Person: SEMERCİ, NESLİHAN
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SEMERCİ
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NESLİHAN
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Publication Metadata only Monitoring of population shifts in an enriched nitrifying system under gradually increased cadmium loading(ELSEVIER SCIENCE BV, 2008) ÇALLI, BARIŞ; Mertoglu, Bulent; Semerci, Neslihan; Guler, Nuray; Calli, Baris; Cecen, Ferhan; Saatc, Ahmet MeteThe changes in nitrifying bacterial population under cadmium loading were monitored and evaluated in a laboratory scale continuous-flow enriched nitrification system. For this purpose, the following molecular microbiological methods were used: slot-blot hybridization, denaturing gradient gel electrophoresis (DGGE), real-time PCR followed by melting curve analysis, cloning and sequence analysis. The initial cadmium concentration was incrementally increased from 1 to 10mg/l which led to a drop in ammonia removal efficiency from 99 to 10%. inhibition was recovered when cadmium loading was stopped. During the second application of cadmium. nitrifying population became more tolerant. Even at 15 mg/l Cd, only a minor inhibition was observed. To investigate the variations in ammonia and nitrite oxidizing bacteria populations in a period of 483 days, ammonia monooxygenase (amoA) and 16S rRNA genes-based molecular techniques were used. An obvious shift was experienced in the diversity of ammonia oxidizers after the first application of 10mg/l Cd. Metal-tolerant ammonia oxidizing species became dominant and the microbial diversity sharply shifted from Nitrosomonas and Nitrosococcus sp. to Nitrosospira sp. which were observed to tolerate higher cadmium loadings. This result indicated that the extent of nitrification inhibition was not only related to the metal concentration and quantity of microorganisms but also depended on the type of species. (C) 2008 Elsevier B.V. All rights reserved.Publication Metadata only Inhibition of respiration and distribution of Cd, Pb, Hg, Ag and Cr species in a nitrifying sludge(ELSEVIER, 2010) SEMERCİ, NESLİHAN; Cecen, Ferhan; Semerci, Neslihan; Geyik, Ayse GuelThe study investigated the inhibitory effects of the heavy metals Cd, Pb, Hg, Ag and Cr (as Cr3+ and Cr6+) on a nitrifying sludge. The aim was to assess the IC50 concentrations leading to 50% inhibition. The method is based on respiration of nitrifying sludge in the presence of these metals. Both O-2 consumption and CO2 production were taken into account. The order of the inhibitory effect was Ag > Hg > Cd > Cr3+ = Cr6+. Metal speciation was calculated in terms of free metal, inorganic metal complexes and bound metal. Pb largely precipitated and 50% inhibition was never reached. Ag was always in the form of the free ion or labile complexes. Hg had apparently a lower toxicity than Ag, since most of it was initially highly complexed with ammonia. Cd was present in the form of free ion and complexes which caused inhibition although a large part of them were precipitated. The inhibitory effects of trivalent chromium (Cr3+) and hexavalent chromium (Cr6+) were similar. The latter was present in the form of the anion CrO42- and was not taken up by biomass. The study highlighted that IC50 values alone do not have an explanatory power of inhibition unless speciation is also considered. (C) 2010 Elsevier B.V. All rights reserved.Publication Metadata only Effect of continuous Cd feeding on the performance of a nitrification reactor(SPRINGER, 2009) SEMERCİ, NESLİHAN; Semerci, Neslihan; Cecen, FerhanThe inhibitory effect of Cd on nitrification was investigated in a continuous-flow system with enriched nitrifying bacteria. The maximum specific ammonium utilization rate and the half-saturation constant were found as 671 mg NH4-N/g VSS day and 0.48 mg/l, respectively. In the case of continuous Cd input at 1 and 2.5 mg/l, nitrification was inhibited by 30% and 47%, respectively. Inhibition ranged from 20% to 40% and no further increase in inhibition was exhibited in new runs except at 10 mg/l influent Cd. At 10 mg/l influent Cd, specific ammonium utilization and nitrate production rates were inhibited by 90%. On the contrary, a serious nitrite accumulation was not observed during this period. When Cd feeding was stopped, recovery from inhibition was observed after 37 day which was seen by the improvement in ammonium utilization and nitrate production rates. A shift in microbial population from the initial Nitrosomonas sp. to the Cd-tolerant Nitrosospira sp. was observed in the recovery period from severe Cd inhibition. After the domination of Nitrosospira species, redosing at 10 mg/l and then at 15 mg/l did not affect the performance as before.