Organics removal in oily bilgewater by electrocoagulation process

This study investigated the treatment of oily bilgewater using an electrocoagulation technique. Electrocoagulation process was evaluated at laboratory scale (1.7 l electrolytic cell) and involved utilization of two kinds of electrodes (iron and aluminium) arranged either in bipolar (BP) or monopolar (MP) configuration. Results showed that the best performance was obtained using mild steel MP electrode system operated at a current intensity of 1.5A, through 60 or 90 min of treatment. Under these conditions, removal yields of 93.0+/-3.3% and 95.6+/-0.2% were measured for BOD and O&G, respectively, whereas CODs and CODt were removed by 61.3+/-3.6% and 78.1+/-0.1%, respectively. Likewise, 99.4+/-0.1% of n-C10 to n-C50 hydrocarbons was removed from oily bilgewater. Electrocoagulation was also efficient for clarification of OBW. Removal yields of 99.8+/-0.4% and 98.4+/-0.5% have been measured for TSS and turbidity, respectively. Electrocoagulation process operated under the optimal conditions involves a total cost of 0.46 US$ per cubic meter of treated OBW. This cost only includes energy and electrode consumptions, chemicals, and sludge disposal.     

Heavy metal removal from waste waters by ion flotation

Flotation studies were carried out to investigate the removal of heavy metals such as copper (II), zinc (II), chromium (III) and silver (I) from waste waters. Various parameters such as pH, collector and frother concentrations and airflow rate were tested to determine the optimum flotation conditions. Sodium dodecyl sulfate and hexadecyltrimethyl ammonium bromide were used as collectors. Ethanol and methyl isobutyl carbinol (MIBC) were used as frothers. Metal removal reached about 74% under optimum conditions at low pH. At basic pH it became as high as 90%, probably due to the contribution from the flotation of metal precipitates.     

Optimization of oil removal from oily wastewater by electrocoagulation using response surface method

Electrocoagulation process with sacrificial aluminium anode was used to separate oil from oily wastewater emulsion. A preliminary experimental study was performed to evaluate the most accurate operating parameters, which are then used for the determination of oil removal efficiency. An experimental design using response surface method (RSM) was then applied and oil separation was estimated by measuring turbidity and chemical oxygen demand (COD). An optimal region characterised with low values of turbidity and COD was found. As part of the optimized process, the main effects of the operational parameters were also investigated. The experimental results indicated that electrocoagulation was very efficient and able to achieve 99% turbidity and 90% chemical oxygen demand (COD) in less than 22 min and current density of 25 mA cm(-2). Analysis of variance (ANOVA) showed a high variance coefficient (R(2)) value of 0.998, thus ensuring a satisfactory adjustment of the second-order regression model with the experimental data.     

The investigation of parameters affecting boron removal by electrocoagulation method

Boron removal from wastewaters by electrocoagulation using aluminum electrode material was investigated in this paper. Several working parameters, such as pH, current density, boron concentration and type and concentration of supporting electrolyte were studied in an attempt to achieve a higher removal capacity. The experiments were carried out by keeping the pH of solution constant and optimum pH of solution was determined 8.0 for the aluminum electrode. Although energy consumption increased with decreasing boron concentration, which conductivity of these solutions were low, boron removal efficiency was higher at 100 mg/L than that of 1000 mg/L. Current density was an important parameter affecting removal efficiency. Boron removal efficiency and energy consumption increased with increasing current density from 1.2 to 6.0 mA/cm2. The types of different supporting electrolyte were experimented in order to investigate to this parameter effect on boron removal. The highest boron removal efficiency, 97%, was found by CaCl2. Added CaCl2 increased more the conductivity of solution according to other supporting electrolytes, but decreased energy consumption. The results showed to have a high effectiveness of the electrocoagulation method in removing boron from aqueous solutions.     

Boron removal from aqueous solutions by ion-exchange resin: column sorption-elution studies

A column sorption-elution study was carried out by using a strong base anion-exchange resin (Dowex 2 x 8) for the removal of boron from aqueous solutions. The breakthrough curve was obtained as a function of feed flow rate and the total and breakthrough capacity values of the resin were calculated. The boron on the resin was quantitatively eluted with 0.5M HCl solution at different flow rates. Three consecutive sorption-elution-washing-regeneration-washing cycles were applied to the resin in order to investigate the reusability of the ion-exchange resin. Total capacity values remained almost the same after three sorption-elution-regeneration cycles. The Thomas and the Yoon-Nelson models were applied to experimental data to predict the breakthrough curves and to determine the characteristic column parameters required for process design. The results proved that the models would describe the breakthrough curves well.     

