Water situation in general
Water is essential for human life and the foundation of all animal and plant existence on Earth A consistent supply of fresh, pure water is crucial for civilization, as the hydrosphere covers about 75% of the planet's surface However, 97% of Earth's water is salty and unsuitable for most human uses The remaining 3% of freshwater is largely trapped in glaciers and icebergs, with only 20% found as groundwater Merely 1% of the total freshwater is easily accessible, existing in rivers, lakes, soil moisture, and as water vapor in the atmosphere.
The rapid advancement of science and technology has led to a significant increase in the demand for pure water across various industries Over the past century, global water consumption has surged sixfold, outpacing population growth by double This population boom has further intensified the need for clean water for both household and industrial use High population density and accelerated industrialization have resulted in considerable pollution of the hydrosphere with inorganic and organic substances Additionally, the use of harmful chemicals like pesticides and herbicides in agriculture to meet food demand has exacerbated the scarcity of clean water resources.
Groundwater contamination, primarily from toxic metal ions due to both natural and human activities, poses a significant threat to clean water supplies It is crucial to evaluate the quality of water used for industrial, household, and drinking purposes Recognizing the vital role of clean water in human life, many countries have tightened their environmental regulations to protect these resources To address water pollution and comply with stricter standards, scientists are enhancing existing water purification processes and exploring alternative treatment technologies to improve decontamination efficiency Global awareness of water pollution's seriousness has increased, leading to a collective understanding that water is a finite resource that must be safeguarded and used wisely.
An effective water treatment process must completely mineralize toxic organic components without generating harmful by-products and recover toxic metals from wastewater Various methods, including biological, mechanical, thermal, chemical, and physical treatments, or their combinations, are utilized based on the specific pollutants present and the desired contamination levels in the treated water The primary objectives of water treatment studies are to reduce contaminant levels in discharged streams to comply with environmental standards and to purify water to ultrapure levels for use in industries like semiconductor, microelectronics, and pharmaceuticals Additionally, the cost and effectiveness of these processes are crucial in selecting the appropriate treatment method Commonly used techniques include biodegradation, activated carbon adsorption, air stripping, incineration, ion exchange, coagulation-precipitation, membrane separation, and various oxidation methods While each method has its advantages, ongoing technological advancements aim to address their limitations.
Water sterilization
Water sterilization technology plays a vital role in our daily lives, particularly in the treatment of water and sewage systems Common sterilization methods include chemicals, heat, ultraviolet (UV) radiation, and ozone While chemical sterilization, such as using chlorine and peroxide, is favored for its simplicity, it may lead to unintended consequences, including alterations in water quality Additionally, chlorine sterilization can produce odorous substances and bio-hazardous materials, highlighting the need for careful consideration in water treatment processes.
Relying solely on visual inspection to determine water quality is inadequate, as common methods like boiling or using a household activated carbon filter may not eliminate all potential contaminants Even natural spring water, once deemed safe in the 1800s, requires testing today to identify necessary treatments The most reliable approach to assess water quality is through chemical analysis, which, despite its cost, provides essential information for selecting the appropriate purification method.
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 of drinking water is achieved by filtering out harmful microbes and adding disinfectant chemicals as a final step This process effectively kills pathogens that may have bypassed the filters, including viruses, bacteria such as Escherichia coli, Campylobacter, and Shigella, as well as protozoa like Giardia lamblia and other cryptosporidia.
In developed nations, public water systems must ensure a residual disinfectant is present throughout the distribution network, where water can be stored for several days before consumption After the addition of any chemical disinfectant, the water is typically held in temporary storage, known as a contact tank or clear well, to allow sufficient time for the disinfection process to take effect.
Boiling water is an effective and cost-efficient method to eliminate contaminants and microorganisms, particularly in developing countries This technique is practical for small quantities of water, as boiling for 5 to 10 minutes ensures that all pathogens are killed, making the water safe for consumption.
The main disadvantage of this method is that it requires a continuous source of heat and appropriate equipment
Chlorine is highly effective at eliminating pathogens in water but is less effective in reducing turbidity, functioning well up to 20 NTU To enhance turbidity reduction, combining chlorine with methods like rapid sand filtration is recommended For water purification, chlorine bleach can be used at a ratio of 1 part bleach to 10 parts water, with a wait time of at least 30 minutes, or longer if the water remains cloudy However, it is crucial to understand that chlorine bleach does not eliminate all contaminants.
