evaluation of sterilization possibility in water environment of activated nano mno2 coated on...

8/20/2019 Evaluation of sterilization possibility in water environment of activated nano Mno2 coated on calcined laterite

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ĐẠI HỌC QUỐC GIA HÀ NỘI TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN

---------------------------

Cao Việt

EVALUATION OF STERILIZATION POSSIBILITY IN WATER

ENVIRONMENT OF ACTIVATED NANO MnO2 COATED ON CALCINED

LATERITE

CHUYÊN NGÀNH: QUẢN LÝ CHẤT THẢI VÀ XỬ LÝ VÙNG Ô NHIỄM

(CHƯƠNG TRÌNH ĐÀO TẠO QUỐC TẾ)

LUẬN VĂN THẠC SĨ KHOA HỌC

GIÁO VIÊN HƯỚNG DẪN: PGS.TS. TRẦN HỒNG CÔN

Hà Nội - 2011



Table of contents

Abbreviation .................................................................................................................... i

List of Figures ................................................................................................................ ii

List of Tables ................................................................................................................ iii

Chapter 1......................................................................................................................... 1

INTRODUCTION .......................................................................................................... 1

1.1 Water situation in general ...................................................................................... 1

1.2 Water sterilization .................................................................................................. 3

1.2.1 Boiling ............................................................................................................. 4

1.2.2 Chlorine ........................................................................................................... 5

1.2.3. Ozone ............................................................................................................. 5

1.2.4 Ultraviolet light ............................................................................................... 6

1.2.5 Hydrogen peroxide .......................................................................................... 7

1.2.6 Solar disinfection ............................................................................................ 7

1.2.7 Photocatalysis on semiconductors .................................................................. 7

1.2.8 High speed water sterilization using one-dimensional nanostructures ........... 7

1.3 Nanotechnology ..................................................................................................... 8

1.4 Manganese dioxide............................................................................................... 10

1.5 Laterite ................................................................................................................. 11

Chapter 2....................................................................................................................... 13

OBJECTIVES AND RESEARCH METHODS ........................................................ 13

2.1 Objectives ............................................................................................................. 13

2.2 Materials and Research methods .......................................................................... 13

2.2.1 Material and instruments ............................................................................... 13

2.2.2 Research methods ......................................................................................... 14



2.2.2.1 Synthesis of nano MnO2 adsorbents .......................................................... 14

2.2.2.3 Investigation of sterilizing capability of nano MnO2 adsorbents............... 15

Chapter 3....................................................................................................................... 17

RESULTS AND DISCUSSION .................................................................................. 17

3.1 Synthesis of nano MnO2 adsorbents .................................................................... 17

3.2 Investigation of sterilizing capability of nano manganese dioxide ...................... 23

3.2.1 Investigation in static condition .................................................................... 24

3.2.2 Investigation in dynamic condition ............................................................... 28

3.3 Mechanism of sterilization of MnO2 coated on calcined laterite in water ........... 33

3.3.1 Investigation the influence of Mn2+ in sterilizing capability ........................ 33

3.3.2 Examine the mechanism of sterilization of MnO2 ........................................ 35

Chapter 4....................................................................................................................... 38

CONCLUSION............................................................................................................. 38

REFERENCES ............................................................................................................. 40



i

Abbreviation

MD Manganese Dioxide

UV Ultraviolet

DNA Deoxyribonucleic Acid

SODIS Solar Disinfection

CNT Carbon Nanotube

AgNWs Silver Nanowires‟

TEM Transmission Electron Microscopy

SEM Scanning Electron MicroscopeEPA Environmental Protection Agency

E. coli Escherichia coli

BRM Bacteria removing material

MPN Most probable number

EBCT Empty Batch Contact Time



ii

List of Figures

Figure 1: Nanoscale materials ........................................................................................ 10

Figure 3: Coating process............................................................................................... 18

Figure 4: MnO2 nanoparticles with the magnification of 40000 times .......................... 19

Figure 5: MnO2 nanoparticles with the magnification of 60000 times .......................... 20

Figure 6: MnO2 nanoparticles with the magnification of 100000 times ........................ 21

Figure 7: Creation of adsorbent coating by nano MnO2 particles (100k) ...................... 22

Figure 8: Creation of adsorbent coating by nano MnO2 particles (200k) ...................... 22

Figure 9: Shaking equipment for static condition investigation .................................... 23

Figure 10: Column device for dynamic condition investigation ................................... 24

Figure 11: Samples in contact time‟s influence experiment .......................................... 25

Figure 13: Samples in BRM/water ratio‟s influence experiment .................................. 27

Figure 14: Samples in BRM/water ratio‟s influence experiment .................................. 28

Figure 15: Model of column device ............................................................................... 29

Figure 16: Samples in flow rate in BRM column‟s influence experiments ................... 30

Figure 17: Influence of flow rate on bacteria sterilizing in BRM column..................... 30

Figure 18: Samples in the experiments .......................................................................... 32

