Post-treatment of biologically treated wastewater containing organic contaminants using a sequence of H₂O₂ based advanced oxidation processes: Photolysis and catalytic wet oxidation

In this paper the feasibility of a multi-barrier treatment (MBT) for the regeneration of synthetic industrial wastewater (SIWW) was evaluated. Industrial pollutants (orange II, phenol, 4-chlorophenol and phenanthrene) were added to the effluent of municipal wastewater treatment plant.The proposed MBT begins with a microfiltration membrane pretreatment (MF), followed by hydrogen peroxide photolysis (H₂O₂/UVC) and finishing, as a polishing step, with catalytic wet peroxide oxidation (CWPO) using granular activated carbon (GAC) at ambient conditions.During the microfiltration step (0.7μm) the decrease of suspended solids concentration, turbidity and Escherichia coli in treated water were 88, 94 and 99%, respectively. Also, the effluent's transmittance (254nm) was increased by 14.7%. Removal of more than 99.9% of all added pollutants, mineralization of 63% of organic compounds and complete disinfection of total coliforms were reached during the H₂O₂/UVC treatment step (H₂O₂:TOCw/w ratio=5 and an UVC average dose accumulated by wastewater 8.80W_UVCscm^-2). The power and efficiency of the lamp, the water transmittance and photoreactor geometry are taken into account and a new equation to estimate the accumulated dose in water is suggested. Remaining organic pollutants with a higher oxidation state of carbon atoms (+0.47) and toxic concentration of residual H₂O₂ were present in the effluent of the H₂O₂/UVC process.After 2.3min of contact time with GAC at CWPO step, 90 and 100% of total organic carbon and residual H₂O₂ were removed, respectively. Also, the wastewater toxicity was studied using Vibrio fischeri and Sparus aurata larvae. The MBT operational and maintenance costs (O&M) was estimated to be 0.59€m^-3.