Cryptosporidium and Giardia are pathogens that cause diarrheal diseases, but chlorine treatment may not effectively eliminate them Determining the appropriate chlorine dosage is challenging; excessive amounts can result in an unpleasant taste, discouraging consumption, while insufficient dosage fails to eradicate harmful germs.
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
Ozone (O3) is an unstable molecule that acts as a potent oxidizing agent, releasing one atom of oxygen and proving toxic to many aquatic organisms Widely utilized in Europe, ozone serves as a strong, broad-spectrum disinfectant, effectively inactivating harmful protozoa that produce cysts.
Ozone is an effective disinfectant that targets a wide range of pathogens and is generated on-site by passing oxygen through ultraviolet light or a cold electrical discharge Its advantages include producing fewer harmful by-products compared to chlorination and leaving no taste or odor in treated water However, ozonation can create small amounts of the suspected carcinogen bromate, although minimal bromine is typically present in the water A significant drawback of ozone is the lack of a disinfectant residual Since the establishment of the first industrial ozonation plant in Nice, France, in 1906, ozone has been recognized as safe by the U.S Food and Drug Administration and is widely used as an anti-microbial agent in food treatment, storage, and processing.
The disadvantage of this method is the high cost for operation
Ultraviolet (UV) light is highly effective in inactivating cysts, provided the water is clear enough for UV to penetrate without obstruction This technology targets viruses, bacteria, and harmful pathogens by altering or destroying their nucleic acids and disrupting their DNA When utilized in a UV filtration system, it ensures the water is free from these potentially dangerous contaminants.
UV light significantly impacts microorganisms by either inhibiting their reproduction or directly killing them, making it an effective method for water purification.
One significant drawback of UV radiation, similar to ozone treatment, is that it does not leave any residual disinfectant in the water As a result, it may be necessary to add a residual disinfectant after using these methods This is commonly achieved by incorporating chloramines, which serve as an effective residual disinfectant while minimizing the negative effects associated with traditional chlorination.
The main disadvantages of this methods is the low efficiency and the dependent on water turbidity
Hydrogen peroxide (H2O2) functions similarly to ozone in disinfection processes To enhance its effectiveness, activators like formic acid are frequently incorporated However, it has notable drawbacks, including a slow action rate, potential phytotoxicity at high concentrations, and a tendency to lower the pH of the treated water.
Solar disinfection (SODIS) is an affordable technique for purifying water using materials that are often readily available This method primarily utilizes the ultraviolet radiation found in sunlight, making it an eco-friendly alternative to traditional water disinfection methods that depend on firewood.
Over the past two decades, heterogeneous photocatalysis on semiconductors has emerged as a promising approach for hydrogen production from water Early research also explored the photooxidation of various organic and inorganic compounds, including cyanide ions In recent years, the focus has shifted towards utilizing these photocatalytic methods for water detoxification, reflecting a growing interest among scientists in environmental applications.
1.2.8 High speed water sterilization using one-dimensional nanostructures
Nanotechnology
Nanotechnology is the science focused on manipulating matter at an incredibly small scale, where atoms and molecules behave in unique ways This innovative field offers a range of surprising and fascinating applications, highlighting the potential of materials at the nanoscale.
The prefix of nanotechnology derives from „nanos‟ – the Greek word for dwarf
A nanometer measures one billionth of a meter, roughly 1/80,000 the width of a human hair Nanotechnology encompasses a broad spectrum of scientific applications, significantly impacting various fields such as environmental science, healthcare, and numerous 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 increasingly integrated into everyday objects, marking just the beginning of its potential This innovative technology promises to overcome limitations in various existing technologies, positioning itself as a transformative force across multiple industries.
Advancements in diagnostic technologies are enabling doctors to conduct comprehensive health assessments efficiently and regularly Personalized medication, tailored to each individual's genetic profile, will minimize adverse side effects Consequently, this shift will transform the healthcare system from a focus on treatment to a proactive, preventative approach.
