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Abstract: Electrical power generated by a photovoltaic cell (PVC) was supplied to diluted industrial wastewater in a mechanically mixed and sealed stainless-steel reactor for hydrogen gas production. Three different electrodes, graphite, stainless steel and aluminum rods were used for comparison. Protons released from decomposition of organic compounds and electrons provided by the DC current reacted to form hydrogen gas. The highest cumulative hydrogen gas formation (CHF) was obtained with the aluminum electrode (120 L in 8 days) and the lowest was with the graphite electrode (4 L). Hydrogen gas production from wastewater was 2.4 times higher than that produced from water when aluminum electrodes were used. TOC content of wastewater was reduced from 2400 to 1700 mg L−1 with nearly 29% TOC removal within 6 days. CHF from wastewater was 76 L within 18 days with the stainless-steel electrodes while CHF from water was only 9.5 L. Fermentative hydrogen gas production from wastewater was negligible in the absence PVC. Energy conversion efficiency for hydrogen gas production (hydrogen energy/electric energy) was found to be 74% with the aluminum electrodes. [Copyright &y& Elsevier]

Abstract: Diluted olive mill wastewater (OMW) was subjected to direct current (DC) voltages (0.5–4.0V) for hydrogen gas production with simultaneous chemical oxygen demand (COD) removal by electrohydrolysis. The highest cumulative hydrogen production (3020ml) and hydrogen yield (2500mlH2 g−1 COD) were obtained with 3V DC voltage while the highest current intensity (80mA), percent hydrogen (95%) in the gas phase, hydrogen gas formation rate (614mld−1), percent COD removal (44%) and energy conversion efficiency (95%) were realized with 2V. Hydrogen gas production by electrolysis of water was negligible for all voltages. COD removal from OMW with no DC voltage application was usually lower than that obtained with DC power application. Hydrogen gas production by electrohydrolysis of OMW was proven to be a fast and effective method with simultaneous COD removal. [Copyright &y& Elsevier]

Abstract: Electrical current generated by a photovoltaic cell (PVC) was supplied to wastewater in a mechanically mixed and sealed reactor using stainless steel electrodes. Hydrogen gas was generated by reaction of protons released from decomposition of organic compounds and electrons provided by electrical current. Gas phase was composed of 75–99% H2 gas. Hydrogen gas produced from electrolysis of water (9.5 L) was only 12.5% of that produced from wastewater (75 L) within 432 h. TOC content of wastewater was reduced from 4800 to 4200 mg L−1 with nearly 12.5% TOC removal. Fermentative hydrogen gas production from wastewater was negligible in the absence PVC power. Wastewater inoculated with anaerobic sludge generated higher hydrogen gas volumes as compared to wastewater with the application of solar power. Energy conversion efficiency for hydrogen production by electrohydrolysis of waste compounds (hydrogen energy/electric energy) was found to be 92% for the wastewater containing anaerobic sludge. [ABSTRACT FROM AUTHOR]

Abstract: Combined dark and photo-fermentation of ground wheat starch was carried out by using different light sources, intensities and lighting regime. A mixture of heat treated anaerobic sludge and Rhodobacter sphaeroides-RV with a certain light/dark bacteria ratio was used in batch experiments. Tungsten, fluorescent, infrared (IR), tungsten + infrared, halogen lamps were used as light sources with a light intensity of 270 Wm−2 along with sunlight. Halogen lamp was found to be the most suitable light source yielding the highest cumulative hydrogen formation (178 ml) and yield (218 ml g−1 starch). Combined fermentations were performed at different light intensities (1–10 klux) using the halogen lamp in the second set of experiments. The optimum light intensity was found to be 10 klux (approx. 352 Wm−2) resulting in the highest cumulative hydrogen (111 ml) and hydrogen yield (139 ml H2 g−1 starch). Hydrogen formation was limited by the availability of light at low light intensities below 10 klux. Durations of dark/light cycles were changed to determine the most suitable lighting regime. Hydrogen gas formation increased with increasing cycle time and continuous lighting resulted in the highest cumulative hydrogen formation and hydrogen yield. [Copyright &y& Elsevier]