Figure 19: Influence of column height on bacteria sterilizing in BRM column ............ 32

Figure 21: Influence of Mn2+

in sterilizing capabilities ................................................. 35



iii

List of Tables

Table 1: Influence of contact time on bacteria sterilizing .............................................. 24

Table 2: Influence of the ratio of BRM and water on bacteria sterilizing ..................... 27

Table 3: Influence of flow rate on bacteria sterilizing in BRM column ........................ 29

Table 4: Influence of column height on bacteria sterilizing in BRM column ............... 31

Table 5: Influence of Mn2+

in sterilizing capabilities .................................................... 34



Chapter 1: Introduction

1

Chapter 1

INTRODUCTION

1.1 Water situation in general

Water is one of the world‟s most essential demands for human life, and the

origin of all animal and plant life on the planet. Civilization would be impossible

without steady supply of fresh and pure water and it has been considered a

plentiful natural resource because the sensitive hydrosphere covers about 75% of

the Earth's surface. Its total water content is distributed among the main

components of the atmosphere, the biosphere, oceans and continents. However,97% of the Earth's water is salty ocean water, which is unusable for most human

activities. Much of the remaining 3% of the total global water resource, which is

fresh-water, is locked away in glaciers and icebergs. Approximately 20% of the

freshwater resources are found as groundwater, and only 1% is thought to be

easily accessible surface water located in biomass, rivers, lakes, soil moisture,

and distributed in the atmosphere as water vapor. [1]

In the process of rapid development of science and technology, the demand for

pure water is increasing to serve multifarious purposes in different types of

industries. Global water consumption raised six folds in the past century, double

the rate of population growth. In addition, the boom in world‟s population during

recent decades, has contributed to the dramatically rising demand of pure water

usage for both household and industrial purposes. The high population density

and industrialization speed have triggered the hydrosphere to be polluted with

inorganic and organic matters at a considerable rate. Moreover, to satisfy the

food demand, a number of harmful chemicals such as pesticides and herbicides




2

are used in order to improve the productivity in agricultural production, which

also causes the scarcity of clean resources. [1]

The contamination of ground water (mostly by toxic metal ions due to both

natural and anthropogenic reasons) is also one of concerning issues on clean

water. It is necessary to assess the quality of water used in industry, household

activities and drinking purpose. Understanding of the importance of clean water

in human life, many countries has gradually adjusted their environmental

regulations more stringently to reserve clean water resources. With the purpose

of overcoming the water pollution problems, and to meet the stricterenvironmental regulations, scientists and researchers have focused on improving

exist water purification processes and approaching to alternative water treatment

technologies as well, so as to increase the efficiency of those decontamination

methods. It is surveyed that human awareness about the seriousness of water

pollution has enhanced over the world. People have also started realizing that

water is not an unlimited resource, hence it needs to be protected and smartly

used.

An ideal water treatment process should have the capability to mineralize

completely all the toxic organic components without leaving behind any harmful

by-products and to recover all toxic metals from wastewater. In broader

classification, biological, mechanical, thermal, chemical or physical treatments,

or their combinations may be applied to purify contaminated water. The choice

of the proper water treatment processes depend on the nature of the pollutants

presenting in water, and on the acceptable contamination level in treated water.

There are two main purposes of water treatment study – the reduction of

contaminant level in the discharged stream to meet environmental standards, and




3

the purification of water to ultrapure water in order to be able to use in

semiconductor, microelectronic and pharmaceutical industries. Moreover, the

cost or effectiveness of the water treatment processes also plays a significant role

in choosing a particular one. Biodegradation, adsorption in activated carbon, air

stripping, incineration, ion-exchange, coagulation-precipitation, membrane

separation, thermal and catalytic oxidation, oxidation by permanganate, chlorine,

ozone and hydrogen peroxide are widely applied in conventional water treatment

processes for organic and inorganic pollutant containing water. Besides

advantages, each process has their own shortcomings which are being improvedgradually via new technologies. [1, 2]

1.2 Water sterilization

Water sterilization technology is useful in various ways for our daily life. For

example, it is used in water and sewerage systems treatment. Methods

commonly used for sterilization include chemicals, heat, ultraviolet (UV)

radiation, and ozone. Chemicals (chlorine, peroxide, etc.) are utilized extensively

for sterilization because of their simplicity; however, they probably form

unexpected effects, such as modifying the quality of the target. In addition,

sterilization by chlorine usually generates odorous substances and bio-hazardous

materials. [2]

It is not totally accurate to assess whether water is of an appropriate quality only

by visual examination. Simple procedures such as boiling or the use of a

household activated carbon filter are not sufficient for treating all the possible

contaminants that maybe present in water from an unknown source. Even natural

spring water – considered safe for all practical purposes in the 1800s – must now

be tested before determining what kind of treatment, if any, is needed. Chemical




4

analysis, while expensive, is the only way to obtain the information necessary for

deciding on the appropriate method of purification. [3]

Simple techniques for treating water at home, such as chlorination, filters, and

solar disinfection, and storing it in safe containers could save a huge number of

lives each year.