Renewable energy is set to become the standard, with advancements such as quantum dot solar cells achieving efficiencies of up to 85% Additionally, the utilization of wind, wave, and geothermal energy will improve through innovative materials, while energy storage and delivery will be enhanced by breakthroughs in batteries and hydrogen fuel cells Furthermore, new ambient sensor systems will enable real-time monitoring of our environmental impact, allowing for prompt corrective actions.
“waiting to see” Nanotechnology will also help us clean up existing pollution and make better use of the resources available to us
Nanomaterials, including quantum dots, carbon nanotubes, and fullerenes, are poised to revolutionize various industries due to their unique properties Quantum dots find applications in solar cells, optoelectronics, and medical imaging diagnostics Carbon nanotubes are utilized in displays, electronic connectors, polymer composites for reinforcement, and nanoscale drug delivery systems Fullerenes serve multiple purposes, including use in cosmetics, drug delivery, medical diagnostics, and nanoscale lubrication.
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 holds immense promise, with the potential to transform society even more significantly than the industrial revolution Its impact will be felt by all, emphasizing the importance of developing this technology in an inclusive manner that benefits everyone.
Manganese dioxide
Manganese dioxide (MnO2) occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules
Manganese dioxide has emerged as a promising material for the removal of heavy metal ions, arsenate, and phosphate from contaminated water, significantly influencing the fate and mobility of these pollutants Research by Kanungo et al demonstrated that manganese dioxide effectively traps toxic metals such as Co(II), Ni(II), Cu(II), and Zn(II) through electrostatic interactions and the formation of inner-sphere complexes Its unique properties make manganese dioxide an effective sorbent for heavy metal ion remediation in aqueous environments.
Manganese dioxide has high oxidation potential so it can disrupt the integrity of the bacterial cell envelope through oxidation (similar with Ozone, Chlorine…).
Laterite
Laterites are residual products, which are formed during prolonged mechanical and chemical weathering of ultramafic bedrocks at the surface of the earth [14]
Laterite profiles are influenced by weathering intensity, geotectonic zones, and the composition of the parent rock This soil type, characterized by high iron content—up to 60.3%—is prevalent in tropical regions like India, Vietnam, the Philippines, and China Laterite consists of ferruginous materials and chemical compositions primarily based on SiO2, Al2O3, and Fe2O3 Additionally, laterite has the capacity to adsorb various ions and heavy metals, including fluoride, cesium, mercury, and lead Its effectiveness as an adsorbent makes laterite a valuable resource in water treatment for removing heavy metals from contaminated groundwater.
Heating laterite to temperatures between 420-900 °C significantly enhances its removal capacity Expanded laterite exhibits unique properties, including high porosity and low density, making it chemically inert and non-toxic As a result, it serves as an excellent filter aid and filler in various processes and materials.
Expanded laterite has a low specific surface area and an acidic surface, limiting its effectiveness as a standalone adsorbent for bacterial removal; however, it serves well as a carrier material In contrast, manganese dioxide (MnO2) nanoparticles possess a large surface area and high oxidation potential, making them highly effective for bacterial removal.
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.
Materials and Research methods
All chemicals used in the experiment were of reagent grade and did not require further purification Laterite ore was sourced from coal and subjected to baking at 900 °C Potassium permanganate (KMnO4), ethanol, sodium hydroxide (NaOH, 98%), and hydrogen peroxide (H2O2) were procured from China, while agar was obtained from Ha Long company and endo agar from Merck Additionally, Petri dishes, distilled water, and other laboratory instruments were sourced from the Faculty of Chemistry's lab equipment.
Structural characterization of the samples was conducted using Transmission Electron Microscopy (TEM) at an operating voltage of 80kV Additionally, surface analysis was performed with a Scanning Electron Microscope (SEM), specifically the Hitachi S-4800, at the National Institute of Hygiene and Epidemiology.
