Low cost and sustainable surface water purification methods using Moringa seeds and scallop powder followed by bio-sand filtration

Safe drinking water is a fundamental need for healthy human life and water has been shown to be linked to the development of all areas including health, nature, urbanization, industrialization, energy production, food security, and equality, etc. (Colwell et al. 2003). In all these areas, not only water but also its cleanliness, purity, safety and quality are required to ensure proper development. According to the United Nations, to meet daily necessities such as drinking, cooking, and personal hygiene, approximately 20–40 L of clean water is required by each individual. In today's world, scarcity of safe water is a burning issue; especially in developing countries where nearly 1.0 billion people lack fresh water for daily uses (Aho & Lagasi 2012).

Approximately 71% of the earth's surface is covered with water and more than 97% of the earth's water is salty sea water, while 2% is stored in glaciers, ice caps, and snowy mountain ranges (Yongabi 2010) and thus less than 1.0% of the earth's water is surface water, of lakes, rivers, streams, ponds (0.022%) and groundwater (0.397%) available for humans for their daily needs (Yongabi 2010). However, all this accessible surface water is not necessarily safe for drinking, and depending on the location and sources, clean water is exposed to a variety of contaminants, many arising from human and animal wastes, debris from homes, chemicals from industries, fertilizers and pesticides from agricultural lands, environmental pollutants and so on (Ngwenya 2006). In addition, insanitary practices of people has greatly contributed to the deterioration of the quality of surface water sources. On the other hand, groundwater is the most important source of water supply in Bangladesh. Groundwater is clear, colorless with little or no suspended solids and has a relatively constant temperature. Groundwater is also free from disease-producing micro-organisms which are normally present in large numbers in surface waters. However, groundwater for drinking purposes has become a problem because of: (1) the presence of arsenic; (2) excessive dissolved iron; (3) salinity in the shallow aquifers in the coastal areas (Sawai et al. 2013); (4) lowering of groundwater level; and (5) rock/stony layers in hilly areas. Among these problems arsenic in groundwater has become a great concern for the water supply in Bangladesh. According to a study by the World Bank's Water and Sanitation Programme (2014), about 28 million Bangladeshis, or just over 20% of the population, are living in harsh conditions for receiving clean water, and the safe, clean water supply situation will worsen in the coming decades to meet the needs of a predicted 200 million people by 2020 (Silvia et al. 2011).

Depending on the water sources, numerous water purification methods were developed to disinfect surface water to make clean water. For decades, the commonly used methods for treating water are reverse osmosis, ion-exchange, ultraviolet (UV)-irradiation, coagulation with aluminum sulfate (alum) and iron (II) chloride etc. The purpose of all these treatments is to inactivate microorganisms and to remove organic and inorganic particles from the water before consumption (Yongabi 2010). However, recent studies claim that these methods are becoming un-ecological, expensive to run, manage and maintain, and most importantly, unhealthy. Excessive use of coagulant chemicals has dreadful consequences for health being linked with cancer, neurological disorders, etc. (Amagloh & Benang 2009; Yongabi et al. 2011; Aho & Lagasi 2012; Mangale et al. 2012). On the other hand, several filtration methods have also been used, depending on the pore sizes, carbon block filters, porous ceramic containing colloidal silver, reactive membranes, fibre or cloth filters, to get clean water (WHO 2011).

To circumvent the use of chemical agents to purify water, scientists have started focusing on natural products which can be used to treat water (Amagloh & Benang 2009). Varieties of plants and their different parts were screened for coagulation and antimicrobial activity (Mangale et al. 2012). Moringa oleifera (drumstick) was found to be a useful plant and numbers of studies have been carried out to establish the coagulation activity of the seed of this plant (Ali et al. 2009; Choubey et al. 2012; Zaman et al. 2013; Kalikawe et al. 2015). Heated scallop shell powder has been permitted to be used as a food additive in many countries. Many study reports demonstrated that heated scallop shell powder treatment successfully decreased bacterial count in shredded cabbage, lettuce, frankfurters, and destroyed Bacillus subtilis spores, and inactivated or removed many foodborne pathogens including Escherichia coli, Salmonella spp., Listeria spp. and Staphylococcus aureus from the surfaces of wide ranges of fruits and vegetables (Sawai et al. 2001, 2003; Kim et al. 2006; Kubo et al. 2013).

