Summary of Doctoral thesis Chemical engineering: Study on internal electrolysis combine with AAO-MPPR to treat TNT wastewater

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This dissertation focuses on establishing the process of manufacturing bimetallic Fe / Cu internal electrolysis nanomaterial, thereby studying some characteristics correlation between corrosive line and TNT decomposition kinetics and time. Setting and optimizing the internal electrolysis process by bimetal Fe / Cu nanomaterials combined with biological method A2O-MBBR (moving bed Biological reactor) to treat TNT wastewater at laboratory scale and Pilot scale at the scene.

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Nội dung Text: Summary of Doctoral thesis Chemical engineering: Study on internal electrolysis combine with AAO-MPPR to treat TNT wastewater

MINISTRY OF EDUCATION VIETNAM ACADEMY OF AND TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY VU DUY NHAN STUDY ON INTERNAL ELECTROLYSIS COMBINE WITH AAO-MBBR TO TREAT TNT WASTEWATER Speciality: Chemical Engineering Code: 9 52 03 01 PhD DISSERTATION SUMMARY ON CHEMICAL ENGINEERING Ha Noi - 2020
The work was completed at: Vietnam Academy of Science and Technology Science instructor: 1. Assoc. Prof. Le Thi Mai Huong 2. Prof. Le Mai Huong Reviewer 1: Reviewer 2: Reviewer 3: The dissertation will be presented in front of Dissertation Evaluation Council at Institute level at the Institute of Natural Products Chemistry - Vietnam Academy of Science and Technology, No. 18 Hoang Quoc Viet, Cau Giay, Hanoi. At , / / The dissertation can be found at: 1, National Library of Viet Nam 2, Library of Institute of Natural Products Chemistry - Vietnam Academy of Science and Technology
I. INTRODUCTION 1.1. Background 2,4,6 trinitrotoluene (TNT) is a chemical widely used in defense and economy. The explosive manufacturing industry discharges a large amount of wastewater containing toxic chemicals such as TNT. In fact, about 50 years after World War II, in places where gunpowder factories were built, large amounts of TNT and their isomers were found in soil and water environments [1, 2, 21]. This proves that TNT is capable of long-term survival in nature or in other words, TNT is difficult to biodegrade. In our country, besides the factories is producing ammunition, explosives, and launchers in the defense industry, there are still a large amount of wastewater containing TNT which needs to be treated in warehouses for repairing and collecting ammunition. The commonly methods are used to treat wastewater containing TNT including: physical method (adsorption by activated carbon, electrolysis); chemical method (Fenton, UV - Fenton, internal electrolysis), biological method (aerobic activated sludge, MBBR, UASB, MBR, plants, enzymes, white rot fungi). These measures may be used independent or combination with each other, depending on the nature of the wastewater and the material facilities and economic conditions of the manufacture establishment. This dissertation focuses on establishing the process of manufacturing bimetallic Fe / Cu internal electrolysis nanomaterial, thereby studying some characteristics correlation between corrosive line and TNT decomposition kinetics and time. Setting and optimizing the internal electrolysis process by bimetal Fe / Cu nanomaterials combined with biological method A2O-MBBR (moving bed Biological reactor) to treat TNT wastewater at laboratory scale and Pilot scale at the scene. At the same time, the first step establishing the control automatic or semi-automatic operation software with the conditions of the treatment process are determined. 1
