Summary of RBF post treatment from other country and its limitations.
Water security in the water treatment plant has been doubted, and the treatment process may have given unreliable and unsafe water to the public. A newspaper reported on November 19, 2011, that laboratory tests on water samples in Kelantan for each year by the Ministry of Health have found harmful bacteria including Escherichia coli (E. coli) in the water samples. More worryingly, it was stated in a study that chlorine in water treated with high chlorine can be harmful to human health. In 2010, Malaysia has begun to approach a natural treatment technique, namely, riverbank filtration (RBF), and firstly used it at the Water Treatment Plant in Jeli, Kelantan, and Kuala Kangsar, Perak. RBF limitation is the invisible groundwater flow that makes it difficult to predict the transport of contaminants. Managing groundwater is important to ensure that water is aligned in compliance with government legislation and environmental protection. Due to that, this study suggests an implementation of an artificial barrier for microorganism in RBF to sustain the good water quality abstracted from the abstraction well. This pretreatment or purifying method is to improve the effectiveness of RBF in removing pollutants during shock loads and reduce the load placed in the water treatment process.
- artificial barrier
- riverbank filtration
- E. coli
- water security
Potable water access globally is now under crisis, which leads to poor human health issue, affecting Malaysia as one of the countries facing this problem. The main reasons why this happens are due to climate change, deterioration of river water quality, unreliable water treatment system, and increase of population, which, at the same time, causes water shortage to occur. During dry weather conditions, further depletion of water occurs. Pertinently, climate changes make the drought season becomes longer and hotter than usual. The dam water becomes low and the river water dries up. The deterioration of river water quality in Malaysia has brought an impact to the water treatment plant due to the increase of treatment cost and maintenance. Chemicals such as PACI, alum, and others will also be increased to treat the polluted river. In the year of 2011, it was stated in a study that chlorine in water treated with high chlorine can be harmful to human health . Thus, water security in the water treatment plant has been doubted, and the treatment process may have given unreliable and unsafe water to the public. Recently,
Providing reliable and safe potable water has become a human right for us. Therefore, finding a solution to these issues is highly desirable to improve the safety and reliability of potable water. In 2010, Malaysia has begun to approach a new treatment technique, namely, riverbank filtration (RBF). RBF is a method using groundwater that is expected to provide a new way to increase water intake and untapped resources in Malaysia, firstly used at the Water Treatment Plant in Jeli, Kelantan, and Kuala Kangsar, Perak. RBF is a natural system in which it involves the entry of river water into underground aquifers and is caused by hydraulic gradients, whereby water retrieval is from collector wells located at banks, at a certain distance from the river . Although it is still less than 10 years in Malaysia, RBF method shows good results to reduce the use of chemicals and produces biologically stable water; the system also improves water quality by removing particles (turbidity and suspended solids), organic pollutants, microorganisms, heavy metals, and nitrogen. One previous experience in Germany shows that RBF provides a strong barrier for various pollutants and can help to ease the temperature fluctuations and concentration peaks when it is associated with spills into rivers. It also replaces and supports other treatment processes and reduces the overall costs of water treatment plant . The removal of sediment, organic and inorganic compounds, and pathogens takes place during the first meters from the river in what is known as the hyporheic zone, which usually presents reducing conditions, due to high microbial activity that consumes oxygen in the water. Within this zone, there are important biochemical processes and redox reactions that affect groundwater quality . In general, every stage of RBF has an environmental influence that is from the river until abstraction well.
Safe potable water is one of the implicit requisites for a healthy human population. In the existence of RBF, artificial barrier is a new efficient purifying method to maintain safer water abstraction. This study demonstrates the potential of a new application of artificial barrier to filtrate
2. Riverbank filtration
2.1 Principle and treatment
RBF has begun to be widely used in Malaysia as to optimize the water supply. The introduction of RBF in Malaysia is started in 2010 at Jeli, Kelantan. The plants’ operation has demonstrated the success of the combination of RBF (as pretreatment) and water treatment plant (as posttreatment). Most RBF in Malaysia have been applied in Kelantan areas. After calculating all the costs (not including the cost of pumps, pipes, valves, etc.), 1 m3 of drinking water costs approximately USD 0.04, which is considered to be a competitive price for the Malaysian. The combined method has therefore proved to be both technologically and financially viable. These findings should pave the way for other municipal authorities to follow suit by introducing their own combined RBF with ultrafiltration.
RBF post water treatment has been employed dating back to the nineteenth century. During RBF, river or lake water is extracted indirectly by drawing it through the subsurface prior to use as inFigure 1. The extraction is accomplished by an infiltration line of well either vertical or horizontal. The well is located at a short (below 30 m) to intermediate (up to 60 m) distance from the riverbank or lake. During extraction of water, the groundwater that discharges into the river decreases, and the groundwater table near the waterline may decrease below the river water level. To ensure a satisfactory purification, the distance between the river and the extraction well should such that the travel time exceeds 30–60 days .