Boron removal from aqueous solutions by activated carbon impregnated with salicylic acid

In this study, the removal of boric acid from aqueous solution by activated carbon impregnated with salicylic acid was studied in batch system. pH, adsorbent amount, initial boron concentration, temperature, shaking rate and salicylic acid film thickness were chosen as parameters. Boron removal efficiencies increased with increasing adsorbent amount, temperature and pH, decreasing initial boron concentration. As thickness of salicylic acid film on activated carbon becomes thin up to 0.088nm, the efficiency increased, and then, the efficiency decreased with becoming thinner than 0.088nm of salicylic acid film. Shaking rate was no effect on removal efficiency. In result, it was determined that the use of salicylic acid as an impregnant for activated carbon led to the increase of the amount of boron adsorbed. A lactone ring, being the most appropriate conformation, forms between boric acid and -COOH and -OH groups of salicylic acid.     

Combined electrocoagulation and electroflotation for removal of fluoride from drinking water

A combined electrocoagulation (EC) and electroflotation (EF) process was proposed to remove fluoride from drinking water. Its efficacy was investigated under different conditions. Experimental results showed that the combined process could remove fluoride effectively. The total hydraulic retention time required was only 30 min. After treatment, the fluoride concentration was reduced from initial 4.0-6.0mg/L to lower than 1.0mg/L. The influent pH value was found to be a very important variable that affected fluoride removal significantly. The optimal influent pH range is 6.0-7.0 at which not only can effective defluoridation be achieved, but also no pH readjustment is needed after treatment. In addition, it was found that SO(4)(2-) had negative effect; Ca(2+) had positive effect; while Cl(-) had little effect on the fluoride removal. The EC charge loading, EF charge loading and energy consumption were 3.0 Faradays/m(3), 1.5 Faradays/m(3), and 1.2 kWh/m(3), respectively, under typical conditions where fluoride was reduced from initial 4.0 to 0.87 mg/L.     

The effects of pH on phosphate removal from wastewater by electrocoagulation with iron plate electrodes

In this study, the effect of pH on phosphate removal from wastewater by electrocoagulation with iron plate electrodes has been investigated. For this aim, experiments have been carried out controlled initial pH values within the range of 3-9. Effects of initial pH have been analyzed on efficiencies of phosphate removal and energy consumptions. From obtained results, it was found that optimal initial pH is 3. Besides, experiments have been carried out controlled system pH. Effects of system variables have been analyzed on constant pH. From obtained results in these experiments, it was found that optimal system pH is 7.     

Optimization of Bomaplex Red CR-L dye removal from aqueous solution by electrocoagulation using aluminum electrodes

In this paper, Taguchi method was applied to determine the optimum dye removal from aqueous solution by electrocoagulation using aluminum electrodes. An orthogonal array (OA(16)) experimental design that allows to investigate the simultaneous variations of five parameters (initial dye concentration, initial pH of the solution, supporting electrolyte concentration, supporting electrolyte type and current density) having four levels was employed to evaluate the effects of experimental parameters. Performance measure analysis was followed by performing a variance analysis, in order to determine the optimum levels and relative magnitude of the effect of parameters. Because the desired characteristic for response has been maximum decolorization, Taguchi's 'the larger the better' performance formula was used. While the optimum conditions were found to be initial dye concentration of 100 mg/L, initial pH of the solution of 3, supporting electrolyte concentration of 0.0 mM, supporting electrolyte type of CaCl(2) and current density of 0.50 mA/cm(2). Under these optimum conditions, energy consumption is 0.607 kWh/kg dye, when the system evaluated also based on the energy consumptions it can be said that optimum conditions should be modified as follows: supporting electrolyte concentration of 2.5 mM; supporting electrolyte type NaCl, for 100 mg/L initial dye concentration; initial pH of the solution of 3; current density of 0.50 mA/cm(2).     

An empirical model for parameters affecting energy consumption in boron removal from boron-containing wastewaters by electrocoagulation

In this study, it was investigated parameters affecting energy consumption in boron removal from boron containing wastewaters prepared synthetically, via electrocoagulation method. The solution pH, initial boron concentration, dose of supporting electrolyte, current density and temperature of solution were selected as experimental parameters affecting energy consumption. The obtained experimental results showed that boron removal efficiency reached up to 99% under optimum conditions, in which solution pH was 8.0, current density 6.0 mA/cm(2), initial boron concentration 100mg/L and solution temperature 293 K. The current density was an important parameter affecting energy consumption too. High current density applied to electrocoagulation cell increased energy consumption. Increasing solution temperature caused to decrease energy consumption that high temperature decreased potential applied under constant current density. That increasing initial boron concentration and dose of supporting electrolyte caused to increase specific conductivity of solution decreased energy consumption. As a result, it was seen that energy consumption for boron removal via electrocoagulation method could be minimized at optimum conditions. An empirical model was predicted by statistically. Experimentally obtained values were fitted with values predicted from empirical model being as following; [formula in text]. Unfortunately, the conditions obtained for optimum boron removal were not the conditions obtained for minimum energy consumption. It was determined that support electrolyte must be used for increase boron removal and decrease electrical energy consumption.     