Abstract: Dark fermentation effluent of wheat powder solution was subjected to light fermentation for bio-hydrogen production using different light sources and intensities. Tungsten, fluorescent, infrared (IR), halogen lamps were used as light sources with a light intensity of 270Wm−2 along with sunlight. Pure culture of Rhodobacter sphaeroides-RV was used in batch light fermentation experiments. Halogen lamp was found to be the most suitable light source yielding the highest cumulative hydrogen formation (CHF, 252ml) and yield (781ml H2 g−1 TVFA). In the second set of experiments, light fermentations were performed at different light intensities (1–10klux) using halogen lamp. The optimum light intensity was found to be 5klux (approx. 176Wm−2) resulting in the highest CHF (88ml) and hydrogen yield (1037ml H2 g−1TVFA). Hydrogen formation was limited by the availability of light at low light intensities below 5klux and was inhibited by the excess light above 5klux. [Copyright &y& Elsevier]

Biological treatment of synthetic wastewater containing Cu(II) ions was realized in an activated sludge unit with pre-adsorption of Cu(II) onto powdered waste sludge (PWS). Box-Behnken experimental design method was used to investigate Cu(II), chemical oxygen demand (COD) and toxicity removal performance of the activated sludge unit under different operating conditions. The independent variables were the solids retention time (SRT, 5–30d), hydraulic residence time (HRT, 5–25h), feed Cu(II) concentration (0–50mgL−1) and PWS loading rate (0–4gh−1) while percent Cu(II), COD, toxicity (TOX) removals and the sludge volume index (SVI) were the objective functions. The data were correlated with a quadratic response function (R 2 =0.99). Cu(II), COD and toxicity removals increased with increasing PWS loading rate and SRT while decreasing with the increasing feed Cu(II) concentration and HRT. Optimum conditions resulting in maximum Cu(II), COD, toxicity removals and SVI values were found to be SRT of 30d, HRT 15h, PWS loading rate 3gh−1 and feed Cu(II) concentration of less than 30mgL−1. [Copyright &y& Elsevier]

Abstract: Due to the toxic effects of trichlorophenol (TCP) on microorganisms, biological treatment efficiencies of TCP containing wastewaters are usually low. Synthetic wastewater containing 2,4,6-TCP was biologically treated in a hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with effluent recycle in order to improve COD and TCP removals. Effects of the feed TCP concentration on COD, TCP and toxicity removal performance of the system were investigated for the feed TCP between 50 and 450mgL−1 while the sludge age (solids retention time, SRT) and hydraulic residence time (HRT) were kept constant at 20d and 25h, respectively. Biomass concentrations in the packed column and in the aeration tank decreased with increasing feed TCP concentrations due to toxic effects of TCP on the organisms. Low biomass concentrations in the system at high feed TCP contents resulted in low COD, TCP and toxicity removals. Therefore, percent TCP, COD and toxicity removals decreased with increasing feed TCP concentrations especially above 400mgL−1. The effluent TCP concentrations were lower than 20mgL−1 for the feed TCP concentrations below 390mgL−1 resulting in TCP and COD removals above 90%. Specific rates of TCP and COD removals increased with the feed TCP due to low biomass concentrations at high TCP contents. The system should be operated at a feed TCP lower than 400mgL−1 in order to obtain more than 90% TCP, COD and toxicity removals under the specified experimental conditions. [Copyright &y& Elsevier]

Synthetic wastewater containing Cu(II) in concentrations between 0 and 22 mg L −1 was treated in an activated sludge unit, and chemical oxygen demand (COD), Cu(II), and toxicity removals were investigated. The feed Cu(II)o concentrations were varied between 0 and 22 mg L −1 while the feed CODo, hydraulic residence time (HRT) and solids retention time (SRT) were kept constant at 2,000 ± 100 mg L −1, 10 h and 10 days, respectively. The effluent CODe and Cu(II)e concentrations, toxicity, and the sludge volume index (SVI) increased, but the biomass concentration in the aeration tank decreased with the feed Cu(II)o content due to Cu(II) toxicity on the organisms. The feed and the effluent toxicities were determined by using the resazurin assay based on dehydrogenase activity. Cu(II) toxicity in the feed and the effluent wastewater increased linearly with the Cu(II) concentrations. Adverse effects of Cu(II) were more pronounced for the feed Cu(II)o above 10 mg L −1, resulting in sharp decreases in biomass concentration and percent COD removal. A kinetic model describing the Cu(II) inhibition on COD removal rate was developed and the Cu(II) inhibition constant was found to be 2.85 mg L−1. [ABSTRACT FROM AUTHOR]

