Bahadır K. Körbahti

CONTINUOUS ELECTROCHEMICAL TREATMENT OF PHENOLIC WASTEWATER IN A TUBULAR REACTOR

The electrochemical treatment of phenolic wastewater in a continuous tubular reactor, constructed from a stainless steel tube with a cylindrical carbon anode at the centre, was investigated in this study, being first in literature. The effects of residence time on phenol removal was studied at 25 degrees C, 120 g l(-1) electrolyte concentration for 450 and 3100 mg l(-1) phenol feed concentrations with 61.4 and 54.7 mA cm(-2) current densities, respectively. The change in phenol concentration and pH of the reaction medium was monitored in every run and GC/MS analyses were performed to determine the fate of intermediate products formed during the electrochemical reaction in a specified batch run. During the electrolysis mono, di- and tri-substituted chlorinated phenol products were initially formed and consumed along with phenol thereafter mainly by polymerization mechanism. For 10 and 20 min of residence time phenol removal was 56% and 78%, respectively, with 450 mg l(-1) phenol feed concentration and above 40 min of residence time all phenol was consumed within the column. For 1, 1.5, 2 and 3h of residence time, phenol removal achieved was 42%, 71%, 81% and 98%, respectively, at 3100 mg l(-1) phenol feed concentration. It is noteworthy that more than 95% of the initial phenol was converted into a non-passivating polymer without hazardous end products in a comparatively fast and energy-efficient process, being a safe treatment.

Determination of optimum operating conditions of carmine decoloration by UV/H2O2 using response surface methodology.

In this study, the photolytic decoloration of carmine (C.I. Natural Red 4) via UV radiation in the presence of H2O2 was optimized using response surface methodology (RSM). According to analysis of variance (ANOVA) results, the proposed model can be used to navigate the design space. It was found that the response of carmine degradation is very sensitive to the independent factors of carmine concentration, H2O2 concentration, pH and reaction time. The proposed model for D-optimal design fitted very well with the experimental data with R2 and R(adj)2 correlation coefficients of 0.998 and 0.997, respectively.

Photolytic decolorization of Rose Bengal by UV/H2O2 and data optimization using response surface method

Rose Bengal (C.I. name is Acid Red 94) was irradiated with UV light in the presence of hydrogen peroxide. The photoinduced decolorization of the dye was monitored spectrophotometrically. The apparent rate of decolorization was calculated from the observed absorption data and was found to be pseudo first order. A systematic study of the effect of dye concentration and H(2)O(2) concentration on the kinetics of dye decolorization was also carried out. Dye decolorization increased with increasing H(2)O(2) concentration and decreasing dye concentration. The maximum dye decolorization was determined as 90% with 0.005 mM dye at optimum 0.042 M H(2)O(2) and pH 6.6. Additionally, the effect on decolorization of this dye in the presence of some additives (ions) was also investigated. It was seen that sulphite caused a maximum effect on % decolorization of the dye solution. A plausible explanation involving the probable radical initiated mechanism was given to explain the dye decolorization. The experimental data was also optimized using the response surface methodology (RSM). According to ANOVA results, the proposed model can be used to navigate the design space. It was found that the response of Rose Bengal degradation is very sensitive to the independent factors of dye concentration, H(2)O(2) concentration, pH and reaction time. The proposed model for D-optimal design fitted very well with the experimental data with R(2) and R(adj)(2) correlation coefficients of 0.85 and 0.80, respectively.

Continuous electrochemical treatment of simulated industrial textile wastewater from industrial components in a tubular reactor.

The continuous electrochemical treatment of industrial textile wastewater in a tubular reactor was investigated. The synthetic wastewater was based on the real process information of pretreatment and dyeing stages of the industrial mercerized and non-mercerized cotton and viscon production. The effects of residence time on chemical oxygen demand (COD), color and turbidity removals and pH change were studied under response surface optimized conditions of 30 degrees C, 25 g/L electrolyte concentration and 3505 mg/L COD feed concentration with 123.97 mA/cm(2) current density. Increasing residence time resulted in steady profiles of COD and color removals with higher treatment performances. The best column performance was realized at 3h of residence time as 53.5% and 99.3% for COD and color removals, respectively, at the expense of 193.1 kWh/kg COD with a mass transfer coefficient of 9.47 x 10(-6) m/s.

Non-passivating polymeric structures in electrochemical conversion of phenol in the presence of NaCl.