Sterilization is accomplished both by filtering out harmful microbes by and also

adding disinfectant chemicals in the last step in purifying drinking water. Water

is disinfected to kill any pathogens which pass through the filters. Possible

pathogens include viruses, bacteria, including Escherichia coli, Campylobacter and Shigella, and protozoa, including Giardia lamblia and other cryptosporidia.

In most developed countries, public water supplies are required to maintain a

residual disinfecting agent throughout the distribution system, in which water

may remain for days before reaching the consumer. Following the introduction

of any chemical disinfecting agent, water is usually held in temporary storage -

often called a contact tank or clear well to allow the disinfecting action to

complete. [4]

1.2.1 Boi li ng

Boiling is an easy, cheap and common way to eliminate contaminations and

microorganisms in developing countries, but this method is only practical for

small amounts. When the water has boiled for 5 – 10 min all the pathogens have

been killed and the water is safe to drink. [2]

The main disadvantage of this method is that it requires a continuous source of

heat and appropriate equipment.




5

1.2.2 Chlor ine

Chlorine is most effective against pathogens and not as much for turbidity; it will

function relatively effectively up to 20 NTU [2]. If chlorine were combined with

other methods such as rapid sand filtration the turbidity would decrease.

Chlorine Bleach can be used to purify water with the dosage of 1 part of bleach

and 10 parts of water and wait for 30 min, or longer if the solution still looks

cloudy [3]. It is important to note that chlorine bleach does not kill

Cryptosporidium and may not kill Giardia, a pathogen and a parasite that both

give diarrheal diseases [5]. It is difficult to determine the correct chlorine dosage,too much gives an unpleasant taste and people will be reluctant to drink it, but a

too small dosage will not kill the germs [4].

The drawback of this method is that it the storage of chlorine and its use must

need careful handling, large chlorine residual may cause bad taste.

1.2.3. Ozone

Ozone (O3) is an unstable molecule which readily gives up one atom of oxygen

providing a powerful oxidizing agent which is toxic to most waterborne

organisms. It is a very strong, broad spectrum disinfectant that is widely used in

Europe. It is an effective method to inactivate harmful protozoa that form cysts.

It also works well against almost all other pathogens. Ozone is made by passing

oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as

a disinfectant, it must be created on-site and added to the water by bubble

contact. Some of the advantages of ozone include the production of fewer

dangerous by-products (in comparison to chlorination) and the lack of taste and

odor produced by ozonization. Although fewer by-products are formed by

ozonation, it has been discovered that the use of ozone produces a small amount




6

of the suspected carcinogen bromate, although little bromine should be present in

treated water. Another of the main disadvantages of ozone is that it leaves no

disinfectant residual in the water. Ozone has been used in drinking water plants

since 1906 where the first industrial ozonation plant was built in Nice, France.

The U.S. Food and Drug Administration has accepted ozone as being safe; and it

is applied as an anti-microbiological agent for the treatment, storage, and

processing of foods. [6]

The disadvantage of this method is the high cost for operation.

1.2.4 Ul traviolet lightUltraviolet light is very effective at inactivating cysts, as long as the water has a

low level of colour so the UV can pass through without being absorbed.

Ultraviolet light works against viruses, bacteria, pathogens and other potentially

harmful particles by modifying and even destroying their nucleic acids and

disrupting their deoxyribonucleic acid (DNA). When employed in a UV filter,

UV light can have two effects on these microorganisms. It can either eliminate

their ability to reproduce, or can kill them outright, a more desirable outcome

where water purification is concerned.

The main disadvantage to the use of UV radiation is that, like ozone treatment, it

leaves no residual disinfectant in the water. Because neither ozone nor UV

radiation leaves a residual disinfectant in the water, it is sometimes necessary to

add a residual disinfectant after they are used. This is often done through the

addition of chloramines, discussed above as a primary disinfectant. When used

in this manner, chloramines provide an effective residual disinfectant with very

few of the negative aspects of chlorination. [6]




7

The main disadvantages of this methods is the low efficiency and the dependent

on water turbidity.

1.2.5 Hydrogen peroxide

Hydrogen peroxide (H2O2) works in a similar way to ozone. Activators such as

formic acid are often added to increase the efficacy of disinfection. It has the

disadvantages that it is slow-working, phytotoxic in high dosage, and decreases

the pH of the water it purifies. [6]

1.2.6 Solar disinfection

One low-cost method of disinfecting water that can often be implemented withlocally available materials is solar disinfection (SODIS). It partially relies on the

ultraviolet radiation that is part of sunlight. Unlike methods that rely on

firewood, it has low impact on the environment. [6]

