Yüksek konsantrasyonda amonyak içeren atık suların döner diskler ile nitrifikasyonu

Abstract

ÖZET Azotun çeşitli türlerinin yüzeysel sularda oluşturduğu olumsuz etkiler arasında, ikinci kademe olarak da tanımlanan oksijen ihtiyacı önemli bir yer tutmaktadır. Azotun sebep olduğu ötrofikasyon, zehirlilik v.b. gibi bitkiler ve hayvanlar üzerindeki kötü etkiler, azot türlerinin alıcı ortama deşarj edilmeden Önce mutlaka yeterli bir oranda arıtılması gerekti ğini ortaya çıkarmıştır. Azotun arıtılmasında konvansiyonel sistemlerin yüksek oranlarda verimlilik sağlıyamaması biyolojik nitrifikasyon sürecini en önemli seçeneklerden biri olarak günümüze getirmiştir. Bu çalışmada yüksek konsantrasyonda amonyak içeren atık suların döner diskler ile arıtılmasının incelenmesi yanı sıra, reaktöre yüksek konsan trasyonlarda amonyak beslemesi nedeni ile ortaya çıkabilecek olan amonyak ve/veya nitrit inhibisyonunun sınırlarını tesbit etmek olmuştur. Tesbit edilen bu inhibisyon sınırı reaktör kademeli olarak beslenmek suretiyle daha yukarı bir seviyeye çıkarılmıştır. Birinci bölümde çalışmanın önemi vurgulanarak amaç ve kapsamı belirtilmiştir. İkinci bölümde nitrifikasyon konusunda daha evvel yapılmış çalışmalar genel bir çerçeve içerisinde ele alınmıştır. Bu bölümde amonyağın fiziksel ve kimyasal özellikleri dolayısıyle sahip olduğu uçuculuk üzerinde durul muş ve bu hususun yüksek amonyak konsantrasyonda amonyak içeren atık suların nitrifikasyonunda önemli bir yeri olduğu vurgulanmıştır. Üçüncü bölümde biyof ilmin genel bir tanımlaması yapılarak, yüzeyde geli şen sistemlerin askıda gelişen sistemlere göre farklılıkları belirtilmiş ve giderim mekanizması hakkında bilgi verilmiştir. Dördüncü bölümde döner disk sistemlerinde nitrif ikasyon süreci ile ilgili daha evvel yapılmış çalışmalar iki bölüm halinde incelenmiştir. Düşük ve yüksek konsantrasyon tanımı içinde birinci kısımda 85 mg/lt'ye kadar amonyak içeren atıksuların nitrif ikasyonu, ikinci kısımda ise yüksek kon santrasyon olarak tanımladığımız 85 mg/lt'nin üzerinde amonyak içeren atıksuların nitrif ikasyon sürecine etki eden parametreler incelenmiştir. Beşinci bölümde döner disklerde azot giderilmesine kavramsal olarak yak laşılmış ve sistem için yapılan biyofilm kalınlığının giderim hızı üze rinde etkili olduğu gösterilmeye çalışılmıştır. Altıncı bölümde deneylerde kullanılan sistem belirtilerek deneylerde kul lanılan atık suyun bileşimi de verilmiştir. Ayrıca çalışmalar sırasındaki çevresel koşullar belirtilerek ölçüm ve analizlerin nasıl yapıldığı açık lanmıştır. Yedinci bölümde çalışmalar sonunda elde edilen bulgular ve tartışmalar yer almaktadır. Bu bölümde sistemin nitrif ikasyon yeteneğinden bahsedil miş ve giriş amonyak konsantrasyonunun artmasıyla sistemin nitrif ikasyon yeteneğinin azaldığı bulunmuştur. Sistemde giderim hızı üzerinde etkili olan hidrolik yükleme ve amonyak yüklemesi ile giriş konsantrasyonunun sistemi nasıl etkilediğine ait bulgular ve tartışma bu bölümde yer almak tadır.

