Effect of photochemical treatment on the biocompatibility of a commercial nonionic surfactant used in the textile industry

The degradability of surfactants is a frequent and complex issue arising both at domestic as well as industrial treatment facilities. The present paper describes a laboratory study conducted to elucidate the photochemical and biochemical treatability of a nonionic, alkyl polyethylene ether-based surfactant formulation commonly used in the textile preparation stage. The application of H₂O₂/UV-C advanced photochemical oxidation appeared to be a suitable treatment alternative and 90% COD removal (COD₀≈500 mg/L) could be achieved under optimized process conditions. A significant COD removal efficiency (74%) could also be reached after biodegradation (final COD=135 mg/L) of the surfactant; however, necessitated an acclimation period of at least 6 weeks for the achievement of steady-state conditions. H₂O₂/UV-C treatment efficiency was seriously retarded upon elevation of the initial COD to around 1000 mg/L, resulting in 46% COD and 38% TOC removal after 120 min photochemical oxidation (H₂O_2,0=1020 mg/L; pH₀=9.1). The BOD₅/COD ratio increased from 0.23 to 0.31 after the application of H₂O₂/UV-C revealing that photochemical pretreatment may have a positive effect on the ultimate biodegradation of the nonionic surfactant. Although the time required for activated sludge treatment to reach steady-state conditions could be reduced to 3 weeks for the photochemically pretreated surfactant formulation biochemical COD removal efficiency dramatically decreased from 74% to 39% for the nonionic surfactant being subjected to H₂O₂/UV-C pretreatment (ultimate COD after activated sludge treatment=265 mg/L).