1.2.7 Photocatalysis on semiconductors

The processes of heterogeneous photocatalysis on semiconductors, developed

during the last twenty years, were firstly regarded as potential methods for

hydrogen photoproduction from water. However, even at the very beginning of

their development, some papers appeared which dealt with photooxidation of

organic and some inorganic (e.g. CN- ions) compounds. For more than ten years

the interest of scientists has turned into application of the heterogeneous

photocatalytic methods to water detoxification. [6]

1.2.8 H igh speed water ster il ization using one-dimensional nanostructures

One-dimensional nanostructures have been extensively explored for a variety of

applications in electronics, energy and photonics. Most of these applications

involve coating or growing the nanostructures on flat substrates with

architectures inspired by thin film devices. It is possible, however, to make




8

complicated three-dimensional mats and coatings of metallic and

semiconducting nanowires, as has been recently demonstrated in the cases of

superwetting nanowire membranes and carbon nanotube (CNT) treated textiles

and filters. Silver nanowires‟ (AgNWs) and CNTs‟ have unique ability to form

complex multiscale coatings on cotton to produce an electrically conducting and

high surface area device for the active, high-throughput inactivation of bacteria

in water. [6]

1.3 Nanotechnology

Nanotechnology is the science of the small; the very small. It is the use andmanipulation of matter at a tiny scale. At this size, atoms and molecules work

differently, and provide a variety of surprising and interesting uses.

The prefix of nanotechnology derives from „nanos‟ – the Greek word for dwarf.

A nanometer is a billionth of a meter, or to put it comparatively, about 1/80,000

of the diameter of a human hair. Nanotechnology should not be viewed as a

single technique that only affects specific areas. It is more of a „catch -all‟ term

for a science which is benefiting a whole array of areas, from the environment, to

healthcare, to hundreds of commercial products.

Although often referred to as the 'tiny science', nanotechnology does not simply

mean very small structures and products. Nanoscale features are often

incorporated into bulk materials and large surfaces.

Nanotechnology is already in many of the everyday objects around us, but this is

only the start. It will allow limitations in many existing technologies to be

overcome and thus has the potential to be part of every industry:

Health and medicine - With advances in diagnostic technologies, doctors will

be able to give patients complete health checks quickly and routinely. If any




9

medication is required this will be tailored specifically to the individual based on

their genetic makeup, thus preventing unwanted side-effects. As a result, the

health system will become preventative rather than curative.

Society and the environment - Renewable energy will become the norm. For

example, solar cells based on quantum dots could be as much as 85% efficient.

Wind, wave, and geothermal energy will also be tapped more effectively using

new materials and stored or delivered more efficiently through advances in

batteries and hydrogen fuel cells. New ambient sensor systems will allow us to

monitor our effect on the environment and take immediate action, rather than“waiting to see”. Nanotechnology will also help us clean up existing pollution

and make better use of the resources available to us.

New materials - Nanomaterials such as quantum dots, carbon nanotubes and

fullerenes will have applications in many different sectors because of their new

properties. So quantum dots can be used in solar cells, but also in

optoelectronics, and as imaging agents in medical diagnostics. Carbon nanotubes

can be used in displays, as electronic connectors, as strengthening materials for

polymer composites, and even as nanoscale drug dispensors. Fullerenes can be

used in cosmetics, as “containers” for the delivery of drugs, in medical

diagnostics, and even as nanoscale lubricants.




10

Figure 1: Nanoscale materials

Nanoscale materials and devices hold great promise for advanced diagnostics,

sensors, targeted drug delivery, smart drugs, screening and novel cellular

therapies. [7]

The future of nanotechnology has great potential. However, it also has the

potential to change society more than the industrial revolution. It will affect

everyone and so should be developed for everyone.

1.4 Manganese dioxide

Manganese dioxide (MnO2) occurs naturally as the mineral pyrolusite, which is

the main ore of manganese and a component of manganese nodules.

In the past decades, Manganese dioxide have been exploited for heavy metal

removal from aqueous media, i.e., heavy metal ions [8], arsenate [9], and

phosphate [10] from natural water has attracted considerable attention, because it

would significantly mediate the fate and the mobility of the target pollutants in

water [11, 12]. For example, Kanungo et al. [12] and Kanungo et al. [13] studied




11

the sorption of Co(II), Ni(II), Cu(II), and Zn(II) ions on manganese dioxide

particles in the presence of different electrolytes. They found that these toxic

metals can be effectively trapped by manganese dioxide through electrostatic

forces and formation of inner-sphere complexes. The specific properties of

manganese dioxide render it a potential sorbent for heavy metal ion removal

from contaminated water.

Manganese dioxide has high oxidation potential so it can disrupt the integrity of

the bacterial cell envelope through oxidation (similar with Ozone, Chlorine…).

1.5 LateriteLaterites are residual products, which are formed during prolonged mechanical

and chemical weathering of ultramafic bedrocks at the surface of the earth [14].

It was found that laterite‟s profiles depend on the conditions of weathering

intensities, geotectonic zones and the parent rock‟s compositions. Laterite is used

to describe soils, ferruginous materials, weathering profiles, and chemical

compositions, which are based on SiO2, Al2O3, and Fe2O3 [15]. Laterite is

categorized as soil which contains up to 60.3% iron [16] and is available in many

tropical regions, such as India, Vietnam, Philippines and China [17-19].

