Microorganism in drinking water sources.
An increase of pathogenic bacteria (E. coli) in river water is a concern as it is the main precursor to health hazard disinfection in conventional drinking water treatment systems. Riverbank filtration (RBF) is a non-chemical techniques and natural treatments that efficient in reducing or removing the contaminants in the water. Therefore, this study aimed to remove Escherichia coli (E. coli), and reduce the concentration with low-frequency electromagnetic fields (LF-EMF) as a component of the non-ionising radiations in RBF. This research design and construct a LF-EMF device on horizontal coiled columns that were capable of producing uniform magnetic fields in the frequency range of 50 Hz. A magnetic field density was varied at 2, 4, 6, 8, and 10 mT. The diameter of column was 50 mm, which underwent 6 hours of LF-EMF exposure at 50 mL/min of water flowrates. The maximum removal efficiency of E. coli in was 100% at 6, 8, and 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.
- electromagnetic field
- E. coli.
- river water
Water is a fundamental need, and the most abundant of resources . However, the World Health Organisation (WHO) stated that, in 2012, about 780 million people were without an adequate drinking water source . Hence, the demand for good quality and clean drinking water has increased, especially among Malaysian consumers. Raw water originating from surface water and groundwater needs to be treated before the water is made potable. According to statistics in 2017, in Malaysia, 500 water treatment plants (WTP) were in operation to treat raw water, and produced about 16,536 million litres per day (MLD) of drinking water to consumers.
Clean and safe water is one of the most pressing global health-affecting and environmental issues. Generally, in Malaysia, surface water is exposed to organic, inorganic, and microbial pathogen contamination due to poor management of septic tanks, wastewater, and agricultural runoff and earthwork products . Approximately 99% of water supply for domestic uses in Malaysia originate from surface water such as rivers and streams, while another 1% originate from groundwater . The surface water in the country has also been polluted with, for example, biological contaminants such as viruses, bacteria, and protozoa which are capable of causing illnesses in humans like bloody diarrhoea, affecting human health as well as the environment .
According to the Department of Environment (DOE) Malaysia’s annual report, 48% of the 473 rivers monitored in 2014 have been contaminated by these sources. This high percentage reflects that the water resources in Malaysia are contaminated, and the condition may continue to worsen. Among all the pollutant loads entering surface water, bio-colloids are the major pollutants attributed by wastewater discharge and surface runoff. These bio-colloids usually refer to microorganisms in the water, such as bacteria and protozoa . About 842,000 death cases involving diarrhoeal illnesses because of drinking water contamination were reported . The situation can worsen during extreme weathers such as El Nino (drought), and El Nina (floods) that have a great impact on the quality and quantity of the water resource . According to previous studies, contamination of bacteria significantly increases in surface water during these events . This poses more challenges to the authorities in delivering and providing safe drinking water via the conventional treatment system because of the low surface water level, and high pollutant loads . Therefore, to ensure a stable and safe drinking water supply, alternative methods for water management are necessary especially during extreme weather conditions.
Riverbank filtering (RBF) is an attractive option that can be applied for effective water treatment. RBF is a technique that covers both shallow groundwater and river water that have crossed through the banks of rivers, or riverbanks to well extractions . Most of the suspended and dissolved contaminants, including viruses and pathogenic bacteria, are filtered out as surface water is filtered through aquifer materials, and the sediments of the riverbed . Abstracting of riverbank water can overcome water shortage due to extreme events such as floods and droughts that cause water levels to increase on the ground, or reduce underwater intake pipes, causing disruptions in water transfer to treatment plants . Although RBF is a capable method for improving surface water quality, it does not abolish the problem. Abstracted well water quality is highly dependent on several factors, such as groundwater and river water quality, temperature and pH of water, water residence time, medium porosity, and oxygen concentrations . According to Levantesi et al. study, the breakthrough of bacteria and turbidity occurred in a shallow drilled well (3–6 m) due to the short travel time, especially during monsoon seasons . This condition urges for appropriate treatment applications to further enhance the ability of RBF in bacteria and inorganic substance removal.
