Treatment of azo dye production effluents with Photo-Fenton-like advanced oxidation process

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. Anahtar Kelimeler: İleri oksidasyon prosesleri (İOP), azo boyar madde sentez atıksuları, Foto-Fenton-benzeri proses, cevap yüzey metodu, proses modelleme ve optimizasyon, OH radiakl tutucu.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 acid- substituents, 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 non-selectively 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-Fenton-like 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. Keywords: Advanced oxidation processes (AOPs), azo dye production wastewater, Photo-Fenton-like process, response surface methodology, process modeling and optimization; OH radical scavenger

Assessment of chemical treatability of olive mill wastewaters by coagulation and electrocoagulation

Zeytinyağı üretiminde ortaya çıkan karasuyun arıtımı yüksek biyokimyasal oksijen ihtiyacı (BOİ5 = 15-135 g/L), kimyasal oksijen ihtiyacı (KOİ = 37-318 g/L), askıda katı madde (AKM = 6-69 g/L) ve toplam fenol (TF = 2-5 g/L) içeriği nedeniyle önem taşımaktadır. Zeytinyağı endüstrisi atıksuları aynı zamanda 10 g/L'yi aşan fenolik ve tannik asit içerikleri nedeniyle biyolojik olarak zor ayrışan bir yapıya sahip olup antimikrobiyal aktiviteye, başka bir deyişle toksisiteye sebep olmaktadırlar. Bu çalışmada, zeytinyağı karasuyundan koagülasyon ve elektrokoagülasyon yöntemleriyle organik madde giderimi hedeflenmiştir. Sönmüş kireç (Ca(OH)2), demir(III) klorür (FeCl3.6H2O), alum (Al2(SO4)3.18H2O) ve demir bazlı ticari koagülan ve pıhtılaştırma yardımcısı kullanılarak gerçekleştirilen koagülasyon deneylerinde elde edilen en yüksek KOİ ve TOK giderim verimleri, kireç ile çöktürme için pH 11’de % 49 ve % 38, demir(III) klorür ile çöktürme için pH 7.0’de 1000 mg/L FeCl3 dozajında % 44 ve % 53, alum ile çöktürme için pH 6.5’da 1500 mg/L dozajda % 40 ve % 36 ve demir bazlı ticari bir koagülan ve pıhtılaştırma yardımcısı ile çöktürme için ise % 46 ve % 43 olarak belirlenmiştir. Uygulanan kimyasal arıtma prosesleri arasında en yüksek organik madde giderimi, çelik elektrodlar kullanılarak gerçekleştirilen elektrokoagülasyonda KOİ ve TOK bazında sırasıyla % 60 ve % 65 oranlarında elde edilmiştir. Elde edilen deneysel sonuçlar değerlendirildiğinde, koagülasyon ve elektrokoagülasyon arıtma proseslerinin organik karbon ve fenolik madde gideriminde yaklaşık olarak aynı düzeyde giderim sağladığı sonucuna varılmıştır. Bu çalışma çerçevesinde incelenen kimyasal arıtma proseslerinin karasu ön arıtımı için uygun ve uygulanabilir yöntemler olduğu tespit edilmiştir. Anahtar Kelimeler: Antioksidan aktivitesi, elektrokoagülasyon, koagülasyon, organik karbon giderimi, toplam fenol, zeytinyağı karasuyu.Olive oil industry is of vital economic importance for many Mediterranean countries, accounting for approximately 95% of the olive oil production worldwide. Generation and disposal of around 30 million m3 of olive mill wastewater per year constitute a serious environmental problem for the Mediterranean Region, due to the unique features associated with this type of agro-wastewater, namely seasonal (typically between November and February) and localized production and the high organic carbon content quite resistant to biodegradation. The characteristics of olive mill wastewater generated in the small-to-medium scale companies largely depend on the type of extraction process employed -the traditional press method or the continuous, three-phase centrifugation process. Accordingly, the high and refractory organic content of olive mill wastewater varies in the range of 37 - 318 g/L chemical oxygen demand (COD), 15 - 135 g/L biochemical oxygen demand (BOD5), 6-69 g/L suspended solids and 2.5 g/L total phenolic content (TPh). Different physical, chemical and biological processes have so far been proposed for olive mill wastewater treatment. Recently, olive mill wastewater was subjected to sequential coagulation/ flocculation/sedimentation /filtration processes as well as lime treatment, resulting in 62-73% phenolics removal depending upon the process applied for olive oil extraction. More than 40% COD and about 95% oil and grease removals were obtained in these studies. Olive mill wastewater could also be partially treated via coagulation using different polyelectrolyte materials; nearly complete reduction in suspended solids was accomplished accompanied with partial reductions in COD and BOD5 up to 55% and 23%, respectively. The use of conventional coagulants such as alum and ferric chloride was also reported, resulting in 90-91% total phenols and 94-95% COD removals after preliminary acid cracking. Biological treatment methods such as the activated sludge process and anaerobic digestion were also investigated, all reporting different operating problems due to the high toxicity and bio-inhibitory effect of the olive mill wastewater on heterotrophic biomass. Therefore, the elimination of polyphenolic compounds from olive mill wastewater via appropriate chemical pretreatment methods was considered as an important criterion for toxicity reduction. As briefly summarized above, results of previous experimental work on the treatability of olive mill wastewater, although extensive, are too diverse and conclusive, mainly because they only focus on collective parameters describing the organic carbon content of wastewater, such as COD, BOD5, etc. Within the scope of the present experimental study, organic carbon removal from olive mill wastewater via different chemical treatment processes (coagulation and electrocoagulation) was investigated. For this purpose, hydrated lime (Ca(OH)2), ferric chloride (FeCl3.6H2O), alum (Al2(SO4)3.18H2O) and commercial grade iron base coagulant and coagulant aid were employed as coagulants. Highest COD and TOC removals were obtained with lime precipitation at pH 11 as 49% and 38%, with 1000 mg/L ferric chloride at pH 7.0 as 44% and 53%, with 1500 mg/L alum at pH 6.5 as 40% and 36%, and with commercial grade iron base coagulant and coagulant aid as 46% and 43%, respectively. Highest organic carbon removal was achieved with electrocoagulation using stainless steel electrodes resulting in 60% and 65% COD and TOC abatement respectively, accompanied with 55% antioxidant activity and 52% total phenolics removals. It could be concluded that applying electrocoagulation (with stainless steel electrodes) that has recently received great interest because of its enigmatic treatment performance, resulted in considerably higher treatment performance as compared to the other chemical treatment processes due to its combinative abatement modes featuring redox reactions as well as coagulation, adsorption, precipitation and flotation. Considering the obtained experimental results, it can be concluded that coagulation and electrocoagulation are suitable treatment options for organic carbon and phenolic matter removal from olive mill wastewater. In the light of the experimental findings, it can be inferred that all investigated chemical processes are suitable for chemical pretreatment of olive mill wastewater. Keywords: Antioxidant activity, coagulation, electrocoagulation, olive mill wastewater, organic carbon removal, total phenol.

