Feasibility of magnetic water treatment on industrial wastewater

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FEASIBILITY OF MAGNETIC WATER TREATMENT ON INDUSTRIAL WASTEWATER

Mohammed Tarikul Islam MSc thesis MSc Degree Program in General Toxicology and Environmental Health Risk Assessment University of Eastern Finland, Department of Environmental and Biological Sciences October, 2020

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UNIVERSITY OF EASTERN FINLAND, Faculty of Science and Forestry

Master´s Degree Program in General Toxicology and Environmental Health Risk Assessment Mohammed Tarikul Islam: Feasibility of magnetic water treatment on industrial wastewater MSc thesis 51 pages

Supervisors: Eila Torvinen, PhD. University of Eastern Finland, Department of Environmental and Biological Sciences. Maarit Janhunen, M.Sc., RDI-specialist, Savonia University of Applied Sciences

October, 2020

Keywords: Magnetic water treatment, pulp and paper wastewater, TiO2, Zeta Potential, PCD Device.

ABSTRACT

Magnetic treatment for water systems has been using for decades in households and industries.

One of the main applications of magnetic water treatment is to reduce the hardness of water and to reduce scale formation from the inner surface of the boilers, heat exchangers, and pipelines.

CaCO3 is one of the main causes to produce hardness in water and scale formation in the water pipeline. Several studies have found that magnetic water treatment not only changes the crystal morphology of the CaCO3 but also affects over zeta potential and particle charge and particle size of the CaCO3 particle. Coagulation-flocculation is an important process in wastewater treatment technology. One of the main aims of the coagulation-flocculation process is charge neutralization. This study was done to check if the magnetic water treatment affects the particle charge of the water and if this can also aid the coagulation-flocculation process.

In this study, a magnetic water treatment device containing a neodymium magnet was used. It can produce an altering frequency magnetic field orthogonal to the water flow. Titanium dioxide mixed water and pulp and paper mill wastewater were used as samples. The samples were treated in the magnetic water treatment device for several hours with or without coagulant, depending on the experiment. Particle charge was measured by using a particle charge detector, which can measure the particle charge with the aid of polymer (or polyelectrolyte) titration.

It has been found out that the magnetic water treatment process can reduce the particle charge of the samples, which can aid the coagulation-flocculation process by reducing the use of coagulant. The reaction time is within one hour of the treatment process. The results also showed that the process works better if the sample contains more particles.

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ACKNOWLEDGEMENT

First, I want to show gratitude and thanks to Professor Simo O. Pehkonen. Who allowed me to start the thesis and do the experimental part of the thesis. With his proper guidance and assistance, I learned the method and meaning of scientific experiments.

I also want to show my deepest gratitude and special thanks to my supervisor Eila Torvinen (Ph.D.). With lots of patience, she taught me scientific writing, gave me valuable information, and help me to finish my thesis. Without her help, it was impossible to finish the thesis.

Special thanks go to Maarit Janhunen for giving me valuable information on water chemistry.

Special thanks also go to Laura Antikainen and the Savonia University of Applied Science and Technology for giving me a chance to use the joint water lab for my experiments.

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Water is one of the basic needs of human life. 70% of the earth's surface is covered with water but only a small percentage of that vast amount of water is usable and accessible to humans as for drinking and other use. Industrial revolution makes our life easier as we get our basic commodities more easily and cheaper in our day to day life. This vast amount of industrial activities needs a large amount of water which leads to water pollution. To control water pollution governmental organizations set rules and regulations to treat the polluted water before it returns to the environment. As a result, industrial authorities use more chemicals to remove chemicals from the polluted water. This increases production costs. In developed countries where rules and regulations are strict, industrialists are bound to obey the rules and regulations of the government but in underdeveloped countries, where rules and regulations are not that strict, treating wastewater is a burden and extra cost for industrialists.

Wastewater treatment is a process to remove contaminants from the wastewater. Industrial wastewater treatment consists of three stages: primary treatment, secondary treatment, and tertiary treatment. In primary treatment, the wastewater is temporarily held in a basin to settle heavy solids and the lighter solids and chemicals such as oil and grit float above the surface of the wastewater. After removing the settled and floating materials remaining wastewater is subjected to secondary water treatment where most of the dissolved and suspended chemicals and biological materials are removed by using biological and chemical techniques. In tertiary treatment, the treated water goes into an additional process that ensures that the treated water is not harmful to the ecosystem and the environment. The conventional wastewater treatment process has several drawbacks which include high maintenance and running costs and a great need for chemicals, yet the outcome may be low.

Magnetic water treatment (MWT) is non-chemical water treatment. It has several applications in medical, industrial, and environmental fields. MWT has been an effective system for reducing hardness and scale formation for decades and for this purpose it is a popular device also in households. Water hardness is one of the main causes of scale formation. So, if hardness can be removed, scale formation will also be reduced. Some of the advantages of the MWT are that it is non-chemical, non-polluting, and easily installed.

Water is a paramagnetic compound. Like other paramagnetic compounds, water molecules are attracted slightly by the magnetic field. When water flows under the magnetic field, some of

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the physicochemical properties of water and its dissolved chemicals are changed, for example, zeta potential, which is a measure for particles' electrical charge. Barrett and Parsons (1998) showed that MWT can reduce CaCO3 particle’s zeta potential, particle size, and crystal morphology. Barrett and Parsons (1998) also showed that controlled pH in an experimental set up can influence the results.

In the secondary industrial wastewater treatment stage, the biological treatment process such as the activated sludge process is used to remove impurities from water. Industrial wastewater contains hydrophilic and hydrophobic fine particles. In the biological treatment process, many of these fine particles are useful for biological treatment but some are harmful. These particles need to be removed from the wastewater. To remove these tiny colloidal particles, they need to be converted into large suspended particles so that they can be removed from the solution by settling. These particles are kept apart from each other by repulsive electrical charges as magnets the same poles react with each other. During the secondary treatment stage, chemicals are added to suppress the particles repulsion forces or surface charge, i.e. to suppress the zeta potential of the particles, so that the particles are started to attach. Such a chemical is known as a coagulant (Hopcroft, 2014). A coagulant is typically a metallic salt which contains positive and negative ions or charge. The coagulant is added to the water and the coagulant’s opposite charge overcome the repulsive charge; this activity destabilizes the suspension. For example, alum is a coagulant which creates positively charge ions and destabilizes the negatively charged colloidal particles. The repulsive charges of colloids get neutralized by the positive alum ions, then van der Waals forces cause the particles to agglomerate together and the agglomerated particles form micro floc (Abbasian et al. 2008).

