Enhanced efficiency of treatment of tnt wastewater by internal electrolysis reaction use bimetalic materials fe-Cu - Vu Duy Nhon

Journal of Science and Technology 54 (4B) (2016) 11-18 11 ENHANCED EFFICIENCY OF TREATMENT OF TNT WASTEWATER BY INTERNAL ELECTROLYSIS REACTION USE BIMETALIC MATERIALS Fe-Cu Vu Duy Nhan1, 2, *, Nguyen Van Tu1, Nguyen Thi Nhan1, Le Mai Huong3, Le Thi Mai Huong4, Cao Dinh Thanh5 1Institute of Chemistry and Materials, 17 Hoang Sam Street, Cau Giay, Hanoi 2Graduate University of Science and Technology, VAST, 18 Hoang Quoc Viet, Hanoi 3Institute of Natural Products Chemistry, VAST, 18 Hoang Quoc Viet, Hanoi 4Isntitute for technology of radioactive and rare elements, VINATOM, 48 Lang Ha, Hanoi 5Vietnam Atomic Energy Isntitute, VINATOM, 59 Ly Thuong Kiet, Hoan Kiem, Hanoi *Email: vuduynhantshu@gmail.com Received: 15 August 2016; Accepted for publication: 10 November 2016 ABSTRACT In this article, wastewater containing 2,4,6 trinitrotoluen (TNT) was treated by internal microelectrolysis with bimetal Fe-Cu materials. Components of TNT pollutant content was identified by HPLC method. Examined factors: pH, time, temperature, concentration of Fe-Cu bimetal to efficient treatment of TNT in the wastewater. With conditions at pH 5, bimetal Fe-Cu dosage of 50 g for l litre of wastewater, TNT original content in the wastewater infected about 95-106.4 mg/l, temperature of 25 0C, after 6 hours of processing time, content TNT rest 0.2 - 0.5 mg/l, after 6 hours not observed. Keywords: bimetal Fe-Cu, treatment TNT, internal microelectrolysis. 1. INTRODUCTION 2,4,6 Trinitrotoluen (TNT) is a chemical widely used in national defense and industrial ammunition. In fact, about 50 years after World War II, in the building where Army ammunition factory still find large amounts of TNT and their isomers [3, 6]. This demonstrates the long-term viability in the wild of these substances in other words they are hard biodegradation. In the industrial manufacture of explosives discharged a large amount of wastewater containing TNT. To treat these wastewater TNT, researchers often use combinations [3, 5, 6, 7] the methods of physics, chemistry and biology together. Physical methods commonly used activated carbons such as powder or granular to absorb TNT. These methods have high treatment efficiencies, but have relatively high processing costs Vu Duy Nhan, et al 12 and cause secondary pollution. Chemical methods which commonly use to treat wastewater containing TNT are: methods include redox chemistry, electrochemistry, oxidation by O3, O3- UV, Fenton, flocculation, and extraction. The disadvantages of these methods are difficult to apply to the wastewater that have high concentrations of waste, require complex equipments, highly cost difficultly scale up and often cause secondary pollution. In recent years, the researchers have developed new technologies known as internal electrolyte base on material of Fe-C. Internal electrolysis technology has been used to pretreat wastewater containning difficultly biodegradable wastes, and high concentration of pollutants, such as: textile wastewater, pharmaceuticals, paper industry, the pesticide industry, the drug industry the manufacture of explosives, plating industry, petrochemical industry, industrial production of nitrogen fertilizers [1 - 8]. According to the documents published, the English name of internal electrolysis method can be written as: Internal microelectrolysis, Interior microelectrolysis, Micro-electrolysis [3], Iron carbon Internal- electrolysis [4, 14], Bimetallic Fe-Cu process [1, 8] Ferric-Carbon micro electrolysis [4], micro cell bed filter process [6]. Internal electrolysis reaction is electrochemical reaction occurs itself by internal electrolyte materials (metals - alloys created microgalavanic) exposed to water. In making this alloy into water will form a multitude of micro batteries, in which some more electronegativity metals will play anode, the less electronegativity metals will serve the cathode, oxygen electrode reactions redox goes as follows [1-8]. Reaction at anode： Fe-2e = Fe2+ Eo(Fe2+/Fe) = -0.44 V (1) If the solution appears the organic material: RX (organochlorine compound), RNO2 (nitro aromatic compounds), which are components capable of accepting electrons from the anode surface (Fe metals), they will be reduced according to the reaction removing of chlorination and amines. Thus, pollutant