9 research outputs found
Metabolic and mathematical modeling of phosphate and glycogen accumulating organisms
Get PDFFosfor depolayan organizmalar (PAO) ve glikojen depolayan organizmalar (GAO) hücre içi enerji kaynakları dışında benzer metabolizmaya sahiptirler. Her iki organizmada anaerobik şartlarda asetatı hücre içinde PHA olarak depolarlar. PAO’lar hem glikoliz hem de Poly-P kırılması ile içsel enerjilerini elde ederken GAO’lar sadece glikoliz ile enerji sağlarlar.Bu çalışmada, fosfor ve glikojen depolayan organizma karışık kültürünün anaerobik koşullarda asetat alımı için bir metabolik model önerilmektedir. Anaerobik şartlar için önerilen biyokimyasal modele ait temel reaksiyon ifadeleri tanımlanmıştır. Önerilen model stokiyometrisi, esas alınan metabolik yolların organik karbon, enerji ve indirgeme kuvvetlerinin dengelenmesi suretiyle elde edilmiştir. Bu model, fosfor depolayan organizmaların PHA sentezini gerçekleştirmek üzere gerekli indirgeme kuvvetlerini glioksilat metabolik yolunu kullanarak elde edebilecekleri esasına dayanmaktadır. Bu nedenle, model değişken bir stokiyometriye sahiptir. Ayrıca bu çalışmada, biyolojik aşırı fosfor gideriminin mevcut matematik model, asetat için rekabet eden glikojen ve fosfor depolayan organizmaların mekanistik ifadesi ve daha sonra glikojen metabolizmasının modele ilave edilmesi ile geliştirilmiştir. Heterotroflar, ototroflar ve fosfor depolayan organizmaların tanımlandığı. ASM2d modeli esas alınmış, glikojen depolayan organizmaların prosesleri ve fosfor depolayan organizmaların glikojen mekanizmaları modele dâhil edilmiştir. Önceden geliştirilen metabolik kavram ve modellere dayanılarak karışık kültürler için yeni bir proses stokiyometrisi tanımlanmıştır. Geliştirilen matematik modelde yukarıda önerilen metabolik model ile uyumlu olmak üzere PAO’lar ve GAO’lar arasında asetatın paylaştırılması da tanımlanmıştır. Anahtar Kelimeler: Biyolojik aşırı fosfor giderimi, fosfor depolayan organizmalar, glikojen depolayan organizmalar, matematik model, metabolik model.It is now widely accepted that EBPR occurs as a result of the predominance of a group of bacteria, commonly called phosphate accumulating organisms (PAOs), with the capability of storing polyphosphate within the cell. EBPR is only sustained when the activated sludge system is operated in an anaerobic/aerobic sequence and the biomass is fed with short chain fatty acids (SCFAs) like acetate, during the anaerobic phase. In this phase, PAOs activate the metabolic tools to take up acetate and to store it as polyhydroxyalkanoates (PHAs), mainly polyhydroxybutyrate (PHB). PHA storage proceeds using the internal polyphosphate (poly-P) pool as energy source resulting in a release of orthophosphate (Pi). In the subsequent aerobic stage, PAOs grow on the internally stored PHA and take up orthophosphate for the replenishment of poly-P reserves that increase the P content of sludge. Higher P removal is achieved by withdrawing excess sludge with high P-content. Some observations given in the literature may be related to the presence of other types of bacteria, later called glycogen accumulating organisms (GAOs), that are capable of storing substrate under anaerobic conditions without using energy from P release. This implies the involvement of an energy source other than poly-P in EBPR systems, thus leading to a drastic decrease in the P released/substrate uptake ratio. It should be noted that during anaerobic acetate metabolism in GAOs, energy and reducing power are provided only by glycogen degradation without any poly-P involvement. This necessitates a metabolic pathway for the regeneration of the surplus NADH2 produced during glycolysis to maintain the redox balance inside the cell. This paper proposes a biochemical model for the acetate uptake by a mixed culture of PAOs and GAOs under anaerobic conditions. The proposed model is used to establish basic stoichiometric balances for organic carbon, ATP and reducing power, through appropriate metabolic pathways. PAOs and GAOs have similar metabolism except for their internal energy sources. Both of them uptake acetate anaerobically and store it as PHA. During PHA storage, the redox balance is regulated by the consumption of glycogen. Their metabolisms basically differ in the energy source utilized: While PAOs have the metabolic complement to use both poly-P cleavage and glycolysis as their energy supply; GAOs solely depend on glycogen for this purpose. Basic reactions of the metabolic model are given involving the same sequence for the two types of microorganisms, except for the formation of propionyl-CoA: Acetate uptake and activation to Acetyl-CoA, glycogen degradation to pyruvate, oxidative decarboxylation of pyruvate, formation of propionyl-CoA from pyruvate, formation of propionyl-CoA from acetyl-CoA, PHB synthesis, PHV synthesis and Poly-P cleavage. With this model, behavior of enhanced biological phosphorus systems is better evaluated in terms of the resulting overall stoichiometry of