Bu çalışmada, ayrık evsel atıksuların membran biyoreaktörde (MBR) arıtılma mekanizmaları araştırılmıştır. Çalışma, siyah ve gri atıksuların beslendiği pilot ölçekli iki ayrı batık MBR kullanılarak gerçekleştirilmiştir. Biyolojik arıtmanın kirletici boyutu üstüne etkisinin incelenmesi ve membranların verimli süzme boyut aralığının belirlenmesi amacıyla, atıksu ve aktif çamur örnekleri üstünde, KOİ için boyut dağılım analizi gerçekleştirilmiştir. Aktif çamur örnekleri üstünde gerçekleştirilen kirletici boyut dağılım analizi sonuçları ile membran süzüntüsünün konsantrasyonu karşılaştırılarak membranın verimli süzme boyutu tahmin edilmiştir. Buna göre, bu çalışmada kullanılan membranlar mikrofiltrasyon sınıfında ve 400 nm gözenek açıklığına sahip olmasına karşın, MBR içinde membran yüzeyinde biyofilm oluşması ve ikinci bir bariyer görevi görmesi sebebiyle verimli süzme boyutunun yaklaşık 8 nm değerine düştüğü ve ultrafiltrasyon sınıfında yer aldığı belirlenmiştir. Dolayısıyla membranın sadece biyokütle ile su fazının ayrılmasını sağlamakla kalmadığı, büyük molekül ağırlığına sahip ayrıştırılamayan çözünmüş organik maddelerin de reaktör içinde tutulmasını sağladığı belirlenmiştir. Bu noktadan hareketle, çözünmüş kalıcı KOİ’nin MBR’larda akibetinin araştırılması için atıksu, MBR içinden alınan aktif çamur numunesi süzüntüsü ve membran süzüntüsü arasında kararlı denge için kütle dengesi eşitliği kurulmuştur. Kütle dengesi eşitlikleri sonucunda, konvansiyonel sistemde ayrıştırılamayan bir kısım çözünmüş kalıcı KOİ’nin MBR’larda ayrıştığı belirlenmiştir. Her iki MBR’da da çözünmüş kalıcı KOİ’nin ayrışma verimi, reaktör içinde tutulan fraksiyon değerlendirildiğinde %95, çözünmüş kalıcı KOİ’nin tamamı dikkate alındığında ise %50 civarında bulunmuştur. Anahtar Kelimeler: Membran biyoreaktör, gri su, siyah su, çözünmüş kalıcı organik madde.Worldwide, one in five persons does not have access to safe drinking water, whereas half of the world's population does not have access to sufficient sanitation (WHO, 2000). In addition, stress on water resources increases because of pollution, ineffective water use, increasing water demand and droughts. In the current conventional wastewater management, end of pipe, approach all types of wastewater are mixed, transported in a sewer system, and treated in a wastewater treatment plant. However, the sewer systems usually do not end up with an appropriate treatment plant. As a result, uncontrolled wastewater discharges cause serious problems in the receiving environment. Recently, "decentralised sanitation and re-use" (DESAR), which is a logical on-site source separation and reuse based approach, was proposed as an alternative to current "end of pipe" approach. On household level, two main sources of wastewater are recognized which are grey and black water. In this framework, treatment by MBR may be a promising alternative for small scale systems with the high hygienic standard effluent quality, reduced reactor volume, smaller footprint and operation easiness due to reduced net sludge production at high sludge ages. Two pilot-scales submerged MBRs were constructed for grey and black water treatment equipped with plate and frame type membrane modules. In the first part of this study, detailed characteristics of grey and black water in terms of aerobic biodegradability related kinetic and stoichiometric model parameters, which are missing in the literature, were determined based on batch experimental study and respirometric tests. Assessment of biodegradable COD fractions and kinetic and stoichiometric constants were done by model fitting of the OUR data (Insel etal., 2003). The OUR data was analyzed according to endogenous decay modified ASM1 (Orhon and Artan, 1994). For the case of black water as the large fraction likely to cover a wide range of compounds with different biodegradation pattern, dual hydrolysis rate is assigned. For the case of grey water, a single hydrolysis rate is sufficient to explain the hydrolysis. The results of aerobic biodegradability characterization showed that the kinetic and stoichiometric coefficients of grey and black water were in accordance with the previously reported values for domestic wastewater. Compared with black water, hydrolysis rate of grey water was found to be lower, which is attributed to the slowly biodegradable detergents, soaps and cleaning agents heavily found in grey water. The combined wastewater followed the kinetics of black water. Wastewater characterization usually includes, a single filtration size (450 nm), which conventionally differentiates soluble and particulate COD components. In this study, size information of pollutants has been explored in a much wider range between 2nm to 11 m for a better understanding of feed water characteristics. Furthermore, size distribution study was also performed on the reactor bulk liquids of the MBRs mainly for better understanding of membrane separation and the fate of soluble non-biodegradable organics in MBRs. It is found that due to biofilm formation, serving as an additional separation barrier on the surface of the membranes, the effective filtration size is in the range of ultrafiltration, around 5-14 nm, although the membrane itself is in the size range of microfiltration with the 400 nm pore size. In conventional activated sludge systems, HRT controls the retention time of soluble COD, which is the filtrate of 450 nm filter. On the other hand, in MBRs this statement is not true anymore. Membrane separation decides the residence time of pollutants depending on the effective filtration range of the membrane and size of pollutants. As a result of size distribution analysis of bulk liquid, it is found that the retained soluble residual organics, which are accepted as non-biodegradable in conventional activated sludge systems, are slowly biodegraded, around 50% and 95% for overall soluble residual organics and the retained fraction in the reactor bulk liquid respectively. Similar results were obtained for both of the MBRs. According to the findings of this study, it can be concluded that the difference between MBRs and conventional activated sludge systems is not just a physical separation by a membrane. Furthermore, better understanding of fate of soluble organics in MBRs will be a step for better understanding of membrane fouling mechanisms. Keywords: Membran Bioreactors, grey water, black water, DESAR, soluble residual organics
