The effectiveness of a plant integrated lowcost treatment system to treat well water in coastal regions

Most of the developing countries in Asia, such as Sri Lanka, India, Pakistan, Bangladesh, as well as many African nations, are suffering from a water crisis. When located in the coastal region, the problem becomes severe (Jayalakshmi et al. 2017). Fresh water resources are scarce in rural communities in the coastal area where both shallow and deep groundwater are frequently brackish, and freshwater wells have been increasingly salinized by tidal fluctuations mostly in dry seasons. Apart from that, freshwater aquifers are not available at suitable depths and freshwater ponds are increasingly salinized by salt-water intrusion (Islam et al. 2015). Salt-water intrusion is one of the major threats in coastal regions for groundwater pollution. In addition, the rapid population growth of coastal regions and agricultural practices also affect the surface and groundwater considerably (Lawrence et al. 1988; Amarathunga & Sureshkumar 2013; Amarathunga & Kazama 2016; Kithmini et al. 2018). The sandy soil of these areas led to an increase in the contamination level of the groundwater, due to high infiltration capacity. This is accompanied by the sustainability of operation and maintenance of water supply infrastructure that has hindered access to water near coastal areas (Kumar 2014; Dammala et al. 2020). Kumar (2014) revealed that the assurance of drinking water safety is a powerful environmental determinant of health.

The common methods utilized for drinking water purification at the domestic level include boiling (Fahey 2005), distillation (solar) (LeMar et al. 1995), filtering (Fahey 2005), passing ultraviolet light (Ancy et al. 2016), chlorination using water ozonation (Khurana et al. 2009) and softeners (Motsi et al. 2009), which assist in the removal of suspended and colloidal particles (Huang et al. 2000), heavy metals (Eilbeck & Mattock 1987), turbidity, organic matter (Lens et al. 1994), microorganisms, and other substances in the water. In the past, it was evident that people used different conventional water treatment methods to obtain pure water, for instance, boiling, natural coagulation, sedimentation flocculation, filtration, disinfection, placing hot metal instruments and clay pots in before drinking (Rajendran et al. 2013). The tradition-based knowledge has led to the use of herbal materials to treat water various scales emphasizing the need of medicinal and economic feasibility (Sathish & Amuthan 2014). Thus, low-cost water treatment systems with natural materials are significant for the treatment of water (Amarathunga & Kazama 2014) or purification of drinking water to improve the potable water quality at the household level, because household water treatment systems are operated with minimum energy, minimum maintenance, cost effectiveness, environmental friendliness, are implementable with ease and can be developed by local artisans (Mikhayel & Anitha 2018). All over the world, these rural communities have adapted some simple and traditional water treatment techniques to remove visible impurities like twigs or large suspended particles and leaves from polluted water (Vigneswaran & Sundaravadivel 2009).

Many researches have been focused on improving traditional plants-based water treatment methods because they play a critical role in treating contaminated water at the household level. Though the available literature on the assessment of water filtration using traditional herbal plants in the coastal water wells are limited, numerous effective filter materials based on plants have been identified. For example, Moringa olifiera (Murunga) (Ndabigengesere et al. 1995; Wijeyaratne & Subanky 2017), Nelumbo (Nelum), Strychnos potatorum (Ingini), Vetiveria zizanioides (Sevendara), Terminalia arjuna (Kumbuk), Madhuca longifolia (Mee), Aponogeton (Kekatiya), Solanum incunum (Kalukammeriya), Ocimum sanctum (Gas thala) (Parthiban et al. 2017), Azadirachta indica (Neem) (Parthiban et al. 2017), Triticum aestivum (Thiringu) (Somani et al. 2011), Zea mays (Iringu) has been reported for use as its ability to purify water through its coagulation properties and is usually presumed safe for ‘human health’ (Padmapriya et al. 2015) with freely available natural resources (Ab Aziz et al. 2014). Most of these extracts are derived from the seeds, pieces of bark or sap, leaves, roots, and fruit extracts of trees and plants (Pritchard et al. 2009). Traditionally, a large number of plant materials have been used over the years; the seeds from Moringa oleifera have been shown to be one of the most effective primary coagulants for water treatment, especially in rural communities (Ndabigengesere et al. 1995; Sotheeswaran et al. 2011).