a mixed culture of PAOs and GAOs competing for the same substrate under anaerobic conditions. Besides, the modeling of enhanced biological phosphate removal is improved by introducing the mechanistic description of a mixed culture of glycogen and phosphate accumulating organisms competing for acetate, and glycogen metabolism of the latter. A new process stoichiometry is defined for the mixed culture based upon previously developed metabolic concepts and models. Thus, ASM2d is considered as a base-model since it basically embodies three different types of microorganisms: heterotrophs, autotrophs and phosphorus accumulating organisms describing the nutrient removal processes in activated sludge systems. In ASM2d, the phosphorus accumulating organisms, XPAOs takes up acetate in the availability of acetate and store only in the form of polyhydroxyalkanoate, XPHA with the stoichiometric ratio of HAc/PHA:1. In subsequent aerobic or anoxic conditions, the processes of XPAOs growth and the phosphate uptake utilize XPHA. The stoichiometry and processes for the autotrophs and heterotrophs are taken as the same in ASM2d, accordingly. Glycogen metabolism of PAOs and GAO metabolism included into the model, individually. It is assumed that under anaerobic condition, the PHA pool is replenished by the consumption of both external acetate and glycogen with the stoichiometry of YSA and 1-YSA, respectively by assuming PHA is equal to unit COD. Model development mainly relied on evaluation of critical coefficients based on proposed metabolic relationships related to the interactive growth of GAOs and PAOs in the mixed cultures. The model is able to describe the split of acetate utilization between PAOs and GAOs, accurately as predicted by related metabolic relationship. Keywords: Enhanced biological phosphate removal, phosphate accumulating organisms, glycogen accumulating organisms, mathematical model, metabolic model
Microbiological features of aerobic granular EBPR biomass
Get PDFTam-ölçekli konvansiyonel bir biyolojik arıtma tesisinden alınan floküler biyokütle ile başlatılan laboratuvar-ölçekli ardışık kesikli reaktörde, anaerobik/aerobik işletme ve fosfor ile besleme sonucu biyolojik aşırı fosfor giderimi (BAFG) elde edilmiştir. Çökelme süresinin kısaltılması (15 dak), ilk hacmin düşürülmesi (V0 1.8 L), hacimsel karbon yüklemesinin yükseltilmesi (1.41 kg KOİ/m3.gün) ve havalandırma kaynaklı kesme kuvvetinin artırılması (0.19 cm/s) ile, fosfor depolayan organizmalar (PAO) gibi yavaş-büyüyen organizmaların varlığı ile iyileşeceği öngörülen aerobik granülasyon süreci desteklenmiştir. Üstün çökelme özelliklerine (ÇHİ< 40-50 mL/g) sahip aerobik granüler BAFG biyokütlesi ile kararlı halde %92 karbon, %99 fosfor ve %78 azot giderimi elde edilmiştir. Sistemin biyokimyasal performansının izlenmesine paralel olarak, aerobik granüler BAFG biyokütlesinin mikrobiyolojik değerlendirmesi için morfolojik ve ekofizyolojik incelemeler gerçekleştirilmiştir. Hücre-içi poli-P (poli-fosfor) ve PHB (poli-hidroksi-bütirat) depolarının görsel tespiti için uygulanan Neisser ve Sudan Black B boyamaları sonucu, biyokütlenin morfolojik ve ekofizyolojik açılardan çeşitlilik gösterdiği saptanmıştır. Sistemde baskın tür, tanımlanmış morfolojileri ve ekofizyolojileri ile çubuksu PAO’lardır. Bunların yanısıra, morfolojik olarak glikojen depolayan organizmalara (GAO) benzeyen ancak ekofizyolojik özellikler açısından GAO-fenotipine uymayan tetrad/sarcina-benzeri hücreler (TFO) belirlenmiştir. Ayrıca, diplo-kokkoidlere, yoğun kokoid topluluklara, az miktarda filamentlere ve çeşitli protozoalara rastlanmıştır. Mikroskopik gözlemler niteliksel olmakla birlikte, sistemin biyokimyasal dönüşüm süreçleri bağlamındaki niceliksel performansı ile örtüşmektedir. Burada mikrobiyolojik özellikleri özetlenen aerobik granüler BAFG biyokütlesinin, mühendislik uygulamaları bağlamındaki üstün özellikleri nedeniyle, bu uygulamanın biyolojik atıksu arıtımında yeni ve gelecek vaadeden bir seçenek olacağı öngörülmektedir. Anahtar Kelimeler: Biyolojik aşırı fosfor giderimi, aerobik granüler biyokütle, morfoloji, ekofizyoloji.A lab-scale sequencing batch reactor (SBR) was inoculated with a floccular biomass obtained from a conventional full-scale biological wastewater treatment plant. Enhanced Biological Phosphorus Removal (EBPR) was obtained through application of a sequential anaerobic/aerobic operational mode together with the metabolic selection strategies of anaerobic feeding (with acetate as sole C-source) and supply of phosphate. The first strategy was applied to maintain absolute elimination of the feast period, where direct and fast growth on acetate was possible together with simultaneous C-storage; the former promoting growth and dominance of fast-growers having a negative impact on aerobic granulation. The merit of the anaerobic-feeding strategy was the possibility of directing the entire flux of externally available C-source to anaerobic C-storage mechanism, thus selecting the micro-organisms