Removal of Color and Chemical Oxygen Demand Using a

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Removal of Color and Chemical Oxygen Demand Using a Coupled Coagulation Electrocoagulation Ozone Treatment 363. In solution Al3 3OH Al OH 3 6 180 190 rpm followed by 10 min of slow mixing at 30 rpm. Afterward samples were filtered through filter paper. Compared with conventional water treatment processes. in which chemicals are added to water to cause precipitation Electrochemical reactor and electrocoagulation. and enhance flocculation electrocoagulation has several ad. vantages including reduction of waste volume lower cost and A batch electrochemical reactor was constructed for the elec. improvised solid liquid separation 29 trocoagulation step The electrode system is monopolar Fig 1. On the other hand ozonation is one of the most attractive shows a schematic diagram of the electrochemical reactor. alternatives for solving the problem of color in textile effluents The reactor cell contains an array of 8 parallel Al elec. Ozone is an extremely strong oxidant E 2 07 V and reacts trodes Each electrode is 0 15 m long by 0 1 m wide with a. rapidly with most organic compounds Ozone is selective and surface area of 0 03 m2 for a total anodic surface Aa of 0 12. preferentially attacks the unsaturated bonds of chromophores m2 The distance between the electrodes was of 2 cm Each 2 5. which are often associated with color 30 dm3 batch of water was treated in a bucket which served as the. Ozone reacts with water and wastewater compounds in supply vessel for the reactor A study of variation of the current. two different ways namely direct molecular and indirect free density was conducted to evaluate the best conditions for the. radical type reactions Both pathways are important for color electrocoagulation experimental applying 15 15 33 33 45 45. removal Application of ozone to decolorize different classes and 66 6 A m 2 using DC power source. of textile dyes is a well known process and has been used for. two decades 31 Ozonation, Ozonation rarely produces complete mineralization to car. bon dioxide and water but leads to partial oxidation sub prod Previously treated wastewater was used in the ozone reactor. ucts such as organic acids aldehydes and ketones 30 The Ozonation experiments were carried out in a 0 5 L Pyrex reactor. mineralization of organic compounds strongly depend on the with a continuous 5 g h 1 supply of O3 Ozone was generated by. oxidation conditions means of a Pacific Ozone Technology instrument using air as. Ozonation is regularly used as a pre oxidation step for or a feeding gas The ozone air mixture was fed through diffusers. ganic matter prior to coagulation followed by filtration and or placed at the bottom of the reactor Ozone gas concentration in. as a final purification disinfection step during the treatment of the influent and effluent gas was measured by the Potassium. surface waters for the production of drinking water 32 Iodide Method 33 The gaseous outlet from the reactor was. In this study we present the results of a combined coagu led to a killer where the remaining ozone was destroyed by. lation electrochemical and ozone treatment into an integrated means of a reaction with KI All experimental procedures were. process as a promising alternative for the treatment of waste realized by duplicate. water containing compounds with high color values and low. biodegradability Methods of analysis, The initial evaluation of the electrochemical and ozone treat. Experimental ments was determined by analysis of the COD Color Pt Co. unit pH and turbidity at different time intervals as indicated. Wastewater samples in the standard methods procedures 33. Samples of wastewater were collected at the outlet of an indus Cyclic Voltammetric measurements. trial process which uses offset dyes to print cardboard boxes. The wastewater has different colors blue green black and Cyclic voltammetry of crude and treated wastewater was per. red depending on the printing jobs done This wastewater formed using a standard three electrode cell The waveforms. contained is highly turbid were generated by a potentiostat model BAS 100W controlled. The daily volume of residual wastewater was 12 m3 The by BAS software The carbon paste electrodes CPE were. circular with a surface area of about 5 mm2 The CPE was pre. samples were collect in plastic containers and cooled to 4 C. pared from a 1 1 mixture of 99 99 pure single crystal graphite. then transported to the laboratory for analysis and treatments. Alfa AESAR and nujol oil Fluka The paste was transferred. Coagulation, In coagulation experiments Al2 SO4 3 analytical grade Fer. mont and aluminum hydroxychloride AHC from Clariant. 90 of purity were used as coagulants added to the aqueous. dye solutions at a volume of 0 5 L The pH of the dye sample. was not adjusted The jar test was used to perform these experi. ments under the following conditions 2 3 min rapid mixing at Figure 1 Schematic diagram of the electrochemical reactor. 364 J Mex Chem Soc 2014 58 3 Gabriela Roa Morales et al. into a PVC tube and compacted to eliminated trapped air then Table 1 Color and turbidity reduction using Al2 SO4 3. a copper conductor was inserted before the paste set The sur Parameter Raw 1000 4000 7000 8500. face of the electrode was renovated after each potential scan Dose mg L 1. The scan rate was 100 mV s 1 The reference electrode was an pH 8 8 8 8 8 7 8 6 8 5. Ag AgCl saturated with KCl and the counter electrode was a. Color Pt Co 5 69x106 5 69 x106 5 69 x106 2 79x106 40 x106. platinum wire, Turbidity 3 15x105 3 15x105 3 15x105 1 65x105 5 0x105. UV Vis spectrometry, COD mg L 1 5 3x105 5 30x105 5 3x105 1 8 x105 9 3 x104.