Feasibility of the use of electrocoagulation process sludges as adsorbents for the removal of dyestuffs

Bu çalışmada, elektrokoagülasyon (EK) prosesinden kaynaklanan arıtma çamurlarının tekstil son işlemleri boya banyolarında yaygın olarak kullanılan reaktif boyarmaddelerin adsorpsiyon yöntemi ile gideriminde adsorban olarak kullanılabilirliği araştırılmıştır. Elektrolit olarak 1500 mg/L NaCl kullanılarak, 22.5 mA/cm2 akım yoğunluğunda EK uygulamaları yürütülmüş ve 10 ile 90 dakika arasında değişen sürelerde elektrokoagülatörden alınan çamurların adsorban olarak kullanılabilirliği çelik ve alüminyum elektrodların kullanılması durumları için ayrı ayrı incelenmiştir. Çalışma kapsamında adsorpsiyon özellikleri incelenen Reactive Black 5, Crimson HEXL ve Yellow HE4R reaktif boyar maddeleri, çelik elektrodların kullanıldığı elektrokoagülasyon uygulamalarında üretilen arıtma çamurları ile %90’ın üzerinde verimlerle giderilmişlerdir. EK prosesi ile üretilen Fe(OH)3 çamurunun proseste gerçekleşen oksidasyon redüksiyon reaksiyonları çerçevesinde yüzeyinin modifiye olup olmadığının araştırılması ve karşılaştırma yapmak amacı ile FeCl3 kullanılarak gerçekleştirilen koagülasyon ve bu prosesle oluşturulan taze Fe(OH)3 floklarının kullanımıyla yürütülen adsorpsiyon deneylerinde elde edilen giderim verimleri ise Reactive Black 5 için %2-14, Crimson HEXL için %10-12, Yellow HE4R için ise %13-18 olarak bulunmuştur. Elde edilen bu sonuçlar ışığında EK uygulaması esnasında taze oluşturulan Fe(OH)3 floklarının yüzeylerinin modifiye olduğu söylenebilmektedir. Alüminyum elektrodların kullanılması durumunda ise Reactive Black 5 boyar maddesi için ancak 5 g/L gibi çok yüksek absorban dozajında %63 gibi bir giderme verimi elde edilebilmiştir. Crimson HEXL ve Yellow HE4R için ise 1 g/L adsorban dozajında %95’in üzerinde boyar madde gideriminin olduğu tespit edilmiştir. Alüminyum elektrodlar kullanıldığı EK prosesi ile oluşturulan Al(OH)3 çamurunun adsorbsiyon kapasitesinin çelik elektrotlar ile oluşturulan Fe(OH)3 çamuruna göre çok daha düşük olduğu elde edilen sonuçlar ışığında söylenebilmektedir. Anahtar Kelimeler: Adsorpsiyon, alüminyum elektrodlar, çelik elektrodlar, elektrokoagülasyon, reaktif boyar madde, tekstil endüstrisi.The textile industry plays a significant role in the economy of several countries around the world. Dyeing is a fundamental operation during textile fiber processing. This operation causes the production of more or less colored wastewater, depending on the degree of fixation of the dyestuffs on the substrates, which varies with the nature of the substances, the desired intensity of coloration, and the application method. Little attention has been paid to color since it was considered a problem only of aesthetics. Recently the color in textile wastewaters has been investigated for its effects on wastewater treatment systems and on the environment. Color, depending on its origin, is not only a problem of aesthetics but also of toxicity and reduced biodegradability because of the complex nature of used dyestuff. Disposal of this colored water into receiving water may cause toxicity to aquatic life. The dyes can upset the biological activity in water bodies. They also pose a hazard because they may be mutagenic and carcinogenic and can cause severe damage to human beings. Various treatment methods including, physical, physico-chemical and chemical processes have been investigated for treating dye bearing effluents. All these methods have different color removal capabilities, capital and operating costs. Among these processes, adsorption has been found to be superior to other techniques for wastewater