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

Comparison of the effect of endogenous decay rates for the conventional and multi-component modelling approaches on the sludge production

Aktif çamur sistemlerinin modellenmesinde günümüzde kullanılan yöntemler geleneksel aktif çamur modellenmesi ve çok bileşenli aktif çamur modellemesi şeklinde sınıflandırılabilmektedir. Geleneksel aktif çamur modellenmesi, çözünmüş oksijene ilaveten, karbon yapıdaki besi maddesi ve biyokütle olmak üzere sadece iki ana bileşenden oluşmaktadır ve biyokütlenin içsel solunum katsayısına (kd) bağlı olarak azalması toplam uçucu askıda katı madde üzerinden verilmektedir. Aktif çamur modellenmesinde, sistemde oluşacak çamurun giriş atıksu karakterizasyonuna önemli ölçüde bağlı olduğu ve bu nedenle de modelleme kapsamında sadece iki parametreden ziyade çok bileşenli aktif çamur modellenmesinin gerekliliği yapılan birçok çalışma sonucunda ortaya konulmuştur. Çok bileşenli aktif çamur modellemesinde, geleneksel sistemden farklı olarak, biyokütle heterotrofik biyokütle olarak tanımlanmakta ve biyokütledeki azalma içsel solunum katsayısına (bH) bağlı olarak ifade edilmektedir. Bu çalışma kapsamında, geleneksel aktif çamur modellenmesi ile çok bileşenli modelleme yaklaşımı detaylı bir şekilde incelenip, partiküler bileşenlerin oluşum ve davranışına etki eden unsurlar ele alınmış ve bu bağlamda aktif çamur sistemlerinde oluşan fazla çamur miktarlarının hesabında her iki modelleme yaklaşımı ile elde edilebilecek veriler değerlendirilmiştir. Geleneksel aktif çamur modellemesinde, sistemde oluşan bütün çamur için bir içsel solunum katsayısı verilmekte ve buna bağlı olarak çamur azalması hesaplanmaktadır. Buna karşılık çok bileşenli aktif çamur modellenmesinde ise çamurun bileşenleri tanımlanabilmekte ve içsel solunum katsayısı sadece heterotrofik biyokütle için tanımlanabilmektedir. Bu nedenle geleneksel metodla elde edilen çamur üretim miktarı çok bileşenli aktif çamur modellenmesinden elde edilen çamur miktarından daha az olarak hesaplanmaktadır. Bu bağlamda eğer geleneksel aktif çamur modellemesi kullanılarak çamur hesabı yapılacak ise, içsel solunum katsayısı (kd) sabit alınmayıp aktif biyokütleye bağlı bir değişken olarak ele alınmalıdır. Anahtar Kelimeler: Aktif çamur, bH, çamur oluşumu, içsel solunum katsayısı, kd, modelleme.Activated sludge systems rely on the removal of pollutants from wastewater through a series of biochemical reactions. The pollutants removed during biochemical reactions constitute mainly the biodegradable portion of the wastewater. During the design the activated sludge systems two significant parameters that should be considered are oxygen consumption and the excess sludge production in the system. In order to define these parameters accurately the particulate matter and the effect of the endogenous respiration process on these particular matter should be defined clearly. In order to design and operate an activated sludge system under steady state conditions it is important to characterize accurately the endogenous decay kinetics in addition to the growth kinetics of the biomass. Activated sludge systems can be modeled using two approaches namely traditional design approach and multi-component design approach. Traditional modeling approach mainly focus on the carbon removal. In this concept, the reaction kinetics were evaluated by means of two component system as substrate parameter that reflect all biodegradable organic compounds measured as Biological Oxygen Demand (BOD5) or Chemical Oxygen Demand (COD), and overall biomass parameter, X in addition to the oxygen parameter. In traditional modelling approach overall decrease in biomass concentration is traditionally defined by means of a first-order rate expression with respect to biomass concentration where, kd is the endogenous decay coefficient. Endogenous metabolism can be defined as the sum of all biochemical activities of microorganisms in the absence of utilizable extracellular compounds likely to serve as sources of energy and biosynthesis. In the expression of the microbial decay, biomass is defined in terms of the volatile suspended solids (VSS). It should be pointed out that in traditional modeling approach accurate description of the microbial decay process as well as the excess sludge production is restricted with the limitations of VSS parameter. Assessment of the amount of biodegradable substrate is one of the main concerns for wastewater treatment. Appropriate wastewater characterization with respect to organic carbon is a key issue in order to design and model an activated sludge system. Identification of different COD fractions with different biodegradation characteristics is one of the major milestone in the understanding of biological treatment of wastewaters. In multi-component mo-delling approach a detailed differentiation of soluble and particulate components, the endogenous decay process is introduced together with the concept of viability. This approach also differentiates active biomass from other particulate biomass components. In this approach, the components of the excess sludge can be classified as heterotrophic active biomass, XH, slowly biodegradable particulate COD, XS, particulate inert COD, XI and particulate metabolic products, XP. In activated sludge systems, the chosen hydraulic retention time is usually enough for the removal of the slowly biodegradable particulate COD, XS. Therefore, it is not necessary to take into account this parameter during the excess sludge calculations.  The microbial decay accounts for the fate of active heterotrophic biomass fraction of the activated sludge and becomes directly related to the endogenous respiration. This way, in multi-component modelling approach the endogenous decay coefficient, bH is defined as a function of the active heterotrophic biomass concentration, XH in the reactor in a first-order rate expression. In the traditional modelling approach the amount of the sludge decrease as a result of endogenous respiration can be calculated with an endogenous decay constant for all the sludge generated in the system. However, in the multi-component approach all of the constituents of the excess sludge can be defined separately and the endogenous decay coefficient can be attributed for only heterotrophic active biomass. In activated sludge systems, the amount of the excess sludge generation calculated with traditional modelling approach can be significantly different than the one calculated using multi-component modelling approach. If the sludge production calculated using multi-component modeling approach was used to calculate kd values in the traditional modeling approach, new kd values would be definitely lower than the constant kd value used in traditional modeling approach. Thus, it can be concluded that kd used in traditional modelling approach is not a constant value and varies as a function of the active fraction of the biomass. Keywords: Activated sludge, bH, excess sludge, endogenous decay coefficient, kd, modeling

