Research improving the process preparing superoxidized sulution and application in disifecting hospital wastewater

1 MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ...*** NGUYEN THỊ THANH HAI RESEARCH IMPROVING THE PROCESS PREPARING SUPEROXIDIZED SULUTION AND APPLICATION IN DISIFECTING HOSPITAL WASTEWATER Major: Environmental Technique Code: 62 52 03 20 SUMMARY OF ENVIRONMENTAL TECHNIQUE DOCTORAL THESIS Hanoi, 2018 2 The work was completed at: Graduate University of Science and Technology – Vietnam Academy of Science and Technology Science instructor 1: Assoc. Professor, Dr. Nguyen Hoai Chau Science instructor 2: Assoc. Professor, Sc.D. Ngo Quoc Bưu Reviewer 1: Reviewer 2: Reviewer 3: The dissertation will be protected at the Council for Ph.D. thesis, meeting at the Graduate University of Science and Technology – Vietnam Academy of Science and Technology at ... hour ... ', date ... month ... 201 ... . The dissertation can be found out at: - Library of the Graduate University of Science and Technology - National Library of Vietnam 3 INTRODUCTION 1. Statement The electrochemical activation phenomena were discovered by Russian engineer Bakhir in 1975. Then the electrochemical activation (ECA) technology has been widespreading in Russian Federation and many other countries in the world, including Vietnam. In Vietnam, since 2005 a researcher group of Institute of Environmental Technology, VAST, has began to study and fabricate the ECA divices by using imported from RF different electrochemical chambers suchs as FEM-3, FEM-7, MB-26, especially the latter model MB-11, which seemed to be the most suitable in work under tropical climate of Vietnam. However, after operating in real weather conditions our ECA device based on an electrolytical chamber MB-11 has exhibited some disadvantages such as ECA chamber’s temperature increasing, rapid deposition on the catode etc..., resulting in worsening product’s quality as well as decreasing equipment’s lifespan. The need to improve the ECA solutions produced on the MB-11 - based ECA devices has become urgent since 2011. The research group of the Institute of Environmental Technology, among which author of this thesis has played an important role, have found out the solution to constrain the temperature increasing effect of the electrolytical process by changing the hydraulitic scheme of the device. The success of the improved designing of the ECA equipment using MB-11 module will open new possibilities to solve the problems of disinfection of hospital waste water which the Institute of Environmental Technology is dealing with for 15 years. 2. Objectives of the thesis To investigate and improve the technological process of producing superoxidation solutions in order to produce ECA device suitable for Vietnamese climatical conditions and apply the solutions of this device for disinfection of hospital wastewater. 3. Main contents of the thesis - Improvement of the technological process of producing superoxidation solutions suitable for the real tropical conditions in Vietnam; - Application of superoxidation solution to disinfect hospital wastewater. 4. New contributions of the thesis The thesis has successfully investigated and set up a new hydraulytic diagram of the superoxidation water (SUPOWA) device producing superoxidation solution (SOS) with a capacity of 500 ± 5 g of oxidants/day in Vietnam. The improved hydrolytic diagram was based on the non-circulating catholite flow instead of the original circulating one. This operational mode was done by setting up the relationship between the number of catholite turns 4 and the quality of the supowa solution produced and the MB-11’s lifespan. Due to this improvement the temperature of the module could be kept below 39 o C during operation of the device, which resulted in the increased longevity and stable operation of the electrolytic module in tropical climates, meeting the requirements of the small hospitals wastewater stations or healthcare centers with a capacity of about 150 beds. In addition, the results of the thesis also demonstrated the possibility of localization of the supowa devices except for the imported ECA electrolytic modules. Results of the thesis have opened a new direction in application of high technology to disinfect drinking and waste water. The improved ECA technology is friendly with environment and able to reduce significantly the risk of chlorine gas poisoning for operating workers. The SOS produced on the improved ECA devices are cost-effective, safe and powerful disinfectant for treatment of hospital waste water. CHAPTER 1. OVERVIEW 1.1. Super oxidation solution and its general characteristics 1.1.1. Introduction tot superoxidation sollution (SOS) 1.1.1.1. Electrochemical activation solution Electrochemical