products will be turned to less toxic or non-toxic, easily biodegradable by biological methods. However, to further improve the processing efficiency by the zero-valent iron (Feo) method, recently researchers used internal electrolysis reaction, by combining iron with copper metal, which has more high voltage values [1, 4, 8]. To improve the efficiency of wastewater treatments containing TNT; we studied the influences of factors such as pH, temperature, treatment time, dosage Fe-Cu bimetal materials on the reduction of TNT in the wastewater. Furthermore, we determined the effectiveness of TNT treatment by Fe-Cu bimetal material and applicability into practice and initially explained the mechanisms of internal electrolyte reaction. 2. EXPERIMENTS 2.1. Preparation materials 2.1.1. Sample of Fe-Cu bimetal preparation Proceed collected samples of steel shavings from the mechanical workshops around Hanoi city, preliminary washed to remove impurities, cut short with the average length of 3 - 5 cm, immersed in NaOH solution of 30 % for 30 minutes for degreasing and entire surface cleaning, surface activation by washing repeatedly and handling in the HCl:H2O solution (1 : 5; v/v) for 30 minutes. Next washed several times with water, dried at 105 oC for 2 h, cooled, maintain in sealed glass jars. The composition of elements in steel CT3 is shown in Table 1. Improve efficiency of treatment TNT wastewater by bimetal materials Fe-Cu 13 Table 1. Composition of additional elements of steel CT3. Elements C Si Mn Ni S P Cr Cu As Content (wt.%) 0.14 - 0.22 0.05 - 0.17 0.4-0.65 0.03 0.05 0.04 0.03 0.03 0.08 Bimetal Fe-Cu samples were treated as follows: Using of steel shavings CT3 entered into CuSO4 solution with a concentration of 1 %, 3 %, 5 %, in the period time of 0.5; 1; 2; 3; 4; 5 minutes, then washed several times with water and dried at a temperature of 105 oC during 3-4 h. 2.1.2. Sample preparation and wastewater containing TNT treatment Wastewater samples were collected directly from the factories Z121, Z113, Z131 and Z115 at different times, with different content of TNT. The characteristics of wastewater containing TNT from factories that was surveyed are given in Table 2. Table 2. The composition of TNT contaminated in wastewater. Name factory COD (mg/l) BOD5 (mg/l) TNT (mg/l) NH4 (mg/l) pH T-P (mg/l) Color Z113, Enterprise A6 155 - 210 30 – 56 25 - 56 23 - 45 6.5 – 7.6 0.25 Dark brown red Z121, Enterprise 4 250 - 270 42 – 67 32 -128 35 - 42 7.9-8.2 0.13 Red-brown, yellow Z 131, Enterprise 2 165 -207 37.5 – 52 35 - 94 42 - 57 6.8-8.2 - Dark brown red Z131, Enterprise 3 148 -243 37 – 58 27 - 105 32 - 47 6.8-7.8 - Red-brown, yellow Z115, Workshop AD1 128 - 310 28.3– 35 43 - 92 68 - 79 7.2 0.38 Red-brown, yellow 2.2. Method and equiment research Bimetallic Fe-Cu sample material after plating were analyzed by scaning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) methods (SEM-EDS, S4800, Hitachi). Components of TNT pollutant content was identified by HPLC method (Agilent 7900 ICP-MS (Cananda)) at the Institute of new Technology, Institute of Military Technology. Measurement conditions: Column Hypersil C18 + (200 x 4 mm);The percentage of mobile phase MeOH: H2O = 70: 30 (V / V); Flow rate of 0.8 ml/min; Pressure: 280 bar. Proceeding: After set the necessary parameters, conducting pumping wash, wash columns, running the baseline and steady pressure for 30 ÷ 45 minutes. Using a micropipette to take 5ml of analysis sample put in the sample chamber, the machine will automatically record the parameters: retention time (RT), pic heights and electrical properties as well as the percentage (%) of each structure element in the mix [11]. Vu Duy Nhan, et al 14 3. RESULTS AND DISCUSSION 3.1. Survey bimetallic Fe-Cu material Selecting fabrication conditions: Using CT3 steel shavings entered CuSO4 solution with different concentrations: 1 %, 3 %, 5 %, for the period of 0.5; 1; 2; 3; 4; 5 minutes. Sensory results showed: With CuSO4 solution concentration of 1 % in the plating period of 0.5; 1; 2; 3; 4; 5 minutes, coating all surfaces not coated steel shavings. As for the concentration of 5 % for a period of 0.5 to 1 minute, the plated coating is too thick, less durable. When using CuSO4 solution 3 % concentration with time from 0.5 to 1 minute, the coating obtained thin, if continued plated with 4 or 5 minutes time, the coating is too thick, porous, poor durability, with 2 minutes time, plated surfaces are covered evenly, have a good link with CT3 steel surfaces. From the above results, we establish time of 2 minutes and plated CuSO4 solution with a concentration of 3 % for the next sample. 