The research objective of the dissertation completes the technological process of modulating super oxidation solution, thereby manufacturing equipment to suit Vietnamese conditions and applying this solution to disinfect hospital wastewater.
MINISTRY OF EDUCATION AND VIETNAM ACADEMY OF TRAINING 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 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 INTRODUCTION 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 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 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 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 ± 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 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 39oC 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 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 Table 1.1 Characteristics of nomal electrochemical activation solution and superoxidizing solution No Technical parameters Conventional Superoxidation ECA solution solution Mineralization (TDS), ~4500 ÷ 5000 ~ 1000 ÷ 1500 mg/L) Oxidants concentration, ~300 ~500 mg/L Oxidation Reduction > +800 > +800 Potential (ORP), mV pH 6,5 ÷ 7,5 6,5 ÷ 7,5 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 Figure 1.4 Electrochemical compared with the previous module type module MB-11 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, 1O2, 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 Fingure 1.5 Diagram of FEM-3 Fingure 1.6 Digram of MB-11 priciples to produce catalytic newtral principles to produce supowa anolyte ANK solution [Error! solution based on receiving the Reference source not found.] 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 NaCl 10-20 g/L Figure 1.9 Some anolit Fingure 1.8 Diagram of modulation schemes of Russia [62] the improved process allows for the generation of ANK high oxidant content on the improved STEL-30-ECO-C 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 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 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 - 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 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 STELANK-PRO-01 of Delphin Figure 3.1 Schematic diagram of the (Russia) 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 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 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 3.1.1.3 Effects of the voltage applied to the electrodes of MB-11 on the SOS parameters (a) (b) Figure 3.4 Influence of electrolytic potential on oxidants concentration and oxidants capacity 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 ÷ 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 Fingure 3.6 Effect of supplied salt on oxidants productivity Fingure 3.5 Effect of supplied salt quantity on SOS quality 10 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 oC ÷ 40oC) 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 Optimal operating mode of the circulating catholyte diagram Thông số Unit Value attained Oxidants concentration of superoxidizing mg/L 500 anolyte 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 g g/g 2,26 ÷ 2,91 of oxidants O Cathode chamber’s temperature C 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: toC, EC, pH = f (n) toC - 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 = 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 11 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 into the supowa output to adjust the pH, and the rest is flushed out This scheme is expected to avoid scale formation due to the formation of hard carbonates and hard salts of metals in the cathode compartment and excessive overheating of the electrochemical reaction chamber during operation 3.1.2 Preparation of low-mineralization SOS using non-circulating catholyte method 3.1.2.1 Set up the diagram and the producing process 3.1.2.2 Effects the catholyte flow on the supowa parameters SOS Supowa is obtained with a flow rate of 16 L/h, oxidants concentrations of approximately 500 mg/L, ORP ~ +910 mV, neutral pH and TDS ~ 950 mg/L The parameters of the supowa prepared by non-circulating catholyte scheme are similar to the supowa that prepared by circulating catholyte scheme, and to the Figure 3.9 Schematic diagram of product prepared by the manufacturer’s the oxidation solution with nonscheme (Delphin Corporation - Russia) circulating catholyte Figure 3.10 Influence of the noncirculating catholyte