The effect of temperature on the nitrification rate in moving bed sequencing batch biofilm systems

Bu çalışmada hareketli yataklı ardışık kesikli biyofilm reaktörlerinde (HYAKBR) sıcaklığın nitrifikasyon hızı ve maksimum ototrofik çoğalma hızı üzerindeki etkilerinin ortaya konulması amaçlanmıştır. Çalışma kapsamında laboratuar ölçekli bir HYAKBR’de evsel nitelikli sentetik atıksu kullanılarak üç farklı sıcaklıkta (20, 15 ve 10°C) nitrifikasyon hızı ve kinetik katsayılar belirlenmiştir. Nitrifikasyon hızı, sıcaklıktan önemli derecede etkilenmiş, 20°C için 0.241 g NOX-N m-2gün-1 ve 10°C için 0.178 g NOX-N m-2gün-1 değerini almıştır. Aynı etki, maksimum ototrofik çoğalma hızı değerleri üzerinde de görülmüş, 20°C için 0.50 gün-1, 15°C için 0.32 gün-1 ve 10°C için 0.09 gün-1 olarak elde edilmiştir.Anahtar Kelimeler: Aktif Çamur; biofilm; hareketli yataklı ardışık kesikli biofilm reaktör; nitrifikasyon.This study investigates the effect of temperature on the nitrification rate and the maximum growth rate of an autotrophic biomass sustained in a moving bed sequencing batch biofilm reactor (MBSBBR). This type of a reactor is a novel hybrid system combining the advantages of attached and suspended activated sludge together with sequencing batch reactors. In this system, biofilm grows on small carrier elements that move along with the water in the reactor by aeration (aeration phase) or by mechanical stirring (anoxic/anaerobic phase). Experimental studies were carried out in a lab-scale MBSBBR, receiving a synthetic influent that had domestic wastewater characteristic, and operated at three different temperatures (20, 15, and 10°C). Evaluation of the results revealed that removal of organic matter at high rates and with efficiencies over 90% was secured at all operation conditions applied. Nitrification rate was significantly influenced by changes in temperature, resulting in a decrease from 0.241 g NOX-N m-2d-1 at 20°C to 0.178 g NOX-N m-2d-1 at 10°C. The same influence was observed on maximum autotrophic growth rate; values of 0.50 d-1, 0.32 d-1, and 0.09 d-1 at 20°C, 15°C, and 10°C were obtained, respectively. In the further studies, heterotrophic and autotrophic kinetic constants should be determined for municipal and different industrial wastewaters.Keywords: Activated sludge; biofilm; moving bed sequencing batch biofilm reactor; nitrification

Modelling of longterm simultaneous nitrification and denitrification performance of a pilot scale membrane bioreactor

