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Abstract: Para-chlorophenol (4-chlorophenol, 4-CP) containing synthetic wastewater was treated using a rotating perforated tubes biofilm reactor (RTBR). Box–Wilson statistical experiment design and response surface methodology (RSM) were used to investigate the effects of the feed COD, 4-CP contents and the A/Q (biofilm surface/flow rate) ratio on percent COD, 4-CP and toxicity removals. Increases in A/Q ratio and the feed COD contents improved COD, 4-CP and toxicity removals. High feed 4-CP contents adversely affected the system performance due to toxic effects of 4-CP on microorganisms. High A/Q ratio and feed COD contents were required for effective 4-CP and toxicity removals at high feed 4-CP contents. More than 95% 4-CP and toxicity removals were obtained with an A/Q ratio of 186m2 d m−3, and feed COD of 6000mg L−1 with the feed 4-CP content of 1000mg L−1. The RTBR was proven to be more efficient than the RBBR used for the same purpose in our previous studies. [ABSTRACT FROM AUTHOR]

Synthetic wastewater containing 2,4-dichlorophenol (DCP) was biologically treated using a hybrid-loop bioreactor system consisting of a packed column biofilm reactor (PCBR) and an aerated tank with effluent recycle. Effects of the feed DCP concentration on COD, DCP and toxicity removals were investigated. Biomass concentration in the packed column and in the aeration tank decreased with increasing feed DCP content due to toxic effects of DCP on the microorganisms. Low biomass concentrations at high DCP contents resulted in low COD, DCP and toxicity removals. Therefore, percent DCP, COD and toxicity removals decreased with increasing feed DCP content. Nearly 70% COD removal was achieved with a feed DCP content of 380mgL−1. The system should be operated with the feed DCP lower than 100mgL−1 in order to obtain DCP, COD and toxicity removals above 90%. [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]

Abstract: A newly developed rotating brush biofilm reactor was used for DCP, COD and toxicity removal from 2,4-dichlorophenol (DCP) containing synthetic wastewater at different feed COD, TCP concentrations and A/Q (biofilm surface area/feed flow rate) ratios. A Box–Wilson statistical experiment design was used by considering the feed DCP (50–500mgl−1), COD (2000–6000mgl−1) and A/Q ratio (73–293m2 dm−3) as the independent variables while percent DCP, COD, and toxicity removals were the objective functions. The experimental data were correlated by a quadratic response function and the coefficients were determined by regression analysis. Percent DCP, COD and toxicity removals calculated from the response functions were in good agreement with the experimental data. DCP, COD and toxicity removals increased with increasing A/Q ratio and decreasing feed DCP concentrations. The optimum A/Q ratio resulting in the highest COD (90%), DCP (100%) and toxicity (100%) removals with the highest feed COD (6000mgl−1) and DCP (500mgl−1) contents was nearly 210m2 dm−3. [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]

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with effluent recycle was used for biological treatment of 2,4,6-tri-chlorophenol (TCP) containing synthetic wastewater. Effects of hydraulic residence time (HRT) on COD, TCP and toxicity removal performance of the reactor were investigated for the HRT values between 5 and 30h, while the feed COD (2700±100mgl−1), TCP (300±10mgl−1) and the solids retention time (sludge age, SRT, 20d) were constant. Percent TCP, COD and toxicity removals increased with increasing HRT resulting in more than 90% COD, TCP and toxicity removals at HRT values above 25h. Biomass concentrations in the packed column and in the aeration tank increased with increasing HRT resulting in low reactor TCP concentrations and therefore high TCP, COD and toxicity removals at high HRT values. Volumetric and specific rates of TCP and COD removals decreased with increasing HRT due to increased biomass and decreased flow rates at high HRT levels. Volumetric and specific removal rates of COD and TCP were maximum at an HRT of 5h. [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]

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), TCP, and toxicity removal performance of the system were investigated for sludge ages between 5 and 30 days, while the feed COD (2600±100 mg L-1), TCP (370±10 mg L-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 TCP, COD, and toxicity removals. More than 95% of COD, TCP, 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 gX-1 day-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, TCP, and toxicity removal. [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: 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]