with the metabolic capability of taking up the acetate under anaerobic conditions, converting it to intracellular C-storage products (i.e., PHB: poly-hydroxy-butyrate), and then growing slowly on these storage materials at the aerobic phase; the metabolic processes described for the PAO (Phosphate Accumulating Organisms) and GAO (Glycogen Accumulating Organisms) phenotypes. The second strategy was applied to promote dominance of the PAOs in the system. Aerobic granulation process, suggested to be enhanced by the presence and dominance of slowly-growing microorganisms (like PAOs), was supported via lowering operationally determined settling time and initial reactor volume (TS decreased from 30 to 15 min and V0 decreased from 2.9 to 1.8 L), increasing volumetric COD load (from 0.24 to 1.41 kg/m3.d), and slightly increasing the shear rate due to aeration (vSAir increased from 0.14 to 0.19 cm/s). Monitoring the long-term steady state system performance in terms of biochemical conversion processes indicated that it was possible to secure high carbon, nitrogen and phosphorus removal efficiencies (92% COD removal, 99% EBPR, 78% overall N-removal) with the aerobic granular biomass upholding superior settling properties (SVI< 40-50 mL/g). Parallel to the evaluations with regard to biochemical system performance, morphological and ecophysiological examinations via conventional microscopy and chemical staining techniques were also executed to determine the microbiological features of the aerobic granular EBPR biomass, and to help confirm and interpret system performance with respect to presence of different microbial groups. Application of Neisser's and Sudan Black B stains to the biomass samples for visualization of intracellular volutin poly-P (poly-phosphate) granules and lipophilic PHB inclusions, respectively, revealed a microbial community rich in terms of morphological and eco-physiological traits. The dominant phenotype in the system was the PAOs with their conventional rod-shaped morphology and typical EBPR-physiology of being strongly poly-P(-) and strongly PHB(+) at the end of anaerobic phase, whereas being mostly poly-P(+) and partly PHB(-) at the end of the aerobic-period. In addition to the PAOs, tetrad/sarcina-like cells resembling the GAOs in terms of morphological features were also of significance. However, phenotypic properties of these microorganisms were not in line with those of the GAO-phenotype. Thus, the tetrad/sarcina-like cells, which were PHB(-) both at the end of the anaerobic- and aerobic-phases, were named as "TFOs" (Tetrad Forming organisms), a term for morphological differentiation, rather than "GAOs", a term related with functional properties. The PAOs and the TFOs co-existed with some other morphotypes like diplococci-shaped cells, staphylococci-like clustered populations, and a few filaments with an abundancy of 0-1 in accordance with subjective-scoring. Presence of some fixed protozoa like Vorticella campanula and Carchesium spp., typical for activated sludge systems, was also recorded. Despite the microscopic observations were qualitative, they correlated well with the quantitative biochemical performance data. Finally and from an engineering stand-point, operational flexibility of the SBR configuration, superior settling properties of granular biomass thus possibility of working with smaller reaction volumes or with shorter reaction times, and possibility of decreasing aeration related costs due to presence of an anaerobic phase, together demarcate the Aerobic Granular EBPR Technology as a promising biological wastewater treatment alternative enabling to decrease capital and operational costs while securing desired removal efficiencies. Keywords: Enhanced Biological Phosphorus Removal, aerobic granular biomass, morphology, eco-physiology
The effect of temperature and sludge age on COD removal and nitrification in a moving bed sequencing batch reactor
Get PDFThis 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
Biochemical basis and modeling of oxygen requirement in activated sludge
Get PDFBu 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
The effect of glucose on the enhanced biological phosphorus removal in a sequencing batch reactor
Get PDFBu çalışmada evsel atıksularda yaygın olarak bulunan glikozun biyolojik fosfor giderimi üzerine etkisi incelenmiştir. Laboratuvar ortamında glikozla beslenen anaerobik-aerobik Ardışık Kesikli Reaktörler (AKR) işletilmiş; çalışma süresince proses performansında ve mikrobiyal türlerde meydana gelen değişimler izlenmiştir. AKR’nin ilk döneminde Biyolojik Aşırı Fosfor Giderimi (BAFG) aktif olarak görülmüştür. Ancak reaktörün ikinci döneminde BAFG aktivitesi bozulmaya başlamış, son döneminde ise kabarma problemi ile karşılaşılmış ve koşullar iyileştirilemediği için işletilmesine son verilmiştir. AKR’nin başlangıç döneminde laktik asit oluşması ve oluşan laktik asitin anaerobik süreçte tüketilmesi sonucu fermentasyon bakterileri ile fosfor depolayan