Influence of pH on soluble substrate generation with primary sludge fermentation

Çalışma kapsamında pH’nın ön çökeltme çamuru fermentasyonu sonucu çözünmüş besi maddesi oluşumuna etkisi incelenmiştir. Bu kapsamda pH kontrollü ve konrolsüz koşullarda paralel deney setleri yürütülmüştür. 20°C sabit sıcaklıkta gerçekleştirilen ön çökeltme çamuru fermentasyonu sonucunda çözünmüş Kimyasal Oksijen İhtiyacı (KOİ) salımı ortalama 14 mg/L olarak hesaplanmıştır. Bu değere karşı gelen Uçucu Yağ Asiti (UYA) oluşumu ise 11.7 mg/L KOİ olarak hesaplanmıştır. Elde edilen bu değer, toplam biyolojik ayrışabilir KOİ içeriğinde %5 artışa karşı gelmektedir. Bu değere karşı gelen UYA üretimi ise ortalama 9.2 mg KOİ/L olarak belirlenmiştir. Fermentasyon sonrasında azot (0.4 mg/L) ve fosfor (0.1 mg/L) şeklinde besi maddesi salımlarının ihmal edilebilecek düzeyde olduğu gözlemlenmiştir. Yapılan bütün deneylerin sonucunda asetik asit üretimi toplam UYA’nın %45’inden fazlasını oluşturmuştur. Yüksek pH değerlerinde ve başlangıç UAKM değerlerinin arttığı durumlarda UYA’nın asetik asit içeriğinde düşüş, propiyonik asit ve C4-C5 asitlerinin oranlarında artış gözlenmiştir. Ön çökeltme çamurunda pH ayarının ve kontrolünün 5.5 ve 6 değerlerinde fermentasyon reaksiyonunu olumsuz yönde etkileyerek daha düşük konsantrasyonda UYA oluşumuna neden olduğu belirlenmiştir. Aynı zamanda pH ayarının ve kontrolünün 5.5 ve 6 değerlerinde asidojenik fazda gecikmeye ve reaksiyon süresinin uzamasına neden olduğu görülmüştür. Yüksek pH değerlerinde ise (pH 7.5) hidroliz fazında iyileşme saptanmış, ancak düşük pH değerlerinde olduğu gibi yüksek pH değerlerinin de asidojenik fazı olumsuz etkilediği gözlemlenmiştir. Çamurun başlangıç pH değerine yakın olan pH 6.5 ve 7 kontrollü setleri ise kontrolsüz setlerle aynı sonuçları verdiği için pH kontrolünün ekonomik anlamda uygulanabilir olmadığı belirlenmiştir. Anahtar Kelimeler: Besi maddesi giderimi, çözünmüş fermentasyon ürünleri, KOİ bileşenleri, kütle dengesi, uçucu yağ asitleri.A significant function of primary sludge fermentation is now regarded as the generation of soluble organic compounds, in particular Volatile Fatty Acids (VFAs), that are necessary for Biological Nutrient Removal (BNR) processes. VFAs are by nature readily biodegradable and therefore most suitable carbon source for denitrification. Their presence in sufficient quantity is also required for biological phosphorus removal systems. The merit of primary sludge fermentation is partial conversion of the settled Chemical Oxygen Demand (COD) into soluble and mostly readily biodegradable components and especially VFAs. In fact, pre-fermentation essentially sustains the first phase of anaerobic biodegradation. It is basically characterized by the generation of soluble COD. The study was undertaken to evaluate the effect of pH control on the generation of soluble fermentation products from primary sludge. The effect was tested by running parallel experiments under pH controlled and uncontrolled conditions. Primary sludge samples were taken from the Atakoy treatment plant, a small domestic wastewater treatment facility located in Istanbul, Turkey. The effect of pH on primary sludge fermentation was assessed using a series of experiments where the pH of the anaerobic reactor was sequentially adjusted and maintained at the following pH values: 5.5, 6, 6.5, 7, and 7.5 throughout the tests (controlled series). In fermentation experiments conducted at 20 ºC without pH control, the average soluble COD release was 14 mg per liter of wastewater treated, representing a potential increase of 5% in the biodegradable COD content of the primary sedimentation effluent. 