treatment in terms of initial cost, simplicity of design, ease of operation and insensitivity to toxic substances. For instance activated carbon which has a high adsorption capacity for organic molecules is commonly used as an adsorbent for color and organic material removal from wastewater. But the activated carbon is an expensive adsorbent and its recycling processes are extra costly for operation. Several wastes and residues have been investigated for the adsorption of dye bearing effluents with varying success. However, new economical and highly effective adsorbents are still needed. Electrochemical technologies contribute in many ways to a cleaner environment and cover a very broad range of techniques. There has been a growing interest in the use of environmental electrochemistry. Environmental electrochemistry involves electrochemical techniques in order to remove impurities and to prevent environmental pollution. Among these techniques, electrocoagulation (EC) is an electrolytic process that generates metallic hydroxide flocks in situ via electro-dissolution of the soluble sacrificial anode immersed in the wastewater. The electrochemically generated metallic ions can be hydrolyzed next to the anode and generate a series of metal hydroxides. The generated metal hydroxides are believed to be responsible for the adsorption of the dissolved pollutants. Therefore the use of electrochemically generated metal hydroxide sludge can be a potential adsorbant for adsorptive removal of dyestuffs from aqueous solution. In this study, use of sludges generated through the electrocoagulation process which is of a common interest, for the removal of reactive dyestuffs that are frequently used in the textile industry, by adsorption was investigated. Scope of the study included the adsorption of Reactive Black 5, Crimson HEXL and Yellow HE4R reactive dyes onto the sludges generated through electrocoagulation using stainless steel and aluminum electrodes. Study results indicated that all dyestuffs were removed with efficiencies over 90% using the sludges produced by the use of stainless steel electrodes. 66 and 100% removals were observed for Crimson HEXL with 200 and ³1000 mg/L of electrochemically generated Fe(OH)3 sludge. The same trend was also seen for Reactive Black 5 and Yellow HE4R. This increase in color removal efficiencies was attributed to the increase in available adsorption area with the increase in adsorbent dose. The sludges produced by coagulation using FeCl3 were used to compare the adsorption capacities of freshly coagulated Fe(OH)3 and electrochemically generated Fe(OH)3 sludges. Fresh coagulation sludges provided removals 2-14%, 10-12% and 13-18% for Reactive Black 5, Crimson HEXL and Yellow HE4R, respectively. From the results of experimental studies it can be concluded that the surface modification of Fe(OH)3 sludges occured during electrocoagulation thus increasing the adsorption capacity. However, the sludges generated by the use of aluminum electrodes yielded over 95% removal of Crimson HEXL and Yellow HE4R dyes at 1 g/L solid doses, while Reactive Black 5 could be removed 63% at a high solid dose of 5 g/L. The results of the study indicated that electrochemically generated Fe(OH)3 sludge is an effective adsorbent for reactive dye stuff. All studied reactive dyestuffs have been effectively removed by adsorption on electrochemically generated Fe(OH)3 sludge. Keywords: adsorption, aluminium electrodes, electrokoagulation, reactive dyestuff, stainless stell electrodes, textile industry

Endokrin bozucu dimetil fitalatın elektrokoagülasyon ve elektrokoagülasyon/Fenton prosesleri ile arıtımı