activation is a combination of electrochemical effects on the dilute aqueous solution of ions and molecules in the space near the electrode surface (anode or cathode) in a flow-through electrolytic module (FEM) with a semipermeable membrane separating the anodic and cathodic spaces. Under the electrochemical impact some part of the polarisation energy is transformed into inner potential energy. As a result of the electrochemical activation the near-electrode medium comes into a metastable state characterized by anomal activity of electrons and other physico-chemical parameters. Simultaneously changing in time, these perturbed parameters of the near-electrode medium gradually attain equilibrium values during relaxation process. This phenomenon is called electrochemical activation, while solution produced by the technology based on these phenomena is called electrochemical activation solution [19]. Whilst superoxidation solution or superoxidatin water (supowa) is electrochemical activation solution with highly oxidizing activity while mineralization is extremely low [22]. Characteristics of “coventional” ECA solution and superoxidation solution are shown in Table 1.1. 5 Table 1.1. Characteristics of nomal electrochemical activation solution and superoxidizing solution Superoxidation solution used in the experiments below was made by an ECA device with MB-11 module (an improved module of electrochemical activation technology with a little diffirence in structure and technical characteristics compared with the previous module type. MB-11 module has more stable anode coatings, higher polarization voltage ( 3000 mV), allowing the activation of solutions with much lower mineralization. The supowa solution consisted of a series of high active oxidants such as HClO, H2O2, Cl  , HO  , HO2  , O3, 1 O2, O  , Cl2, ClO2, O3, etc. [21]. It was well known that all these substances present in living organisms (in cytochromes), so that supowa solution posseses a broad spectrum capacity for killing pathogenic microorganisms, including bacteria, viruses, and fungi, while it doesn’t damage human cells and other higher organisms. The difference is due to the difference in the cell structure [25]. Except for the Russian researchers, there are many others in the world who have studied the SOS, which are essentially ECA solutions under various trade names such as Sterilox®, Sterisol®, Medilox®, Dermacyn®, Microcyn®, Varul®, Esterilife® and Estericide® QX, ... Each of them has different components [30]. Most opinions suggest that superoxidant water (SOW) has a great potential for disinfection in all fields of life, but it requires an in-depth research into applications for each field. 1.1.2 Some methods for production of SOS 1.1.2.1 Principles of anolyte production technology No. Technical parameters Conventional ECA solution Superoxidation solution 1 Mineralization (TDS), mg/L) ~4500 ÷ 5000 ~ 1000 ÷ 1500 2 Oxidants concentration, mg/L ~300 ~500 3 Oxidation Reduction Potential (ORP), mV > +800 > +800 4 pH 6,5 ÷ 7,5 6,5 ÷ 7,5 Figure 1.4. Electrochemical module MB-11 6 Fingure 1.5 Diagram of FEM-3 priciples to produce catalytic newtral anolyte ANK solution [Error! Reference source not found.] Fingure 1.6. Digram of MB-11 principles to produce supowa solution based on receiving the wet oxidants gas mixture [21]. Operation principle of the SOS technology using MB-11 module is as follows: Pure water is supplied to the cathode chamber of the MB-11module, while sodium chloride solution is directed to the anode chamber. Under conditions of transmembrane pressure PA (anode chamber) is greater than the PC transmembrane pressure (cathode chamber). Na+ ions along with water will travel from the anode chamber to the cathode chamber to form catholyte. After the catholyte solution passes through the gas separation chamber to discharge H2 gas and metal hydroxides, it is drawn to absorb the wet gas mixture of oxidants outgoing from the anodic space [19]. 1.1.2.2. Some supowa modulation technologies have been applied Fingure 1.8. Diagram of the improved process allows for the generation of ANK high oxidant content on the improved STEL-30-ECO-C Figure 1.9. Some anolit modulation schemes of Russia [62] NaCl 10-20 g/L 7 1.1.3. Studies on superoxidation solutions (abbreviated as SOS) in Vietnam In Vietnam, 2000, a research group in the National Center for Natural Science and Technology (now: Vietnam Academy of Science and Technology) was formed to manufacture equipments producing anolyte according to the technological model STEL-10H-120-01 by using PEM-3 module imported from Russia. Researchers at Institute of Environmental Technology (IET) have conducted research, design and production ECA equipments. The aim of these studies was to clarify the differences in