Klinoptilotil ve kum filtresi kullanılarak amonyak piklerinin giderilmesi

Abstract

Azot formları içinde çevre mühendisliği açısından önemli olanları amonyak, nitrit ve ' nitrattır. Atıksularda azotun bir formu olarak amonyak genellikle amonyum iyonu ve serbest amonyak formlarında bulunur. Bilindiği gibi moleküler amonyak toksik etkiye sahipken amonyum iyonu toksik değildir. Serbest amonyak özellikle suda yaşayan canlılar için zehirleyici etkiye sahiptir. Ayrıca amonyağın nitrite ve nitrata oksidasyonu sırasında oksijen tüketildiğinden dolayı alıcı ortamlarda çözünmüş oksijen seviyesinde düşmeye sebep olur. Bu sebeplerden dolayı su kaynaklarında ve atıksu arıtımında azot kontrolü çok önemlidir. Diğer yandan son zamanlarda özellikle nutrient kontrolünde önceliğe sahip hassas bölgelerde standartlara getirilen kısıtlamalar özellikle pik yüklemelerin geldiği zamanlarda mevcut sistemler tarafından karşılanmasında zorluklar ortaya çıkmış ve ikinci kademe amonyak giderimi gündeme getiririlmiştir. Bu sebeplerden dolayı amonyak giderimi için yeni ve ek uygulamalara gidilmesi zorunlu hale gelmiştir. Yapılan yeni çalışmallarda amonyak piklerinin biyolojik arıtmayı takiben iyon değişimi prosesiyle ve biyolojik aktiviteli filtreler ile giderilmesi düşünülmüştür. Bu çerçevede, amonyak piklerinin Türkiye'de filtre malzemesi olarak kullanılan kum ile iyon değiştiricinin birlikte kullanıldığı bir sistem ile giderilmesi ve amonyağın ikinci kademe arıtımı düşünülerek sistemi yansıtmak üzere kolon deneyleri üzerinde çalışılmıştır. Bu şekilde amonyağın, hem iyon değişimi prosesiyle hem de biyolojik aktiviteyle giderilmesi amaçlanmıştır. Özellikle pik yükler ardından gelen düşük konsantrasyonlar boyunca amonyak iyon değiştirici yüzeyinden desorplanmakta ve yeni kullanımlar için iyon değiştirci yüzeyleri serbest hale gelmektedir. Bu şekilde daha sonra gelecek piklerin giderimi için klinoptilolit daha fazla aktif yüzeye sahip olmaktadır. Diğer yandan, yüksek konsantrasyondan düşük konsantrasyonlara geçişte iyon değiştirici yüzeyinden bırakılan amonyak, filtre malzemesi üzerinde gelişen nitrifierler tarafından nitrifikasyon mekanizmasıyla kullanılarak giderimi sağlanmaktadır. Ayrıca, nitrifikasyon mekanizması ile klinoptilolitin kısmi rejenerasyonu yapılabilmektedir. Çalışma kapsamında iyon değişimi prosesinin esaslarından bahsedilmiş ve iyon değişimi yöntemiyle amonyak giderimi üzerine yapılan literatür çalışmaları değerlendirilmiştir. Laboratuvar çalışmalarında temel deneysel sistem kurulmuş ve kırılma noktası analizleri (breakthrough) yapılarak kırılma noktası (breakthrough) eğrileri oluşturulmuştur. Analiz sonucunda uygun bulunan debi ve temas süresine göre farkü kolon çaplarında, iyon değiştiricinin farklı miktarlarında ve kumla karıştırılarak, sabit ve pik yüklemeler için sistem çalıştırılmıştır. Çalışmada son aşama olarak Türkiye'de Bigadiç bölgesinde bulunan klinoptilolitin iyon değişimi kapasitesi belirlenmek üzere kırılma noktası analizleri (brekthrough) yapılmıştır.