organizmaların (PAO) biyolojik fosfor giderimini birlikte gerçekleştirdiği belirlenmiştir. Laktik asit bakterilerinin glikozu laktik asite fermente ettiği ve PAO’ların anaerobik fosfor salınımından enerji sağlayarak oluşan laktik asidi polihidroksialkonata (PHA) dönüştürdüğü düşünülmüştür. Bu dönemdeki mikroskobik gözlemlerde poli-P depolayan kokların yoğun olarak görülmesi ve filogenetik analiz sonucunda Firmicutes filumuna ait Lactococcus türlerinin mikrobiyal topluluğun önemli bir bölümü olarak tespit edilmesi bu varsayımı desteklemektedir. Ayrıca oluşan PHA’nın %77’sinin 3-hidroksivalerat (3HV) olması ve anaerobik süreçte laktik asitin tüketilmesi laktik asitin PAO’larca kullanılan esas karbon kaynağı olduğunu kanıtlamaktadır. AKR’nin 29’uncu gününde glikojen depolayan organizmalar (GAO) olarak tanımlanan Candidatus Competibacter Phosphatis türü filogenetik analizde yoğun olarak gözlemlenmiş ve BAFG aktivitesinin bozulmasının bu türün baskı hale gelmesinden kaynaklandığı belirlenmiştir. 29’uncu günle birlikte glikojen tüketiminin önemli miktarda artması, glikoz tüketimine karşı salınan fosfor değerinin (0.07 mol P/ mol C) düşmesi sistemde GAO’ların aktif olduğunu göstermektedir. Anahtar Kelimeler: Biyolojik aşırı fosfor giderimi, fosfat depolayan organizmalar, glikojen depolayan organizmalar, glikoz.Since short chain fatty acid (SCFA) is believed to be the favorable substrates for biological phosphorus removal, the majority of the studies on enhanced biological phosphorus removal (EBPR), focus on the metabolism of acetate. However EBPR process can also occur successfully with organic substrates other than acetate. A wide range of organic substances like carboxylic acids, sugars and amino acids can be taken up anaerobically by phosphate accumulating organisms (PAO) enriched sludges but the metabolism of these organic substrates is not clear yet. Hence, the effect of carbon sources other than acetate on EBPR has to be considered deeply. The composition of the organic substrates in domestic wastewater varies remarkably among countries and/or wastewater treatment plants and glucose is a significant simple sugar found widely in wastewaters with an important role in biochemical pathways. EBPR mechanism with glucose found wide interest but results of the reported studies in the related literature are not consistent with each other indicating many different mechanisms of anaerobic uptake and storage of glucose can act in favor of, or against EBPR. The objective of this study was to investigate the effect of glucose feeding on the performance of the enhanced biological phosphorus removal process. The effect of glucose on process performance and microbial community was studied by operating laboratory-scale alternating anaerobic-aerobic sequencing batch reactors (SBRs). The SBR fed with glucose as sole carbon source achieved biological phosphorus removal but deteriorated gradually along the operation of the reactor. During the good EBPR period (day 9), 63% of the glucose fed to the reactor was metabolized within 10 minutes of the anaerobic period and a rapid increase in glycogen concentration observed which showed the conversion of external glucose into glycogen. Lactate and acetate were detected in the supernatant and pH was dropped upon the glucose addition which indicated that part of the glucose was fermented to mainly lactate and to small amount of acetate. The results of the molecular analysis performed during this period showed the presence of many diverse fermentative bacteria proving clearly the glucose fermentation. It is assumed that lactate was the major substrate converted to polyhydroxyalkaonates (PHA) by PAOs due to the significant amount of 3-hydroxyvalerate (3HV) formation and low level of glycogen consumption under anaerobic conditions. But if lactate was the only substrate uptaken by PAOs to be converted to PHA, lactate should be metabolized to acetyl-CoA and propionyl-CoA equally to maintain the redox balance which will result in formation of 3HV and 3-hydroxy-2-methylbutyrate (3H2MB) only. However 12% of the PHA was consisted of 3-hydroxy-2-methylvalerate (3H2MV) and small amount of glycogen was also consumed. Hence glycogen consumption together with lactate changed the ratios of acetyl-CoA and propionyl-CoA metabolized which could explain the formation of 3H2MV. Thus PHA was thought to be derived not only from the lactate but also from glycogen and from small amount of acetate fermented from glucose. The EBPR activity was remarkably deteriorated on the 29th day of the SBR operation. The occurrence and predominance of Candidatus Competibacter Phosphatis detected on day 29 sludge was significant. 