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Advanced oxidation of simazine in aqueous solution by the peroxone (hydrogen peroxide/ozone) treatment was investigated using Box-Behnken statistical experiment design and response surface methodology. Effects of pH, simazine and [[H.sub.2][O.sub.2]] concentrations on percent simazine and total organic carbon (TOC) removals were investigated. Ozone concentration was kept constant at 45 mg [L.sup.-l]. The optimum conditions yielding the highest simazine and TOC removals were also determined. Both simazine and peroxide doses affected simazine removal while pH and pesticide dose had more pronounced effect on mineralization (TOC removal) of simazine. Nearly 95% removal of simazine was achieved within 5 min for simazine and peroxide concentrations of 2.0 and 75 mg [L.sup.-1], respectively at pH=7. However, mineralization of simazine was not completed even after 60 min at simazine doses above 2 mg [L.sup.-1] indicating formation of some intermediate compounds. The optimum [[H.sup.2][O.sub.2]]/pH/Simazine ratio resulting in maximum pesticide (94%) and TOC removal (82%) was found to be 75/ll/0.5(mg [L.sup.-l]). DOI: 10.1061/(ASCE)EE.1943-7870.0000112 CE Database subject headings: Oxidation; Design; Hydrogen peroxide; Degradation; Biological processes; pH; Pesticides.

Advanced oxidation of diuron in aqueous solution by photo-Fenton treatment was investigated by batch experiments. Effects of operating parameters, namely, the concentrations of pesticide (diuron), hydrogen peroxide ([H.sub.2][O.sub.2]), and ferrous ion [Fe (II)] on oxidation of diuron were investigated by using Box-Behnken statistical experiment design and the response surface methodology. Diuron oxidation by photo-Fenton treatment was evaluated by determining the total organic carbon (TOC), diuron, and adsorbable organic halogen (AOX) removals. Concentration ranges of the reagents resulting in the highest level of diuron oxidation were determined. Diuron removal increased with increasing [H.sub.2][O.sub.2] and Fe (II) concentrations, up to a certain level. [H.sub.2][O.sub.2] concentration had a more profound effect than diuron and Fe (II) on removal of diuron, TOC, and AOX from the aqueous solution. Complete (100%) disappearance of diuron was achieved after a 15 min reaction period. However, 85% of diuron was mineralized after 240 min, indicating a low level of intermediate formation. Optimal [H.sub.2][O.sub.2]/Fe (II)/diuron ratio resulting in maximum diuron (100%), TOC (85%), and AOX (100%) removals was found to be 267/36/25 (mg [L.sup.-l]). DOI: 10.1061/(ASCE)0733-9372(2008)134:12(1006) CE Database subject headings: Oxidation; Soil pollution; Water pollution; Agriculture; Organic matter.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2006.10.017 Byline: Fikret Kargi, Sinem Cikla Keywords: Biosorption; Fed-batch reactor; Powdered waste sludge (PWS); Zn(II) ions Abstract: Biosorption of zinc (II) ions onto pre-treated powdered waste sludge (PWS) was investigated using a completely mixed tank operating in fed-batch mode instead of an adsorption column. Experiments with variable feed flow rate (0.05-0.5Lh.sup.-1), feed Zn(II) ion concentrations (37.5-275mgL.sup.-1) and amount of adsorbent (1-6g PWS) were performed using fed-batch operation at pH 5 and room temperature (20-25[degrees]C). Break-through curves describing variations of aqueous (effluent) zinc ion concentrations with time were determined for different operating conditions. Percent zinc removal from the aqueous phase decreased, but the biosorbed (solid phase) zinc ion concentration increased with increasing feed flow rate and zinc concentration. A modified Bohart-Adams equation was used to determine the biosorption capacity of PWS (q'.sub.s) and the rate constant (K) for zinc ion biosorption. Biosorption capacity (q'.sub.s=57.7gZnkg.sup.-1 PWS) of PWS in fed-batch operation was found to be comparable with powdered activated carbon (PAC) in column operations. However, the adsorption rate constant (K=9.17m.sup.3 kg.sup.-1 h.sup.