An Assessment of the Use of Static Magnetic Field for Sodium Fluoride Defluoridation and Removal of Escherichia Coli and Rotavirus Pathogens from Water

. The use of chemicals such as chlorine in water purification leaves harmful biproducts in the water while filtration techniques such as reverse osmosis, ultrafiltration, nanofiltration, and forward filtration are costly and require external energy for their operation. Ceramic water filters that would have addressed these issues are brittle and incapable of filtering viruses. In this work, we report on the efficiency of water purification using a 0.8 T static magnetic field from permanent magnets in defluoridation of sodium fluoride and purification of Escherichia coli , and Rotavirus. The contaminated water was circulated at varying velocities of 0.1 ml/s to 2.0 ml/s at an ambient temperature of 16.0 °C to 40.0 °C for 0.5 hours to 9.0 hours. It was found that when ionized water was circulated under the static magnetic field for nine hours, its pH was lowered by 9.7% and the velocity of water in circulation did not affect the purification efficiency. The static magnetic field equally lowered the replication of Escherichia coli and Rotavirus by 9.8% and 7.1% respectively. Furthermore, 14.1% of defluoridation of water was also achieved. Thus, a 0.8 T static magnetic field was not able to purify water to recommended levels.


Introduction
A magnetic field can be employed in water treatment by circulating contaminated water through a dynamic or static magnetic field and it has been used in water treatment for almost two centuries now but its development has been hampered by negative criticism [1].Though there have been controversial views over the performance of the magnetic treatment, their continuous increase in the market seems to point out its capability in water purifications.Many assertions over the effects of magnetic fields in water have been made especially in changing the physicochemical properties of water, surface tension, pH value, and chemical equilibria [2], [3].Flowing and static water were tested by Tombacz et al (1991) [4] using magnetic fields ranging from 0.1 T to 0.8 T. It was found that the effect of MF is best observed in flowing water.Similar results were observed by Kobe et al (2001) [5] when they used a magnetic flux density of 0.5 T to carry out their experiments.Chang and Weng (2006) on the other hand, showed that when water flows through a magnetic field of 1.0 T to 10.0 T the hydrogen bond gets enhanced by 34%.They attributed the hydrogen-bond strength enhancement to increased electron delocalization in the hydrogen-bonded molecules.It has also been observed by many researchers that magnetic induction increased with an increase in the exposure time while the flux of water exerts minimal influence [7].There have also been reports of the magnetic field being used in scale reduction [8] of calcium carbonate [5], [9]- [11], and calcium sulfate from water pipes [12].Despite the many studies done on the effect of MF on water, there is limited research focused on its applicability to water purification.However, pathogens such as Escherichia coli [13], [14], Leclercia adecarboxylata, and Staphylococcus aureus [13] have been investigated outside water and MF was reported to reduce their multiplication.However, the effect of microbe (in water) multiplication has not been investigated.It is for the aforementioned reasons that we investigate the application of static magnetic in the development of an effective point-of-use water purification system.

Escherichia coli Test
To prepare the 10 6 CFU/ml E. coli solution, first, the MacConkey Broth Purple w/ BCP solution was prepared by dissolving 40.0 g into 1.0 L of distilled water, then boiled to dissolve into a purple solution.The samples were classified as either double or single strength.For purposes of minimizing contamination, the Durham tubes and their contents were also autoclaved at 121.0 º C for fifteen minutes.
At the same time, the E. coli was inoculated from the stock to the plate and incubated at 37.0 º C for 18.0 to 24.0 hours under Cystine-Lactose-Electrolyte-Deficient Agar (CLED agar).Later the plate was visually examined for the growth of characteristic colonies.Several colonies were then taken from the culture emulsified in sterile distilled water to obtain a suspension of 10 8 concentrations of the colony-forming unit, CFU/ml.The solution was then diluted to form ten liters of 10 1 CFU E. coli solution.At an ambient temperature of 24.0 o C, the 10 1 CFU/ml solution was made to circulate in a 1.5 cm (diameter) pipe under a static magnetic field of 0.8 T provided by ten one Tesla Neodymium cylindrical permanent magnets of 1.5 cm (diameter) by 4 cm thickness).The magnets were clipped on a plastic pipe, 10.0 cm apart).The water circulation time ranged from 0.5 hours to 9.0 hours.The concentration of Escherichia coli was noted after every half an hour and the concentration of Escherichia coli in water was determined using ELISA.Before the contamination of the ionized water, the effect of the static magnetic field on the pH of the ionized water was studied by circulating the water in the presence and absence of the magnetic field for 9.0 hours and the pH was noted after every 30.0 minutes.Then a constant volume of 10.0 liters of different solutions of the contaminated water was made to circulate (one at a time) through the pipe at varying velocities of 0.1 ml/s to 2.0 ml/s.Later the ambient temperature under which the experiments were carried out varied from 16.0 °C to 40.0 °C in steps of 2.0 °C and the concentration of the contaminants were noted using ELISA.