Membran biyoreaktörlerin nütrient giderim kapasitesi son yıllarda bu sistemlerdeki karbon gideriminden daha çok dikkat çekmiştir. Membran biyoreaktörlerde toplam azot giderimi için konvansiyonel olarak bilinen proseslerin yanında eşzamanlı nitrifikasyon ve denitrifikasyon (SNdN) gelecekte en çok araştırma gerektiren prosestir. SNdN’in tüm etkisini ve esaslarını tanımlamak amacıyla pilot bir membran biyoreaktör teşkil edilmiştir. Bu çalışma, membran biyoreaktör sistemlerinin azot gideriminde etkili olan ana mekanizmalarının ve özellikle SNdN’in etkisinin değerlendirilmesi üzerine odaklanmıştır. Bu kapsamda yeni bir matematik model geliştirilerek model sonuçlarının ölçülen değerlerle uyumluluğu üzerinden kalibrasyon gerçekleştirilmiştir. Önerilen bu matematik modelde ilk olarak membran biyoreaktörler esas olarak biyokütlenin tamamının sistem içinde tutulduğu ve geri devrettirildiği ve bu sayede yüksek biyokütle  konsantrasyonlarının sağlandığı askıda çalışan bir aktif çamur prosesi olarak tanımlanmıştır. Bu kapsamda, AÇM1 (Aktif Çamur Modeli 1) baz olmak üzere içsel solunum fazı yaklaşımına dönüştürülmüş yeni bir aktif çamur modeli geliştirilerek ölçüm sonuçlarının dinamik olarak modellenmesi ve kalibrasyonu yapılmıştır. Yüksek biyokütle konsantrasyonlarında difüzyonun sistem performansı ve denitrifikasyon üzerine olan önemli etkisi ortamdaki oksijen konsantrasyonuna bağlı olarak nitrifikasyon ve denitrifikasyonu kontrol eden anahtar fonksiyonları sayesinde başarı ile açıklanabilmiştir. Geliştirilen model sonuçları, ölçülen sonuçlar ile oldukça yüksek bir uyumluluk göstermiştir. Bu uyum da modelin güvenilirliğini teyit etmiştir. Membran tank içinde oksijenin flok içine olan difüzyon limitasyonu, anahtar fonksiyonlarında yer alan yarı doygunluk sabitlerine spesifik değerlerin verilmesiyle açıklanabilmiştir. Söz konusu yarı doygunluk sabitleri KOH=1 mg/L, KOA=1.25mg/L, KNH=2mg/L ve KNO=2 mg/L olmak üzere önceki aktif çamur modellerine göre oldukça yüksek değerler olarak belirlenmiştir. Anahtar Kelimeler: Eşzamanlı nitrifikasyon ve denitrifikasyon, difüzyon limitasyonu, azot giderimi, çözünmüş oksijen, oksijen yarı doygunluk sabiti, membran biyoreaktör.Membrane bioreactors (MBR) are simply described as a membrane filtration process where the activated sludge flocs are filtered through a porous medium with a cutoff size of 0.1-0.4µm. Complete retention of sludge is maintained within the system whereas suspended solids are usually not detectable on the permeate side. Membranes are either submerged within the activated sludge reactor or configured externally in a separate tank. Membrane bioreactors provide superb treatment efficiency in terms of organic and nutrient removal. Although the organic removal efficiency of membrane bioreactors is very well known; nitrogen removal and especially simultaneous nitrification and denitrification capacity of membrane bioreactors still remains to be explored. Simultaneous nitrification and denitrification (SNdN) brings the advantage of high nitrogen removal efficiencies due to increased denitrification potential. A better understanding of the biological reactions occuring in a membrane bioreactor will provide an optimized design and energy consumption which in turn will promote the faster commercialization of the membrane bioreactors. This study focuses on two initiatives and objectives: i. to identify the true potential of membrane bioreactors for nitrogen removal