A Study on Brine Resource Utilization in Desalination Plants. Chen-Yu CHANG 1,*, Chiung-Ta WU 2, Yi-Ying LI 2 and Yung-Hsu HSIEH 2

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1 2017 2nd International Conference on Environmental Science and Engineering (ESE 2017) ISBN: A Study on Brine Resource Utilization in Desalination Plants Chen-Yu CHANG 1,*, Chiung-Ta WU 2, Yi-Ying LI 2 and Yung-Hsu HSIEH 2 1 Center for General Education, National Taitung College, Taiwan 2 Department of Environmental Engineering, National Chung-Hsing University, Taiwan *Corresponding author Keywords: Desalination plant, Concentrated brine, Resource utilization, Electrolytic catalysis technology, Multi-oxidants. Abstract. In this study, we utilized electrolytic catalysis technology and the concentrated brine from the Matsu Nankan Desalination Third Stage Plant to develop a brine resource utilization process, producing a multi-oxidant with disinfection efficacy, containing chlorine dioxide (ClO 2 ), chlorine (Cl 2 ), ozone (O 3 ) and hypochlorous acid (HOCl). This experimental result is expected to achieve waste resource utilization by using the waste concentrated brine as an electrolyte material to produce disinfectants by an electrolysis procedure. The disinfectant generated can also be used in many sterilizing processes in the plant. In the study, the optimal operational conditions were controlled at 40 for temperature and 12 V for cell voltage. 6 % NaClO 2 was added into the same brine. Under these optimum conditions, the major product became ClO 2 with a maximum concentration of 1074 mg L -1. Comparing the disinfection efficacies between 1 ppm of commercial 10 % hypochlorous acid and the multi-oxidant produced in this study, the efficacies of hypochlorous acid and the multi-oxidant reached 28 % and 93 %. The latter was three times greater than the former. In conclusion, the multi-oxidant produced by recycling the brine from desalination plants was expected to have applicability and economic value. Introduction Membrane methods, including Reverse Osmosis, (RO) and Ultra Filtration, (UF), are the most widely used types and technologies in desalination plants [1-4]. When they are applied in desalination processes, the major waste output is concentrated brine. The concentrated brine generated from desalination is usually discarded into the surrounding sea, resulting in a negative impact to the marine environment and endangering native marine life and ecosystems [5-7]. Over-disposal can even cause a rapid salinity increase in specific sea areas, resulting in dead seas. Therefore, seeking an efficient recycling method for the waste concentrated brine is an issue having research value and development necessity. A desalination plant, no matter which type or technology, it applies, usually needs to consume large amounts of disinfectant to treat raw seawater, to clean treatment devices and to sterilize freshwater outflow from desalination processes. Therefore, we used concentrated brine from the Nankan Third Stage Desalination Plant as the study target. Currently, disinfectant is required in the water taking well system, UF filtration system and desalination system. The average daily disinfectant demand is 70 kg day -1. Because the major component of concentrated brine is NaCl, which is the electrolyte used in electrolysis chlorine production technology, it can be used to produce a multi-oxidant 283