27% lower VFA production was observed at pH 5.5, 18% at pH 6.0 and 12% at pH 7.5. The corresponding average VFA generation was 9.2 mg COD/L. Similarly, soluble COD generation was 10% lower at pH 5.5 and remained practically the same at pH 6.0. Increasing the pH to 7.5 resulted in 26% higher soluble COD generation indicating that higher pH favored hydrolysis but not acidification. Experimental assessment of VFAs composition indicated the predominance of acetic acid in fermentation products. In the majority of runs, the acetic acid fraction of the total VFA was over 45%. The average COD equivalent of VFAs was computed as 1.36 mg COD mg/L VFA for uncontrolled pH conditions. Increasing the pH level of primary sludge fermentation, the acetic acid percentage of the generated VFAs significantly decreased leading to the production of more propionic acid and C4?C5 (butyric, izobutyric, valeric ve izovaleric) acids. The highest percentage of the acetic acid production was around 70%, observed at pH 5.5. In experiments where pH was not controlled, the soluble TKN concentration released changed in the range of 75?175 mg/L with an average value of 97 mg/L, presumably depending on wastewater quality and resulting primary sludge characteristics. The soluble TKN represented on the average 2% of the VSS reduced, 4.6% of the soluble COD released and 5.7% of the VFA COD generated (0.057 mg N/mg CODVFA). Soluble P release was practically the same for experiments with pH controlled and uncontrolled runs with an average value of around 20 mg/L. This level corresponded to 1.3?1.4% of the VFA COD produced (0.013 mg P/mg CODVFA). Sludge fermentation experiments without pH control induced an average soluble COD release of 14 mg/L, which varied in the range of 8.4?19.6 mg COD/L. In terms of mass balance, this represents 5% of the biodegradable COD in the primary sedimentation effluent, which would be increased to 279 mg COD/L if the fermenter supernatant were to be added back to the effluent stream. The corresponding average VFA generation was calculated as 11.7 mg COD/L. Also, 0.6 mg/L of the nitrogen and 0.1 mg/L of phosphorus removed by settling were released with primary sludge fermentation. pH adjustment and control outside the initial pH of the primary sludge had a negative effect on VFA generation. Two general comments may be associated with the pH control (i) delay in acidification/ longer fermentation times (ii) lower VFA production. pH adjustment and control in the range of 5.5?6.0 had a negative effect on fermentation efficiency, mainly observed as lower VFA generation and delay in acidification and longer fermentation times. A similar negative effect was also observed when the pH was increased to 7.5. pH control in the 6.5?7.0 range, close to the initial pH of the primary sludge essentially yielded the same results and did not prove meaningful. Keywords: Nutrient removal, soluble fermentation products, COD fractions, mass balance, volatile fatty acids

Effect of primary sludge fermentation products on mass balance for biological nutrient removal system