with simultaneous nitrification and denitrification thereby deriving the denitrification potential of the system with respect to available carbon and dissolved oxygen (for longterm conditions)  ii. to minimize and to avoid irreversible fouling to a maximum time extent by implementing a different operational mode from the ones conducted in previous studies. For the above mentioned objectives, a pilot scale membrane bioreactor based on microfiltration technology was setup at a domestic sewage treatment plant. The plant was fed with municipal wastewater. Flatsheet membranes with a cutoff size of 0.4mm were used. Total membrane area was 8 m2 and the operating flux was constant at 0.5 m3/m2-day. The membrane module was supplied from Kubota Inc., Japan. The system setup for nitrogen removal was based on predenitrification. Coarse bubble aeration was used to supply oxygen for the microorganisms to carry out the biological reactions where it also simultaneously provided the necessary scouring effect on the membrane surface. System was biologically modelled for all runs using BioWin 2.2 software from Envirosim Associates Ltd. whilst physical modelling was done by GPS-X from Hydromantis Inc. Physical-chemical methods were used to determine the influent readily biodegradable COD(SS) and the influent  inert COD(SI). The modified model characterized the measured effluent COD efficiently. The effluent total COD only consisted of inert soluble fraction (SI) and inert soluble microbial products (SSMP). Under low dissolved oxygen (DO), the system yielded high and stable nitrogen removal performance in spite of oscillating COD/TKN ratio in the influent. Considering that the average influent TKN and ammonia concentrations were 45-60 mgN/L and 30-45 mgN/L respectively, the level of denitrification in the MBR tank which is oxic was observed to be approximately 20-30 mg/L. The level of denitrification is related to the denitrification potential, NDP within the MBR reactor which is solely dependant on available COD. However in membrane bioreactors, it can be stated that the level of dissolved oxygen inside the MBR also plays an important role in defining denitrification potential. The level of SNdN occuring in the membrane bioreactor suggests that this level of diffusion limitation is so high that it is even causing the anoxic fraction of biomass inside the floc to be dominant during high DO levels. It can be concluded that during high DO levels, this fraction of biomass shifts from being anoxic to aerobic decreasing the level of SNdN. The oxygen diffusion limitation from the bulk liquid into the flocs can be explained by assigning specific values to half saturation constants in the corresponding switching functions namely KOH=1 mg/L, KOA=1.25 mg/L , KNH=2 mg/L and KNO=2mg/L which are much higher than the values adopted to previous models. It can be concluded that the factors and parameters triggering SNdN in MBR can be listed as i.dissolved oxygen concentration, ii. floc size, iii. MLSS concentration of the bulk liquid which the latter two severely affects diffusion limitation of oxygen from the bulk liquid into the floc. The SNdN was also very sensitive to the hD factor which governed the degree of denitrification occuring during anoxic decay. Keywords: simultaneous nitrification and denitrification, diffusion limitation, nitrogen removal, dissolved oxygen, oxygen half saturation constant, membrane bioreactor