2.2.2.1 Synthesis of nano MnO 2 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
MnO2 nanoparticles were synthesized by modifying a method that utilizes potassium permanganate (KMnO4) as a precursor The process involved vigorously stirring a 100 ml water-ethanol (1:1, v/v) solution at room temperature for 10 minutes, followed by the gradual addition of 5 ml of 0.05 M KMnO4 After steady stirring, hydrogen peroxide (H2O2) was slowly introduced until a brown-black color developed, which required approximately 10 ml of 10% H2O2 The resulting colloidal nano MnO2 solution was then analyzed for nanoparticle formation and its application in coating calcined laterite.
To synthesize laterite/MnO2, dried calcined laterite with a grain size of 0.1 to 0.5 mm was immersed in a MnO2 nanoparticles solution at a solid-to-liquid ratio of 1:1 for 8 to 24 hours After soaking, the liquid phase was removed, and the solid phase was washed to eliminate dissolved ions before being dried to obtain bacterial removing material (BRM).
For structural characterization, Transmission Electron Microscopy (TEM) was employed, operating at 80kV This technique involves transmitting a beam of electrons through an ultra-thin specimen, allowing for interaction that forms an image The resulting image, magnified and focused, can be captured on various imaging devices, including fluorescent screens, photographic film, or sensors.
Surface analysis was performed using a Scanning Electron Microscope (SEM), which utilizes a focused beam of high-energy electrons to produce various signals from solid specimens These signals, resulting from interactions between the electrons and the sample, provide valuable information about the surface characteristics of the material.
2.2.2.3 Investigation of sterilizing capability of nano MnO 2 adsorbents
Routine monitoring of drinking water's bacteriological quality is essential and primarily utilizes indicator organisms like Escherichia coli (E coli) and coliforms These indicators signify fecal contamination and highlight potential water quality issues, including disinfection failures, bacterial regrowth in distribution systems, or contamination ingress.
Membrane filtration is the primary method used to detect microorganisms in water In this process, 100ml of water is concentrated through membrane filtration, and the membranes are subsequently placed on selective media like Endo agar, which suppresses the growth of gram-positive bacteria Samples are appropriately diluted (10^-2) and filtered through 0.45μm membrane filters The plates are then incubated for 24 hours to allow for the growth of the target organisms.
37 o C on endo agar for total coliform
The bacteria number was determined in initial water sample and followed the time of sterilizing process
The study investigated the sterilizing capability of MnO2 nanoparticles under both static and dynamic conditions, focusing on key parameters such as contact time and the ratio of material to water sample Additionally, factors influencing these parameters in dynamic conditions, including column height and flow rate, were also considered to provide a comprehensive assessment of the nanoparticles' effectiveness.
2.2.2.4 Examine the mechanism of sterilization of MnO 2 coated on calcined laterite in water
This section aims to investigate two key aspects: first, it explores how the high oxidation potential of MnO2 affects the sterilization mechanism of MnO2 coated on calcined laterite Second, it examines the impact of varying concentrations of Mn2+ on the sterilization process facilitated by MnO2.
Synthesis of nano MnO 2 adsorbents
A working solution of MnO2 nanoparticles was created by mixing 50ml of distilled water with 50ml of ethanol, followed by the addition of 5ml of 0.05M KMnO4 while stirring continuously Hydrogen peroxide (H2O2) solution was then gradually introduced until a brown-black color developed, which required approximately 10ml of 10% H2O2 The resulting colloidal nano MnO2 solution was analyzed for nanoparticle size and formation using Transmission Electron Microscopy (TEM).
Dried calcined laterite grains, measuring 0.1 to 0.5 mm in diameter, were immersed in a nanosilver solution at a 1:1 solid-to-liquid ratio for soaking periods ranging from 8 to 24 hours After soaking, the liquid phase was drained, and the solid phase was washed to remove dissolved ions before being dried to produce a bacterial removing material (BRM) The physical structure of the solid phase was analyzed using Scanning Electron Microscopy (SEM).
Consequently, the coating process was carried out as shown in Figure 3
TEM images of the MnO2 nanoparticles solution demonstrate a significant presence of nanoparticles that aggregate into a barbed sphere shape, with an approximate diameter of 30 nm, as illustrated in Figures 4-6.
