Azo boyar madde üretimi atıksuların foto-fenton-benzeri ileri oksidasyon prosesi ile arıtımı

Treatment of azo dye production effuents with photo-fenton-like advanced oxidation process

Özet

Boya üretimi atıksuları içerdikleri ham maddeler, ara ürünler, yardımcı kimyasallar ve kalıntı boyalar nedeniyle yoğun renk ve yüksek kimyasal oksijen ihtiyacına sahip biyolojik olarak zor ayrışabilir nitelikte atıksulardır. Bu atıksuların çevresel özellikleri dikkate alındığında, demir bazlı fotokatalitik ileri oksidasyon prosesleri ile arıtımın iyi bir alternatif oluşturduğu görülmektedir. Bu çalışmada azo boyar madde sentez atıksularının Foto-Fenton-benzeri ileri oksidasyon prosesiyle (Fe3+/H2O2/UV-A) arıtılabilirliği incelenmiştir. Seçilen proses parametrelerinin (başlangıç Fe3+, H2O2 konsantrasyonları, KOİ içeriği ve reaksiyon süresi) renk, KOİ ve TOK giderimleri üzerindeki etkilerinin belirlenmesi, modellenmesi ve proses optimizasyonu amacıyla cevap yüzey metodu kullanılmıştır. 200 mg/L KOİ’ye sahip Asit Mavi 193 içeren sentetik asit boyar madde sentez atıksuyu için optimum işletme parametreleri; 1.5 mM Fe3+, 35 mM H2O2 ve 45 dakika reaksiyon süresi olarak bulunmuştur. Bu koşullar altında deneysel olarak elde edilen toplam renk, KOİ ve TOK giderimleri sırasıyla % 98, % 78 ve % 59’dur. Elde edilen deneysel sonuçların cevap yüzey yönteminin oluşturduğu polinomal regresyon modelinin tahminleri ile uyumlu olduğu görülmüştür. Aynı model, sentetik Reaktif Siyah 39 üretimi atıksuyunun foto-Fenton benzeri oksidasyonla arıtımını da başarılı bir şekilde tanımlamıştır. Reaktif Siyah 39 ters osmoz çıkış atıksuyunun arıtımında elde edilen giderim verimleri ise model tahminlerinin oldukça altında kalmıştır. Arıtma performansındaki bu düşüşün nedeni gerçek atıksuyun yüksek Cl- içeriğine bağlanmıştır. Cl- iyonlarının ●OH radikali ile reaksiyonu sonucu ortamdaki aktif oksidan miktarı azalmakta, bu da organik madde gideriminin gerek hızını gerekse verimini düşürmektedir.

Abstract

Dye manufacturing wastewater generally includes residual dyestuffs, dye intermediates as well as unreacted raw materials such as aromatic amines with alkyl-, halogen-, nitro-, hydroxyl-, sulfonic acidsubstituents, and inorganic sodium salts. The effluent is normally characterized by a high chemical oxygen demand and intense color. The volume of the dye manufacturing wastewater is about 100-200 m3/day which is considerably low as compared with textile dye bath effluents. Several waste streams being variable in composition and strength are generated during dye synthesis activities. The COD content of the combined dye manufacturing effluent is around 2000-3000 mg/L. The BOD5/COD ratio of the wastewater is quite low, implying that it bears a considerable amount of non-biodegradable organic matter. Another risk hazard is that the dyes and dye intermediates can be reduced in the aquatic environment to produce carcinogenic compounds (i.e. naphthylamines, substituted phenylamines, benzidine analogues) under anoxic conditions. Dye manufacturing effluent may also contain free and complexed, toxic heavy metals (i.e. cobalt, chromium, copper) that result from the production of metal-complex azo dyes. Various combinations of conventional treatment processes, including physical chemical and biochemical methods have been used for the treatment of dye manufacturing wastewater. Recent studies indicated that advanced oxidation processes (AOPs) might be a good alternative for treating recalcitrant and/or toxic pollutants. AOPs involve the production of strongly oxidizing agents, mainly hydroxyl radicals (●OH) that react rapidly and almost nonselectively with most inorganic and organic compounds including biologically-difficult-to-degrade azo dyes and dye intermediates. The advanced oxidation of dye containing wastewaters with Fenton and Photo-Fenton processes is a promising alternative because of their high efficiency in decolorization, ease of operation and relatively low treatment costs. Specially, the low volume and high recalcitrance of dye manufacturing effluent streams make them ideal candidates for Fe-based AOPs. In the current study, the treatability of acid and reactive azo dye synthesis effluents by Photo-Fentonlike advanced oxidation process was investigated. The effect of several operating parameters (Fe3+ and H2O2 concentrations, initial effluent COD, reaction time) on treatment efficiency for acid dye synthesis effluent bearing Acid Blue 193 was evaluated. Improvement in the color, COD and TOC abatements were observed with the increase in initial Fe3+ concentration, while increasing the initial H2O2 concentration only enhanced the removal of TOC. Increasing the initial COD of the wastewater promoted color and COD removals whereas TOC removal efficiency obviously decreased. Hence, the proper selection of the correct reagent concentrations considering the initial organic carbon content was found to be important to achieve high treatment efficiencies. Response surface methodology was employed for optimization of the process in order to maximize percent color, COD and TOC removal efficiencies. For an initial effluent COD of 200 mg/L, optimum working conditions were established as 1.5 mM Fe3+, 35 mM H2O2 and 45 min treatment time. Under these reaction conditions, experimentally achieved color, COD and TOC removal efficiencies were found as 98%, 78% and 59%, respectively. These actual results fitted well to the model predictions. In the Photo-Fenton-like treatment of synthetic Reactive Black 39 production wastewater, experimentally obtained percent removals were slightly higher than the model predictions in terms of color and COD. On the other hand, experimentally achieved TOC abatement was lower than the predicted value, denoting that complete mineralization of Reactive Black 39 production wastewater is more difficult than that of Acid Blue 193 production wastewater. For the real dye manufacturing effluent experimentally obtained COD and TOC abatements established for optimum treatment conditions were considerably lower than the model predictions, and an appreciable retardation was observed in terms of color abatement rates. The significant decrease in the organic carbon removal efficiency was mainly attributed to the high chloride concentration (Cl- = 3500 mg/L) of the real Reactive Black 39 production effluent, which caused ●OH scavenging reactions. The main conclusion drawn from the present study is that the Photo-Fenton-like oxidation process was found to be effective in the treatment of dye production effluents. However, it is highly recommended to determine the chloride content of the wastewater prior to application of such a photochemical process, since high cloride concentrations could have a significant adverse effect on the oxidation performance.