The effect of temperature and sludge age on COD removal and nitrification in a moving bed sequencing batch reactor

This study investigates the effect of temperature and the sludge age on the performance of a moving bed sequencing batch biofilm reactor (MBSBBR) for COD removal and nitrification. The experiments are conducted in a lab-scale MBSBBR operated at three different temperatures (20, 15 and 10 8C) with a synthetic feed simulating domestic sewage characteristics. Evaluation of the results revealed that removal of organic matter at high rates and with efficiencies over 90% was secured at all operation conditions applied. The nitrification rate was significantly influenced by changes in temperature but complete nitrification occurred at each temperature. The nitrification rates observed at 20 and 15 8C were very close (0.241 mg NOX-N/m2 d, 0.252 mg NOX-N/m2 d, respectively), but at 10 8C, it decreased to 0.178 mg NOX-N/m2 d. On the other hand, the biomass concentration and sludge age increased while the VSS/TSS ratios that can be accepted as an indicator of active biomass fraction decreased with time. It is considered that, increasing biofilm thickness and diffusion limitation affected the treatment efficiency, especially nitrification rate, negatively.TÜBİTAK - YDABCAG-199Y11

Cost analyses based on scientific design for salinity water membrane technology systems can be installed in Turkey

Bu çalışmada Türkiye’de membran teknolojilerinin uygulanabilirliğini inceleyecek nüfusu 500 - 2000000 arası 20 farklı büyüklükte yerleşim bölgesinin içme ve kullanma suyu ihtiyacını karşılayacak sistemlerin tasarım esasları belirlenerek deniz ve nehir sularının kullanılması durumuna göre yatırım ve işletme maliyetleri hesaplanmıştır. Nehir suyu membran teknolojisi sistemlerinin yatırım ve işletme maliyetlerinin deniz suyu arıtan sistemlere göre %50-55 daha düşük olduğu tespit edilmiştir. Nüfusu 500 olan bir yerleşim bölgesi için kurulacak deniz suyu membran teknolojisi sisteminin toplam yatırım maliyeti 2.24 €/m3 iken, nüfusu 15000 olan için 0.60 €/m3 değerine düşmektedir. Diğer yönden nüfusu 500 olan bir yerleşim bölgesi için kurulacak nehir suyu membran teknolojisi sisteminin toplam yatırım maliyeti 1.26 €/m3 iken, nüfusu 15000 olan için 0.26 €/m3 değerine düşmektedir. Türkiye’de içme ve kullanma suyu üretiminde kurulacak membran teknolojisi sistemleri için yatırım stratejilerinin belirlenmesi durumunda nüfusu 15000’den büyük; tesis çıkış kapasite değeri olarak 2000 m3/gün’den yüksek tesislerin kurulması önerilmiştir. Yapılan hesaplamalarda membran teknolojisi sistemlerinin ön arıtılma ünitelerinde ultrafiltrasyon sistemleri kurulduğunda yatırım maliyetlerinin % 10-20 daha yüksek olduğu görülmüştür. Akdeniz suyuna uygun membran teknolojisi sistemlerinde işletme maliyetlerinin yaklaşık %65-69’unu elektrik oluşturmaktadır. bu sistemlerin 20 yıl işletilmeleri boyunca; elektrik tarifesinde %20 artışta %6-9; %40 artışta %11-17; %60 artışta %16-23 bir m3 üretilen su için toplam yatırım maliyetlerinde yükselme olacağı tespit edilmiştir. Anahtar Kelimeler: Ters osmoz, ultrafiltrasyon, deniz suyu, nehir suyu, yatırım ve işletme maliyetleri.In todays world, membrane technology systems are used in a wide range of dissolved solid concentration and particle size for sea, river, well, lake waters and are even especially produced for different types of industrial wastewaters. One of the most important properties of the membrane technology is that the technology is open to continuous improvement. As a proof; the permeate water of a membrane filter today has increased three times of the permeate produced in 1980 while the production cost of the membrane is reduced to one tenth in the same period of time. This means that it is today possible to produce 30 times of the permeate produced in 1980 with the same investment cost of reverse osmosis system. In this study, the design criteria is presented for the membrane technology systems producing drinking and potable water of 20 different sized accommodation areas with populations from 500 to 2 000 000. As the designs of these processes vary too much according to the Total Dissolved Solids and particle sizes, different first investment and operation costs are calculated whether sea or river waters are used. The main parameters like equipment, construction, project, electricity and their affects on the investment costs are investigated separately for each plant. As a result of this study, both investment and operation costs are put into graphics for produced m3 water per each accommodation area with population from 500 to 2 000 000 and it is proven that the values are in accordance with the values published in the similar literature studies. Another result of this study is that the membrane technology systems producing drinking and potable water from sea waters are much higher than the membrane technology systems producing drinking and potable water from river, well, lake waters as the sea water has higher salinity. For this reason, it is suggested in this study to give priority to the membrane technology plant investments producing drinking or potable water from wells, rivers or lakes rather than sea water if both are available in the same area, as the plants operated with well, river and lake water have 60% lower investment+opera-tion costs compared to the plants operated with sea water. The first investment and operation costs per m3 of produced water of the membrane technology  systems using seawater and well waters decreases as the plant capacity increases. As a result of this study it is suggested for the central or local administrations that may be at the stage of planning their strategy regarding the membrane technology systems to make their investment plans if the population of their accommodation area is over 15 000 or the capacity equivalent is higher than 2 000 m3/day. Also in the case of ultrafilration units would be preferred instead of conventional pretreatment units in membrane technology systems, then investment costs can be higher as 10-20%. In addition, it is determined that energy costs are affecting about 65-69%. of the total operation cost. If electricity tariff is increased 20% then total investment cost increases by 6-9%; if electricity prices increases 40%, the operational cost increases by 11-17%; if electricity prices increases 60%, the operational cost increases by 16-23% in membrane technology systems producing drinking and potable water from sea water. The total investment and operation costs per m3 of produced water of the membrane technology systems using seawater and well waters decreases as the plant capacity increases; while the total investment and operational cost of a sea water membrane system of an accommodation area with a population of 500 is 2.24 ?/m3, the total investment and operational cost of a sea water membrane system of an accommodation area with a population of 15 000 is 0.60 ?/m3. While the total investment and operational cost of a river water membrane system of an accommodation area with a population of 500 is 1.26 ?/m3, the total investment and operational cost of a sea water membrane system of an accommodation area with a population of 15 ,000 is 0.26 ?/m3. Keywords: Reverse osmosis, ultrafiltration, sea water, brackish water, investment and operation costs