Drying Dried laterite grains Nano solution
Figure 4: MnO 2 nanoparticles with the magnification of 40000 times
Figure 5: MnO 2 nanoparticles with the magnification of 60000 times
Figure 6: MnO 2 nanoparticles with the magnification of 100000 times
A: Before coating B: After coating Figure 7: Creation of adsorbent coating by nano MnO 2 particles (100k)
Figure 8: Creation of adsorbent coating by nano MnO 2 particles (200k)
SEM images at the same scale clearly illustrate the distinct surface characteristics of the material before and after the application of MnO2 nanoparticles Prior to coating, the laterite surface appeared smooth; however, post-coating, it exhibited a dense distribution of barbed sphere-shaped MnO2 nanoparticles across the surface.
The adhesion of MnO2 nanoparticles to the surface of calcined laterite has been acknowledged for potential applications; however, the underlying mechanisms of this phenomenon remain unclear Key questions regarding the presence of chemical bonds, binding energy, and whether the nanoparticles undergo reformation or inactivation need to be thoroughly investigated in future studies.
Investigation of sterilizing capability of nano manganese dioxide
This research focused on total coliform as the indicator bacteria for assessing bacterial removal The initial water sample was analyzed to determine the bacterial count, which was monitored throughout the sterilization process.
Static and dynamic condition were chosen to conduct the experiments
Figure 9: Shaking equipment for static condition investigation
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 a crucial factor in assessing sterilization effectiveness In this experiment, raw water was treated and diluted before being mixed with polluted water in conical beakers at a solid-to-liquid ratio of 2g to 100ml (BRM:polluted water) The mixture was then agitated on a shaking table for varying durations of 10, 20, 30, 40, 50, and 60 minutes Following the agitation, all samples were filtered to quantify the bacterial content, with results presented in Table 1 and Figures 11-12.
Table 1: Influence of contact time on bacteria sterilizing
Figure 11: Samples in contact time’s influence experiment
Figure 12: Samples in contact time’s influence experiment
Figure 12 illustrates that a detention time of less than 30 minutes results in insufficient contact time for bacteria to reach the Bio-Reactive Material (BRM), leading to low efficiency rates of 56 and 28 Conversely, when the detention time exceeds 30 minutes, all bacteria effectively interact with the BRM, resulting in their elimination Thus, the optimal detention time for maximum efficiency is determined to be 30 minutes.
3.2.1.2 Influence of the ratio of BRM and water on bacteria sterilizing
The ratio of BRM to water is a crucial parameter that indicates the effectiveness of the materials used A low BRM ratio suggests reduced consumption, allowing for material savings In this experiment, the detention time was maintained based on prior results, and the BRM/polluted water ratio was systematically increased in increments of 0.25/100, 0.5/100, 1/100, 1.5/100, and 2/100 g/mL The findings of these experiments are detailed in Table 2 and illustrated in Figures 13 and 14.
Table 2: Influence of the ratio of BRM and water on bacteria sterilizing
Figure 13: Samples in BRM/water ratio’s influence experiment
Figure 14: Samples in BRM/water ratio’s influence experiment
In the first sample, the bacteria colony count is significantly high at 154 with a ratio of 0.25/100 However, when the ratio is increased to 0.5/100, the bacteria count drops dramatically to 21 This reduction is attributed to the higher amount of Bioactive Residual Material (BRM) in the second sample, which increases the likelihood of bacteria interacting with BRM As illustrated in Figure 14, the optimal amount of BRM is determined to be 1.5g per 100ml of water.
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.cm 2 )
The diameter of column is 1.8cm; the height of material is 5cm
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
Flow rate (ml/min.cm 2 ) 0.18 0.39 0.5 0.53 0.71 0.88
Sample 4 Sample 5 Sample 6 Figure 16: Samples in flow rate in BRM column’s influence experiments
Figure 17: Influence of flow rate on bacteria sterilizing in BRM column
In samples 4, 5, and 6, the total coliform levels were measured at 12, 56, and 140 MPN/100mL, indicating ineffective bacterial elimination This ineffectiveness is attributed to insufficient contact time between the bacteria and MnO2.
At a flow rate of 0.53 mL/min.cm², the analysis indicates a remaining concentration of 12 MPN/100ml Despite a significant improvement in removal capacity, the results still fall short of the drinking water standards set by the Environmental Protection Agency.