As MWT influences the zeta potential of the dissolved chemical particles of the water, it can be an alternative to the chemical coagulation process for some industrial wastewater treatment plants.

In this study, it was tried to find out if the MWT can replace the chemical coagulation process or if it is possible to use MWT along with the chemical wastewater treatment process to reduce the chemical coagulant consumption. If MWT can reduce chemical consumption or can replace the coagulation-flocculation process of the industrial wastewater treatment method, industrialists in developing countries will be more interested to treat wastewater properly similarly to developed countries. This will reduce the environmental damage magnificently what is caused by humans and by the fresh water-hungry industries.

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2 LITERATURE REVIEW

2.1 INDUSTRIAL WASTEWATER TREATMENT

Industrial wastewater is water that has been used as a part of the manufacturing process and produced as a byproduct of industrial activities. Industrial wastewater is different from domestic wastewater or sewage and based on the production process, industrial wastes generally contain organic and inorganic material in various concentrations. The wastewater can be highly acidic or basic, can contain toxic material, and material high in biological oxygen demand. The wastewater can also contain the color, odor, and can be low in suspended solids. In the chemical industry, many materials are carcinogenic, mutagenic, hardly biodegradable, and toxic. In the chemical industry surfactants, emulsifiers, and petroleum hydrocarbons are used, which can reduce the performance efficiency of many treatment unit operations (EPA, 1998).

Treatment of industrial wastewater can be done by some biological oxidation methods such as rotating biological contactor (RBC), trickling filters, lagoons, or activated sludge (Nemerow, and Dasgupta, 1991; Jobbágy, 2000). Pollutants with a molecular size larger than 10000-20000, can be treated and sedimented or floated by coagulation-flocculation method (Hu, Goto and Fujie, 1999). Due to the rapid increase of population and increasing demand for commodities, also industrial activities increase, and this means more exploitation of natural resources and pollution. Production of pulp and paper generates a huge amount of pollutants, which contain a high amount of chemical oxygen demand (COD), biological oxygen demand (BOD), total dissolved solids (TDS), total solid (TS), color, and toxicity. The usage of water is high in the pulp and paper industry as per ton paper product water is needed 76m³ to 230 m³of water (Nemerow and Dasgupta, 1991).

Various types of industries have different types of wastewater treatment systems according to their generated wastewater characteristics. Generally, the wastewater treatment plant has three stages, primary, secondary, and tertiary. The different stages of paper mill wastewater treatment are shown in figure 1.

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Figure 1: Schematic view of a paper mill wastewater treatment plant (Möbius and Helble, 2004).

The primary treatment of wastewater is also known as mechanical treatment. Wastewater contains a large amount of floating and submerged solid material. This bigger floating and merged solid materials need to be removed before the wastewater enters the secondary wastewater treatment. In secondary wastewater treatment, wastewater is treated chemically or biologically or sometimes together when it is called a simultaneous treatment. The secondary treatment uses coagulants and flocculants to remove dissolved materials from the wastewater system. The coagulated materials are removed as sludge. In biological treatment plants, microbes are used to treat the wastewater, where dissolved chemicals are used as nutrients by the microbes of the wastewater system (Nasr et al., 2007).

In the tertiary stage, also known as the advanced stage, treated water in the secondary stage is treated more with ozone treatment, reverse osmosis, ultrafiltration, or nanofiltration and disinfection to meet the water parameter in an acceptable range to release to the environment.

The best strategy to clean wastewater which is highly contaminated toxic is to treat them at the source (Nasr et al., 2007).

2.2 COAGULATION - FLOCCULATION

Colloidal particles generally repel each other in the water because generally, they have a net negative charge in water solution. That is why without the help of another chemical, colloidal particles do not settle at all or do not settle in a reasonable time. Chemicals such as iron and aluminum salts or polyelectrolytes contain positive ions. They can reduce the negative surface charge of the particles of the water solution. So, the particles will be destabilized and separate.

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This kind of chemical, which contains a positive charge, is known as a coagulant. To ensure effective dispersion, under rapid mixing, a coagulant is added. In the flocculation stage, under slow mixing, destabilized particles aggregate and form flocs. To improve floc quality and to make the flock bigger and more settleable, another chemical, known as a flocculant, can be used. The flocs float up or settle down in a few minutes when mixing is stopped. For floc separation, filtration and flotation and sedimentation are also widely used. The coagulation- flocculation processes can effectively remove colloidal particles and suspended solids. Some soluble compounds which contain net negative charges, such as fulvic acid and humic acid, can also be removed by the coagulation-flocculation process. Removal of non-charged substances such as carbohydrates is not effective (Leiviskä, 2009). Aluminum and iron salts such as aluminum sulfate, aluminum nitrate, and ferrous sulfate are used mostly as coagulants. Not only inorganic chemicals but also organic polymers are also extensively used in the coagulation- flocculation process as flocculants. Polymers are found in a wide range of molecular weights.

Polymers are also available in a wide range of charge densities: high molecular weight > 10⁶, medium molecular weight 10⁵ –10⁶, and low molecular weight < 10⁵ (Bolto and Gregory, 2007).

Ionic polymers are known as polyelectrolytes.

In water treatment, when iron salts and aluminum are used as a coagulant, the sludge formation, dosage requirement, and the ion concentrations of the residual in the purified water are high.

On the other hand, the dosage requirements and the amount of precipitates are lower in the case of polymers. The floc properties are also improved. Moreover, the organic polymers do not form any ash if the precipitates are burned to produce energy. However, organic polymers are more costly than inorganic chemicals. Cationic polyelectrolytes are more toxic to aquatic organisms than anionic or non-ionic polyelectrolytes (Bolto and Gregory, 2007).

Depending on the different types of particles, different types of mechanisms are used in the coagulation-flocculation processes, such as bridging, patching, charge neutralization, and sweep coagulation. Among these processes, the most important process type is charge neutralization. In the case of charge neutralization, by the coagulant chemicals, the surface charge of the particles is neutralized, then the neutralized particles are aggregated with each other. For example, Al³⁺ forms positive aluminum species in water; they are adsorbed by negative particles, which results in neutralization. Overdosing of this coagulant leads to restabilization.

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Iron hydroxide or insoluble aluminum precipitates and sweep down the suspended material in the sweep coagulation-flocculation process. The polymer adsorbs on the surface of an anionic particle form local positively charged regions which are known as patches in the patch mechanism. The differently charged regions of particles create strong interaction between particles and this initiates flocculation. A long-chain polymer is adsorbed on the surface of a particle and the polymer’s loops and tails of are free to attach themselves with other particles.