1.2. Research objectives Bimetal Fe / Cu internal electrolytic nanomaterials Internal electrolysis method and biological method A2O - MBBR to treat wastewater containing TNT 1.3. New contributions 1.3.1. Successfully fabricated bimetallic Fe / Cu electrolytic internal materials with average size of 100 nm, potential (voltage) E0 = 0.777 V. In electrolyte solution pH=3 with TNT concentration of 100 mg/L, corrosive current is reaching 14.85*10-6 A/cm2 and corrosion speed reach 8. 87*10-2 mm / year. Therefore has increased the reaction rate, processing efficiency is higher, faster. Concurrently, It has been determined corrosion current and its relationship with LnCt / C0 depend on the duration of the TNT reduction process by the corrosion current measurement method. There has not been any announcement using this method. Some related publication determined the relationship between TNT reduction speed and reduction speed of H+ to H2. 1.3.2. Establishing TNT treatment technology by combining the internal electrolysis method using bimetal Fe/Cu nanomaterials with biological method A2O-MBBR. Nowadays, no announcement has been made which combined these two methods to treat wastewater. The microorganisms in the A2O-MBBR system used to treat wastewater containing TNT has been identified, among them two strains can be new: Novosphingobium sp. (HK1-II, HK1-III) have bootstrap value of 97.4-97.92% to Novosphingobium sediminicola sp. and Trichosporon (HK2-II, TK2-II and HK2-III) have bootstrap value of 97.7% to middelhonenii sp. These two species were published on the international gene bank with the code GenBank: LC483151.1; LC483155.1 and the corresponding link are: https://www.ncbi.nlm.nih.gov/nuccore/LC483151; https://www.ncbi.nlm.nih.gov/nuccore/Lc483155 2
1.4. The layout of dissertation The dissertation consists of 191 pages with 24 tables, 101 pictures, 139 references and 2 appendices. The layout of dissertation: Introduction (3 pages), Chapter 1: Literature review (44 pages), Chapter 2: Materials and methods (15 pages), Chapter 3: Results and discussion (79 pages) ), Conclusion (2 pages), Published works (1 page), References (15 pages), Appendix (17 pages) II. CONTENTS INTRODUCTION The introduction refers to the scientific and practical significance of the dissertation CHAPTER 1: LITERATURE REVIEW Overview of international and domestic studies on issues such as: The studies on treatment methods wastewater containing TNT The studies on the internal electrolysis method to treat wastewater Studies on Fe / Cu bimetallic materials fabrication method for wastewater treatment. Studies on combines biological method of A2O-MBBR to wastewater treatment The studies on software controls the wastewater treatment system. CHAPTER 2: MATERIALS AND METHODS 2.1. Materials Pure TNT Wastewater containing TNT is collected from national defense production facilities 121 100 nm size iron powder. 2.2. Methods  Analytical methods: Analytical methods to determine the structure, size, composition of Fe / Cu bimetal nano: SEM, ERD, EDX. Methods of measuring corrosive lines: potential range -1.00V- 0.0V, scanning speed 10 mV/s, Electrodes compare Ag/AgCl 3