Phthalic acid esters (phthalates) are frequently used as plasticizers for cellulosic and vinyl ester resins, but also in ceramic, paper, cosmetic, ink and paint industries. Phthalates are readily adsorbed through the skin and have negative impacts on human health and fertility. They have been detected in surface and groundwater in the ng/L-mg/L concentration range and associated with birth defects, organ damage, infertility, as well as testicular cancer, and are also known to be among the major endocrine disrupting compounds. The short-chained esters such as dimethyl phthalate (DMP), which mainly originate from industrial wastewater discharge and leaching and volatilization from plastic products during their usage and after disposal, are among the most frequently, identified phthalates in diverse environmental samples. Studies of DMP's biodegradation in fresh water, marine water, sediment, wastewater and sludge, have revealed a low degradation rate in the range of several days to a few months. Thus the destruction of these bio-recalcitrant organic pollutants requires the application of advanced treatment technologies such as electrocoagulation (EC) and electrocoagulation/ Fenton (EC/Fenton) processes. EC offers high removal efficiencies in compact reactors with simple equipments for control and operation of the process. In an EC reactor, the coagulant is generated in the reaction solution from a sacrificial electrode (e.g. iron, aluminum) leading to the in-situ formation of the respective metal hydroxides. A complex and yet not deeply understood reaction mechanism is thought to be involved in the EC process featuring a complex scheme of coagulation, particle entrapment, adsorption, absorption, flotation and redox reactions. In EC/Fenton process, strong oxidizing hydroxyl radicals (HO·) are generated in the solution by the well-known Fenton's reaction between H2O2 and electrochemically generated Fe2+ ions from sacrificial iron anodes. HO· is one of the most reactive free radical (oxidation potential: + 2.8 eV) and can indiscriminately degrade organic compounds. The number of parameter involved in the design and operation of the EC and EC/Fenton processes is relatively high and thus an efficient design and operation of the processes call for a detailed and careful evaluation and optimization. The main targets of the present study were: to assess the performance of EC and EC/Fenton processes in the treatment of aqueous solution of DMP selected as a model phthalate and to determine the most appropriate operating conditions for maximizing the processes performances. In this study, classical optimization method (a single-factor-at-a-time approach) and Central Composite Design (CCD) Response Surface Methodology (RSM) were used to optimize the treatment of aqueous DMP by EC and EC/Fenton with stainless steel electrodes, respectively. The effects of the key process variables such as initial DMP concentration (DMPo), current density (Jc), electrolyte concentration (NaCl) and treatment time (tr) and H2O2 dosage on DMP and total organic carbon (TOC) removals were evaluated. According to the second-order polynomial regression models, established for EC process by CCD-RSM, DMP and TOC removal efficiencies were affected by the process variables in the following decreasing order; Jc>tr>DMPo>NaCl (negative impact), tr>DMPo (negative impact)>Jc>NaCl (negative impact). Analysis of variance indicated that the experimental design models obtained for the EC treatment of aqueous DMP solutions in terms of the model pollutant and mineralization were statistically significant. For aqueous DMF concentration of 100 mg/L, current density of 13.5 mA/cm2, electrolyte concentration of 1250 mg/L NaCl and treatment time of 120 min were found to be as optimum conditions. At these conditions at the end of 120 minutes, 95% DMP and 7% TOC removals were obtained. The results of the present study also clearly indicated that the EC/Fenton process run with stainless steel electrodes is an effective treatment application for DMP destruction as well as mineralization. The optimum operational conditions for the EC/Fenton process were determined as follows: initial pH of 2.0, current density of 22 mA/cm2, an electrolyte concentration of 1500 mg/L NaCl, and H2O2 dosage of 40 mM for the treatment of aqueous DMP (100 mg/L). Under these conditions at the treatment time of 120 minutes 94% DMP and 71% TOC removal were obtained. Keywords: Dimethyl phthalate, endocrine disruptive substances, electrocoagulation process, electrocoagulation/Fenton process, response surface methodology.Fitalik asit esterleri (fitalatlar) endüstriyel uygulamalarda yaygın olarak kullanılan ve Dünya genelinde yıllık üretim miktarları 2.7 milyon ton gibi yüksek değerlere ulaşan, toksik özellik gösteren, kanserojen, endokrin bozucu ve birikim potansiyeline sahip maddelerdir. Bu çalışmada konvansiyonel yöntemlerle istenilen düzeyde arıtılamayan fitalat benzeri kirleticilerin gideriminde elektrokoagülasyon (EK) ve elektrokoagülasyon/Fenton (EK/Fenton) proseslerinin kullanımı araştırılmış ve bu iki prosesin verimleri ana madde ve toplam organik madde (TOK) giderimleri dikkate alınarak karşılaştırılmıştır. Her iki proses için en uygun işletme koşullarının belirlenmesi amacıyla optimizasyon çalışmaları yürütülmüştür. Her iki proses için en uygun işletme koşullarının belirlenmesi amacıyla optimizasyon çalışmaları yürütülmüştür. EK prosesinin optimizasyonu “Cevap Yüzey Yöntemi” metodolojisi kullanılarak, EK/Fenton prosesinin optimizasyonu ise geleneksel optimizasyon çalışmaları ile gerçekleştirilmiştir. EK/Fenton prosesi ile yürütülen çalışmalarda, 100 mg/L DMF sulu çözeltisi için optimum koşullar 22.5 mA/cm2 akım yoğunluğu, 1500 mg/L NaCl elektrolit konsantrasyonu, başlangıç pH’sı 2 ve H2O2 dozajı 40 mM olarak belirlenmiştir. Bu koşullarda 60 dakikalık reaksiyon süresi sonunda %100 DMF ve %90 TOK giderimi elde edilmiştir. EK prosesi için ise farklı giriş DMF konsantrasyonları (20-100 mg/L) için optimum işletme koşulları cevap yüzey yöntemi ile belirlenmiştir. 100 mg/L DMF sulu çözeltisi için optimum koşullar 13.5 mA/cm2 akım yoğunluğu, 1250 mg/L NaCl elektrolit konsantrasyonu ve başlangıç pH’sı 6 olarak belirlenmiş ve bu koşullarda 120 dakika sonunda %95 DMF ve %7 TOK giderimleri elde edilmiştir. Anahtar Kelimeler: Dimetil fitalat, endokrin bozucu maddeler, elektrokoagülasyon prosesi, elektrokoagülasyon/Fenton prosesi, cevap yüzey yöntemi

Dimethyl phthalate degradation by Peroxymonosulfate (oxone)/UV-C photochemical process

