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Kor-Bicakci G.,Technical University of Istanbul | Ubay-Cokgor E.,Technical University of Istanbul | Orhon D.,Technical University of Istanbul | Orhon D.,ENVIS Energy and Environmental Systems Ltd.
Bioresource Technology | Year: 2015

The study evaluated acute impact of tetracycline on the biodegradation of acetate by microbial cultures acclimated to different growth conditions. Two fill/draw reactors were operated to obtain acclimated cultures at sludge ages of 2 and 10. days. Acclimated biomass seeding was used in two series of batch experiments. The first run served as control and others were started with tetracycline doses of 100. mg/L and 400. mg/L. Parallel batch reactors were also operated for oxygen uptake rate (OUR) measurements. Acute impact was evaluated by model calibration of OUR, chemical oxygen demand (COD) and intracellular storage profiles. Exposure to tetracycline did not impair COD removal but induced a shift in acetate utilization toward polyhydroxybutyrate (PHB) storage. This shift was more pronounced for fast growing biomass; it identified itself both in related process kinetics and the modified stoichiometry between the magnitude of acetate directly used for microbial growth and converted to PHB. © 2015 Elsevier Ltd.

Insel G.,Technical University of Istanbul | Cokgor E.,Technical University of Istanbul | Tas D.O.,Technical University of Istanbul | Sozen S.,Technical University of Istanbul | And 2 more authors.
Water, Air, and Soil Pollution | Year: 2015

The study provided a critical appraisal of the extended aeration process as a single-sludge system for nitrogen removal, emphasizing its inherent deficiencies. For this purpose, the system was designed first using the prescribed procedure in the German practice, ATV A-131. The design used the basic data reported in different studies related to conventional characterization and chemical oxygen demand (COD) fractionation defining the biodegradation characteristics of domestic wastewater. A critical appraisal of the design was made with emphasis on the fate of biodegradable COD and oxidized nitrogen in the anoxic phase by process modeling and evaluation. The results obtained were evaluated using basic stoichiometry and mass balance for major nitrogen fractions. The A-131 design based on a total sludge age of 20 days defined a system with a hydraulic residence time of 1.2 days where half of the volume was operated under anoxic conditions; the effluent nitrate concentration was reduced to 8.3 mg N/L with an internal recycle (nitrate) ratio of 4.9. Model evaluation of the prescribed design indicated that oxidized nitrogen was totally consumed within the first 25-30 % portion of the anoxic volume. The remaining volume was forced to operate under anaerobic conditions, where no appreciable endogenous decay would occur. ATV A-131 procedure, relying on empirical coefficients and expressions, was neither consistent with process stoichiometry nor justifiable by modeling. Evaluations based on modeling and process stoichiometry revealed significant inherent weaknesses of extended aeration for providing a sustainable basis for nitrogen removal. © 2015 Springer International Publishing Switzerland.

Sayi-Ucar N.,Technical University of Istanbul | Sarioglu M.,MWH Global | Insel G.,Technical University of Istanbul | Cokgor E.U.,Technical University of Istanbul | And 2 more authors.
Water Research | Year: 2015

The study involved experimental observation and performance evaluation of a membrane bioreactor system treating municipal wastewater for nutrient removal for a period 500 days, emphasizing the impact of high temperature on enhanced biological phosphorus removal (EBPR). The MBR system was operated at relatively high temperatures (24-41 °C). During the operational period, the total phosphorus (TP) removal gradually increased from 50% up to 95% while the temperature descended from 41 to 24 °C. At high temperatures, anaerobic volatile fatty acid (VFA) uptake occurred with low phosphorus release implying the competition of glycogen accumulating organisms (GAOs) with polyphosphate accumulating organisms (PAOs). Low dissolved oxygen conditions associated with high wastewater temperatures did not appreciable affected nitrification but enhanced nitrogen removal. Dissolved oxygen levels around 1.0 mgO2/L in membrane tank provided additional denitrification capacity of 6-7 mgN/L by activating simultaneous nitrification and denitrification. As a result, nearly complete removal of nitrogen could be achieved in the MBR system, generating a permeate with no appreciable nitrogen content. The gross membrane flux was 43 LMH corresponding to the specific permeability (K) of 413 LMH/bar at 39 °C in the MBR tank. The specific permeability increased by the factor of 43% at 39 °C compared to that of 25 °C during long-term operation. © 2015 Elsevier Ltd.

Kor-Bicakci G.,Technical University of Istanbul | Pala-Ozkok I.,Technical University of Istanbul | Rehman A.,Albert Ludwigs University of Freiburg | Jonas D.,Albert Ludwigs University of Freiburg | And 3 more authors.
Bioresource Technology | Year: 2014

The study evaluated the chronic impact of sulfamethoxazole on metabolic activities of fast growing microbial culture. It focused on changes induced on utilization kinetics of acetate and composition of the microbial community. The experiments involved a fill and draw reactor, fed with acetate and continuous sulfamethoxazole dosing of 50. mg/L. The evaluation relied on model evaluation of the oxygen uptake rate profiles, with parallel assessment of microbial community structure by 454-pyrosequencing. Continuous sulfamethoxazole dosing inflicted a retardation effect on acetate utilization in a way commonly interpreted as competitive inhibition, blocked substrate storage and accelerated endogenous respiration. A fraction of acetate was utilized at a much lower rate with partial biodegradation of sulfamethoxazole. Results of pyrosequencing with a replacement mechanism within a richer more diversified microbial culture, through inactivation of vulnerable fractions in favor of species resistant to antibiotic, which made them capable of surviving and competing even with a slower metabolic response. © 2014 Elsevier Ltd.

Ozdemir S.,Technical University of Istanbul | Ucar D.,Technical University of Istanbul | Cokgor E.U.,Technical University of Istanbul | Orhon D.,Technical University of Istanbul | Orhon D.,ENVIS Energy and Environmental Systems Ltd.
Desalination and Water Treatment | Year: 2014

Abstract: The study evaluated the role of endogenous decay and microbial activity in aerobic stabilization of biological sludge. Biomass acclimated to acetate in a fill and draw reactor operated at a sludge age of 8 d was subjected to aerobic stabilization with no external substrate for a period of 70 days. Achieved volatile suspended solids reduction remained limited to around 43% after 30 days. The magnitude of endogenous decay, presumably responsible for stabilization, was quite different with bH values of 0.21/d and 0.06/d depending on the implemented respirometric procedure. Model profiles simulated with these values could not predict the observed VSS profile, mainly due to the accumulation of particulate metabolic products and residual organic cellular debris of disintegrated biomass during the process providing conclusive evidence that the total organic content of the stabilized biomass cannot be reduced below a critical level by means of biological processes. © 2013, © 2013 Balaban Desalination Publications. All rights reserved.

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