Theses supervised by Prof. Dr. Fikret Kargı
11 theses · Dokuz Eylül University
Hydrogen gas production by electrohydrolysis of cheese whey using photovoltaic cells (PVC)
Cheese manufacturing industry generates large amounts of high strength wastewater characterized by high chemical oxygen demand (COD) concentration and its disposal constitutes a serious environmental problem with total sugar being mainly responsible for its high COD contents. In this respect the production of hydrogen gas from cheese whey using electrohydrolysis method with simultaneous COD removal presents a promising and novel approach.In this study, hydrogen gas production with simultaneous COD removal was observed by application of different DC voltages to cheese whey wastewater with DC power suppliers connected to power grid and also with electrical power generated by a photovoltaic cell (PVC). Hydrogen production yields, hydrogen production rates, energy conversion efficiencies, COD removals were considered as criteria for performance comparison.
Degradation and mineralization of diuron and simazine in aqueous solution by advanced oxidation processes
The first part of the thesis consists of experimental studies on removal of pesticides from aqueous solution by advanced oxidation processes (Fenton, photo-Fenton and peroxone oxidation) using Box-Behnken statistical experiment design. Effects of pesticide (diuron or simazine), hydrogen peroxide and ferrous ion concentrations and initial pH on the extent of pesticide and total organic carbon (TOC) removals were investigated. Optimum reagent doses yielding the highest pesticide and TOC removals were determined. Complete removal of pesticides was accomplished within fifteen minutes while complete mineralization was not achieved even within sixty minutes indicating formation of some intermediate compounds. In photo-Fenton treatment, the highest complete pesticide removal and mineralization (eighty-five percent) were obtained for diuron-containing water. In advanced oxidation of simazine ozone/peroxide (peroxone) treatment yielded higher mineralization (ninety-four percent) although there were no differences in simazine removals. The initial rate of pesticide degradation was found to be first-order with respect to the initial pesticide concentration for Fenton and photo-Fenton processes.The second part of the thesis was on treatment of pulp mill effluent by different AOPs. In the treatment of pulp mill effluent, photo-Fenton treatment yielded comparable TOC (eighty-five percent), color (eighty-two percent) and AOX (ninety-three percent) removals within five minutes due to oxidations by UV light in addition to the Fenton?s reagent. When pulp mill effluent from different sources was used, the TiO2-assisted photo-catalysis resulted in the highest TOC (eighty percent) and toxicity (ninety-five percent) removals under alkaline conditions within sixty minutes.
Biohydrogen production by dark / light fermentation of hydrolysed wheat starch
Biological hydrogen gas production from acid hydrolyzed wheat starch (AHWS) solution was investigated using batch dark and continuous dark, photo and combined fermentation systems. Hydrogen production yield and specific hydrogen production rate were considered as the criteria for performance comparison.In batch dark fermentation experiments, initial waste wheat and biomass concentrations on hydrogen gas production rate and yield were investigated using heat pre-treated anaerobic sludge (ANS) and acid hydrolyzed wheat starch. Continuous experiments of dark fermentation were performed to investigate the effects of hydraulic residence time (HRT) on hydrogen gas production rate and yield.Hydrogen gas production by light fermentation using volatile fatty acid (VFA) containing batch dark fermentation effluent (DFE) was investigated. The effects of hydraulic residence time (HRT) on hydrogen gas production rate and yield were investigated using pure culture of Rhodobacter sphaeroides NRLL-1727.In combined dark and photo fermentations of AHWS, the effects of hydraulic residence time (HRT) on hydrogen gas production rate and yield were investigated by using heat pre-treated anaerobic sludge (ANS) and pure culture of Rhodobacter sphaeroides NRLL-1727. Continuous experiments were performed by periodic feeding and effluent removal.