Ön çökeltme çamuru fermentasyonunun kolay ayrışabilir organik madde oluşturma potansiyeli ve karbon, azot ve fosfor olmak üzere oluşan ön çökeltme ürünlerinin kütle dengesine olan etkisi, laboratuvar ortamında, 20°C sabit sıcaklıkta gerçekleştirilen kesikli deneyler ile incelenmiştir. Fermentasyon sonucunda, ön çökeltme çamurundaki uçucu askıda katı madde’nin %18’den %30’a varan oranlarda çözünmüş biyolojik ayrışabilir KOİ’ye dönüştürüldüğü gözlenmiştir. Fermentasyon sonrasında, çözünmüş KOİ’nin %85’inin uçucu yağ asitlerinden oluştuğu belirlenmiştir. Uçucu Yağ Asitlerinin (UYA) dağılımı, %47 asetik asit, %35 propiyonik asit, %9 bütirik asit ve %9 valerik asit olarak bulunmuştur. Toplamda oluşan UYA’ların KOİ karşılığı 1.38 mg KOİ/ mg UYA olarak hesaplanmıştır. Biyolojik fermentasyon sonrasında elde edilen ve toplam uçucu yağ asitlerinin yaklaşık yarısını oluşturan asetat, denitirikasyon ve biyolojik besi maddesi gideren sistemlerde çok önemli bir karbon kaynağıdır. Ön çökeltme çamurunun fermentasyonu sonucunda, çözünmüş azot üretiminde 0.7 - 3.6 mg NH4-N/g KOİ ve çözünmüş fosfor üretiminde 0.3 - 0.8 mg PO4-P/g KOİ dönüşüm oranları belirlenmiştir. Fermentasyon ürünlerinin, 0.4’ten 0.1’e doğru düşen anoksik hacmin proses hacmine oranı (VDN/V) çalıştırma koşullarına bağlı olarak ön çökeltme çıkış akımında denitrifikasyon potansiyelini (NDP) %10 - 20 arasında arttırdığı görülmüştür. Fermente olmuş ön çökeltme çamurunun üst fazının geri kazanılabilen kısmı, çıkış akımının kolay ayrışabilir KOİ içeriğini %5 ve aynı zamanda çözünmüş azot ve fosfor içeriğini de %2 arttırabilmektedir. Anahtar Kelimeler: Aktif çamur, besi maddesi giderimi, çökelebilen KOİ, fermentasyon ürünleri, KOİ bileşenleri, kolay ayrışabilir KOİ, ön çökeltme.Nutrient removal from wastewater is the main concern, especially in areas sensitive to eutrophication. Coastal zones open to touristic activities require wastewater treatment involving maximum nutrient control in order to maintain the delicate balance between excessive land use and desired water quality. Effective biological nitrogen and phosphorus removal requires full utilization of the internal pool coming from the process influent. In most cases, primary settling is the commonly prescribed step before biological wastewater treatment. It removes a significant portion of the influent COD, around 30 to 40% in domestic sewage. Primary settling step is sometimes omitted to increase the internal carbon potential in cases where the magnitude of the COD available in the influent is critically limiting for the desired level of nutrient removal. It is a fact that, the nature and the biodegradation rate of the available carbon are important factors for an efficient system operation. The COD fractionation identifying fractions with different biodegradation rates has been a milestone in understanding and modeling the substrate utilization, especially in nutrient removal. This study evaluates mass balance applicable to internal organic carbon pool of domestic sewage in terms of different COD fractions, with the specific objective of investigating the potential of simple (uncontrolled) primary sludge fermentation for the generation of readily biodegradable substrate. Fermentation products were also evaluated by means of respirometric analyses. Batch experiments were conducted, at 20°C constant temperature, to investigate the potential of primary sludge fermentation for the generation of readily biodegradable substrate and to evaluate the effect of primary sludge fermentation products on mass balance including nitrogen and phosphorus. Limited fermentation without pH control converted 17% of the particulate COD removed from sewage by means of primary settling to simpler soluble compounds, mainly to VFAs through acidification of the sludge in the fermenter. Experimental evaluation shows that fermentation converted between 18 to 30% of the initial volatile suspended solids (VSS) in the sludge into soluble biodegradable COD. Approximately 85% of the soluble COD is volatile fatty acids after the fermentation process. The net yield giving the fraction of the total COD in the primary sludge converted into volatile fatty acids (VFA's) varied in the range of 0.095 to 0.19 g VFA COD/g COD. The average fraction of the VFA's in fermentation is 47% acetic acid, 35% propionic acid, 9% butyric acid and 9% valeric acid. Based on these observations, the COD equivalent of VFA was calculated as 1.38 mg COD/mg VFA. The recoverable fraction of the fermented sludge supernatant was calculated to have the potential of increasing the biodegradable COD content of the primary effluent by 5% and the readily biodegradable COD in the effluent by 30%. The results clearly showed that the predominant fermentation products are always acetic and propionic acid, independent of the values of the operational parameters. The most important volatile fatty acids obtained during the biological fermentation process is acetate with approximately half of total VFA concentration, which is one of the most important carbon source for denitrification and biological nutrient removal processes. Ammonium and phosphate release during biological fermentation process were less than 1% and 2%, respectively. Therefore, the fermentation may be used directly in the BNR process without any separation of ammonia and phosphate. Primary settling reduced NDP of the raw sewage by 17 to 29%, approaching the level of the COD fraction removed as VDN/V ratio increases. Fermentation products provided an additional denitrification potential of around 2 mg N/L, increasing NDP of the primary effluent in the range of 10 to 20% depending on the gradual decrease of the operating VDN/V ratio from 0.4 to 0.1. Model simulation indicated that fermentation products could improve the biological P removal potential of the primary effluent reducing the effluent P concentration from 2.7 mg P/L to 0.6 mg P/L. The recoverable fraction of the fermented sludge supernatant may potentially increase the readily biodegradable COD content of the primary effluent by 5% and soluble nitrogen and phosphorus content by 2%. Keywords: Activated sludge, nutrient removal, settleable COD, fermentation products, COD fractionation, readily biodegradable COD, primary settling

