Optimization of H2O2 dosage in microwave-H2O2 process for sludge pretreatment with uniform design method

A microwave-H₂O₂ process for sludge pretreatment exhibited high efficiencies of releasing organics, nitrogen, and phosphorus, but large quantities of H₂O₂ residues were detected. A uniform design method was thus employed in this study to further optimize H₂O₂ dosage by investigating effects of pH and H₂O₂ dosage on the amount of H₂O₂ residue and releases of organics, nitrogen, and phosphorus. A regression model was established with pH and H2O2 dosage as the independent variables, and H2O2 residue and releases of organics, nitrogen, and phosphorus as the dependent variables. In the optimized microwave-H₂O₂ process, the pH value of the sludge was firstly adjusted to 11.0, then the sludge was heated to 80°C and H₂O₂ was dosed at a H₂O₂:mixed liquor suspended solids (MLSS) ratio of 0.2, and the sludge was finally heated to 100°C by microwave irradiation. Compared to the microwave-H₂O₂ process without optimization, the H₂O₂ dosage and the utilization rate of H₂O₂ in the optimized microwave-H₂O₂ process were reduced by 80% and greatly improved by 3.87 times, respectively, when the H₂O₂:MLSS dosage ratio was decreased from 1.0 to 0.2, resulting in nearly the same release rate of soluble chemical oxygen demand in the microwave-H₂O₂ process without optimization at H₂O₂:MLSS ratio of 0.5.