During infiltration and travel through the soil and aquifer sediments, surface water is subjected to a combination of physical and chemical and biological processes of filtration. The top few centimeters of the riverbank materials formed are a screen or filter medium that removes the suspended solids present in the water. Heavy metal, phosphorous, and hydrophobic organic compounds present in the water are removed by adsorption onto certain aquifer materials. In the presence of biomass, the organic matter is further biodegraded (initially under oxic conditions and later under anoxic conditions). The water quality in most cases is improved by dilution of the surface water source with native groundwater . When a particle becomes attached to the biofilm on the sand grain, microorganism may degrade that particle. There is an interception when particles are carried by one of the streamlines closest to the sand grain and a brushing effect occurs. There is general agreement that straining, adhesion, attachment, chemical adsorption, sedimentation, and biological growth all operate to some extent.
The conventional treatment commonly involves screening, aeration, coagulation, flocculation, sedimentation, slow sand filtration, and chlorination. The chemical treatment and waste product will increase if the pollutants in surface water increased. The RBF reduces the posttreatment step from six to only two steps which is removal of heavy metals (usually iron and manganese) by either aeration, activated carbon filter, or ultrafiltration and chlorination for taste and odor. This RBF system as a pretreatment technique applied in countries like the Netherlands, Germany, China, Korea, India, Egypt, and others has already succeeded in optimizing the potable water supply. The underground passage ensures the high quality of drinking water, which does not need any further treatment or disinfection before supply .
The posttreatment after RBF depends on the water abstraction water quality. Each RBF site has a different technique step for posttreatment. Previous study shows the most common pollutants that occur in RBF sites are iron and manganese. The treatments used to remove these contaminants in water are aeration, activated carbon filter, and ultrafiltration method. The second contaminant that occurs is taste and odor which are usually removed using chlorination. The third contaminant was microbiology which is solved by using ozonation and UV disinfection. This all posttreatment technique is commonly used at RBF site and summarized in Table 1. Meanwhile, there are RBF sites which are not using a posttreatment as a means for direct usage such as in China. However, in several years there will be oocyst problems.
2.2 Benefits and limitation
The RBF is a sustainable natural treatment process which avoids or reduces the use of chemicals and produces biologically stable water. The system improves water quality by removing particles (turbidity and suspended solid), organic pollutants, microorganism, heavy metals, and nitrogen. The RBF also helps to dampen the temperature fluctuations and concentration peaks when it is associated with spills into a river or lake. This treatment process also replaces and supports the other treatment processes by providing a robust barrier for multiple contaminants and reduces the overall cost of water treatment .
RBF limitation is the invisible groundwater flow that makes it difficult to predict the transport of contaminants. A specific concern of the RBF limitation is due to hydrology and dynamics of the river and groundwater, which have different climate variations (drought and rainy seasons), and thus, the groundwater level patterns result in significant fluctuation of contaminants in well stream loads. In rainy season, the rate of groundwater flow increases to a maximum level and causes small particles and pollutants to absorb into the soil where it encloses the flow along the groundwater flow, which initiates pollutants to enter the borehole. On the other hand, in dry season, minimum and ideal flow rates for pollutants are attached to the local soil. Moreover, since maximum groundwater flow rate occurs frequently in Malaysia, this incident is predicted to often result in significant fluctuations of underground hydraulic conductivity of groundwater and shock load of pollutants. Significant amount of pollutants may exist in borehole water due to high hydraulic conductivity and soil feature, which concludes that RBF is a natural treatment method that depends on natural behavior. In general, the quality of RBF water is influenced by the environmental conditions, where managing groundwater is important to ensure that water is aligned in compliance with government legislation and environmental protection.
The posttreatment step in most RBF sites is usually focused on iron and manganese treatment which result in the usage of aeration, activated carbon filter, and ultrafiltration treatment process. The weakness of this treatment which cannot be ignored has been discussed in the above section. The occurrence of the pollutants can be worse during shock load and clogging. Due to that, artificial barrier seems important which can increase the hydraulic conductivity of the underground water flow, reduce the pressure load to the aquifer during clogging, and enhance the pollutants adsorption during shock load. This can reduce the consumption of chemical treatment and strengthen the RBF barrier.
2.3 Factors influencing optimization of RBF
There are four basic important criteria affecting the performance of RBF which are hydrogeological conditions, source water quality and mixing with native groundwater, distance of the well from riverbank and spacing of wells and pumping rates, and sediment permeability. The effectiveness of RBF for removing surface water contaminants depends largely on hydrogeological conditions. It is about the soil microbiology, characteristic of the bank materials and streambed, and scouring characteristic . In many countries, the alluvial soil aquifers hydraulically connected to a water course would be preferred sites for drinking water production . The actual biochemical interactions that sustain the quality of the pumped bank filtration depend on numerous factors, including aquifer mineralogy and the extent of the aquifer .
The RBF shows a decreasing RBF water level with an increasing distance of the well apart from the riverbank. In addition to the decreasing RBF water level due to increasing distance, there is no cross flow of natural groundwater that the well could abstract river water . Pumping test result shows that the water in well (below 60 m) comes from river water. However, the low-lying coastal aquifer is generally fragile and easily depleted due to anthropogenic activities and overexploitation of groundwater and agriculture. To manage and protect precious groundwater resources in a sustainable manner, the characterization and understanding of the natural evolution of groundwater chemistry are crucial to elucidate their geochemical nature and its relation.