3.1.1. SEM image analysis of bimetalic Fe-Cu Snapshot of iron shavings material samples by electron microscope before and after plating with 3 % concentration in 2 minutes CuSO4 shown in Figure 1. The results show that stable coating, sized particles reasonable to get the durable and surfaces porous to easily participate in chemical reactions. Figure 1. SEM images of original material (a) Iron shavings original material; (b) Bimetalic Fe-Cu material after plating (c) Performance of TNT decomposition by Fe-Cu system at different pH. 3.2. The influence of some factors on the efficiency of TNT wastewater treatment 3.2.1. Influence of pH Experiments conducted with 5 g of internal electrolyte material, at a pH value of 3 to 7, the reaction temperature of 25 °C, shaking speed of 120 rpm, TNT wastewater had initial concentration of 105 mg/l. The pH value of the processing can affect response performance. The experimental results of Fe-Cu material system on the different pH are shown in Figure 1c. Results showed that, with pH values from 3 to 5, after 6 hours treatment, the effect of TNT decomposition is equivalent, achieved processing performance nearly 98 %. Initial values of pH are 3 and 4, after the internal electrolyte reaction is completed, the respectively increased pH 5.5 and 6, and initial value of pH is 5, the pH increased to reach 6.5-6.6 after treatment. pH value of 6.5 to 6.6 is considered to be consistent with the biological treatment process followed. Also in wastewater, pH value is closely related to the amount of necessary acid to adjust the degree of 3 4 5 6 7 0 20 40 60 80 100 TN T of re m ov al (% ) pH (c) Improve efficiency of treatment TNT wastewater by bimetal materials Fe-Cu 15 environmental friendliness and operating cost. For these reasons we selected on the pH value of 5 for the next study. 3.2.2. Influence of temperature Conducting experiments with 5 g of internal electrolyte material, adding 100 ml of wastewater into 250 ml flasks, withshaking speed of 120 rpm, carried out in the different temperature 25 oC and 30 oC. The results were as follows: in the first phase, at a temperature of 30 °C, faster reaction speed, after 2 hours of treatment, treatment efficiency in two above temperatures were different, however after 6 hours treatment, the processing efficiency did not have much difference, concentration achieved from 0.5 - 1.5 mg/l. In industrial wastewater treatment, for practical applications, the temperature factor is very important, in addition to the direct impact on processing efficiency, also indirectly affect processing costs and initial investment. Generally, very few technological processes intervene in the wastewater temperature conditions, ie raising or lowering the temperature than natural conditions. Because this process consumed a lot of electrical power, as well as to invest in equipment for heating or cooling. Therefore, the effectively of handling at two temperatures 25 °C and 30 °C is not much different after 6 hours of treatment, the concentration of TNT reaches 0.5 - 2 mg/l. The temperature is 25 - 26 °C are popular in ponds with climatic conditions in our country; despite of different seasons, the water temperature did not have the large changes. We decided to select 25 0C temperature conditions for subsequent experiments. Influence of temperature are shown in Figure 2a. Figure 2. (a)The influence of temperature on efficiency of TNT treatment, (b) Effect of conten of internal electrolyte material. 3.2.3. Influence of Fe-Cu bimetal content Experiments conducted with Fe-Cu bimetal, which were produced by the above method [2.1.1], with different dosages 0.5; 1.0; 3.0; 5.0; 7.5; 10 g. Adding 100 ml of wastewater into 250 ml flasks, adjusting the pH 5, the processing time is 6h, the shaking speed is 120 rpm, temperature of 25 °C. Results are presented in Figure 2b. Results showed that, after processing time of 6h, the internal electrolyte material doses from 50 to 100 g per 1 liter of wastewater, the amount of TNT in the wastewater decreased from 105 mg/l to 0.5 - 2 mg/l. Levels of internal electrolyte materials have a large impact on the processing efficiency, because the amount of used internal electrolyte materials are more, leading to surface area of reaction electrode are large. Meanwhile, the electrochemical oxidation were stronger, cause of many [OH*] and [OH-], Fe2+- newly formed. However, the too large internal electrolyte material levels in the reactor will also affect to the amount of wastewater is stored in the reactor. 