Ardışık kesirli reaktörlerde azot giderimi
Nitrogen removal in sequencing batch reactors
- Tez No: 46581
- Danışmanlar: DOÇ.DR. NAZİK ARTAN
- Tez Türü: Yüksek Lisans
- Konular: Çevre Mühendisliği, Environmental Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 71
Özet
ÖZET Bu çalışmada AKR sistemi ile çalışan bir aktif çamur modelinde azot giderimi göz önüne alınmıştır. Değişik atıksu karakterizasyonunda ve işletme koşullarında bu model uygulanmıştır. Birinci bölümde günümüzde AKR sisteminin ve azot gideriminin önemi belirtilerek çalışmanın amaç ve kapsamı açıklanmıştır. İkinci bölümde AKR kavramı, gelişimi, kullanım alanları ve günümüzde tercih edilmesinin sebepleri üzerinde durulmuş, genel bir AKR tanımı yapılmıştır. Üçüncü bölümde partiküler biyokütle, çözünmüş organik madde substrat olmak üzere iki bileşen göz önüne alınarak AKR'nın kinetik tanımı yapılmıştır. AKR'de yer alan prosesler ve kinetik katsayılar bir matris ile ifade edilip formülasyona geçilmiştir. Dördüncü bölümde azot giderimi üzerinde durulmuştur. Azotun özellikleri ve çevreye etkilerinden söz edildikten sonra azot gideriminde yer alacak iki basamak olan nitrifikasyon ve denitrifikasyonun biyolojik, stokiometrik ve kinetik tanımları yapılmıştır. Beşinci bölümde ise azot gideriminin AKR modeli ile gerçekleştirilmesinde yer alacak prosesler ve dizayn kriterleri üzerinde durulmuştur. Kinetik katsayılar ve proses ifadeleri bir matris ile gösterilip, proseslerle ilgili kinetik ifadeler elde edilmiştir. AKR'nın karaklı bir dengede çalışması gerektiğinden başlangıç ve çıkış koşullarının nasıl ifade edildiği belrtilmiştir. Altıncı bölümde çalışma aşamaları, elde edilen veriler ve bunların değerlendirilmesi yer almaktadır. Bu bölümde AKR'de farklı atıksu karakterizasyonlarında ve farklı işletme koşullarında azot giderimi incelenmiştir. Son olarak yedinci bölümde ise yapılan çalışma ve araştırmalarda elde edilen sonuçlar belirtilmiştir.
Özet (Çeviri)
SUMMARY NITROGEN REMOVAL IN SEQUENCING BATCH REACTORS Since the beginning of 20 th century Activated sludge processes have been used. Because continuous flow systems provide required removal efficiencies with minimum operational problems, in a short time they substituted the fill and draw systems which were the first application of activated sludge systems. Recently, due to increasing population, rapid urbanization and industrialization, natural resources and especially water resources have been adversely affected. Because of the increasing pollution, effluent discharge standards have been revised and new water quality standards have been established. As it is difficult to secure the new limitations with continuous flow systems especially in the case of variable flows or concentrations and industrial wastewaters, a search has begun for new systems. Among the proposed systems is the Sequencing Batch Reactors (SBR) which is widely used in the U.S.A. and Australia. On the other hand it has been observed that beside carbon removal nitrogen removal is necessary to achieve stringent water quality standards. One of the relatively new restrictions on the quality of effluent discharges is the limitation on nitrogen. Ammonia-nitrogen which is toxic to fish at very low concentrations is one of the main pollutants contained in wastewaters. Ammonia accelerates the eutotrophication rate of receiving waters by serving as a plant nutrient and by exerting a demand on the available dissolved oxygen. The autotrophic conversion of ammonia to nitrite and nitrate requires oxygen, and so the discharged ammonia-nitrogen will lower the dissolved-oxygen levels in receiving waters dramatically. Nitrate acts as an algal nutrient and may cause a health hazard if accumulated in water supplies. Since the nitrification reaction was discovered approximately 100 years ago, a considerable attention has been given to application of nitrification to wastewater. Research has shown that nitrification is the initial step in biological nitrogen removal. Nitrification is associated with the metabolism of a group chemoautotrophic bacteria, all obligate in their reliance upon inorganic nitrogen compounds for energy. Species of the genus of Nitrosomonos were observed to xicompounds for energy. Species of the genus of Nitrosomonos were observed to derive their energy from the oxidation of ammonia to N02, and Nitrobacter species were found to depend on N02 oxidation as their energy source. The stoichiometry of nitrification basically defines a chemoautotrophic process where NH4 serves as the electron donor, 02 as the electron acceptor and C02 as the carbon source. The second step is Denitrification which is the most widely used nitrogen removal process for wastewaters. It is essentially a biological reaction which converts oxidized inorganic nitrogen to a gaseous nitroge species. Denitrification relies on the reduction of nitrate nitrogen serving as the terminal electron acceptor in the electron transport chain, in the absence of molecular oxygen. The process is also called anoxic respiration, as an alternative to aerobic respiration: Under anoxic conditions, denitrifying bacteria, reduce nitrate by a mechanism called nitrate dissimilation in which nitrite or nitrate replaces oxygen in cell respiration. As opposed to nitrification, a relatively broad range of bacteria can accomplish denitrification. A number of bacterial species that are selectively sustained in the activated sludge process are also capable of denitrification. Nitrification is effected in activated sludge systems through two alternative operating schemes. Because it has been considered that heterotroph activity may adversely affect the performance of the nitrifying bacteria, the first option entails a two stage configuration with respective isolation of carbonaceous and nitrogenous waste oxidative steps. The alternative design combines the two reactions into a single stage, and thereby concurrent oxidation of the organic carbon and nitrogen species. The relative advantages and disadvantages of either option have been debated not only with respect to oxidative capacity, but also in regard to sludge production, biomass settleability, process sensitivity to shock loads and basic economics. In the past, two stage configuration was generally favored but in recent years the single stage option has been shown to be aviable process strategy that consequently has drawn increasing interest owing to