Sewage Water

The design of magnetic systems for sewage systems allows for installation of a slot magnetic system at the main system entrance. You can improve the functionality of the sewage system in the following ways:

The rate of solid sedimentation accelerates by 1.5-2 times,
Collection of fine fractions improves by an average of 20%,
Dissolved solids in the clarified water decrease by 15-25%,
Biological oxygen demand goes down by 10-15%,
Sludge digestion time reduces by 30%,
The probability of blocking the tank filter drops nearly two-fold.

Below is an explanation of how and why magnetic systems can benefit water treatment facility operations.

Understanding the Magnetic Field Impact on Water Dispersed Systems

Magnetic treatment alters the physical and chemical properties of water and aqueous solutions. Hydration of salt ions and other impurities slides down and improves technological characteristics of the water treated by magnetic field, i.e. better salt solubility, kinetic changes in salt crystallization and accelerated coagulation. Water structural modifications induced by magnetic treatment have been endorsed through many years of research from scientific societies in Russia, United States, Belgium, and Canada.

The research has shown that all structural changes of water dispersed systems treated by magnetic fields have to do with the ions of substances present in the water, colloidal particles of considerable magnetic susceptibility and water changes. Commencing with the theory that links structural changes of water dispersed systems to ion formation, the magnetic field affects the ions making their way through it and brings about the Lorentz forces, which can be calculated by way of the following equation:

F = K • q • v • H • sin a, (1) given that, K - coefficient of proportionality; q - ion charge; v - ion velocity; H - magnetic field strength; a - angle of magnetic field direction with the ion flow.

The equation (1) shows that the Lorentz forces intensify with the growth of ion charge, magnetic field strength, flow velocity and perpendicularity of ions crossing magnetic field lines. The Lorentz forces act on positively and negatively charged ions (cations and anions) and make them diverge in opposite directions.

Magnetic field energy E per volume unit can be described in the following manner:

E = µ H 2 / 2, (2) given that, µ - magnetic susceptibility of the medium.

For ions of short radius (Ca +, Mg +, Li, etc.) Δ E is greater than 0. This is in conformity with the adhesion pattern of closest molecules (positive hydration). Ions of long radius (Cs, K, Cl, Br, etc.) have Δ E < 0 (negative hydration). Water molecules prove to be more mobile when next to such ions. Therefore, on falling into the water the ion is hydrated and alters the translation motion of the nearest water molecule.

Impurity ions may be a part of translation travel independent of solution molecules and in their presence. Translation movement is a galloping motion of particles. A change of translation motion in the liquid corresponds to a change of mean number of local discharges in the liquid. This will lead to a shift in liquid alkalinity.

Fig. 1 shows a typical graph of (ΔV' - ΔV)/ΔV - ion concentration (CaCl2, KCl, MgCl2) with ΔV' being density of aqueous solution in the mode of magnetic treatment and ΔV - same for usual water.

As is seen, (ΔV'-ΔV)/ΔV rises as the ion concentration increases. However, from 30 mg-eqv./l onwards the growth of (ΔV- ΔV)/ΔV as a concentration fraction retards.

Fig. 1. Relation between (V' - V)/V and ion concentration of CaCl2 (1), KC1 (2) and MgCl2 (3).

Treatment of water dispersed systems by an outward magnetic field, creates a precession of individual electron shells and polarization of electron clouds in molecules occurs. The latter gains induced magnetic moment anti-parallel to outside magnetic field. Against the backdrop of these developments, the energy of hydrogen bonding undergoes changes. The bonds are "bent" and partially broken which causes re-alignment of molecules and, therefore, alterations of water structure. This process, brings about changes in density, surface tension and viscosity.

Polarization of electron clouds intensifies as the strength of magnetic field grows. At the same time, deformations in hydrogen bonds go up with a larger amount of molecules, which have shifted from the equilibrium state in the lattice points out to fill the voids. As a result, the density of water builds up.