flow on the supowa parameters Figure 3.11 Influence of the noncirculating catholyte flow on the cathlyte chamber’s temperature It can be seen that the larger the catholyte flow, the lower oxidants concentration, the lower mineralization of the supowa and the lower temperature of the reaction chamber Appropriate catholyte flow was chosen to be about 2.0 L/h, much smaller than the catholyte prepared by the revolving catholyte modulation scheme (Figure 3.1) 12 3.1.2.3 Dependence of the supowa parameters on the electrolytic potential (b) (a) Figure 3.12 Effects of electrolytic potential on the supowa parameters Appropriate voltage values are chosen between 7.5 and volts, which higher than that used in the circulating catholyte scheme This value is within the manufacturer's instruction range (6 ÷ V), but a little higher compared with non-circulating catholyte scheme This leads to an increase in the cost of electricity compared with the Russian version 3.1.2.4 Effects of sodium chloride quantity used on the supowa parameters Figure 3.13 Dependence of the supowa parameters on the amount of NaCl supplied The amount of NaCl supplied was chosen from 18 to 24 g/h, equivalent to the amount of NaCl supplied in the diagram of supowa producing with revolving catholyte 3.1.2.5 pH adjustment of the supowa solution To obtain neutral supowa solution, the wet-gas oxidants mixture should be mixed with a portion of catholyte of pH 10 to 11 The optimal mixing ratio of the catholyte with the oxidants mixture should be selected Fig 3.14 The change of pH of to obtain a neutral supowa solution supowa follow depending on the (pH 6.5 to 7.5) The value is choosen oxidants/catholyte ratio in a range of ÷ 4% 13 3.1.2.1 Operation of SUPOWA equipment system in an optimal mode: The results in Table 3.3 shows that this device uses a higher voltage than the circulating catholyte method, because the resistance of the noncirculatingcatholyte is higher than the revolving catholyte However, the operating temperature of the electrolysis chamber is lower, the operating mode is more stable, the frequency of electrode washing is lower because of the low deposition and precipitation of carbonate salts and metal hydroxide on the membrane The parameters of the supowa prepared by non- circulating catholyte scheme are similar to the supowa using circulating catholyte scheme, as well as to the product prepared by the Russian device Table 3.3 Optimal operating mode of non-circulating catholyte diagram Parameters Unit Value The concentration of oxidants in the mg/L 500 anolyte product Oxidants capacity g/h >7,5 pH 6,5 ÷ 7,5 Voltage UDC V 7,5 ÷ 8,0 Catholyte flow rate L/h 2,0 ÷ 2,5 Amount of NaC salt supplied g/h 18÷24 Electricity power consumed to produce W.h/g 9,0 ÷ 9,6 one unit of oxidants Amount of salt consumed to produce one g/g 2,3 ÷ 2,91 unit of oxidants in the product o The temperature of the cathode chamber C 38 ÷ 39 Oxidants/catholyte mixing ratio % 3÷4 3.1.2 Study the storage capability and product quality’s changes during storage In this study, the supowa parameters used are as follows: pH 6.59; ORP 900 mV; TDS 1100 mg/L; Oxidants concentration 528 mg/L, stored for 96 hours (4 days) in two plastic bags B1 and B2 with lids, at room temperature of 25°C B1 has a surface area of 1256 cm2, B2 has a surface area of 50 cm2 The parameters of the supowa solution change with storage time as shown in Table 3.5: Table 3.5 Supowa parameters depend on storage time Store Parameters TN TN TN TN TN TN TN TN mode Time (h) 24 48 72 96 B1 pH ORP(mV) TDS (mg/L) [Oxidants] (mg/L) 6,59 900 6,66 899 6,58 898 6,55 887 6,55 884 6,53 885 1100 1100 1090 1075 1060 1047 1028 1000 528 469 455 440 528 6,55 902 523 14 6,69 898 496 493 B2 pH ORP(mV) TDS(mg/L) [Oxidants] (mg/ L) 6,59 6,62 6,64 6,58 6,51 900 901 898 898 896 1100 1100 1100 1095 1086 6,36 897 1080 6,34 893 1065 6,33 891 1045 528 486 482 469 528 520 510 499 The experiment data showed that for both modes of solution storage in B1 and B2 with lids, the supowa parameters (pH, TDS, ORP, oxidants concentration, ) have decreased slowly over time This is because the metastable components in the solution undergo dissipative degradation according to the law of increasing entropy to return to the thermodynamic equilibrium However, degradation in B2 is slower than that in B1 thanks to its small surface area, which significantly limits evaporation of oxidants It can be seen that, in order to storage longtime the SOS while maintaining