Comparison between electrocoagulation and chemical precipitation for metals removal from acidic soil leachate

This paper provides a quantitative comparison between electrocoagulation and chemical precipitation based on heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) removal from acidic soil leachate (ASL) at the laboratory pilot scale. Chemical precipitation was evaluated using either calcium hydroxide or sodium hydroxide, whereas electrocoagulation was evaluated via an electrolytic cell using mild steel electrodes. Chemical precipitation was as effective as electrocoagulation in removing metals from ASL having low contamination levels (30 mg Pbl(-1) and 18 mg Znl(-1)). For ASL enriched with different metals (each concentration of metals was initially adjusted to 100 mg l(-1)), the residual Cr, Cu, Pb and Zn concentrations at the end of the experiments were below the acceptable level recommended for discharge in sewage urban works (more than 99.8% of metal was removed) using either electrocoagulation or chemical precipitation. Cd was more effectively removed by electrochemical treatment, whereas Ni was easily removed by chemical treatment. The cost for energy, chemicals and disposal of metallic residue of electrocoagulation process ranged from USD 8.83 to 13.95 tds(-1), which was up to five times lower than that recorded using chemical precipitation. Highly effective electrocoagulation was observed as the ASL was specifically enriched with high concentration of Pb (250-2000 mg Pbl(-1)). More than 99.5% of Pb was removed regardless of the initial Pb concentration imposed in ASL and, in all cases, the residual Pb concentrations (0.0-1.44 mg l(-1)) were below the limiting value (2.0 mg l(-1)) for effluent discharge in sewage works.     

Arsenic removal by electrocoagulation using combined Al-Fe electrode system and characterization of products

Combination of electrodes, such as aluminum and iron in a single electrochemical cell provide an alternative method for removal of arsenic from water by electrocoagulation. The removal process has been studied with a wide range of arsenic concentration (1–1000 ppm) at different pH (4–10). Analysis of the electrochemically generated by-products by XRD, XPS, SEM/EDAX, FT-IR, and Mössbauer Spectroscopy revealed the expected crystalline iron oxides (magnetite (Fe₃O₄), lepidocrocite (FeO(OH)), iron oxide (FeO)) and aluminum oxides (bayerite (Al(OH)₃), diaspore (AlO(OH)), mansfieldite (AlAsO₄·2(H₂O)), as well as some interaction between the two phases. The amorphous or very fine particular phase was also found in the floc. The substitution of Fe³⁺ ions by Al³⁺ ions in the solid surface has been observed, indicating an alternative removal mechanism of arsenic in these metal hydroxides and oxyhydroxides by providing larger surface area for arsenic adsorption via retarding the crystalline formation of iron oxides.     

A quantitative comparison between electrocoagulation and chemical coagulation for boron removal from boron-containing solution

This paper provides a quantitative comparison of electrocoagulation and chemical coagulation approaches based on boron removal. Electrocoagulation process delivers the coagulant in situ as the sacrificial anode corrodes, due to a fixed current density, while the simultaneous evolution of hydrogen at the cathode allows for pollutant removal by flotation. By comparison, conventional chemical coagulation typically adds a salt of the coagulant, with settling providing the primary pollutant removal path. Chemical coagulation was carried out via jar tests using aluminum chloride. Comparison was done with the same amount of coagulant between electrocoagulation and chemical coagulation processes. Boron removal obtained was higher with electrocoagulation process. In addition, it was seen that chemical coagulation has any effect for boron removal from boron-containing solution. At optimum conditions (e.g. pH 8.0 and aluminum dose of 7.45 g/L), boron removal efficiencies for electrocoagulation and chemical coagulation were 94.0% and 24.0%, respectively.     

Boron removal by membrane contactors: the water that purifies water

The potential of membrane contactors for treating boron containing waters were investigated. In particular, experimental tests at lab scale on flat membrane modules with 40 cm² of membrane area were carried out, to identify the effect of different parameters, such as temperature, flow rate, boron concentration, etc. on the efficiency of the process. Water was chosen as the extractant in order to avoid the pollution of the feed stream and two symmetric microporous hydrophilic flat membranes with different pore size and porosity were used. From these tests, it results that the boron removal increases with the extractant temperature and with the operating flow rates. However, it is independent on the initial boron concentration in the feed water. Moreover, higher removals are obtained with the membrane with larger pore size and higher porosity. Based on the experimental results, an integrated reverse osmosis-membrane contactor system, where the membrane contactor works on the reverse osmosis permeate, was proposed and designed for a 100 m³/h fresh water production (with a boron content ≤0.4 ppm). In particular, membranes with higher porosity and lower thickness than those used in the experimental tests were considered for the calculations, in order to work at 25°C (so, there is no need of heating the extractant stream) with reasonable membrane areas. The comparison of the proposed plant to that actually used, has shown that the proposed one appears to be more effective in terms of size, energy and chemical consumption, flexibility and modularity.     