A number of strong bonds between water molecules increase. The kinetic energy of water molecule oscillations near temporary equilibrium during magnetic treatment does not change (constant temperature). A rise in the relative amount of strong bonds between molecules causes a reduction of ionic water product. However, the structure formed during motion in the magnetic field cannot be stable. On exiting the scope of magnetic field, this structure tends to regain its former condition that shows a minimum of energy and a maximum of hydrogen bonds between molecules in specific environment.

Distillated water has equal molecules and, consequently, observed differences of physical properties prior to and following magnetic treatment are quite insignificant and depend weakly on the magnetic field strength. Adding salts and rising charged ions upsets the water structure to a greater extent as the solution concentration thickens. In this case, the cation force fields pull the electron pairs away from the nearest water molecule oxygen, which results in an additional layer of eight electrons around the cations. In other words, free electric levels in the cations are filled making the latter more or less bonded with water molecules, which reside next to the ion (close hydration). The structure of water molecules is tampered with not only in the adjacent layers but also in those next to the hydrated ion owing to polarization.

Structural water changes set off by addition of dissolved substances (impurities) can be of different degrees and are dependent upon the value and nature of charge distribution in ions (particles), their sizes, configuration and other reasons. Impurities enter the voids of the water hexagonal cage with stabilizing or destroying effects subject to the size of additives. That is why both the structure and properties of water dispersed systems hinge upon the nature of the dispersed phase, concentration and temperature.

When a magnetic field is applied from outside, water dispersed systems have a precession of individual particle shells in the water. Magnetization also initiates polarization of electron clouds in water molecules. However, unlike pure water with nearly same precession in identical atoms because of equality of all molecules, identical atoms do not precede at the same interval in solutions. This is caused by diversified polarization of molecules by ion electric fields. There is also a different shift of electric shells of water molecules that envelop the ions.

Magnetic fields are known to create the asymmetry of hydrated shells due to the effect on water molecules situated around the ion (near and far). Likewise, magnetic fields weaken the bonds between certain ions and amplify others. These changes result in conditions for ionic associates or crystal embryos. The reversal of magnetic flux and, consequently, modified direction of ion movements greatly facilitate the formation of ion pairs and more sophisticated aggregates. This can be attributed to a higher probability of attracting particles to close with one another.

The theory of magnetic field impact on technological processes for water treatment falls into two main chapters:

Crystallization at magnetic water preparation and
Impurity coagulation in water systems.

Crystallization is the formation of crystals when a substance enters a transition phase from less stable thermodynamic state into more steadfast condition.

Equal chemical potentials are the principal consideration for thermodynamic phase equilibrium:

xk = xc, (3) where, xk - substance potential in crystalline condition; xc - same substance potential in solution.

Equilibrium departure is the thermodynamic driving force of crystallization. When xc - xk > 0, there is a crystal formation and growth. For xc - xk < 0, decrystallization occurs.

A number of crystalline aggregates formed per unit of volume/time shall be computed with the following equation:

given that, ∏- density of atoms in a crystal; ∏3- a number of particles in embryo's surface layer; Z - probability of adding one particle to the crystal embryo per unit of time; n - a number of particles in embryo's surface layer; A - height of potential barrier to be cleared by the system for formation of viable embryo; K - Boltzmann's constant; T - absolute temperature. For spherical embryo: given that, Ω- specific volume per one particle in a crystal; α- specific free energy of separation surface.

Given appropriate conditions, it may be expected that molecules or ions clash and set up short chains or flat molecular layers. Once the attractive force exceeds the one of repulsion, a crystal embryo is generated as an elementary particle of solids. The stability of a particle is directly related to its size. For the size in excess of the critical one, the expenditure of energy for the particle to grow would be at the lowest and in the process of constant enlargement. In case of the size less than the critical dimensions, destruction is most likely to take place. As a rule, the following pattern is observed: the more supersaturation, the less activity involved in generation of a critical embryo, the smaller embryo size and faster rates of formation. The crystallization rate is positively affected by exposure to microgroups of a new phase, which accelerate their growth to the size of stable embryos. The embryo birth and crystallization degree also depend on electric interaction between particles when the work required for embryo formation can be significantly reduced.