17% of the g-Proteobacteria were closely related to the Candidatus Competibacter Phosphatis. They were postulated as putative glycogen accumulating organisms (GAO) as they compete with PAOs. The dominance of GAOs detrimentally affects phosphorus removal by out-competing the PAOs since glycogen can be used as the energy source and reducing power for PHA accumulation reducing the dependency on polyphosphate degradation for energy supply. The significant increase in glycogen consumption was in accordance with the predominance of GAOs on day 29. The decrease in the total phosphorus content of the sludge (4.3% of the MLVSS) and phosphate release/carbon uptake ratio (0.07 mol P/mol C) indicated clearly the abundance of GAOs over PAOs. SBR was ended due to the bulking problem at the 54th day of operation. In the beginning of the operation of the SBR, the fermentation products were depleted at the end of the anaerobic period but in the latter phase of the operaion significant amounts of fermentation products were detected at the end of the anaerobic period and these fermentation products probably stimulated the growth of filamentous bacteria. The lactate accumulation at the end of the anaerobic phase was related to the abundance of GAOs over PAOs. Keywords: Enhanced biological phosphorus removal, phosphate accumulating organisms, glycogen accumulating organisms, glucose
Çapraz akışlı filtrasyon kullanan aktif çamur sistemleri ile tuzlu atıksulardan azot giderimi
Get PDFGaz rezervlerinden sondajlama işlemi ile çıkarılan ham doğal gaz, çeşitli hidrokarbonlar (etan, propan, butan, pentan), su buharı, H2S, CO2, helyum, azot gibi bileşenleri içermektedir. Ham doğal gazın bu bileşenlerden arındırılarak saf metanın elde edilmesi işlemi sonucunda yüksek konsantrasyonda amonyum azotu ve tuzluluk içeren atıksu oluşturmaktadır. Çalışma kapsamında, doğal gazın üretimi sonucunda oluşan atıksuda, tuzluluğun nitrifikasyon ve denitrifikasyon proseslerine etkisinin araştırılması hedeflenmiştir. Bu amaçla, çalışmada, laboratuvar ölçekli sürekli beslenen çapraz akış filtrasyonlu aktif çamur prosesi kullanılmıştır. Özellikle son yıllarda, membran biyoreaktörlerin nutrient gideriminde kullanılması ile ilgili çalışmalar ve uygulamalar gün geçtikçe artmaktadır. Membran biyoreaktörler, düşük hidrolik bekletme sürelerinde ve uzun çamur yaşlarında, aktif çamur sistemlerinde sıkça rastlanan biyokütle yıkanması problemine neden olmadan işletilebilmektedir. Yüksek yükleme potansiyeline sahip olması, sistemden atılacak atık çamurun minimum olması, kabarma problemi olmadan yüksek verimde işletilebilmesi başlıca avantajlarıdır. Bu çalışmada aşırı tuzlu atıksudan, çapraz akışlı filtrasyon kullanan aktif çamur sistemleri ile toplam azotun yüksek verimde giderilebileceği gösterilmiştir. Membran biyoreaktörlerin uzun çamur yaşlarında ve yüksek biyokütle konsantrasyonlarında işletilebilmesi sayesinde aktif çamur, aşırı tuzlu atıksuya alıştırılarak halofilik (tuz seven) mikroorganizmalar ortamda baskın hale gelebilmiştir. Bunun sonucunda da tuzluluğun azot giderme verimi üzerine olumsuz etkisi gözlemlenmemiştir. Çalışma kapsamında, toplam azot giderimi için optimum koşullar, çevrim içi analizler ve kesikli deneylerle belirlenerek toplam azot giderimi % 95 verimle sağlanmıştır. Anahtar Kelimeler: Çapraz akışlı filtrasyon, denitrifikasyon, nitrifikasyon, tuzluluk.Natural gas production is generally based on the purification of methane from hydrocarbons (ethane, propane, butane, pentane), H2S, CO2, helium and nitrogen after drilling from the gas well reservoirs and during the purification process of raw natural gas, wastewater containing high concentration of ammonium nitrogen and salinity is generated. The objective of this study was to investigate the effect of salinity on the nitrification and denitrification processes. Within this context the optimum conditions were determined for complete nitrogen removal in saline wastewater by an activated sludge process with cross-flow filtration. In recent years, membrane bioreactors have been widely used for nutrient removal. Biomass seperation membrane bioreactors can be operated at low hydraulic retention times and long sludge ages without the problem of biomass washout, which is very common in activated sludge systems. They enable complete solids removal from effluent, have a capability of high loading, produce low/zero sludge, effectively can be operated without sludge bulking problem. In this study, a bench scale continuous feeding activated sludge process with cross-flow filtration was used. Polysulfon ulta-filter with nominal molecular weight cut-off value of 200000 Da and filtration area of 35 cm2 was used for biomass seperation and nitrification-denitrification was performed with intermittent aeration in the reactor vessel. The gas well wastewater containing 3% NaCl similar to marine water and 200 mg/l NH4-N was seeded with activated sludge provided from a fish processing plant. The operational conditions of the reactor was set up as 6 hours intermittent cycle, 3 hours of anoxic and 3 hours of aeration with 10 minutes of feeding at the beginning of the anoxic period and the effluent was withdrawn during the aeration period and the system was run with NH4-N loading rate of 0.1 g/l-day, and methanol loading rate of 0.19 g/l-day in the starting phase. Nitrification