxidation treatment of sewage sludge from the membrane-enhanced biological phosphorus removal process

This study investigated the effectiveness of bench and pilot-scale microwave enhanced advanced oxidation process (MW-AOP) for treatment of sewage sludge in neutral, acidic (pH 4) and alkaline (pH 9) conditions. The MW-AOP treatments were very effective: total suspended solids reduction and chemical oxygen demand solubilization were better in the sets at pH 9 than at pH 4. Alkaline conditions would be more favorable for the subsequent anaerobic digestion for biogas production. Release of orthophosphate, particle size distribution, dewatering properties and settling of the sets at pH 4 were better than at pH 9. The supernatants obtained from the sets at pH 4 had a high orthophosphate concentration and a low total suspended solids content, which were more suitable for struvite (a fertilizer) recovery process. Energy consumption was lower for the pH adjusted treatment sets compared to those of MW only and MW-AOP at neutral conditions; energy for the pH adjusted sets varied between 0.32 and 0.41 kWh/L of sludge treated. The results indicated that the MW-AOP could reduce the volume of sludge for disposal, and produce a high quality treated effluent suitable for further resource and energy recovery. Depending on the needs of each wastewater treatment plant’s treatment priority, the experimental conditions applied in the process can be adjusted accordingly.