Magnetic field causes formation of crystal microembryos in supersaturated aqueous solutions and, therefore, influences immensely the nature of crystallization. In this particular case, the embryos are more plentiful in number and are of smaller sizes than those in the solutions untreated by magnetic field. Furthermore, magnetic fields will shorten a magnetic period of crystallization and will allow for an earlier isolation of solid phase. These changes are predominantly linked to the direct impact of magnetic fields on impurity ions. The forces acting on the ions of unlike charges are opposite in direction and will induce opposite ion motions when the aqueous solution is in transit of magnetic field.

The radius of ion movement around the force lines of magnetic field is subject to the ion weight and the Lorentz force. At the same time, the radius of ion orbit is dependent upon the magnetic field strength and the velocity of water solution passing through it.

In some cases, the radius is small enough to set off ion fluctuation. For instance, at the magnetic field strength H = 80 kA/m and the flow rate 1-3 m/s the circumference radius of calcium and sulphate ions are ~0/17 and ~0.04 mcm, respectively.

Despite negligible action of the Lorentz force, there is quite a considerable change in the nature of ion movement whereas the fluctuation of ion concentration caused by the latter is fairly noticeable. The distribution of ion concentration along the cross-section of the flow perpendicular to magnetic force lines can be defined by the equation:

given that, C - concentration of ions; σ- electric conductivity of solution; Bo - magnetic field induction; k - constant; - mean velocity of solution movement; Ha - Hartman number; η- viscosity of solution; z - coordinate of the field direction; a - flow half-width.

The edges of magnetic field present the highest probability for ion associations. It happens due to severe nonuniformity of magnetic field in its marginal areas, which favours the wave formation and the travel of ions in the direction of wave propagation. In the meantime, there will be electric field oscillations in the boundary conjugates that are likely to lead to additional fluctuations of ion concentration.

Direct effects of magnetic field on impurity ions in the water cause changes in the structure of the water system proper.

In particular, magnetic field facilitates an activation hurdle and makes it easier to yield calcium hexaqua complexes [Ca(OH2O)5]2+ and large meta-stable complexes {[Ca(H20)5]20H20}2+.

Stabilization of clustered water structures by a calcium hexaqua complex with application of magnetic field promotes the formation of extra crystallization centers in the water. Short of hexaqua complex instability, its existence is rather long. The degree of order of water structures influenced by magnetic field reduces remote ion hydration and, hence, has a favorable impact on adsorption, coagulation, etc.

Coagulation may proceed much faster if there is a hard surface in the solution since the energy required for crystal growth is much less than that needed for the birth of embryo in the solution. Crystallization takes place on the crystal surface of any given or isomorphous substance as long as the surface is capable of adsorbing the molecules or ions present in the solution. Initially, there is an adsorptive layer, which gradually builds up and, ultimately, turns into a layer of the crystalline substance.

Silica particles (for readily soluble salts) and ferrous compounds, which occur in the water as colloids are used to seed crystallization in the water when magnetic treatment is applied. Colloidal'particles of ferromagnetic iron oxides, such as magnetites, present in the water may coagulate by the action of both magnetic attraction and pandemotor forces that speed up mutual attraction of the particles. Newly born particles of the size in excess of crystal particles will absorb molecules or ions from the solution and serve as a basis for crystallization.

Colloidal centers may be activated by magnetic field with subsequent effects on the growth kinetics of hardness salt crystals. It has been found now that this phenomenon is a polyextreme function of magnetic field strength and an extreme function of water flow rate. Besides, it has also been established that after magnetic treatment of calcium bicarbonate solution, the formation of crystallization centers is more active than under usual crystallization conditions.

