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SEMERCİ, NESLİHAN

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SEMERCİ

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NESLİHAN

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2007 - 200922010 - 20191
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Subject: HEAVY-METALS ×

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    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 Mete
    The 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.
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    Importance of cadmium speciation in nitrification inhibition
    (ELSEVIER, 2007) SEMERCİ, NESLİHAN; Semerci, Neslihan; Cecen, Ferhan
    In this study, the influence of Cd speciation on nitrification inhibition was investigated in batch suspended growth activated sludge systems which contain biomass enriched in terms of nitrifiers. For this purpose, parallel measurements of specific oxygen uptake rates (SOUR), ammonium utilization rates (q(NH4)-N) and Cd uptake were carried out. Cd speciation was adjusted with a strong complexing agent, ethylenediaminetetraacetic acid (EDTA). Free and biosorbed Cd concentrations were theoretically determined by using the MINEQL+ program and the Cd adsorption constant, whereas labile Cd was determined by voltammetric measurements. The presence of EDTA decreased nitrification inhibition by lowering the available Cd species and by preventing biosorption of Cd. Almost complete recovery from inhibition was attained by EDTA addition to nitrifying bacteria which were inhibited by Cd for a certain time. These results suggested that the sites sensitive to Cd were rather located on the surface of bacterial cell than inside. Nitrification inhibition depended on equilibrium concentrations of free (Cd2+), labile (Cd-volt) and biosorbed Cd (Cd-volt) and did not correlate with the total Cd. The measurement of labile metal by voltammetry in inhibition studies is a promising approach since it is easy to apply in practice. (C) 2007 Elsevier B.V. All rights reserved.
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    Phosphorus recovery from sewage sludge ash with bioleaching and electrodialysis
    (ELSEVIER SCI LTD, 2019) ÇALLI, BARIŞ; Semerci, Neslihan; Kunt, Busra; Calli, Baris
    Phosphorus is an essential element for all living organisms and for plants. However, phosphate rock, which is the main source of phosphorus, is limited and thus it must be recovered from secondary sources like sewage sludge ash (SSA). SSA is one of the most promising secondary sources because it contains considerable amounts of phosphorus. The drawback of SSA as a secondary source is the presence of heavy metals along with phosphorus. In this study, a bioleaching process was applied to solubilize the phosphorus more economically, thus bioleaching bacteria was used to obtain acidic conditions for phosphorus leaching. For this purpose, batch bioleaching experiments were carried out with Sulfur oxidizing bacteria (SOB) to optimize the process in terms of phosphorus dissolution. Experiments were conducted with different amounts of ash, inoculum volumes, and sulfur concentrations. Because the application of the bioleaching process leads to solubilization of heavy metals beside phosphorus, an electrodialysis process was used to separate phosphorus from heavy metals. Electrodialysis experiments were performed in a 3 compartment electrodialysis reactor with gold coated copper electrodes. The maximum phosphorus bioleaching was obtained with 2 g of ash, 40% inoculum, and 10 g.l(-1) elemental sulfur. Electrodialysis studies with gold coated copper electrodes lasted for 14 days and 24.6% of the phosphorus was transported to the anode.