Ftalik asit esterleri (ftalatlar) kağıt, karton, kozmetik, deterjan, şampuan, sabun, tıbbi malzeme, plastik kap ve boya üretiminde hammadde veya yardımcı kimyasal madde olarak kullanılmaktadır. Endüstrilerde, malzemelerin esneklik özelliğini arttırmak için kullanılan ftalatlar, toksik özellik gösteren, kanserojen, endokrin bozucu ve birikme potansiyeline sahip maddelerdir. Ftalatların arıtımında konvansiyonel arıtma prosesleri ile yüksek giderme verimleri elde edilememekte ve bu nedenle arıtımlarında adsorpsiyon ve ileri oksidasyon proseslerinden yararlanılmaktadır. Bu çalışma kapsamında endokrin bozucu ve toksik etkileri nedeniyle kullanımlarında yasal düzenlemeler yapılmış ftalatlara örnek teşkil etmek üzere seçilen dimetil ftalat (DMF) model kirleticisinin sulu çözeltisinin fotokimyasal ileri oksidasyon proseslerinden olan peroksimonosülfat (PMS-okson)/UV-C ile arıtımı incelenmiştir. Giriş PMS konsantrasyonunun ve başlanıç pH değerinin proses giderim verimi üzerine etkisi araştırılmış ve prosesin arıtma performansı DMF ve TOK ölçümleri yapılarak değerlendirilmiştir. Gerçekleştirilen deneysel çalışmalarda PMS/UV-C prosesi ile DMF’nin gideriminin birinci dereceden hız kinetiğine uyum sağladığı belirlenmiştir. Belirli bir değere kadar (50mM) artan PMS konsantrasyonu ile DMF giderimi için birinci dereceden hız sabitinin arttığı tespit edilmiştir. En yüksek hız sabiti k40mM= 0.276 L/dk olarak bulunmuştur ve PMS konsantrasyonu 50 mM’a arttırıldığında hız sabiti k50mM= 0.246 L/dk değerine düşmüştür. TOK giderimi incelendiğinde ise artan PMS konsantrasyonu ile tam mineralizasyonun sağlandığı arıtma süreleri azalmaktadır. Optimum PMS konsantrasyonunda (40mM) 40. dakikanın sonunda tam mineralizas-yon sağlanmıştır. Elde edilen sonuçlar ışığında DMF gideriminde PMS/UV-C prosesinin uygulanabilir etkin bir arıtma prosesi olduğu sonucuna varılmıştır.  Anahtar Kelimeler: Dimetil ftalat; elektrik enerjisi tüketimi; endokrin bozucu maddeler; fotokimyasal arıtma; kimyasal oksidasyon; peroksimonosülfat (okson).Phthalate esters (PAEs) are used as plasticizers to impart flexibility and resilience to plastic products. Other uses of phthalates are in ceramic, paper, cosmetic, ink, and paint industries. In recent years, PAEs have become a controversial issue because many phthalates are suspected to be mutagens, hepatotoxic agents and endocrine disruptors, and can lead to adverse effects on organisms even in a low concentration. The short-chained esters such as dimethyl phthalate (DMP), which mainly originate from industrial wastewater discharge and leaching and volatilization from plastic products during their usage and after disposal, are among the most frequently, identified PAEs in diverse environmental samples including marine water, surface waters and sediments. Studies of DMP?s biodegradation in fresh water, marine water, sediment, wastewater and sludge, have revealed a low degradation rate in the range of several days to a few months. Thus the destruction of these bio-recalcitrant organic pollutants requires the application of vigorous oxidizing agents, such as those used in advanced oxidation processes (AOPs). Recently, sulfate radical based-AOPs have attracted great scientific and technological interest in the area of wastewater treatment and other environmental applications. OxoneÒ, the commercial name of potassium peroxymonosulfate, is a triple salt with the composition of 2KHSO5·KHSO4·K2SO4 is a convenient source of generating sulfate radical (SO4·-). Peroxymonosulfate (PMS), is a mono-SO3- substituted hydrogen peroxide (H2O2) and has been used in a restricted way as an oxidant in light induced processes. Radiolysis, photolysis, or thermal activation of PMS leads to the formation of both SO4·- and hydroxyl radical (HO·). The use of UV light leads to the generation of SO4·- and HO· through the photolysis of the PMS. SO4·- is a very strong oxidant (Eo = 3.1 eV) and engages in at least three reaction modes with organic compounds similar to HO·: by abstracting a hydrogen atom from saturated carbon, by addition to unsaturated or aromatic carbon, and by removing one electron from carboxylate anions and from certain neutral molecules which may eventually lead to the mineralization of the organic substance. The main targets of the present study were: to assess the performance of PMS/UV-C process in the treatment of aqueous solution of DMP (100 mg/L) selected as a model PAE and to explore the effect of some important operating parameters, such as reaction pH (3-9), initial PMS concentration (0-60 mM) and reaction time (0-120 min) on DMP and organic carbon abatement rates. The  results of this study is expected provide fundamental and practical information as a guide for the treatment of bio-recalcitrant organic pollutants by the PMS/UV-C process. For the initial pH values tested, it was found that lowering the initial pH of the aqueous DMP solution slightly improved the degradation rate of DMP. For instance, higher than 95% DMP abatement was achieved after 60 min at pH 3 while the extended reaction times, i.e. 90 and 120 min, required in order to achieve the same level of DMP reduction at initial pH values of 6 and 9 for 5 mM initial PMS concentration, respectively. However, TOC abatements were slightly enhanced with increasing the initial pH. Based on these results pH 3 was selected as the most effective pH for the degradation of DMP. DMP abatement increased with elevating initial PMS concentrations from 5 to 40 mM. Further increase in initial PMS concentration to 50 and 60 mM, however, slightly reduced the extent of DMP removal. With an initial DMP concentration about 100 mg/L, more than 95% of DMP could be removed at time of 20 min under an initial PMS concentration of 40 mM. DMP degradation by PMS/UV-C process successfully represented by a pseudo first-order kinetic model and the highest reaction rate constant was calculated as 0.276 L/min for 40 mM initial PMS concentration. As aforementioned further increase of the PMS concentration slightly reduces the DMP removal rates to 0.246 L/min for 50 mM and 0.243 L/min for 60 mM initial PMS concentrations. The photodegradation of aqueous organic pollutant is an electrical-energy-intensive process, and electrical energy typically represents a major fraction of the operating costs. The lowest electrical energy per order (EE/O) value for DMP oxidation by PMS/UV-C process was calculated as  2.9 kWh m-3 order-1 at the case of 40 mM PMS concentration. Keywords: Dimethyl phthalate; operating cost analysis; endocrine distrupting compounds; photochemical treatment; peroxymonosulfate (oxone), chemical oxidation