Mechanisms of segregated household wastewater treatment by Membrane Bioreactor

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

Benzo[a]anthracene'nin aktif çamur üzerine kronik etkisinin respirometrik incelenmesi

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

Biochemical basis and modeling of oxygen requirement in activated sludge

Bu çalışmada, aktif çamur sistemlerinde oksijen tüketimi, değişik biyokimyasal dönüşümleri yansıtan temel süreçler yardımı ile belirlenip modellenmiştir. Modellemede, sübstrat kullanımı ve biyokütle oluşumu esas alınmıştır. Oksijen tüketimini belirten ifadelerde sübstrat ve biyokütlenin tanımı için kullanılan değişik parametre çiftleri kullanılmıştır. Kullanılan modellerin kinetiği ve stokiyometrisi matris formatında her parametre çifti için ayrı ayrı tanımlanmıştır. Oksijen tüketimi için geçerli olan değişik ifadeler bu modellere göre türetilmiş ve bu yaklaşımla literatürde verilen benzer tanımların biyokimyasal temelleri ortaya konmuştur. İncelemede, Türkiye’de aktif çamur tesislerin tasarımında oksijen gereksiniminin hesaplanması için yönetmeliklerde kullanılması önerilen ifadeler de ele alınmış ve bu ifadelerdeki katsayıların geçerliliği değerlendirilmiştir.  Anahtar Kelimeler: Aktif çamur, biyokütle, modelleme, oksijen gereksinimi, sübstrat.In this study, oxygen requirement in activated sludge is evaluated and modelled in terms of fundamental  processes reflecting different biochemical transformations. Modern modeling concepts define substrate  utilisation and endogenous decay as major processes requiring final electron acceptor. In aerobic systems, dissolved oxygen acts as, and therefore, is consumed as the final electron acceptor. Substrate and biomass may be defined in terms of different parameters. Chemical oxygen demand (COD) and biochemical oxygen         demand (BOD5) are the traditional substrate parameters. COD also serves to define biomass along with the more traditional volatile suspended solids (VSS) parameter. Model alternatives covering basic biochemical processes in activated sludge are defined in a matrix format for different substrate and biomass parameters, each associated with a different stoichiometry. These modeling alternatives are used to derive different       oxygen requirement expressions, all compatible among themselves, for each substrate/biomass couple. The biochemical bases of the coefficients in these expressions are set in terms of fundamental model constants. As a practical implication of the conceptual evaluation approach, this study also covers a critical appraisal of formulations proposed in the regulations implemented by the authorities in Turkey, for the evaluation of the oxygen requirements in activated sludge design. Keywords: Activated sludge, biomass, modeling, oxygen requirement, substrate

Identification and modelling of aerobic hydrolysis in activated sludge systems, application of optimal experimental