Copper(II) ion toxicity onto activated sludge organisms was eliminated by addition of powdered waste sludge (PWS) to the feed wastewater for removal of Cu(II) ions by biosorption before biological treatment. The synthetic feed wastewater containing 14 or 22mgl−1 Cu(II) was mixed with PWS in a mixing tank where Cu(II) ions were adsorbed onto PWS and the mixture was fed to a sedimentation tank to separate Cu(II) containing PWS from the feed wastewater. The activated sludge unit fed with the effluent of the sedimentation tank was operated at a hydraulic residence time (HRT) of 10h and sludge age (SRT) of 10 days. To investigate Cu(II), COD and toxicity removal performance of the activated sludge unit at different PWS loadings, the system was operated at different PWS loading rates (0.1–1gPWSh−1) while the Cu(II) loading rate was constant throughout the operation. Percent copper, COD and toxicity removals increased with increasing PWS loading rate due to increased adsorption of Cu(II) onto PWS yielding low Cu(II) contents in the feed. Biomass concentration in the aeration tank increased and the sludge volume index (SVI) decreased with increasing PWS loading rate due to elimination of Cu(II) from the feed wastewater by PWS addition. PWS addition to the Cu(II) containing wastewater was proven to be effective for removal of Cu(II) by biosorption before biological treatment. Approximately, 1gPWSh−1 should be added for 28mgCuh−1 loading rate for complete removal of Cu(II) from the feed wastewater to obtain high COD removals in the activated sludge unit. [Copyright &y& Elsevier]

Abstract: 2,4,6-Trichlorophenol (TCP) containing synthetic wastewater was biologically treated using a novel rotating brush biofilm reactor for TCP, COD and toxicity removal. Effects of major operating variables such as the feed TCP and COD concentrations and A/Q (biofilm surface area/feed flow rate) ratio on the performance of the biofilm reactor were investigated. A Box-Behnken statistical experiment design method was used by considering the feed TCP (0–400mgL−1), COD (1000–4000mgL−1) and A/Q ratio (37–256m2 dm−3) as the independent variables while percent TCP, COD, and toxicity removals were the objective functions. The data were correlated with a quadratic model and the response function coefficients were determined by regression analysis. Percent TCP, COD and toxicity removals determined from the response functions were in good agreement with the experimental results. TCP, COD and toxicity removals increased with increasing A/Q ratio and decreasing feed TCP concentrations. Optimum conditions resulting in maximum COD, TCP and toxicity removals were found to be A/Q ratio of nearly 194m2 dm−3, feed COD of nearly 4000mgL−1 and feed TCP of less than 400mgL−1. [Copyright &y& Elsevier]

A mathematical model was developed to describe the Cu(II) ion inhibition on chemical oxygen demand (COD) removal from synthetic wastewater containing 15mgl−1 Cu(II) in an activated sludge unit. Experimental data obtained at different sludge ages (5–30days) and hydraulic residence times (HRT) (5–25h) were used to determine the kinetic, stoichiometric and inhibition constants for the COD removal rate in the presence and absence of Cu(II) ions. The inhibition pattern was identified as non-competitive, since Cu(II) ion inhibitions were observed both on maximum specific substrate removal rate (k) and on the saturation constant (K s) with the inhibition constants of 97 and 18mgl−1, respectively, indicating more pronounced inhibition on K s. The growth yield coefficient (Y) decreased and the death rate constant (b) increased in the presence of Cu(II) ions due to copper ion toxicity on microbial growth with inhibition constants of 29 and 200mgl−1, respectively indicating more effective inhibition on the growth yield coefficient or higher maintenance requirements. The mathematical model with the predetermined kinetic constants was able to predict the system performance reasonably well especially at high HRT operations. [Copyright &y& Elsevier]

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−1), 4-CP (500mgl−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. [Copyright &y& Elsevier]

