Karışık karbon kaynağı ortamının nişasta giderim performansı ve bakteriyel kompozisyon üzerine etkisi

The microbial processes have been extensively investigated for the efficiently design and operation of the activated sludge systems. The experimental studies have often focused on the single representative carbon source, although, microorganisms have to remove wastewater which is the mixture of several different type carbon sources. Under such conditions, bacteria often utilize one carbon source preferentially and other carbon sources are consumed only, when the preferred one is exhausted. The carbon source providing the best growth rate and/or growth yield is preferred, and the successive utilization of the substrates is often represented (Monod, 1942). In the environmental engineering point of view, it is important to understand the interaction between the removal mechanisms of different carbon sources which have a different degree of complexity. Although, recent studies have mainly focused on the biodegradation kinetics of the industrially produced starch as the only pollutant in wastewater, the simultaneous use of multiple substrates, such as the co-treatment of the industrially produced wastewater with the domestic wastewater produced in the facility, can lead to differences in biodegradation kinetics of any individual organic constituent as well as in the bacterial community. The researches with bacteria and higher organisms have revealed that selective carbon source utilization is common and that glucose is the preferred carbon source by many organisms. Moreover, the presence of glucose often prevents the use of other, secondary, carbon sources (Gorke and Stülke, 2008). In a study carried out under aerobic conditions with a mixture of similar type substrates (i.e. a mixture of acetic, lactic and propionic acid), a strong decrease in the removal rates of acetic and lactic acid was observed when treated in the presence of another substrate (Dionisi et al., 2004). This strong interaction among different substrates was explained with the interconnected pathways utilized by microorganisms for the removal of these substrates. Less clear evidences are available when dealing with mixtures of different type substrates, like volatile fatty acids and carbohydrates. Carta et al. (2001) reported that there were no differences in the uptake rate of acetate and glucose under mixed substrate environment compared to single substrate environment. In addition to the substrate uptake rates, the degradation kinetics and rates of the storage compounds were also reported as the same. In another study, when starch and acetate were treated together, slightly lower rates were observed in terms of individual carbon removal of acetate and starch, as well as respective storage of PHA and glycogen compared to treatment of substrate alone (Karahan et al., 2008). The fate of slowly biodegradable carbon source was evaluated in a SBR acclimated to starch as the sole carbon source and mixture of starch and acetate. The SBRs were operated with the same organic loading rate at two different sludge ages. Acetate, which is the one of the volatile fatty acid, was used as secondary pollutant as the volatile fatty acids have been reported as the main constituents of the domestic wastewaters. Although, the carbon source was fed to the SBRs in continuous mode throughout the cycle, the production of the storage polymer, namely glycogen, was observed in all SBRs. The relatively constant storage ratios were observed in SBRs fed with different carbon sources. The COD removal efficiency of the SBRs operated at the sludge ages of 8 days was significantly affected from the presence of acetate in the environment, although the COD removal efficiencies were constant at the sludge ages of 2 days independently from the presence of the secondary substrate. The bacterial characterization studies performed with fluorescent in situ hybridization (FISH) showed the decrease in the Actinobacteria phylum which was reported as the main starch consumer when the starch removal was performed in the multiple substrate environments at the sludge ages of 8 days. On the other hand, the detection of different groups at different sludge ages indicated the importance of the sludge age for evaluating treatment performance in activated sludge systems.  Keywords: Starch; dual substrate; substrate removal kinetic; FISH, activated sludge system. Evsel atıksuların arıtımında yaygın olarak kullanılan aktif çamur sistemlerinin başlıca kirletici parametre olan karbon kaynağının giderim performansı açısından değerlendirilmesi, sistemin en uygun tasarım kriterlerinin belirlenmesi açısından büyük önem taşımaktadır. Bu konuda yürütülen çalışmalarda, evsel atıksuların içeriğini yansıtacak şekilde seçilen tek bir karbon kaynağı model substrat olarak kullanılmaktadır. Fakat farklı karbon kaynaklarının bir arada veya ayrı ayrı arıtılmaları mikrobiyal dinamikler doğrultusunda farklı giderim performansları elde edilmesine neden olabilmektedir. Bu kapsamda, çalışmanın amacı evsel atıksuların karbonhidrat içeriğini yansıtan ve hedef karbon kaynağı olarak ele alınan nişastanın, başka bir karbon kaynağı ile beraber aktif çamur sisteminde arıtılması durumunda, giderim veriminde ve bakteriyel komposizyonda oluşabilecek farklılıkların tespit edilmesidir. 2 farklı çamur yaşında işletilen sistemde, ikincil karbon kaynağı olarak evsel atıksu kompozisyonun büyük bir kısmını oluşturan uçucu yağ asitlerini temsilen asetat seçilmiş ve bu sayede farklı giderim mekanizmaları ile giderilen farklı yapıdaki karbon kaynaklarının birbirlerine etkileri araştırılmıştır. Elde edilen veriler, 8 gün çamur yaşında nişasta giderim performansının, ortamda asetatın bulunmasından etkilendiğini ancak, 2 gün çamur yaşında karışık karbon kaynağı ortamının nişasta giderim performansı bakımında önemli bir etkisi olmadığını göstermiştir. Farklı koşullarda işletilen reaktörlerde bulunan baskın türlerin Flüoresanlı yerinde hibritleşme tekniği (FISH) yöntemi ile analizi sonucunda, 8 gün çamur yaşında karışık karbon kaynağı ortamının sadece mikrobiyal aktivite üzerinde değil aynı zamanda mikrobiyal seleksiyon üzerinde de etkisi olduğunu göstermiştir. Ayrıca, deneysel sonuçlar, çamur yaşının sistem performansı ve bakteriyel kompozisyon üzerinde etkili bir parametre olduğunu ve bu nedenle aktif çamur tesislerinin tasarımında öncelikli olarak ele alınması gerektiğini ortaya koymuştur.  Anahtar Kelimeler: Nişasta; karışık karbon kaynağı; karbon kaynağı giderim kinetiği; FISH; Aktif Çamur Sistemi.&nbsp

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