Kentsel Atıksu Arıtma Tesisi Mikrobiyal Yapısı Ve İşletme Performansının Beklenen Tasarım Kabulleri İle Karşılaştırılması

Abstract

Bu çalışmada, tesis tasarımında kabul edilen şartların ve beklenen performansın gerçek işletme ve farklı model ile karşılaştırılması yapılarak nutrient giderim sistemlerinde sağlanması gereken efektif azot giderim işletme koşulu ve bununla birlikte azot gideriminin gerektirdiği proses tanklarındaki oksik/anoksik hacmin optimum şekilde belirlenmesi amaçlanmaktadır. Tasarım kabullerinin işletme performansı üzerindeki etkisi ve tasarımlarda dikkat edilmesi gereken noktalar araştırılıp, yapılacak mikrobiyolojik karakterizasyon ile işletme şartlarının mevcut durumu ortaya konularak işletme için alınabilecek önlemler için fayda sağlaması hedeflenmektedir. Birinci bölümde, yapılan çalışmanın önemi vurgulanarak amaç ve kapsamı açıklanmıştır. Yapılan tasarımlarda kullanılan tasarım kabullerinin gerçek işletme açısından önemi vurgulanarak kullanılacak model ve tesis gerçek işletme verilerinin tasarım kabulleri ile karşılaştırılacağı belirtilmiştir. İkinci bölümde, aktif çamur sitemleri arıtma konfigürasyonları, aktif çamurun mikrobiyal karakterizasyonu ve neden olduğu problemler, çamur çökelebilirliği, aktif çamur modelleri hakkında geniş bir literatür bilgisi verilmiştir. Üçüncü bölümde, İSKİ Paşaköy İleri Biyolojik Atıksu Arıtma Tesisi tanıtılmış, tesis tasarımında baz aınan tasarım metodu hakkında bilgi verilmiş, çalışmada kullanılan model tanıtılarak yapılan kimyasal ve mikrobiyolojik analizler açıklanmıştır. Yapılan analiz sonuçları ile tesisin işletme durumu ortaya konulmuş olup, bu değerler modelgirdisi olarak kullanılmıştır Dördüncü bölümde, modelde iki farklı işletme koşulu için simülasyon sonuçları, tasarım methodu hesaplama sonuçları, mikrobiyolojik inceleme sonuçları ve çamur çökelebilirliği testi sonuçları verilmiş, bu sonuçlar ilişkilendirilerek değerlendirme yapılmıştır. Simülasyonda oluşturulan işletme koşullarında proses tanlarında farklı oksik/anoksik hacimler kullanılarak farklı VD/VT oranlarının özellikle azot giderim verimine etkisi araştırılmıştır. Yapılan kabuller ile hesaplanan tasarım metodu sonuçları gerçek işletme verileri ve model sonuçları ile karşılaştırılmıştır. Mikrobiyolojik inceleme ile, sistemin mevcut mikrobiyal karakterizasyonu yapılıp, baskın türler ortaya konmuştur. Aktif çamurun çökelebilirliği incelenerek, çökelme parametreleri belirlenmiştir. Farklı VD/VT oranlarının çamur çökelebilirliği ve mikrobiyal analiz ile ilişkisi açıklanmış ve değerlendirmeler yapılmıştır.