Abstract: Effects of hydraulic residence time (HRT) and the sludge age (solids retention time, SRT) on the performance of an activated sludge unit treating synthetic wastewater containing 14mgl−1 Cu(II) ion were investigated. Percent COD removal increased with increasing sludge age for both Cu-free and Cu(II)-containing wastewater. However, percent COD removal was lower in the presence of Cu(II) due to Cu(II) ion toxicity on the microorganisms at all sludge ages. Cu(II) ion toxicity was eliminated at high sludge ages (30 days) due to high biomass concentrations. Percent toxicity removals and biomass concentrations increased, but the sludge volume index (SVI) decreased with increasing sludge age. Increases in hydraulic residence time also resulted in increases in percent COD and toxicity removals and also in biomass concentrations, but decreases in the sludge volume index (SVI) for both in the absence and presence of Cu(II) ions. Percent COD removals were much higher in the absence of Cu(II) ions for all HRT levels tested. Copper ion toxicity on COD removal performance of the activated sludge unit was partially eliminated by operation at high sludge ages (30 days) and HRTs (25h). [Copyright &y& Elsevier]

Abstract: Waste sludge samples from different plants were tested for Cu(II) ion biosorption capacities with and without pre-treatment. Waste sludge from a paint industry wastewater treatment plant was found to perform better than the others after pre-treatment with 1% H2O2. Powdered waste sludge (PWS) from the paint industry wastewater treatment plant was used for recovery of Cu(II) ions from aqueous solution by biosorption after pre-treatment with 1% H2O2. Batch kinetics and isotherms of biosorption of Cu(II) ions were investigated at variable initial Cu(II) concentrations between 50 and 400mgl−1 with a PWS particle size of 64μm. The pseudo-first and -second order kinetic models were used to correlate the experimental data. The kinetic constants were determined for both models and the second order kinetic model was found to be more suitable. The Langmuir, Freundlich and the generalized isotherm models were used to correlate the equilibrium biosorption data and the isotherm constants were determined. The Langmuir isotherm was found to fit the experimental data better than the other isotherms tested. The maximum biosorption capacity (116mgg−1) of the pre-treated powdered waste sludge for Cu(II) ions was found to be superior as compared to the other biosorbents reported in literature [Copyright &y& Elsevier]

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–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−1 after 6h of incubation. Similar to percent dyestuff removal, the rate of adsorption was maximum at a PWS concentration of 4gl−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. [Copyright &y& Elsevier]

Abstract: Biofilm processes offer considerable advantages for biological treatment of chlorophenol containing wastewaters since such industrial effluents are difficult to treat by conventional activated sludge processes. A rotating perforated tubes biofilm reactor (RTBR) was developed and used for treatment of 2,4-dichlorophenol (DCP) containing synthetic wastewater. Effects of COD and DCP loading rates on COD, DCP and toxicity removals were investigated. Percent COD removal decreased and effluent COD increased with increasing COD and DCP loading rates due to toxic effects of high DCP content in the feed. DCP and toxicity removals showed similar trends. As the DCP loading rate increased the effluent DCP content increased yielding high toxicity levels in the effluent. COD and DCP loading rates should be below 90gCODm−2 d−1 and 2.8gDCPm−2 d−1 in order to obtain more than 90% DCP and toxicity removals. However, DCP loading rates lower than 1gDCPm−2 d−1 are required to obtain more than 90% COD removal. Empirical equations were developed to estimate percent COD, DCP and toxicity removals as functions of COD and DCP loading rates. The coefficients of the empirical equations were determined by using the experimental data. Empirical model predictions for percent COD, DCP and toxicity removals were in good agreement with the experimental data. [Copyright &y& Elsevier]

Toxic chlorophenol compounds present in many chemical industry wastewaters cause severe problems in biological wastewater treatment. Para-chlorophenol (4-chlorophenol, 4-CP) containing synthetic wastewater was treated in an activated sludge unit at different sludge ages varying between 3 and 30 days, while the feed chemical oxygen demand (COD) (2,500 mg L−1), 4-CP (500 mg L−1) and hydraulic residence time (HRT, 25 h) were constant in order to investigate the effects of sludge age on COD, 4-CP, and toxicity removals. Biomass concentration in the aeration tank increased from 1,500 to 6,250 mg L−1 with increasing sludge age from 3 to 30 days, resulting in considerable increases in COD, 4-CP, and toxicity removals. Percent COD removal increased from 61 to 93%, while 4-CP and toxicity removals increased from 4 to 99% when the sludge age was raised from 5 to 30 days. The Resazurin method, based on dehydrogenase activity, was used for assessment of the feed and effluent wastewater toxicity. Sludge volume index decreased with increasing sludge age, indicating improved settling characteristics of the sludge at high sludge ages. Specific rates of COD removal increased, but 4-CP removal decreased with increasing reactor 4-CP content, indicating 4-CP inhibition on 4-CP removal for 4-CP concentrations above 200 mg L−1 in the reactor. The system should be operated at a sludge age of 10 days or above in order to obtain more than 90% COD and nearly complere removal of 4-CP and toxicity. [ABSTRACT FROM AUTHOR]