When the flow rate decreases to 0.5mL/min.cm 2 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.cm 2 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 rate was 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.cm 2
The results are given in Table 4, Figure 18-19
Table 4: Influence of column height on bacteria sterilizing in BRM column
Sample 2 Sample 3 Figure 18: Samples in the experiments
Figure 19: Influence of column height on bacteria sterilizing in BRM column
The total coliform levels in samples 1 and 2 were measured at 250 and 100 MPN/100mL, indicating that the bacteria were not effectively eliminated This ineffectiveness is attributed to insufficient contact time between the bacteria and MnO2, as the column height was inadequate.
At a height of 3cm, the analysis indicates a remaining concentration of 10MPN/100ml, demonstrating a significant increase in removal capacity; however, it still falls short of meeting the EPA drinking water standards.
When the height increases to 4cm or higher, the sterilizing capabilities is completely
The sterilizing effectiveness of the BRM column is significantly affected by both its height and the water flow rate As the height of the BRM layer increases, the column's sterilizing ability also improves Conversely, higher flow rates lead to a reduction in this sterilizing capability.
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 2 h = 3.14 x 0.9 2 x 4 = 10.17 cm 3 q = 2.8 mL/min
In the case of the investigation, the minimum EBCT for safely bacterial sterilizing is 3.63 min.
A working solution of manganese dioxide (MnO2) nanoparticles was created by mixing 50ml of distilled water with 50ml of ethanol Following this, 5ml of 0.05M potassium permanganate (KMnO4) was added while stirring continuously Hydrogen peroxide (H2O2) solution was then gradually introduced until a brown-black color developed, which required approximately 10ml of 10% H2O2 The resulting colloidal nano MnO2 solution was subsequently analyzed for nanoparticle size and formation using Transmission Electron Microscopy (TEM).
Dried calcined laterite grains with a diameter of 0.1 – 0.5 mm were immersed in a nanosilver solution at a 1:1 solid-to-liquid ratio for soaking periods ranging from 8 to 24 hours Afterward, the liquid phase was drained, and the solid phase was washed to remove dissolved ions before being dried to produce a bacterial removing material (BRM) The physical structure of the solid phase was characterized using Scanning Electron Microscopy (SEM).
Consequently, the coating process was carried out as shown in Figure 3
TEM images of the MnO2 nanoparticles solution demonstrate a significant presence of nanoparticles that aggregate into a barbed sphere shape, with an approximate diameter of 30 nm, as illustrated in Figures 4-6.
Drying Dried laterite grains Nano solution
Figure 4: MnO 2 nanoparticles with the magnification of 40000 times
Figure 5: MnO 2 nanoparticles with the magnification of 60000 times
Figure 6: MnO 2 nanoparticles with the magnification of 100000 times
A: Before coating B: After coating Figure 7: Creation of adsorbent coating by nano MnO 2 particles (100k)
Figure 8: Creation of adsorbent coating by nano MnO 2 particles (200k)
SEM images at the same scale reveal distinct surface characteristics of the material before and after the application of MnO2 nanoparticles Initially, the laterite surface appears smooth; however, post-coating, it is densely populated with MnO2 nanoparticles exhibiting a barbed sphere shape.
The interaction between MnO2 nanoparticles and calcined laterite surface has been identified for potential applications, yet the underlying mechanism behind this phenomenon remains unclear Several questions arise, including the presence of chemical bonds, the binding energy involved, and whether the nanoparticles undergo reformation or inactivation Further investigation is necessary to elucidate the nature of this interaction and provide a deeper understanding of the underlying processes.
3.2 Investigation of sterilizing capability of nano manganese dioxide
This research focused on total coliform bacteria as an indicator for assessing bacterial removal The initial water sample was analyzed to determine the bacterial count, which was then monitored throughout the sterilization process.
Static and dynamic condition were chosen to conduct the experiments
Figure 9: Shaking equipment for static condition investigation
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 a crucial factor in assessing sterilization effectiveness In this experiment, raw water was treated and diluted before being mixed with polluted water in conical beakers at a solid-to-liquid ratio of 2g to 100ml (BRM: polluted water) The mixture was then agitated using a shaking table, with detention times incrementally set at 10, 20, 30, 40, 50, and 60 minutes Following this, all samples were filtered to quantify bacterial levels, with results detailed in Table 1 and illustrated in Figures 11-12.