UV Vis spectra were obtained from samples of raw and treated. wastewater using a double beam Perkin Elmer 25 spectropho. tometer The scan rate was 960 nm s 1 within the 200 900 nm Table 2 Color and turbidity removal using AHC. wavelength range The samples were scanned in quartz cells Parameter Raw 5 10 15 20 25. with a 1 cm optical path Dose mL L 1,pH 8 8 8 6 8 2 8 0 7 9 7 7. Sludge Characterization Color Pt Co 5 69x106 4 8x106 2 3x106 2 6x105 2 070 575. Turbidity 3 15x105 2 83x105 1 8x105 6 000 16 1, The sludge generated by the coagulation process was analyzed. by scanning electron microscopy SEM and energy dispersive. X ray EDX microanalysis The analysis was performed on COD mg L 1 5 3x105 5 2x105 2 9x105 6 1x104 9 870 6 870. a Philips XL 30 microscope to observe the composition and. configuration of the structure SEM provides images of material. with resolution down to fractions of a micrometer while EDX AHC is a pre polymerized Al III compound containing a. offers in situ elemental analysis range of hydrolysis and polymeric species which are relatively. large and carry a high cationic charge Their enhanced surface. activity and improved charge neutralizing capacity may make. them more effective at a comparatively lower dose than alu. Results and discussion, minum sulfate Our results agree with other reports that indi. Wastewater characteristics cate that compared to conventional Al III salts AHC has the. following advantages rapid aggregation velocity larger and. The offset printing process uses a wide range of dyes The heavier flocs and lower required dosage 5 34. most common colors are black red blue yellow and green. However the red removal requires the strongest conditions of Electrocoagulation. all Therefore the following conditions correspond to the red. treatment which ensures that all the dyes producing color in Wastewater samples were taken from the previous coagulation. wastewater can be eliminated experiments with a COD of 9870 mgL 1 then electrochemically. Because the wastewater contains a high concentration of treated using the reactor described earlier adjusting the pH us. suspended solids using direct electrocoagulation makes that ing NaOH or H2SO4 and applying 4 A of current. electrodes passivate due to the accumulation of the suspend Current density not only determines the coagulant dosage. ed particles so it was decided to remove them previously by rate but also the bubble production rate and the floc growth. chemical coagulation as shown below which can influence the treatment efficiency of the electro. coagulation Therefore the effect of current efficiency on the. Coagulation removal of pollutants was investigated. Figure 2 shows the variation of the COD as a function of. Coagulation experiments were carried out using the jar test The current density At 50 min of treatment time the three highest. optimal AHC and Al2 SO4 3 doses are shown in Tables 1 and 2 current densities produce similar COD reductions 33 3 A m 2. In Table 1 the initial dye concentration in the residual wastewa 61 27 45 45 A m 2 61 71 and 60 6 A m 2 62 3. ter is high but increasing the coagulant dose reduces the COD Moreover higher current densities have been found to increase. color and turbidity Table 1 shows that using Al2 SO4 3 is not the need for maintenance and cleaning of the electrodes so. very effective since small pollutant reductions are reached with current densities around 20 25 A m 2 are recommended from. additions as high as 500 mgL 1 Indeed a huge dose of 8500 mg a maintenance standpoint 35. L 1 is required to achieve an 83 reduction in COD The best experimental conditions for the electrocoagula. It is interesting to observe in Table 2 that a high reduction tion treatment were at pH 8 and 33 3 A m 2 of current density. of the COD is attained when AHC is added to wastewater Table 3 shows the COD color and turbidity reduction as a. However beyond 20 mL of AHC the reduction is less dramatic function of treatment time under these conditions. Therefore an optimum dose of 20 mL AHC was selected for The COD reduction as a function of time is show in. further treatment Fig 2, Removal of Color and Chemical Oxygen Demand Using a Coupled Coagulation Electrocoagulation Ozone Treatment 365. 50 minutes taking the data of Fig 2 with the conditions of pH. 8 and 33 3 A m 2 The value for the first order rate constant is. k1 0 019 min 1 with R2 0 9105 however the second order. model gives R2 0 9622 and k2 3x10 6 dm3 mg 1min 1 The. second order model equation 7 describing the decrease in. COD with time is,k CCOD 2 7, Where CCOD represents the COD mg dm 3 t represents.