Hydrogen gas production from waste ground wheat by dark and light fermentations
Bio-hydrogen gas production from waste ground wheat powder solution was investigated using batch and continuous dark and light fermentation systems. Continuous experiments were conducted at optimum operation conditions that were determined during batch experiments. Hydrogen production yield and specific hydrogen production rate were considered as the criteria for performance comparison. Combined fermentation experiments were conducted after completing dark and light fermentation experiments.In dark fermentation experiments heat pre-treated anaerobic sludge was found to be the most effective bacterial culture compared to pure cultures. Effects of sludge pre-treatment method, medium composition and initial wheat powder and biomass concentrations on hydrogen production rate and yield were investigated.Hydrogen production by light fermentation using volatile fatty acid containing dark fermentation effluent was investigated under different conditions. Hydrogen production performances of pure Rhodobacter sphaeroides species and their combinations were compared and the mixed culture was found to be the most efficient culture for light fermentation. The optimum initial total volatile fatty acid, ammonium nitrogen and biomass concentrations and the most suitable light source and intensity were determined.In combined dark and light fermentations of wheat powder solution, the optimum light to dark biomass ratio, initial biomass and waste wheat powder concentrations were determined. Effects of light source, light intensity and lighting regime on hydrogen production rate and yield were investigated.Finally continuous experiments of combined dark and light fermentation were performed using a hybrid annular bio-reactor in order to investigate the effects of hydraulic residence time (HRT) on hydrogen production rate and yield.
Removal of heavy metals from wastewater by biosorption using excess sludge
Activated sludge obtained from a paint industry wastewater treatment plant was found to be the most suitable among the others tested resulting in the highest biosorption capacity. Pre-treatment by 1 percent hydrogen peroxide solution was found to be superior to the other methods yielding the highest biosorption capacity.Effects of operating parameters on batch biosorption kinetics of copper ions onto pre-treated powdered waste sludge (PWS) were investigated. Batch isotherms of biosorption of Cu ions were investigated and the langmuir isotherm was found to fit the experimental data better than the other isotherms tested.Biosorption of Cu ions onto pre-treated powdered waste sludge (PWS) was also investigated using a fed-batch operated completely mixed reactor. Breakthrough curves describing variations of effluent copper ion concentrations with time were determined for different operating conditions.In order to investigate the adverse effects of Cu ions on performance of an activated sludge unit, synthetic wastewater containing Cu ion was treated in an activated sludge unit and COD, Cu, toxicity removals were investigated. Copper ion toxicity on COD removal performance of the activated sludge unit was partially eliminated by operation at high sludge ages (30 days) and HRT?s (25 hours).Copper ion toxicity onto activated sludge organisms was eliminated by addition of powdered waste sludge (PWS) to the feed wastewater for removal of Cu ions by biosorption before biological treatment. Box-Behnken experimental design method was used to investigate Cu, chemical oxygen demand (COD) and toxicity removal performance of the activated sludge unit under different operating conditions.
Ethanol Production from cheese whey powder solution by fermentation
Ethanol production from cheese whey powder (CWP) solution was investigated using batch, fed-batch and continuous fermentation systems. In batch experiments ethanol production from cheese whey, CWP and lactose solutions with the same initial sugar contents were compared by using two different Kluyveromyces marxianus strains (NRRL?1109, NRRL?1195) in order to determine the most suitable substrate and the yeast strain.Then, the effects of initial pH, CWP concentration and external nutrient supplementation on ethanol production were investigated using K. marxianus NRRL-1195. The rate and extent of ethanol formation did not increase with external nutrient addition indicating no requirement for external nutrients. Final ethanol and the rate of ethanol formation increased with increasing CWP indicating no substrate or product inhibitions, but substrate limitations.Performances of two different K. marxianus strains (NRRL-1195 and DSMZ-7239) were compared for ethanol fermentation. DSMZ-7239 was found to be the most suitable strain and was used in further experiments.Effects of initial CWP and yeast concentrations were investigated and a kinetic model describing the rate of sugar utilization as function of the initial substrate and the biomass concentrations was developed in batch fermentation.Then, a five- cycle repeated fed- batch operation with different feed CWP concentrations was used for the same purpose. The growth yield coefficient (Yx/s) decreased and product yield coefficient (Yp/s) increased with increasing feed sugar content.A continuous culture at different feed sugar contents and hydraulic residence times (HRT) was tested for ethanol production. Material balances for yeast growth, sugar utilization and ethanol formation with suitable kinetic models were used to predict the system performance and to determine the kinetic constants.Finally, a continuously operated packed column bio-reactor (PCBR) using olive pits as support particles was used at different HRTs and feed sugar cotent. Sugar concentration decreased and ethanol increased with the height of the column operated in up-flow mode. Effluent ethanol increased with increasing HRT and feed sugar content up to certain levels. Ethanol yields closer to the theoretical predictions were obtained
Biological treatment and toxicity removal from wastewaters containing chlorinated aromatic compounds in rotating perforated tubes and brush biofilm reactors