Coagulation is the adherence of particles to one another in dispersed systems and, especially, colloidal dispersion. This process reduces particles of a dispersed system and increases their weight. Coagulation happens under the action of molecular forces on collision of particles as a result of Brownian motion or some exterior factors. Coagulation may proceed in the form of aggregates shaped by particle coalescence and aggregate flake-like sedimentation or gel, a solid coagulation structure. The rate of coagulation may be calculated by the equation:

dn / dt = K • n2, (8) given that, n - a number of particles per volume unit; K - coagulation constant. The coagulation constant of spherical particles of various values is defined by the formula: given that, r1, r2 - radius of coagulating particles; A - number factor depending on the properties of particle surface; L - length of particle's free run; k - Boltzmann's constant; T - absolute temperature.

The equation analysis shows that K grows significantly as the particle radius ratio goes up. This is why the particles vanish rapidly in heavily polydispersed medium.

The coalescence of particles suspended in the water hinges upon the rate of hydration and the value of electrokinetic potential on the surface of particles.

The coagulation of particles depends immensely on the wetting changes of their hard surface, which are caused by magnetic field.

Magnetic treatment of water affects its wetting capacity of solid surfaces owing to changed interaction patterns of water molecules as it has been mentioned before. This "pushes" the water molecules off the surface. The benefits of water magnetic treatment are also attributive to altered adsorption of individual ions on the surface. Therefore, the surface charge undergoes changes too.

Improved wetting of hard surfaces after magnetic treatment of water enhances coagulation of suspended particles and increases aggregate instability of suspensions.

The findings of amplified aggregate suspension instability resulted from magnetic treatment are in perfect harmony with the data on adhesion enhancement of solid particles in condensed systems (sediments).

The formation of easy-to-precipitate floes with developed surfaces within the shortest possible time is of special interest to the water treatment practice. Such flakes ensure quick separation of heterogeneous systems. One of the commonly used technological methods to intensify the coagulation for water treatment is injection of chemical agents such as active silicic acid into the clarified water. However, in many cases it entails considerable consumption of the reactant. At the same time, the coagulant activity may be remarkably strengthened when treating the water solution of coagulant by magnetic field. In this case, it can be inferred from the mechanism of magnetic field impact on aqueous solutions that ionic salt associations are raised in the coagulant solution due to weakened ion hydration and some other factors caused by the positioning of outside magnetic field. Ionic associates existing in the aqueous solution may work as coagulation centers.

Ferromagnetic particles (iron ions) always present in different numbers in the treated water can have a certain influence on crystallization during magnetic water treatment. The research has shown that during magnetic treatment of water, aggregation of ferromagnetic particles emerges and accelerates the crystallization. In addition, the agglomerates of ferromagnetic particles get a coating of calcium carbonate, which can also become a crystallization centre.

Any method of water treatment pursues the general object of isolating insoluble contaminants through coalescence and fusion. The sedimentation of species is regarded as a mass process that changes in time.

Qualitative and quantitative indicators of sedimentation are greatly determined by the process kinetics, which imply the nature of velocity changes and the mechanism for separation of particles in time.

With a considerably lengthy sedimentation time, the separation zones do not vanish completely. This can be attributed to statistical factors and, primarily, collisions of particles, flow discontinuity along them, etc. Hence, the pattern for fraction distribution of various density is of statistical nature.

Wastewater is a relatively rough suspension, which contains fine and colloidal species. The water contains dissolved electrolytes and, therefore, suspended fine particles carry same electric charges that repel one another, Fine colloidal particles suspended in the water are on the constant move and resemble the Brownian motion.

Several zones emerge some time later following the start of solid sedimentation in the wastewater (Fig. 2).

The lower part has the sediments of large particles that settle in the first place at the highest rate of precipitation.

Zone 4 houses a stratum of thickened sediments with particles situated at the closest range to one another, which stops any further sedimentation. The pressure of the above-lying strata continuously compresses this section. It should be noted that part of water is gradually squeezed upwards, which makes it possible to consolidate the given layer.