high disinfection effect, it is necessary to store the solution in a closed space 3.1.4 Comments It is possible to summarize and compare on some advantages and disadvantages of the two methods producing SOS in table 3.6 Table 3.6 Comparison of advantages and disadvantages of methods Method producing SOS by Method producing SOS by noncirculating catholyte diagram circulating catholyte diagram Consume lower voltage, which means Consume higer voltage, which means more electric power are saved (about more electric power are consumed W/g chlorine) (about 10 W/g chlorine) Have to clean the electrode more The working time without electrode frequently because of the deposition cleaning is long (cleaning time per in cathode chamber (daily, maximum months, up to months) beacause the days), which means more time and deposition in cathode chamber is less, chemicals are consumed (at least 160 which means more time and chemicals minutes and liters of chemicals for are saved (about 20 minutes and liter cleaning the electrodes in months) of chemicals for electrode cleaning in months) The operating mode will be less stable if The operating mode is more stable the electrode cleaning is not frequently The complexity of the details when Cost of production are saved by manufacturing equipment will simplifying the details increase the cost of production It can be seen that each method of preparing the SOS has its own advantages and disadvantages It is difficult to confirm which diagram is better The choice a suitable diagram should be made base on the operating conditions and the specific benefits 15 3.2 Research on the improvement of equipment for the preparation of SOS 3.2.1 Technological design 3.2.1.1 Production diagram: shown in Figure 3.8 3.2.1.2 Capacity of equipment The device is designed to use the MB-11 electrolytic chamber, which has oxidants capacity of 30 g/h (equivalent to 60 liters of solution) 3.2.1.3 Flow diagram of the electrolytic chambers: Figure 3.19 Ra catolit Ra anolit siêu oxy hóa Figure 3.19 Flow diagram of four electrolytic chambers Dung dich nước NaCl Nước vào 3.2.1.4 Scheme of power supply for electrolytic cells: shown in Figure 3.20 Figure 3.20 Power supply diagram for electrolytic cells 3.2.1.5 Technology Diagram of equipment producing supowa: Figure 3.21 Figure 3.21 Technological Diagram for preparing the SOS using MB-11 modules (1) Electrolytic Cell MB-11 (2) DC power (3) Control cabinet (4) Filter µm (5) System for washing electrode with acid HCl (6) Ion exchange (column soften the water) 16 (7) Salt solution tank (8) Salt solution pump (9) Softened water tank (10) Supowa tank (11) Flow meter (12) Softened water pump 3.2.2 Manufacturing equipment Figure 3.22 Supowa equipment Figure 3.23 ECA system with MB - 11 modules 3.2.3 Equipment testing Experimental data showed that the supowa equipment operate quite stable during the 30-hour trial period Oxidants capacity can be achieved: 0.5233 g/L × 59.1 L/h × 16 h/d = 494.8 g/d Compared with similar equipment manufactured by Delphin company (Russia), the SOS of the two equipments have similar characteristics The Supowa equipment consumes more power than Russian device due to its higher voltage (8 V vs 6.6 V), but the Supowa operates more stable due to less deposit on the electrode Furthermore, the temperature of electrochemical chamber is more stable so the product quality is not so much affected 3.2.4 General comment Successful improvement of the hydraulic diagram of the superoxidizerd solution production system using non-circulatingcatholyte scheme instead of revolving mode has reduced the cathode temperature during operation The equipment is more stable in the tropical climate of Vietnam - It is possible to make localization of equipment for the production of SOS except for the import of electrochemical chamber - The equipment Supowa producing SOS has achieved all the requirements set out: the quality of the supowa, the construction fitness of equipment, the level of simplicity and flexibility when installing, using, maintenance and replacement; - The Supowa equipment system which produces SOS operates stably, met the requirements of continuous operation for wastewater treatment stations in small hospitals (or medical centers) with a capacity of 150 beds 3.3 Studies on the application of SOS to disinfect hospital wastewater 3.3.1 The disinfection effect of the SOS on some pathogenic microorganisms commonly encountered in hospital wastewater 3.3.1.1 