Treatment of surfactants by advanced oxidation processes: Process optimization and toxicity analysis

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.

Evaluation of aerobic stabilization of biological treatment sludges

Ülkemizde uygulanan çevre mevzuatı gerekleri, atıksu arıtma tesislerinde oluşan çamurun arıtımını ve nihai uzaklaştırılmasını zorunlu kılmaktadır. Evsel ve endüstriyel atıksu arıtma tesislerinden kaynaklanan arıtma çamurları üzerinde yapılan analizler sonucu, bu çamurların özellikle toplam ve çözünmüş organik karbon değerlerinin yönetmelikteki değerleri sağlamadığı ve çamurların bu parametreler bakımından tehlikeli atık sınıfında değerlendirmesi gerektiğini ortaya koymaktadır. Bu çalışma kapsamında Marmara Bölgesi’nde yer alan çeşitli evsel ve endüstriyel arıtma tesisinden kaynaklanan çamurların organik madde içerikleri değerlendirilmiş ve bu çamurların stabil hale getirilmesi için aerobik stabilizasyon işlemi uygulanmıştır. Aerobik stabilizasyon reaktörlerinde, 15 gün süreyle organik madde içeriklerinin değişimi UAKM, TOK ve ÇOK parametreleri esas alınarak ve evsel çamur numuneleri için zehirlilik parametresi de dikkate alınarak incelenmiştir. Elde edilen sonuçlara göre aerobik stabilizasyon sonunda genel olarak TOK değerleri azalırken, ÇOK değerlerinde çamur numunelerine bağlı olarak artış ya da azalmalar gözlenmiştir. İncelenen evsel çamurların ikisinde de TOK konsantrasyonu %50’den daha fazla azalırken ÇOK değerlerinde artış tespit edilmiştir. Endüstriyel atıksu arıtma çamurları arasında en yüksek TOK giderimi %62 ile Nevresim Endüstrisi çamurunda gözlenmiş olup, bu endüstri ÇOK giderimde de en yüksek verimi sağlamıştır. Elde edilen bu sonuçlar ışığında, aerobik stabilizasyon işleminin uygulanma aşamasından önce her tesis için ayrıca değerlendirme yapılması gerekliliğini ortaya koymuştur. Her çamur örneği için standartların sağlanması aerobik stabilizasyon ile mümkün olamamasına rağmen, bu işlemin bazı organik maddelerin giderilmesini sağladığı aerobik stabilizasyon sonrasında evsel numunelerdeki zehirliliğin tamamen giderilmesi ile ortaya konmuştur. Anahtar Kelimeler: Çamur, stabilizasyon, aerobik, evsel- endüstriyel-tehlikeli atık.The main waste-product of the biological wastewater treatment processes is the excess sludge which needs to be disposed properly to prevent the entry of the pollutants back into the water cycle, especially after the disposal of the wasted sludge cakes into the landfill area. During the adaptation period of European Union membership of Turkey, the increase in the number of both municipal and industrial Wastewater Treatment Plant (WWTP) due to the stringent new regulations for wastewater treatment will pose more significant sludge disposal and sanitation problems in the future for Turkey. Treatment and ultimate disposal of domestic and industrial wastewater treatment plant sludges is obligated according to the regulations in Turkey. Treatment sludges categorized in three different groups namely: inert sludge, non-hazardous sludge and hazardous sludge according to the characteristics of the sludge. The total organic carbon (TOC) concentration of the sludge itself and dissolved organic carbon (DOC) concentration in the eluent of the sludge are mainly used for this classification. The higher levels of TOC and DOC values qualifies the domestic and industrial wastewater treatment sludges as hazardous sludge. The principal objective of sludge treatment is its stabilization, that is a controlled decomposition of easily degradable organic matter resulting in a significant reduction of volatile suspended solids (VSS) content, a change of an unpleasant smell into an earthy one, and an elimination of sludge putrescibility. Aerobic biological stabilization at ambient conditions has traditionally been undertaken for the stabilization of treatment sludges originated from both domestic and industrial wastewater treatment plants. In this study the characterization of the different treatment sludges originated from domestic and industrial wastewater treatment plants in Turkey was investigated and the stabilization level of these sludges was evaluated by using aerobic stabilization process. The stabilization level of sludges was evaluated by monitoring the VSS, TOC and DOC content of the sludge. Moreover, ecotoxicological assays were conducted on domestic wastewater treatment plant sludges to observe the effect of stabilization on the toxicity. Respirometric and modeling studies were also performed to assess the decrease in the organic content of the domestic wastewater treatment plant sludge during aerobic stabilization. The results of analysis conducted on the sludge itself and sludge eluent indicated that the sludges are in hazardous nature. These results suggest that the treatment sludge generated from both domestic and industrial treatment plants have to stabilized before ultimate disposal. During the course of the aerobic stabilization experiments, VSS, TOC and DOC measurements were performed at the beginning and 15 days after the beginning (at the end of the stabilization experiment) in order to monitor the extent of VSS, TOC and DOC removal. Measured TOC and DOC concentrations during the stabilization experiments of studied treatment sludges did not show a consistent trend during the 15 days of stabilization. However, the stabilization of the industrial wastewater treatment plants sludges showed a paralel stabilization to the domestic sludge. However, it is important to conduct laboratory studies prior to the application of aerobic stabilization to a treatment plant on the case basis. The acute toxicity as EC20 (%) and EC50 (%) shows the toxic value in terms of effective concentrations (%) of tested solutions that result in 20 and 50% of bioluminescence decrease. The EC20 and EC50 values were found between 0.3 and 7.3% for the studied raw domestic sludges which is in accordance with the literature data. Significant decrease in the toxicity of domestic wastewater treatment plant sludges were observed at the end of the 15 days of aerobic stabilization. The evaluation of the results obtained in this study showed that aerobic stabilization could be an alternative for stabilization of sludges originated from domestic and industrial wastewater treatment plants. However, the organic content of the sludges mainly depend on the influent wastewater characterization of wastewater treatment plant which affects the stabilization performance. Sludge stabilization results indicate higher VSS, TOC and DOC removal efficiencies for domestic wastewaters compared to the industrial sludges. Although aerobic stabilization was not successful for the compliance with the standards in each case, the removal of toxicity exerted by sludges after 15 day-stabilization suggest that at least some toxic organic material has been succesfully biodegraded during the stabilization. In order to provide appropriate municipal and industrial sludge management in Turkey, more elaborate research and engineering experience should be gained. Keywords: Sludge, stabilization, aerobic, domestic- industrial-hazardous waste