This process is known as bridging flocculation. Apart from electrostatic interaction, hydrogen bonds or ion binding can also adsorb a polymer (Bolto and Gregory, 2007). In the ion binding process, the anionic polyelectrolyte adsorbed on negatively charged surfaces in the presence of divalent positive metal ions, which form a bridge between the negative surface and anionic polyelectrolyte (Berg, Claesson and Neuman, 1993).

the pH value has a major influence on the coagulation process because the charge of the particles is dependent on pH. Generally, when the pH is decreased the number of negative charges also decreases, and the number of positive charges increases. Coagulants also have an optimum pH range. The residual concentration of aluminum and iron in purified water is pH-dependent, that is why optimum pH needs to be determined for each type of water and metal salt (Leiviskä, 2009).

2.3 TITANIUM DIOXIDE

Titanium occurs naturally in soil. It is the tenth most abundant metal found in the earth's crust (Hampel, 1968). Titanium has numerous industrial applications such as metal alloying, aerospace applications, and biomedical devices, sunscreen, cosmetics, and applications in the paint and paper industry. Approximately 95% of titanium is refined and transformed to TiO2 by treatment of Ti bearing ores with carbon, chlorine, oxygen, and sulfuric acid (USGS, 2020).

TiO2 is commercially available as a dry powder or as a liquid. In food products, TiO2 is used for whitening the product and to increase opacity or modify the texture of the product (Mattigod et al., 2005). TiO2 ranges in size from ten to hundreds of nanometers, the common mean diameter being 200 nm. Daily human intake of TiO2 is 5.4 mg per day (Lomer et al., 2000).

Excreted TiO2 that is ingested by a human is transported to the municipal wastewater treatment plant. Surprisingly very few publications are reported on the removal of TiO2 in wastewater treatment plants.

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In nanotechnology-based consumer products, TiO2 is most frequently used. Consumer products such as cosmetics sunblock and sunscreen and wall paints also contain TiO2 nanomaterial.

Studies have shown that nanomaterials such as TiO2 can be introduced in the aquatic environment via product use, disposal, and recycling (Wiesner et al., 2006). TiO2 nanomaterial is measured significantly in the urban surface runoff after a rainstorm (Kaegi et al., 2008). This is a concern because removing it by traditional treatment is uncertain (Honda et al., 2014).

The exact level of TiO2 nanomaterial in the environment is unknown due to the limitation of the current measurement method (Gottschalk and Nowack, 2011) but about 0.180-1.230 mg/l has been reported as levels found in wastewater biosolids (Westerhoff et al., 2011). As food- grade TiO2 is used highly in personal care products such as toothpaste, chewing gum, and candies, it has the highest probability to be introduced to the environment. About 5000 tons of food-grade TiO2 is produced annually (Weir et al., 2012). Nonfood-grade TiO2 also can be added to the stream through industrial discharge, e.g from the pulp and paper industry.

Nanomaterials such as TiO2 are considered as emerging pollutants that can introduce and create an impact on the water supply. Nanoscale TiO2 had been reported to cause adverse effects such as oxidative stress in the human cell (Long et al., 2006) and genetic instability in mouse cells (Trouiller et al., 2009).

The pulp and paper production industry is one of the largest users of titanium dioxide. Low end or low-grade paper uses china clay, talcum powder, and calcium carbonate as filler while high end or high-grade paper uses titanium dioxide (Rawski and Bhuiyan, 2017). Using talcum powder, calcium carbonate, and china clay will increase the weight of the paper and reduce the strength. The products which need to be strong but weightless and be decorative, such as religious books, dictionaries, magazines, magazines cover, decorative cover paper, and banknotes use titanium dioxide (Rawski and Bhuiyan, 2017). Using titanium dioxide in paper reduces the weight by 15-30% compared to the normal low-end paper. Titanium dioxide makes the paperwhite, shiny, thin, smooth, and of high strength. It also improves the printing. Under the same conditions, paper with titanium dioxide is ten times more nontransparent then the paper with talcum powder and calcium carbonate. The decorative paper is also known as titanium white paper and it is mainly used to produce flooring and wallpaper. Rutile, a form of Titanium dioxide, is used for anti-aging paper. Titanium dioxide is also used in low ash paper, for example, the Bible paper and banknotes are produced with low ash paper because both require a good opacity of paper. As the economic development is happening in China there is a large demand for high-end furniture, home improvements, so the amount of decorative paper is

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rising rapidly, and the use of titanium dioxide is also rising. The amount of titanium dioxide used in the decorative paper is 20%-40%, while in the other paper titanium amount is 1%-5%.

The amount of titanium dioxide used in the decorative paper is over 30,000 tons per year in China (fire7teeth, 2013).

2.4 PULP AND PAPER MILL WASTEWATER

Though pulp and paper mills have been developing over the past decades, they still consume lots of water. Water consumption of pulp and paper industry varies depending on the pulp production technology, the sequence of the pulp and paper bleaching process, and the restriction of wastewater discharge.

About 20000 to 60000 gallons of 76m³ to 230 m³of water is used per ton of product (Nemerow and Dasgupta, 1991) which also results in high amounts of wastewater generation. The average water use for pulp and paper production in India is 200-259 m³/ton (Gune, 2000). The pulp and paper mill wastewaters cause a huge impact on the environment, such as thermal impacts, slime growth, scum formation, color and odor problem, and loss of aesthetic beauty. The pulp and paper wastewater also increase toxic substances amount in the water, which can cause death to the zooplankton, fish, and other living creatures in the water body. Pulp and paper mill wastewater also affect the terrestrial ecosystem (Pokhrel and Viraraghaban, 2004).

Paper production contains two stages. The first stage is pulp making and the second stage is paper production. The pulping process contains various stages, of which most polluting steps are wood preparation, pulping, pulp washing, and bleaching. In the pulping process, especially in the chemical pulping process, high strength wastewater is generated. This wastewater contains soluble wood materials and wood debris. Pulp bleaching has traditionally used chlorine to brighten the pulp and chlorine is one of the most toxic substances in the wastewater (Pokhrel and Viraraghaban, 2004). Though in developed countries alternative chlorine bleaching, such as oxygen and enzyme bleaching without any chlorine or chlorine product, is used nowadays, chlorine is still used in large numbers in various countries' pulp and paper industry (Finnish Forest Association, 2020).

The pollutants at various stages of the pulp and paper making process are presented in figure 2.