The dependence of the disinfection effect of the SOS on oxidants concentration and time of exposure 17 The object studied was coliforms 104 CFU/ml Coliform exposed to the SOS at concentrations of 0; 0,1; 0.25; 0.5; 1.0 mg/L for minutes The result showed that the minimum concentration of SOS used to kill coliforms 104 CFU / mL is 0.5 mg/L in minute of exposure time Figure 3.24 The dependence of the Figure 3.25 The dependence of disinfection effect of supowa solution the disinfection effect of the SOS on the oxidants concentration and sodium hypochlorite (with the same concentration) on the time of exposure Similar experiments were performed with sodium hypochlorit The results shown in Figure 3.44 Results showed that the SOS had significantly higher disinfection efficacy than sodium hypochlorit This demonstrates that in the SOS there is not only a disinfecting agent ClO- (the main ingredient in sodium hypochlorite) may also be the presence of other highly active oxidants such as H2O2, O3, 1O2, HO, HO2 …[67, 70] This is the main reason for the difference in disinfection efficiency of SOS compared to sodium hypochlorit in particular and other chlorinated chemicals in general 3.3.1.2 The dependence of the disinfection effect of the supowa solution on the pH of the solution: Coliform 106 CFU/100 mL exposed to SOS with oxidant concentration of 0.5 mg/L for 30 seconds The pH of the mixture was adjusted from 6.0 to 8.0 Figure 3.26 The dependence of the disinfection effect of the supowa solution on the solution pH 18 Some studies have also shown that the antimicrobial activity of electrochemical oxidized solutions at low pH is higher than when it is at high pH, but with high pH, corrosion is reduced [83] and the stability is enhanced [40], it also provides appropriate ability to kill germ [84] 3.3.1.3 The dependence of the antiseptic effect of SOS on the amount of ammonia contained in the mixture which needs to be sterilized The object studied was coliform 106 CFU/100 mL in mixtures of ammonium at concentrations of 1, 3, 10, 20, 30 mg / L; exposed to SOS for 30 seconds, minutes, 30 minutes disinfectant activity than hypochlorous acid The higher the ammonium concentration, the lower the disinfection effectiveness of supowa Thus, the presence of ammonium in the mixture which needs to be sterilized influences significantly on the disinfection effect of supowa solution This Figure 3.27 The dependence of the may be due to the fact that disinfection effect of the oxidation ammonium ions reacted with solution on the NH4+ concentration is HOCl in the SOS forming in the solution chloramine with a lower 3.3.1.4 The dependence of the disinfection effect of supowa solution on BOD5 in the mixture which needs to be sterilized, compared with sodium hypochlorite The object studied was coliform 106 MPN/100 mL in solutions with the following composition: BOD5 = mg/L, COD = 29 mg/L; BOD5 = 28,6 mg/L, COD = 61mg/L; BOD5 = 43,2 mg/L, COD = 89 mg/L; BOD5 = 89,6 mg/L, COD =168 mg/L;BOD5 = 173 mg/L; COD =327 mg/L; These solutions were exposed to supowa and sodium hypochlorite (for comparison) at mg/L for minutes, 15 minutes, 30 minutes The results are shown in Figure 3.28 They showed that the disinfection effect of the supowa solution decreased with increasing of BOD value This is due to the oxidants in supowa solution exposed to a solution containing bacteria and Figure 3.28 The dependence of the disinfection effect of supowa solution organic substances that oxidized on BOD5 content in solution, compared with sodium hypochlorite 19 BOD to other compounds which are not antiseptic or weakly disinfectants [96] In addition, the activation elements in SOS such as O3, O, O2, H2O2, HO2, HO,etc., can also be easily reduced to a stable state or lower activation because of the organic ingredients Therefore, the disinfection effect of the SOS is also weakened Compared to sodium hypochlorite, it can be seen that even in cases when the organic content of the disinfected solution is high, supowa solution still exhibits higher disinfection efficacy than sodium hypochlorite However, at larger exposure times, the difference of disinfection efficiencies is reduced Thus, with the BOD5 value in wastewater is about 50 mg/l, the disinfection efficiency of the SOS can be achieved to 100% when the concentration of the disinfectant is mg / L and the disinfection time is 15 minutes In case of BOD5 value in wastewater increase, it is necessary to increase the