(saturation). The corrosion line and the corrosion potential were measured using Autolab PG30 (Netherlands). TNT analytical methods: HPLC, Von – Amper Methods of determining Fe content Proceed to determine Fe ion content according to EPA 7000B method on Contraa 700 device Method of determining COD, T-N, T-P, NH4 +: According to TCVN or ISO.  Experimental method 1. Fabrication of Nano Fe / Cu materials: by CuSO4 plating method on powder Fe average size of 100 nm on magnetic stirrer. 2. Treatment of TNT wastewater: Prepare a 100 mg/L TNT solution into a 500 ml erlenmeyer flask, change the conditions reaction as pH, temperature, shaking speed, Fe/Cu content to each corresponding research. 3. Experimental planning method: Follow the quadratic planning Box- Behnken and Design-Expert optimization software version 11. 4. Isolation of activated sludge: To activate, take activated sludge from wastewater containing TNT treatment stations of production facilities 121, 115. Then, activated sludge in anaerobic, anoxic and oxic activated condition of 30 days. Then proceed to isolate microorganism system in the sludge is activated. 5. Microbiological classification method: Conduct DNA sequencing of selected strains, then compare with the DNA sequence of 16S are published species by the DDBJ, EMBL, GenBank. CHAPTER 3: RESULTS AND DISCUSSIONS The chapter’s content includes: establishing conditions for manufacturing bimetal Fe/Cu nanomaterials, the effects of internal electrolytic factors, A2O-MBBR to treat wastewater containing TNT and optimize treatment conditions, Kinetic characteristics of internal electrolytic reaction, the diversity of microorganisms in the A2O- MBBR system, the software control the internal electrolytic system combined with A2O-MBBR to treat wastewater containing TNT. 4
3.1. Fabrication of internal electrolytic materials Nano bimetal Fe/Cu This section write details the results of the research to establish the reaction conditions for creating Fe / Cu materials: Fe powder of 100 nm size is plated by CuSO4 solution at a concentration of 6% in 2 minutes. Fe/Cu materials have Cu concentration on the surface of 68.44% and copper atomic mass reaches 79.58%. a b Figure 3.1: SEM image (a) and EDS spectrum of Fe / Cu bimetallic nanomaterials Survey results and comparison of corrosion lines between 2 types of bimetal nanomaterials Fe/C and Fe/Cu are shown in Figure 3.2: a b Figure 3.2: Tafel line of galvanic corrosion of Fe/C electrode system (a) and Fe/Cu after plating (b) at different time values From Figure 3.2, it can be seen that the corrosion potential (EĂM) of Fe materials has the descending rule towards the negative side. However, the potential of Fe/Cu electrolytic internal materials reaches - 0.563 V÷-0.765 V with absolute value higher than the corrosion potential of Fe/C, only from - 0.263 V÷- 0.6693V. 5
Figure 3.3 shows that the corrosion speed of Fe / Cu material is 8,187.10-2 mm/year, which is nearly 2 times higher than that of Fe / C material, only 4,811.10-2 mm/year. 1.6E-5 Dong an mon ir (A) 1.4E-5 1.2E-5 Fe/Cu Fe/C 1.0E-5 8.0E-6 6.0E-6 4.0E-6 20 40 60 80 100 120 Thời gian (phút) Figure 3.3: The dependent on time of corrosion line of electrode material system: Fe/C before plating -- (a) and Fe/Cu after chemical plating -■- (b) Thus, bimetallic Fe/Cu electrolytic internal material has been synthesized with average size of 100 nm, potential voltage E0 = 0.777 V. In electrolyte solution which have pH=3, concentration of TNT 100 mg/L, Fe/Cu materials have corrosion current density 14.85*10-6 A/cm2 and corrosion speed 8,187*10-2 mm/year. 3.2. Effect of factors on the efficiency of TNT treatment 3.2.1. Effect of pH The effectiveness of TNT treatment depends on the initial pH value of the electrolyte solution. The results are shown in the Figure 3.4: 100 100 2 80 2.5 80 3 3.5 60 4 60 4.5 TNT(mg/L) TNT (mg/L) 5 5.5 40 40 6 20 20 0 0 0 20 40 60 80 100 120 140 160 180 2 3 4 5 6 pH Thời gian (phút) Figure 3.4: Treatment efficiency of Figure 3.5: Dependence TNT in different initial pH treatment efficiency on initial pH conditions at the time of 90 minutes over time 6