Many studies have attempted to use traditional methods of herbal plants materials and sand for water purification but focused either on plant species or on specific plant parts. Indigenous plant species are used for water treatment without restriction of plant parts and type. T. arjuna (Kumbuk) plant species, commonly known as Ajruna or Arjun, belongs to the family Combretaceae and occurs naturally in subtropical and tropical, moist regions of the country. From traditional knowledge, it has been identified that T. arjuna roots have abilities to purify water (Rao et al. 2016). The study of Shanthamareen & Wijerathne (2017) found that T. arjuna leaf powder can be used as an effective low cost householder treatment method to reduce nitrate and total hardness (TH) and they studied T. arjuna leaf powder which can be used as an effective low-cost household treatment method to improve the water quality in terms of TH and nitrate N.

Jayalakshmi et al. (2017) reported that S. potatorum (Igini) seeds were used as a clarifier between the fourteenth and fifteenth centuries BC in India which indicated that they were the first reported plant-based coagulant used for water treatment. The ripe seeds are used for clearing muddy water (Yadav et al. 2014). Packialakshmi et al. (2014) asserted that the effectiveness of S. potatoram in the removal of turbidity, pH, TH and total dissolved solids (TDS) have been investigated. Yet, the reduction in turbidity was dependent on the raw water. It can enhance the extracts coagulation capability which enables effective filtration. A mixture of polysaccharide fraction extracted from S. potatorum seeds contained galactomannan (non-ionic) and galactan capable of reducing up to 80% turbidity of kaolin solution (Packialakshmi et al. 2014). The findings claimed that the galactomannans are made up of a main chain of 1, 4-linked d-mannopyranosyl residues bearing terminal d-galactopyranosyl units linked at the 0–6 position of some mannose residues (Vijayaraghavan et al. 2011). Moreover, according to the results, direct filtration with S. potatorum seed is effective for drinking water treatment and against the pathogenic organisms (Packialakshmi et al. 2014). S. potatorum seeds have been reported to be successfully employed in municipal treatment plants in combination with alum (Sutherland et al. 1990) due to their ability to reduce alum in drinking water through their coagulation properties (Padmapriya et al. 2015).

The tree of P. emblica is generally found in small and medium size and in all the tropical areas in the world. P. emblica plant materials are utilized as a traditional medicine. For instance, P. emblica is used for the treatment of diarrhea, jaundice and inflammatory disorder (Jaijoy et al. 2010). However, previous experiments have been carried out regarding the water purifying property of P. emblica woods, barks, seeds and roots. A past study found that P. emblica bark has good physical characteristics for the adsorption of fluoride ions from groundwater (Patil et al. 2016). Sathish & Amuthan (2014) reported that P. emblica wood treatment reduced hardness and the amount of magnesium and sulphate in drinking water. It also increases the amount of calcium and iron. According to Padmapriya et al. (2015), the wood has shown a high coagulation activity for high-turbidity water though the coagulation activity was found to be low for low-turbidity water and there was a reduced magnesium level in water. Microbial load was also remarkably reduced after treatment which may be due to biological agents present in the plant and its antimicrobial activity (Ancy et al. 2016). Somani et al. (2011) discovered that the percentage removal of E. coli was recorded as 41.03% by treating P. emblica wood. Conversely, the acidity was increased, and taste was affordable. Sathish & Amuthan (2014) reported that P. emblica wood reduced the hardness, magnesium and sulphate in drinking water. It enhanced the amount of calcium and iron in the filtrate and it was not successful in killing microbes in water. Water soaked with the wood/root of P. emblica made more safe and healthy drinking water. Previous studies have shown that P. emblica seeds can be used as an effective adsorbent for fluoride removal from aqueous solutions and the degree of fluoride removal depends on the contact time, adsorbent dose, and reaction temperature (Veeraputhiran & Alagumuthu 2011). Nevertheless, the nature and the extent of the pollutant removals using these media are different in coastal and non-coastal area-based waters.