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Figure 2: Pollutants from various sources of pulp and paper making (US EPA 1995, Pokhrel and Viraraghaban, 2004)

2.5 COLLOIDS

Naturally chemically pure water in our environment does not exist. Impurities of water come from soil and air in the environment. Impurities of water can be three types

• Suspended solids

• Colloidal solids

• Dissolved solids

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Particles within the range of 0.001 micrometers to about 1 micrometer in diameter are known as colloidal particles. Colloidal particles are too small and light that gravity force could not be effective on them. Thus, it takes a huge time to settle them or they do not settle at all at the bottom or float up at the surface of the solution. They remain dispersed in the solution (Gregory, 2005).

Colloids are affected by the two forces in the opposite direction. The molecular force pulls the colloids together. On the other hand, colloids are often charged with similar charges, positive or negative, and these charges always repel each other. The surface charge of the colloid particles depends on the pH. (Manahan, 2000)

Colloids can be classified into three types: Hydrophobic, Hydrophilic, and Association colloids Hydrophilic colloids are generally macromolecules, such as protein or synthetic polymer.

Hydrophilic colloids have a strong interaction with water that is why when they are placed in water, they create a spontaneous formation of colloids. Generally, hydrophilic colloids are solutions of very large molecules or ions. Hydrophilic colloid’s suspension is generally less affected by the addition of salts to water while suspensions of hydrophobic colloids are more affected by the addition of salts to the water. (Manahan, 2000)

Hydrophobic colloids interact lesser with water and are stable because they contain negative or positive charges at their surface. Generally, all the colloid particles contain the same electrical charges, either positive or negative that is why they repel each other, as shown in figure 3.

Figure 3: Negatively charged hydrophobic colloidal particles surrounded in positively charged counter-ions solution (Manahan, 2000).

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The charged particles and the opposite charge surrounded by the particles build a double layer of charges which is known as an electrical double layer (figure 4). In the electric double layer opposite charges surrounded over the particle is known as the Stern layer.

Figure 4: Schematic of a diffuse double layer of a charged particle in the vicinity of a charged solid/wall surface (Yan et al., 2018).

Colloidal particle characteristics are determined by their physical, chemical properties. Their characteristics also depend on high interfacial energy, high specific area, and high surface/charge density ratio. Colloids play an important role in understanding the properties and behavior of natural waters and wastewaters. An important influence of colloids in aquatic chemistry is their ability to transport various kinds of organic and inorganic contaminants.

(Manahan, 2000)

One of the main characteristics of colloidal particles is turbidity. Particles scatter light and give rise to turbidity in water. Turbidity is the most common visible evidence of particles in water (Gregory, 2005). Turbidity can be measured by nephelometers. Longer wavelength lights are more transmitted while shorter wavelength light is diffuse and reflected by scattering. This scattering effect is known as the Tyndall effect (Uni-hannover.de, 2019). Under this theory Nephelometer measures turbidity in a solution.

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2.6 ZETA POTENTIAL

By zeta potential, the stability of a colloidal system can be described. The large zeta potential of the particle means the colloidal system is stable. The particle tends to aggregate if the zeta potential of the particle of the system is close to zero (Abbasian et al., 2008). Chemicals are used in wastewater treatment plants to destabilize the colloidal particles. In some industries, for example, the ink and paint industry, chemicals are used to make colloidal particles stable. The zeta potential measurement is an important parameter for various kinds of industries such as ceramics, brewing, medicine, pharmaceuticals, mineral processing, and water treatment.

It is important to understand the colloidal system and particle charge which is discussed in chapter 2.5 and 2.7 To understand zeta potential. Zeta potential is shown in figure 5, where the distribution of the ions in the surrounding interfacial region is affected by net charge development at the surface of the particle, as a result, the concentration of counterions near the surface of the particle increased. That is how an electrical double layer formed or exists around each particle. The surrounded liquid layer of the particle exists as two parts; the first one is the stern layer or inner region, where the ions are strongly bound and the second one is the outer layer or diffuse layer region, where they are associated less firmly. Within this diffuse layer and the stern layer, a notional boundary exists, which is known as the clipping plane. Within the slipping plane, the particle acts as a single entity. The potential (mV) at this boundary is known as the Zeta potential (Hunter, 1981).

Figure 5: Zeta potential (Williams, 2016)

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pH is the most important factor that affects zeta potential. If alkali or basic solution (OH^-) is added in a solution, the particle will gain negative charge, again on the same solution if acid is (H⁺) added then at some point the positive and negative charge will be neutralized. And again, if more acid is added to that solution the particle will get a positive charge. Thus, there will be a point where the zeta potential will be zero. This state is known as the Isoelectric point.

Normally the colloidal system is least stable at this point (Morel and Hering, 1993).

Generally using just Zeta potential or the particle charge analyses do not provide a proper understanding of colloidal systems because zeta potential and particle charge complement each other (Leiviskä and Rämö, 2007). In general, the total amount of positive or negative charges is described by the charge quantity, while the magnitude of the charges is showed by Zeta potential. The optimum dose or the required dosage of the coagulant or flocculant is usually close to that required to neutralize the surface charge carried by the particles, and that is why it can be used in determining the coagulant/flocculant dosage (Beulker and Jekel, 1993).

2.7 PARTICLE SURFACE CHARGE

The surface charge is the electric charge of a particle surface with a polar fluid such as water.

Because of the bent shape of the water molecule, water molecules are polar. Water contains two hydrogen atoms and one oxygen atom. The negative charge comes from the oxygen atom and the positive charge comes from the hydrogen atom. Because of the electronegativity difference between hydrogen and oxygen atom the water molecule became bent shape. Oxygen atom electronegativity is 3.5 while hydrogen is 2.1. Due to this small difference of electronegativity atoms form a covalent bond. Though the hydrogen and oxygen atoms of water are in covalent bond and polar, but water molecule is neutral electrically because each water molecule has 10 electrons and 10 protons, thus the net charge is zero (Camp, 1963).

As the water can attract positive or negative electrical charges in a solute it is a polar solvent.

The oxygen atom has a slight negative charge near it that is why it attracts nearby hydrogen atoms from water or other molecules which have a positive charge near it. The hydrogen side of each water molecule has some positive charge which attracts other oxygen atoms and attracts other molecules that have some negative charge near it. The surface charge will be positive if the number of absorbed positive ions exceeds the number of negative ions. Retrospectively, the surface charge will be negative if the number of absorbed positive ions is less than the number of negative ions.

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According to Stumm and Morgan (1981) and (Stumm et al. (1992) solid surface particles can gain surface charge in three principal ways:

1. Many solid surfaces contain ionizable functional groups, such as -OH, -COOH, -SH.

These particle charges are dependent on their degree of ionization and their solution’s pH.