Rotating perforated tubes and rotating brush biofilm reactors were used for 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), COD and toxicity removals from synthetic wastewater. Box-Wilson and Box-Behnken statistical experiment design methods were used to evaluate the experimental results and determine the optimum operating conditions maximizing chlorophenol, COD and toxicity removals. Toxicity of wastewater was analyzed by dehydrogenase enzyme activity known as resazurin assay method.Both reactors were found to be very effective in removing chlorophenols over a large range of operating conditions. Chlorophenols and their degradation intermediates were the major toxic compounds causing low COD and chlorophenol removals. Nearly complete removal of chlorophenols required high biofilm surface area (high A/Q ratio) and high feed COD contents yielding high biomass densities. Percent chlorophenol and toxicity removals increased with increasing feed COD and A/Q ratio and with decreasing chlorophenol concentrations for both reactors. Percent COD removal increased with increasing feed COD up to a certain concentration and decreased with further increases in the feed COD. High A/Q ratio and low feed chlorophenol concentrations yielded high COD removals. To avoid inhibition of high chlorophenol concentrations on the biofilm microorganisms and to obtain high COD, chlorophenol and toxicity removals, the system should be operated at high A/Q ratio and feed COD.RTBR seemed to be more effective for removal of COD and chlorophenols when operated under the same A/Q ratio due to formation of thicker and denser biofilms on the tube surfaces. Similar trends were observed for percent toxicity removals.RTBR performed better than RBBR at high chlorophenol concentrations yielding high COD, chlorophenol and toxicity removals.
Advanced oxidation treatment of antibiotic containing water
In advanced oxidation experiments, Amoxicillin was selected as the pollutant, and was used in form of Amoxicillin trihydrate. Studying degradation and mineralization of Amoxicillin in aqueous solution by using advanced oxidation methods, namely the Fenton and photo-Fenton treatments were the major objectives of this thesis. Various concentrations of Amoxicillin containing synthetic wastewater were prepared and used in experimental studies.Antibiotic (Amoxicillin) and TOC measurements were carried out to determine the most effective catalyst, oxidant and antibiotic concentration combinations and reaction time for advanced oxidation of Amoxicillin by Fenton and photo-Fenton and to compare the tested methods and conditions to select the most suitable method and conditions. Box-Behnken statistical experiment design method was used to determine the effects of reagent concentrations on degradation and mineralization of amoxicillin.Advanced oxidation experiments were carried out with synthetic medium containing Amoxicillin. The most suitable dosages yielding the highest Amoxicillin degradation and mineralization were determined using the Fenton and photo-Fenton treatments. In oxidation experiments; hydrogen peroxide (35 percent) was used as oxidant. The catalyst was ferrous sulphate. Sulfuric acid was used for pH adjustment. Advanced oxidation methods were compared in terms of removal performances. In advanced oxidation of antibiotic containing synthetic wastewater by Fenton?s reagent, maximum antibiotic and TOC removal efficiencies were 100 percent and 37.08 percent, respectively. In photo-Fenton oxidation, maximum antibiotic and TOC removal efficiencies were 100 percent and 50.25 percent, respectively.Both methods were proven to be effective for Amoxicillin removal. However photo-Fenton oxidation was more effective for TOC removal or mineralization.
Utilization of nitrogen fixing organisms in biological treatment of nitrogen deficient wastewaters
IV ABSTRACT Biological treatment of nitrogen deficient wastewaters are usually accomplished by external addition of nitrogen sources to the wastewater. The operational costs increase with the external addition of nitrogenous compounds such as ammonium, urea and nitrate salts. Also, externally added nitrogen may partly end up in the effluent of the wastewater treatment plants, which reduces the effluent quality. As an alternative for effective biological treatment of nitrogen deficient and carbon rich wastewaters, nitrogen fixing bacteria can be used along with activated sludge culture. When nitrogen fixing bacteria was mixed with other activated sludge organisms, the performance of the system treating the nitrogen deficient wastewater may improve. The major objective of this thesis is to improve the treatment performance of nitrogen deficient wastewaters by using nitrogen fixing bacteria in an activated sludge unit. Azotobacter vinelandii was used as the nitrogen fixing bacteria since those organisms are obligate aerobes and can easily be adapted to an activated sludge system. Biological TOC and COD removal efficiencies of nitrogen deficient synthetic wastewater were investigated in batch and continuous systems by using Azotobacter vmetofc/H-supplemented activated sludge culture. Performance of Azotobacter added and free cultures of activated sludge were compared at different initial TN/ COD ratio in batch experiments. The results indicated clear advantage of using Azotobacter in the activated sludge culture to improve TOC removal performance at low TN/ COD ratios. More than 90 % TOC removal efficiencies were obtained withpure Azotobacter or Azotobacter added activated sludge culture from nitrogen deficient wastewaters. Azotobacter vinelandii was used with activated sludge culture for treatment of nitrogen deficient wastewater in a continuously operating activated sludge unit. COD removal performance of Azotobacter-sapplemeated activated sludge was compared with Azotobacter-fxee activated sludge culture for biological treatment of nitrogen deficient synthetic wastewater. Effects of important process variables such as TN/COD ratio, sludge age, hydraulic residence time, feed COD concentration and the COD loading rate on the COD removal performance were investigated. Kinetic constants of the system were determined by using the experimental data. It was proven that Azotobacter addition to the activated sludge in biological treatment of nitrogen deficient wastewater (TN/ COD < 0.06 ) has improved the COD removal performance significantly. Nearly, 90% COD removal efficiency was obtained from nitrogen deficient wastewater (TN/COD< 3%) by using Azotobacter supplemented activated sludge culture at HRT of 14 hours and SRT of 10 days.