Furthermore, laterite adsorbs other ion and heavy metals, such as fluoride (F),

cesium (Cs), mercury (Hg II) and lead (Pb) [20-22]; in water treatment, laterite

has been found to be effective and feasible as an adsorbent in removing some

heavy metals in contaminated groundwater.

When laterite heated to 420-900oC, the removal capacity is even better.

Expanded laterite has special properties such as high porosity (and consequently,

low density), it is chemically rather inert, non-toxic, thus it can be used as

excellent filter aid and as a filler in various processes and materials.




12

Because of it low specific surface area and acidic surface, expanded laterite was

found to be of limited use as an adsorbent for bacterial removal on its own, but it

can be utilized as an appropriate carrier material. On the other hand,

nanoparticles MnO2 have a large surface area and high oxidation potential which

make them excellent candidates for the bacterial removal in general.



Chapter 2: Objectives and Methodology

13

Chapter 2

OBJECTIVES AND RESEARCH METHODS

2.1 Objectives

When materials possess nanoparticle size, they will have special

properties in chemical, physical, adsorption and electrode, etc. Therefore, the

research objectives are addressed as follows:

- To synthesize MnO2 nanoparticles coated on calcined laterite;

- Analyzing of MnO2 nanoparticles formation portion and its physical structure;

- To investigate the sterilization possibilities of created material;- To examine the mechanism of sterilization of MnO2 coated on calcined laterite

in water.

2.2 Materials and Research methods

2.2.1 Mater ial and instruments

All chemicals were reagent grade and they were used without further

purification. Laterite ore was taken from coal and baked at 900oC. Potassium

permanganate (KMnO4), ethanol, sodium hydroxide (NaOH, 98%), and

hydrogen peroxide (H2O2) were made in China. Agar was purchased from Ha

Long company, endo agar from Merck. Petri disks, distilled water and others

instruments which were used in the experiment, taken from Faculty of Chemistry

lab equipment.

For structural characterization, the samples were taken to use Transmission

Electron Microscopy (TEM) operated at 80kV. Surface analysis was done using

Scanning Electron Microscope (SEM) (Hitachi S-4800) in National Institute of

Hygiene and Epidemiology.




14

2.2.2 Research methods

2.2.2.1 Synthesis of nano MnO2 adsorbents

According to Environmental Protection Agency (EPA) [23], particles are

classified regarding to size: in term of diameter, coarse particles cover a range

between 10,000 and 2,500 nanometers. Fine particles are size between 2,500 and

100 nanometers. Ultrafine particles, or nanoparticles are sized between 100 and

1 nanometers. Therefore, our goal is to create particles which have the size

between 100 and 1 nanometers.

The MnO2 nanoparticles were synthesized using potassium permanganate(KMnO4) as a precursor using a slight modification of method [24] in the

following way: stirring vigorously a 100ml water:ethanol (1:1, v/v) solution

using magnetic stirrer at room temperature for 10 min, and then the solution was

added 5ml of KMnO4 0.05M, stirring steady then put slowly H2O2 until brown

black color appears (around 10ml H2O2 10%). Finally, colloidal nano MnO2

solution was taken for analyzing of nanoparticles formation portion and coating

on calcined laterite.

To synthesize laterite/MnO2, the dried calcined laterite, which was grained with

size of 0.1 – 0.5 mm diameter, was poured into MnO2 nanoparticles solution

with the volumetric portion of solid and liquid was 1/1. The soaking time was 8

to 24 hours. Then the liquid phase was drained off. Solid phase was washed out

of dissolved ions and dried to get bacterial removing material (BRM).

2.2.2.2 Structural characterization

For structural characterization, the samples were taken to use Transmission

Electron Microscopy (TEM) operated at 80kV. TEM is a microscopy technique

whereby a beam of electrons is transmitted through an ultra thin specimen,




15

interacting with the specimen as it passes through. An image is formed from the

interaction of the electrons transmitted through the specimen; the image is

magnified and focused onto an imaging device, such as a fluorescent screen, on a

layer of photographic film, or to be detected by a sensor. [25]

Surface analysis was done using Scanning Electron Microscope (SEM). The

SEM uses a focused beam of high-energy electrons to generate a variety of

signals at the surface of solid specimens. The signals that derive from electron-

sample interactions reveal information about the sample. [26]

2.2.2.3 Investigation of sterilizing capability of nano MnO2 adsorbentsThe routine monitoring of the bacteriological quality of drinking water relies on

the use of the indicator organisms Escherichia coli (E. coli) and coliforms which

are used to indicate fecal contamination or other water quality problems such as

failures of disinfection, bacterial regrowth within the distribution system or

ingress.

