Bio-Electro-Fenton: A novel method for treating leachate in Da Phuoc Landfill, Vietnam

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Leachate is a noticeable pollution problem because it contains a considerable amount of persistent organic pollutants (POPs). If leachate isn't treated thoroughly, its leak will negatively affect the environment. Therefore, appropriate treatment technologies are required to remove them. Bio-Electro-Fenton (BEF) is a new method using microorganisms such as electrolytes to convert chemical energy into electricity to help create H2O2 support advanced oxidation process (AOPs).

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Science & Technology Development Journal, 23(1):461-469 Open Access Full Text Article Research Article Bio-Electro-Fenton: a novel method for treating leachate in Da Phuoc Landfill, Vietnam Ho Nhut Linh, Ho Truong Nam Hai* ABSTRACT Introduction: Leachate is a noticeable pollution problem because it contains a considerable amount of persistent organic pollutants (POPs). If leachate isn't treated thoroughly, its leak will Use your smartphone to scan this negatively affect the environment. Therefore, appropriate treatment technologies are required to QR code and download this article remove them. Bio-Electro-Fenton (BEF) is a new method using microorganisms such as electrolytes to convert chemical energy into electricity to help create H2 O2 support advanced oxidation process (AOPs). Realizing the potentials that BEF brings, this study applies BEF to assess the effectiveness of leachate treatment at Da Phuoc landfill (operation period > 12 years), Ho Chi Minh City, which to save costs and energy for Fenton process. Methods: The BEF pilot scale model (30 x 10 x 10 cm) is divided by a proton exchange membrane (PEM) (Nafion® 112) into two chambers (anode and cathode). Cathode chamber used a graphite electrode, the anode chamber used a carbon fabric electrode. The experiments aimed to determine the optimal conditions of parameters affecting the BEF system by determining the efficiency of COD removal and BOD5 /COD ratio in leachate. Results: At optimal conditions of the model including pH 3, [Fe2+ ] = 4g/L, current intensity = 1A, reaction time 60 minutes and airflow = 12 L/min, as a result COD was reduced by 68.2 ± 1.04 % from 4950 ±14 mgO2 /L to 1574.1 ± 51.4 mgO2 /L, the ratio of BOD5 /COD = 0.1 Conclusion: The study result showed thatBio-electro-Fenton process is effective for wastewater with high concen- trations of pollutant and difficult to treat as leachate suggesting that the appropriate method for pre-treatment processes support the thorough elimination of pollutants. Key words: Leachate, Bio-Electro-Fenton, AOPs, treatment. INTRODUCE as non-selective pollutants oxidation, easily react at Faculty of Environment, University of room temperature. Typical AOPs such as tradition Science, Vietnam National University The population explosion and industrialization in re- - Ho Chi Minh City cent years have increased the demand for consump- Fenton and Electro-Fenton have been proven to effi- tion of goods, materials, and energy which leads to ciently treat leachate. However, the traditional Fen- Correspondence a rapidly increasing amount of domestic waste gen- ton process requires the supply of a large amount of Ho Truong Nam Hai, Faculty of Environment, University of Science, erated. According to the estimation of The National H2 O2 and Fe2+ . Besides the amount of reagent added Vietnam National University - Ho Chi Environment Statistics report in 2017 of The Ministry is unstable and requires partial treatment of the chem- Minh City icals remain after the reaction. For Electro-Fenton, of Natural Resources and Environment, the amount Email: htnhai@hcmus.edu.vn the process requires large energy for the generation of of domestic solid waste in urban areas increases by History an average of 10 - 16% per year. The majority of do- H2 O2 . To deal with these disadvantages, it is nec- • Received: 2019-12-14 essary to progress a low-cost Fenton process which mestic waste in Vietnam has been treated by the land- • Accepted: 2020-02-17 fill method. When using this method, a consider- ensures treatment efficiency, therefore BEF method • Published: 2020-03-19 able amount of leachate will be generated, which does was invented. The BEF method uses microorganisms DOI : 10.32508/stdj.v23i1.1736 harm to the environment because leachate contains to decompose organic matter creating energy