This study attempted to reveal the scientific possibility of water purification by natural filter media and to develop a LCWPS to reduce groundwater contamination in coastal areas using indigenous knowledge and locally available herbal material like S. potatorum seeds, T. arjuna roots, P. emblica leaves, and sand. Various natural and synthetic remediation methods have been studied to improve the quality of contaminated groundwater. However, the possibility of using those filter media as a plant-based water treatment method is not currently practiced or researched in coastal regions. This water filtration system was made by vertical free flow system, which will focus on cutting down the cost while maintaining filter effectiveness, and by providing affordable water filters for the rural and remote coastal areas. Hence, this study's objectives were to elucidate the quality of water before and after filtration in terms of concentration of nitrate N, total suspended solids, total hardness, dissolved phosphate, ammonia, alkalinity, chloride and other basic water quality parameters and to assess the effectiveness of different filter media filtration through a low-cost water treatment system.

In Jaffna and Dikowita areas, groundwater is the primary water source for domestic, agricultural and industrial purposes. Nevertheless, increased water pollutants and concentration of chemical compositions of water are the two major water quality problems prevalent in this area (Shanthamareen & Wijerathne 2017). In the Jaffna peninsula, high nitrate concentrations in groundwater that exceeds the WHO guidelines are reported to be widespread (Foster 1976; Gunesekaram 1983; Dissanayake et al. 1984), with concentrations locally in excess of 200 mg/L. In addition, high oil and grease levels indicate a potential source of crude oil contamination in the Jaffna area. Therefore, it is recommended to continuously monitor the nitrate and oil and grease concentrations in well water and to apply suitable water treatment methods to reduce excess nitrate and oil and grease in drinking water (Wijeyaratne & Subanky 2017). Consequently, both freshwater and available groundwater resources are not suitable for human consumption (Welker et al. 2005). In both areas, people depend on tap water for drinking purposes (Ashraf et al. 2016). Shallow well water, which is commonly available throughout the Dikowita area, is often contaminated and usually consumed untreated in day-to-day activities, excluding drinking purposes. Many people in that area closed their wells without use. The treatment of water for potable purposes in coastal area is fraught with issues (Al-Khalili 1999).

The samples collection was conducted from August to October in 2019. Pre-cleaned 2.5 L volume sampling bottles, which were rinsed three times with deionized water to avoid the risk of contamination, were used to collect samples. Triplicate water sample (n = 12) were taken randomly from the domestic well in Dikowita and Thanankilappu sampling sites in Jaffna area and preserved in accordance with American Public Health Organization (APHA 2012). These sample bottles were sealed, transported to the Laboratory of National Aquatic Resources Research & Development Agency (NARA), and placed in a dark environment at a constant temperature below 4 °C temperature to avoid any contamination and the effects of light and temperature.

Accordingly, the adsorption media were prepared as follows. S. potatorum seeds were collected from a herbal shop. First, size reduction was achieved by cutting the seeds into pieces using nutcrackers. Later, seed particles with different grain sizes were obtained. Second, seeds were sieved from using a 1 mm mesh sieve and the remaining seeds were selected. Third, seeds pieces were rinsed five times using de ionized water to remove all the unnecessary materials and prevent any absorbents. Fourth, it was placed in an oven at 50 °C for 1 day. The resulting seeds were stored in a desiccator in a cool dry place until use in the filtration experiment. T. arjuna roots were collected from the paddy area and rinsed with deionized water to remove unnecessary particles. Roots were cut down into small pieces without harming the fibrous roots and the roots were sun dried for several days. The resulting roots were stored in a desiccator in a cool dry place until use in the filtration experiment. P. emblica leaves were collected from a home garden. Then, fresh mature P. emblica leaves were rinsed with distilled water and placed in the shade and sun dried for 1 week and then stored at room temperature and preserved until further use). The shade dried leaves were grinded into powder form using a grinder (Bright elegant- 240V6A). The resulted powder was stored in a desiccator in a cool dry place until use in the filtration experiment.

In terms of onsite analysis of quality of raw water, temperature, pH, salinity, Electrical Conductivity (EC), and Dissolve Oxygen (DO) were measured. The standard methodology for each parameter was followed as shown in Table 2.

Then the raw water samples were preserved by using concentrated sulfuric acid in accordance with (APHA 2012) and transported to the laboratory. The laboratory analysis was performed by following the methodologies described in APHA (1912) to assess the water quality of before and after filtered samples (Table 3).