Figures 3.4 and 3.5 show that during the first 90 minutes, the reaction speed was very fast, achieving high processing efficiency. At 90 minutes, the TNT concentration reached 1.61; 1.62; 1.71 and 1.72 mg/L and treatment efficiency in turn 98.29; 98.22; 98.34 and 98.22% correspond to the initial pH values of 2.0; 2.5; 3.0; 3.5. For pH 4.0; 4,5; achieved a lower efficiency and the corresponding TNT concentration was 3.05; 13.09 mg/L. Values pH 5.0; 5.5 and 6 have the lowest treatment efficiency, with TNT concentrations respectively are 26.03; 56.36 and 89.03 mg/L. From 90th to 180th minute, the processing efficiency slows down and does not change significantly. 3.2.2. Effect of Fe/Cu material content Conducting survey on the influence of different Fe/Cu material content inTNT treatment efficiency. The experiments have been conducted with 10; 20; 30; 40; 50; 60 g/L of Fe/Cu. The result is shown in Figure 3.11; 3.12 and 3.13. 32 100 90 28 80 10 g/L 24 70 20 g/L 30 g/L 20 60 40 g/L TNT(mg/L) 50 g/L TNT(mg/L) 50 16 60 g/L 40 12 30 8 20 10 4 0 0 -100 30 60 90 120 150 180 10 20 30 40 50 60 Hàm lượng Fe/Cu (g/L) Thời gian (phút) Figure 3.6: Dependence of TNT Figure 3.7: Change of TNT treatment efficiency at 90th concentration over time at minutes on the content of Fe / Cu different Fe / Cu content The Figures 3.6 and 3.7 show that the content of materials has effectted on the efficiency of TNT treatment. Thus, the effectiveness of TNT treatment depends on the content of Fe/Cu electrolytic internal materials into the reaction. With material content Fe/Cu is 30; 40; 50; 60 g/L, after 180 minutes of reaction, reached the highest treatment efficiency of 99.99% and pH value increased to 5.5. 7
3.2.3. Effect of temperature Temperature has an effect on the rate of internal electrolysis reaction, the higher the temperature, the faster the reaction speed and conversely. 6 100 5 20 80 25 4 30 60 35 TNT(mg/L) TNT (mg/L) 40 8 3 45 40 4 2 0 20 80 120 160 1 0 020 25 30 35 40 45 0 20 40 60 80 100 120 140 160 180 Nhiệt độ (o C) Thời gian (phút) Figure 3.8: Dependence of Figure 3.9: The change in TNT TNT treatment efficiency on concentration is treated by internal temperature at first 90 minutes electrolyte material according to reaction time at different temperatures. Figures 3.8 and 3.9 show that the higher the temperature and the faster the reaction speed and conversely. At the time of 90 minutes, the temperatures at 40℃ and 45℃ treated TNT were most effective, the concentration of TNT decreased to 0.57; 0.63 mg / L; next at 30℃, 35℃ is 1.76; 1.71 mg / L and finally at 20℃, 25℃ to 5.31; 3.60 mg / L. Thus, it is clear that the higher the temperature and the faster the reaction speed, the highest processing efficiency is at 45℃ and the lowest is 20℃. The next phase, from 90 to 120 minutes, the reaction speed slows down. 3.2.4. Effect of TNT concentration The initial concentration of TNT affects the reaction speed and the processing efficiency due to the following reasons: (1) contaminants and intermediate decomposition products will compete with each other on the surface of electrodes. (2) Different concentrations of contaminants make the dispersion phase in contact between pollutants with Fe / Cu electrode surface different: 8