2 with disinfection efficacy, containing chlorine dioxide (ClO 2 ), chlorine (Cl 2 ), ozone (O 3 ) and hypochlorous acid (HOCl), by properly controlling the electrolyzer hardware components and operating parameters. It is expected to achieve waste resource utilization by using the waste concentrated brine generated after desalination as the electrolyte material to produce disinfectant with electrolysis procedure. The disinfectant generated can also be used in many sterilizing processes in the plant. Experimental Materials and Methods Electrolytic catalysis technology was utilized to perform brine tests in the Matsu Nankan Third Stage Desalination Plant, in order to produce a multi-oxidant. We found the major control parameters and the optimum controlling conditions to produce a multi-oxidant, containing chlorine dioxide (ClO 2 ), chlorine (Cl 2 ), ozone (O 3 ) and hypochlorous acid (HOCl), by using the brine generated from desalination processes. The multi-oxidant was tested for its applicability in part of disinfection, including disinfection byproduct composition analysis [8-10]. Result and Discussion The diaphragm electrolysis method applied in this study was modified from the Hooker S-3 Type Salt Diaphragm Electrolysis Method. Two patents have been obtained: Production Equipment for Multi-Oxidant and Multifunctional Electrolyzor. In the analysis test for different installation parameters related factors, such as voltage intensity and catalysis species, were applied in a factor comparative experiment. The optimum production parameters and the best preservation conditions of the multi-oxidant, containing chlorine dioxide, chlorine, ozone and hypochlorous acid, were found to be the reference of following applications and operations. Test for Chlorine-dioxide-contained Multi-oxidant Production from Brine In this section, the brine from the Matsu Nankan Desalination Plant was taken to perform a chlorine-dioxide-contained multi-oxidant production test. The test equipment was also the diaphragm electrolyzer used in the previous experiment, with ruthenium coated titanium anode, titanium cathode, and DuPont Nafion N-2030 ion film diaphragm. Table 1 shows the initial properties of brine from the Matsu Nankan Desalination Plant. The brine was the outflow from the concentration end of RO process, thus its property did not change too much in the year. Because it had higher chlorine ion concentration than normal sea water (1.5 times higher), the concentrated brine could fulfill the electrolyte requirement in this plan to produce chlorine-dioxide-contained multi-oxidant by electrolysis. Item Table 1. Initial Properties of the Brine. Measurement Conductivity 7870 µs cm -1 (25 ) Chloride mg L -1 Total dissolved solids mg L -1 Na mg L -1 Batch Electrolysis for Pure Brine In this experiment, the electrolysis operation parameters were set with the optimum parameters of the diaphragm electrolyzer in standard operation (according to the previous studies in the lab). The sample of disinfecting solution mixture product was 284

3 taken at the outflow end of the venturi. The major setting items were: venturi flowrate, operation voltage, initial temperature of anode electrolyte and NaOH concentration of cathode electrolyte. NaOH solution was used as the cathode electrolyte because it could accelerate the entire electrolysis reaction, upgrading the operational efficiency. The fixed parameters are shown in Table 2. Items Table 2. Fixed Parameters in Electrolysis Operation. Setting parameter anode electrolyte brine initial temperature of anode electrolyte 30, 40 cathode electrolyte 0.5 % NaOH venturi flowrate 1 L min -1 operation voltage 8, 10, 12 V Figures 1 illustrated the electrolysis reaction results of concentrated brine at 30, 12V. The figure obviously showed that Cl 2 concentration could reach 376mg L -1 and the ClO 2 concentration was only 6.9 mg L -1 after 60 minutes of electrolysis operation using concentrated brine as the anode electrolyte. Figure 1. Electrolysis reaction of concentrated brine at 30 and 12 V. Batch Electrolysis for Brine Added Sodium Chlorite The results of the previous experiment showed that pure brine was not beneficial for electrolysis batch operation test, although the brine was 1.5 times more condensed than normal seawater (of concentration). The salinity of brine was only 11.3 % of saturated brine (27 % NaCl). For batch resource recycling technology evaluation of the raw material, brine, the anode electrolyte composition was adjusted under the best temperature parameters found previously in this study, in order to upgrade the oxidant production efficiency. Figures 2 and Figures 3 show the production amounts of Cl 2 and ClO 2 in the multi-oxidant generated from the brine added 6% NaClO 2 (weight ratio of NaClO 2 to brine) at different temperatures. Figure 4 obviously shows that the ClO 2 concentration significantly increased after adding 6% NaClO 2 into the anode electrolyte. As the temperature rose, the concentration could reach 587 mg-clo 2 L -1. As the reaction time prolonged, however, ClO 2 did not keep increasing but re-reacted to become Cl 2 due to the reactant decrease in the batch reaction (shown in Figure 5). Figure 5 shows that the Cl 2 concentration also increased although not as significantly as ClO 2. It also increased as the temperature rose but not much different between 30 and

4 Figure 2. Production amount of ClO 2 generated from the brine added 6 % NaClO 2 at different temperatures. Figure 3 Production amount of Cl 2 generated from the brine added 6 % NaClO 2 at different temperatures. Figure 4. Production amount of ClO 2 generated from the brine added 6 % NaClO 2 at different voltages. Figure 5. Production amount of Cl 2 generated from the brine added 6 % NaClO 2 at different voltages. 286