Disinfection of surface water by boiling is an effective and better practice, because it will kill all waterborne pathogenic microorganisms. However, boiling practices are not routinely used in villages because of high costs and a limited supply of fuel and wood in rural Bangladesh. Moreover, during severe flooding, which frequently occurs in Bangladesh, there are geographical areas that experience a reduction in the quality of life to mere survival, when even the barest necessities are difficult to obtain and building fires to boil water is simply not possible. Thus, the common practice in villages in Bangladesh is to use cloth, frequently a flat, unfolded piece of an old sari, to filter water and home prepared drinks (Huq et al. 2010). Hence, a sari filter was used in this study.

We were looking for a simple, inexpensive and environmentally friendly technology using locally available natural coagulant and antimicrobial agents followed by bio-sand filtration to convert surface water to drinking water. Thus, in this study, Moringa seed powder alone and/or in combination with scallop powder was used in treating surface water and then passed through sari or natural bio-sand filtration (sand, charcoal, and gravel) to make clean and potable water at the household level.

Surface water samples were collected from Shahidullah Hall, Jagannath Hall, Bangla Academy pond of Dhaka University area, Dhanmondi Lake and river water was collected from Shitalakshya River at Narayangonj, Padma River at Manikgong, and Meghna River at Bhola District of Bangladesh. Care was taken while choosing locations and point of water collection of ponds, rivers, and lakes. Immediate vicinities of the pond corner were avoided and samples were collected from approximately 150 cm distance from the corner of the ponds. Water samples from a depth of 4.0–6.0 cm were collected in sterile polyethylene terephthalate (PET) bottles according to the standard procedures of APHA (1992) and transported to the laboratory in an insulated cool box maintaining a temperature of 6–8 °C within 4–6 hours of collection. Microbiological and physico-chemical analysis of the collected water was done on the same day. The collected water samples were either filtered through eight-fold cotton sari to reduce/eliminate protozoa and debris, or not filtered before analysis.

One of the cheapest ways of removing turbidity is by filtering the turbid water with cotton clothes. These fabrics are cheap and readily available, which make them perfect materials for water treatment in rural areas. Cotton sari clothes (a traditional garment of unstitched cloth ranging from 4 to 9 m in length that is draped over the body of women) is folded over three times (eight layer) and a water sample was passed through the folded sari. Both non-filtered and filtered water were analyzed for physico-chemical and microbiological analysis.

A bio-sand filter is a point-of-use water treatment system adapted from traditional slow fine sand filters. Bio-sand filters for this study were typically constructed using a PVC pipe with a tightly fitted lid to prevent contamination and unwanted pests from entering the filter. A 3-step bio-sand filtration was constructed as shown in Figure 1. At the top of the filter, fine sand (0.1–0.3 mm in diameter) column (12 cm), below the sand column, a layer of charcoal (0.8–1.0 mm in diameter) (12 cm) and below the charcoal column, a layer of gravel (3.0–4.0 mm in diameter) (12 cm) was placed. Each layer was separated by using plastic mesh that prevents sand particles entering into the charcoal column and charcoal particles into gravel layer. A water sample was passed through the bio-sand filter and both the non-filtered and filtered water was analyzed for physico-chemical and microbiological analysis.

The physico-chemical properties including color, odor, taste, pH, turbidity, total dissolved solids (TDS), biological oxygen demand (BOD), chemical oxygen demand (COD), conductivity, major metal (Fe, Na, Ca, Mg and Zn) contents, heavy metals (As, Cd, Cr, Pb) contents were carried out according to the US EPA (2015) and BSTI (2001) standard methods.

The bacteriological analysis includes total aerobic bacteria, total coliform, fecal coliform and presence of E. coli, Salmonella sp. and Vibrio sp. was carried out according to the USFDA Bacteriological Analytical Methods (2001). Spread plate technique on selective and non-selective agar media was used to identify specific bacteria. Tryptic Soy Agar (TSA, Fluka, USA) for total aerobic microbial count, Hichrome TM Coliform Agar (Fluka, USA) for total coliform count, Sorbitol MacConkey Agar (Oxoid, UK) for E. coli, Bismuth Sulfite Agar (BD, USA) for Salmonella sp., and Thiosulfate–Citrate–Bile salts–Sucrose Agar for Vibrio sp. were used in this study. All the agar plates were incubated at 35 °C for 24–48 hours before being counted. At least five randomly picked presumptive colonies of E. coli, Salmonella sp. and Vibrio sp. were isolated from selective agar and confirmed using API 20E kit (bioMerieux sa, Marcy-l'Etoile, France) and biochemical test.