Indicator bacteria, including the total coliforms,
Despite the numerous advantages of RBF, it also has several limitations . Seasonal variations have an impact on the concentrations of
1.1 Malaysia’s drinking water resources
Malaysia has had abundant and rich water resources throughout the years. The main source of drinking water in Malaysia is groundwater and surface water. Approximately 99% of water for domestic uses in Malaysia are from surface water, while another 1% of the supply is from groundwater . Malaysia’s internal water sources are estimated to be about 580 km3/year, with 30% of water production for municipal uses . Water supply from surface water is widely used as drinking water, such as water withdrawn from Sungai Kinta, Sungai Langat, and Sungai Selangor . Water supply from groundwater intake from a few states in Malaysia such as Terengganu, Kelantan, Perlis, Kedah, Pahang, Sabah, and Sarawak are also used for drinking water . According to the data published by Suruhanjaya Perkhidmatan Air Negara (SPAN) in 2015, only 1.5% of total groundwater supply is present in Malaysia, and there was an increase in groundwater usage by 3.3% from the year 2014 to 2015 (SPAN, 2015). Nonetheless, the key issue to be considered is the quality of the water sources for drinking water supply. Both surface and groundwater sources are easily affected by the surrounding changes, whether manmade or natural. Therefore, it is important to determine undesired constituents, and monitor the characteristics of the water sources to ensure the pollutants in the water do not exceed the standard limits for water supply stated by the National Water Quality Standards for Malaysia (NWQS), and the Ministry of Health (MOH).
1.1.1 Quality of water
The Department of Environment (DOE) uses the National Water Quality Standards for Malaysia (NWQS) and Water Quality Index (WQI) to evaluate the status of the water source quality . The WQI, introduced by the DOE, has been practiced in Malaysia for about 25 years, and serves as the basis for the assessment of environment water quality, while the NWQS classifies the beneficial uses of the watercourse based on WQI . To design the drinking water quality management system, the assessment of water quality is an important step in determining the possible problems in the quality of the drinking water source. Basically, the characteristics of water quality are determined by physical, chemical, and biological factors to describe the overall condition of the water quality and its suitability for a specific use.
1.1.2 Microorganism pollution
The occurrences of pollution and indicator pathogenic bacteria in potable water depend on a number of factors, including the intrinsic and chemical characteristics of the catchment area, and the range of human activities and animal sources that release pathogenic bacteria to the environment. Sources of pathogenic bacteria in potable water are numerous and, for operational efficiency, are typically assessed by faecal indicator bacteria investigation. In terms of biological characteristics for safe drinking water supply and drinking water distribution systems, water is one of the transmission routes for pathogenic microorganisms . In spite of having enhanced water management and sanitation, waterborne-diseases and outbreaks may continue to occur . Drinking water polluted by microorganisms of faecal origin is a current worldwide health concern because of epidemic occurrences globally in relation to microbial-contaminated water. In drinking water, these microorganisms of interest include protozoa, bacteria, viruses, algae, and helminths. An overview of these microorganisms is given in Table 1.
Faecal coliforms are bacteria which fulfil all the criteria used to define total coliforms, with the additional requirement that they grow and ferment lactose with the production of acid at a scientifically accurate 44.5°C . This bacteria of the coliform subgroup has been found to have a positive correlation with faecal contamination of warm-blooded animals . However, several thermotolerant coliform bacteria, by definition by the genus
Recently, the faecal coliform group has been extended to include other characteristics, such as β-D-
1.2 Riverbank filtration (RBF)
Subsurface or groundwater in Malaysia are natural water sources that can be exploited to meet the demands for water of high quality. The RBF process is an existing method referring to the process of extracting potable water at the riverbank, utilising subsurface or groundwater to supply sources of high quality water . RBF systems and natural treatment processes typically take place during water infiltration. Figure 1 shows the natural process of extracting treated water from an adjacent pumping well to a river.
As illustrated in the figure above, the difference in hydraulic gradient causes the water from the river to flow towards the well during the pumping process. Additionally, the RBF process is known as a sustainable and economical method to improve poor surface water quality. A complex attenuation method occurs during the transportation of water through the aquifer layer, resulting in raw water of high quality. The high quality raw water is then supplied to the water treatment plants, making it easier to be treated at low operating costs by conventional treatment systems. Therefore, water from the well can be directly consumed with very minimum treatment in certain areas.