Triplicate data were tabulated using Microsoft Excel (2013) and then rechecked for accuracy to ensure quality assurance and quality control measures. Subsequently, the mean value of each parameter was calculated using Microsoft Excel (2013). IBM SPSS Statistics 23 software package was used for statistical analysis. A paired sample t-test was used to assess the water quality parameters before and after filtration where observations in one sample can be paired with observations in the other sample. In this test, before and after observations of three filter media on the same subjects were statistically analyzed. The results of the paired sample t-test were used (α = 0.05, CI = 95%) to assess the difference between raw water and after filtration of T. arjuna, S. potatorum, and P. emblica.

The obtained mean values were compared with SLS standards to assess the suitability of treated water with SLS drinking water quality standards (SLSI 614, SLSI 2013).

The measured water quality parameters of the water samples collected from coastal wells in Jaffna and Dikowita before and after filtration through the three-filter media are given in Tables 4 and 5 respectively.

The filtration through T. arjuna roots significantly reduced the mean EC from 7460.33 ± 63.80 to 5178.33 ± 22.42 μs/cm, TSS from 0.0086 ± 0.001 to 0.0047 ± 0.001 mg/L, DO from 6.44 ± 0.04 to 8.07 ± 0.24 mg/L, ammonia from 0.368 ± 0.008 to 0.098 ± 0.035 mg/L, nitrite from 0.088 ± 0.001 to 0.391 ± 0.009 mg/L, phosphate from 0.169 ± 0.006 to 0.134 ± 0.005 mg/L, TH from 441.67 ± 22.15 to 309.00 ± 6.08 mg/L, alkalinity from 723.33 ± 6.01 to 537.50 ± 11.27 mg/L and chloride significantly reduced from 1755 ± 43.59 to 1166.67 ± 7.27 mg/L in the Jaffna area (Table 4). Filtration through S. potatorum seeds significantly declined the EC, nitrite, nitrate, TH, and alkalinity concentration of the water samples. Furthermore, filtration through P. emblica leaves significantly reduced the concentration of the selected parameters. However, filtration through T. arjuna roots did not significantly change the pH and nitrate concentration of the water samples. Filtration through S. potatorum seeds did not have a significant effect on TSS, DO, ammonia, phosphate, and chloride concentrations (Table 4).

The T. arjuna roots had a significant effect on the EC, TSS, nitrate, phosphate, TH, alkalinity, and chloride concentration of the filtered well water in the Dikowita area. Filtration through S. potatorum seeds significantly reduced the EC, ammonia, nitrate, and TH concentration of filtered well water samples but did not create a significant difference for the other parameters.

The filtration through P. emblica seeds significantly reduced the mean EC from 1359.33 ± 18.85 to 906.66 ± 7.31 μs/cm, TSS from 1359.33 ± 18.85 to 906.66 ± 7.31 mg/L, DO from 5.61 ± 0.11 to 12.54 ± 0.14 mg/L, ammonia from 0.057 ± 0.001 to 0.0387 ± 0.002 mg/L, phosphate from 0.117 ± 0.001 to 0.060 ± 0.008 mg/L, TH from 298.33 ± 8.82 to 142.67 ± 5.61 mg/L, alkalinity from 268.33 ± 8.82 to 211.67 ± 7.26 mg/L, and chloride concentration from 221.67 ± 4.41 to 165.00 ± 2.89 mg/L of the water samples. However, filtration through the selected filter media did not change the pH and nitrite concentration of the water samples significantly (Table 5).

Based on the SLS 614: 2013 drinking water quality standards, pH, dissolved phosphate, nitrite, and nitrate concentrations values of both locations were recorded within the SLSI standards for safe drinking water before and after purification. However, herbal materials significantly reduced these parameters of the treated water.