The collector well can be far from the river if the soil type is sand and gravel such as RBF at Yellow River, China. The combination of vertical and horizontal collector well can maximize the water capacity such as RBF at Elbe River, Germany. However, clayey alluvial soil will limit the water capacity as RBF site at Lek River, Netherlands, shows the water capacity is only 0.01 MLD, compared to clayey alluvial soil at Nakdong River, Korea, which can be abstracted to 10 MLD water capacity. This shows clayey alluvial soil type needs deeper built collector well near the riverbank. The nearer to riverbank, the more water capacity can be abstracted than collector well at Nakdong River, Korea, which is only 10 MLD with 150 m distance from river, and collector well at Nile River, Egypt, with 22 MLD. Some sites do not contain gravelly sand alluvial soil type but can apply RBF such as Kali River, India. The highly pollutant river demands to use RBF methods; however, it only can abstract 0.8 MLD water capacity because the transmissivity of brownish red silty loam alluvial soil is low. Sites with clayey alluvial soil can apply limestone to increase the transmissivity of water such RBF sites at Ohio River, Kentucky, and Great Miami River, USA. Malaysia RBF sites at Sungai Semerak contain gravelly sand and shallow vertical well collector type. The shallow collector well nearer to riverbank helps RBF to avoid problem with iron and manganese. Thus, the RBF site that can supply huge water capacity is 25 MLD.
Escherichia coli in riverbank filtration
The abstracted water from RBF is very clear which has less contaminants than river water. According to previous study from other RBF sites, the contaminants that are below drinking water standard are turbidity, color, pH, TDS, chloride, ammonia, COD, BOD5, sulfate, iron, manganese, total coliform, and
This study is focusing mainly on
In natural conditions at RBF sites, water percolates through the organic soil where dissolved oxygen (DO) is consumed by the decomposition of organic matter and microbes in the soil. The decomposition process reduces the pH due to microbial action. When groundwater is pumped up to the surface, it gets into contact with air (O2) which enters the solutions and starts the oxidation process that releases carbon dioxide (CO2) from the groundwater to the atmosphere.
The reason for choosing
4. The possibility of
Escherichia coli infection in riverbank filtration
The site was located at coordinates 5° 07′38.61“ N and 100° 35’44.24”, Lubok Buntar, Kedah. The examined site was influenced by the water from the Kerian River which was also influenced by the discharge of the wastewater from palm oil, mining industry, and poultry farming area at Sungai Mahang (upstream). The river water and borehole water samples were taken for laboratory (characteristics) test. Figure 2 shows concentration plots of
The depth of borehole was 30 m signifying that this borehole was under unconfined aquifer. The unconfined aquifer is recharged more rapidly when raining and groundwater hydraulic conductivity at maximum due to infiltration and runoff . The increase of solute concentration during rainy season due to the groundwater flow exceeded the permeability of alluvial soil. Groundwater flow was maximized when raining which creates pressure to the alluvial soil. This leads small particle to flow together into abstraction well which in turn increases contaminant concentrations in abstraction water. For that reason, the application of artificial barrier seemed beneficial since it will increase the permeability of aquifer near the river avoiding small particles to flow together to abstraction well during rainy season. Besides raining,
The experiment shows that the application of artificial barrier as RBF water purification method seems important to avoid the possibility of
5. Artificial barrier for riverbank filtration
The fixed-bed flow studies were carried out to evaluate their ability to remove
The water samples used in the column were taken from the Kerian River at coordinates 5° 07′38.61“ N and 100° 35’44.24” E. The sand, GAC, and zeolite were oven dried for 24 hours at 105°C. Before placing the sand, GAC, and zeolite in the column, the column was washed with a solution of 3% acid nitric. The removal of
5.2 Result and discussion
In this study, 15 mixture components that are represented by soil, GAC, and zeolite bed height (in real site of RBF equal to distance of abstracted well water to river) were chosen for the optimization studies since they influenced the presence of
The GAC morphology (Figure 5(a)) showed that the surface structure and pore were well developed similar to honeycomb structure. The surface morphology of the GAC was also comparable to the analysis done by Hameed and Ahmad . However, the adsorption of
The enumeration of
Until now, the health effects endemic to human for groundwater supply in Malaysia are not investigated. Casemore  notes that the occurrence of sporadic or pseudo-sporadic infection is particularly important in the context of groundwater-related infection. This is because the groundwater is often seen as pure quality and therefore not examined as potential sources of enteric infections that occur, thus leading to important effect.
The performance of RBF depended on alluvial soil particles’ size distribution, soil gradation, and soil structure. From the monitoring, results show that the possibility of
The authors would like to acknowledge the Ministry of Education Malaysia for providing LRGS Grant on Water Security entitled Protection of Drinking Water: Source Abstraction and Treatment (203/PKT/6720006).
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