Application of electro-Coagulation for treatment of wastewater from package printing process

Vietnam Journal of Science and Technology 55 (4C) (2017) 192-197 APPLICATION OF ELECTRO-COAGULATION FOR TREATMENT OF WASTEWATER FROM PACKAGE PRINTING PROCESS Nguyen Thi Thuy 1 , Chu Thien Bao 2 , Dao Xuan Son 1 , Uong Dinh Bao 1 , Dang Van Thanh 3, * , Nguyen Nhat Huy 2, * 1 HCMC University of Food Industry, 140 Le Trong Tan Street, Tan Phu District, Ho Chi Minh City 2 HCMC University of Technology, VNU-HCM, 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City 3 TNU-University of Medicine and Pharmacy, 284 Luong Ngoc Quyen road, Thai Nguyen City * Email: thanhdv@tnmc.edu.vn, nnhuy@hcmut.edu.vn Received: 1 August 2017; Accepted for publication: 14 October 2017 ABSTRACT Printing wastewater is generally considered as hazardous waste whose treatment and disposal are strictly regulated. Although electro-coagulation (EC) process has been successfully applied for the treatment of different types of wastewater, its application for printing wastewater is rarely reported. In this study, EC was applied to treat the printing ink wastewater, taken from a paper packing factory in An Giang Plant Protection Join Stock Company, which was highly colored and contaminated with organic compounds. The treatment process was performed using aluminum electrodes for two hours. Effects of applied voltage (5 - 40 V), pH (5 - 9), electrodes distance (1 - 5 cm), salt concentration in electrolyte solution (0.05 - 0.4 g/L), and the rotational speed of stirring (0 - 400 rpm) on the removal efficiencies of color and COD were investigated. Based on the effects of various factors, optimum condition for the treatment was given. Results showed that the EC process can effectively remove color and COD for 30 min. The effluent quality in terms of color and COD met well National Technical Regulation on Industrial Wastewater (QCVN 40-2011/BTNMT, column B). Finally, a comparison in removal efficiencies between the processes of EC and chemical-coagulation was also presented. Keywords: electro-coagulation, print ink wastewater, chemical-coagulation. 1. INTRODUCTION The wastewater generated from the printing processes usually has low volume but with strong color and high amount of organic compounds. These organic components are generally synthetic organic polymers. Additionally, there are plenty of substances and heavy metal ions, which could inhibit biological degradation, causing difficulty for biological treatment of such Application of electro-coagulation for treatment of wastewater from package printing process 193 wastewater. Due to the harmful effect on human health and the environment, as well as the aesthetical aspect, the printing ink wastewater cannot be directly discharged into the environment without any treatment. Practically, various methods have been used to treat this wastewater, including chemical coagulation, adsorption, oxidation, biological treatment, and electrolysis [1]. Among these methods, electrocoagulation (EC) has been proposed as an effective method for treatment various types of wastewater from textile, paper mill, baker’s yeast, restaurant, and chemical mechanical polishing [2, 3]. However, there is very rare report on the application of this technique for printing ink wastewater [4]. The goal of this study was to investigate the effect of EC operational conditions (i.e., input voltage, pH, electrode distance, mixing speed, and electrolyte concentration) on the removals of color and COD from real printing ink wastewater. Moreover, the EC treatment was performed at optimum condition and wastewater parameters such as COD, BOD, TSS, and color in the effluent were measured. Finally, removal efficiencies of electrocoagulation and chemical coagulation (by PAC) were compared. 