In many countries, river water has been treated to complement the existing water supply system through bank filtration, such as in Germany, Finland, France, Switzerland, Hungary, and the Netherlands. RBF has become an efficient, well accepted technique for surface water treatment in many European countries. In Switzerland, 80% of the drinking water comes from RBF wells, with 50% in France, 48% in Finland, 40% in Hungary, 16% in Germany, and 7% in the Netherlands. Recently, other countries like Malaysia, India, as well as China and South Korea have started implementing RBF for drinking water supply .
Generally, RBF wells constructed in aquifers primarily consist of sand and gravel, with thin layer of granular aquifers (clay or silty sands). Removal of pollutants using RBF involves complex biological, hydrological, and geochemical activities through the aquifer layer during the filtration and infiltration of water. These processes consist of physical filtration, dilution, microbial degradation, precipitation, and sorption processes [1, 16]. According to recent studies in Europe and America, the RBF process is able to provide appropriate defence against microbial contaminants, and reduce the possibility of disinfection by-product formation. Additionally, RBF is also an effective method of removing common microbial pathogens such as
E. coliremoval via riverbank filtration
RBF is a water treatment technology that involves extracting water from rivers by pumping wells located in the adjacent alluvial aquifer. In the underground passage, a series of physical, chemical, and biological processes take place, improving the quality of the surface water, while substituting or reducing conventional drinking water treatments. A study based on a model-oriented approach by Wang et al. used an example of riverbank wells near the Kuybyshev Reservoir, Russia . The wells were designed in order to minimise the uncertainties in the estimated hydraulic parameters. During water transport towards the RBF wells, the water quality improved significantly, aided by processes like microbial degradation, ion exchange, precipitation, sorption, filtration, dispersion, and groundwater dilution.
Faecal and total coliforms are bacterial indicators that are widely used to monitor microbial water quality in developed and developing regions of the world. Faecal contamination of drinking water supplies is a public-health concern because they could contain pathogens that cause gastroenteritis, meningitis, and other waterborne diseases . Potential sources of faecal contamination include direct discharge from human and animal wastes as well as non-point sources (agricultural and storm water runoffs). Majority of the RBF systems used in European countries and America alike have achieved excellent total coliform removal percentages, ranging from 99.2 to 99.99% (2.1–5 logs).
1.3 Principles of electromagnetic field treatment
Extremely low-frequency electromagnetic fields (ELF-EMFs) are ubiquitously present in various environments in everyday life. Generally the ELF-EMF spectrum is defined by frequencies from 3 to 3000 Hz . These fields are generated via high-tension electrical distribution networks from residential and occupational sources by power lines and electrical devices. Normally, electric and magnetic fields occur together, and both fields weaken with increasing distance from the source. However, both these fields produce different effects on living organisms. In a large part of the world and Europe, 50 and 60 Hz (in the U.S.) sine wave signals resemble the household alternating current electrical power supply.
The principles and behavioural effects of electromagnetic fields (EMFs) have been reported since the 1970s. Recent studies in the field have shown that exposure to electromagnetic and non-ionising radiations can induce numerous biological effects . For example, exposure to ELF-EMFs ranging from 0 to 100 Hz is capable of activating cellular immune responses. Various approaches have fixated on the probability of analogous effects regarding non-ionising radiation. Despite this, there have been an increasing number of studies suggesting that exposure to ELF-EMFs can affect and slow down the growth of
1.3.1 Low-frequency electromagnetic fields
Low-frequency electromagnetic fields (LF-EMFs) are widely applied in electrical appliances and different equipment such as television sets, computers, and kitchen appliances. EMFs are classified into seven categories: (1) Extremely low frequency (0–300 Hz) used in biological processes, (2) low frequency (300 Hz–30 kHz), (3) middle frequency (30 kHz–30 MHz) used for amateur radio and remote controls, (4) ultrahigh (30–300 MHz) used in radio and TV, (5) super high (300 MHz–30 GHz) used in satellite communication, (6) extremely high frequency (30–300 GHz) used in radars, and (7) infrared (300 GHz–300 THz) and visible light (429–750 THz) used in light spectrums. The EMFs are characterised by a frequency of 50 or 60 Hz, and thus occupy the extremely low frequency (ELF), non-ionising range of the electromagnetic spectrum (3 Hz to 3 × 103 Hz) . Although ELF-EMFs do not break molecular bonds or heat body tissue, they may interact with the human body through the weakly generated electric currents.
