Field investigation of advanced oxidation of secondary effluent from municipal wastewater treatment plant

Successful treatment of the secondary effluent ensures its safe disposal and water reclamation for water reuse. To understand the effect of ultraviolet (UV) irradiation in combination with hydrogen peroxide (H2O2) on secondary effluent under field conditions, an advanced oxidation system, UV+H2O2, was installed and fed with the effluent at 1.0, 1.5 and 2.0 m(3) h(-1) over a period of 6 months. The electrical energy density for the UV reactor was varied between 0.5 and 5.2 kWh m(-3) and H2O2 added at concentrations of 0, 13 or 26 mg L-1. The feed and product water samples were taken periodically and analyzed for biological (heterotrophic plate count-HPC, total and fecal coliform-TC and FC) and chemical (NH4+-N, NO3--N, NO2--N and total organic carbon-TOC) parameters. For the treatment of UV+26 mg L-1 H2O2, flow rates of 1.0, 1.5 and 2.0 m(3) h(-1) resulted in > 4-log removal of HPC with a maximum survivor of 20 CFU mL(-1) and > 4 log reduction of FC with a survivor of 8 CFU (100 mL)(-1). The electrical energy density of 1.5 kWh m(-3) was optimum for the inactivation. The NO2--N concentrations of the product water were 0.09-0.42 mg L-1 compared with 0.04-0.09 mg L-1 in the feed. With or without H2O2 addition, NO2--N concentration increased with increases in UV electrical energy density. The highest increase in NO2--N was associated with the maximum energy density of 5.2 kWh m(-3). Increase in H2O2 dose reduced NO3--N concentration by 2.0 to 5.7%. The overall results showed that the advanced oxidation technology prepared the effluent for safe disposal and/or for water reclamation for reuse.