2. MATERIALS AND METHODS 20 L of print ink wastewater were collected from the paper packing factory in An Giang Plant Protection Join Stock Company. This wastewater was highly colored and contaminated with organic compounds. Wastewater characteristics are given in Table 1. NaCl, acid, and base were of analytical grade (Xilong, China) whereas PAC was of industrial grade, purchased from Viet Hoang Long Company (HCMC, Vietnam). All the analyses such as COD, BOD5, true color, and TSS were done in Consultancy Center of O.S.H & Environmental Technology (HCMC, Vietnam). pH was measured using PHS-550 (Taiwan). Color was measured according to the Platinum-Cobalt standard method using a photolab 6100 VIS spectrophotometer (Germany) operated at 455 nm. The treatment of print ink wastewater was performed using a 1-L batch cell made out of glass (Fig. 1). Two similar aluminum plate electrodes with effective area of 84 cm 2 were placed vertically in the cell and connected to a DC power supply. Samples with volume of 15 mL were taken from electrocoagulation cell at certain operating times for true color and COD analyses. The process was separately conducted at various voltages (5-30 V), pH (5-8), electrolyte concentrations (NaCl) (0.05 - 0.4 g/L) and inter-electrode distances (1-5 cm). When optimum operating condition was obtained, the removal efficiencies of COD, BOD5, true color and TSS were measured at this condition. In chemical coagulation (CC), PAC was added into a 1-L reactor containing printing ink wastewater. The reactor was rapidly mixed (120 rpm) for 1 min, followed by slow mixing (30 rpm) for 10 min, then let to settle for 30 min. The samples were then taken for COD and color measurements after the experiment. Effects of pH (from 5-9, at PAC concentration of 1.0 mg/L) and PAC concentration (from 0.2 - 1.2 mg/L, at pH 7) on color and COD removals were also investigated. Removal efficiencies of COD, BOD5, TSS, and color were calculated based on the Eq. 1. Energy consumption for removal of one kg of COD by EC process was calculated based on Eq. 2. H (%) = (Co-C1) ×100 /Co (1) where H is removal efficiency (%); Co, C1 are initial and final concentrations of COD, BOD5, TSS, and color. Nguyen Thi Thuy, et al 194 Figure 1. Experimental setup of EC treatment. (2) where E is energy consumption (kWh/kgCOD); U is applied voltage (V); I is applied current (A); t is time for EC treatment (min); V is the volume of wastewater to be treated (L); Co, C1 are initial and final COD concentrations (mg/L). 3. RESULTS AND DISCUSSION 3.1. Effect of applied voltage on treatment efficiency This experiment was conducted in two hours with the voltages of 5, 10, 20, 30 and 40 V (current intensities of 0.0024, 0.0036, 0.0083, 0.0131, and 0.0143 A/cm 2 , respectively), at pH 7, electrode distance of 2 cm, without electrolyte and without mixing. Time (min) 0 15 30 45 60 75 90 105 120 C O D ( m g /L ) 0 500 1000 1500 2000 2500 U=5V U=10V U=20V U=30V U=40V Time (min) 0 15 30 45 60 75 90 105 120 C o lo r (P t- C o ) 0 10000 20000 30000 40000 50000 U=5V U=10V U=20V U=30V U=40V Figure 2. Effect of voltage by time on COD (a) and color (b) in the effluent. As can be seen in Fig. 2, similar trends of COD and color reductions in the effluents were found at each voltage, i.e. the reduction was fast at the beginning, then slow, before reaching almost unchanged values. It is also obvious that decolonization process was faster than COD removal. With the increase of applied voltage from 5 to 30 V, there was a substantial increase in the removal efficiencies of COD and color. This behavior can be easily explained by the increase in the generation rate of coagulant and bubble, as a result of the increase in current density [4]. However, there were not much different in both COD and color in the effluents obtained by 30 and 40 V-EC treatments. Hence, we selected U at 30 V for further experiments. At this voltage, the suitable times for COD and color treatment were 30 and 10 min, respectively, resulted in COD effluent of 147 mg/L and color effluent of 66 Pt-Co. Because these values of COD and color already met the national standard for discharging of industrial wastewater and little change in COD and color was observed in longer time of treatment, we selected the treatment time of 30 min. 3.2. Effects of electrode distance and pH (a) (b) Application of electro-coagulation