to form heavy metals, ammonium, and POPs. The composi- H2 O2 for Fenton processes. As a result of the BEF tion and characteristics of leachate are complicated by method is a multipurpose method which save costs seasonal changes and burial time hence leachate treat- by reducing electrical energy consumption and using Copyright ment is extremely sophisticated. chemicals. © VNU-HCM Press. This is an open- There are many different methods for treating The BEF is a completely new technology. In Viet- access article distributed under the terms of the Creative Commons leachate such as flocculation, adsorption, oxidation, nam, there has not been any previous article about Attribution 4.0 International license. etc. AOPs are the most outstanding treatment method BEF application in wastewater treatment. Therefore, which form hydroxyl (• OH) free radicals to decom- in this study, we optimize the parameters affecting the pose organic pollutants base on characteristics such BEF method in a complex matrix, with the purpose of Cite this article : Nhut Linh H, Truong Nam Hai H. Bio-Electro-Fenton: a novel method for treating leachate in Da Phuoc Landfill, Vietnam. Sci. Tech. Dev. J.; 23(1):461-469. 461
Science & Technology Development Journal, 23(1):461-469 evaluating the applicability of the method in leachate In addition, the energy generated helps restore Fe2+ treatment. The experiments had been conducted to (Equation (5)). find optimal conditions through COD treatment effi- ciency and BOD 5 /COD ratio of leachate. O2 + 2H+ + 2e → H2 O2 (2) MATERIALS AND METHODS H2 O2 + Fe2+ →• OH + OH + Fe3+ (3) Sampling • OH + RP → oxidation products (CO2 , H2 O) (4) Samples had collected at the Da Phuoc Solid Waste Treatment Complex in Ho Chi Minh City in March 2019. Sampling, transportation, and preservation Fe3+ + e− → Fe2+ (5) techniques complied with TCVN 5999: 1995. Sam- ples had precipitated and stored in 2 plastic containers All chemicals and reagents used for the experiments 30L. were of analytical grade and supplied by Merck (Ger- According to Table 1, leachate has neutral pH, COD many). In each experiment, 500 mL of leachate was is 4950 mgO2 /L, BOD5 is 1500 ± 59.7 mgO2 /L, and added at the cathode chamber, pH was adjusted us- BOD5 /COD ratio of 0.3 is quite low. Da Phuoc land- ing NaOH 1N, H2 SO4 1N. The agents used in the fill came into operating in 2007, after over 10 years, Fenton process includes FeSO4 .7H2 O 5%. All exper- the main component of leachate is organic substances, iments were performed at 30o C temperature and at- which are difficult or non-biodegradable. Leachate is mospheric pressure in a batch mode manner. Data gradually shifted to the stable phase. are representative with three replicates and their av- erage are reported. BEF pilot system and operation BEF pilot scale model (30 x 10 x 10 cm) divided by Chemical analysis a PEM (Nafion ® 112) into two chambers. The vol- pH value of wastewater was measured by Schott - LAB ume of each chamber (anode and cathode chambers) 850 - Germany. The parameters COD, BOD5 , Total was 1.5 L with a working volume of 1.134 L. Cathode Phosphor, Total Nitrogen, and TSS were determined chamber used a graphite electrode, the anode cham- according to the Standard Methods for the examina- ber used a carbon fabric electrode with size (7.5 x 5 x tion of water and wastewater 2 . 0.4 cm). The electrodes connected with copper wire COD, BOD5 were observed throughout the exper- of 2 mm diameter and 40 cm length through an exter- iment. For the Bicromate method, the amount of nal transistor of 100 Ω and DC supply with voltage 0 - residual H2 O2 and Fe2+ in sample after the reaction 30V, current 0 - 5A to adjust to each test requirement affect the results of COD determination according to (Figure 1a, c). the reaction (Equations (6) and (7)) 3 . At the first stage of the survey, anode chamber was 7 + 3H2 O2 + 8H → 2Cr + Cr2 O2− + 3+ loaded with anaerobic sludge and 500 mL of artifi- (6) cial wastewater (glucose 30 g/L, KH2 PO4 4.33 g/L, 3O2 + 7H2 O Na2 HPO4 2 g/L, NH 4 Cl 0.2 g/L, KCl 0.13 g/L) 1 to 2+ + H+ → Cr3+ + Fe3+ + H O Cr2 O2− 7 + Fe 2 (7) help anaerobic microorganisms grow and develop sta- bly. The microorganisms decompose glucose to H+ In this study, reaction in sample after treatment will be and produce electrons (Equation (1)): stopped immediately by adding NaOH 2.5 N to pH 10 C6 H12 O6 + 6H2 O → 6CO2 + 24H+ + 24e− (1) - 11 to precipitate iron, then heat at 70-800 C within 30 minutes to