Boron removal and recovery from concentrated wastewater using a microwave hydrothermal method

Boron compounds are widely-used raw materials in industries. However, elevated boron concentrations in aqueous systems may be harmful to human and plants. In this study, calcium hydroxide (Ca(OH)(2)) alone and Ca(OH)(2) with phosphoric acid (H(3)PO(4)) addition (P-addition) were used to remove and recover boron from wastewater using hydrothermal methods. A microwave (MW) hydrothermal method was used and compared with the conventional heating (CH) method in batch experiments. Physicochemical properties of the precipitates obtained from both methods were analysed by XRD, SEM with EDX and BET. For the case of Ca(OH)(2) alone and the MW method, experimental results showed that boron recovery efficiency reached 90% within 10 min, and crystals of Ca(2)B(2)O(5)·H(2)O were found in the precipitates as indicated by the XRD analysis. For the case of P-addition and the MW method, boron recovery efficiency reached 99% within 10 min, and calcium phosphate species (CaHPO(4)·H(2)O, CaHPO(4) and Ca(10)(PO(4))(6)(OH)(2)) were formed. The experimental results of this study indicate that the required reaction time of the MW method was much less than that of the CH method, and the MW method is an effective and efficient method for boron removal and recovery from concentrated wastewater.     

Simulation the kinetics of fluoride removal by electrocoagulation (EC) process using aluminum electrodes

In this study, iron-rich natural Camlica Bentonites, CB1 and CB2, were used for the sorption of boron in water samples. Boron was determined by newly progressed fluorimetric azomethine-H method. The optimum conditions found using factorial designs are pH 10, 45 degrees C, 0.250 g of clay and 20 mL of sample volume. It was found that 180 min is enough time for the equilibrium state to be reached in boron adsorption. At these conditions, boron sorption percentage was 80% for CB1 and 30% for CB2. The adsorption isotherms are well described by linear Freundlich model. Various geothermal waters in our country were also studied for boron sorption.     

Effects of alternating and direct current in electrocoagulation process on the removal of cadmium from water

In practice, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of cadmium from water using aluminum alloy as anode and cathode. The results showed that the removal efficiency of 97.5 and 96.2% with the energy consumption of 0.454 and 1.002 kWh kl⁻¹ was achieved at a current density of 0.2 A/dm² and pH of 7.0 using aluminum alloy as electrodes using AC and DC, respectively. For both AC and DC, the adsorption of cadmium was preferably fitting Langmuir adsorption isotherm, the adsorption process follows second order kinetics and the temperature studies showed that adsorption was exothermic and spontaneous in nature.     

The optimization of Cr(VI) reduction and removal by electrocoagulation using response surface methodology

In this study Response Surface Methodology (RSM) was employed to investigate the effects of different operating conditions on the removal of hexavalent chromium (Cr(VI)) by the electrocoagulation with stainless steel electrodes. Central Composite Design (CCD) was used for the optimization of the electrocoagulation process and to evaluate the effects and interactions of process variables: applied electric current, electrolyte concentration and application time on the removal of Cr(VI). A sample of metal finishing industry wastewater having a high Cr(VI) concentration of 1470 mg/L was used in the experimental study. The optimum conditions for complete (100%) Cr(VI) removal were established as 7.4A applied electric current, 33.6 mM electrolyte (NaCl) concentration and 70 min application time. The amount of sludge produced under the conditions optimized based on the results from the model was lower than the amount generated by chemical treatment with FeSO(4).7H(2)O and non-hazardous in nature.     

Radon concentration in waters of geothermal Euganean basin--Veneto, Italy

Since ancient times the warm thermal waters of Euganean basin, Italy, have been used for therapeutic purposes. The radioactive characteristics, assumed in depth, are due, in particular, to radon gas, which when released during the therapies in the indoor thermal room, determines exposure for the workers. The preliminary results of the project, the purpose of which is to analyze the totality of thermal springs, are presented. The concentrations, obtained by gamma spectrometry, show a high variability, and are comparable to those in other thermal springs in Italy and abroad. Possible correlations with geophysical factors, such as the temperature and depth of springs, have been investigated. A geostatistical analysis of the radon data has also been carried out, through the study of the experimental variogram, obtained by kriging one map of the radon concentration: such an approach is useful not only for mapping but also for giving one possible interpretation of the examined phenomenon through structural geologic characteristics.