Wastewaters containing chlorophenol compounds are difficult to treat by biological means because of the toxic effects of those compounds on microorganisms. To investigate the adverse effects of chlorophenols on microorganisms, synthetic wastewater containing 2,4 dichlorophenol (DCP) was biologically treated in an activated sludge unit al different hydraulic residence times (HRTs) between 5 and 40 hours, whereas the teed chemical oxygen demand (COD). DCP concentrations, and sludge age were kept constant al 2500 ± 50 me/L, 150 mg/L, and 20 days, respectively. The resazurin tin method based on dehydrogenase activity was used for assessment of the feed and effluent wastewater toxicity. Percent COD, DCP, and toxicity removals increased, and the effluent COD, DCP, and toxicity levels decreased with increasing HRT. Biomass concentration in the aeration tank increased with increasing HRT because of low levels of DCP at high HRT levels. resulting in high COD, DCP, and toxicity removals. The sludge volume index decreased with increasing HRT. yielding well-settling organisms as a result of low levels of toxicity mid high concentrations of active cells. Percent DCP and COD removals decreased with increasing specific DCP loading rate, The rates of DCP and COD removals showed a maximum al a low DCP concentration of 6 mg/L in the aeration tank, corresponding to a 25-hour HRT. Water Environ Res., 78, 686 (2006). [ABSTRACT FROM AUTHOR]

Abstract: Chlorinated phenolic compounds present in some chemical industry wastewaters cause severe toxic effects on the organisms and often are resistant to biological degradation. Synthetic wastewater containing different concentrations of para-chlorophenol (4-chlorophenol, 4-CP) was biologically treated in an activated sludge unit for COD, 4-CP and toxicity removal. Effects of feed 4-CP concentration on COD, 4-CP, toxicity removals and on sludge volume index were investigated at a constant sludge age of 20 days and hydraulic residence time (HRT) of 25h. Resazurin method based on dehydrogenase activity was used for determination of the toxicity of the feed and effluent wastewater. COD and 4-CP removals were not affected by the presence of 4-CP in the wastewater up to feed 4-CP concentration of 925mgl−1 because of almost complete degradation of 4-CP yielding lower than 50mgl−1 4-CP in the aeration tank. Percent COD, 4-CP and toxicity removals decreased and the effluent COD, 4-CP and toxicity levels increased with further increases in the feed 4-CP concentrations above 925mgl−1 because of inhibitory concentrations of 4-CP in the reactor. Biomass concentration in the aeration tank decreased and the sludge volume index (SVI) increased with feed 4-CP concentrations above 925mgl−1 resulting in lower COD and 4-CP removal rates. The rates of COD and 4-CP removals indicated substrate (4-CP) inhibition for the feed 4-CP concentrations above 925mgl−1 corresponding to the reactor 4-CP of above 200mgl−1. The system should be operated at the feed 4-CP concentrations of less than 900mgl−1 (4-CPR <200mgl−1) in order to obtain high rates and extents of COD, 4-CP and toxicity removals at a sludge age of 20 days and HRT of 25h. [Copyright &y& Elsevier]