-1) in fed-batch operation was an order of magnitude larger than those obtained in adsorption columns because of elimination of mass transfer limitations encountered in the column operations. Therefore, a completely mixed tank operated in fed-batch mode was proven to be more advantageous as compared to adsorption columns due to better contact between the phases yielding faster adsorption rates. Author Affiliation: Department of Environmental Engineering, Dokuz Eylul University, Buca, Izmir, Turkey Article History: Received 22 February 2006; Revised 8 October 2006; Accepted 25 October 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2006.04.002 Byline: Fikret Kargi, Isil Konya Keywords: Activated sludge; 4-Chlorophenol (para-chlorophenol); Hydraulic residence time (HRT); Toxicity removal Abstract: Due to the toxic nature of chlorophenol compounds present in some chemical industry effluents, biological treatment of such wastewaters is usually realized with low treatment efficiencies. Para-chlorophenol (4-chlorophenol, 4-CP) containing synthetic wastewater was treated in an activated sludge unit at different hydraulic residence times (HRT) varying between 5 and 30h while the feed COD (2500mgl.sup.-1), 4-CP (500mgl.sup.-1) and sludge age (SRT, 10 days) were constant. Effects of HRT variations on COD, 4-CP, toxicity removals and on settling characteristics of the sludge were investigated. Percent COD removals increased and the effluent COD concentrations decreased when HRT increased from 5 to 15h and remained almost constant for larger HRT levels. Nearly, 91% COD and 99% 4-CP removals were obtained at HRT levels above 15h. Because of the highly concentrated microbial population at HRT levels of above 15h, low effluent (reactor) 4-CP concentrations and almost complete toxicity removals were obtained. High biomass concentrations obtained at HRT levels above 15h were due to low 4-CP contents in the aeration tank yielding negligible inhibition effects and low maintenance requirements. The sludge volume index (SVI) decreased with increasing HRT up to 15h due to high biomass concentrations at high HRT levels resulting in well settling sludge with low SVI values. Hydraulic residence times above 15h resulted in more than 90% COD and complete 4-CP and toxicity removals along with well settling sludge. Author Affiliation: Department of Environmental Engineering, Dokuz Eylul University, Buca, Izmir, Turkey Article History: Received 30 September 2005; Revised 11 April 2006; Accepted 18 April 2006

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with an effluent recycle was used for biological treatment of 2,4,6 tri-chlorophenol (TCP) containing synthetic wastewater. The effects of sludge age (solids retention time) on chemical oxygen demand (COD), TCR and toxicity removal performance of the system were investigated for sludge ages between 5 and 30 days, while the feed COD (2600 [+ or -] 100 mg [L.sup.-1]), TCP (370 [+ or -] 10 mg [L.sup.-1]), and the hydraulic residence time (25 h) were constant. Percent TCP, COD, and toxicity removals increased with increasing sludge age resulting in nearly complete COD, TCP, and toxicity removal at sludge ages above 20 days. Biomass concentrations in the packed column and in the aeration tank increased with increasing sludge age resulting in low reactor TCP concentrations, and therefore, high TCE COD, and toxicity removals. More than 95% of COD, TCR and toxicity removal took place in the packed column reactor. Volumetric rates of TCP and COD removal increased due to increasing biomass and decreasing effluent TCP and COD concentrations with increasing sludge age. The specific rate of TCP removal was maximum (120 mg TCP g[X.sup.-1] [day.sup.1]) at a sludge age of 20 days. TCP inhibition was eliminated by operation of the system at sludge age above 20 days to obtain nearly complete COD, TCE and toxicity removal. DOI: 10.1061/(ASCE)0733-9372(2007)133:3(340) CE Database subject headings: Wastewater management; Water treatment; Biological treatment; Reactors; Biofilm; Toxicity.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2006.05.011 Byline: Serpil Ozmihci, Fikret Kargi Keywords: Adsorption; Isotherms; Kinetics; Powdered waste sludge (PWS); Textile dyestuffs Abstract: Acid pre-treated powdered waste sludge (PWS) was used for removal of textile dyestuffs from aqueous medium by adsorption as an alternative to the use of powdered activated carbon (PAC). The rate and extent of dysetuff removals were determined for four different dyestuffs at different PWS concentrations varying between 1 and 6gl.sup.