Optimization of sludge supernatant treatment using advanced oxidation processes via Response surface methodology

Returned supernatant from dewatered sludge to the treatment plant, without primary treatment, leads to an increase in organic load. In the present study, the optimum condition of supernatant treatment using ultrasonic combined with photocatalytic process was investigated via response surface methodology (RSM). Nanoparticles synthesized from zinc acetate were used as photocatalyst. Chemical oxygen demand (COD) and phosphorus (P) were removed from sludge supernatant using a UV light source and ultrasonic waves under ambient temperature and pressure. Experiments were designed via RSM. Effects of operational parameters including retention time (1.5-4.5 h), UV light intensity (0-20 kW/m(2)), concentration of nanoparticles (0.5-2 g/L), pH (2.75-10.25), and ultrasonic power (0-360 W) on removal efficiency of phosphorus and COD was evaluated in this study. Results showed that an increase in operational parameters, enhanced the removal efficiency of COD and phosphorus. The maximum removal efficiency of COD (93.34%) and phosphorus (97.3%) was obtained under the optimal condition of 3.36 h retention time, 14.77 kW/m(2) UV light intensity, 1.74 g/L of nanoparticles concentration, and pH 8.98.