**3.1 Effects of magnetic field (β)**

 The column experiments consisted of LF-EMF coiled columns and river water, which was varied to analyse the effects of the magnetic field exposure on the removal of *E. coli*. Varying magnetic field intensities of 2, 4, 6, 8 and 10 mT reacted with the water samples at 50 and 100 mL/min flowrates. The data on the initial concentration of *E. coli* and the percentage of removal from the water samples were obtained.

 Removal rates of *E. coli* in the water samples were measured at five different magnetic field intensities for column test. The diameter of column test was 50 mm, which underwent 6 hours of LF-EMF exposure at 50 mL/min (Q1), and 100 mL/min (Q2) water flowrates. **Figure 6** illustrates the percentage of *E. coli* removal after LF-EMF exposure. The maximum removal efficiency of *E. coli* in column test was 100% at 6, 8, and 10 mT of magnetic field exposure for Q 1. However, percentage of

*Removal of Escherichia Coli Using Low-Frequency Electromagnetic Field in Riverbank Filtration DOI: http://dx.doi.org/10.5772/intechopen.85296* 

#### **Figure 6.**

*Percentage of E. coli removal of column test (ᴓ = 50 mm) for Q 1 and Q 2.* 

 *E. coli* removal for Q2 was 67% at 2 mT, and 100% of removal at 10 mT of magnetic field exposure. These results indicated that the *E. coli* in the sample of water that was exposed to the LF-EMF was statistically significantly decreased. The magnetic intensity of the LF-EMF changed the characteristic responses for *E. coli* bacteria [24].

 From **Figure 6**, the results obtained demonstrated that column test achieved 100% *E. coli* removal, which increased with the increase of magnetic field exposure at Q1 and Q2. These results indicated that the magnetic field intensity was affected by the surface area of the coiled column. The 50 mm diameter of column test was effective for *E. coli* removal by LF-EMF exposure. This situation is possibly due to the influence of magnetic flux at various flow velocities, where the magnetic field killed the *E. coli* during the exposure at the surface area of the column. Thus, these results indicated that the removal of *E. coli* in column test was 100%, and also showed that the increase of *E. coli* removal is dependent on the increase in intensity of magnetic field along with other parameters of the column.

#### **3.2 Effect of contact time in column test**

In order to investigate the effect of LF-EMF exposure for varying durations of 2–6 hours on the removal of *E. coli*, the treatment conditions of exposure intensity were varied from 2 to 10 mT LF-EMF in column test. **Figure 7** illustrates the experimental results of the LF-EMF exposure hourly. The results demonstrated that the removal of *E. coli* approximately increased with the longer of exposure time. The

**Figure 7.**  *Effect of time on removal of E. coli (Ø = 50 mm).* 

percentages of removal in column test achieved 100% at 4 hours of treatment at 10 mT of magnetic field intensity at Q1 and Q2. **Figure 7** is seen below.

 The optimal time of magnetic field exposure on column test for *E. coli* removal is shown in **Figure 7**, which was at 4–6 hours exposure for both Q1 and Q2. The removal was 100% from 4 to 6 hours of 10 mT of LF-EMF exposure. These results indicated that the velocity (*V*) of water samples through column test was effective. Therefore, the removal rates of *E. coli* were constant after 4 hours of contact time with the magnetic field for Q1 and Q2. The magnetic field decreased the concentration of *E. coli*, and thus suggests that it affects the behaviour of *E. coli*. Strašák et al. reported that the inhibitory effects on *E. coli* concentration were increased with length of exposure [55]. Also Gaafat et al. applied extremely LF-EMF for 6 and 16 hours on the *E. coli*, and found that an exposure period of 6 hours decreased the concentration of *E. coli*, but after a 16-hour exposure period, they became more resistant towards it.

 The effect of the exposure to LF-EMF at 2–10 mT on *E. coli* removal was determined by experimental results performed on the entire data for column test with water flowrates of Q1 and Q2. This effect generally depended on the magnetic field intensity and time of exposure [56], whereby the significant effect on *E. coli* removal was increased according to exposure time. From the experimental study, the R2 results gave practical importance on exposure time for the removal of *E. coli*. From the results, it was found that the removal of *E. coli* and exposure time on column test were significantly correlated with high R2 values for 2–8 mT of LF-EMF. However, at 10 mT of magnetic field intensity, the non-linear regression with polynomial R2 at second order for Q1 was 0.9721, while R2 for Q2 was 0.9958. These results showed that the *E. coli* removal at 10 mT exposure was 100% after 4 hours of exposure.

*Removal of Escherichia Coli Using Low-Frequency Electromagnetic Field in Riverbank Filtration DOI: http://dx.doi.org/10.5772/intechopen.85296* 