110 1.7 40 100 60 90 80 80 100 1.6 70 40 60 TNT (mg/L) TNT(mg/L) 50 20 40 0 1.5 30 30 40 50 60 70 80 90 100 20 10 1.4 0 -10 20 40 60 80 100 120 140 160 180 40 50 60 70 80 90 100 Thời gian (phút) Nồng độ TNT ban đầu (mg/L) Figure 3.10: Dependence of Figure 3.11: The change of TNT TNT concentration remaining concentration after treatment after treatment on the initial over time with different initial concentration TNT concentrations Figure 3.10; 3.11 shows that the lower the concentration of TNT, the higher the processing efficiency and conversely. After 90 minutes, the remaining TNT concentration was 1.35; 1.42; 1.51; 1.68 mg/L corresponds to the initial TNT concentrations of 40; 60; 80; 100 mg / L. In the next phase, from 90 to 180 minutes, the effect of the initial TNT concentration on the processing speed and efficiency is almost no difference. At 180 minutes, the remaining TNT concentration was corresponding to 0.15; 0.19; 0.21 and 0.23 mg/L. 3.2.5. Optimize the process of treating TNT wastewater Applying Box-Behnken method for pH, temperature, shaking speed, reaction time for regression equations: Y = 93.16 + 1.05B + 3.02C + 8.62D - 0.265BC - 4.73CD + 1.12A2 - 1.11C2 - 3D2. Optimal conditions are determined from the regression equation corresponding to: pH = 3.24, temperature at 32.6 ℃, shaking speed of 91 rpm for 140 minutes and get TNT treatment efficiency of 98.29%. Among the factors that affect TNT's processing performance, the time is greatest affect, follow is the temperature, but to a lesser, the shaking speed and pH have little effect. a b 9
c d e f Figure 3.12: Relationship between factors on efficiency of TNT treatment. (a): pH and time; (b) pH and temperature; (c) pH and shaking speed; (d) temperature and time; (e) temperature and shaking speed; (f) shaking speed and time. 3.3. Some kinetic characteristics of the internal electrolysis process TNT 3.3.1. Iron corrosion rate and TNT decomposition kinetics This section presents the results of the iron corrosion rate and the correlation between the rate of TNT decomposition. 11 1.0 10 0.8 9 0.6 8 Cion Fe(mg/L) Ct/Co 7 0.4 6 0.2 5 0.0 4 0 50 100 150 200 250 300 350 3 Thời gian (phút) 0 20 40 60 80 100 120 Thời gian (phút) . Figure 3.13: Dependence of Figure 3.14: Dependence of dissolved Fe content on reaction TNT concentration on the time of internal electrolysis process internal electrolytic reaction time of Fe / Cu materials 10
Figure 3.13 and Figure 3.14 show the causal relationship between the rate of iron corrosion and the iron concentration in TNT treatment process depend on time. Figure 3.15: Relationship between logarithms of concentration and time Figure 3.15 proves that TNT is reduced by Fe / Cu internal electrolysis reaction fit Level 1 Kinetic assumptions model. The reaction rate constant is calculated by the slope (angular coefficient) of the linear regression line. 3.3.2. Effect of pH and Fe/Cu content 0.0 0.5 -0.5 0.0 -0.5 -1.0 -1.0 ln(Ct/Co) -1.5 pH=2 k=0.0371 -1.5 ln(Ct/Co) pH=2.5 k=0.0369 -2.0 pH=3 k=0.0367 -2.0 pH=3.5 k=0.0366 10 g/L k=0.0126 -2.5 -2.5 pH=4 k=0.0307 20 g/L k=0.0205 pH=4.5 k=0.0224 30 g/L k=0.0339 -3.0 pH=5 k=0.0084 40 g/L k=0.0452 -3.0 pH=5.5 k=0.0059 -3.5 50 g/L k=0.0459 pH=6 k=0.0011 60 g/L k=0.0459 -3.5 -4.0 0 20 40 60 80 -4.5 0 20 40 60 80 Thời gian (phút) Thời gian (phút) Figure 3.16: Effect of initial pH Figure 3.17: Effect of Fe / Cu content on the rate of TNT decomposition on the rate of TNT decomposition 3.3.3. Effect of shaking speed and temperature 0 0 -1 -1 -2 -2 -3 ln (Ct/Co) ln(Ct/Co) -3 -4 20 oC k=0.0325 -4 25 oC k=0.0382 -5 30 oC k=0.0462 60 rpm k=0.013 35 oC k=0.0543 -5 90 rpm k=0.025 40 oC k=0.0691 120rpm k=0.044 -6 45 oC k=0.0746 -6 -7 0 20 40 60 80 100 120 140 160 180 0 20 40 60 80 Thời gian (phút) Thời gian (phút) Figure 3.18: Effect of shaking speed Figure 3.19: Effect of temperature on the rate of TNT decomposition on the rate of TNT decomposition 11