Abstract: Powdered waste sludge (PWS) was used for removal of copper(II) ions from aqueous solution by biosorption. Waste activated sludge obtained from a paint industry wastewater treatment plant was pre-treated with 1% hydrogen peroxide solution dried, ground and sieved to a number of fractions with different particle sizes. Biosorption capacity of pre-treated PWS for Cu(II) ion removal was investigated as function of particle sizes (external surface area), copper(II) and PWS concentrations and also pH using batch biosorption experiments. Biosorbed copper ion concentrations increased with increasing specific external surface area of PWS, initial Cu2+ concentration and pH, but decreased with increasing PWS concentration. Percent copper removal from the solution also increased with increasing external surface area or decreasing particle size of the adsorbent, PWS concentration and pH, but decreased with increasing initial copper ion concentration. The maximum biosorption capacity was 156mg Cu2+ gPWS−1 when PWS concentration was 0.25gl−1 with an average particle size of 64μm. The initial volumetric rate of biosorption also increased with increasing specific external surface area of PWS resulting in nearly 70mg Cul−1 h−1 at a specific external surface area of 943cm2 g−1 with the smallest particle size (53μm) tested. Optimal pH resulting in maximum biosorption was 5 with a minimum zeta potential (−15.6mV) on the surface of the PWS particles. [Copyright &y& Elsevier]

Abstract: A recently developed rotating perforated tubes biofilm reactor (RTBR) was used for treatment of 2,4-dichlorophenol (DCP) containing synthetic wastewater. Effects of important operating variables such as A/Q ratio, feed wastewater DCP/COD ratio and DCP concentration on percent COD, DCP and toxicity removals were investigated. Percent COD, DCP and toxicity removals increased and effluent COD, DCP and toxicity levels decreased with increasing A/Q ratio because of larger biofilm surface area at high A/Q ratios. A/Q ratio above 130m2 dm−3 resulted in more than 97% COD, DCP and toxicity removals when the feed COD and DCP contents were 5000 and 100mgl−1, respectively. Increasing feed DCP concentrations did not affect percent DCP and toxicity removals considerably resulting in more than 97% removals for the feed DCP up to 393mgl−1. However, percent COD removal decreased with increasing feed DCP content probably because of natural selection of DCP degrading organisms and potential inhibitory effects of DCP degradation products on COD removing microorganisms. A kinetic model describing the COD removal rate was developed and the kinetic constants were determined by using the experimental data. Kinetic model estimations of the system performance were in good agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: COD, nitrogen, phosphate and para-chlorophenol (4-chlorophenol, 4-CP) removal from synthetic wastewater was investigated using a four-step sequencing batch reactor (SBR) at different sludge ages and initial para-chlorophenol (4-CP) concentrations. The nutrient removal process consisted of anaerobic, oxic, anoxic and oxic phases with hydraulic residence times (HRT) of 1/3/1/1h and a settling phase of 0.75h. A Box–Wilson statistical experiment design was used considering the sludge age (5–25days) and 4-CP concentration (0–400mgl−1) as independent variables. Variations of percent COD, NH4-N, PO4-P and 4-CP removals with sludge age and initial 4-CP concentration were investigated. Percent nutrient removals increased with increasing sludge age and decreasing 4-CP concentrations. Low nutrient removals were obtained at high initial 4-CP concentrations especially at low sludge ages. However, high sludge ages partially overcome the adverse effects of 4-CP and resulted in high nutrient removals. COD, NH4-N, PO4-P and 4-CP removals were 76%, 72%, 26% and 34% at a sludge age of 25days and initial 4-CP concentration of 200mgl−1. Sludge volume index (SVI) also decreased with increasing sludge age and decreasing 4-CP concentrations. An SVI value of 104mlg−1 was obtained at a sludge age of 25days and initial 4-CP of 200mgl−1. [Copyright &y& Elsevier]

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−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−1 resulting in lower COD and DCP removal rates. The system should be operated at feed DCP concentrations of less than 150mgl−1 in order to obtain high COD, DCP, and toxicity removals. [Copyright &y& Elsevier]

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−1 h−1) and release rates (2.23mgPl−1 h−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%). [Copyright &y& Elsevier]

Abstract: Effective treatment of dyestuff containing wastewaters require advanced treatment technologies such as adsorption for the removal of dyestuffs. Powdered activated carbon (PAC) has been the most widely used adsorbent for the removal of dyestuffs from wastewaters. As an alternative to PAC, powdered activated sludge (PAS) was used as adsorbent for dyestuff removal from synthetic wastewater in this study. The colour removal performance of PAS was compared with that of PAC under the same experimental conditions. Turquoise Blue-G was used as the dyestuff and the effects of adsorbent concentration on the rate and extent of colour removal were investigated for both adsorbents. The colour removal performance of PAS was comparable with that of PAC at high adsorbent concentrations above 4gl-1, resulting in nearly 95% colour removal with 200mgl-1 initial dyestuff concentration. The rates of dyestuff removal were comparable for both adsorbents when initial adsorbent concentration was larger then 4gl-1. Maximum dyestuff removal rates obtained with 6gl-1 adsorbent concentration were 85 and 80mgl-1h-1 for PAS and PAC, respectively. Three different isotherms were tested for correlation of the equilibrium adsorption data and the Langmuir isotherm was found to be the most suitable one. The maximum adsorption capacities of PAC and PAS were approximately 100 and 92mgg-1, respectively. [Copyright &y& Elsevier]

