Octylphenol ethoxylate treatment with zero-valent aluminum based advanced oxidation process

Alkylphenol ethoxylates (APEs) are non-ionic surfactants and the more important members of them are nonylphenol (NP) and octylohenol (OP). APEs are being used in the formulations of cleaning products, paints, ink dispersants, textile and leather processing (preparation, dyeing and finishing), pulp and paper manufacturing, metal processing, cosmetics and personal care products. It has been postulated that APEs have estrogenic activity and is classified as an endocrine disrupting compound (EDC). There is growing concern on the influence of APEs, Due to their high consumption rate and adverse health effects on wildlife. APEs are discharged to wastewater treatment facilities or directly released into the environment and are a potential source of contamination in the aquatic environment. Primary degradation of APEs in wastewater treatment plants or in the environment generates more persistent shorter chain APEs. Due to the fact that biotreatment requires long retention times and connot degrade APEs completely, rapid and efficient treatment process including advanced oxidation process (AOPs) have successfully been developed to the efficient treatment of APEs. AOPs are based on the generation of very reactive species free radicals. ZVAl exhibits a capacity to degrade organic pollutants under acidic conditions. In the presence of O2, ZVAl/oxidant showed high oxidation capacity due to the high stability of aqua-complexed Al3+ over a wider pH range and leads to generation of OH● and SO4- free radicals by an electron transfer mechanism from ZVAl to oxidant. In this study, nanoscale zero-valent aluminum (nZVAl)-activated hydrogen peroxide (HP), persulfate (PS) and peroxymonosulfate (PMS) oxidation of commercially important octylphenol polyethoxylate type nonionic surfactant namely Triton™ X-45 (TX-45), was investigated. Consequently, it is of major importance to follow changes in toxicity during the application of AOPs, preferrably by conducting battery tests to examine potential toxic effects on tests organisms belonging to different trophic levels. Two different acute toxicity tests using Vibrio fischeri and Pseudokirchneriella subcapitata as well as the UMU-Chromo genotoxity test were undertaken to evaluate the ecotoxicological effects of TX-45 and its oxidation products. In the first part of the study, TX-45 abatement with different initial concentration, oxidant consumption and pH changing were investigated in the nZVAl/O2/H+ system, mere oxidant process and nZVAl/Oxidant treatment methods. Thereafter, treatment performances were evaluated in distilled water (DW), raw surface water (SW), tap water (TW) and effluent from a domestic wastewater treatment plant (WW) to estimate TX-45 degrade as well as its TOC content. TX-45 removals in the absence of nZVAl (mere HP, PS and PMS treatments) and oxidants (nZVAl/O2/H+ treatment) were obtained between 5%-38%. Activation of HP, PS and PMS with nZVAl enhanced TX-45 degradation substantially. Complete TX-45 degradation occurred in DW with the nZVAl/PS and nZVAl/PMS treatment combinations after 90 min and 60 min, respectively, whereas only 76% TX-45 removal was obtained with nZVAl/HP after 120 min (TX-45=2 mg/L; nZVAl=1 g/L; HP- xx PMS=0.25 mM; PS=0.5 mM; pH=3). In DW, TX-45 removal efficiencies decreased as follows; nZVAl/PMSnZVAl/PS>nZVAl/HP and as nZVAl/PMS> nZVAl/HP> nZVAl/PS in SW and WW. Additionally, it should be mentioned that the TOC contribution of the 2 mg/L TX-45 in the SW, TW and WW samples was relatively minor (10-20%) that could not have affected the TOC removal considerably. Toxicity test results indicated that the nZVAl/PS-treated TX-45 samples did not exhibit toxic effects on V. fischeri; the relative inhibition increased from 15% to 26% in DW and decreased to practically non-toxic levels (<8%) in SW after 120 min treatment. During the early stages of nZVAl/PS treatment, the growth inhibition test conducted with the microalgae P. subcapitata revealed that the relative inhibition value was increased from 35-39% to 44% and 52% in DW and SW samples, respectively. After 120 min treatment, it dropped back to 40 and 25% in DW and SW samples, respectively. The battery test results demonstrated not TX-45, but the oxidation products of the treatment process caused inhibitory effects and also results revealed that the most sensitive organism to TX-45 and its degradation products was P. subcapitata. According to the UMU-Chromo test results the original and nZVAl/PS-treated TX-45 neither exhibit cytotoxic nor genotoxic effects.