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]

High chemical oxygen demand (COD), high ammonium-N content and presence of toxic compounds such as heavy metals result in low removal efficiencies in direct biological treatment of landfill leachate. Raw landfill leachate was subjected to pre-treatment by coagulation-flocculation and air stripping of ammonia before biological treatment. Pre-treated leachate was subjected to biological treatment in an aeration tank operated in repeated fed-batch mode in the absence and presence of powdered activated carbon (PAC) as adsorbent. Three different cycles of 1×30 h, 3×10 h, and 5×6 h were used in the absence and presence of 2 g l−1 PAC. The results clearly indicated that PAC addition has improved COD removal significantly as compared to PAC-free biological treatment. Repeated fed-batch treatment also resulted in lower effluent COD and higher COD removal efficiencies as compared to single-cycle operation. The feed COD of 7000 mg l−1 was reduced to final COD values of 365 mg l−1 and 875 mg l−1 in repeated fed-batch experiments with 5×6 h cycles in the presence (2 g l−1 PAC) and absence of PAC, respectively. Repeated fed-batch operation with 3×30 h cycle length resulted in percent COD removal and final COD content of 94% and 285 mg l−1, respectively, with 2 g l−1 PAC addition. [Copyright &y& Elsevier]

Landfill leachate obtained from the solid waste landfill area contained high chemical oxygen demand (COD) and ammonium ions which resulted in low COD and ammonium removals by direct biological treatment. COD and ammonium ion contents of the leachate were reduced to reasonable levels by chemical precipitation with lime and air stripping of ammonia. The pre-treated 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% NH4-N removals were obtained after 30 h of operation with a flow rate of 0.21 l h−1 and the feed COD content of 7000 mg COD l−1. 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. [Copyright &y& Elsevier]

Due to high chemical oxygen demand (COD), ammonium–N content and presence of toxic compounds such as heavy metals, direct biological treatment of landfill leachate results in low removal efficiencies. In order to improve biological treatability of the leachate, coagulation–flocculation and air stripping of ammonia were used as pre-treatment. Pre-treated leachate was treated biologically using an aeration tank operated in fed-batch mode in the absence and presence of powdered activated carbon (PAC) as adsorbent. PAC addition improved COD removal significantly especially at concentrations above 0.5 g l−1. However, improvements in COD removals were marginal for PAC concentrations above 2 g l−1. Nearly 86% COD removal was achieved with 2 g l−1 PAC added biological treatment whereas, COD removals by only biological oxidation and only PAC adsorption were nearly 74 and 38%, respectively at the end of 30 h of fed-batch operation. An empirical equation was developed to describe the contribution of adsorption over biological treatment as a function of PAC concentration. [Copyright &y& Elsevier]

Biological treatment of saline wastewater in a rotating bio-disc contactor (RBC) was investigated under different operating conditions, such as A/Q ratio, feed COD, COD loading and salt concentrations. COD removal efficiencies were determined and correlated with the aforementioned variables. The constants of the proposed empirical equation were determined using experimental data. Plots of COD removal efficiency as functions of these variables were established in order to estimate the performance of the system under different operating conditions. [Copyright &y& Elsevier]

External addition of nitrogenous compounds is the most common practice used in biological treatment of nitrogen deficient wastewaters. However, this method adds an extra cost to the treatment. As an alternative for effective biological treatment of nitrogen deficient wastewaters, nitrogen fixing bacteria, Azotobacter vinelandii was used in activated sludge culture in this study. COD removal performance of Azotobacter-supplemented activated sludge was compared with Azotobacter-free activated sludge culture for biological treatment of nitrogen deficient synthetic wastewater. Effects of important process variables such as N/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. Azotobacter addition to the activated sludge in biological treatment of nitrogen deficient wastewater (N/COD<0.06) improved the COD removal performance significantly. [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]