Performance of sequencing batch reactor for nutrient removal as functions of operating variables
Sequencing batch reactors were originally used for COD and phosphate removal from wastewaters. Recent regulations over nutrient discharges to natural water systems resulted in modifications in sequential batch reactor (SBR) systems to achieve nitrification, denitrification along with COD and phosphate removal. An SBR treatment system consists of a sequencing operation including the steps of fill, react, settle, decant, and idle in the same reactor. When biological nutrient removal is desired, the steps in the react cycle are adjusted to provide anaerobic, anoxic and aerobic phases in certain number and sequence. Since the same reactor is used for biological oxidation and sedimentation in SBR operations, capital and operating costs are lower than conventional activated sludge processes. Therefore, SBR operations may be more advantageous for treatment of small volume wastewaters in rural areas. In this respect, this thesis is composed of six main parts investigating different number of steps, different hydraulic retention times (HRT), different sludge ages, different carbon sources, different medium compositions and different specific nutrient loading rates (SNLR) on the biological nutrient removal from a synthetic wastewater. In the first part of this study, three different operations with different number of steps were used and their nutrient removal performances were compared. Those operations were a three-step operation consisting of anaerobic/ anoxic/ oxic( An/ Ax/ Ox ) phases; a four- step operation consisting of anaerobic/ oxic/ anoxic/ oxic ( An/ Ox/ Ax/ Ox ) phases and a five-step operation consisting of ( An/ Ax/ Ox/ Ax/ Ox ) phases. Effects of different operations on percent COD, nitrogen (NH4-N, NO3-N)Ill and phosphate removal (PO4-P) performances were investigated. The sludge age was constant at 10 days. The best percent nutrient ( nitrogen and phosphate ) and percent carbon removals were achieved when the five step operation was used. The highest percent COD, NH4-N and PO4-P removals obtained with the five-step operation were 94%, 90 %, and 57 %, respectively. In the second part of this study, nutrient removal from synthetic wastewater by a five-step sequencing batch operation was studied at different hydraulic retention times (HRT). The nutrient removal process consisted of anaerobic (An), anoxic (Ax), oxic (Ox), anoxic (Ax), oxic (Ox) and settling phases. Sludge age was kept constant at 10 days, while hydraulic retention times (HRT) of each phase was varied. Effects of hydraulic retention time of each phase on percent COD, nitrogen (NH4-N, NO3-N) and phosphate (PO4-P) removals were investigated. Hydraulic retention time of each phase was varied at five different levels and the the most suitable retention time resulting in maximum overall percent nutrient removal was determined. The highest observed percent COD, nitrogen (NH4-N and NO3-N) and phosphate (PO4-P) removals were 96%, 87%, 81% and 90%, respectively which were obtained with An/ Ax/ Ox/ Ax/ Ox phase retention times of 2/ 1/ 4.5/ 1.5/ 1.5 h. In the third part of the study, nutrient removal was studied at different sludge ages by using a five-step SBR operation at the pre-determined hydraulic retention times. The nutrient removal process consisted of anaerobic, anoxic I, oxic I, anoxic II, oxic II and settling phases. Hydraulic retention times (HRT) of the aforementioned phases were kept constant at 2/1/4.5/1.5/1.5 h. Settling phase was Vi h for all experiments. Sludge age was varied between 5 to 30 days at six different levels. Effects of sludge age on percent COD, nitrogen (NH4-N, NO3-N) and phosphate (PO4-P) removal were investigated and the optimal sludge age resulting in maximum percent nutrient removal was determined. The highest percent COD (94%), NH4-N (84%) and P04-P (70%) removals were obtained at the sludge age of 10 days, although a sludge age of 15 days resulted in slightly lower values. Sludge ages larger than 15 days resulted in lower percent nutrient removals as compared to those obtained at 10 or 15 days of sludge age. Sludge volume index (SVI) was also minimum (55 mL/g) at sludge ageIV of 10 