Evaluation of aerobic stabilization of biological treatment sludges

Ülkemizde uygulanan çevre mevzuatı gerekleri, atıksu arıtma tesislerinde oluşan çamurun arıtımını ve nihai uzaklaştırılmasını zorunlu kılmaktadır. Evsel ve endüstriyel atıksu arıtma tesislerinden kaynaklanan arıtma çamurları üzerinde yapılan analizler sonucu, bu çamurların özellikle toplam ve çözünmüş organik karbon değerlerinin yönetmelikteki değerleri sağlamadığı ve çamurların bu parametreler bakımından tehlikeli atık sınıfında değerlendirmesi gerektiğini ortaya koymaktadır. Bu çalışma kapsamında Marmara Bölgesi’nde yer alan çeşitli evsel ve endüstriyel arıtma tesisinden kaynaklanan çamurların organik madde içerikleri değerlendirilmiş ve bu çamurların stabil hale getirilmesi için aerobik stabilizasyon işlemi uygulanmıştır. Aerobik stabilizasyon reaktörlerinde, 15 gün süreyle organik madde içeriklerinin değişimi UAKM, TOK ve ÇOK parametreleri esas alınarak ve evsel çamur numuneleri için zehirlilik parametresi de dikkate alınarak incelenmiştir. Elde edilen sonuçlara göre aerobik stabilizasyon sonunda genel olarak TOK değerleri azalırken, ÇOK değerlerinde çamur numunelerine bağlı olarak artış ya da azalmalar gözlenmiştir. İncelenen evsel çamurların ikisinde de TOK konsantrasyonu %50’den daha fazla azalırken ÇOK değerlerinde artış tespit edilmiştir. Endüstriyel atıksu arıtma çamurları arasında en yüksek TOK giderimi %62 ile Nevresim Endüstrisi çamurunda gözlenmiş olup, bu endüstri ÇOK giderimde de en yüksek verimi sağlamıştır. Elde edilen bu sonuçlar ışığında, aerobik stabilizasyon işleminin uygulanma aşamasından önce her tesis için ayrıca değerlendirme yapılması gerekliliğini ortaya koymuştur. Her çamur örneği için standartların sağlanması aerobik stabilizasyon ile mümkün olamamasına rağmen, bu işlemin bazı organik maddelerin giderilmesini sağladığı aerobik stabilizasyon sonrasında evsel numunelerdeki zehirliliğin tamamen giderilmesi ile ortaya konmuştur. Anahtar Kelimeler: Çamur, stabilizasyon, aerobik, evsel- endüstriyel-tehlikeli atık.The main waste-product of the biological wastewater treatment processes is the excess sludge which needs to be disposed properly to prevent the entry of the pollutants back into the water cycle, especially after the disposal of the wasted sludge cakes into the landfill area. During the adaptation period of European Union membership of Turkey, the increase in the number of both municipal and industrial Wastewater Treatment Plant (WWTP) due to the stringent new regulations for wastewater treatment will pose more significant sludge disposal and sanitation problems in the future for Turkey. Treatment and ultimate disposal of domestic and industrial wastewater treatment plant sludges is obligated according to the regulations in Turkey. Treatment sludges categorized in three different groups namely: inert sludge, non-hazardous sludge and hazardous sludge according to the characteristics of the sludge. The total organic carbon (TOC) concentration of the sludge itself and dissolved organic carbon (DOC) concentration in the eluent of the sludge are mainly used for this classification. The higher levels of TOC and DOC values qualifies the domestic and industrial wastewater treatment sludges as hazardous sludge. The principal objective of sludge treatment is its stabilization, that is a controlled decomposition of easily degradable organic matter resulting in a significant reduction of volatile suspended solids (VSS) content, a change of an