The LF-EMF is an effective technique in water treatment to prevent scale formation, and detach already-formed scale in industrial water systems. Many related studies have been conducted in the past 60 years, and several devices have been developed. Some researchers have found that EMFs can be implemented in soil and agriculture wastewater disinfection, in therapeutic practices, and in food protection technologies. It was also found that the EMFs have potential in controlling and removing bacterial growth on water treatment systems.
General operations of EMFs in water treatment systems involve the physics of interaction between a magnetic field and moving electric charges. The electromagnetic system consists of magnetic fields generated by coils wrapped around a pipe. The small electrical device treats the water with a patented technology by inducing variable electric currents at a continuous frequency to generate the magnetic field. The magnetic field removes the bacteria (
1.3.2 Low-frequency electromagnetic fields for
Over the past few decades, it has been well established that non-thermal, non-ionising, extremely low frequency (<300 Hz) and low amplitude (0.2–20 mT) EMFs cause a number of different biological effects. The radiation is said to be capable of inducing physiological effects too . Several studies have been performed to verify the direct effects exerted by EMFs on cellular functions. Bacteria were also tested in some studies using the ELF-EMF wave. The biological effects of EMFs are quite heterogeneous, depending on the types of cell studied, intensity, and types of field used. For more than three decades, various forms of electrical stimulation, including capacity coupling, direct current, and combined magnetic fields have been used as a therapeutic remedy. The current, and one of the most useful methods to investigate antibacterial effects due to magnetic fields is to use low-frequency EMFs, especially frequencies ranging from 50 to 60 Hz. On the contrary, even with some publications claiming the bio-effects of EMFs, there are plenty of studies showing no significant effects on living organisms. Podda et al. reported no change in oxidative DNA damage after 50 Hz EMF exposure was applied .
The implementation of magnetic fields in water treatment systems is a non-chemical method that covers a wide range of technologies. A recent study reported that EMFs had a positive effect on the efficiency in the number of bacteria removed in biological wastewater treatment . EMFs also intensify the stationary-phase-specific transcription activity of the
The data on LF-EMFs on
1.3.3 Design and construction of LF-EMF exposure column pipe
The initial LF-EMF column structure was designed using the ANSYS Maxwell software program. A geometrical design of the model was created and drawn with the selected parameters. A fully-automatic meshing procedure was applied before the simulation was begun, after the structure had been modelled. In the ANSYS Maxwell 3D, the solutions were based on meshes by using thousands of LF-EMF coiled column elements. Accurate solutions based on coarse meshes using relatively few elements were obtained. To assist the meshing, the coil workpiece was created with multi-layers depending on the skin depth. The aim of this simulation was to generate a uniform magnetic field inside the column pipe, and assign the number of coil turns for the LF-EMF coiled column. Figure 3 illustrates the cross-section structure of the LF-EMF coiled column, as well as the dimensions for one of the five column test models in this study.