Thus the activation energy Ea is calculated based on the graph of the relationship between Ln k and 1 / T (Figure 3.20). -2.6 Equation y = a + b*x Weight No Weighting Residual Sum 0.00467 of Squares Pearson's r -0.99563 -2.8 Adj. R-Square 0.98911 Value Standard Error Intercept 7.64344 0.49879 lnk Slope -3246.34703 152.20171 -3.0 lnk -3.2 -3.4 0.00315 0.00320 0.00325 0.00330 0.00335 0.00340 1/T Figure 3.20: Relationship between Lnk and 1/T: y = - 3246x + 7.6434 R2 = 0.9891 In Figure 3.20, it can be seen that the correlation coefficients of these 6 points on the regression line reach 0.9915, the Lnk and 1/T have a strong linear relationship. The activation energy of the entire reaction has been calculated: Ea = 3246 * 8.314 = 26.99 KJ/mol and indicates that the TNT decomposition is in the diffusion domain, which in accordance with the above research results. 3.3.4. Evaluate TNT molecular reduction process Extreme spectrum Von - Amper for analyzing the position of NO2- radicals. Thereby it is possible to assess the existence of 3 NO2- radicals on the TNT molecule. In other words, it is possible to evaluate the reduction of 3 NO2- radicals of TNT molecule into NH2 amine. The result is shown in Figure 3.21 as follows: TNT TNT TNT -160n TNT -140n TNT3 TNT1 TNT2 -140n -120n -120n TNT1 I (A) -100n I (A) -100n TNT2 -80.0n TNT3 -80.0n -60.0n -60.0n -40.0n 0.10 0 -0.10 -0.20 -0.30 -0.40 -0.50 0.10 0 -0.10 -0.20 -0.30 -0.40 -0.50 U (V) U (V) a b 12
TNT TNT TNT -100n TNT -200n -80.0n -175n -150n -60.0n I (A) I (A) -125n TNT1 -40.0n -100n TNT3 -20.0n -75.0n TNT1TNT2 0 -50.0n 0.10 0 -0.10 -0.20 -0.30 -0.40 -0.50 0.10 0 -0.10 -0.20 -0.30 -0.40 -0.50 U (V) U (V) c d Figure 3.21: Von - Amper spectrum of TNT decomposition process at time 0 minutes (a); 15 minutes (b); 90 minutes (c); 330 minutes (d) It can be seen that, at the 0 minutes, there were still 3 spectral peaks equivalent to 3 NO2- radicals, after 15 minutes response the spectral peaks was lower and to 90 minutes, there was only 1 spectral peak but it was lower so many. At 330 minutes, the spectral peaks of the NO2- radical are nearly flat. In other words, the NO2- on the TNT molecule no longer exists. 3.3.5. Operating TNT wastewater treatment at laboratory with Fe / Cu material This section presents the results of TNT wastewater treatment at laboratory using electrolytic internal material for 30 days. Table 3.1: TNT wastewater treatment efficiency Initial After treat Eficiency (%) COD (mg/L) 220 - 270 85 - 110 59, 2 - 61,3 TNT (mg/L) 95 –106,4 0 100 BOD5/COD 0,18 –0,2 0, 55 – 0,56 - pH 5 6,5 – 6,6 - 3.3.5.1. Treatment efficiency of TNT 120 100 80 In TNT(mg/l) 60 En 40 20 0 0 2 4 6 8 10 12 14 16 Times(day) Figure 3.21: Treatment efficiency of TNT 13
a b Figure 3.24: HPLC spectrum of pre-treatment (a) and post-treatment (b) 3.3.5.2. COD removal efficiency 280 0.7 260 0.6 240 0.5 220 200 IN BOD5/COD 0.4 COD(mg/l) 180 EN 0.3 160 0.2 140 0.1 120 100 0.0 3 4 5 6 7 pH 0 2 4 6 8 10 12 14 16 Time(day) Figure 3.25: COD removal efficiency Figure 3.26: The change of BOD5 / COD ratio after treatment. 3.4. Techniques A2O-MMBR treating TNT 3.4.1. Research isolated activated sludge 3.4.1.1. Isolation Table 3.2: Characteristic of domesticated activated sludge Mixed Liquor Condition Suspended Solids Characteristics MLSS (mg/L) yellowish brown, mud suspended, Aerobic 2120 ± 50 the suspension Dark brown, big mud cotton, rapid Anoxic 1596 ± 50 sedimentation black, heavy mud, very rapid Anaerobic 1103 ± 50 sedimentation 14