for treatment of wastewater from package printing process 195 This experiment tested the effect of electrode distance (1 - 5 cm), for 30 min and applied voltage of 30 V. As shown in Fig. 3 (a), the distance of 2 cm provided the highest efficiency for both COD and color removal. Increasing or reducing this distance resulted in lower removal efficiencies. This trend is reasonable since shorter inter-electrode gaps increase the mass transfer and reduce ohmic loss, but too short distances cause the reduction of swirling velocity of liquid medium between the electrodes [3]. Beside the possible reason given above, we also observed that the current was inversely proportional to the gap, which additionally explains for the reduction of removal efficiency when the electrode distance increased. (a) Distance (cm) 0 1 2 3 4 5 6 C o lo r (P t- C o ) 0 150 2000 4000 6000 8000 10000 12000 14000 C O D ( m g /L ) 0 150 300 450 600 750 900 1050 1200 1350 1500 Color QCVN COD (b) pH 4 5 6 7 8 9 10 C o lo r (P t- C o ) 0 50 100 150 200 2000 3000 4000 5000 C O D ( m g /L ) 100 150 200 250 300 350 400 450 500 Color COD QCVN Figure 3. Effects of electrode distance (a) and pH (b) on COD and color in the effluents. Initial pH would affect the conductivity of the solution, dissolution of the electrodes, speciation of hydroxides, and zeta potential of colloids particles [3], hence the removal efficiency. According to Fig. 3 (b), the treatment at initial pH from 5 to 8 eliminated color in the wastewater to the same value (i.e. 6.1 Pt-Co), which were significantly lower than that obtained at initial pH of 9. Differently, COD in the effluent reached the lowest value of 146 mg/L at initial pH of 7 and either further increasing or reducing the initial pH resulted in the higher COD effluent. This finding is agreement with Bensadok et al [5] who found the maximum removal of COD and turbidity at neutral pH. 3.3. Effects of mixing speed and electrolyte concentration Since many studies conducted the EC treatment with mixing conditions to maintain the homogenization of the solution [4, 5], we also tested the effects of mixing and different stirring speeds (100-400 rpm) on the removals of COD and color. As can be seen from Fig. 4(a), the application of stirring caused a slightly negative effect on the removal of COD as compared to the treatment without stirring. No improvement of color removal was found when stirring was applied (Fig. 4(b)). This was a new finding since almost of EC former studies applied stirring to homogenize the treatment condition. Additionally, allowing the treated wastewater to settle for 30 min after electrocoagulation slightly improved COD removal (Fig. 4(a)). For the next experiments, the EC treatment was conducted without mixing, and the EC treated effluent was let to settle for 30 min before taking for analysis. Nguyen Thi Thuy, et al 196 (a) Speed (rpm) No mixing 100 200 300 400 C O D ( m g /L ) 0 50 100 150 200 250 300 COD after settling COD Before settling (b) Speed (rpm) No mixing 100 200 300 400 C o lo r (P t- C o ) 0 2 4 6 8 10 12 Figure 4. Effects of rotating speed (a and b) and electrolyte concentration (c). NaCl is generally added into the EC processes to increase the conductivity, decrease power consumption, and additionally provide water disinfection [6]. Results from our study indicated that at the NaCl concentration of 0.05 g/L, effluent COD was 128 mg/L, which was lower than that achieved from the treatment without NaCl addition (i.e. 134 mg/L) (Fig. 4(c)). However, continuing to increase NaCl concentration up to 0.4 g/L resulted in the higher effluent COD. 3.4. EC treatment at optimum condition and the comparison of EC and CC treatment After investigating the effects of different parameters on COD and color removals, we conducted the EC treatment at optimum condition of 30 V, 30 min, pH 7, electrodes distance of 2 cm, 0.05 g/L NaCl, without mixing, and with 30 min settling. Results showed that except for BOD5, other parameters met the National regulation for discharging of industrial wastewater, Colum B (Table 1). Table 