unpleasant smell into an earthy one, and an elimination of sludge putrescibility. Aerobic biological stabilization at ambient conditions has traditionally been undertaken for the stabilization of treatment sludges originated from both domestic and industrial wastewater treatment plants. In this study the characterization of the different treatment sludges originated from domestic and industrial wastewater treatment plants in Turkey was investigated and the stabilization level of these sludges was evaluated by using aerobic stabilization process. The stabilization level of sludges was evaluated by monitoring the VSS, TOC and DOC content of the sludge. Moreover, ecotoxicological assays were conducted on domestic wastewater treatment plant sludges to observe the effect of stabilization on the toxicity. Respirometric and modeling studies were also performed to assess the decrease in the organic content of the domestic wastewater treatment plant sludge during aerobic stabilization. The results of analysis conducted on the sludge itself and sludge eluent indicated that the sludges are in hazardous nature. These results suggest that the treatment sludge generated from both domestic and industrial treatment plants have to stabilized before ultimate disposal. During the course of the aerobic stabilization experiments, VSS, TOC and DOC measurements were performed at the beginning and 15 days after the beginning (at the end of the stabilization experiment) in order to monitor the extent of VSS, TOC and DOC removal. Measured TOC and DOC concentrations during the stabilization experiments of studied treatment sludges did not show a consistent trend during the 15 days of stabilization. However, the stabilization of the industrial wastewater treatment plants sludges showed a paralel stabilization to the domestic sludge. However, it is important to conduct laboratory studies prior to the application of aerobic stabilization to a treatment plant on the case basis. The acute toxicity as EC20 (%) and EC50 (%) shows the toxic value in terms of effective concentrations (%) of tested solutions that result in 20 and 50% of bioluminescence decrease. The EC20 and EC50 values were found between 0.3 and 7.3% for the studied raw domestic sludges which is in accordance with the literature data. Significant decrease in the toxicity of domestic wastewater treatment plant sludges were observed at the end of the 15 days of aerobic stabilization. The evaluation of the results obtained in this study showed that aerobic stabilization could be an alternative for stabilization of sludges originated from domestic and industrial wastewater treatment plants. However, the organic content of the sludges mainly depend on the influent wastewater characterization of wastewater treatment plant which affects the stabilization performance. Sludge stabilization results indicate higher VSS, TOC and DOC removal efficiencies for domestic wastewaters compared to the industrial sludges. Although aerobic stabilization was not successful for the compliance with the standards in each case, the removal of toxicity exerted by sludges after 15 day-stabilization suggest that at least some toxic organic material has been succesfully biodegraded during the stabilization. In order to provide appropriate municipal and industrial sludge management in Turkey, more elaborate research and engineering experience should be gained. Keywords: Sludge, stabilization, aerobic, domestic- industrial-hazardous waste