Zone 3 is a transition sector. Here the particles are steadily thickened in a downward direction. Zone 2 has the water with fine-dispersed suspensions. This water is very similar to the source wastewater in terms of composition without large species, which have settled before. Finally, Zone 1 contains clarified water.

According to the above-mentioned information, compounds and ions present in the water have certain magnetic properties characterized by magnetic susceptibility that defines the capacity of ions and compounds to change their magnetic moment once magnetic field is applied from outside. Augmentation of magnetic susceptibility will enhance the magnetization of particles, induced moment and will, ultimately, better interaction between the particles. Such a process intensifies the coagulation of particles in Zone 3, which will consequently consolidate the species in Zone 4 and press additional clarified water out to Zone 1.

Operational experience of magnetic systems at various sewage plants has shown that the quantity of quickly settling particles (Im/s and above) during magnetic treatment nearly doubles. Likewise, the concentration of sediments in the suspended layer advances by 1.2-1.5 times. This will allow the convenience of increasing the capacity of sewage facilities.

2. Feasibility Studies for Adaptation of Magnetic Technologies at

According to the information submitted by Indah Water, it is understood that all Malaysian sewage plants fall into 4 categories:

Communal Septic Tanks (CST).
Imhoff Tanks (IT).
Oxidation Ponds with Pump Station (OPPS).
Extended Aeration Plants (EA).

Based on the available papers, it can be concluded that the diversity of sewage plants in Malaysia calls for individual technical solutions to customize and adapt magnetic systems to the existing facilities.

2.1. Communal Septic Tank

CST is a two-chamber settler with horizontal hydraulic flow. In the first chamber solids from the incoming sewage settle to the bottom and form a "sludge blanket". This necessitates magnetic treatment of the sewage water as early as at the first stage. The magnetic application will intensify the separation process of a heterogeneous system such as the wastewater. The partially clarified sewage proceeds to the second chamber for further sedimentation where it also should be exposed to magnetic treatment. This will facilitate coalescence and flocculation of the particles present in the water and will shorten the formation period of large flakes, which precipitate with ease. Finally, dissolved solids will also settle due to accelerated crystallization.

Thus, the magnetic techniques will secure a higher purity treatment of the wastewater, which will inevitably lower both the biological oxygen demand and total dissolved solids by 50-60% and 35-40%, respectively.

However, installation of magnetic systems online at the inlet to the CST is not expedient, for the sewage water entering the CST does not go through mechanical treatment. Therefore, it will be necessary to frequently remove the systems for cleaning, which will considerably push up the operational expenses and depreciate the operational safety of the CST. In the light of these challenges, the following options are the most acceptable for magnetic treatment of the incoming CST wastewater:

Installation of magnetic systems on the centralized water supply pipeline inlet of a residential house to treat the flow in passing (Fig. 3).
Installation of strap-on magnetic systems on the sewage outlet pipe of every residential house (Fig. 3).

#	Description	Unit	System#1	System#2	System#3
1	Unit code	-	Ut-1	Ut-2	Ut-3
2	Flange inside diameter	mm	250	100	50
3	Unit length	mm	500-700	500-700	500-700
4	Pressure limit	bar	6	6	6
5	Flow capacity	m³/hr	180	40	28
6	Temperature limit	°C	90	90	90

The detailed sketches of magnetic systems suggested for installation at the CST, Imhoff tank, oxidation pond and extended aeration plant are shown in Fig. 8, 9, 10, 11.

#	Place of Installation	Qty.	A, mm	B, mm	C, mm	D, mm
1	After Pump Station (with flange)	2	500	50	500	250
2	After Aeration Tank (with flange)	2	500	50	500	250
3	After Settling Tank	1	120	40	500	112.5
4	After Sludge Digester Tank	1	350	50	500	175

Understanding the Magnetic Field Impact on Water Dispersed Systems

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