days. Biomass(MLSS) concentration increased with sludge age resulting in MLSS concentration of 3500 mg/L at sludge age of 30 days. On the basis of these results, a sludge age of 10 days was found to be optimal resulting in maximum percent nutrient removals and minimum sludge volume index. In the fourth part of the thesis, a three-step sequencing batch operation was used for nutrient (COD, NH4-N, PO4-P) removal from synthetic wastewater by using different carbohydrates and organic acids as carbon sources. The operation consisted of anaerobic, anoxic and oxic ( An/ Ax/ Ox ) phases with durations of 2/ 1/ 4.5 h. Different carbohydrates glucose, lactose, sucrose, maltose and a mixture of glucose / maltose (50/50) were used as the sole carbon source in the first phase of experiments. Sludge age was kept constant at 10 days. Glucose was found to be the most suitable carbohydrate source with percent COD, NH4-N and PO4-P removals of 96%, 99% and 94%, respectively. Nutrient removals obtained with sucrose as the sole carbon source were close to those obtained with glucose. A mixture of glucose and organic acids (50/50) such as acetic, citric, propionic and butyric acid were used as carbon source in the second phase of the experiments. Percent COD, NH4-N and PO4-P removals were 93%, 97% and 96%, respectively when a mixture of glucose and acetic acid (50/50) was used. Glucose-citric acid (50/50) combination also resulted in comparable nutrient removals. Changing the ratio of glucose / acetic acid in the mixture did not improve the nutrient removal performance. In the fifth part of this study, nutrient removal from synthetic wastewater was studied as a function of nutrient medium composition using a five-step sequencing batch reactor (SBR). The nutrient removal process was consisted of anaerobic, anoxic, oxic, anoxic, oxic phases with hydraulic retention times (HRT) of 2/ 1/ 4.5/ 1.5/ 1.5 h. Sludge age and settling phase were 10 days and 14 hour, respectively in all experiments. Initial chemical oxygen demand (COD) concentration was constant at 1200 mg/L. COD/N and COD/P ratios in the nutrient medium were considered as independent variables. Box-Wilson statistical experiment design was used to determine the effects of independent variables on percent COD, NH4-N, PO4-P removals. The results were correlated by a response function and the coefficientswere determined by regression analysis. The COD/N/ P ratio resulting in maximum percent COD, NH4-N and PO4-P removals was determined to be 100 / 2 / 0.54 resulting in 95% COD, 94% NH4-N and 99% P04-P removals. In the last part of this study, nutrient removal from a synthetic wastewater by a five-step SBR operation was studied at different specific nutrient loading rates (SNLR ). The operation consisted of anaerobic (An), anoxic (Ax), oxic (Ox), anoxic (An) and oxic (Ox) phases with hydraulic retention times (HRT) of 2 / 1 / 4.5 / 1.5 / 1.5 h, respectively with a 45 minutes settling phase. Initial COD concentration was varied between 600 to 4800 mg/L at eight different levels with constant COD / N / P ratio of 100 / 3.33 / 0.7. Effects of specific nutrient loading rates (SNLR) on percent COD, NH4-N and PO4-P removal were investigated. Percent nutrient removals decreased and effluent nutrient levels increased with increasing nutrient loading rates. The highest percent COD (99%), NH4-N (99%) and PO4-P (97%) removals were obtained with the initial COD concentration of 600 mg/L at COD loading rate of nearly 40 mg COD/g biomass.h. However, the sludge volume index (SVI) decreased with increasing COD loading rate resulting minimum SVI of 46 mL/g at COD loading rate of nearly 86 mg COD/g biomass.h. Biomass concentration increased with increasing specific nutrient loading rate resulting in biomass concentration of 3.84 g/L at COD loading rate of 86 mg COD/g biomass.h. In summary, nutrient removal from a synthetic wastewater was extensively studied and a five-step SBR operation with 10 days sludge age was found to be the most suitable among the others tested. The effects of hydraulic retention times of each step, wastewater composition and the nutrient loading rates on the system performance were investigated and the optimum operational values were determined.