IV - NITRIFICATION OF STRONG AMMONIA WASTES BY ROTATING DISCS The Compounds of nitrogen play an important role in the life processes, therefore it is of a major interest to environment engineering. An examination of the nitrogen cycle reveals the vital function of nitrogen compounds in the growth of variou: life forms and their interrelations through the continious conversions of nitrogenous compounds. The complexity of the interrelations between the nitrogen forms, also constitutes < critical balance in terms of their amounts in certain media and transformation rates. This balance has been threatened b< pollution and its shift has lead to undesirable consequences EntrophicaC ion, toxicity to aquatic life and men, oxygen depletion in water courses are amogn the important results o pollution caused by nitrogenous matter carrying wastes. As the amount of nitrogen compounds being discharged to natural waters, in creased due to both industrial activities and population expansions, treatment of such discharges beyond the levels provided by conventional treatment shemes has become necessary. Ammonia is the most commonly encountered form of the nitrogen compounds. It is also the end product of organic nitrogen through chemical and biological reaction While ammonia is one of the easily d iges t ib le - f orm by the microorganisms, Lt is quite toxic to higher organisms. Ammonia exerts oxygen demand through the biological oxidatio to nitrate. Based one this biological oxidation, a processV - termed nitrification is developed. Nitrification process is one of the most commonly applied method of the treatment of ammonia containing «astevaters. In this study, the treatability ofwastes that contein high concentrations of ammonia by the nitrification process carried out in the rotating biological contactors, is investigated. Within this context, ammonia and nitrite inhibitions which frequently occur in case of treatment of high concentrations, is also studied. Studies involve in experimental part in which a pilot seale rotating biological contactor is used. Study covers the modeling and prediction of ammonia removal, determination of the basic and operational parameters of the process and their limitations. In the first chapter description of the problem of concern is outlined and the scope and purpose of the study is given. Scope of the study can be summarized as follows: 1- To investigate the nitrification of wastewaters containing ammonia concentrations in the range of 85- 1000 mg/1 NH3-N which is considered high concentrations of ammonia, within the fixed film growth and its kinetics. Tor this purpose to use a pilot scale RBC unit which is fed with the high concentrations of ammonia defined above, and to apply hydraulic loadings in the range 0.0022-0.0400 m3/m2-day. Assessment of the effect of hydraulic leading and influent? vt - concentrations on the removal rate. To find out the effect of high ammonia concentrations on the nitrific tion process at various hydraulic loadings. 2- To assess the threshold concentrations for the amraoni and/or nitrite inhibition employing high ammonia loadings and to observe the effect of such inhibition on the system. 3- To investigate the applicability of ammonia concentra tions higher than the inhibition thresholds by faadin the influent to different compartment of the reactor which are connected in series. In the second chapter a review of literature concerni the subject is given. Chemical and physical characteristics of ammonia is studied. Volatility of ammonia and its importa for the high concentration ammonia containing wastewater nitrification is pointed out. Wastes that contain high concentrations of ammonia has ahigh pH and under these circumstances a part of ammonia can be lost to the atmospher through vo I at i l i zat ion. Th is will make it difficult to determine the net amount removed by the nitrification to account for the ammonia loses during the nitrification proce a series of experiments are conducted. In these experiments the volatile part of ammonia of different concentrations and at different pH values are determined. In the nitrification process environmental factors, such as pH, temperature,VII - dissolved oxygen play an important zole. These variables and their effects to the process are studied and optimum conditions for the experiments are chosen. Inhibition of ammonia and nitrite are also studied. In the third chapter a general definition of the bio- film and mechanisms of biological removal within the biofilms are given and a comparison with the suspended culture is made. The theory of substrate removal theory is summarized and reaction and diffusion mechanisms are illustrated. The removal of substrates in fixed films are expressed for zero order, first order and half order reaction kinetics. A comparison of these reaction kinetics with the Monod expression is also made. Different modes of fixed film systems and their similarities and dissimilarities to biodisc system are briefly mentioned. In the fourth chapter, literatüre concerning the nitrification process is reviemed in two parts. In the first part the treatment of the wastes containing ammonia concentrations of less than 85 mg/1 is considered and perfinent literature is reviewed to find out the mechanisms involved. A dicrepancy between thererooval rates given in the literature is pointed out. Another point that merits to note that the high removal rates have been measured for the systems in which the substrate are synthetic wastewaters prepared in the 1 abor at ory.- VIII - la the second pact the ni t r i f icat ion processes with high ammonia concentration are taken on and their characteristi are evaluated in terras of operational parameters such as ammonia loading, hydraulic loading, influent ammonia concentration. In the ifith chapter the mechanisms of nitrogen removal in biodiscs are reviewed. The assumptions of uniformity of biofilm an the disc surface and completely mixed regime of reactor are discussed. The effect of biofilm thickness on the removal rate is pointed out. The theoretic; basis of the transition between the zero, half and first ordi kinetics are considered and illustrated. In the sixth chapter the characteristics of pilot sea biodisc reactor in which the experiments are carried out, are given. Biodisc reactor is a four-compartment tank whose total volume is 25 1. There are 5 discs in each compartment. Discs are all the same size with 30 cm. diameter. Total surfa 2 area of discs is 2.84 m. Total disc surface area to water volume ratio is 113 ra, /m->. Â synthetic wastewater is used in experiments. Environmental conditions in which the experimen are run are specified. Experimental procudures and methods are also explained. In the sevneth chapter results of the study are evaulated and discussed. The results can be summarized as fol lows.- IX Nitrification efficiency is decreasing with the increasing influent ammonia concentrations. Conversion provided by the nitrification is 1:1 up to 200 mg/1 NH3-N and deviations are observed at higher concent rati ons. Influent ammonia concentrations of up to 800 tng/1 NH3-N could be treated with the efficiencies over 90 % at one day retention time by the RBC. Higher concentrations will require longer retention times for efficient treatment. Dissolved oxygen concentration in the wastewater is found to be rate limiting at the high ammonia concentration feeding experiments. Two factors of importance affecting the removal rate are hydraulic loading and influent concentration. Hydraulic loading is found to have a pronounced effect at low values and this effect diminishes after a certain value. Similarly the effect of influent ammonia concentration decreases with the increasing concentrations. Eiofiltn thickness is decreasing through the compartments being maximum in the first compartment. This can be explained with the fact that ammonia concentration of the treated wastewater in the compartments is decreasing beginning with the first compartment. Each compartment has a completely mixed flow regime. Therefore, biofilm thickness can be con sidered as a function of influent concentration. Because ofX - the variation of the biofilm thickness the removal rata whic is estimated employing the zero order model, is not a constant value hut is rather a distribution. This can explai the different values for the removal rates encountered in th literature which has been attributed only to the use of wastewaters of different origine. Inhibition of nitrification is occurred in-the treatm of high ammonia concentration influent in the first and seco 2 compartments where the ammonia loading is 24.8 g/m -day. By dividing the influent line into two equal separate lines and feeding one line to the first and the other to the third compartment, the beginning of inhibition is observed at the 2 loading of 28.0 g/m -day. Above conclusions are presented in the eighth chapter