3.4.1.2. Evaluation of activated sludge particle size Time (days) Anaerobic Anoxic Aerobic 30 12,11329 µm 13,57996 µm 20,44160 µm 90 14,13µ𝑚 82,88 µm 163,55µ𝑚 180 14,12941 µm 14,32089 µm 67,01550 µm Figure 3.27: Spectral size distribution of activated sludge 3.4.1.3. Survey of biological polymer content Conducting SEPS and BEPS content survey for 6 months and give results shown in Figure 3.28; 3.29; 3.30: Proteins Proteins Pollysaccharides Pollysaccharides 0.8 Total Total 1.0 0.7 0.8 0.6 0.5 BEPS (mg/g) SEPS (mg/g) 0.6 0.4 0.4 0.3 0.2 0.2 0.1 0.0 0.0 T1 T2 T3 T4 T5 T6 T1 T2 T3 T4 T5 T6 Thoi gian Thoi gian a b Figure 3.28: Polymer content of anaerobic tanks: SEPS (a) and BEPS (b) 15
Proteins Proteins Pollysaccharides Pollysaccharides Total 0.7 Total 0.6 0.6 0.5 0.5 BEPS (mg/g) SEPS (mg/g) 0.4 0.4 0.3 0.3 0.2 0.2 0.1 0.1 0.0 T1 T2 T3 T4 T5 T6 0.0 T1 T2 T3 T4 T5 T6 Thoi gian Thoi gian a b Figure 3.29: Polymer content in anoxic tanks: SEPS (a) and BEPS (b) Proteins Proteins Pollysaccharides Pollysaccharides Total 0.40 Total 0.6 0.35 0.5 0.30 0.4 BEPS (mg/g) 0.25 SEPS (mg/g) 0.3 0.20 0.15 0.2 0.10 0.1 0.05 0.0 0.00 T1 T2 T3 T4 T5 T6 T1 T2 T3 T4 T5 T6 Thoi gian Thoi gian a b Figure 3.30: Polymer content of aerobic tank: SEPS (a) and BEPS (b) 3.4.2. Treatment of TNT by A2O-MBBR method 3.4.2.1. Evaluate the processing efficiency of A2O-MBBR system The results of monitoring the change of pH in the reaction tanks are shown in Figure 3.31. 8 7 pH 6 pH influence %(3) pH Ky Khi %(4) 5 0 5 10 15 20 25 30 Time (day) Figure 3.31: The change of pH at the reaction tank The efficiency of wastewater treatment containing TNT by the independent A2O-MBBR method is shown in Figure 3.32; 3.33 as follows: 16
25 0 4.5 4.0 20 20 TNT removal (%) TNT concentration ( mg/L) 3.5 TNT removal (%) 15 40 3.0 Ky Khi Thieu khi 2.5 Hieu Khi Abs 10 Remove 60 2.0 Vao Ra 1.5 5 80 1.0 0 100 0.5 0 5 10 15 20 25 30 Time (day) 0.0 200 250 300 350 400 Wave Figure 3.32: TNT removal efficiency by A2O - MBBR system Figure 3:33: The transformation of substances in A2O-MBBR system Treatment efficiency of COD and NH4+ 300 50 45 B 250 Before C 40 After 200 35 NH4-N(mg/l) IN COD(mg/l) EN 30 150 25 100 20 15 50 0 2 4 6 8 10 12 14 16 10 0 2 4 6 8 10 12 14 16 Times Times Figure 3.34: COD removal Figure 3.35: Ammonium efficiency removal efficiency 3.4.3. Combining the method of internal electrolysis and A2O- MBBR 3.4.3.1. COD removal efficiency COD treatment results of the reaction system are presented in Figure 3.36: 120 110 100 90 80 70 COD mg/L 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 Time (day) Figure 3.36: COD removal efficiency on A2O-MBBR system 17
3.4.3.2. Efficient treatment of NH4 NH4 treatment results are presented in Figure 3.37: 35 30 25 NH4(mg/l) 20 Pre-treat 15 10 Post-treat 5 0 0 20 40 60 80 Time(day) Figure 3. 37. NH4 treatment efficiency of A2O-MBBR 3.4.3.3. TNT treatment efficiency Through internal electrolysis process, TNT has been completely decomposed, however, we still tested the TNT content in A2O- MBBR system by high-pressure liquid chromatography and the results shown in Figure 3.38: a b c Figure 3.38: HPLC spectrum of TNT in anaerobic tanks (a); anoxic (b); aerobic (c) Table 3.3: Efficiency before and after electrolysis treatment Internal A2O- Pre-treat Post-treat electrolytic MBBR COD (mg/l) 220 - 270 85 - 110 33 -38 86 – 89 % TNT (mg/l) 95 – 106,4 0 0 100 BOD5/COD 0,18 – 0,2 0, 55 – 0,56 0,29 -0,5 - + NH4 (mg/l) 23 - 45 18 - 32 5,8 -7,9 73- 82 pH 5 6,5 – 6,6 6,5-7,2 - Thus, the process of combining the internal electrolysis method and A2O-MBBR to treat TNT and NH4NO3 in the actual wastewater samples at the factory were successful, in which the efficiency of TNT, COD and NH4 removal, respectively were 100%, 86 - 89%, 73-85%. 18