concentration of disinfectant or increase the time of exposure The above results suggest that it is possible to use SOS to reduce BOD5 value in wastewater and to disinfect wastewater, but it requires the use of higher doses of oxidants 3.3.1.5 Testing on mixed samples The study assumed that hospital wastewater contains: coliform 106 MPN/100ml, NH4+ = 10,6 mg/L, BOD5= 52,3 mg/L, COD = 101,4 mg/L; pH =7,1 The exposition to supowa is at 1; 1,5; 2; 2,5; mg/L in 15 minutes The results showed that with 15 minutes exposure in the organic environment, all coliforms were killed only by supowa with a concentration of 1mg/L (Table 3.9) The same experiment was conducted with a mixture of four specific bacteria in hospial wastewater The study assumed hospial wastewater contains: coliform 106 MPN/100mL, Salmonella 106 bacterias/100mL, Shigella 106 bacterias /100mL and Vibrio cholera 106 bacterias /100mL; NH4+ = 10,6 mg/L, BOD5/COD = 52,3/101,4 mg/L; pH =7,05 Supowa concentrations used are and 1.5 mg/L; exposure time: 15 minutes Results are shown in Table 3.10 Table 3.10 Results of the determination of alive bacterias after disinfecting wastewater by supowa at different concentrations Exp Supowa Alive erim concentrati Coliform ent ons (mg/L) 01 2.4 x 107 (control) 02 1,0 9,3 x 101 03 1,5 Not Detected Alive Salmonella Alive Shigella 7.0 x 106 2.5 x 106 1,2 x 101 Not Detected Not Detected 20 Alive Vibrio Alive cholera Vibrioparahaemol ity-cus Not 2.8 x 106 Detected Not 1,4 x 101 Detected Not Not Detected Detected Results showed that oxidation concentration at 1.0 mg/L of supowa with 15 minutes of exposure was not enough to completely kill four coliforms 106 MPN/100mL, Salmonella 106 bacteria/100mL, Shigella of 106 bacterias/100mL and Vibrio cholera 106 bacterias/100mL at the same time, but it could decrease by more than log10 in all four categories Disinfection efficiency of 99.99% demonstrates strong bactericidal activity of supowa solution This is more evident with the supowa content of the oxidants at a concentration of 1.5 mg/L: all four types of bacteria in the hospital wastewater with a density of 106 bacteria/100mL were completely killed Bacterial density was decreased > log10 after the disinfection Thus, this concentration of supowa is suitable for the disinfection of hospital wastewater with the simultaneous presence of four bacteria species characteristic of the hospital at a density of 106 bacteria/100mL, NH4 + concentrations of about 10mg/L and BOD5 concentrations of about 50mg/L (this is the standard limit of hospital wastewater treatment must be reached physico-chemicaly before the disinfection) Compared with the active chlorine dose regulation for wastewater disinfection after completing the biological treatment of g/m3 for a minimum 30 minutes exposure [10], using supowa has saved up to 50% of the disinfection cost and exposure time 3.3.2 Applying supowa solution to disinfect hospital wastewater 3.3.2.1 Study of the possibility of trihalomethane formation during water disinfection process by supowa solution Experimental water samples were sterilized with different disifectants: chlorine gas, NaOCl and supowa at the dose of mg/L and ozone concentration of mg/L Results of THMs analysis of water samples are shown in Figure 3.29 Figure 3.30 Possibility of forming Figure 3.31 The amount of THMs THMs of different disinfectants increases with the amount of disinfectant The results showed that the increase in total THMs content was almost proportional to the amount of disinfectants in the water (Figure 3.30) In the 21 four types of disinfectants used, supowa solution produced considerably lower byproduct (only after ozone) These results are similar to the results of Fenner and Reynolds [11] from University of West of England when studying the formation of THMs in water which contained natural organic matter They found that the chloroform concentration formed decreases by up to 50% when using electrochemical activation water (ECAW) as a disinfectant instead of using hypochlorite for water which contained algae and humic compounds This can be explained that ClO- is very active agent for THMs formation [12] In addition, studying the effect of pH and temperature of the water which need to be sterilized by supowa, the obtained data showed that the dependence of THMs concentration on pH was not follow linear proportions, it tended to increase slowly at high pH When pH was increased from 5.3 to 9.2, total THMs concentration