Model based process optimization of enhanced wastewater treatment plants

Avrupa Birliği’ne uyum sürecinde ele alınan atık sorunu kapsamında, alıcı ortamlara yapılacak deşarjlarda konvansiyonal parametrelerin yanısıra azot ve fosfor (besi maddesi) parametrelerinin de belli standart değerlerin altına indirilmesi gerekli hale gelmiştir. Bu nedenle, “Kentsel Atıksu Arıtımı Yönetmeliği, 2006” ile uyum sürecinde olan ülkemizde azot ve fosfor standartları mevzuatımıza dâhil edilmiştir. “Kentsel Atıksu Arıtımı Yönetmeliği, 2006” kapsamında mevcut tesislerin besi maddesi giderimine yönelik olarak geliştirilmesi, yeni kurulacak tesislerin ise besi maddesi giderecek şekilde en uygun arıtma teknolojisi kavramı çerçevesinde boyutlandırılması gereklidir. Besi maddesi giderimine yönelik en uygun arıtma teknolojisi biyolojik prosesler, bunlar arasında en ekonomik çözüm ise aktif çamur sistemleri olarak tanımlanmaktadır. Bu çalışma aktif çamur tesislerinin, Avrupa Birliği normlarında performansını sağlayabilecek optimum tasarım ve işletme süreçlerinin değerlendirilmesini amaçlamaktadır. Bu kapsamda, bir örnek olarak ele alınan İstanbul Su ve Kanalizasyon İdaresi (İSKİ) Paşaköy İleri Biyolojik Atıksu Arıtma Tesisi’nde mevcut durumda atıksu karakterizasyonu ve sistem performansı deneysel olarak belirlenmiş, elde edilen bilgiler kullanılarak sürekli kullanıma uygun olacak model-bazlı tasarım ile işletme simülasyon programları hazırlanmış ve işletme optimizasyonu çerçevesinde çıkış besi maddesi konsantrasyonlarının düşürülmesi amacıyla işletme senaryoları oluşturularak önerilerde bulunulmuştur. Yürütülen senaryo analizleri ile, havalandırma tanklarındaki çözünmüş oksijen seviyelerinin uygun ayarlanması, tesisin geri devir denitrifikasyonu prensibi yerine A2O veya UCT tipi sistem şeklinde işletilmesi ile sistem veriminin arttırılabileceği ve dolayısıyla çıkış besi maddesi konsantrasyonlarının azaltılabileceği belirlenmiştir. Anahtar Kelimeler: İleri biyolojik atıksu arıtma tesisi, atıksu karakterizasyonu, model-bazlı tasarım, işletme optimizasyonu.The Urban Wastewater Treatment Directive published in the Official Gazette No. 26047 of 08.01.2006 was adapted from the “The Council Directive (91/271/EEC)” concerning urban waste-water treatment was accepted in European Union Countries, which imposes enforcements about the collection and treatment of wastewater. This directive requires that also nitrogen and phosphorus (nutrients) to be removed together with the conventional parameters. In this context, it is very important to follow and apply the technological advances while the harmonization of legislations in Turkey with European Union Standards. Mathematical models are frequently used for the design and optimum operation of wastewater treatment systems. In order to use the activated sludge models for the process design and control, it is crucial to understand the behavior of complex biological reactions under steady and dynamic conditions. The initial step for the use of models should be, a model calibration according to the data obtained from the treatment plant and an analysis of the behavior of the treatment plant under dynamic influent and environmental conditions (Vanrolleghem et al., 2003). After the calibration of the prepared model according to the operational conditions of the treatment plant, the model can be used for the optimization of the plant, meeting the effluent quality standards, minimizing operational costs and for developing appropriate process control strategies. On the other hand the effect of changes in the process conditions on the model stability should be taken into consideration (Insel et al., 2007). The aim of this study was to evaluate the optimum design and operational criteria of advanced biological wastewater treatment plants by applying international monitoring and evaluation mechanisms that will increase the performance to norms required in the European Union. Accordingly, İSKİ Paşaköy Advanced Biological Wastewater Treatment Plant (ABWWTP) was chosen as a model plant and in the first stage on influent wastewater characterization, chemical oxygen demand (COD) fractionation and performance of the activated sludge system were experimentally determined. In the second stage, using the dimensions of the İSKİ Paşaköy ABWWTP units and the experimentally determined operational parameters, model calibration