the time and k the rate constant in dm3 mg 1 min 1. The kinetics of the electrocoagulation COD reduction is. Figure 2 COD at different electrocoagulation current densities shown in Figure 3. Recent research supports second order kinetics for the. COD reduction for electrocoagulation treatment 37 38. After 50 min of treatment reductions of 62 of COD 55. of color and 81 of turbidity were obtained These values are Ozonation. consistent with data reported in the literature in which the use. of electrocoagulation with aluminum electrodes in wastewater The previous coagulated electrocoagulated sample was used. from a plant paste processor results in near COD removal of with the parameters that are given in the first column of Table. 64 at pH 8 during 45 min of treatment applying 18 2 mA 4 and the ozonation was applied under those conditions. m 2 28 Another study indicates that contamination of textile The ozone treatment had little effect on COD or pH of. wastewater can be made using electrocoagulation with alumi wastewater However there is a significant color reduction. num electrodes and 100 A m 2 of current density during 10 indeed the satisfactory time for the application of this treat. min producing a reduction of 50 COD 5 The discoloration ment is 15 min. of the dye Remazol red RB 123 by means of electrocoagula. tion with aluminum electrodes to pH 6 obtaining 100 color. removal when the initial concentration of the dye was 100 mg. L 1 and 70 color removal when the initial concentration of. the dye was 1000 mgL 1 after 10 min of a 100 A m 2 current. density These investigators conclude that the greater the initial. concentration of dyes the smaller the reduction in color 4 Fi. nally electrocoagulation with aluminum electrodes for discol. oration and removal of phenolic compounds and observed that. the efficiency in the color removal during 30 min of treatment. at pH 8 was 82 and with respect to the COD an efficiency. of 52 is had using 300 A m 2 of current density 36. The COD reduction kinetics was evaluated using the first Figure 3 Second order kinetics fit of the COD reduction at pH 8 and. and second order equations through a final electrolysis time of 33 3 A m 2 of current density. Table 3 Color turbidity and COD removal using electrocoagulation. Parameter Process time min Pre treated water 10 20 30 40 50. pH 7 9 8 1 8 5 8 6 8 6 8 7,Color Pt Co 2 070 1 446 1 300 1 020 952 915. Turbidity NTU 16 12 4 3 3 3,COD mg L 1 9 870 6 970 5 285 4 300 3 976 3 750. Table 4 Color turbidity and COD removal using ozone. Parameter Ozone time min AHC treated water Electrocoagulation 5 10 15 20 25. pH 8 7 8 5 8 1 8 0 7 9 7 8,Color Pt Co 915 220 128 92 83 73. Turbidity NTU 3 1 1 0 0 0,COD mg L 1 3 750 3 550 3 450 3 430 3 430 3 420. 366 J Mex Chem Soc 2014 58 3 Gabriela Roa Morales et al. The efficiencies obtained in this investigation by means. of ozonation were 90 of color removal and nearly 9 of. COD reduction during 15 min of treatment Another study in. wastewater that contains dyes originating from the textile in. dustry use oxidation by ozone during 15 min of treatment and. obtains efficiencies of 92 of color removal to a wavelength. of 436 nm 96 8 to a wavelength of 525 nm and 100 to a. Removal of Color and Chemical Oxygen Demand Using a Coupled Coagulation Electrocoagulation Ozone Treatment of Industrial Wastewater that Contains Offset Printing Dyes Gabriela Roa Morales 1 Carlos Barrera D az 1 Patricia Balderas Hern ndez 1 Francisco Zaldumbide Ortiz 1 Horacio Reyes Perez 2 Bryan Bilyeu3

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