The most commonly employed technique for the detection of these organisms in

water is membrane filtration. Normally, water (100ml) is concentrated by

membrane filtration and the membranes placed onto a selective and differential

medium such as Endo agar [27] which inhibits the growth of gram positive

bacteria. Appropriately diluted (10-2) sample (100mL in volume) volumes were

filtered through 0.45µm membrane filters. Plates were then incubated for 24h at

37oC on endo agar for total coliform.

The bacteria number was determined in initial water sample and followed the

time of sterilizing process.

http://serc.carleton.edu/research_education/geochemsheets/electroninteractions.html







16

The experiments were performed in the static condition as well as the dynamic

condition to estimate the sterilizing capability of MnO2 nanoparticles.

Specifically, contact time and the ratio between material and water sample were

chosen as fundamental parameters. Therefore, other parameters which affect the

alteration of contact time and the ratio between material and polluted water

sample, such as the column height, the flow rate, etc in the dynamic condition,

were taken into consideration.

2.2.2.4 Examine the mechanism of sterilization of MnO2 coated on calcined

laterite in waterThere are two main purposes in this part: One is to examine whether the

mechanism of sterilization of MnO2 coated on calcined laterite is influenced by

the high oxidation potential of MnO2. The other is to survey the effects of Mn2+

on sterilizing process of MnO2 by changing the concentration of Mn2+.



Chapter 3: Results and Discussion

17

Chapter 3

RESULTS AND DISCUSSION

3.1 Synthesis of nano MnO2 adsorbents

Working solution of MnO2 nanoparticles was prepared by stirring solution of

50ml distilled water and 50ml ethanol. Afterwards, the solution was added 5ml

KMnO4 0.05M, stirring steadily then dropped slowly H2O2 solution into the

solution until brown black color appears (around 10ml H2O2 10%). The

experiment product, colloidal nano MnO2 solution, was taken for analyzing of

nanoparticles size and formation portion by Transmission Electron Microscopy(TEM).

The dried calcined laterite grains with size of 0.1 – 0.5 mm diameter were

poured into nanosilver solution. The volumetric portion of solid and liquid was

1:1. The soaking time was from 8 to 24 hours. Then the liquid phase was drained

off. Solid phase was washed out of dissolved ions and dried to get bacterial

removing material (BRM). The surface of solid phase was characterized using

Scanning Electron Microscope (SEM) to obtain information on its physical

structure.

Consequently, the coating process was carried out as shown in Figure 3.




18

Figure 3: Coating process

The TEM images of MnO2 nanoparticles solution clearly reveal the presence of a

large quantity of nanoparticles and assemble to form barbed sphere shape with

the diameter approximately 30nm (as shown in Figure 4-6)

Soaking

Sucking excess liquid

Drying

Washing

Drying

Dried laterite grains Nano solution




19

Figure 4: MnO2 nanoparticles with the magnification of 40000 times




20





21





22

A: Before coating B: After coating

Figure 7: Creation of adsorbent coating by nano MnO2 particles (100k)

A: Before coating B: After coating

Figure 8: Creation of adsorbent coating by nano MnO2 particles (200k)

On SEM images in the same scale, it is easy to recognize different surface

pictures of the material before and after coating MnO2 nanoparticles. Before

coating, the surface of laterite was quite smooth; but after coating there were

nanoparticles of MnO2 in barbed sphere shape distributed tight all over laterite

surface.




23

The clinging of MnO2 nanoparticles on calcined laterite surface was recognized

for application purpose, but the essence of this phenomenon was not determined

so far. There may were any chemical bond, what was binding energy, was there

reformation of nanoparticles or inactivation, etc. That confusion should be

investigated in following time.

3.2 Investigation of sterilizing capability of nano manganese dioxide

In this research, total coliform was chosen as indicating bacteria for all bacterial

removing investigation. The bacteria number was determined in the initial water

sample and followed the time of sterilizing process.

Static and dynamic condition were chosen to conduct the experiments.

Figure 9: Shaking equipment for static condition investigation




24

Figure 10: Column device for dynamic condition investigation

3.2.1 Investigation in static condition

3.2.1.1 Influence of detention time on bacteria sterilizing

Detention time is an important parameter to determine the sterilizing ability. In

this experiment, the raw water was treated, diluted then the material is poured

into polluted water in conical beakers with the phase ratio of

solid:liquid=2g:100ml (BRM:polluted water). Next, they are shaken up by

shaking table. The time increased along the row of 10, 20, 30, 40, 50, 60

minutes. Afterwards, all the samples are filtered and determined the bacteria

amount. The results are shown in Table 1, Figure 11-12.Table 1: Influence of contact time on bacteria sterilizing