and denitrification performance in highly saline wastewater was determined by carrying out batch tests. Nitrification rate was gradually increased from 94 mg N/l.day to 370 mg N/l.day and stable nitrification was obtained up to 70th day of the study. The performance of the reactor on the 50th day was studied and it was observed that nitrate concentration during nitrification period increased to a stable value within 90 minutes therefore the intermittent cycle was decreased to 4 hours; 2 hours anoxic and 2 hours aeration, which lead to an increase in flow and in nitrogen loading rate to 750 ml/day and 0.15 g/l.day respectively. In the first phase of this study, methanol was added in theoretical value of stoichiometric equation of denitrification but it was observed that this value was not enough for complete denitrification. Thus addition of methanol was increased to 1.5 times of its theoretical value. The batch denitrification tests showed that methanol as an external carbon source worked efficiently whereas denitrification performance of the original activated sludge was not good with methanol. Nitrogen removal efficiency increased from 53% to 90% and denitrification rate increased from 22 mg/l.day to 254 mg/l.day on the 37th day and reached to 414 mg/l.day on the 57th day of the study due to the addition of methanol. So it was concluded that halophilic (salt-loving) microorganisms became dominant within the acclimation to saline environment. Batch nitrification tests also proved the acclimation of the activated sludge to highly saline wastewater, as the nitrification rates were better than that of the activated sludge in low salinity wastewater. In literature, it was emphasized that denitrifiers possessed a higher tolerance capability and better adaptation to high salinity when it is compared with the nitrifiers which was also observed in this study that nitrification process was more sensitive to salinity than denitrification. In the last phase of this study, the nitrogen load was increased from 0.1 to 0.15 g/ l.day and the sludge was removed daily with a sludge age of 40 days. It was observed that in this period the mixed liquor concentrations became stable with a higher ratio of VSS/SS and the removal efficiency of total nitrogen reached to 95%. Consequently, it was demonstrated that the complete nitrogen removal in highly saline wastewater can be accomplished with cross-flow filtration due to the capability of operating at high nitrogen loading and longer sludge ages. Keywords: Cross-flow filtration, denitrification, nitrification, salinity
Effect of primary sludge fermentation products on mass balance for biological nutrient removal system
Get PDFÖn 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
Modelling of inert soluble product formation in the activated sludge process
No full textTez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1988Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 1988Bu çalışmada aktif çamur sistemlerinde çözünmüş ürün oluşumu mekanizmasını da içeren bir matematik model geliş tirilmiştir. Birinci bölümde, aktif çamur sistemlerinin tasarım ve işletilmesinde model kullanmanın önemi vurgulanmış, kon- vansiyonel modellerin özellikle çıkış KOI konsantrasyonunun bulunmasında yetersiz kalması nedeniyle yeni bir model ge liştirilmesi gereği ortaya konmuştur. Çalışmanın amaç ve kapsamı açıklanmıştır. ikinci bölümde, aerobik arıtmanın temel prensipleri ele alınmış ve aktif çamur kinetiği ve stokiometrisi hak kında daha önce yapılmış çalışmalar değerlendirilmiştir. Bu bölümde özellikle aktif çamurda çözünmüş ürün oluşumu süreci üzerinde durulmuş, ürünlerin yapıları ayrıştırıla- bilirlikleri araştırılmış ve mikrobiyoloji literatüründe ürün oluşumu için verilen kinetik ifadelerin aktif çamura uygulanabilirliği tartışılmıştır. Üçüncü bölümde, aktif çamur modelleri tarihsel ge lişimi içinde ele alınmış ve her modelin vurguladığı ve ihmal ettiği konular açıklanmıştır. Dördüncü bölümde,. aktif çamurda substrat ve biyokit- le ölçümünde kullanılan parametrelerin anlamı üzerinde durulmuş ve bunların model değişkenleri olan büyüklükleri ne derece yansıttığı tartışılmıştır. Aktif. çamur modelle rinde kullanılan kinetik katsayıların hesaplanma yöntemleri ele alınmış ve bulunan sabitlerin ölçüm yöntemlerinden nasıl etkilendiği araştırılmıştır. Beşinci bölümde, bu çalışmada geliştirilen "çözünmüş kalıcı ürün oluşumu" modeli anlatılmış ve çeşitli tipteki reaktörler için belirlenen model denklemlerinin çözümü verilmiştir. Altıncı bölümde, model yardımı ile elde edilen so nuçların bir değerlendirmesi yapılmış ve son bölümde çalış mada elde edilen sonuçlar özetlenmiştir. The activated sludge process, which dates back to the dawn of wastewater treatment, still possesses a central place in wastewater engineering. The design of activated sludge systems, like other engineering systems, call for the utili zation of models. Design of an appropriate activated sludge system for a given wastewater/treatment goal