Atıksularda Kimyasal Oksijen İhtiyacı (KOİ) fraksiyonlarının ve bunlara ait giderim  kinetiğinin belirlenebilmesi aktif çamur tasarımı ve işletilmesi açısından büyük önem taşımaktadır. Özellikle, yavaş ayrışan organik maddenin atıksularda yüksek miktarlarda olduğu bilinmektedir. Genelde, ayrışabilen KOİ fraksiyonlarını hızlı ve yavaş ayrışan KOİ olarak sınıflandırmak mümkündür. Ancak, atıksuyun tipi ve özelliğine bağlı olarak bu fraksiyonlar değişkenlik gösterdiği gibi çözünmüş, partiküler veya çökelebilir formlarda bulunabilmektedir. Hidroliz prosesi aktif çamur tesislerinin işletilmesinde çıkış suyu kalitesinin, fazla çamur oluşumu, oksijen ihtiyacı ve nutrient giderimi açısından büyük rol oynamaktadır. Özellikle deri, tekstil vb. endüstriyel atıksularında olduğu gibi çok yüksek miktarda yavaş ayrışan çözünmüş formdaki organik maddeye ait biyolojik giderim atıksu arıtma tesisi çıkış suyu kalitesi açısından önem taşımaktadır. Bu çalışma kapsamında, kesikli yürütülen respirometrik   deneylerin kullanılması ile çoğalma ve hidroliz kinetiğine ait sistem tanımlanması yapılmıştır. Seçilen aktif çamur modeli çoğalma, hidroliz ve ölüm olmak üzere 3 proses ve 7 parametreden oluşmaktadır. Sistemin tanımlanması, teorik ve pratik sistem tanımlama adımlarını kapsamaktadır. Teorik sistem tanımlamada, Taylor Serileri ile lineerize edilen modelden respirometrik verileri kullanarak hangi parametre gruplarının elde edilebileceği bulunmuştur. Pratik sistem tanımlamada ise gerçek veriler kullanılarak, parametre tahminleri yapılmış ve güvenilirlik aralıkları belirlenmiştir. Optimal Deney Tasarımı simülasyonlarından, deneyin başlangıç F/M (Substrat/Mikroorganizma) oranının azaltılmasının deneyin güvenilirliğini arttıracağı ancak bunun yanında parametreler arasındaki korelasyonu  da arttıracağı kanıtlanmıştır. Anahtar Kelimeler: Modelleme, hidroliz, sistem tanımlama, oksijen tüketim hızı, Optimal Deney Tasarımı.Appropriate determination of accurate COD fractionation together with degradation kinetics of organic matter has a prime importance on the design and operation of activated sludge systems. In general, regarding the total biodegradable COD, raw domestic wastewaters approximately contain readily biodegradable and slowly biodegradable substrates at fractions around 30% and 70%, respectively. On the other hand, compared to domestic wastewaters, industrial wastewaters contain much higher fraction of slowly biodegradable substrate which directly influence the effluent quality of treatment plants. In this respect, the determination  of slowly biodegradable matter as well as its degradation characteristics are crucial in terms of wastewater treatment plant design and operation. Hydrolysis process has already been known as the rate limiting step in organic carbon removal from industrial and domestic wastewaters. Considering the effluent quality, hydrolysis mechanism also plays a dominant role in delicate balance of electron donor/electron acceptor ratios in biological nutrient removal type activated sludge systems as an important carbon source. In addition to that, sludge production from activated sludge plant is also affected by the nature of slowly biodegradable matter. In parallel to the vast developments in activated sludge modeling, respirometry has always been effectively utilized as a convenient tool for influent wastewater characterization which can be regarded as a corner stone of activated sludge modeling. To date, numerious respirometric tests have been applied for gathering information on the stoichiometry and kinetics of biodegradable substrates in raw wastewaters. However, the proposed methodologies were mostly devoted to the estimation of growth associated parameters such as maximum growth rate, active fraction of biomass, heterotrophic yield and half saturation growth constant for heterotrophs etc. In this study, surface-saturation type hydrolysis kinetics was investigated based on short-term oxygen uptake rate measurements. An identifiability study were performed in order to find out best identifiable parameter groups from respirometric data with the aid of non-linear degradation model. Basically, the model has been constitued using the reactions of (i) aerobic heterotrophic growth (ii) hydrolysis of particulate matter and (iii) endogenous decay processes. Basically, the model has 7 parameters to be estimated from a single respirogram. The model identification procedure comprises the theoretical and practical identifiability studies. In theoretical identifiability study, identifiable combinations of model parameter that can be extracted from available data is studied for a certain model. Non-linear model under study was linearized with the aid of Taylor Series Expansion method. By neglecting the growth of heterotrophs under low initial F/M ratio, 6 parameter combinations were found to be theoretically identifiable from batch respirogram. On the other hand, the maximum rates governing the growth (mH) and hydrolysis (kh) were found to be individually identifiable if considerable growth of heterotrophs are taking place during the course of the experiment. From the identifiability study, it was also found that all parameters combinations include the heterotrophic yield coefficient, YH. In addition, the parameter combinations containing hydrolysis parameters always include the initial active heterotrophic biomass, XH0 as a state variable. In practical identifiability, the identifiable parameter combinations of a selected model were estimated. In this study, the information of the experiments were simulated for different initial F/M (Food/Microorganism) ratio by comparing the amount of information as well as the correlation degree among the estimated parameters. The information contents of the experiments were evaluated on the basis of Optimal Experimental Design (OED) methodology. In this regard, the effects of initial conditions on information content of experiments was evaluated via comparing the scalar functions of Fisher Information Matrix (FIM). These scalar functions were selected as the D-Criterion and E- Criterion which summarize the information volume and the correlation degree among parameters, respectively. Finally, it was found that applying lower initial F/M ratio increases the information content of the experiment, on the other hand it also increases the correlation among the estimated parameters. Keywords: Modelling, hydrolysis, identifiability, oxygen uptake rate, optimal experimental design