0 1 2 3 4 5 6 0 20 40 60 80 100 120 250C 300C C on ce nt ra tio n of T N T( m g/ l) Time (h) (a) 0 10 20 30 40 50 60 70 80 90 100 0 20 40 60 80 100 E ff ic ie nc y of T N T tr ea tm en t ( % ) Content of internal electrolyte materials (g/l) (b) Vu Duy Nhan, et al 16 For optimal processing efficiency we selected dose internal electrolyte materials for l liter 50 g of wastewater in the next study. 3.2.4. Influence of time Experiments conducted with 5 g of internal electrolyte material, at a pH value of 5, the reaction temperature of 25 °C, shaking speed of 120 rpm, TNT wastewater initial concentration of 105mg/l. The results are shown in Figure 3a: Results showed that, within the first 1 h, the effective of decay TNT was not high; TNT content decreased from 105 mg/l to 88 mg/l. However, in about reaction time from 1h to 2h, the decomposition efficiency had a fast increase, content of TNT dropped from 88 mg/l to about 28 mg/l. In the period from 2 hours to 4 hours, the decomposition performance TNT became slow, TNT content fell from 28 mg/l was 12mg/l. At the time of 5 hours treatment, concentration of TNT reduced to levels of TNT 2mg/l. After 6 hours of treatment, the effective of decomposition achieved stable ,TNT at concentrations of 0.2 - 0.3 mg/l. After 8 hours, no longer detect TNT. Figure 3. (a) Influence of time on efficiecy of TNT treatment, (b) Efficiency of TNT treatment. Oviously, when changing system Fe-C electrode to electrode Fe-Cu system, the processing efficiency is significantly increased. Compared with 6 hours of processing time, the Fe-C system with TNT remaining amount is 0.5 - 2 mg/l, the Fe-Cu system is also 0.2 - 0.5 mg/l and TNT is completely decomposion with time 8 h. The reason of internal electrolysis reaction of Fe-Cu bimetal has more effectiveness than Fe-C, due to the presence of copper (Cu) as agent to promote and increase the speed of the reaction of iron with contaminated water. This is explained by the electrochemical oxidation efficiency of internal electrolyte material according to the following equation: Fe – 2e → Fe2+ E0(Fe2+/Fe) = - 0.447 V and Cu + 2e →Cu E0(Cu2+/Cu) = 0.337 V. Between iron and copper have difference standard voltage (E0) in the solution, so they will take on the role of different electrodes and thereby forming the battery system with the reaction of the line are: Fe + Cu2+ → Fe2+ + Cu. Meanwhile, the electromotive of the battery system is: E0 = E0 (Cu2+/Cu) - E0(Fe2+/Fe) – 0.337 + 0.44 = 0.777 V. Alternatively, – ΔG = nG = 2×0.77×.96500=149.961 (kJ), ie ΔG is negative, so the Fe-Cu bimetal soluble process is easier than Fe-C bimetal. 0 1 2 3 4 5 6 7 8 0 20 40 60 80 100 120 C on ce nt ra tio n of T N T( m g/ l) Time(h) (a) 0 2 4 6 8 10 12 14 16 0 20 40 60 80 100 120 Wastewater containing TNT before treated Wastewater containing TNT after treated C on ce nt ra tio n of T N T( m g/ l) Times(day) (b) Improve efficiency of treatment TNT wastewater by bimetal materials Fe-Cu 17 3.2.5. Efficient treatment for wastewater containing TNT To evaluate the effectiveness of the implemented TNT treatment, the experiments were conducted within 12 days, with original TNT concentrations ranging from 95 to 106.4 mg/l with treatment conditions at pH 5, the amount of Fe-Cu bimetal is 50 g per 1 liter of wastewater, temperature 25 0C, the processing time after 8 am the results are presented in Figure 3b and 4. Results showed that efficiency of TNT treatment in the internal electrolysis system is relatively stable, after a reaction time, TNT were completely decomposed. In the relatively stable operating condition with an excess of the internal electrolyte material was added, the consumable materials component did not have effects on the results. Figure 4. HPLC analysis spectrum of TNT-contaminated water (a) the content of the original TNT (b) content TNT after treament by internal microelectrolysis method. 4. CONCLUSION We examined factors: pH, time, temperature, content of Fe-Cu bimetal to the efficient of TNT contaminated water treatment. 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