Table 1: Influence of contact time on bacteria sterilizing
Figure 11: Samples in contact time’s influence experiment
Figure 12: Samples in contact time’s influence experiment
Figure 12 illustrates that when the detention time is less than 30 minutes, bacteria lack sufficient time to interact with the BRM, resulting in low efficiency levels of 56 and 28 In contrast, a detention time exceeding 30 minutes ensures complete bacterial contact with the BRM, leading to their elimination Consequently, the optimal detention time is identified as 30 minutes.
3.2.1.2 Influence of the ratio of BRM and water on bacteria sterilizing
The BRM to water ratio is a crucial parameter that influences the effectiveness of the materials used A low ratio suggests minimal BRM consumption, allowing for material savings In this experiment, the detention time was based on previous findings, and the BRM/polluted water ratios were systematically increased to 0.25/100, 0.5/100, 1/100, 1.5/100, and 2/100 g/mL The experimental results are detailed in Table 2 and illustrated in Figures 13 and 14.
Table 2: Influence of the ratio of BRM and water on bacteria sterilizing
Figure 13: Samples in BRM/water ratio’s influence experiment
Figure 14: Samples in BRM/water ratio’s influence experiment
In the first sample, the bacteria colony count is significantly high at 154 with a ratio of 0.25/100 However, when the ratio increases to 0.5/100, the bacteria count dramatically decreases to 21 This reduction is attributed to the higher amount of Bioactive Residual Material (BRM) in the second sample, which increases the likelihood of bacteria interacting with BRM The optimal amount of BRM is identified as 1.5g per 100ml of water, as illustrated in Figure 14.
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.cm 2 )
The diameter of column is 1.8cm; the height of material is 5cm
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
Flow rate (ml/min.cm 2 ) 0.18 0.39 0.5 0.53 0.71 0.88
Sample 4 Sample 5 Sample 6 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 total coliform levels in samples 4, 5, and 6 were measured at 12, 56, and 140 MPN/100mL, indicating that the bacteria were not effectively eliminated due to insufficient contact time with MnO2.
At a flow rate of 0.53 mL/min.cm², the analysis indicates a remaining concentration of 12 MPN/100ml Despite a significant increase in removal capacity, the results still fall short of the drinking water standards set by the Environmental Protection Agency.
When the flow rate decreases to 0.5mL/min.cm 2 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.cm 2 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 rate was 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.cm 2
The results are given in Table 4, Figure 18-19
Table 4: Influence of column height on bacteria sterilizing in BRM column
Sample 2 Sample 3 Figure 18: Samples in the experiments
Figure 19: Influence of column height on bacteria sterilizing in BRM column
The total coliform levels in samples 1 and 2 were measured at 250 MPN/100mL and 100 MPN/100mL, respectively These results indicate that the bacteria were not effectively eliminated due to insufficient contact time with MnO2, attributed to an inadequate column height.
At a height of 3cm, the analysis indicates a presence of 10 MPN/100ml, demonstrating a significant increase in removal capacity; however, it still falls short of meeting the EPA drinking water standards.
When the height increases to 4cm or higher, the sterilizing capabilities is completely
The sterilizing effectiveness of the BRM column is significantly impacted by both the height of the BRM layer and the water flow rate As the height of the BRM layer increases, the column's sterilizing ability improves Conversely, an increase in the flow rate of water leads to a reduction in this sterilizing capability.
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 2 h = 3.14 x 0.9 2 x 4 = 10.17 cm 3 q = 2.8 mL/min
In the case of the investigation, the minimum EBCT for safely bacterial sterilizing is 3.63 min
3.3 Mechanism of sterilization of MnO 2 coated on calcined laterite in water
3.3.1 Investigation the influence of Mn 2+ in sterilizing capability
The experiment was performed to analysis the influence of Mn 2+ on water sterilizing capability of MnO2 nanoparticles
The four different concentrations which are ranging 0.1, 1 and 10 ppm of Mn 2+ were put into water samples with the available of MnO nanoparticles material