Rotavirus
Attenuated Rotavirus of 10 6 viral particles/ml was mixed in ionized water to form different Rotavirus concentrations of 10 1 viral particle/ml to 10 5 viral particle/ml.The solutions were then made to pass through the magnetic field.After circulation, the purified water was collected in sterile 50.0 ml bottles.Two drops of the water were mixed with the buffer, shook, and left for five minutes.Two drops of the sample were placed in the sample well while the remaining were stored at -20.0 °C and were defrosted to room temperature when needed.The content was left for 15.0 minutes at the sample well of the ELISA test.The positive result showed two lines at the control and the reaction site while the negative result only showed one single line at the control site.Later the absorbance of the samples was also determined using the standard curve plotted from the known samples.

Sodium Fluoride Test
To determine the defluoridation abilities of the static magnetic field, 50.0 g of sodium fluoride (Sigma-Aldrich, St. Louis) of analytical standards were dissolved in 1.0 liters of water to form a highly concentrated 500.0mg/l NaF solution whose pH was noted.For purposes of determining the efficiency contaminant removal efficiency of the field, the contaminated solutions were diluted separately to different concentrations of sodium fluoride, ranging from 50.0 mg/l to 5.0 mg/l.Each suspension was then passed through the 0.8 T as described in Section 2.1 and the samples were collected in sterile 50.00 ml bottles.The pH of samples with known concentrations was used to determine the concentration of the unknown samples using a standard curve.

ELISA Test
To prepare the diluent, 0.5 g of peptone was mixed with 4.25 g of NaCl uniformly, then dissolved in 500.0ml of ionized water.The mixture was stirred and autoclaved at 121.0 °C for 15.0 minutes obtained and cooled.Three drops of the prepared diluent were put in a sterile test tube and mixed with 25.0 ml of filtered water.One drop of the content was added to the ELISA stripe and left for fifteen minutes to allow the antigen to react with the sample.After five minutes the positive samples showed two lines at the control and test points while the negative test only showed one line at the control.The absorbance of the positive samples was taken and compared with the absorbance of the known samples using a standard curve.

Fig 1(a)
shows the pH of different water solutions circulated in the presence and absence of the 0.8 T static magnetic field at an ambient temperature of 24.0 °C.The pH of the ionized water was not affected when the water was circulated in the absence of the static magnetic field.However, the presence of the magnetic field reduced the pH of water by 9.8% after 9.0 hours of circulation.
The acidity of water increased with an increase in circulation time.Ionized water contaminated with Escherichia coli showed a decrease in pH both in the presence and absence of the static magnetic field.However, the pH of water contaminated with Rotavirus was not affected when samples were circulated in the presence and absence of a magnetic field.The pH of fluoridated water was also not affected when the solution was circulated in the absence of a static magnetic field but in the presence of the magnetic the pH dropped from 8.2 to 7.84 after 9.0 hours of circulation The replication curves of E. coli and Rotavirus at the ambient temperature of 24.0 °C are shown in Fig 1(c) and (d).The multiplication of E. coli (Fig 1 (c)) was characterized by a power curve in the presence and absence of the static magnetic field.The multiplication of the bacteria was slow in the first two hours and then increased steadily as the time of circulation increased.However, the multiplication of Rotavirus took the form of a linear curve with a positive slope.Similarly, the magnetic field slowed the multiplication of Rotavirus as shown in Fig 1 (d).The velocity of water was found to have a very minimal effect on the efficiency of E. coli purification from water as shown in Table 1.Similar results were observed in Rotavirus.And the velocity of water had equally a very minimal effect on the efficiency of defluoridation of water.
The efficiency of purification of water was found to increase with the time the water was circulated under the magnetic field as shown in Fig 3.

pH
The pH of the ionized water decreased with an increase in the circulation time as shown in Figure 1 (a) because the static magnetic field made the water acidic by enhancing its OH bond [6], [15].The pH was found to reduce most in fluoridated water because NaF forms Na + and F -ions in water aligned themselves in the presence of the external magnetic field causing the decreased pH.Escherichia coli on the other hand produced acidic wastes (Shiga toxin) that reduced the pH of its solution [16]- [18].However, Escherichia coli reused some of the acidic wastes in proton form for transportation of minerals, which explains why the observed slope of pH is lower than the one observed in NaF.The pH of the water solution containing Rotavirus coincided with the one of ionized water as shown in Fig 1(b) because the multiplication of RNA viral particles involves the mechanism of transporting protein which leads to the build-up of viral proteins in viroplasms [19] and does not affect the pH of its surrounding.On the whole, a static magnetic field was found to alter the pH of the water just as was reported in the literature [20].