Example: Hydrous oxide’s electric charge can be explained by the acid-base behavior of the surface hydroxyl groups S-OH

at high pH, a negatively charged surface can be seen, while in low pH a positively charged surface can be seen. At some intermediate pH, the net surface charge will be zero

2. Lattice imperfections at the solid surface can cause surface charge at the phase boundary and by replacements of isomorphous in the lattice.

Example: if in an array of solid SiO2 tetrahedra a Si atom is replaced by an Al atom (Al has one electron less than Si), a negatively charged framework is established:

Similarly, isomorphous replacement of the Al atom by Mg atoms in networks of aluminum oxide octahedra leads to a negatively charged lattice. Clays are representative examples where such atomic substitution causes the charge at the phase boundary.

Sparingly soluble salts also carry a surface charge because of lattice imperfections.

3. By adsorption of a surfactant ion or a hydrophobic species, a surface charge may be established. From bonding via hydrogen bonds or from so-called hydrophobic bonding or from London-van der Waals interactions preferential adsorption of a "surface-active"

ion can arise. The sorption mechanism of some ions is not certain, such as fulvates or humates. Ionic species carrying a hydrophobic moiety may bind inner-spherically or

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outer-spherically. This characteristic depends on the surface-coordinative or hydrophobic interaction.

2.8 PARTICLE CHARGE MEASUREMENT DEVICE

Generally, all colloidally dissolved and solid particles in an aqueous solution have positive or negative charges. This leads to a concentration of oppositely charged ions, which is known as counterions, on the surfaces of the colloids. If these oppositely charged ions or counter-ions are separated from or sheared off the dissociated particle or macromolecule, a streaming current or potential can be measured in the millivolt (mV). Zero mV of a streaming current denotes the point of zero charges, where all the charges which exist in the water sample are neutralized. If the measured streaming current is bigger or smaller than zero, the measured value indicates that the charge is positive or negative (cationic or anionic), respectively, in the water solution (BTG Mütek, 2003).

The total surface charge of the particles can be used to estimate the zeta potential of the colloidal system. It can be measured e.g. with a particle charge detector device. BTG Mütek GmbH PCD 03 is an example of a particle charge detector device. A BTG Mütek GmbH PCD 03 particle charge detector is shown in figure 6.

Figure 6: BTG Mütek GmbH PCD 03 device. (BTG Mütek, 2003).

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According to the operation manual of BTG Mütek GmbH PCD 03 device, the streaming current is a relative parameter which depends on different influential factors, such as

• Temperature

• Measuring cell cleaning

• Chemical properties of the sample

• The electrical conductivity of the sample dispersion

• Sample viscosity

• Particle sizes and molecular weight of the sample

• The dimension of the measuring cell.

The figure of the test setup of the device is shown in figure 7.

Figure 7: Figure of test setup (1-Display, 2-Electronics, 3-Electrodes 4-Plastic measuring cell, 5-Displacement piston, 6-Motor) (BTG Mütek, 2003)

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Streaming current measurements with a particle charge detector device are based on the following principles:

a plastic measuring cell is a central element that is fitted with a displacement piston. If the measuring cell is filled with a water sample or an aqueous sample, colloidally dissolved molecules will adsorb on the plastic surface of the piston and the cell walls while the counter- ions remain comparatively free because of the van der Waal forces. Between the cell wall and the piston, a narrow gap is provided. The piston oscillates in the measuring cell with the help of the motor, this oscillation creates a liquid flow. This flow entrains the free counter-ions and separates them from the adsorbed sample material. The counter-ions induce a current at the built-in electrodes, which is rectified and amplified electronically. The streaming current then can be seen in the display with the appropriate sign (BTG Mütek, 2003).

A polyelectrolyte (ionic polymers) titration needs to be conducted for quantitative charge measurements of a sample. Where the streaming current is used to identify the point of zero charges (0 mV). An oppositely charged polyelectrolyte, in which charge density is known is added to the sample as a titrant. The charges of the titrant neutralize the existing charges of the sample. When the point of zero charges (0 mV) is reached, the titration is discontinued. Titrant consumption in ml is the actual measured value which is the basis for further calculations (BTG Mütek, 2003).

Apart from charge density measurements, a particle charge detector device is also used to identify the isoelectric point of dispersions. According to the operation manual of BTG Mütek GmbH PCD 03 device (BTG Mütek, 2003), the isoelectric point is the pH-dependent point of zero charges of a particle. In this context, existing layers of specifically adsorbed charge carriers are considered. By the dropwise addition of an acid or base titrant, the sample’s pH’s are shifted until the point of zero charges is reached. Cationic samples are titrated with a base and anionic samples are titrated with an acid up to the point of 0 mV. The pH value is detected with the streaming current or streaming potential. Calculating the isoelectric point from a graph is shown in figure 8.

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Figure 8: Isoelectric point (BTG Mütek, 2003)

2.9 MAGNETIC WATER TREATMENT

The nonchemical water treatment device was first introduced as a means of scale control in 1865 and the first US patent for a water treatment device, which uses a magnetic field was received in 1873 by A.T. Hey (Busch and Busch, 1997). MWT devices can be with a permanent magnet or neodymium magnet-activated with the help of electricity. Now a day’s MWT is an effective system for reducing scale formation and hardness.

Water hardness is one of the main causes of scale formation. So, if hardness can be removed, scale formation will also be reduced. Latva et al. (2016) showed that MWT is an effective technique not only for reducing scale formation but also for reducing existing scale from the household drinking water pipelines. The cause of water hardness is mainly calcium carbonate (CaCO3). Calcite and aragonite are the most common natural forms of CaCO3. Several studies (Higashitani et al., 1993; Barrett and Parsons, 1998; Coey and Cass, 2000; Kobe et al.,2001;

Kobe et al., 2002; Botello-Zubiate, 2004; Knez and Pohar, 2005; Coey, 2012) have found that MWT reduced calcite in water and increased aragonite formation. Calcite tends to build up the hard scale on the surface while aragonite forms a slushy precipitate which can easily wash away.

Several studies (Baker and Judd, 1996; Parsons et al., 1997a; Barrett and Parsons, 1998;

Myśliwiec et al., 2016) showed that MWT can reduce CaCO3 particles zeta potential, particle size, and crystal morphology. Barrett and Parsons (1998) also showed that controlled pH in an experimental set up can influence the results. Coey (2012) told about dynamically ordered

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liquid-like oxyanion polymer (DOLLOP) theory or waters memory effect which influences CaCO3 to form crystal by increasing nucleation state.