completely remove residual H2 O2 before Then ion H+ passed through the PEM to the cath- conducting COD analysis 4 . ode chamber. Due to the potential difference in volt- age, electrons formed at the anode chamber will trans- Data processing fer the external resistor and to the cathode electrode. - Processing efficiency (H%) is calculated according In the cathode chamber, the pump supplies oxygen to the formula: for the reaction (Equation (2)) to form H2 O2 . The C0 − C amount of H2 O2 produced will immediately react H= ∗ 100 C0 with the amount of Fe (II) added to form hydroxyl radicals (• OH) (Equation (3)) which oxidize persis- Where: C0 is the initial concentration (mg/L) tent organic compounds in leachate (Equation (4)). C is the final concentration (mg/L) 462
Science & Technology Development Journal, 23(1):461-469 Table 1: Composition, characteristics of Da Phuoc leachate Parameter Unit Result Viet Nam National Technical Regula- tion – 25:2009/MONRE Column B1 pH - 7.8 - BOD5 mgO2 /L 1500 ± 59.7 100 COD mgO2 /L 4950 ± 14 400 BOD5 /COD - 0.3 - Total Phosphor mg/L 12.4 ± 0.43 - [Fe] total mg/L 44.1 ± 2.24 - Total Kjeldahl Nitrogen mg/L 1477 ± 62.6 60 Ammonium mg/L 589.67± 25 22.11 Total Suspended Solid mg/L 15.3 - Figure 1: (a) Photograph (b) Electro transfer mechanism in the BEF system (c)Schematic drawing of the experi- mental setup of the BEF system 463
Science & Technology Development Journal, 23(1):461-469 Figure 2: COD removal efficiency (%) (±SD) and BOD5 /COD ratio of treated leachate following various pH in cathode chamber onthe Bio-Electro-Fenton process. Reaction conditions: [Fe2+ ]= 1.4 g/L, reaction time 60 minutes, current intensity = 1 A, airflow = 4 Lair /minute RESULTS tion time of 60 minutes, the airflow rate of 12 L/min yiel ded the highest COD removal efficiency, reaching To determine the maximum treatment efficiency of 62.42 ± 0.99 % and 68.20 ± 1.04 %, respectively. the method for leachate as well as evaluate the influ- ence of important parameters in the BEF model, ex- DISCUSSION periments are performed to optimize each parameter in a complex matrix of effects. The result show sim- Effect of pH on the Bio-Electro-Fenton pro- ilarity to other Fenton processes, the optimal pH of cess BEF is at 3 (Figure 2). Both of case pH is too low and too high are effect to A larger concentration of Fe2+ catalyst will increase the efficiency of the Fenton process 4 . The Fenton pro- COD treatment efficiency significantly, up to 4 g/L. cess can be inhibited because of very low pH values However, when concentration is too high, it will (pH < 3). Fe2+ , which exists as Fe[H2 O6 ]2+ , has a reduce processing efficiency. Treatment efficiency slower reaction rate with H2 O2 than Fe[H2 O5 ]2+ at tends to decrease at increasing iron concentration pH = 3 which leads to less hydroxyl (• OH) genera- (Figure 3). The COD removal efficiency decreased tion 5 . Besides, when the pH is too low H+ will react from 54.82 ± 2.04 % to 51.22 ±1.53 %, while with H2 O2 to form peroxone (H3 O2 + ) according to the BOD5 /COD ratio increased when concentration the reaction H2 O2 + H+ → H3 O2 + . The peroxone [Fe2+ ] increased from 1 g/L to 1.4 g/L, respectively. do not react with Fe2+ therefore it will decrease • OH When the concentration [Fe2+ ] is from 1.4 g/L to 4 formation efficiency which leads to reduces the pro- g/L, the treatment efficiency increases linearly with cessing efficiency of the Fenton process. [Fe2+ ]. The BOD5 /COD ratio reached the highest At high pH (pH ≥ 4), the formation of ferrous/ferric values of 0.15 at 3 g/L and the lowest value of 0.04 at hydroxide complexes leads to the catalyst deactiva- 6 g/L. tion, which decreases the quantity of • OH 6 . In ad- For current intensity, the addition of an external cur- dition, the decomposition of H2 O2 into H2 O and O2 rent to the system helps to accelerate the Fenton pro- also increases with increasing pH 7,8 . The accumula- cess due to electrons are increased with electrons tion of protons due to the slow and insufficient pro- made from anaerobic organisms decompose glucose tons diffusion through membrane would cause a de- in the anode chamber. The optimum current for the crease of pH in anode chamber 6 . Therefore, the cath- system is recorded at 1 A (Figure 4). ode electrode material as a source to self-regulate the The reaction time and airflow rate provided to the sys- supply of Fe2+ under neutral conditions is necessary tem were also surveyed. (Figures 5 and 6) The reac- to reduce the cost of pH adjusting chemicals. 464