Time
The replication of Escherichia coli was found to increase with an increase in circulation time as shown in Fig 1(c) because the cells of the bacteria subdivide continuously to form new cells [21].The presence of a static magnetic field slowed down the replication of the bacteria because the production of the oxygen free radicals in water by magnetic fields made the water slightly acidic by enhancing the hydrogen bond and killing the pathogens [22].In the presence of a magnetic field, the molecules aligned themselves to the applied magnetic field [23], which in turn affected the embedded ion channel altering their activation kinetics [23], [24].Furthermore, the magnetic field affected the behavior of the long-lived ionic quantum states causing an imbalance in ion-protein stability which resulted in the death of pathogens [25].The replication of Rotavirus also increased with time due to similar reasons as shown in Fig. 1 (d) and the presence of the static magnetic field also slowed down its multiplication.It is this same acidity that influenced the pH of the fluoridated water observed earlier in Fig 1(a).The decrease in the concentration of the contaminants can also be attributed to magnetic memory and their magnetic susceptibility.When the magnetic susceptibility of a certain material exceeds a certain level the organism may die or show growth reduction due to particle aggregation and change in pH of water [26], [27].

Temperature
Fig. 2 shows that an increase in temperature increased the replication of E. coli.An increase in temperature increased the enzyme activities which in turn increased the protein activities essential for the E coli growth.This explains why the replication of the bacteria increased continuously from 16.0 °C to 37.0 °C.However, from 37.0 °C to 40.0 °C the protein phases became saturated and there was no increase in the number of bacteria when the temperature of the water was increased because the activities of the bacteria are enzyme sensitive.The growth of Rotavirus on the other hand was found to decrease with an increase in temperature just as was reported in the literature [28].An increase in the ambient temperature caused the outer envelope of the virus to melt to a liquid phase thereby slowing down the multiplication of the virus.This liquid phase allowed other elements of water to mix with it causing the death of the virus.At the same time, an increase in temperature increased the pH of fluoridated water because more and more NaF was dissolved in water and increased its pH.

Velocity of water
Table 1 shows that the flow rate of water had very little effect on the replication of E. coli and Rotavirus because diamagnetism changes observed in this work are initiated by atomic orbital states of the material and the applied static magnetic field.Hence the flow rate of water does not affect the replication of the living organisms [29], [30].

Purification Efficiency
In the first five hours, the purification efficiency of E. coli and Rotavirus increases rapidly as shown in Fig. 3 because the organisms had not adjusted to living with the effects of the magnetic field.These effects include reduced pH in water, instability in the ion-protein ratio in the embedded ions of the organism, and the change in the kinetics of the organisms' stability.Further, exposure to the magnetic fields allowed the pathogens to adjust to these changes resulting in a reduced purification rate.Similarly, the defluoridation curve was steep during the five hours because most of the NaF molecules were not aligned to the applied static field.But as the fluoridated water continued circulating the molecules got fully aligned to the applied field causing increased acidity of water.Using the optimal temperature, (37.0 °C for E. coli, 16.0°C for Rotavirus, and 40.0 °C for NaF), and a time of 9.0 hours the magnetic field was able to reduce NaF by 14.1%, E. coli by 9.8%, and 7.1% Rotavirus.The concentrations of the contaminants after nine hours of purification were 8.6 mg/l, 4.1E 5 CFU/ml, and 4.0E 3 viral particles per liter of NaF, Escherichia coli, and Rotavirus respectively.The above concentrations are way above the recommended levels for safe drinking water.E. coli and Rotavirus should be non-detectable in any 100.0ml of drinking water as recommended by the World Health Organization and sodium fluoride should range from 0.5 mg/L to 1.0 mg/L.Thus, purification of water from the three contaminants to recommendable levels using a static magnetic field from permanent magnets was not achieved.

Conclusion
This work has shown that the use of a static magnetic field in water purification reduced NaF in water by 14.1% and slowed the growth of pathogens by 9.8% and 7.1% in the case of Escherichia coli and Rotavirus respectively.However, this technique does not defluoridate, and purify water of Escherichia coli and Rotavirus to recommended levels.Thus, a static magnetic field should not be used independently in water purification but should be used in conjunction with other methods to purify water to recommendable levels.More research should also be done in this area to improve the efficacy of water purification using magnetic fields

Fig. 1 .
Fig. 1.(a) shows the pH value of different water solutions circulated in the presence and absence of a 0.8 T static magnetic field at an ambient temperature of 24.0 °C.(b) shows the magnified part of the graph that is highlighted in (a), (c) shows the replication curves of Escherichia coli and Rotavirus (b) Pathogens in the presence and absence of the static magnetic field at the same ambient temperature of 24.0 °C.The concentration of Escherichia coli in water shown in Fig 2 was found to increase with the increase in temperature up to 37.0 °C when the concentration was optimized.However, the concentration of Rotavirus decreased with an increase in temperature.And the pH of fluoridated water increased with an increase in temperature.

Fig. 2 .
Fig. 2. The variation of E. coli concentration, Rotavirus concentration, and pH of Rotavirus with the temperature at the velocity of 2.0 ml/s.

Fig. 3 .
Fig. 3.The plot of the contaminants' purification efficiency of contaminants against time used to purify the water at an ambient temperature of 24.0 °C

Table 1 .
The pH of contaminated water under different velocities.