The ammonia, TH, alkalinity, and chloride concentration in the raw water sample of Jaffna were significantly higher than the SLSI standards. However, chloride concentration was below the SLSI standards and ammonia, TH and alkalinity exceeded the SLSI standards for safe drinking water in the Dikowita raw water sample. The reduction of ammonia, TH, alkalinity, and chloride concentration in Jaffna after filtration through all filter media have not achieved the SLSI standard for safe drinking water. Nevertheless, Figure 3(d) and 3(e) shows that the treatment materials were able to successfully meet the SLS drinking water quality standard for TH and alkalinity after filtration of Dikowita groundwater samples. TH and alkalinity of the water samples were significantly decreased by filtration through P. emblica leaf and T. arjuna roots. Based on the results of Figure 3, it is clearly shown that ammonia (Figure 3(c)) and chloride concentration (Figure 3(f)) in well water did not exceed the drinking water quality standard before and after purification. On the other hand, high concentrations of ammonia and chloride before and after filtering Jaffna samples exceeds drinking water quality. However, all the filter media contributed positively in the reduction of these concentrations.

pH concentration was found to be slightly alkaline in Jaffna raw water samples. However, the pH, dissolved phosphorus, nitrate and nitrite concentration in both initial water samples and the ammonia and chloride concentration in Dikowita raw water samples are within the tolerable limit for drinking water quality standards according to the SLS 614: 2013. However, the highest concentration of ammonia and chloride concentration were recorded in Jaffna. These levels significantly exceeded the SLSI drinking water standard. Further, the EC and TSS in well water were also observed to exceed the WHO (2008) recommended drinking water standard in Jaffna. However, EC and TSS levels in the Dikowita sample was slightly higher than the drinking water standard. The observed results have shown that the highest concentration of total hardness and alkalinity in both well water samples exceeded the safe drinking water standards in Sri Lanka.

There was a clear difference in the reduction percentage of phosphate compared to filter media. The findings showed that after passing through the S. potatorum seeds medium in Dikowita location, the lowest percentage reduction was recorded for phosphate with 0.44% and for pH with 0.41%. However, all three-filter media in both locations have an analogous effect on TSS, TH, alkalinity, and chloride removal efficiency. Moreover, the observed results illustrate that the most significant removal efficiency was found from dried P. emblica leaves with 86.83% in Dikowita. Furthermore, the minimum effectiveness was found from S. potatorum seeds from both locations. However, it can be noted that there is a significant impact on removal efficiency for all parameters after filtration through the filter media.

The results of the present study indicated that water quality in terms of ammonia, TH, alkalinity, and chloride concentration at the study areas are not suitable for drinking. Therefore, it is extremely important to remove these harmful substances from drinking water to prevent adverse effects on human health. Therefore, household purification procedures, which are the most basic and affordable technologies, are crucial to removing impurities from contaminated water in coastal areas. The filter was designed by trial-and-error methods.

The physicochemical characters of this study's samples were undesirable before treatment. Considering the raw water sample in Jaffna, raw water contamination is higher than the Dikowita well water samples. This well water cannot be used for drinking and other domestic consumption, therefore proper treatment is needed to ensure the water quality is at acceptable standard levels. The Jaffna sampling location is located close to the open sea and the seepage of seawater may be the reason for such higher hardness concentration in the water. Thus, all samples in Jaffna could not meet the SLSI standard except nutrients and pH concentration, for TH concentration 329.6, 355.3 and 294.6 mg/L, alkalinity concentration 573.5, 630 and 503.3 mg/L and chloride concentrations in 1166, 1270 and 1156.6 mg/L in T. arjuna, S. potatorum and P. emblica respectively. These high levels of hard water concentration can be reduced by increasing the packing density of the filter medium. Wijeyaratne & Subanky (2017) reported that TH in well water in Jaffna Peninsula is relatively high due to the presence of calcium, magnesium, chloride, and sulphate ions. In addition, calcium is the major cause of high hardness levels in groundwater in the Jaffna Peninsula (Shanthamareen & Wijerathne 2017). Calcium and magnesium are primarily found in groundwater due to the dissolution of limestone and the substantial contribution from the weathering of rocks depending on the interaction of other factors, such as pH and alkalinity (Panabokke & Perera 2005). Although the residents of Jaffna Peninsula have consumed water with high levels of dissolved solids and hardness over the decades, water exceeding the drinking water standards cannot be recommended for consumption without treatment as hard water may cause formation of bladder stones due to the higher phosphate concentration from sampled wells (Shanthamareen & Wijerathne 2017). Further, the majority of the population is dependent on fisheries and agriculture as their major livelihood in the Thanankilappu area. In recent years, intensification of agricultural activities has resulted in excessive use of artificial fertilizer, thus resulting in leaching of excess fertilizer to groundwater in the Jaffna peninsula (Sutharsiny et al. 2014). However, the nitrate, nitrite and phosphate concentrations recorded in the present study are comparatively lower than previous studies. Additionally, the values of the present study do not exceed the SLSI standards for safe drinking water. However, the groundwater of the Jaffna is recorded to have high levels of nitrate, nitrite, and dissolved phosphate levels compared to the Dikowita samples. Salt water seepage including fertilizers extensively used for their intensive agriculture in Jaffna, may be the main reason for the high nutrient concentration in the wells. In addition, the tidal fluctuations in certain areas greatly affected water contamination with increasing EC and salinity concentration. Furthermore, the addition of abundant nitrogenous waste and synthetic and animal fertilizers was identified as the major cause for nutrient contamination (Dissanayake et al. 1984). The proximity of toilets and poor design of soakage pits also may contribute to the high nutrient levels in the wells (Wijeyaratne & Subanky 2017).