Science & Technology Development Journal, 23(1):461-469 Figure 3: COD removal efficiency (%) (±SD) and BOD5 /CODratio of treated leachate following various Fe2+ concentration in cathode chamber on the Bio-Electro-Fenton process. Reaction conditions: pH = 3, re- action time 60 minutes, current intensity = 1 A, airflow = 4 Lair /minute Figure 4: COD removal efficiency (%) (±SD) and BOD5 /CODratio of treated leachate following various cur- rent intensity incathode chamber on the Bio-Electro-Fenton process. Reaction conditions: pH = 3, reaction time 60 minutes, [Fe2+ ] = 4 g/L, airflow = 4 Lair /minute 465
Science & Technology Development Journal, 23(1):461-469 Figure 5: COD removal efficiency (%) (±SD) and BOD5 /COD ratio of treated leachate following various re- action times on the Bio-Electro-Fenton process. Reaction conditions: pH = 3, [Fe2+ ] = 4 g/L, current intensity = 1 A, airflow = 4Lair /minute Figure 6: COD removal efficiency (%) (±SD) and BOD5 /COD ratio of treated leachate following various air- flow into cathode chamber on the Bio-Electro-Fenton process. Reaction conditions: pH = 3, [Fe2+ ] = 4 g/L, reaction time 60 minutes, current intensity = 1A 466
Science & Technology Development Journal, 23(1):461-469 Effect of [Fe2+ ] on the Bio-Electro-Fenton from microbial electrolysis cells (MEC) to the micro- process bial fuel cell (MFC). Besides, increasing the current Fe2+ is an extremely important factor that directly af- too high will affect processing efficiency while wasting fects the Fenton process. Considering that the H2 O2 a significant amount of energy. In this case, optimized production rate and yield could be constant at de- current intensity is usually chosen to attain the max- fined conditions in bio-electro-chemical system, Fe2+ imum H2 O2 production rate and yield, and its value as catalyst could be a key factor for the final treatment quite depends on the cathode material used 6 . performance 9 . As a result, a certain amount of Fe2+ The current increased (0,5 to 1A) with the increas- saves chemicals and makes the process more efficient. ing rate of pollutant degradation (49.60 ± 2.17 % to 62.42 ± 1.81 %) since more H O are formed at a given At low [Fe2+ ] concentration, hydroxyl (• OH) pro- time. However, the COD concentration decreased duced just enough to oxidize the biodegradable or- as the current increased above 1A, the efficiency de- ganic compounds. When the dose of Fe2+ increased, creased from 62.42 ± 1.81 % to 50.75 ± 1.72 % at amount of hydroxyl is more produced. The oxida- 2.5A. The current cannot be increased indefinitely tion of organics with• OH occurs through well-known since the cathode potential would be changed by the pathways, principally H atom abstraction (mainly applied voltage, resulting in the side reactions, and from aliphatics) and addition to C = C bonds (mainly thereby decreasing current efficiency and pollutants with aromatics leading to the formation of hydrox- removal efficiency. The side reactions can involve: ylated aromatic derivatives) 10 . The persistent or- (i) high current density by adding high external volt- ganics changes into a biodegradable form, increasing age would enhance the H2 O2 electrochemical reduc- the BOD value, increasing the BOD5 /COD ratio and tion through (Equation (10)), (ii) the H2 O2 reaction leading to a reduction in processing efficiency. with Fe3+ via (Equation (11)) and (Equation (12)) At higher concentration [Fe2+ ], from 4 g/L to (iii) the destruction of • OH with H2 O2 and Fe2+ via 6 g/L, treatment efficiency decreases due to re- (Equation (13)) and (Equation (8)) 6 , (iv) The reac- duction of radicals• OH according to the reaction tions forming H2 at the cathode are more dominant (Equation (8)) 11 : via (Equation (14)) 4 . • OH + Fe2+ → Fe3+ + OH− (8) H2 O2 + 2H+ + 2e− → 2H2 O (10) In addition, the Fe3+ ions formed can react with H2 O2 to reduce the mineralization of organic sub- Fe3+ + H2 O2 → Fe2+ + HO•2 + H+ (11) stances (Equation (9)) 12 : Fe3+ + HO•2 → Fe2+ + O2 + H+ (12) H2 O2 + Fe3+ → Fe2+ +• OOH + H+ (9) H2 O2 + • OH → H2 O + HO•2 (13) Excess iron salts increase the amount of dissolved salt (TDS) and conductivity. Besides, after stopping the 2H+ + 2e− → H2 (14) reaction, treated wastewater must be adjusted to neu- tral pH. pH raising create a large amount of iron de- posits in the sludge 12 . Effect of reaction time on the Bio-Electro- Fenton process Effect of current intensity