different technological diagrams, the stability in time of ECA solutions as well as the characteristics of their disinfection capability in specific tropical conditions of Vietnam to improve the effectiveness of ECA technology in our country. Based on the use of FEM-3 modules imported from Russia, IET has successfully fabricated the classic equipments "STEL-ANK" called ECAWA with a capacity of 20 ÷ 500 L/h, ORP of 800 ÷ 900 mV and oxidants concentration of 300 ÷ 350 mg/L. Since 2002, ECAWA has been used widely throughout the country for medical and water disinfection [23,40], environmental pollution treatment [23,100], shrimp seed production [101], seafood processing [100,102], animal husbandry [103] and poultry slaughter and farming [104]. Since 2011, IET has received STEL 2nd and 3th generation equipments delivered by Russian [23] for research and evaluation. After a period of testing in Vietnam, these equipments have revealed some drawbacks that need to be overcome: unstable operation, frequent clogging of the membrane, electrode damage, increasing temperature of electrochemical chamber, etc. that directly affect the products quality and equipment’s lifespan 1.2. Hospital wastewater and pollution characteristics Hospital wastewater contains not only conventional pollutants but also a lot of pathogens such as bacteria, viruses, hamful protozoa, worm eggs, etc., especially wastewater from infectious hospitals, tuberculosis hospitals and other infection areas. Specific types of bacteria presenting in hospital wastewater are: Vibrio cholerae, coliforms, Salmonella, Shigella etc. Coliforms are considered as a sanitary indicator. These species are usually resistant to antibiotics. 1.3. Methods of hospital wastewater disinfection Current agents used for hospital wastewater disinfection are mainly chlorine compounds, ozone and ultraviolet light. popularly,among which chlorine compounds are more commonly used. The disadvantages of these agents are high corrosion, toxic byproducts, poor disinfection efficiency, unsafe for producers and users. 8 The hospital wastewater disinfection method using ECA solutions is a solution to improve the effectiveness of chlorine-containing disinfectants. Although there have been initial studies confirmed the strong antiseptic activity and safety, environmental friendly but there is no yet comprehensive research on medical wastewater disinfection In summary, based on the results of the improvement in design of technological SOS diagrams to suit for tropical conditions in Vietnam, this thesis proposes the application of SOS for medical waste water disinfection. This will address the shortcomings of traditional wastewater disinfection methods and open new directions for application of the advanced ECA technology to disinfect water in general and in particular hospital wastewater. CHAPTER 2. CONDITIONS AND METHODS OF EXPERIMENT 2.1. Research Subjects + Receiving SOS with low mineral concentration, using improved process technology, fabrication and perfect the device producing low-mineral SOW. + Wastewater from Huu Nghi and Quan Y 354 hospitals. 2.2. Methods of improvement of the technology for preparing SOS 2.2.1. Methods of studying the absorption technology of wet-gas oxidants mixture for the supowa preparation. 2.2.1.1. Design a pilot scheme for the preparation of supowa 2.2.1.2. Operating conditions 2.2.1.3. Operating parameters to be achieved 2.2.2. Studies on storage capacity and oxidation loss during storage of SOS 2.2.3. Manufacturing equipment producing SOS 2.2.3.1. Equipment requirement 2.2.3.2. Select the technological diagram of the device and the related details 2.2.3.3. Design, manufacture and commissioning 2.2.3.4. Perfect the equipment, set up the operating procedures to achieve basic SOS parameters 2.2.3. Methods of determining the SOS parameters 2.3. Studies on the application of the SOS for hospital wastewater disinfection 2.3.1. Evaluation method of sterilization effect of the superoxidizing solution 2.3.2. Method of evaluating the effect of pH, ammonium, COD and BOD5 in wastewater on disinfection effect of SOS 2.3.3. Comparing the formation of THMs in supowa solution with other disinfectants 2.3.4. Study of the application of SOS for hospital wastewater disinfection 2.4. Materials used 9 - Disinfectants; - International bacterial strains; - Other materials and chemicals. - Other materials and chemicals. 