Adsorptive biological treatment of pretreated landfill leachate by fed-batch operation
Ill ABSTRACT Early biological treatment studies with the raw leachate did not yield high COD and nitrogen removals. In order to improve biological treatability,, the landfill leachate was subjected to pretreatment by chemical coagulation-floccularion followed by air stripping of ammonia at pH =12. Three different chemical coagulants, alum (Aİ2(S04)3 ), FeCİ3 and lime (CaO) were used in different concentrations tor COD and nitrogen removal by cwagulation-flocculation- COD concentrations of the three coagulants at low doses (0.5-1.0 g/L) were comparable. Considering the problems associated with the use of high coagulant doses such as more sludge formation and high cost of coagulation, low doses of coagulants such as 1 g/L were preferred. Percent COD removals for the three coagulants at the dose of 1 g/L were almost the same as 45%. Supernatant solution after coagulation with lg/L lime at pH =12 was subjected to air stripping at different pH levels to remove excess ammonia from the leachate. Ammonium concentration was reduced to nearly 700 mg/L from 1200 mg/L after 45 minutes of air stripping at pH=12. The pretreated leachate was subjected to aerobic biological treatment in an aeration tank by fed-batch operation. The effects of the feed wastewater COD content and flow rate on COD and ammonium ions removal were investigated. Nearly 76% COD and 23% NH*-N removals were obtained with a flow rate of 0.21IV L/h and the feed COD content of 7,000 mgCOD/L. COD removal efficiency decreased with increasing COD loading rates. A kinetic model for COD removal was developed and the kinetic constants were determined by using the experimental data. In order to improve the extent of COD and ammonium nitrogen removals, pretreated leachate was subjected to adsorbent supplemented biological treatment in an aeration tank operated in fed-batch mode by using powdered zeolite (PZ) and powdered activated carbon (PAC) as adsorbents. Adsorbent concentrations were varied between 0 g/L and 5 g/L. Percent COD and ammonium-N removals increased with increasing adsorbent concentrations. COD removals with PAC addition were significantly higher than those obtained with zeolite. However, zeolite performed better than the PAC in ammonium-N removal from the leachate. Nearly 87% and 77% COD removals were achieved with PAC and zeolite concentrations above 2 g/L, respectively. Ammonium-N removals were 30% and 40% with PAC and zeolite concentrations of 5 g/L, respectively at the end of 30 hours of fed-batch operation. An empirical equation was developed to describe the contribution of adsorption over biological treatment as a function of PAC and zeolite concentrations. To further decrease effluent COD and ammonium concentrations, two sets of repeated fed-batch experiments with different operation times (3x10 h and 5x6 h) were performed with and without PAC addition. When the operation time was divided to 3x10 hours and 5x6 hours, better results were obtained than that of the 30 hours single cycle operation with and without PAC addition. The effluent COD and NH4-N concentrations were 365 mg/L and 360 mg/L in the repeated fed-batchoperations of 5x6 hours with 2 g/L PAC addition. To observe system performance at longer operation times, a three-cycle operation with 30 hours durations was used (3x30 h) in repeated fed-batch mode in the presence of 2g/L PAC. At the end of 90 hours repeated fed-batch operation (3x30 h), the effluent COD and NH4-N concentrations were 285 mg/L and 224 mg/L, respectively which are considerably lower than those obtained with 5x6h operation. Apparently, longer operation times in repeated fed-batch operation resulted in better effluent water quality. Effects of N/COD ratio in the fed wastewater on COD and ammonium removal in PAC added biological treatment were investigated. Percent COD removals increased and the final COD contents decreased with increasing Lnh4-n/Lcod ratio. Lnh4-n/Lcod=0-05-0.08 rati0 was optimum resulting in 85% COD and 44 % NH4-N removal. Percent COD removal decreased to 78%, when Lnh4-n/Lcod was reduced to 0.03. Chemical oxidation was used to further reduce COD content of landfill leachate after PAC added biological treatment. Three oxidizing agents (H2O2, Fenton's reagent, NaOCl) were used in different concentrations for chemical oxidation. Chemical oxidation by Fenton reagent resulted in higher COD removals as compared to H2O2 and NaOCL Nearly, %68 COD removal, 95 mg/L effluent COD and 2 mg/L NH4-N have been obtained with 150/250 mg/L H202/FeS04 ratio.