5 Because the concentration of ClO 2 significantly rose after adding 6 % NaClO 2 into anode electrolyte, different ratios of NaClO 2 were also added in the following experiment, in order to understand the effect of NaClO 2 addition ratio. Figures 15 and 16 show the electrolysis production test results of Cl 2 and ClO 2 generated from the brine added different ratios of NaClO 2 ( 2 %, 4 %, 6 % and 8 % ) at 40 and 12V. The figures obviously show that production amount of ClO 2 increased as more NaClO 2 was added, yet Cl 2 did not significantly increase. Therefore, higher NaClO 2 addition ratio was more beneficial for producing chlorine-dioxide-contained multi-oxidant from brine and for improving resource utilization. Figure 6. Production amount of ClO 2 generated from the brine added different ratios of NaClO 2. Figure 7. Production amount of Cl 2 generated from the brine added different ratios of NaClO 2. Test for Disinfection Efficacy of the Brine-Produced Multi-Oxidant In this study, the disinfection efficacy of lab-electrolysis-produced multi-oxidant was compared with the one of 1 ppm commercial 10 % hypochlorous acid. Because the multi-oxidant contained approximately 40 % Cl 2, the concentration of 1ppm was calculated from the concentration of effective chlorine. Figure 8 showed that both of the disinfectants could achieve their maximum disinfecting effect after 10 minutes of contact. The disinfection efficacy of hypochlorous acid and the multi-oxidant reached 28 % and 93 %, yet the latter was three times greater than the former. Because the multi-oxidant contained not only ClO 2 but also 40 % Cl 2 and a few strong oxidizing agents, O 3 and H 2 O 2, it had better disinfection performance than hypochlorous acid on the same basis. 287

6 Figure 8. Comparison of disinfection efficiency of the multi-oxidant and commercial hypochlorous acid. Conclusion This study was the first application case of multi-oxidant electrolysis production with concentrated brine from a desalination plant in Taiwan. It could be a reference for other plants. It solved the problems of transportation difficulty and disinfectant recession in outlying islands. This study provided a safe and simple oxidant production method. The result of this study can be used as an operational reference and to help in operational cost down for related desalination industries in Taiwan. Acknowledgement We thank the Ministry of Science and Technology of Taiwan for the financial support to this research (NSC E CC2). References [1] Khawaji AD, Kutubkhanah IK, Wie JM. A 13.3 MGD seawater RO desalination plant for Yanbu Industrial City, Desalination 2007, 203: [2] Oh BS, Oh SG, Jung YJ, Hwang YY, Kang JW, Kim IS. Evaluation of a seawater electrolysis process considering formation of free chlorine and perchlorate, Desal. Wat. Treat., 2010, 18: [3] Oh BS, Park SY, Jung YJ, Baek KW, Hwang TM, Cho KS, Kang JW. Application of platinum and titanium materials as an electrode for hygiene purpose, Mater Sci Forum, 2007, : [4] C. Belmont. Coplanar interdigitated band electrodes for electrosynthesis. Part 4: Application to sea water electrolysis, Electrochimica Acta 44, 1998, [5] Byung Soo Oh., Formation of hazardous inorganic by-products during electrolysis of seawater as a disinfection process for desalination, Science of the Total Environment, 2010, [6] Bergmann H, Rollin J. Product and by-product formation in laboratory studies on disinfection electrolysis of water using boron-doped diamond anodes, Catal Today, 2007, 124:

7 [7] Jung YJ, Oh BS, Kang JW, Page MA, Phillips MJ, Mariñas BJ. Control of disinfection and halogenated disinfection byproducts by the electrochemical process, Water Sci Technol, 2007, 55: [8] Munichandraiah N, Sathyanarayana S. Kinetics and mechamism of anodic oxidation of chlorate ion to perchlorate ion on lead dioxide electrodes. J Appl Electrochem, 1987, 17: [9] Yi S, Ma Y, Wang X, Jia Y. Green chemistry: pretreatment of seawater by a one-step electrochemical method, Desalination 2009, 239: [10]Withers A. Options for recarbonation, remineralisation and disinfection for desalination plants. Desalination 2005, 179:

Mercury, membrane or diaphragm

Mercury, membrane or diaphragm Introduction The chloro-alkali industry is a major branch of the chemical industry. Its primary products are chlorine, sodium hydroxide and hydrogen which are produced from