Sample 1 2 3 4 5 6 7 8

Detenti on time (mins) 10 20 30 40 50 60 70 80

Bacteri a colony (MPN/100mL) 56 28 0 0 0 0 0 0




25

Sample 1 Sample 2 Sample 3


Sample 7 Sample 8

Figure 11: Samples in contact time’s influence experiment




26

Figure 12: Samples in contact time’s influence experiment

Figure 12 shows that when the detention time is lower than 30 minutes, the

bacteria do not have enough time to approach to BRM, so the efficiency would

be undesirable (56 and 28). If the detention time is longer than 30 minutes, all

bacteria would contact to the BRM and be killed. Therefore, the optimal

detection time is 30 minute.3.2.1.2 Influence of the ratio of BRM and water on bacteria sterilizing

The ratio of BRM and water is important parameter since it represents the

effectiveness of the materials. Moreover, if the ratio is low, this may indicate that

the BRM consumption is small and we can save material. At this experiments,

the detention time was chosen as previous result. And the ratio of BRM/polluted

water increased along the row 0.25/100, 0.5/100, 1/100, 1.5/100, 2/100 g/mL.

The results of experiments are shown in Table 2, Figure 13-14.




27

Table 2: Influence of the ratio of BRM and water on bacteria sterilizing

Sample 1 2 3 4 5

BRM /polluted water (g/mL) 0.25/100 0.5/100 1/100 1.5/100 2/100Bacteri a colony (MPN/100ml) 154 21 5 0 0


Sample 4 Sample 5

Figure 13: Samples in BRM/water ratio’s influence experiment




28

Figure 14: Samples in BRM/water ratio’s influence experiment

In the first sample, the bacteria colony number is very high (154) at the ratio of

0.25/100. When the ratio increases to 0.5/100, the bacteria number decreases

dramatically to 21. This happens as the amount of BRM in the second sample is

higher than that of the first one, which leads to more chances for bacteria to

contacting with BRM. Figure 14 shows the optimal amount of BRM is 1.5g per

100ml water.

3.2.2 Investigation in dynamic condi tion

The parameters such as flow rate and the height of BRM column were tested to

see their influence on the sterilizing capability.

3.2.2.1 Influence of flow rate on bacteria sterilizing in BRM column

The raw water was treated, diluted then transferred to a 2L tank. The flow rate

was controlled by input and output valves.

The flow rate of water column increased along the row of 1, 2.2, 2.8, 3, 4, 5

ml/min (0.18, 0.39, 0.5, 0.53, 0.71, 0.88 mL/min.cm2).

The diameter of column is 1.8cm; the height of material is 5cm.




29

The results of this investigation are given in Table 3, Figure 16-17

Figure 15: Model of column device

Table 3: Influence of flow rate on bacteria sterilizing in BRM column

Sample 1 2 3 4 5 6

F low rate (ml/min .cm 2 ) 0.18 0.39 0.5 0.53 0.71 0.88

Bacteri a colony (MPN/100mL) 0 0 0 12 56 140





30


Figure 16 : Samples in flow rate in BRM column’s influence experiments

Figure 17: Influence of flow rate on bacteria sterilizing in BRM column

The amount of total coliform in sample 4, 5 and 6 is 12, 56 and 140

MPN/100mL respectively. Those results mean that the bacteria had not been

killed effectively due to the lack of contact time between bacteria and MnO2.

If the flow rate is 0.53mL/min.cm2, the analysis result shows that there is still

12MPN/100ml available. Even the removal capacity increased remarkably, it




31

still did not meet the drinking water standard of Environmental Protection

Agency [28].

When the flow rate decreases to 0.5mL/min.cm2 or lower, the sterilizing

capability is complete.

Figure 17 indicates that the slower the flow rate is, the better sterilizing is

achieved. For the optimal flow rate, 0.5 mL/min.cm2 will be chosen for the next

experiments.

3.2.2.2 Influence of column height on bacteria sterilizing in BRM column

The raw water was treated, diluted then transferred to the 2L tank. The flow ratewas controlled by input and output valves.

The height of material column increased along the row of 1, 2, 3, 4, 5 cm.

The diameter of column is 1.8cm; the flow rate is 0.5ml/min.cm2.

The results are given in Table 4, Figure 18-19.

Table 4: Influence of column height on bacteria sterilizing in BRM column

Column height (cm) 1 2 3 4 5

Bacteri a colony (MPN/100mL) 250 100 10 0 0





32

Sample 2 Sample 3

Figure 18: Samples in the experiments

Figure 19: Influence of column height on bacteria sterilizing in BRM column

The amount of total coliform in the sample 1 and 2 were 250 and 100

MPN/100mL respectively. The results mean that the bacteria had not been killed

effectively because of the insufficiency of contact time between bacteria and

MnO2 (the column height is not long enough).




33

If the height is 3cm, the analysis result shows that there is still 10MPN/100ml

available. Even the removal capacity increased remarkable but it still did not

meet the EPA drinking water standard [28].

When the height increases to 4cm or higher, the sterilizing capabilities is

completely.

It is apparent that the height of BRM column and the flow rate of water strongly

influence the sterilizing ability. The sterilizing ability of column increases along

with the increase of the BRM layer height. In contrast, it decreases when the

flow rate increases.At current time, in many published reports, authors used parameter EBCT

(Empty Batch Contact Time) for characterization of both of column filter

parameters above.