four superior features of SBR. First, batch reactors behave as ideal plug flow reactors with respect to kinetic response. Secondly, control of performance in these periodic systems, particulary reaction time and maintenance of sludge solids are straightforward. Third, reactions that must be physically separated in conventional continuous flow systems, like nitrification and denitrification, can be carried out in the same tank by a single sludge biomass and separate clarifiers are unnecessary. Finally, flow equalization and attenuation of peak organic loads are inherent in the bacth process. In contrast to the conventional continuous flow stirred-tank reactor (CFSTR), the sequencing batch reactor (SBR) concept also provides an operating regime compatible with concurrent organic carbon oxidation and nitrification. SBR operates on a cyclic basis of: Fill, React, Settle, Drain and Idle phases. xnThe term“Sequencing Batch Reactor”refers to biological reactors which are repeatedly filled and drained. During each cycle certain process conditions are varied, such as availability and deficiency of oxygen and soluble organics. The sequence of process conditions is repeated over and over again as the SBR cycles follow each other. As a result, selection, enrichment and activation of various types of microorganisms can be effectively controlled. With an initial anoxic period, the aeration phase of sequence controls organic carbon removal only slightly, but it completely determines nitrification. To achieve complete nitrogen removal, aeration is stopped after nitrification to allow denitrification using endogenous carbon and energy sources in the sludge floes. In the first chapter a description of the problem and the general objectives of this study are given. The objective on this study, is the determination of the effects of wastewater characteristics, operation conditions some kinetic and stoichiometric parameters on the design of SBR A general description of SBR is given in the second chapter. Some literature survey on the application of SBR systems is also underlined. SBR is preferred because of many advantages listed below. a) Because peak flows and shock loads can be tolerated easily, SBR does not need an additional equalization tank. b) Since reaction and sedimentation take place in the same tank, application of SBR becomes easier. c) Carbon removal, nitrification and denitrification can be carried out in the same tank with high efficiency. d) In SBR sludge recycle pumping is not needed, since there is no separate settling tank. e) Filamentous growth can be controlled by changing operating strategy during fill phase. In the third chapter, the basic principles of aerobic treatment which is based on oxidation of organic substances by microorganisms named activated sludge are explained. The balance equations of componenets are given in the modelling of SBR part. Extensive literature survey on nitrogen and nitrogen removal takes part in the fourth chapter. The effects of nitrogen on the receiving waters and the biological, kinetic and stoichiometric description of nitrification and denitrification processes which provide nitrogen removal are pointed out. And also the effects of pH and temparature on nitrification and denitrification has been given in this chapter. xmIn the fifth chapter detailed information about SBR is given. Nitrogen removal is carried out in SBR systems in five phases as fill, react, settle and drain phases. Besides, the principles of nitrogen removal in SBR and balance equation for nitrogenous and carbonaceous components are pointed out. These evaluated components are; soluble substrate, Ss, biodegradable nitrogen consists of ammonia, Snh, nitrate-nitrogen concentration, SN0, soluble non-biodegradable COD, S,, heterotrophic biomass, XH, autotrophic biomass, XA, particular substrate, Xs, inert biomass, Xj and endogenous products, XE. Apart from these, some important characteristics of SBR which includes initial conditions and steady state results and relevant equations have been underlined. A mathematic model has been developed for nutrient removal in SBR systems and the effect of wastewater characterization, operation conditions, kinetic and stoichiometric parameters have been investigated and evaluation of results have been presented in the sixth chapter. Firstly, to investigate the impact of total fill time (TF) and the ratio of first fill time (TFi/TF) on SBR system's performance, the model has been operated for four different TF as lh, 2h, 3h and 4h. TF1/TF ratio has been selected between 0.5 and 0.9 for every TF value. Secondly, influent wastewater characterization has been changed to search the effect of SSi/Cslon nitrate removal efficiency. For this reason the model has been operated for three different Ssivalues as 50, 100 and 150 mg/1 by accepting CS1 as constant in the same operation conditions. Thirdly, to search the impact of a kinetic constant, KH on SBR design, the model has been operated for four different KH values as 5, 10, 15 and 20 with the same wastewater characterization and operation conditions. Influent wastewater characterization has been changed one more time to inquire the impact of COD/TKN ratio on the performance of SBR. For this reason Snhj is accepted as 70 mg/1 in the operation of SBR To improve the nitrogen removal efficiency of SBR, a different sludge age is accepted as 1 5 days and the model has been operated with this sludge age. Finally, a new SBR model containing periodic aerobic and anoxic phases has been developed and operated. In this study TM/TT ratio has been accepted between 0.4 and 0.5. In the last chapter, the results are given, which can summarized as follows. 1) Nitrogen efficiency of SBR is not affected by total fill time but affected by TF1/TF ratio. xiv2) Ssl/CSı ratio has no proper effect on effluent nitrate concentration. 3) At lower KH values, amount of Xs in the reactor increases. But KH values have no important impact on effluent nitrate concentration. 4) When the effluent COD/TKN ratio is increased, high effluent nitrate concentrations are obtained due to increase in oxidized nitrogen in the system. 5) Better nitrogen removal efficiency can be obtained by increasing sludge age. 6) Higher nitrogen removal efficiency can not be obtained by increasing number of aerobic and anoxic phases in a cycle. xv
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