Bauer water technology Ltd produces an MWT device for household water treatment. All their devices produce altering frequency magnetic field of a maximum 26 mT intensity orthogonal to the water flow. In figure 9 we can see a schematic view of a magnetic device that contains a magnetic jacket and the magnetic field is orthogonal to the water flow.

Figure 9: Diagram of a magnetic water system (Yadollahpour et al., 2014).

Though it was controversial in many experiments (Parsons et al. 1997) before, it is now well established that MWT is an effective method to reduce scale formation (Latva et al., 2016).

General wastewater treatment depends on coagulation and flocculation. Coagulation is the process where particles neutralize the charge or zeta potential and form larger particles. As Barrett and Parsons (1998) showed that MWT reduces the zeta potential of CaCO3 in water, it also changes the morphology and increases the particle size of the smaller particles. It may also be possible to use the MWT in the wastewater system to reduce coagulant used in water or enhance the coagulant performance in the water.

There are lots of publications on scale formation and removal by MWT but very few studies have been conducted on the application of magnetic treatment in wastewater treatment. In most of them, the magnetic field is used only for the separation of solids or attached microorganisms from effluent (Ozaki et al. 1991).

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Magnetic field exposure can increase microbiological activity because magnetic field characteristics can increase bacterial activity. The effect was far more noticeable in heterogeneous cultures such as sewage than in pure culture (Yadollahpour et al., 2014). Another important outcome of magnetic fields is their ability to detoxify toxic compounds (Yadollahpour et al., 2014).

Jung et al. (2007) showed the effect of magnetic fields on phenol biodegradation by using immobilized activated sludge in a study. In that study, biodegradation increased 30% by applying a magnetic south pole with 0.45 T strength on the bioreactor with microorganisms immobilized on the beads as compared to the control. On the other hand, irradiation of the magnetic north pole inhibited this type of bio-oxidation. Optimum pH 7.5 was reported for the activated sludge treatment with and without magnetic field application. The studies of Jung et al. (2007) showed that magnetic fields do not have a lethal effect on activated sludge efficiency.

With 17.8 mT magnetic field had a positive effect on the substrate removal rate. Low strength of the magnetic field, such as 9 mT, showed no effect at all. In a higher magnetic field of around 54 mT, microbial growth rates were negative.

Effectiveness of MWT over scale elimination and prevention, the biodegradability by microorganisms and wastewater treatment depends on the chemical properties of the treated medium, strength, and configuration of the magnetic field, thermodynamics properties of the water, and the fluid flow characteristics (Yadollahpour et al., 2014). To achieve the desired outcome four important conditions should be observed:

• The water flow is perpendicular to the magnetic line of force

• Water should first cross the south pole line and then continue to break wider and denser alternating reversing polarity line until leaving the magnetic chamber through the north pole line

• The capacity of a magnetic reactor can be determined by the gauss strength, flux density, area surface, of the exposure of the number of the fields, and the distance of the alternating poles

• Water should be under pressure and flowing with as minimum turbulence as possible during its travel through the magnetic reactor (Yadollahpour et al., 2014).

The biological process is used to convert organic materials of wastewater into settleable biological and inorganic solid. Activated sludge and modified versions of the activated sludge process are the most used biological process. Some studies have found the effect of the magnetic

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field on living organisms negative (Gerencser et al. 1962) though lots of studies have found enhancement of growth (Moore, 1979; Ramon et al.1987). The magnetic effect on organic materials depends on the strength of the magnetic field and exposed microorganism type. Also, it depends on the type of magnetic pole, exposure duration, and intensity (Yadollahpour et al., 2014).

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3 AIM OF THE STUDY

It is proven that MWT can prevent scale formation by CaCO3 from the drinking water system and can reduce scale formation in an existing household water system. It was also proved that the MWT effects on the particle charge and zeta potential of CaCO3 particles. According to (Leiviskä, 2009) colloidal particle in water has a net negative and positive charge, this net negative and positive charge can be reduced by adding coagulants. The idea of MWT is also the same, to reduce the surface charge of the particles or to achieve zero charges with the help of MWT with less coagulant. If the magnetically treated water needs less polymer titrant to reach zero charges, the same polymer could be used as a coagulant in less amount.

This study aims to find out the effects of MWT on the particle charge of the TiO2 solution and the particle charge of pulp and paper mill wastewater.

The reason to use the TiO2 solution in this study is that TiO2 forms a colloidal solution in water.

The use of TiO2 in pulp and paper manufacturing and other manufacturing is increased, as a result, it occurs more in the current wastewater. It was also easier to study the effect of MWT on a homogeneous TiO2 solution and later study the effect of MWT in heterogeneous organic material rich pulp and paper wastewater.

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4 MATERIALS AND METHOD

4.1 GENERAL SETUP OF THE STUDIES

In this study, a magnetic reactor from Bauer Watertechnology Oy was used. It consists of a neodymium magnet (PJ-20i HST) which can produce an altering frequency magnetic field of a maximum 26 mT intensity orthogonal to the water flow and a 60-liter stainless steel storage tank. The principle of all the experiments was to pour sample water (15 l or 30 l) into the magnetic reactor storage tank and the water was let circulate in the reactor for several hours.

Particle charges of the treated samples were measured with the Mütek PCD03 device (Mütek Systemtechnik, Herrsching, Germany). This device can analyze 33 ml of the sample at once.

Every time, at 1-hour intervals, 30 ml of the magnetic treated sample was poured into the device, and measurement was made according to the manual provided by Mütek Systemtechnik (Herrsching, Germany).

The experiments were done with two types of samples, TiO2 mixed water, and pulp and paper mill wastewater. Charge neutralization at MWT was studied by polymer titration by adding the polymer drop by drop to the PCD03 device to achieve zero charges. The idea was to achieve zero charges with the help of MWT with less coagulant. If the magnetically treated water needs less polymer titrant to reach zero charges, the same polymer could be used as a coagulant in less amount. In pulp and paper mill wastewater experiments (chapter 4.3.2) the effect of coagulants was also studied, and they were added to the sample before magnetic treatment. The details of the experiments are told in the following chapters.

4.2 TITANIUM DIOXIDE EXPERIMENTS

Liquid TiO2 in an unknown concentration was obtained from Solensis (Tampere, Finland). It was dried in an oven at 120°C for 20 min and dried TiO2 was mixed with deionized water and used in every experiment.