2.5. Techniques used: All measurements, breeding techniques, methods of identification of indicators, preparation of test solutions, sampling, etc. are in accordance with the current international and Vietnamese standards. CHAPTER 3. RESULTS AND DISCUSSIONS 3.1. Preparation of superoxidation solution (SOS) 3.1.1. Preparation of low-mineralization SOS using circulating catholyte method 3.1.1.1. Set up diagram and production process The supowa superoxidized water is obtained at a flow rate of 15 L/ h with oxidants concentration of approximately 500 mg /L , ORP ~ 905mV, neutral pH and TDS ~ 1000 mg/L. equivalent to the product obtained from STEL- ANK-PRO-01 of Delphin (Russia). Figure 3.1. Schematic diagram of the oxidation solution with revolving catholyte 3.1.1.2. Influence of catholyte flow on the SOS parameters The larger the catholyte flow, the lower the concentration of oxxidants, TDS (Fig.3.2) and temperature of the reaction chamber. However, continuing to increase catholyte flow would reduce the concentration of oxidants in supowa to less than 500 mg/L. Therefore, catholyte flow from 20 L/h to 25 L/h was chosen . Figure 3.2. Effect of circulating catholyte flow on oxidant concentration and mineralization in the superoxidizing solution Figure 3.3. Effect of revolving catholyte flow on activated electrochemical chamber temperature 10 3.1.1.3. Effects of the voltage applied to the electrodes of MB-11 on the SOS parameters Increasing the electrolytic potential facilitated the increase of oxidants concentration and the decrease of TDS concentrations of the products. However, the supowa capacity (Figure 3.4b) increases linearly only when the electric potential is 6.6 V ÷ 6.8 V, then the increase slows down due to the competition of the water electrolytic reaction, which increases the electricity cost. Increased voltage also increases the electrochemical chamber temperature, leading to reduced electrode life. Thus the applied voltage ranged between 6.6 and 6.8 volts. This value is within the manufacturer's guide range (6 ÷ 8 V). This is very valuable because in order to achieve the same product parameters, the lower the voltage, the lower the cost of electricity. 3.1.1.4. Influence of the salt quantity used on the supowa parameters Consumption of salt has a great influence on the quality of the products. The high consumption of salt results in increase of oxidants concentration, but TDS content in the product also increased, leading to a decrease in the SOS activity. The results showed that the appropriate salt levels ranged from 18 ÷ 24 g/h. Figure 3.4. Influence of electrolytic potential on oxidants concentration and oxidants capacity Fingure 3.5. Effect of supplied salt quantity on SOS quality Fingure 3.6. Effect of supplied salt on oxidants productivity (a) (b) 11 3.1.1.5. Operation in optimal mode as shown in Table 3.1 It can be seen that preparation SOS with low-mineralization and catholyte-circulating scheme allows to apply a lower voltage (6.7 ÷ 6.8V). The experimental data presented in tabl 3.1 showed that operation conditions and product parameters are similar to those of the same type of ECA device manufactured by Russia. However, the electrochemical chamber temperature (measured outside the chamber) rapidly increased to a high level (39 o C ÷ 40 o C) in a short time. Within 72 hours of operation, a decrease in the amount of oxidant in the product was recorded due to the deposition of metal hydroxide precipitates on the membrane . Table 3. 1. Optimal operating mode of the circulating catholyte diagram Thông số Unit Value attained Oxidants concentration of superoxidizing anolyte mg/L  500 Oxidants capacity g/h ≤ 7,5 pH of anolyte 6,5÷7,5 Electrolytic potential applied V 6,6÷6,8 Catholyte flow rate L/h 20÷25 Sodium chloride supplied g/h 18÷24 Electricity power consumption W.h/g 7,0 ÷ 7,2 Quantity of NaCl required for obtaining 1 g of oxidants g/g 2,26 ÷ 2,91 Cathode chamber’s temperature OC 39 - 40 Practical operation of the device has shown that the catolit turn-over mode increases the temperature, pH and conductivity of the catolite. These three quantities depend on several factors that can be described as follows: t o C, EC, pH = f (n) t o C - electrolyte chamber temperature (on cathode surface); EC - conductivity of catolite solution pH - pH of the catolite solution n - number of catolit turns However, the dependence on the number of catolit turns is best demonstrated by the conductivity of the catolite solution. The relation between the conductivity of the catolite solution and the number of cycles of catolit turn is: y = 0.4773x + 350.79 (3.1) (with R 2 = 0.7603) The greater the number of catolite cycles, the greater the electrical conductivity (or TDS) of the catolite solution, the higher the mineral content in the catolite, the greater the deposition potential on the electrode and the 12 diaphragm. In other words, to reduce these negative effects, the maximum number of catolit turns must be reduced. A modification for the hydraulic diagram has been performed, in which the catholyte does not circulate but goes straight forward into the gas separation chamber, extracted in part