In this study, activated sludge taken from İstanbul ISKI Paşaköy Biological Treatment Plant, acclimated to synthetic peptone mixture for 6 months. Benzo[a]anthracene (B[a]A) was selected as model xenobiotic and the effect of B[a]A to the acclimated activated sludge was investigated. B[a]A is a toxic and carcinogen polycyclic aromatic hydrocarbon (PAH) and generated via cigarette smoke, diesel exhaust, commercial solvents etc. B[a]A is also listed in Environmental Protection Agency (EPA) priority pollutant list. In this study, 0.011 g/L B[a]A was added to the sequencing batch reactor (SBR). The chronic effect of B[a]A to activated sludge, were performed and monitored through respirometric studies as well as conventional parameters. The activated sludge operated 10 sludge ages for chronic effects. The chronic effect was estimated by using a multi-component model. 0.011 g/L B[a]A addition has no effect on COD removal. While biodegradation of peptone mixture, the B[a]A addition effects hydrolysis rate and PHA storage mechanism. The amount of B[a]A in activated sludge and supernatant monitored through high performance liquid chromatography (HPLC). PAHs, which are a class of xenobiotic, are unique contaminants in the environment because they are generated continuously by the inadvertently incomplete combustion of organic matter. PAHs include 70 natural and anthropogenic organic compounds constituted by aromatic rings, ranging between two and seven, and mainly derived from petroleum activities. In the 20th century there was a great increase of anthropogenic production of PAHs by combustion of fossil fuel. Beside of predominating anthropogenic sources e.g. road traffic and combustion of fossil fuels, there are also natural sources, e.g. volcanic eruptions and forest fires. PAHs consist of fused benzene rings in linear, angular or clustered arrangements and contain by definition only carbon and hydrogen atoms. However, nitrogen, sulfur and oxygen atoms may readily substitute in the benzene rings to form heterocyclic aromatic compounds, which are commonly grouped with the PAHs. Due to their toxicity, 16 PAHs were listed by U.S. Environmental Protection Agency (USEPA) as priority pollutants, which should be monitored in aquatic and terrestrial ecosystems. The increase in the hydrophobicity and electrochemical stability is associated with an increase in the number of benzene rings and angularity of a PAH molecule. The high molecular weight (HMW) PAHs are more persistent and recalcitrant than the low molecular weight (LMW) PAHs. The stability and distribution of the PAHs in the natural environment is influenced by the configuration of the aromatic rings, physico-chemical properties. PAHs are considered as important environmental pollutants since many of the compounds in this group are of major concern to environmental agencies and researchers worldwide due to their mutagenic, toxic, genotoxic and carcinogenic properties depending upon the number and configuration of the benzene rings and the presence and position of their substituents. Microorganisms, such as bacteria and fungi, may transform the PAHs to other organic compounds or to inorganic end products such as carbon dioxide and water. The latter process has been referred to as mineralization. Some PAH-degrading microorganisms, primarily bacteria, are capable to use the PAHs as a carbon and energy source, and may thus transform the contaminants into molecules that can enter the organisms’ central metabolic pathways. Other microorganisms have the capacity to degrade PAHs, while living on a widely available substrate. Such co-metabolism does not always result in growth of the microorganism, and sometime the cosubstrate, i.e. the PAH, is only transformed into another compound without any apparent benefit for the organism. Keywords: Xenobiotic, PAH, activated sludge, Benzo[a]anthracene, modeling, respirometer.Benzo[a]anthracene (B[a]A), toksik ve karsinojen bir polisiklik aromatik hidrokarbon (PAH) olup sigara dumanında, dizel araçların egzoz dumanında, yangın sonucu çıkan dumanlarda, ticari solventlerde vb. bulunmaktadır. B[a]A, Amerika’daki Çevresel Koruma Ajansı (Environmental Protection Agency - EPA) tarafından öncelikli kirleticiler listesinde yer alan 16 PAH’tan biridir. Bu çalışmada, benzo[a]anthracene (B[a]A), model zenobiyotik olarak seçilmiş ve B[a]A’nın sentetik pepton karışımına alışmış aktif çamur üzerindeki kronik etkisi incelenmiştir. Aklimasyon çalışmaları İSKİ Paşaköy İleri Biyolojik Atıksu Arıtma Tesisi’nden alınan biyokütle ile başlatılmış, hidrolik bekletme süresi 1 gün olan doldur-boşalt reaktörler çamur yaşı 10 gün olarak işletilmiştir. Kronik deneylere başlamadan önce sistem 3 ay süre ile organik madde olarak evsel atıksuyu en iyi temsil ettiği düşünülen sentetik pepton karışımı (600 mg KOİ/L) ile beslenmiştir. Kronik etkinin belirlenmesi için günde iki çevrim ile çalıştırılan çamur yaşı 10 gün olan bir ardışık kesikli reaktör (AKR) sistemi kullanılmıştır. Sadece sentetik pepton karışımı ile beslenen AKR sistemi, kronik etkinin belirlenmesi için 21 gün boyunca sabit miktarda B[a]A (0.011 g/L) eklenerek izlenmiştir. B[a]A’nın aktif çamur üzerine olan kronik etkisi, respirometrik yöntemin yanı sıra konvansiyonel parametreler ile de incelenmiştir. 0.011 g/L B[a]A eklemesinin KOİ giderimi açısından AKR sistemi üzerine bir etkisi olmadığı anlaşılmıştır. Yürütülen modelleme çalışması, respirometrik testler aracılığıyla Modifiye Edilmiş Aktif Çamur Modeli No. 3’teki kinetikler hakkında deneysel veri desteği ve bilgi sağlamıştır. Pepton karışımının biyolojik parçalanmasında B[a]A ilavesi hidroliz hızında bir artışa neden olmuştur. Bunun yanısıra sistemin depolama mekanizması üzerinde de bir etkisi olduğu görülmüştür. Anahtar Kelimeler: Zenobiyotik, PAH, aktif çamur, Benzo[a]anthracene, modelleme, respirometre