increased to nearly 60% Some studies have shown similar phenomena when using chlorine gas as a disinfectant [12,132] The researchers suggested that in high pH environment, activated chlorine converts to ClO- which interact very easily with organic acids (such as humic acid) to form THMs Total THMs formed when sterilizing at 38°C were more than twice as effective at 15°C This has been found in some THMs concentration surveys in water treatment plants in summer and winter This may be explained that the THMs forming reactions are heat-absorbing reactions, which will be more favorable at high temperatures Therefore, in cases where there is a strict regulation on the content of THMs in water after treatment, the factors affecting the formation of THMs such as active ingredient, temperature, pH, etc of the disinfection process still need to be considered Under normal circumstances, the use of supowa can reduce the formation of THMs by 40% to 50% compared to chlorine gas or NaOCl 3.3.2.2 Testing on the hospital wastewater sample Testing object: wastewater of Huu Nghi Hospital Analytical results of wastewater before and after disinfection with supowa solution (of concentration was 1.5 mg/L) for 15 minutes (indicators following the QCVN 28:2010/BTNMT) showed that: In fact, the wastewater after physiological treatment of the Huu Nghi Hospital was not reached the standard (ammonium concentration was times higher than the prescribed) However, only the coliform appeared and the remaining three other bacterias were not detected in the water In this case, the concentration of 1.5mg / L of the supowa disinfectant still ensures complete the disinfection Inaditon, it also reduced significantly the levels of ammonia and BOD5 by supporting the oxidation of these pollutants Another experiment was also conducted on wastewater from the Huu Nghi Hospital, but coliform count was 106 MPN/100mL, Salmonella count 22 was 106 bacterias/100mL, Shigella count was 106 bacterias/100mL Vibrio cholera count was 106 bacterias/100mL All of these bacteria were added in The mixture was disinfected with supowa 1.5 mg/L and mg/L for 15 minutes The amount of bacteria that survived after the disinfection was determined Results showed that the supowa concentration of 1.5 mg/L can reduce 4÷5 log10 bacteria count in wastewater A supowa concentration of mg/L (2 g/m3) can sterilized completely the hospital wastewater with bacteria count of about 106 MPN (bacteria)/100mL (under other physicochemical norms is eligible under QCVN 28: 2010/BTNMT) 3.3.2.3 Testing at the hospital wastewater treatment plant The object studied was the wastewater treatment system of the Huu Nghi Hospital and 354 Military Hospital The disinfectant used at that time was chloramine B with concentration of 2g/m3 Alternative disinfectant is supowa with concentration of 2g/m3 The tested samples was taken at the after-treatment tap of the system These experiments were conducted simultaneously by the Institute of Environmental Technology and the Biochemistry Departments of both hospitals The results demonstrate the remarkable disinfection performance of supowa, in particular compared with chloramine B With the same concentration of disinfectant, supowa completely killed coliform count of 106 - 108 MPN / 10mL, while chloramine B reduced only ÷ log10 3.3.2.1 Xây dựng quy trình cơng nghệ khử trùng nước thải bệnh viện sử dụng nước siêu oxy hóa 3.3.2.4 Developing the disinfection process the hospital wastewater by SOS The disinfection method using the new disinfectant will be devoloped based on the existing process and just the disinfection method (concentration of disinfectant, disinfection time, method of mixing the disifectant) will be changed to be suitable SOS was stored in a container and pumped into the wastewater treatment system by dosing pump This dosing pump is electrically connected and operated simultaneously with the before-treatment wastewater pump (Figure 3.35) Beforetreatment wastewater pump Standard wastewater treatment system before the sterilization (depends on each specific object) Dosing pump Wastewater after treatment Superoxidized solution (supowa, anolit) Figure 3.35 Location of addition the disinfection solution 23 CONCLUSION The scientific basis of the application of non-circulating catholyte operation mode to manufacture equipment producing supowa solution in Vietnam was established, allowing to reduce the operating temperature of the module to below 39oC This has