EBCT = =

From the results, V = πR 2h = 3.14 x 0.92 x 4 = 10.17 cm3

q = 2.8 mL/min

So EBCT = = 3.63 mins

In the case of the investigation, the minimum EBCT for safely bacterial

sterilizing is 3.63 min.

3.3 Mechanism of sterilization of MnO2 coated on calcined laterite in water

3.3.1 I nvestigation the in fl uence of M n 2+ in ster il izing capabili ty

The experiment was performed to analysis the influence of Mn2+ on water

sterilizing capability of MnO2 nanoparticles.

The four different concentrations which are ranging 0.1, 1 and 10 ppm of Mn2+

were put into water samples with the available of MnO2 nanoparticles material.




34

The processes were conducted in static condition (100mL waste water was

treated by 0.5g BRM; contact time was 10 minutes; initial MPN in wastewater

was 380). The results are shown in Table 5, Figure 20-21.

Table 5: Influence of Mn2+ in sterilizing capabilities

Sample 1 2 3 4

Mn 2+ added (ppm) 0 0.1 1 10

Bacteria colony

(MPN/100ml)

63 36 15 0


Sample 3 Sample 4

Figure 20: Samples in the experiments




35

Figure 21: Influence of Mn2+ in sterilizing capabilities

Figure 21 illustrates that the Mn2+ added in samples affects dramatically on the

sterilizing capability, from 60 MPN/100ml of no Mn2+ to 0 MPN/100ml of

10ppm Mn2+.

Consequently, MnO2 added Mn2+ have better sterilization possibility than MnO2

itself. In other words, ion manganese (II) has been shown to have effects on thesterilizing capability of BRM.

3.3.2 Examine the mechanism of ster il ization of M nO 2

The mechanism of MnO2 for bacterial removal is still unclear. Therefore, a

mechanism of the process was proposed as follows:

1. MnO2 attached (attacks) on bacteria cell as Figure 22:




36

Figure 1: Bacteria destruction

- A healthy bacillus bacterial cell.

- Zooming in closer, MnO2 (light green) comes into contact with the cell

wall. The cell wall is vital to the bacteria because it ensures the organism can

maintain its shape.

- As MnO2 molecules make contact with the cell wall, a reaction called an

oxidative burst occurs which literally creates a tiny hole in the cell wall.

- A new hole created in the cell wall has injured the bacterium.

- The bacterium begins to lose its shape while MnO2 molecules continuecreating holes in the cell wall.

- After thousands of MnO2 collisions over only a few seconds, the bacterial

wall can no longer maintain its shape and the cell dies.

2. As can be seen from the previous results, ion manganese (II) has been

shown to have effects on the sterilizing capability of BRM. Therefore, the

mechanism could be as follow:

MnO2 + Mn2+ → [MnO2 .Mn]2+ (1)

[MnO2 .Mn]2+ + nO2 → [MnO2.Mn].nO2 (2)

[MnO2 .Mn].nO2 → 2MnO2 + (n-1)O2 (3)




37

Disintegration process of semi-product [MnO2.Mn].nO2 appeared trivalent

or/and pentavalent Mn – high oxidation potential and very active species. These

species play as strong sterilization substances.

Therefore, in some circumstances, some raw water resources with Mn2+

pollution will have better performance in treating by nano MnO2 adsorbent.



Chapter 4: Conclusion

38

Chapter 4

CONCLUSION

- The nano MnO2 solution was prepared as 2.2.2.1. The TEM images of solution

clearly reveal the presence of a large quantity of MnO2 nanoparticles with

lozenge shape and barked sphere with the diameters around 30nm.

- The BRM was prepared from calcined laterite and nano MnO2 solution. The

SEM images of material‟s surface shows the distribution of barked sphere

shaped nano MnO2 all over laterite surface.- Sterilizing possibilities is under the static condition was studied. The detention

time selected is 30 minute, and the preferable ratio of BRM/polluted water is

1.5g:100mL.

- Water can sterilize by means of use BRM as column filter. All bacteria in water

could safely exterminate when flowing through column filter with the minimum

layer height of BRM 4cm and the maximum flow rate 0.5ml/min.cm2 or EBCT

was guaranteed at least 3.6 minutes. Both MnO2 nanoparticles solution and BRM

were non toxic and economic, so they have a high potential to be applied for

water sterilizing in water plants as well as at household scale.

- Ion manganese (II) affects the sterilizing capability of BRM. It reacts with

MnO2 to create semi-products [MnO2.Mn].nO2 which play as strong sterilization

substances.

- The research obtains some positive results in creating a new material for

wastewater sterilization, which may account for the global effort of saving clean

water resources – which is currently one of the most concerning issues not only

in Vietnam but also in other countries. However, in order to apply those study



Chapter 4: Conclusion

39

results in the real world, it is still required further investigations on the

mechanism and the harms of manganese dioxide to water after treatment.



40

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