The present study indicated that the T. arjuna roots, S. potatorum seeds and P. emblica leaves significantly reduced the EC, ammonia, nitrite, TH and alkalinity concentration of the filtered well water samples in Jaffna and significantly reduced EC and TH concentration in the Dikowita sample. However, filtration through the filter media did not change the pH level of both well water samples significantly (Tables 4 and 5). According to the optimum removal efficiency of impurities by filtration through T. arjuna roots, it could significantly reduce all contamination in the water. As a consequence, the highest effectiveness was given by the reduction of phosphate concentration at 86.83% and nitrite concentration of 85.34% from Dikowita and Jaffna respectively (Figure 4(a) and 4(b)). Therefore, the roots from T. arjuna have been shown to be one of the most effective primary coagulants for water treatment. In comparison to other commonly used medicinal plants, the bark of T. arjuna contains a very high level of flavonoids. Some of the flavonoids obtained from its bark include pelargonidin, arjunolone, flavones, kempferol, quercetin, and bicalein. The bark, leaves, roots and fruit possess glycosides, and large quantities of flavonoids, tannins, and minerals (Nema et al. 2012). The capability of T. arjuna roots can be used in small scale to reduce water contamination as the T. arjuna tree is commonly distributed in tropical countries including Sri Lanka (Rao et al. 2016). Shanthamareen & Wijerathne (2017) reported that after filtration through the powdered mature leaves of T. arjuna, the TH and Nitrate-N was reduced significantly. They also stated that T. arjuna leaf powder can be used as an effective low-cost household treatment method to improve water quality in terms of TH and Nitrate-N. The study of (Rao et al. 2016) determined the adsorption properties of T. arjuna fruit powder for the removal of lead (Pb) (II) from aqueous solution.

Comparison of the SLS 614: 2013 drinking water quality standard of the pH, nitrite, nitrate and dissolved phosphate values from before and after filtered water was recorded within the standard levels in both locations (Figure 3). The upper limit range of the ammonia, TH, alkalinity and chloride values exceeded the standard levels for safe drinking water in filtered Jaffna water.

Thus all filter media seems to be more effective in reducing the initial concentration of ammonia, TH, alkalinity and chloride concentrations in the Dikowita sample to meet the standards stipulated by SLS 614: 2013. However, there are no standard limits for TSS and EC under SLS 614: 2013 drinking water standards. The reported EC value in Jaffna raw water sample exceeded the WHO (2008) recommended drinking water standard. The compliance or exceedance probability of SLS 614: 2013 standard was used to describe the effectiveness of the treatment options rather than the removal efficiency, as they represent how well the treatment method is capable of reducing the contaminant concentration to meet the SLS 614: 2013 drinking water quality standard (Smeets & Medema 2006).