Model based process optimization of enhanced wastewater treatment plants

Avrupa Birliği’ne uyum sürecinde ele alınan atık sorunu kapsamında, alıcı ortamlara yapılacak deşarjlarda konvansiyonal parametrelerin yanısıra azot ve fosfor (besi maddesi) parametrelerinin de belli standart değerlerin altına indirilmesi gerekli hale gelmiştir. Bu nedenle, “Kentsel Atıksu Arıtımı Yönetmeliği, 2006” ile uyum sürecinde olan ülkemizde azot ve fosfor standartları mevzuatımıza dâhil edilmiştir. “Kentsel Atıksu Arıtımı Yönetmeliği, 2006” kapsamında mevcut tesislerin besi maddesi giderimine yönelik olarak geliştirilmesi, yeni kurulacak tesislerin ise besi maddesi giderecek şekilde en uygun arıtma teknolojisi kavramı çerçevesinde boyutlandırılması gereklidir. Besi maddesi giderimine yönelik en uygun arıtma teknolojisi biyolojik prosesler, bunlar arasında en ekonomik çözüm ise aktif çamur sistemleri olarak tanımlanmaktadır. Bu çalışma aktif çamur tesislerinin, Avrupa Birliği normlarında performansını sağlayabilecek optimum tasarım ve işletme süreçlerinin değerlendirilmesini amaçlamaktadır. Bu kapsamda, bir örnek olarak ele alınan İstanbul Su ve Kanalizasyon İdaresi (İSKİ) Paşaköy İleri Biyolojik Atıksu Arıtma Tesisi’nde mevcut durumda atıksu karakterizasyonu ve sistem performansı deneysel olarak belirlenmiş, elde edilen bilgiler kullanılarak sürekli kullanıma uygun olacak model-bazlı tasarım ile işletme simülasyon programları hazırlanmış ve işletme optimizasyonu çerçevesinde çıkış besi maddesi konsantrasyonlarının düşürülmesi amacıyla işletme senaryoları oluşturularak önerilerde bulunulmuştur. Yürütülen senaryo analizleri ile, havalandırma tanklarındaki çözünmüş oksijen seviyelerinin uygun ayarlanması, tesisin geri devir denitrifikasyonu prensibi yerine A2O veya UCT tipi sistem şeklinde işletilmesi ile sistem veriminin arttırılabileceği ve dolayısıyla çıkış besi maddesi konsantrasyonlarının azaltılabileceği belirlenmiştir. Anahtar Kelimeler: İleri biyolojik atıksu arıtma tesisi, atıksu karakterizasyonu, model-bazlı tasarım, işletme optimizasyonu.The Urban Wastewater Treatment Directive published in the Official Gazette No. 26047 of 08.01.2006 was adapted from the “The Council Directive (91/271/EEC)” concerning urban waste-water treatment was accepted in European Union Countries, which imposes enforcements about the collection and treatment of wastewater. This directive requires that also nitrogen and phosphorus (nutrients) to be removed together with the conventional parameters. In this context, it is very important to follow and apply the technological advances while the harmonization of legislations in Turkey with European Union Standards. Mathematical models are frequently used for the design and optimum operation of wastewater treatment systems. In order to use the activated sludge models for the process design and control, it is crucial to understand the behavior of complex biological reactions under steady and dynamic conditions. The initial step for the use of models should be, a model calibration according to the data obtained from the treatment plant and an analysis of the behavior of the treatment plant under dynamic influent and environmental conditions (Vanrolleghem et al., 2003). After the calibration of the prepared model according to the operational conditions of the treatment plant, the model can be used for the optimization of the plant, meeting the effluent quality standards, minimizing operational costs and for developing appropriate process control strategies. On the other hand the effect of changes in the process conditions on the model stability should be taken into consideration (Insel et al., 2007). The aim of this study was to evaluate the optimum design and operational criteria of advanced biological wastewater treatment plants by applying international monitoring and evaluation mechanisms that will increase the performance to norms required in the European Union. Accordingly, İSKİ Paşaköy Advanced Biological Wastewater Treatment Plant (ABWWTP) was chosen as a model plant and in the first stage on influent wastewater characterization, chemical oxygen demand (COD) fractionation and performance of the activated sludge system were experimentally determined. In the second stage, using the dimensions of the İSKİ Paşaköy ABWWTP units and the experimentally determined operational parameters, model calibration studies were conducted. On this context, theoretical parameters of model-based design and operational simulation programs applied for the plant were evaluated. In the last stage of the study, for operational optimization, according to the results obtained from the experimental and simulation studies conducted at İSKİ Paşaköy ABWWTP, operational scenarios were developed and suggestions were made. In the scenario analysis reduction of effluent phosphorus and total nitrogen concentration was aimed and the effect of (i) the aeration system control, (ii) recycle denitrification (iii) influent VFA concentration was analyzed and the effect of (iv) different system configurations was evaluated. The results of statistical data analysis of wastewater characterization studies conducted at İSKİ Paşaköy Advanced Biological Wastewater Treatment Plant aiming nitrogen and phosphorus removal revealed that due to low influent Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), Total Phosphorus (TP) and Volatile Fatty Acids (VFA) concentrations, high efficiencies of biological phosphorus removal was not achievable. According to the scenario analysis performed for the treatment plant it has been concluded that it is possible to increase the removal efficiency of the system and achieve lower effluent total nitrogen and phosphorus concentrations by setting the dissolved oxygen levels to appropriate levels and operating the systems as an A2O or a UCT type system instead of a recycle denitrification system. It has been concluded that if the scenario analyses were applied it is not possible to meet the European Union Effluent Quality Standard of 1.0 mg/l for the phosphorus parameter. Experimental and model based studies have to be conducted for the installation of a fermentation process together with different system configurations that are required to meet the effluent quality standard by biological treatment. Keywords: Paşaköy wastewater treatment plant, wastewater characterization, model based optimization, process control

