Ferhan Çeçen

Inhibition of respiration and distribution of Cd, Pb, Hg, Ag and Cr species in a nitrifying sludge.

The study investigated the inhibitory effects of the heavy metals Cd, Pb, Hg, Ag and Cr (as Cr(3+) and Cr(6+)) on a nitrifying sludge. The aim was to assess the IC(50) 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 CO(2) production were taken into account. The order of the inhibitory effect was Ag>Hg>Cd>Cr(3+)=Cr(6+). 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 (Cr(3+)) and hexavalent chromium (Cr(6+)) were similar. The latter was present in the form of the anion CrO(4)(2-) and was not taken up by biomass. The study highlighted that IC(50) values alone do not have an explanatory power of inhibition unless speciation is also considered.

Aerobic Co-Treatment of Landfill Leachate with Domestic Wastewater

Addition of landfill leachate to a domestic wastewater treatment system may have negative impacts since leachate is a highly concentrated wastewater both in terms of inorganic and organic pollutants. The aim of this study was to investigate the effluent quality in the cotreatment of sanitary landfill leachate and domestic wastewater and the improving effect of powdered activated carbon (PAC). The volumetric ratio of leachate was varied from 5 to 25% (v/v). Batch activated sludge (AS) reactors were fed with leachate and domestic wastewater. Parallel AS + PAC reactors also contained PAC, which was added at the dose of 100-3,500 mg L-1. The nonbiodegradable soluble COD (SCOD) in leachate was decreased to very low levels by this addition. Experiments were also conducted in Semi-Continuously Fed Batch (SCFB) and Continuous-Flow (CF) activated sludges with recycle. In both types of operations, effluent COD and ammonium nitrogen concentrations increased when the leachate input increased. In all cases, the positi...

Photocatalytic oxidation and subsequent adsorption characteristics of humic acids

Effect of TiO 2 photocatalyzed oxidation on the degradation and decolorization of humic acids was studied. The photocatalytic oxidation products were further investigated in terms of adsorptivity on activated carbon. With photocatalytic oxidation in a lab-scale batch reactor significant decolorization and a decrease in UV 280 and UV 254 took place. Simultaneously there was a decrease in TOC and COD. Parallel to this an evolution of BOD 5 was observed. Thus the BOD 5 /COD ratio increased with irradiation time and more biodegradable substances have been formed. A significant change in the structure of compounds in humic acid took place only after 3-4 hours of irradiation as determined by the decrease in COD/TOC ratio. Generally there was a slight decrease of adsorptivity after irradiation as concluded from the comparison of Freundlich isotherm constants for raw and irradiated humic acid. This decrease increased as the irradiation time increased. But for irradiation times to be used in practice in photocatalytic oxidation no significant change in adsorption is expected.

Effect of powdered activated carbon addition on sludge dewaterability and substrate removal in landfill leachate treatment

Abstract The effect of powdered activated carbon (PAC) addition on substrate removal and sludge dewaterability was investigated in the co-treatment of leachate and domestic wastewater in an activated sludge system. The ratio of leachate in the total wastewater varied from 5 to 25% on a volumetric basis. The inert COD in the leachate could be decreased to very low levels by PAC addition. The specific resistance to filtration (SRF) of the activated sludge peaked during the removal of readily biodegradable COD and then declined when mainly non-biodegradable matter was left over. In the co-treatment case, the SRF of the sludge was shown to increase with an increase in leachate ratio, indicating that the sludge dewaterability (filterability) was negatively affected by the presence of leachate. When leachate was treated alone, the SRF of the sludge was much higher than the SRF of the sludges from domestic wastewater treatment or co-treatment. In any case, the addition of PAC to activated sludge could decrease the residual COD and suppress the peak SRF values. Overall, the results implied that in practice the addition of PAC addition to activated sludge will have a positive impact on substrate removal and sludge dewaterability. This effect will be most obvious at high leachate inputs.

Cometabolic bioregeneration of activated carbons loaded with 2-chlorophenol.

Thermally and chemically activated carbons were used to investigate the extent of cometabolic bioregeneration in laboratory scale activated sludge reactors. Bioregeneration was determined and quantified by measuring the substrate and chloride concentrations, oxygen uptake rates, and deterioration in adsorption capacities. Activated carbons loaded with 2-chlorophenol could be partially bioregenerated in the presence of phenol as the growth substrate. The occurrence of exoenzymatic bioregeneration was also possible during cometabolic bioregeneration of thermally activated carbons. However, cometabolic bioregeneration of chemically activated carbons was much superior compared with thermally activated carbons. In cometabolic bioregeneration of activated carbons loaded with 2-chlorophenol, biodegradation, rather than desorption, was the rate-limiting step. Environmental Scanning Electron Microscopy analyses showed that groups of cocci-shaped phenol-oxidizers were attached to the outer surface or internal cavities of activated carbon as a fingerprint of bioregeneration.

Adsorption and cometabolic bioregeneration in activated carbon treatment of 2-nitrophenol.

The extent of cometabolic bioregeneration of activated carbons loaded with 2-nitrophenol was investigated in lab-scale batch activated sludge reactors. Bioregeneration was quantified by measuring the deterioration in adsorption capacity of a fresh activated carbon after a pre-loading and a subsequent bioregeneration sequence. Activated carbons loaded with 2-nitrophenol could be partially bioregenerated cometabolically in the presence of phenol as the growth substrate. The occurrence of exoenzymatic bioregeneration was also possible during cometabolic bioregeneration of thermally activated carbon. However, cometabolic bioregeneration of chemically activated carbon was higher in accordance with higher desorbability. Rather than biodegradation, desorption was the rate-limiting step in bi-solute bioregeneration of phenol and 2-nitrophenol. The absence of oxidative coupling reactions leads to sufficient reversible adsorption, which eventually makes 2-nitrophenol an ideal compound in terms of bioregenerability.

Monitoring of population shifts in an enriched nitrifying system under gradually increased cadmium loading

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 15mg/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.

Impact of landfill leachate on the co-treatment of domestic wastewater

Landfill leachate and domestic wastewater were co-treated in batch activated sludge reactors and the ratio of leachate varied from 5 to 20% (v/v). The leachates had a non-biodegradable COD fraction of at least 20%. An increase in leachate adversely affected the co-treatment and it was concluded that the leachate ratio should never exceed 20% of the total wastewater or 50% of the initial COD. The initial Total Kjeldahl Nitrogen (TKN) and the free ammonia level were identified as factors influencing the completion of nitrification.

Biosorption of heavy metals from landfill leachate onto activated sludge.

The removal of various heavy metals was studied when activated sludge was exposed to heavy metals in landfill leachate. Batch uptake tests were conducted for this purpose. Adsorption was the main mechanism of removal when biomass was contacted with heavy metals. Activated sludge had a high biosorption capacity and equilibrium was reached in a short time with respect to copper, iron, manganese, zinc and chromium. Adsorption isotherms were generated for those heavy metals and the Freundlich constants were calculated. Among the metals studied, manganese became very concentrated on activated sludge with time.

Nitrification inhibition in landfill leachate treatment and impact of activated carbon addition

Leachate from a municipal landfill was combined with domestic wastewater and treated in batch, semi-continuously fed-batch (SCFB) and continuous-flow (CF) activated sludge systems with and without powdered activated carbon (PAC) addition. In the absence of PAC, nitrification was severely inhibited and nitrite accumulated to about 85–100% of the total NOx-N. Addition of PAC to activated sludge reactors enhanced nitrification. In continuous-flow operation, nitrite accumulation could be completely prevented by PAC addition.