Summary of Environmental Technique Doctoral thesis: Research improving the process preparing superoxidized sulution and application in disifecting hospital wastewater

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

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

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

The dissertation can be found out at:

- Library of the Graduate University of Science and Technology

- National Library of Vietnam

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

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 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

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, 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

No Technical parameters Conventional

ECA solution

Superoxidation solution

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

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 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 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 BOD 5

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 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

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

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

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 (39oC ÷

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 3 1 Optimal operating mode of the circulating catholyte diagram

Oxidants concentration of superoxidizing

anolyte

mg/L  500

Electricity power consumption W.h/g 7,0 ÷ 7,2

Quantity of NaCl required for obtaining 1 g

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 R2 = 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

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

product prepared by the manufacturer’s

scheme (Delphin Corporation - Russia)

Figure 3.9 Schematic diagram of

the oxidation solution with circulating catholyte

non-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)

Figure 3.10 Influence of the

non-circulating catholyte flow on the

supowa parameters

Figure 3.11 Influence of the

non-circulating catholyte flow on the cathlyte chamber’s temperature