contributed to increase the longevity and stable operation of the equipment, satisfied the requirements of 150-bed small hospital waste water treatment plant (or medical centers) The superoxidizing solution obtained from the supowa equipment has the following characteristics: ORP ~ 900 mV, neutral pH, TDS ~ 950 mg/L, oxidants concentration of approximately 510 mg/L The solution can be used to disinfect hospital wastewater up to environmental standards in accordance with QCVN 28: 2010/BTNMT (column A) for microbiological criteria The disinfection power of supowa solution was much stronger than other chlorinated disinfectants (such as sodium hypochlorite, chloramine B 3.The use of supowa solutions to disinfect water sources can reduce the formation of THMs from 40% to 50% compared to chlorine gas or NaOCl The amount of supowa solution for disinfection the hospital wastewater after treatment (with NH4+ ~ 10 mg/L, BOD ~ 50 mg/L, COD ~ 100 mg/L, coliform concentration 106 MPN/100mL, Salmonella 106 bacteria/100mL, Shigella 106 bacteria/100mL and Vibrio cholera 106 bacteria/100mL), with exposure time 15 minutes, range from 1.5 ÷ g/m3 (3 ÷ L/m3) Results of the thesis have opened a new direction in application of high technology to disinfect drinking water and wastewater safely for human, friendly for environment and significantly reduce the risk of poisoning chlorine gas for workers who operate the devices directly With new research results in the world, more specific tasks have been given to put superoxidizing solution to use with low cost, high performance, safe and good for disinfect hospital wastewater, contribute to limiting the spread of pathogens from health facilities 24 LIST OF PUBLIC WORKS Nguyen Thi Thanh Hai, Nguyen Hoai Chau, Nguyen dinh Cuong, Hoang Thi Thanh Binh Study on the method of preparation of superoxidized disinfection solution Vietnam Journal of Science and Technology 2011, 49 (4), 111-116 Nguyen Thi Thanh Hai, Nguyen Hoai Chau, Nguyen Van Ha, Hoang Thi Thanh Binh, Hoang Van Tu, Pham Minh Thinh Study the effect of disinfection of the SOS on pathogenic bacteria commonly found in water Vietnam Journal of Science and Technology, 2012, 50 (2B), 303-309 Nguyen Thi Thanh Hai, Nguyen Hoai Chau Method of water disinfection with anolyte solution in-place prepared Patent Utility Solution No 1285, 2015 National Office of Intellectual Property, Ministry of Science and Technology Nguyen Thi Thanh Hai, Nguyen Van Ha, Nguyen Hoai Chau, Hoang Van tu, Nguyen Anh Vu Study on the possibility of using electrochemical activation solution to minimize the formation of trihalomethane in the process of disinfecting drinking water Vietnam Journal of Science and Technology, 2014 52 (2D), 55-61 Le Thanh Son, Ngo Quoc Buu, Nguyen Hoai Chau, Nguyen Thi Thanh Hai Electrochemical synthesis of disinfecting peroxocarbonate solutions and assessment of their antimicrobial effects Journal of Research in Environmental Science and Toxicology (ISSN: 2315-5698), 2014, 2(8), 161-166 Nguyen Thi Thanh Hai, Hoang Thi Que, Nguyen Thi Nguyet Study the effect of BOD on disinfection effect of supowa, compared with javen Workshop proceedings for starting up cooperation between IET/VAST and CTWW/UTS on environmental training and research, 2016, 62-66 Hoang Thi Que, Nguyen Thi Thanh Hai Study the effect of raw material and water quality on the basic parameters of the SOS Proceedings of the workshop "Youth of Institute of Environmental Technology with scientific research and technological development", 2015, 71-75 Nguyen Thi Nguyet, Nguyen Thi Thanh Hai The effect of pH on the effectiveness of water disinfection of the SOS for pathogenic bacteria commonly found in water sources Proceedings of the workshop "Youth of Institute of Environmental Technology with scientific research and technological development", 2015, 50-54 Nguyen Hoai Chau, Nguyen Trong Boi, Ho Thi Thanh Tam, Huynh Thi Ha, Nguyen Thi Thanh Hai Auto Washing and Disinfection Device of non-metal instruments in microbiological and biochemical laboratories Patent Utility Solution No 1602, 2017 National Office of Intellectual Property, Ministry of Science and Technology 25 ... solve the problems of disinfection of hospital waste water which the Institute of Environmental Technology is dealing with for 15 years Objectives of the thesis To investigate and improve the technological... 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. .. 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