combination, or assessment of probable behaviors of a number of design alter natives under various operational, conditions are also realized through the use of mathematical models. The mathematical model used can be an empirical model obtained by statistical evaluation of data from physical models such as bench or pilot scale reactors, as well as a mechanistic model based upon the fundamental theoretical information concerning the prominent phenomena within the system. Generally speaking, mechanistic models have an obvious advantage over the empirical models, in that the latter may be expected to predict the system behavior with some accuracy, only within the range of conditions under which the data for model construction were collected. Due to restrictions on time and money, it is practi cally impossible to experiment and evaluate all possible solutions with physical models. This necessitates the use of mechanistic mathematical models which afford a quick and inexpensive means of predicting system behavior and assessing various design alternatives under a wide range of operational conditions, and thus singling out a few alternatives which appear most suitable. These selected alternatives can be subjected to further experimentation with physical models. - xiv Predominantly mechanistic models, assuming a direct relationship betwen growth and substrate removal, and employing the concept of rate limiting substrate have been used exten sively since the early 70's. The common conceptual structure underlying these models is that growth is exclusively supported by the original organic substrate in the influent and that the residual organic material in the effluent is the original substrate itself. This conceptualization leads to the prac tical result that the rate limiting substrate concentration in the effluent from a competely mixed reactor is independent of the influent concentration. However, numerous observations on pilot and full scale plants have clearly shown that the influent substrate concentrations do influence the effluent quality, both measured as COD or TOC. Difficulties associated with the measurement of biomass and the organic content of wastewaters have traditionally caused much inconvenience and confusion perhaps to the extent of causing some hindrance in the development of the activated sludge theory. The routinely used collective analytical para meters (e.g. SS, VSS, BOD, COD, TOC) do not correspond to the system variables (i.e. biomass and substrate) of the Monod- Herbert type models. This lack of correspondence is one of the important factors which obscure the validity of model results. BOD, COD, and TOC are the three extensively employed collective parameters for.the measurement of the organic content of wastes. Among these, the COD is the only parameter which enables making materials balance among substrate, bio mass and oxygen consumption in terms of electron equivalents. Another merit of the COD is its being both cheap and quick. With those advantages, COD has an ever increasing importance in academic studies, in the design and operation of treatment plants, and as a control parameter in quality control activities by the authorities. The adoption of COD, by the authorities, as a quality limiting parameter for the secondary effluents make utilization of COD orientated models obligatory i.e. models in which all phenomena having a significant effect on the variation of COD within the system are represented by suitable rate equations. A mechanistic mathematical model has been developed xn rnis study, which is designed to predict the soluble CUD concentration in the activated sludge plant effluent. In the course of model development, the system components and phe nomena associated with organic matter removal and their inter actions have been revised with specific emphasis on soluble inert product generation. - xv - Soluble inert product generation by the activated sludge systems, although evidenced or implied by the data from almost all relevant experimental studies, has been some what ignored and definitely not regarded as a phenomenon worth being represented in activated sludge models. However, as clearly reported by several workers, particularly in the last two decades, the organic substances in the activated sludge effluents are totally different from those in the influent, and are mainly metabolic products of the biomass. This fact, to a great extent explains the inability of a whole genus of models, having as their backbone the rate limiting substrate concept, in simulating activated sludge system behavior. For theoretical accuracy and consequentially for better prediction of activated sludge behavior, it seems necessary to incorporate inert product generation into the models. This necessity becomes more pronounced with increasing adoption of COD as a control parameter. The model developed incorporates six system components and three processes. The components are soluble substrate (Ss), active biomass (X^). particular