In this study, design assumptions and expected performance of treatment plant are compared with simulation model; moreover, detection of optimum effective removal operating condition and oxic/anoxic volume fraction of process tanks were aimed. Effects of design assumptions operating performance and point to consider on designing were investigated and current situation of operating activated sludge was presented with microbiological analysis to avail of plant operators by taking precautions with the results of microbiologcal investigations. In the first section, the aim and the scope of the study were explained by emphasizing the importance of study. Importance of design assumptions in calculations was emphasized for plant operation; moreover, comparison of operating datas and design assumptions was stated. In the second section, a detailed literature search on treatment configurations of activated sludge systems, microbial characterization of activated sludge and its operating problems, sludge settleability, and activated sludge modelling was made. Configurations for phosphorus removal were explained detailed and schematically. Microbial environment of activated sludge has various species and complicated. Assignments of species in the activated sludge was explained. Activated sludge has major problems based on microbiology. Problems were explained with their causes and control ways were suggested. In the third section, Istanbul Water and Sewerage Administration (İSKİ) Paşaköy Advanced Biological Wastewater Treatment Plant was introduced. Design method is informed which was used the plant design. The model program that used in the study was introduced. Chemical analysis and microbiological examinations were explained. By the results of the analysis, operating conditions were established and these results were used in the model. In the fourth section, two different operating conditions simulation results, calculations results of design method, microbiologic examinations results and sludge settleability tests results were given and association of the results were evaluated. Effect of different VD/VT ratio, provided by different oxic/anoxic volume fractions in the process tanks, were investigated on nitrogen removal efficiency. Biowin simulation program is used for modelling the plant. Plant operation datas were used as input parameters in the simulation program. BioWin is an extensive simulation program that is used in design and analysis of biological wastewater treatment plants. This program was developed as assessment tool for process designers and management operators. BioWin is able to analyze the behaviour and analysis of configurations of the complex wastewater treatment plant with single or double data entry. In BioWin, the various modifications from general models and other models (such as ASM1, ASM2 ve ASM3) developed for activated sludge systems removing biological nutrients have been used by Barker and Dold. İSKİ Paşaköy Advanced Biological Wastewater Treatment Plant units were introduces to the Biowin. Wastewater firstly treated in primary treatment units and then anaerobic tanks are placed, after anaerobic tanks anoxic and oxic tanks are placed in İSKİ Paşaköy Advanced Biological Wastewater Treatment Plant. In the model, three anaerobic tanks were created, after anaerobic process first, third and last process were introduced for each except second tank. Second process tank was created as ten pieces. These peaces allowed to change the oxic volume fraction of process tanks. Outputs of models are examined in two different solutions. In the first option, naming first operating condition, in the second process tank operated 60% oxic volume fraction. VD/VT ratio of process were 0,35 in the first operating conditions. Effluent nitrogen concentration is under discharge limitations, however, nitrate nitrogen concentration is nearly zero while ammonium nitrogen concentration is almost total nitrogen. Ammonium nitrogen removal can not be provided in the first operating condition. In the second operating condition, second process tank operated 80% oxic volume fraction which supply the 0,30 VD/VT ratio to the process. Effluent nitrogen concentration is under discharge limitations, moreover, nitrate nitrogen concentration is near total effluent nitrogen concentration while ammonium nitrogen concentration is nearly 0.30 mg/L. As a result of simulation model, low operating the process tanks in the low VD/VT ratio provides ammonium nitrogen removal efficiently. Increasing VD/VT ratio, hinders the ammonium nitrogen removal and can not produce nitrate nitrogen to the effluent. VD/VT ratio has an important role on sludge settleability. Settling property of sludge can be determined in relation with percentage of oxic volume and sludge volume index in process. In 30% - 40% of oxic volume operations, it has been known that the sludge volume index is at maximum trend and settling property of sludge is poor. It can be said that settling property of sludge can be enhanced and better settleable sludge can be achieved with increase of oxic volume from 60% to 70% stated in other words decrease of VD/VT ratio from 0.35 to 0.30. Gram and Neisser dye methods were applied to the samples of microscopically alive and original preparates taken from aeration basin and recycle unit and samples of preparates prepared as to be dried for examination of activated sludge of Paşaköy Advanced Biological Wastewater Treatment System. In between the dates of December 2015 and March 2016, microbiological, chemical and biochemical analysis of taken samples were examined, it was tried to be found out microbiological structure of the system and it was monitored by being viewed important activated sludge microorganisms. Long-term and continuous detection of microbiological structure contributes to increase of treatment plant performance and provides benefit in tems of development and controlled operation. It should not be forgotten that microbiological structure can change in short time in biological treatment systems according to wastewater characterization, operating conditions and physical environmental conditions. These monitoring studies are able to provide a very useful informations about future performance of the plant. It was determined that activated sludge system has 9 species with filament (8 bacteria and 1 fungi) and the 2 species of them are dominant. Species of Type 0092 and Microthrix parvicella have been found widely and they are dominant in the system. Besides, these types have been seen at approximately same number in bulk solution of each floc and free tens of filaments (>20 filaments). Type 0092 can be found numerical a bit more and it is distrubuted in the flocs. The other filamentous bacteria types being less important and quadratic are Type 1701, Type 0675, Type 0765, Nostocoida limicola II ve Beggiatoa spp., Bacillus spp. The number of Type 1701 is 5-15 per floc; Nostocoida limicola II is 3-5 per floc; Type 0675, Beggiatoa spp. and Bacillus spp. are 1-3 per floc. Additionally, Type 0765 is not found every floc, it is 1-2 filament in some flocs and Rhizopus spp. (nonseptate fungi) is 1 filament. There is possibility of change of dominant types with condition changes for advantages of some types especially Type 1701 ve Nostocoida limicola II. In application of settling velocity test, sludge sample was taken from exit of aeration tank of the plant. The samples diluted 2 times, 4 times and 5 times were used with the undiluted sample. These samples were mixed at first and precipitation of samples were observed after adding to cylinders. The sludge volume was measured at 0th, 5th, 10th, 15th, 20th, 25th minutes and the settling velocity was calculated from distance of sludge settlement against time. It was observed that the settling velocity in experiment doing in low concentrations is higher than in high concentrations. Velocity-concentration curves show exponential function and Vesilind and Takács models can be applied. The concentrations against to the velocity trends were adapted to Vesilind model and the exponential trend equations were obtained. Changing VD/VT ratio gives well settling property to sludge; however, it has direct effect on filaments that can cause to bulking problem. It is determined that the 0.6 - 0.7 VD/VT ratio provides the maximum increase of Type 0092 ve Microthrix parvicella filaments being dominant types of the plant system. Besides, it has been predicted that if the VD/VT ratio is decreased from 0.35 to 0.30, increase of Type 0092 ve Microthrix parvicella filaments decrease and sludge bulking problem is prevented. Results of design method calculations using assumptions were compared with plant operation data and model simulation results. Plant microbial characterization was investigated and dominant species identified by microbiologic examination. Settling parameters were determined by settleability tests of activated sludge. Association of VD/VT ratio with sludge settleability and microbial examination was explained and evaluated.