-1. Biosorbed dyestuff concentrations at equilibrium decreased with increasing PWS concentration for all dyestuffs tested. PWS was more effective for adsorption of Remazol red RR and Chrisofonia direct yellow 12 as compared to the other dyestuffs tested. More than 80% percent dyestuff removal was obtained for all dyestuffs at PWS concentrations above 4gl.sup.-1 after 6h of incubation. Similar to percent dyestuff removal, the rate of adsorption was maximum at a PWS concentration of 4gl.sup.-1. Kinetics of adsorption of dyestuffs was investigated by using the first- and second-order kinetic models and the kinetic constants were determined. Second-order kinetics was found to fit the experimental data better than the first-order model for all dyestuffs tested. Adsorption isotherms were established for all dyestuffs used and the isotherm constants were determined by using the experimental data. Langmuir and the generalized adsorption isotherms were found to be more suitable than the Freundlich isotherm for correlation of equilibrium adsorption data. Acid pre-treated PWS was proven to be an effective adsorbent for dyestuff removal as compared to the other adsorbents reported in literature studies. Author Affiliation: Department of Environmental Engineering, Dokuz Eylul University, Buca, Izmir, Turkey Article History: Received 25 July 2005; Revised 6 April 2006; Accepted 1 May 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2005.02.007 Byline: Fikret Kargi, Serkan Eker, Ahmet Uygur Abstract: Chlorophenol compounds present in many chemical industry wastewaters are resistant to biological degradation because of the toxic effects of such compounds on microorganisms. Synthetic wastewater containing different concentrations of 2,4 dichlorophenol (DCP) was subjected to biological treatment in an activated sludge unit. Effects of feed DCP concentration on COD, DCP, and toxicity removals and on sludge volume index were investigated at a constant sludge age of 10 days and hydraulic residence time (HRT) of 25h. The Resazurin method based on dehydrogenase activity was used for assessment of toxicity for the feed and effluent wastewater. Percent COD, DCP, and toxicity removals decreased and the effluent COD, DCP, and toxicity levels increased with increasing feed DCP concentrations above 150mgl.sup.-1 because of inhibitory effects of DCP. Biomass concentration in the aeration tank decreased and the sludge volume index (SVI) increased with feed DCP concentrations above 150mgl.sup.-1 resulting in lower COD and DCP removal rates. The system should be operated at feed DCP concentrations of less than 150mgl.sup.-1 in order to obtain high COD, DCP, and toxicity removals. Author Affiliation: Department of Environmental Engineering, Dokuz Eylul University, Buca, Izmir, Turkey Article History: Received 14 April 2004; Revised 11 February 2005; Accepted 14 February 2005

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2005.01.010 Byline: Fikret Kargi (a), Ahmet Uygur (b), Huseyin SavaA BaAkaya (b) Abstract: A three-step sequencing batch reactor (SBR) was used for nutrient removal from synthetic wastewater with different glucose-organic acid mixtures (1/1). Acetic, butyric, propionic and citric acids were used as organic acids along with glucose. The operation consisted of anaerobic, anoxic and oxic (An/Ax/Ox) phases with durations of 2/1/4.5h. Sludge age was kept constant for 10 days. Phosphate release and uptake rates were determined for different glucose-organic acid mixtures in the feed wastewater. Maximum phosphate uptake (8.1mgPl.sup.-1 h.sup.-1) and release rates (2.23mgPl.sup.-1 h.sup.-1) were obtained with the glucose-citric acid mixture. The highest (96%) percent phosphate removal at the end of the nutrient removal cycle (7.5h) was also obtained with the glucose-citric acid mixture while the glucose-acetic acid mixture resulted in comparable percent phosphate removal (95%). Author Affiliation: (a) Department of Environmental Engineering, Dokuz Eylul University, Buca, Izmir, Turkey (b) Department of Environmental Engineering, Uludag University, Gorukle, Bursa, Turkey