substrate (Xg), soluble inert product (Sp), particular inert product (Xp), and oxygen (Sq ). The processes are growth, decay (loss of activity) and hydrolysis. The substrate removal and inert product formation processes are expressed in terms of associated processes employing suitable stoichiometric coefficients. Methods have been proposed for the measurement of model components and parameters. In the model, distinction has been made between soluble and particular substrate. According to the so called bisub- strate models, the soluble substrates can readily be utilized for growth whereas the particular substrate has to undergo a prior hydrolysis step before it becomes available for growth. The utilization of soluble substrate is expressed in Monod kinetics, with S denoting the bulk concentration. Utilization of particular substrate is expressed following the above men tioned hydrolysis hypothesis of the IAWPRC Task Group. Loss of activity and biomass are modeled in accordance with the death-regeneration concept instead of that the endogenous respiration. Activity loss of biomass leads to conversion to particular substrate and then to soluble sub strate via hydrolysis. The rate of hydrolysis is expressed by a saturation type expression. Oxygen consumption occurs only during growth. Oxygen consumed by regrowth on secondary substrate corresponds to - xvx - endogenous oxygen consumption of the endogenous respiration approach. The release into the bulk solution of numerous organic substances with varying biodegradabilities, by the micro organisms, is represented in the model by a hydrolysis rate expression. Although quite a many of the hydrolysis products are biodegradable, some are practically non biodegradable within the retention times normally employed in secondary treatment plants. Thus, soluble inert product formation is assumed in the model to be directly proportional to hydrolysis. Alternatively, a different version of the model has been constructed, with the soluble inert product generation being proportional to growth, and consequences of two different assumptions on the model results has been evaluated. Sensitivity analyses of the model parameters have been made. Several sets of simulations have been made for different reactor types, and their efficiencies defined according to various criteria have been compared. The results are sum marized in Chapter VII. The greater part of the soluble organic materials in the effluent from an activated sludge plant are microbial products,<*and hence they differ in character from the organic materials in the influent. Since the product formation has a pronounced effect on the effluent substrate concentration, Monad-Herbert models which. merely represent the substrate removal mechanism can only inaccurately predict the substrate removal efficiencies. The soluble microbial products show a wide spectrum of structures and molecular weights. Intermediary products of energy metabolism are low molecular weight compounds, and this type of products formation is not effective in continuous systems, not considering delays due to causes such as bio- synthetic restrictions. Most of the hydrolysis products are also readily biodegradable. Products which are not degraded within the range of detention times normally employed in activated sludge systems are considered to be biologically inert, and designated as inert soluble product (Sp). The Sp production is modeled in two alternate approaches, viz. as being hydrolysis related and growth related. An activated sludge model is formulated, taking into account the soluble inert product formation, and the model is employed to assess the relative significance of variables - xvii - that directly affect the effluent soluble COD concentration. It is found that the Sp formation is proportional to the active biomass in the reactor and is therefore related with influent soluble substrate concentration (Sgo) an^ biological solids retention time 9q, which in turn determine the active biomass concentration. The inert soluble product formation model explains the dependence of the effluent COD concentration on the influent COD concentration in a completely mixed reactor. Theoretically, the effluent COD concentration is independent of the influent concentration, however, since the inert product formation is influenced by the influent substrate concentration, this in turn influences the effluent soluble COD concentration. For every influent substrate concentration there 0is an optimum biological solids retention time which results in a minimum effluent soluble COD. This implies that the sludge age should not be held unnecessarily long, provided that the settling properties are also given due consideration. A completely mixed reactor can be more efficient than a plug flow reactor, when efficiency is defined in terms of soluble COD removal. However, a plug flow reactor is more efficient when the oxygen demand of the wasted sludge. is also taken into account.DoktoraPh.D