on the Bio- The time needed to complete a Fenton reaction will Electro-Fenton process depend on the many variables such as catalyst dose The current intensity produced by the microorganism and wastewater strength. For more complex or more system in the cathode chamber to create H2 O, which concentrated wastes as leachate, the reaction in var- is an extremely important catalyst in the BEF. Higher ious studies fluctuated between 30 minutes and 3 current will increase the amount of H2 O2 , thus in- hours 13 . creasing the number of (• OH) hydroxyl radicals in COD removal efficiency increased gradually and the electrolyte environment. However, in the experi- reached the highest of 62.42 ± 0.99 % at 60 min- ments, the efficiency of the current generation by the utes, BOD in leachate also increased from 50 mgO2 /L microorganism system was quite low, therefore to in- to 191 mgO2 /L. The complex organic is decom- crease the processing efficiency, the experiment used posed into simpler organic substances, thus reduced an external power (DC) to connect the BEF system COD concentration, increased BOD concentration in to supplement the process. The technology converts wastewater, contributed to an increase BOD5 /COD 467
Science & Technology Development Journal, 23(1):461-469 Figure 7: Samples of current intensity after processing. ratio. Increasing the reaction time will create more to (• OH) hydroxyl free radicals non-selectively re- • OH radicals to form H O , while also fostering the 2 2 acts with POPs compounds to create more easily Fenton reactions occur more to thoroughly oxidize biodegradable compounds. the pollution. However, when continuing to increase the airflow After the equilibrium time, COD concentration de- rate, from 12 to 16 L air/minute, COD treatment effi- creased, the BOD5 /COD ratio did not change signifi- ciency decreased from 68.20 ± 1.04 % to 62.22 ± 1.12 cantly. The BOD concentration raised, this can be ex- %, respectively. This is explained by the extremely plained by the persistent organic pollutant degrada- high airflow rate which leads to a chemical imbalance tion which still continues to occur but tends to slow of reaction (2) O2 + 2H+ + 2e− → H2 O2 and reduces down. In addition, intermediates created are more the accumulation of H2 O 14 . 2 difficult to oxidize, which inhibits the Fenton reac- tion. The amount of Fe2+ when being regenerated CONCLUSIONS will be oxidized to Fe2 O3 , thus reducing treatment ef- The results obtained in the study show that the use of ficiency 4 . the Bio-electro-Fenton process is effective for wastew- Effect of airflow on the Bio-Electro-Fenton ater with large concentrations and difficult to treat as leachate. At optimal conditions of the model includ- process ing pH 3, [Fe2+ ] = 4g/L, current intensity = 1A, re- Oxy is one of the key parameters in the BEF system, action time 60 minutes and airflow = 12 LO2 /min, as which is the electron acceptor in the cathode cham- a result COD from 4950 ± 14 mgO2 /L to 1574.1 ± ber to produce H2 O2 . High airflow rate could en- 51.4 mgO2 /L (decreased 68.2 ± 1.04 %). The ratio hance the dissolved oxygen in solution and promote of BOD5 /COD decreased from 0.3 to 0.1 due to Fen- the oxygen mass transfer rate, and thus, is beneficial ton reactions which reduced a large amount of easily for H2 O2 production and accumulation in bioelectro- biodegradable organic matter, suggesting that the ap- chemical systems 6 . It is important to set the optimal airflow rate because if the speed is too low, it will not propriate method for pre-treatment processes support maintain enough dissolved oxygen and if the speed is to thoroughly eliminate pollutants. too high, it will cost a lot of operating energy for the LIST OF ABBREVIATIONS system. COD treatment efficiency increased with increasing AOPs: Advanced oxidation process airflow rate and reached 68.20 ± 1.04 % (Figure 6) BEF: Bio-electro-Fenton at the maximum airflow rate of 12 L air/minute. The PEM: Proton exchange membrane reason is that the excessive high airflow rate could also POPs: Persistent organic pollutants disturb the mass transfer between catholyte and elec- trode and lead to a low catalytic efficiency for pol- AUTHORS’ CONTRIBUTIONS lutants degradation by the Fenton process 6 . The ra- The author Ho Nhut Linh did the experiment. The tio of BOD5 /COD also increased significantly due author Ho Truong Nam Hai discussed the results and 468
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