Dried P. emblica leaves also proved to be a good adsorbent in removal of contaminants in water. However, there were no previous studies carried out to P. emblica leaves used as a filter medium. Most of the research carried out to seeds and woods of P. emblica were for reduction of alkalinity, acidity, TH, chloride, magnesium, DO, BOD, COD in the water sample (Simpi et al. 2011; Padmapriya et al. 2015). From the above results, it is clear that P. emblica leaves can be used to treat hard water at the household level which is contaminated with TSS, TH, EC, alkalinity, chloride, ammonia, nitrite and nitrate and other water related contaminates. Hostettmann et al. (1977), reported ‘these plants containing flavonoids, terpenoids, steroids, phenolic compounds and alkaloids have been reported to have antimicrobial activity’. The study of Ancy et al. (2016) found that treatment with P. emblica wood reduced the hardness related parameters and 1.5 g of wood was found to remove 35% of TDS, 82% of calcium, 41% of magnesium and 86% of TH from the water sample in 2 hours. The wood of P. emblica is used to clear small rain ponds in the Indian peninsula to obtain safe and healthy drinking water. This is practically a low cost and effective way to afford contaminated water fit for human consumption (Durairasan 1999). Padmapriya et al. (2015) revealed that the taste of the hard water before treatment with P. emblica was too salty to taste but after treatment with P. emblica the taste became bearable and the changes were gradual. Moreover, they said that ‘Reduction of contaminant levels in water may be due to the chelation property of P. emblica wood’. Therefore, it reduces the contaminant concentration in water.

The results obtained in this study further showed that minimum removal efficiency was observed from S. potatorum seeds in both coastal waters. As a consequence, a smaller removal rate was observed by pH concentration of 0.41% and phosphate concentration of 0.44%, from Dikowita. Packialakshmi et al. (2014) showed that powdered S. potatorum seeds are very effective for drinking water treatment and for removal of pathogenic organisms. They observed the effectiveness of S. potatoram seeds for removal of turbidity, TH, pH, and TDS. Furthermore, in earlier studies Rajendran et al. (2013) showed that direct filtration with S. potatorum seeds as coagulant appeared effective in clarifying turbid water. As a result, TSS and TDS are removed due to the coagulation formed by proteins and alkaloids. Additionally, Mallikharjuna & Seetharam (2009) alkaloid fractions isolated from S. potatorum seeds were tested for their antimicrobial properties against some pathogens. Those results show considerable antimicrobial activity against both bacteria and fungi.

Considering past studies, plentiful actions can be taken to increase the reduction efficiency of filtered well water. For instance, the flow rates of the filtering system vary with the different filter medium and different packing densities. The efficiency of these parameters could be improved by increasing the packing density, consequently improving the flow rate and retention time of the filtering system (Sosthene et al. 2018). According to the present study, S. potatorum seeds removal is not very efficient for reduction of contaminations in coastal well water. This may be due to the larger particle size of material being used. Particles with smaller grain size or powdered materials will be more suitable for the removal of contaminants.

Based on the findings from this study, all filter media indicated a good reduction of all physical-chemical parameters. However, the results of the present study provide very important information on the ammonia, TH, alkalinity and chloride reduction ability of T. arjuna roots and P. emblica leaves. According to the study, T. arjuna roots and P. emblica leaves are the best filter media for coastal well water filtration to reduce the selected pollutants. In this study, we have investigated the effectiveness of locally available herbal plant materials to improve drinking water quality. The present study can be used as a baseline study to implement an advanced water filtration system to purify the drinking water in coastal region, Sri Lanka.

The water collected from the domestic wells located in Jaffna and Dikowita coastal regions cannot be used for drinking and other domestic uses without any treatment technique. According to the study, T. arjuna roots were the most effective filter medium because they have specific phytoremediation capabilities for water filtration. Similarly, P. emblica leaves have also been shown to be a good adsorbent for removing contaminants in water. Therefore, T. arjuna and P. emblica can be used as a home remedial treatment method for treating contaminated water in coastal regions in Sri Lanka. Further studies are required to identify the phytoremediation that increase the water quality by filtering through T. arjuna roots.

The authors would like to extend sincere thanks to the National Aquatic Resources Research & Development Agency research project and Ocean University of Sri Lanka for providing financial assistance to carry out this work successfully. We express our sincere appreciation to the National Aquatic Resources Research and Development Agency's (NARA) Environmental Studies Division for providing the technical assistance, chemical analytical facilities, and logistical support for the study.

The authors have no competing interests to declare.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.