Karışık karbon kaynağı ortamının nişasta giderim performansı ve bakteriyel kompozisyon üzerine etkisi

The microbial processes have been extensively investigated for the efficiently design and operation of the activated sludge systems. The experimental studies have often focused on the single representative carbon source, although, microorganisms have to remove wastewater which is the mixture of several different type carbon sources. Under such conditions, bacteria often utilize one carbon source preferentially and other carbon sources are consumed only, when the preferred one is exhausted. The carbon source providing the best growth rate and/or growth yield is preferred, and the successive utilization of the substrates is often represented (Monod, 1942). In the environmental engineering point of view, it is important to understand the interaction between the removal mechanisms of different carbon sources which have a different degree of complexity. Although, recent studies have mainly focused on the biodegradation kinetics of the industrially produced starch as the only pollutant in wastewater, the simultaneous use of multiple substrates, such as the co-treatment of the industrially produced wastewater with the domestic wastewater produced in the facility, can lead to differences in biodegradation kinetics of any individual organic constituent as well as in the bacterial community. The researches with bacteria and higher organisms have revealed that selective carbon source utilization is common and that glucose is the preferred carbon source by many organisms. Moreover, the presence of glucose often prevents the use of other, secondary, carbon sources (Gorke and Stülke, 2008). In a study carried out under aerobic conditions with a mixture of similar type substrates (i.e. a mixture of acetic, lactic and propionic acid), a strong decrease in the removal rates of acetic and lactic acid was observed when treated in the presence of another substrate (Dionisi et al., 2004). This strong interaction among different substrates was explained with the interconnected pathways utilized by microorganisms for the removal of these substrates. Less clear evidences are available when dealing with mixtures of different type substrates, like volatile fatty acids and carbohydrates. Carta et al. (2001) reported that there were no differences in the uptake rate of acetate and glucose under mixed substrate environment compared to single substrate environment. In addition to the substrate uptake rates, the degradation kinetics and rates of the storage compounds were also reported as the same. In another study, when starch and acetate were treated together, slightly lower rates were observed in terms of individual carbon removal of acetate and starch, as well as respective storage of PHA and glycogen compared to treatment of substrate alone (Karahan et al., 2008). The fate of slowly biodegradable carbon source was evaluated in a SBR acclimated to starch as the sole carbon source and mixture of starch and acetate. The SBRs were operated with the same organic loading rate at two different sludge ages. Acetate, which is the one of the volatile fatty acid, was used as secondary pollutant as the volatile fatty acids have been reported as the main constituents of the domestic wastewaters. Although, the carbon source was fed to the SBRs in continuous mode throughout the cycle, the production of the storage polymer, namely glycogen, was observed in all SBRs. The relatively constant storage ratios were observed in SBRs fed with different carbon sources. The COD removal efficiency of the SBRs operated at the sludge ages of 8 days was significantly affected from the presence of acetate in the environment, although the COD removal efficiencies were constant at the sludge ages of 2 days independently from the presence of the secondary substrate. The bacterial characterization studies performed with fluorescent in situ hybridization (FISH) showed the decrease in the Actinobacteria phylum which was reported as the main starch consumer when the starch removal was performed in the multiple substrate environments at the sludge ages of 8 days. On the other hand, the detection of different groups at different sludge ages indicated the importance of the sludge age for evaluating treatment performance in activated sludge systems.  Keywords: Starch; dual substrate; substrate removal kinetic; FISH, activated sludge system. Evsel atıksuların arıtımında yaygın olarak kullanılan aktif çamur sistemlerinin başlıca kirletici parametre olan karbon kaynağının giderim performansı açısından değerlendirilmesi, sistemin en uygun tasarım kriterlerinin belirlenmesi açısından büyük önem taşımaktadır. Bu konuda yürütülen çalışmalarda, evsel atıksuların içeriğini yansıtacak şekilde seçilen tek bir karbon kaynağı model substrat olarak kullanılmaktadır. Fakat farklı karbon kaynaklarının bir arada veya ayrı ayrı arıtılmaları mikrobiyal dinamikler doğrultusunda farklı giderim performansları elde edilmesine neden olabilmektedir. Bu kapsamda, çalışmanın amacı evsel atıksuların karbonhidrat içeriğini yansıtan ve hedef karbon kaynağı olarak ele alınan nişastanın, başka bir karbon kaynağı ile beraber aktif çamur sisteminde arıtılması durumunda, giderim veriminde ve bakteriyel komposizyonda oluşabilecek farklılıkların tespit edilmesidir. 2 farklı çamur yaşında işletilen sistemde, ikincil karbon kaynağı olarak evsel atıksu kompozisyonun büyük bir kısmını oluşturan uçucu yağ asitlerini temsilen asetat seçilmiş ve bu sayede farklı giderim mekanizmaları ile giderilen farklı yapıdaki karbon kaynaklarının birbirlerine etkileri araştırılmıştır. Elde edilen veriler, 8 gün çamur yaşında nişasta giderim performansının, ortamda asetatın bulunmasından etkilendiğini ancak, 2 gün çamur yaşında karışık karbon kaynağı ortamının nişasta giderim performansı bakımında önemli bir etkisi olmadığını göstermiştir. Farklı koşullarda işletilen reaktörlerde bulunan baskın türlerin Flüoresanlı yerinde hibritleşme tekniği (FISH) yöntemi ile analizi sonucunda, 8 gün çamur yaşında karışık karbon kaynağı ortamının sadece mikrobiyal aktivite üzerinde değil aynı zamanda mikrobiyal seleksiyon üzerinde de etkisi olduğunu göstermiştir. Ayrıca, deneysel sonuçlar, çamur yaşının sistem performansı ve bakteriyel kompozisyon üzerinde etkili bir parametre olduğunu ve bu nedenle aktif çamur tesislerinin tasarımında öncelikli olarak ele alınması gerektiğini ortaya koymuştur.  Anahtar Kelimeler: Nişasta; karışık karbon kaynağı; karbon kaynağı giderim kinetiği; FISH; Aktif Çamur Sistemi.&nbsp