The formation of non-passivating polymeric structures was investigated during electrochemical conversion of phenol using carbon electrodes and NaCl as electrolyte. The influence of initial phenol concentration, current density and reaction temperature on phenol conversion and polymer morphology was studied by FTIR and STM, while the fate of intermediate compounds was analyzed by GC/MS. Unlike previous work, non-passivating solid polymer was produced at high voltage and current density values in the presence of NaCl. The most orderly polymer formed at 912 mg l(-1) initial phenol concentration, current density 32.9 mA cm(-2), NaCl concentration 120 g l(-1) and temperature 25 degrees C. Higher operational parameters yielded disorderly formed aggregates of the polymer in decreasing surface density on STM images. Along with the polymer, only toxic mono-, di- and tri-chlorophenols were formed as intermediate compounds during the electrochemical conversion, which eventually were polymerized and/or oxidized to final products. FTIR analysis and enlarged STM image implied the repeating phenol units in the polymer structure. The results may lead to appropriate techniques for the removal of phenol from wastewater in the form of a solid polymer.

Bilge Water Treatment in an Upflow Electrochemical Reactor using Pt Anode

Bilge water treatment was studied in an upflow electrochemical reactor (UECR) in order to design a compact onboard wastewater treatment system. The influence of retention time on the removal efficiencies of chemical oxygen demand (COD) and turbidity were analyzed, and optimized using response surface methodology (RSM) for maximizing the removal efficiencies. The best operating performance was obtained at 390 min retention time and 480 min reaction time for cost effective analysis with the composition of 100% bilge water (CODo = 3080 mg/L) and 50/50% seawater/fresh water, 12.8 mA/cm2 current density, and 32°C reaction temperature. Under response surface optimized conditions, the responses were estimated as; 90% COD removal, 97% turbidity removal, outlet pH value of 8.1, mass transfer coefficient of 0.494 × 10−5 m/s, and mean energy consumption of 44.8 kWh/kg COD removed.

Electrochemical Oxidation of Resorcinol in Aqueous Medium Using Boron-Doped Diamond Anode: Reaction Kinetics and Process Optimization with Response Surface Methodology

Electrochemical oxidation of resorcinol in aqueous medium using boron-doped diamond anode (BDD) was investigated in a batch electrochemical reactor in the presence of Na2SO4 supporting electrolyte. The effect of process parameters such as resorcinol concentration (100–500 g/L), current density (2–10 mA/cm2), Na2SO4 concentration (0–20 g/L), and reaction temperature (25–45°C) was analyzed on electrochemical oxidation using response surface methodology (RSM). The optimum operating conditions were determined as 300 mg/L resorcinol concentration, 8 mA/cm2 current density, 12 g/L Na2SO4 concentration, and 34°C reaction temperature. One hundred percent of resorcinol removal and 89% COD removal were obtained in 120 min reaction time at response surface optimized conditions. These results confirmed that the electrochemical mineralization of resorcinol was successfully accomplished using BDD anode depending on the process conditions, however the formation of intermediates and by-products were further oxidized at much lower rate. The reaction kinetics were evaluated at optimum conditions and the reaction order of electrochemical oxidation of resorcinol in aqueous medium using BDD anode was determined as 1 based on COD concentration with the activation energy of 5.32 kJ/mol that was supported a diffusion-controlled reaction.

Modeling of a continuous electrochemical tubular reactor for phenol removal

In this study, the treatment of highly polluted synthetic phenolic wastewater in a tubular continuous electrochemical reactor was modeled and solved by the finite difference method. The reaction conditions were previously optimized with batch reactor experiments, and the synthetic wastewater containing 443 mg/L and 3063 mg/L initial phenol concentrations was treated in the runs at 25°C with 120 g/L electrolyte concentration. For the model solution, the column was divided into 10 nodes in z-direction and 9 nodes in r-direction with the intervals j z=3.5 cm, j r=0.5 cm, and j t=10 s and 1.2 min for 443 mg/L and 3063 mg/L phenol feed concentrations, respectively. The results of the model solution correlated with the experimental data fairly well, which could be useful in the design and scale up of tubular continuous electrochemical reactors for phenol removal.

Optimization of Electrochemical Oxidation of Textile Dye Wastewater Using Response Surface Methodology (RSM)

The electrochemical treatment of textile dye wastewater containing Levafix Blue CA, Levafix Red CA and Levafix Yellow CA reactive dyes was studied on iron electrodes in the presence of NaCl electrolyte in a batch electrochemical reactor. The wastewater was synthetically prepared in relatively high dye concentrations between 400 and 2,000 mg/L. The effects of initial dye concentration, electrolyte concentration and current density on dye removal, turbidity removal and pH change were studied at 28°C reaction temperature. In the study, complete dye removal and effective turbidity removal achieved; the rate of dye removal obtained as Levafix Yellow CA>Levafix Blue CA>Levafix Red CA at all reaction conditions. The flow pattern was analyzed, mass transfer coefficients and mass fluxes were evaluated. At optimized conditions, mean energy consumption were calculated as 8.3, 9.0 and 7.7 kWh/kg COD removed for Levafix Blue CA, Levafix Red CA and Levafix Yellow CA reactive dyes, respectively.