studies were conducted. On this context, theoretical parameters of model-based design and operational simulation programs applied for the plant were evaluated. In the last stage of the study, for operational optimization, according to the results obtained from the experimental and simulation studies conducted at İSKİ Paşaköy ABWWTP, operational scenarios were developed and suggestions were made. In the scenario analysis reduction of effluent phosphorus and total nitrogen concentration was aimed and the effect of (i) the aeration system control, (ii) recycle denitrification (iii) influent VFA concentration was analyzed and the effect of (iv) different system configurations was evaluated. The results of statistical data analysis of wastewater characterization studies conducted at İSKİ Paşaköy Advanced Biological Wastewater Treatment Plant aiming nitrogen and phosphorus removal revealed that due to low influent Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), Total Phosphorus (TP) and Volatile Fatty Acids (VFA) concentrations, high efficiencies of biological phosphorus removal was not achievable. According to the scenario analysis performed for the treatment plant it has been concluded that it is possible to increase the removal efficiency of the system and achieve lower effluent total nitrogen and phosphorus concentrations by setting the dissolved oxygen levels to appropriate levels and operating the systems as an A2O or a UCT type system instead of a recycle denitrification system. It has been concluded that if the scenario analyses were applied it is not possible to meet the European Union Effluent Quality Standard of 1.0 mg/l for the phosphorus parameter. Experimental and model based studies have to be conducted for the installation of a fermentation process together with different system configurations that are required to meet the effluent quality standard by biological treatment. Keywords: Paşaköy wastewater treatment plant, wastewater characterization, model based optimization, process control

Toxicity of Zn-Fe Layered Double Hydroxide to Different Organisms in the Aquatic Environment

The application of layered double hydroxide (LDH) nanomaterials as catalysts has attracted great interest due to their unique structural features. It also triggered the need to study their fate and behavior in the aquatic environment. In the present study, Zn-Fe nanolayered double hydroxides (Zn-Fe LDHs) were synthesized using a co-precipitation method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and nitrogen adsorption-desorption analyses. The toxicity of the home-made Zn-Fe LDHs catalyst was examined by employing a variety of aquatic organisms from different trophic levels, namely the marine photobacterium Vibrio fischeri, the freshwater microalga Pseudokirchneriella subcapitata, the freshwater crustacean Daphnia magna, and the duckweed Spirodela polyrhiza. From the experimental results, it was evident that the acute toxicity of the catalyst depended on the exposure time and type of selected test organism. Zn-Fe LDHs toxicity was also affected by its physical state in suspension, chemical composition, as well as interaction with the bioassay test medium

Toxicity of Zn-Fe Layered Double Hydroxide to Different Organisms in the Aquatic Environment

The application of layered double hydroxide (LDH) nanomaterials as catalysts has attracted great interest due to their unique structural features. It also triggered the need to study their fate and behavior in the aquatic environment. In the present study, Zn-Fe nanolayered double hydroxides (Zn-Fe LDHs) were synthesized using a co-precipitation method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and nitrogen adsorption-desorption analyses. The toxicity of the home-made Zn-Fe LDHs catalyst was examined by employing a variety of aquatic organisms from different trophic levels, namely the marine photobacterium Vibrio fischeri, the freshwater microalga Pseudokirchneriella subcapitata, the freshwater crustacean Daphnia magna, and the duckweed Spirodela polyrhiza. From the experimental results, it was evident that the acute toxicity of the catalyst depended on the exposure time and type of selected test organism. Zn-Fe LDHs toxicity was also affected by its physical state in suspension, chemical composition, as well as interaction with the bioassay test medium