Bu çalışma kapsamında, ülkemizde ve dünyada ticari olarak önem taşıyan tekstil ve kimya başta olmak üzere pek çok endüstride yoğun olarak kullanılan ve çevrede yarattıkları olumsuz etkilerden dolayı önem taşıyan noniyonik (nonil fenol etoksilat), anyonik (dioktil sülfosuksinat) ve katyonik (kuaterner amonyum etoksilat) türü yüzey aktif maddelerin (YAM) Foto-Fenton ve H2O2/UV-C ileri oksidasyon prosesleri ile arıtılabilirlikleri incelenmiştir. Yapılan ön arıtılabilirlik deneyleri sonucunda, incelenen fotokimyasal ileri oksidasyon proseslerinin yüzey aktif maddelerin arıtımı için uygun ve etkin olduğu saptanmıştır. Yüzey aktif maddelerin fotokimyasal arıtımı için seçilen H2O2/UV-C ileri oksidasyon prosesi Cevap Yüzey Yöntemi kullanılarak ana madde, KOİ ve TOK giderimleri açısından modellenip, optimize edilmiştir. H2O2/UV-C prosesi ile yapılan arıtılabilirlik çalışmalarında giriş KOİ değerinin, reaksiyon süresinin ve H2O2 konsantrasyonunun (proses bağımsız değişkenleri) ana madde, KOİ ve TOK giderim verimleri (proses çıktıları/bağımlı değişkenleri) üzerindeki etkileri araştırılmıştır. Yapılan deneysel tasarım çalışmaları sonucunda proses çıktılarını bağımsız değişkenler cinsinden tanımlayan ikinci dereceden eşitlikler türetilip geçerlilikleri istatistiksel araçlar kullanılarak sorgulanmıştır. Yüzey aktif maddelerin H2O2/UV-C prosesi ile ileri oksidasyonunun Cevap Yüzey Yöntemi ile yeterli hassasiyetle modellenebildiği sonucuna varılmıştır. Farklı giriş KOİ değerleri için optimize edilen reaksiyon koşullarında yürütülen fotokimyasal oksidasyon deney sonuçlarının model çıktıları ile uyum gösterdiği gözlenmiştir. Çalışmanın son aşamasında ise yüzey aktif maddelerin ve fotokimyasal oksidasyon ürünlerinin toksisiteleri aktif çamur inhibisyon testi ile belirlenmiştir. Deneysel çalışma sonuçları ışığında YAM içeren çözeltilerin heterotrofik biyokütle üzerindeki inhibisyon etkilerinin fotokimyasal arıtma ile çok yüksek oranda azaltıldığı ve oksidasyon süresi boyunca oluşan oksidasyon ara ve son ürünlerin toksik etkisinin olmadığı söylenebilmektedir. Anahtar Kelimeler: Anyonik, katyonik ve noniyonik yüzey aktif maddeler, H2O2/UV-C arıtımı, cevap yüzey yöntemi, optimizasyon, aktif çamur inhibisyonu.Surfactants are widely used in household detergents, personal care products, paints, inks, polymers, pesticide formulations, pharmaceuticals, mining, oil recovery, pulp and paper, tannery and textile industries. Due to their amphiphilic characteristics, surfactants tend to sorb and hence accumulate onto sludge and soil sediments thus imparting serious ecotoxicological risks in the environment. As a consequence, more effective and at the same time economically feasible treatment processes have to be applied to alleviate the chronic problem of surfactant accumulation in the aquatic ecosystems. Among different alternative treatment options, in particular chemical and photochemical advanced oxidation processes (AOPs) have proven to be good candidates for the destructive treatment of surfactants. Response surface methodology (RSM) is a collection of statistical and mathematical techniques that are employed for the development, improvement and optimization of certain processes in which a response of interest is affected by several process variables and the objective is to optimize this response. RSM offers several advantages over classical experimental optimization methods in which a "one process variable at a time" approach. RSM provides more information from a relatively little number of experiments as compared with conventional optimization procedures, which is less expensive and time consuming. In particular, in more complex treatment systems such as photochemical advanced oxidation processes, interactive and synergistic effects are quite common making these applications ideal candidates for RSM. Considering the above mentioned facts, the present experimental study aimed at investigating the photochemical oxidation of commercially important anionic (a dioctyl sulfosuccinate), cationic (a quaternary ammonium ethoxylate) and nonionic (a nonyl phenol ethoxylate derivative) surfactant types. RSM-Central composite design (CCD) was used to analyze, model and optimize surfactant (parent compound, PC) and organic carbon (COD, TOC) removals during photochemical treatment. Two different experimental and statistical design matrices were developed for the assessment of both surfactants (parent compound) and their organic carbon content removals on the basis of treatment time. Process optimization was based on two photochemical treatment targets; (i) partial oxidation (for COD, TOC removals) to achieve complete parent pollutant abatement and (ii) full treatment for complete oxidation (mineralization) of aqueous surfactant solutions. The established polynomial regression models were validated by running separate experiments under photochemical oxidation conditions being previously optimized for different initial CODs. In the last stage of the study, separate experiments were run at the same local optima to examine the inhibitory effect of photochemical treatment of aqueous surfactant solutions on the oxygen uptake rate of activated sludge microorganisms. In the preliminary baseline experiments, rapid degradation of all studied textile surfactant solutions accompanied with high COD and TOC removals was observed. Surfactant abatements were complete within 15-20 min photochemical treatment, whereas over 90% COD and TOC removals could be achieved after prolonged oxidation periods for an initial surfactant COD of 450 mg/L and an initial pH of 10.5. The efficiency of the H2O2/UV-C process was appreciably influenced by all selected process outputs in the following decreasing order; photochemical treatment time (positive effect) > initial COD content of the surfactant formulation (negative effect) > initially added H2O2 concentration (positive effect, except for parent compound removals, that required low concentrations compared to organic carbon abatements). Analysis of variance revealed that the established factorial design models were statistically significant and described parent compound, COD and TOC removals at satisfactory levels. The highest correlation coefficients were obtained for TOC removals (surfactant mineralization rates). The established response surface models could be used to precisely optimize specific photochemical treatment targets for full and partial (pre-) treatment of different types of surfactants. The experimental design models were also capable of predicting advanced oxidation efficiencies at different photochemical treatment durations and varying initial CODs of the aqueous surfactant solutions. Activated sludge inhibition experiments conducted with heterotrophic biomass indicated that during the application of H2O2/UV-C treatment under optimized reaction conditions, no toxic oxidation products were formed. Keywords: Anionic, cationic and nonionic surfactants, H2O2/UV-C treatment, response surface methodology, optimization, activated sludge inhibition.