A dynamic mathematical model was developed to predict the effluent quality of facultative wastewater stabilization ponds. For a sound representation of sediment–water column, water column–atmosphere interactions and stratification due to variations in dissolved oxygen concentrations, a two-dimensional hydraulic model was employed considering dispersed flow and diffusion in horizontal and vertical directions, respectively. Resulting partial differential equation system was solved using finite difference methods and matrix manipulation techniques. The model has been calibrated and evaluated on the basis of collected data from a full-scale facultative stabilization pond in Selçuk, Izmir. Variations of COD, NH4-N, PO4-P, dissolved oxygen, bacteria and algae concentrations with time and the dimensions of the pond were estimated by using the dynamic model. The model can be used for design of new stabilization ponds and also, for improving the effluent quality of existing ponds. [Copyright &y& Elsevier]

Nutrient removal from synthetic wastewater was investigated using a four-step sequencing batch reactor (SBR) at different phenol (C6H5OH) concentrations in order to determine the inhibition effects of phenol on biological nutrient removal. The nutrient removal process consisted of anaerobic, oxic, anoxic, and oxic phases with hydraulic residence times (HRT) of 1 h/3 h/1 h/1 h and a settling phase of 3/4 h. Solids retention time (SRT) was kept constant at 10 days in all experiments. Initial phenol concentrations were varied between 0 and 600 mg l-1 at seven different levels. The effects of phenol on COD, NH4-N, and PO4-P removals and effluent nutrient levels were investigated. Phenol was almost completely degraded up to 400 mg l-1 phenol concentration resulting in almost negligible inhibition effects on COD, NH4-N, and PO4-P removals. Nutrient removals were adversely affected by phenol at concentrations above 400 mg l-1. Above 95% COD, 90% NH4-N and 65% PO4-P removal was obtained for phenol concentrations below 400 mg l-1. The sludge volume index (SVI) was almost constant around 45 ml g-1 for phenol concentrations below 400 mg l-1 but increased to 90 ml g-1 at a phenol level of 600 mg l-1. [Copyright &y& Elsevier]

Biological treatment of nitrogen deficient wastewaters are usually accomplished by external addition of nitrogen sources to the wastewater which is an extra cost item. As an alternative for effective biological treatment of nitrogen deficient wastewaters, the nitrogen fixing bacterium, Azotobacter vinelandii, was used in activated sludge and also in pure culture. Total organic carbon (TOC) removal performances of Azotobacter-added and free activated sludge cultures were compared at different initial TN/TOC ratios. The rate and extent of TOC removal were comparable for all cultures when initial TN/TOC ratio was larger than 0.12; however, both the rate and extent of TOC removal from nitrogen deficient (TN/TOC < 12%) synthetic wastewater were improved by using Azotobacter-added activated sludge as compared to the Azotobacter-free activated sludge culture. More than 90% TOC removal was obtained with pure Azotobacter or Azotobacter-added activated sludge culture from a nitrogen deficient synthetic wastewater. [Copyright &y& Elsevier]

Nutrient removal from synthetic wastewater was investigated using a four-step sequencing batch reactor (SBR) at different 2,4 dichlorophenol (DCP) concentrations. The nutrient removal process consisted of anaerobic, oxic, anoxic, and oxic phases with hydraulic residence times (HRT) of 1/ 3/ 1/1 h and a settling phase of 45 min. Solids retention time (SRT) was kept constant at 10 days in all experiments. Initial dichlorophenol concentrations were varied between 0 and 240 mg/L at eight different levels. Effects of dichlorophenol on removal of COD, NH4-N, and PO4-P and on effluent nutrient concentrations were investigated. Dichlorophenol was almost completely degraded up to 123 mg/L influent concentration. Adverse effects of dichlorophenol on COD removal were almost negligible for DCP concentrations below 123 mg/L. About 96% COD, 46% NH4-N, and 22% PO4-P removals were obtained at a DCP concentration of 123 mg/L. The sludge volume index (SVI) changed in a range of 59 to 93 mL/g for DCP concentrations below 123 mg/L, which increased to 142 mL/g at a DCP level of 240 mg/L. [ABSTRACT FROM AUTHOR]