4.2.1 Effect of salt on particle charge of TiO2 solution

After every experiment PCD device was cleaned with a solution that contained NaBr salt, according to the manual of the PCD device. That is why the first experiment was done to check

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if any kind of salt influences on the particle charge results. The experiment was done with KCl salt with amounts of 1.3 mg/ml, 1.7 mg/ml, 2.1 mg/ml and 2.4 mg/ml. Each time 30 ml of 0.34 mg/l TiO2 in deionized water and weighted KCl were added to the PCD device. HNO3, 600 µl of 0.01 mol/l was used to lower the pH to pH 3. Then 0.01 mol/l NaOH was added drop by drop to higher the pH to almost pH 11 and the particle charge was measured after every addition.

The experiment was done without MWT. A control experiment was done similarly without KCl salt and without MWT.

4.2.2 Effect of magnetic water treatment on the turbidity of TiO2 solution

This experiment was done to check if the MWT can change the turbidity of the TiO2 solution.

The reason for the turbidity experiment is to check if the dissolved solids (TDS) are influenced due to MWT. 152 mg dried TiO2 was dissolved with 30 liters (5.1 mg/l) of deionized water.

This solution was treated with MWT for 6 hours and 100 ml samples were taken for turbidity analyses at the beginning of the experiment and once an hour during the experiment. The turbidity measurement was done with Hach 2100N IS Turbidometer (Hach Company, Loveland, Colorado) according to its operation manual. A clean <0.1 NTU vial was cleaned with a lint-free soft cloth to remove all the fingerprints and spots. A small bead of synthetic oil was rubbed with an oilcloth from top to bottom of the vial. The rubbing with the oilcloth was done carefully to leave the vial almost dry. Then with the sample, the vial was placed into the device to get the turbidity data. For every sample, the experiment was done three times and the mean value of the turbidity value was calculated.

4.2.3 The effect of magnetic water treatment on particle charge of TiO2

5 mg dried TiO2 mixed with 30 liters of deionized water (0.17 mg/l) was treated with MWT for 11 hours to observe its possible neutralizing effect on particle charge. The 30 ml samples were taken for particle charge analyses in the beginning and once an hour.

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4.3 PULP AND PAPER MILL WASTEWATER EXPERIMENTS

90 liters of untreated pulp and paper mill wastewater was collected from Savon Sellu Oy (Kuopio, Finland). The sample was preserved in cold storage (4 °C) for the experiments. The sample was viscous and brown. Chemical oxygen demand (CODCr) of pulp and paper wastewater was measured with the HACH DR6000 spectrophotometer (Loveland, Colorado, United States) with LCK 1014 method the analyses range of which is from 100 to 2000 mg/l.

For the experiment, the LCK 1014 cuvettes were inverted a few times to mix all the sediments in the suspension, and 2.0ml of the sample was pipetted into the cuvettes. After closing the cuvettes properly, they were inverted again several times to mix all the samples and solution properly, and the outside of the cuvettes was cleaned with a dust-free cloth. Then the cuvettes were heated in a heat block HT200S (Hach. Loveland, Colorado, United States) at 170°C for 15 minutes. After that procedure, the CODCr was measured with a DR6000 spectrophotometer.

For the CODCr experiments, raw pulp and paper wastewater were diluted 5, 25, 50, and 100 times with deionized water.

4.3.1 JAR tests for pulp and paper mill wastewater

JAR tests were done to find out the optimal coagulant and concentration of coagulants for the MWT experiments. Four different coagulants were used: ferric sulfate PIX-322, polyaluminium chlorides, and a cationic polyacrylamide Superfloc C-577. All coagulants were manufactured by Kemira (Espoo, Finland). Pulp and paper wastewater sample was diluted 10 times and 100 ml was taken in each beaker, in which 100 times diluted coagulant was added and mixed with a magnetic stirrer first with 300 rpm for 1 min for flash mixing and then with 30 rpm for 30 min and then the samples let stay for 1 hour for settlement. The experiment was done three times with 200µl 300µl and 400µl of 100 times diluted coagulant each time. Turbidity was measured after a one-hour settlement as explained in chapter 4.2.2. The sample for the turbidity test was collected carefully from the upper portion of the beaker.

4.3.2 Turbidity and CODCr experiment of pulp and paper wastewater with MWT

The optimum coagulant at the optimum concentration obtained from the experiments explained in chapter 4.3.1 was used in these test.15 liters of 10 times diluted pulp and paper wastewater

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sample was treated for 4 hours with MWT, where 45 ml of 100 times diluted (300 µl/100 ml) Superfloc C-577 was used as a coagulant. Coagulant was added in the reactor during the experiment, there was no stirring because, During the MWT, the water circulates from the reservoir to the magnetic reactor. The sample was collected once an hour from the magnetic reactor to check turbidity as explained in chapter 4.2.2 and CODCr reduction as explained in 4.3. A control experiment with the same parameters but without MWT was also done to check if the CODCr and turbidity result alters.

4.3.3 MWT with Superflock C-577 polymer titrant to determine the optimum time for pulp and paper mill wastewater

15 liters of 10 times diluted pulp and paper wastewater sample was treated with MWT for five hours. 30 ml sample was collected once an hour of treatment and the particle charge was measured with a PCD device using 100 times diluted Superflock C-577 (300 µl/100 ml) as polymer titrant. The experiment was done to find out the optimum time to use the coagulant for a pulp and paper wastewater sample in MWT. A 4-hour control experiment with the same parameters but without MWT.

4.3.4 27-hour MWT with Superfloc C-577 of pulp and paper mill wastewater to understand particle charge movement

Considering the results of the previous experiments this experiment was done for a longer time (27 hours) to understand the particle charge movement and how their zero charge state shift from positive to negative or negative to positive. For this experiment, 15 liters of 10 times diluted pulp and paper wastewater sample were used and 100 times diluted Superfloc C-577 was used as polymer titrant as explained in chapter 4.3.3.

4.3.5 Pollution load experiment

The experiment was done with 50 times and 100 times diluted pulp and paper wastewater sample to understand how pollution load affects the MWT and if MWT works better with the less polluted (100 times diluted) sample than with the higher polluted (viscous and thick 50

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times diluted) sample. Both samples have experimented separately and all parameters excluding the dilution were the same. Both samples were treated for 4 hours separately in the magnetic reactor. A 100 ml sample was collected once an hour and it was analyzed for particle charge with a PCD device as explained in Chapter 4.1. 100 times diluted Superfloc C-577 was used as a polymer titrant.