There were five models of LF-EMF coiled columns built using ANSYS Maxwell software with different designs in this study. All the LF-EMF coiled columns were designed using gauge insulated copper wire with the conductivity of wound wires in a vacuum environment. The diameter range of the copper wires used was 1.5 mm. This range coil diameters were used to determine the most effective diameter of coil in generating a magnetic field at different column diameters (Dcolumn), and number of coil turns (N). Theoretically, increasing the number of coil turns, with the same coil and the same current flowing, would increase the magnetic field strength. This relationship is defined as magnetomotive force (MMF), which refers to the flowing of current through a coil of N turns. Therefore, an electromagnetic field strength can be determined by the
The simulations of the coiled columns began with determining the N using 2 A excitation current to generate a magnetic field in the range of 2–10 mT. The magnetic field generated by the electromagnet was proportional to both N and
The strength and intensity of the LF-EMF coiled columns depends on the N of coils, diameter of coils, and also the type of column material used as the core. In this study, five transparent polypropylene cylindrical columns with inner diameters of 50 mm, which were 500 mm in length were used. These cylindrical columns were of non-magnetic material that can be regarded as free space as they have a very low value of permeability. This material had no effect on concentrating the magnetic flux, and the magnetic field created by the current in the coils. The performance parameters of the coil used was dependent the geometry and coil dimension ratios. A smaller diameter of coil required much more number of coil turns, while bigger coil diameters used resulted in larger magnetic fields.
2. Material and methods
LF-EMF was produced with the coiled column and the sinusoidal 50 Hz magnetic field was generated by means of a solenoid, obtained with overlapped winding of copper wire with 500 mm of length and 50 mm diameter of column A and 80 mm diameter of column B. The power of 220 V was connected to solenoid coils waveform generator. The current flowing in the exposure devices was monitored by AC current in parallels of coils. In each coil, the number of turns was between 300 and 600 of 1.5 mm copper wire and the total resistance of the system was 1 Ω. The resulting of the whole inductance coil system was in the range of 2–10 mT. The density of magnetic flux was monitored using Tesla meter (BST600 Gauss meter/Tesla Meter) and field intensity was varied by ±0.05 mT.
According to previous studies, the method of IDEXX Colilert® 18 has been verified as an acceptable alternative to other test methods for the recovery of
2.1 Sample characterisation
The study site is located on Sungai Kerian at Lubok Buntar Kedah, Malaysia (Figure 4). The sample was collected during dry and wet seasons from Sungai Kerian and tube well. One hundred samples were collected; 50 sample for column test. Tube well water samples were collected in sterile amber glass bottles of 125 ml without headspace in order to prevent the formation of air bubbles and were airtight sealed. All laboratory analytical analysis was according to Standard Method . Ten litres of river raw water sample was collected in polyethylene bottles. These samples were preserved in accordance with Water and Wastewater Standards and then stored at a temperature of less than 4°C. Laboratory apparatus used in this study were prewashed with 5% nitric acid (HNO3) and rinsed with deionised water prior to testing.
2.2 Experimental setup
In this study, 13 runs of test with different magnetic field exposures were conducted. The horizontal transparent polypropylene cylindrical columns test with inner diameters of 50 mm were used. The coiled column test was built on the horizontal axis, and the magnetic field was generated by means of a solenoid, obtained with overlapping windings of copper wires, at 500 mm in length. The coils wrapped around the column transformed the magnetic fields controlled by the magnetic field power generating system. The maximum of effective current was 2 A at 50 Hz frequency. The magnetic generator consisted of a pair of solenoid coils, a current amplifier, and a waveform generator controller. The samples were exposed and placed in a horizontal column where uniformity of the magnetic field was optimal. Then, the LF-EMF coiled column experiment was started by pumping water samples in a horizontal direction into the column in order to ensure complete wetting of the particles . A constant discharge rate was maintained using the peristaltic pump model Masterflex L/S HV 07522–20 at 50 and 100 mL/min to allow sufficient contact time between the magnetic field, and for the removal of
3. Result and discussion
Data collected from the experiments were analysed using Microsoft Excel and Origin-Pro 9.1 software. All the data and results are presented in the form of tables and figures. The findings include the simulation results and validation of the LF-EMF exposure, water sample characteristics,
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
Removal rates of
From Figure 6, the results obtained demonstrated that column test achieved 100%
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
The optimal time of magnetic field exposure on column test for
The effect of the exposure to LF-EMF at 2–10 mT on
The ability of LF-EMFs to remove or decrease the concentration of
The authors thank the Ministry Education Malaysia for providing LRGS Grant on Water Security entitled Protection of Drinking Water: Source Abstraction and Treatment (203/PKT/6726001). This project was also partly supported by USM Research University Individual (RUI) Grant (1001/PAWAM/814287).