1. Treatment of printing ink wastewater by EC and CC processes. No. Parameter Initial Effluent EC Effluent by CC National regulation (40: 2011), Colum B 1 pH 7.0 0.1 8.3 0.1 - 6 – 9 2 BOD5 (mg/L) 1125 13 84 11 - 50 3 COD (mg/L) 2593 14 128 4.8 275 8.0 150 4 TSS (mg/L) 438 16 70 8.6 - 100 5 Color (Pt-Co) 53943 19 2.4 1.2 13.5 1.8 150 Removal efficiency of COD was 95.1% which is slightly higher than that obtained from [7] for paint manufacturing wastewater treatment (94 %). The color was almost totally removed, by 99.9 %. In addition, TSS and BOD5 were removed with the high efficiencies of 84.0 and 92.5 %, respectively. It is further noted that BOD5/COD ratio was significantly changed from initial wastewater (0.43) to treated wastewater (0.66), indicating the increase of biodegradability of the wastewater after being treated by EC process. Energy consumption was calculated to be 8.52 kWh/kgCOD under optimum condition, which was comparable with those from the literatures [8, 9] for coffee wastewater treatment by EC process. Meanwhile, the chemical coagulation (CC) at optimum condition of pH 7 and 0.8 g/L PAC provided COD and color removal efficiencies of 89.9 and 99.9 %, respectively, in which COD did not meet the national regulation. Application of electro-coagulation for treatment of wastewater from package printing process 197 4. CONCLUSIONS Electrocoagulation was successfully applied for printing ink wastewater treatment. The removal efficiencies of COD, TSS, color, and BOD5 reached 95.1, 84.0, 99.9, 92.5 %, respectively, at 30 V, treatment time of 30 min, electrode distance of 2 cm, and 0.05 g/L NaCl. Mixing wastewater was not recommended while settling the treated wastewater for 30 min was suggested. While COD, TSS, and color in the effluent met well the national regulation (Colum B), BOD5 was slightly higher than its allowable value. EC treatment showed better COD and color removal than chemical coagulation using PAC, and also increased BOD5/COD ratio, which could be suitable for further application of biological treatment. Future study would focus on the treatment of printing ink wastewater using different electrode materials (e.g. combination of aluminum-iron, iron-iron, and aluminum-inert electrodes) for a better removal efficiency and reducing energy consumption. Acknowledgements. This work was supported by Center of Science and Technology Development for Youth, in HCM city under Grant (22/2017/HĐ – KHCN – VƯ). REFERENCES 1. Ding L., Chen Y., and Fan J. - An overview of the treatment of print ink wastewaters, Journal of Environmental Chemistry and Ecotoxicology 3 (2011) 272-276. 2. Kuokkanen V., Kuokkanen T., Ramo J., and Lassi U. - Recent Applications of Electrocoagulation in Treatment of Water and Wastewater - A Review, Green and Sustainable Chemistry 3 (2013) 89-121. 3. Sahu O., Mazumdar B., and Chaudhari P. K. - Treatment of wastewater by electrocoagulation: a review, Environmental Science and Pollution Research 21 (2014) 2397-2413. 4. Adamovic S., Prica M., Dalmacija B., Rapajic S., Novakovic D., Pavlovic Z., and Maletic S. - Feasibility of electrocoagulation/flotation treatment of waste offset printing developer based on the response surface analysis, Arabian Journal of Chemistry 9 (2016) 152-162. 5. Bensadok K., Benammar S., Lapicque F., and Nezzal G. - Electrocoagulation of cutting oil emulsions using aluminium plate electrodes, Journal of Hazardous Materials 152 (2008) 423-430. 6. Chen G. - Electrochemical technologies in wastewater treatment, Sep. Purif. Technol. 38 (2004) 11-41. 7. Akyol A. - Treatment of paint manufacturing wastewater by electrocoagulation, Desalination 285 (2012) 91-99. 8. Asha G. and Kumar B. M. - Coffee pulping wastewater treatment by electrochemical treatment followed anaerobic sequencing batch reactor, International Journal of Scientific & Engineering Research 6 (2015) 1447-1456. 9. Asha G. and Kumar B.M. - Evaluation of Electrochemical Process for Treating Coffee Processing Wastewater using Aluminum Electrodes, IOSR Journal of Environmental Science, Toxicology and Food Technology 9 (2015) 74-82