With increasing pollutants being discharged into receiving waters over the years, new and more stringent effluent quality standarts have been adopted in various countries of" the world. Thus, upgrades for plants that receive variable influent concentrations and peak loads. For plants receiving peak loads, the immediate remedy is to provide an equalization of some type so as to have an effluent of more or less constant and compliant value. This can classicaly achieved through the use of an equalization basin. Safe operation in terms of compliance under such circumtances may be possible through the use of large safety factors over the average operating conditions. However this will entail higher expenditures, and larger reactor volumes and areas, which may take it a two fold problem for existing plants with limited area for expansion. An alternative to the larger volume single stage reactor is the use of multistage operation which is known to reduce volume/area requirements. Combination of various processes for different stages may be beneficial [17] [18] [19]. A possible second stage may be the utilization of multipurpose filters where a filter system can be used for various purposes including suspended solids removal and biological avtivity [23]. This practice will be cost effective and require smaller volumes. However, during peak loads (approximately 2-5 times the average concentration), the system may not be sufficient to comply with the standards, since the influent peaks cannot be dampened accordingly and there is a repetition of the influent peak pattern in the effluent stream, though at lower levels of concentration. For plants where peak loads are frequently expected, the need for some type of equalization is apparent. The research outlined here has been undertaken to present a possible remedy to that problem, as an alternative to the classical, larger- volume equalization basin. Within the scope of this work, currently in progress, multipurpose filtration with the primary aim of post equalization of ammonia peaks is investigated. The system proposed is a filter with biological activity, used as a second stage unit after a first stage nitrification, consisting of a combination of filter material on which biofilm had been grown with an ion exchanger selective for ammonia, clinoptilolite. In such a system ammonia will be removed both by a biological (nitrification) and a physicochemical (ion exchange) process. The additional benefit of the unit will be the removal of suspended solids. It has been seen that the usage of burned clay (Blaton) for filter material combined with clinoptilolite for removal of ammonia peaks [17][18][19]. However, in Turkey, sand filters are used for filtration in water and wastewater treatment plants. With in VJll the scope of this work the usage of sand filters for multipurpose, combined with clinoptilolite has been evaluated. The basic experimental set-up consists of the three columns shown in Figure 1, containing (A) a mixture of filter media and clinoptilolite (aerated), (B),filter media combined with ion exchanger (not aerated) and (C) clinoptilolite only. The columns are fed with the effluent of the Istanbul Technical University sewer line. The feed, which has been previously aerated (to represent effluent of the biological treatment), filtered and diluted in order to attain desired value. n SF : Sand Filter IE : Ion Exchanger E : Effluent Figure 1 The experimental layout Samples taken from the influent and from each column effluent were routinely analyzed for ammonia nitrogen. Comparison of the analysis results from the electrode and the distilation method has revealed that for concentrations below 50 mg NH3-N/1, values obtained were in good agreement, between 50 - 170 mg NH3/1 a deviation of up to 11% could be expected. IX Fundamental research has been done to determine appropriate service conditions for further services. First, column 2.6 cm. internal diameter tested using 40 g of clinoptilolite in order to format breakthrough curves for different contact times and flow rates: to = 3 min Q = 15 ml/min. tc = 5 min. Q = 10 ml/min. tc = 8 min. Q = 5. 16 ml/min. tc=10min. Q = 4.7 ml/min. It has been observed that, ion exchanger has lost it's efficiency in early stages of service time. Service for 8 and 10 min. contact time gave the the" best result, but for these cases calculated values for surface loadings are out of the range. In addition to this, service conditions must be in accordance with reference study [18]. So, tc = 5 min., Q = 10 ml/min. service condition selected for further services. The second step of the study, two parallel columns i.d. of 4.8 cm. using 80 g of clinoptilolite, one containing only clinoptilolite and the other combination of clinoptilolite and sand filter operated at same service conditions; tc = 5 min., Q = 17 ml/min. From breakthrough curves for this run, between two columns slight difference observed. The third step of the study as given before and illustrated in Fig. 1. three parallel columns i.d. of 2.6 cm. and contain 40 g clinoptilolite operated at the same time. From breakthrough analizes aerated column gives the best results. In this way, biological activity has been formed on sand filter combination with clinoptilolite with aerating the feeding and ammonia removed by both ion exchange and nitrification mechanisms. On the other hand, between sand filter with combination of clinoptilolite (not aerated) and column ion exchanger only, slight difference observed. Similar to third step, 4.8 cm. i.d. columns and 80 g of clinoptilolite are used and operated at to = 5 min., Q = 17 ml/min. service conditions. The results are similar to 2.6 cm. i.d. column results. To determine the efficiency loss in ten times used clinoptilolite, two columns, one containing 30 g of new clinoptilolite and the other 30 g of ten times used and regenerated clinoptilolite operated at 5 min. contact time. From breakthrough curves approximately 10 % efficiency loss for used - regenerated clinoptilolite. The most important step of the study ammonia peaks were studied. The feed is introduced in such concentrations as to give distubances of approximately 2-5 times the average of the regular feed ( approximately 3 - 5 mg NH3 - N/1). The concentration of the feed is regulated at the prescribed value by external addition of ammonium chloride or tap water as needed. Disturbances of 4 hours each are used. The feed which is used for column A is aerated to avoid any oxygen limitations in the column. The packed heights of columns A and B are held constant to see the additional effect of the ion exchanger in the mixed column. Meanwhile, the same weight of the ion exchanger is used in columns B and C so that direct comparisons can be possible. A summary of the operating conditions are given in Table 1. The system has not been stopped for any reason including regeneration. Table 1. Operating conditions System was operated for 14 days and system was not stoped except for short times operating problems. Available data shows that during 3 days no differences between three columns. But, from fourth day aerated combination of sand and clinoptilolite gave the apparent difference from the others. Difference from the others in the fourth day was 0.6 mg/1 in the fifth day arise to 1.5 mg/1. At the end of the 14th day difference between aerated sand filter and clinoptilolite column and clinoptilolite only column arise to 2.5 mg/1. On the other hand, until 8th day, no difference between clinoptilolite only column and sand filter combination of clinoptilolite (not aerated) was observed but, from 8th day sand filter combined with clinoptilolite gave the better results. In this column, biological activity has been formed during 8 days. During peak loads where the rate of incoming ammonia exceeds that of nitrification, the ion exchange process takes over and the ion exchange capacity provided works to eliminate the peaks in the effluent. As such, this seems to be a very useful system and çan conveiently be used in existing systems just by adding the correct amount of ion exchanger into the filter bed. Available data shows that bioregeneration will not by itself be sufficient to abandon additional chemical regeneration, however it extends it extends the service time till breakthrough in comparison to the ion exchanger only column. Filters with biological activity modified with clinoptilolite lend a very promising remedy for maintaining compliant status under peak loads of ammonia. At high concentrations the additional ion exchange capacity takes over to dampen the peaks. During low concentrations on the other hand, ammonia is desorbed from the ion exchanger surface, lending capacity fur further usage. Further more, the desorbed ammonia is removed within the process of nitrification. XI What seems to be attractive side of the system proposed is that in existing plants with filters, performance can be upgraded just by the addition of the correct amount of clinoptilolite in the columns. As a new addition to existing plants or for new systems, it promises to be a powerful tool against ammonia peaks with a comperatively smaller volume/area requirement. There is substantial evidence of bioregeneration at reduced concentrations. However, it is presumed that there will be a need for supplementary chemical regeneration in any case.