Biodegradability of slaughterhouse wastewater with high blood content under anaerobic and aerobic conditions

Abstract: In this work, the biodegradability of wastewater from a slaughterhouse located in Keşan, Turkey, was studied under aerobic and anaerobic conditions. A very high total COD content of 7230mg dm-3 was found, due to an inefficient blood recovery system. Low BOD5/COD ratio, high organic nitrogen and soluble COD contents, were in accordance with a high blood content. A respirometry test for COD fractionation showed a very low readily biodegradable fraction (SS) of 2%, a rapidly hydrolysable fraction (SH) of 51%, a slowly hydrolysable fraction (XS) of 33% and an inert fraction of 6%. Kinetic analysis revealed that hydrolysis rates were much slower than these of domestic sewage. The results underlined the need for an anaerobic stage prior to aerobic treatment. Tests with an anaerobic batch reactor indicated efficient COD degradation, up to around 80% removal. Further anaerobic degradation of the remaining COD was much slower and resulted in the build up of inert COD compounds generated as part of the metabolic activities in the anaerobic reactor. Accordingly, it is suggested that an appropriate combination of anaerobic and aerobic reactors would have to limit anaerobic degradation to around 80% of the tCOD and an effluent concentration above 1000mg dm-3, for the optimum operation of the following aerobic stage