Effect of chemical treatment on soluble residual COD in textile wastewaters

The effect of chemical treatment on the magnitude of soluble residual COD in the biological treatment effluent is investigated for knit fabric finishing wastewater. Bentonite is selected for its potential to remove soluble COD together with color and particulate components. Chemical treatment using bentonite, when applied prior to biological treatment removes around 40% of the biodegradable as well as soluble inert COD initially present in the wastewater. As a chemical post-treatment, it acts as a polishing step, removing particulate matter and a minor portion of around 20% of the remaining soluble COD. These findings suggest chemical pre-treatment as a better alternative for the optimization of soluble COD removal

Scientific basis of dissolved organic carbon limitation for landfilling of municipal treatment sludge – Is it attainable and justifiable?

This study evaluated the scientific and technical basis of the dissolved organic carbon (DOC) limitation imposed on municipal sludge for landfilling, mainly for assessing the attainability of the implemented numerical level. For this purpose, related conceptual framework was analyzed, covering related sewage characteristics, soluble microbial products generation, and substrate solubilization and leakage due to hydrolysis. Soluble COD footprint was experimentally established for a selected treatment plant, including all the key steps in the sequence of wastewater treatment and sludge handling. Observed results were compared with reported DOCs in other treatment configurations. None of the leakage tests performed or considered in the study could even come close to the prescribed limitation. All observed results reflected 10–20 fold higher DOC levels than the numerical limit of 800 mg/kg (80 mg/L), providing conclusive evidence that the DOC limitation imposed on municipal treatment sludge for landfilling is not attainable, and therefore not justifiable on the basis of currently available technology

Comparative Assessment of Sludge Pre-Treatment Techniques to Enhance Sludge Dewaterability and Biogas Production

Effectiveness of ultrasonication, microwave technologies, and enzyme addition prior to anaerobic digestion is investigated using sludge samples taken from the secondary settling tank of a domestic wastewater treatment plant to improve methane production, enhance dewaterability characteristics of the sludge, and to reduce excess sludge. Microwave pre-treatment (1500 W, 10 min at 175 degrees C) results in better extra digester performance (compared to the control reactor) in terms of methane production (25 m(3) ton(-1) suspended solids (SS)) than ultrasound (no improvement) and enzyme pre-treatment (11 m(3) ton(-1) SS). While methane production is not improved as a result of ultrasonication pre-treatment (15 000 kJ kg(-1) SS), a noticeable increase (19%) is observed in the case of microwave pre-treatment. Higher compactibility values are obtained after ultrasonication and microwave application compared to the control (i.e., from 7.1 to 8.7 and 9.2%, respectively) before anaerobic digestion. Although ultrasonication and microwave application decrease the dewaterability of the raw sludge (capillary suction time (CST) from 827 to 1364 and 2290 s, respectively), similar dewaterability results are obtained at the end of the anaerobic digestion process for all pre-treated sludge samples. An economic assessment of this study shows that pretreatment with microwave results in more than 10-fold less net cost compared to the enzyme application.TUBITAK (Turkish National Scientific Council): Management of Domestic/Urban Wastewater Sludges in Turkey [108G167]; I.T.U Research Fund: Effects of Ultrasound Disintegration on Anaerobic Treatment of Domestic/Urban Treatment Sludges [34827]This study was supported by TUBITAK (Turkish National Scientific Council) under the project number 108G167: Management of Domestic/Urban Wastewater Sludges in Turkey and I.T.U Research Fund, Project No: 34827: Effects of Ultrasound Disintegration on Anaerobic Treatment of Domestic/Urban Treatment Sludges