Nutrient removal from synthetic wastewater was carried out by using a labscale sequencing batch reactor. Three different operations consisting of different numbers of steps were tested and their performances were compared. These operations were the three-step operation consisting of anaerobic(An)/anoxic(Ax)/oxic(Ox) steps; the four-step (An/Ox/Ax/Ox), and the five-step (An/Ax/ Ox/Ax/Ox) operations. Effects of number of operating stages and the total cycle time on COD, nitrogen (NH4-N, NO3-N) and phosphate (PO4-P) removal from synthetic wastewater were investigated. Experiments were carried out with a constant sludge age of 10 days. The highest nutrient removals were realized by using the five-step operation with percent COD, NH4-N, NO3-N and PO4-P removals of 94%, 90%, 64% and 57%, respectively. Re-moval efficiencies of COD and NH4-N in three- and four-step operations were slightly higher than those of the five-step operation However,NO3-N and PO4 -P removal efficiencies obtained by the five-step operation were clearly higher than those for the other operations. Therefore, the five-step operation with 10.5 h overall cycle time was selected as the most appropriate one for effective nutrient removal. [ABSTRACT FROM AUTHOR]

Nutrient removal from synthetic wastewater was studied as a function of nutrient composition in a five-step sequencing batch reactor (SBR) in order to determine the most suitable nutrient ratios maximizing nutrient removal. The nutrient removal process consisted of anaerobic, anoxic, oxic, anoxic, oxic phases. Hydraulic residence times (HRT) of the aforementioned phases were kept constant at 2/1/4.5/1.5/1.5 h with 1/2 h of settling phase. Solids retention time (SRT) was constant at 10 days in all experiments. COD/N and COD/P ratios in the nutrient medium were considered as independent variables with a constant initial chemical oxygen demand (COD) of 1200 mg l−1. Box–Wilson statistical experiment design was used to determine the effects of independent variables on COD, NH4-N, and PO4-P removal efficiencies. The results were correlated by a response function and the coefficients determined by regression analysis. COD/N/P ratio resulting in maximum COD, NH4-N and PO4-P removal efficiencies was found to be 100/2/0.54 yielding COD, NH4-N and PO4-P removal efficiencies of 95, 94 and 99%, respectively. [Copyright &y& Elsevier]

The N2-fixing bacterium, Azotobacter vinelandii, was used both in single culture and in combination with activated sludge culture for the treatment of nitrogen-deficient wastewaters as an alternative to external nitrogen supplementation. Azotobacter-supplemented activated sludge culture removed more total organic carbon (TOC), especially at low initial TN/COD (total nitrogen/chemical oxygen demand) ratios, than the Azotobacter-free culture. Up to 95% TOC removal efficiencies were obtained with synthetic media of TN/COD<4 when Azotobacter was used singly or with activated sludge. The results indicated clear advantage of using Azotobacter in the activated sludge to improve TOC removal from nitrogen-deficient wastewaters. [ABSTRACT FROM AUTHOR]

A novel biofilm reactor named as `rotating perforated tubes biofilm reactor' was used for treatment of synthetic wastewater with and without liquid phase aeration. Effects of major process variables such as feed wastewater flow rate, COD concentration and loading rate, liquid phase aeration on the rate and extent of COD removal were investigated. Liquid phase aeration was proven to be advantageous especially for high strength wastewaters at high COD loading rates. Kinetics of COD removal was investigated and kinetic constants were determined by using the experimental data. An empirical design equation was developed to quantify the system's performance as a function of major process variables. [ABSTRACT FROM AUTHOR]

Discusses information on a study which investigated the biological treatment of saline wastewater in a rotating biodisc contactor unit by using an activated sludge culture. Materials and methods; Results and discussion; Mathematical modeling and determination of kinetic constants; Conclusions.