Final disposal evaluation of anaerobically stabilized municipal treatment plant sludge

Bu çalışma, anaerobik yöntemle stabilize edildikten sonra mekanik su alma işlemlerinde susuzlaştırılan kentsel nitelikli arıtma çamurlarının düzenli katı atık depolama tesislerinde bertaraf edilebilirliğinin değerlendirilmesi amacıyla yürütülmüştür. Atıkların düzenli depolama tesislerine depolanabilme kriterleri, Tehlikeli Atıkların Kontrolü Yönetmeliği (2005), EK-11 A kapsamında yer alan eluatta çözünmüş organik karbon (ÇOK) ve orijinal atıkta toplam organik karbon (TOK) parametreleri yüksek organik madde içeriğine sahip kentsel nitelikli arıtma çamurları için önem taşımaktadır. Bu çalışma kapsamında İzmir’de bulunan bir kentsel atıksu arıtma tesisinden alınan biyolojik çamurlar mezofilik sıcaklık koşullarında anaerobik olarak stabilize edilmiştir. Anaerobik çürütme çalışmaları, laboratuvar ortamında kurulan 8.5 L hacimli iki reaktörün farklı çamur alıkonma sürelerinde 30 gün süreyle işletimi ile yürütülmüştür. Anaerobik olarak çürütülen çamurların mekanik su alma işlemlerindeki performansları bir belt-press simülatörü ile tayin edilmiştir. Laboratuvar ortamında elde edilen çamur keklerinde yapılan analizler ile anaerobik çürütme sonrasında mekanik yöntemle susuzlaştırılan çamurların düzenli depolama tesislerine depolanabilirlikleri eluatta ÇOK ve orijinal atıkta TOK parametreleri dikkate alınarak değerlendirilmiştir. Sonuçlar, anaerobik yöntemle stabilize edildikten sonra mekanik olarak susuzlaştırılan çamurların kek katı madde içeriklerinin düşük olması sebebiyle mekanik su alma işlemi öncesinde şartlandırma işlemine tabi tutulması gerekliğini ortaya koymuştur. Bunun yanı sıra anaerobik yöntemle stabilize edilmiş çamur keklerinin EK-11 A’da belirtilen TOK standartları uyarınca inert atık sınıfında yer aldığı ancak ÇOK standart değerleri uyarınca tehlikeli atık sınıfında yer aldığı ve evsel katı atık düzenli depolama tesislerinde bertarafının uygun olmadığı belirlenmiştir. Anahtar Kelimeler: Anaerobik çürütme, biyolojik çamur, düzenli depolama, mekanik su alma, nihai bertaraf. The main by-product of municipal wastewater treatment of waste activated sludge (WAS) has been increasing worldwide as a result of an increase in the amount of wastewater being treated. The sludge should be processed and disposed of in accordance with the environmental health criteria for environmental reasons. The main objectives of sludge treatment and disposal are stabilization of the organic matter contained in the sludge, reduction in the volume of sludge for disposal by removing some of the water, destruction of pathogens, collection of by-products, which may be used or sold to off-set some of the costs of sludge treatment, and disposal of sludge in a safe and aesthetically acceptable manner (Scholz, 2006). For many authorities and engineers, the effective sludge management is still a big challenge since the investment and operational costs (Metcalf & Eddy, 2003). Treatment and disposal of excess sludge in a biological wastewater treatment system requires enormously high cost which has been estimated to be 50-60% of the total expense of wastewater treatment plant (Egemen et al., 2001; Yasui, 1996). Sludge stabilization is an important issue in sludge management field for effective reduction of organic matter, removal of pathogen and odor potential. For this purpose, alkaline stabilization, aerobic and anaerobic stabilization, aerobic thermophilic digestion, and composting are introduced. Among these methods, anaerobic digestion has been widely used with its many advantages. The main advantages of anaerobic digestion in comparison with other processes are; the lower energy requirement, the production of biogas and the lower production of excess sludge including efficient degradation of biodegradable particulate organic matters in sludge (Novak et al., 2003; Speece, 1996). Mechanical dewatering processes have been widely used for reduction in the volume of sludge for disposal by removing some of the water (Scholz, 2006). Mechanical dewatering processes like centrifuging, belt filter press, and filter press reduce the total volume of sludge even further so reducing the ultimate transportation cost of disposal. The resultant sludge is a solid, not a liquid, and so can be easily handled by conveyers or tractors although experience has shown that the dried sludge, known as cake, is more easily handled at solids concentrations of >20%. Its solid nature makes it suitable for many more disposal options than liquid sludge (Gray, 2005). This study was carried out for evaluation of final disposal of anaerobically stabilized sludge after mechanical dewatering in a municipal solid waste landfill area. Total organic carbon (TOC) in sludge cake and dissolved organic carbon (DOC) in eluate are important parameters for treatment plant sludge contained high organic matter in terms of Turkish Hazardous Waste Control Regulation, THWR EK- 11 A, 2005. In this study, anaerobic stabilization was applied to biological sludge samples. . The samples were taken from a municipal wastewater treatment plant located in Izmir, Turkey. Anaerobic sludge digestion studies were carried out using two 8.5 L lab-scale anaerobic reactors. The reactors were operated as semi batch system in mesophilic conditions at 37±2 oC for 30 days of operation period. Different sludge retention time of 5 days and 10 days were used in digestion study. For evaluation of anaerobic digestion performance of reactors, total solids (TS), organic matter (OM), suspended solids (SS), and volatile suspended solids (VSS) were analyzed regularly. Daily methane productions in reactor content were also measured during the operation period. The belt press simulator of crown press was used for evaluation of mechanical dewatering properties of sludge. For final disposal evaluations of dewatered sludge in a municipal solid waste landfill area, TOC parameter in sludge cake obtained from crown-press application and DOC parameter in eluate samples were analyzed regularly during the operation period. Results indicated anaerobic digestion is an effective method for sludge's solids reduction and it leads to decrease organic matter content of sludge. In contrast, anaerobic digestion has not a positive effect on increasing cake solids and some conditioning processes are required before mechanical dewatering operations. In addition, final sludge cake is classified as inert material based on the TOC parameter but it is classified as hazardous waste based on the DOC parameter according to Turkish Hazardous Waste Control Regulation, THWR EK- 11 A, 2005 and it can not be storage in a municipal solid waste landfill area for final disposal purpose. Keywords: Anaerobic digestion, biological sludge, landfilling, mechanical dewatering, final disposal