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5 RESULTS

5.1 TITANIUM DIOXIDE EXPERIMENTS

5.1.1 Effect of salt on particle charge of TiO2 solution

In comparison between figures, 10a - 10e particle charges were similar and positive at a lower pH level. All the graphs reached the isoelectric point at around pH 5 and particle charge results are negative with higher pH. Since all the graphs are showing the same results at higher and lower pH values, it is proved that salt like KCl does not influence the particle charge result.

Figure 1: Particle charges (mV) of the 0.34mg/l TiO2 solution as a function of pH when the KCl addition was a) 1.3mg/ml, b) 1.7mg/ml, c) 2.1mg/ml d) 2.4mg/ml and e) 0mg/ml in the control experiment.

-1000 -500 0 500

0 5 10 15

Particle charge mV

pH (a)

-1000 -500 0 500

0 5 10 15

Particle charge mV

pH (b)

-1000 -500 0 500

0 5 10 15

Particle charge mV

pH (c)

-1000 -500 0 500

0 5 10 15

Particle charge in mV

pH (d)

-1000 -500 0 500

0 5 10 15

Particle charge mV

pH (e)

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5.1.2 Effect of magnetic water treatment on the turbidity of TiO2 solution

From figure 11, we can see that turbidity increased slightly after one hour of MWT and remained almost constant in the whole treatment process. The sixth-hour turbidity was the same as 1^st hour’s turbidity result.

Figure 2: Turbidity value of untreated and after magnetic water treatment for every hour from 1 to 6 hour of TiO2 solution

5.1.3 The effect of magnetic water treatment on particle charge of TiO2

From figure 12, we can see that after 1-hour treatment particle charge of the TiO2 solution was doubled, and it started to reduce after that. Particle charges are completely neutralized, i.e. zero charges were reached between 7^th to 8^th-hour magnetic treatments. The particle charge did not change in the control experiment (figure 13).

Figure 3: Particle charges of TiO2 in 11hour magnetic water treatment, untreated one is without MWT

0 5 10 15 20 25 30 35 40

untreated 1 2 3 4 5 6

turbidity (NTU)

Hours

-50 0 50 100 150 200 250 300

untreated 1 2 3 4 5 6 7 8 9 10 11

Particle charge (mV)

Hours

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Figure 13: Particle charge of TiO2 in the control experiment without MWT

5.2 PULP AND PAPER MILL WASTEWATER EXPERIMENTS

The pulp and paper wastewater contained a high concentration of organic matter. The raw wastewater and 5 times diluted pulp and paper wastewater samples were too strong for CODCr

measurements. CODCr value could be calculated from 25- and 50-times diluted samples. The mean CODCr value of the pulp and paper wastewater was 12 600 mg/l. CODCr values of different dilution factors of pulp and paper mill wastewater are shown in table 1.

Table 1: CODCr value of pulp and paper mill wastewater

The Dilution factor of the pulp and paper mill wastewater sample

CODCr (mg/l) Result

Raw Over range -

5 times diluted Over range -

25 times diluted 523 13075 mg/l

50 times diluted 243 12150 mg/l

Mean 12 613 ̴ 12 600 mg/l

0 20 40 60 80 100 120 140 160

1 2 3

Particle charge (mv)

Hours

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5.2.1 Jar tests for pulp and paper wastewater

As pulp and paper wastewater was very thick and viscous even as 10 times diluted, PIX-322 and PAX-60 could not coagulate particles in the wastewater and therefore no settlement was found (Table 2). PAX-XL 100 coagulated and settled the particles but at a higher concentration than Superfloc C-577 did.

Table 2: Turbidities of 10 times diluted pulp and paper wastewater with different coagulants at different concentrations.

Coagulant (100 times diluted)

Concentration (µl/100 ml) Turbidity (NTU)

PIX-322 200 There was no flocculation as

a result, no settlement either.

300 400

PAX-60 200 There was no flocculation as

a result, no settlement either 300

400

PAX-XL 100 200 There was no flocculation as

a result, no settlement either.

300

400 20

Superfloc C-577 200 6

300 9

400 7

5.2.2 Turbidity and CODCr experiment of pulp and paper wastewater with MWT

In figure 14 it is shown that after one-hour MWT with Superfloc C-577, turbidity and CODCr

were slightly reduced compared with the untreated samples. After two-hour treatment turbidity and CODCr were increased. After 3^rd and 4^th-hour treatment, CODCr and turbidity fluctuated and after four-hour treatment, CODCr and turbidity increased compared with the initial CODCr and turbidity.

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Figure 14: Turbidity and CODCr of 10 times diluted pulp and paper wastewater with Superfloc C-577 as a coagulant in 4-hour magnetic treatment. The first column (untreated) is without magnetic water treatment.

In figure 15 in the control, the experiment result was the same as figure 14 in case of turbidity.

Where turbidity decreased during the 2^nd hour but starts to increase during the 3^rd hour and 6^th- hour turbidity was higher than the initial turbidity. In the case of CODCr resultsin figure 15, results are fluctuating which also happens in figure 14.

Figure 15: Control experiment for turbidity and CODCr without magnetic water treatment with Superfloc C-577 as a coagulant for 6 hours

800 810 820 830 840 850 860 870 880

0 2 4 6 8 10 12 14 16 18 20

Untreated 1 2 3 4

CODcr

turbidity

hour

turbidity in ntu CODcr in mg/l

800 810 820 830 840 850 860

0 1 2 3 4 5 6 7 8

1 2 3 4 5 6

CODcr

Turbidity

Hour

turbidity in ntu CODcr in mg/l

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5.2.3 MWT with Superfloc C-577 polymer titrant to determine the optimum time to add coagulant for pulp and paper mill wastewater

In figure 16 it was shown that the first-hour treatment required less polymer titrant than longer MWT to reach zero charges. Three-hour treatment required the polymer titrant most. In the control experiment without MWT (figure 17), samples from all time points needed the same amount of polymer titrant for the zero charges.

Figure 16: Zero charge state of the pulp and paper mill wastewater particles during five-hour MWT with superfloc C-577 as polymer titrant, the untreated graph is without MWT.

Figure 17: Zero charge state of pulp and paper mill wastewater with Superfloc C-577 as a polymer titrant during the control experiment, no MWT was used for 4 hours.

-300 -200 -100 0 100 200 300 400

0 1 2 3 4 5 6 7 8 9

Superfloc C-577 (mg/l)

untreated 1 hour 2 hour 3 hour 4 hour 5hour

-250 -200 -150 -100 -50 0 50 100 150 200 250

0 1 2 3 4 5 6 7 8 9

Superfloc C-577 (mg/l)

1 hour 2 hour 3 hour 4 hour

Feasibility of magnetic water treatment on industrial wastewater