The cytotoxic effect of Moringa powder and scallop powder was carried out on BHK-21 and HeLa cells using tissue culture methods at the cell culture laboratory of the Centre for Advanced Research in Sciences, University of Dhaka. In brief, HeLa, a human cervical carcinoma cell line, and BHK-21, a baby hamster kidney fibroblast cell line, was maintained in Dulbecco's Modified Eagles medium (Sigma, UK) containing 1.0% penicillin streptomycin (1:1) and 0.2% gentamycin and 10% fetal bovine Serum. HeLa (1.4 × 10⁴/100 μL) and BHK-21 (8 × 10⁴/100 μL) cells were seeded onto 96-well plates and incubated at 37 °C + 5% CO₂ chamber. Cytotoxicity was examined under an inverted light microscope (Optika-XDS: 2ERGO, Italy) after 24 h of incubation. Duplicate wells were used for each sample.

The bacterial endotoxins test is an in vitro assay for detection and quantitation of bacterial endotoxins, a component of the cell wall of Gram negative bacteria. The endotoxins detection was carried out by limulus amebocyte lysate (LAL) test, using a lysate of amebocytes isolated from the horseshoe crab (Limulus polyphemus) clotting reaction. This reaction involves a coagulation cascade of sequentially activated proteases which formed clots with endotoxin. Both the non-treated and treated water samples were tested for bacterial endotoxins according to USFDA (2012) instructions.

All the trials were replicated five times. Reported data represented the mean values obtained from five individual trials, with each of these values obtained from duplicated samples. Data were subjected to analysis using the Microsoft Excel program (Redmond, Washington, DC, USA). Significant differences in plate count data were established by the least significant difference at the 5% level of significance. For other data mean ± SD values are presented in Tables 1 and 4.

However, a rare presence of pathogen was also evident and this finding suggests that complete elimination of pathogen is not possible with these treatment methods (Table 1). In contrast, when the same water samples were treated with MOSP followed by bio-sand filtration, no pathogenic bacteria was detected throughout the study. Similar experimental results were obtained in a challenge test (data not shown). This finding suggests that bio-sand filtration techniques are better than cotton sari and could be useful in eliminating bacterial contaminants in water.

Furthermore, in order to treat river/lake or pond water for drinking purposes, removal of high turbidity, bad taste and odor, and appearance are some of the main challenges and must be removed before being used for drinking purposes. One of the cheapest ways of removing turbidity is by filtering the turbid water with cotton sari clothes. These fabrics are cheap and readily available, which make them perfect materials for water treatment in rural areas. The turbidity of river/lake/pond water and sari filtered and/or bio-sand filtered water is presented in Table 2.

Turbidity is the measure of relative clarity of a liquid and the measurement of turbidity is a key test of water quality. In drinking water, the higher turbidity level may lead to gastrointestinal disease (Mann et al. 2007). Moreover, high turbidity in water is a possible source of microbial contamination and it also reduces the efficiency of the water purification systems (WHO 2011). The suspended solids interfere with water disinfection because the particles act as shields for the virus and bacteria. Similarly, suspended solids can protect bacteria from UV sterilization of water. Irrespective of water sources, higher turbidity ranging from 54.0 to 59.0 NTU was observed in raw water samples. Sari filtration alone can reduce the turbidity to 38.0–42.0 NTU or 30.0% and MOSP treatment further reduced the turbidity to 50% and MOSP treatment followed by cotton sari filtration was able to reduce it to approximately 70%. Goyal (2015) has shown that on passing a water sample through a cotton cloth folded over three times (eight layers), the turbidity of that water sample was reduced by 48.23%. This finding is also similar to this study of turbidity reduction using cotton sari cloths. In contrast, bio-sand filtration alone was able to reduce the turbidity by up to 80% and MOSP treatment followed by bio-sand filtration was able to reduce the turbidity by up to 99.9% and hence would be applicable for water filtration as the best filtration method compared to cotton sari filtration. According to the World Health Organization, the turbidity of drinking water should ideally be less than 1.0 NTU. Water with turbidity more than 1.0 NTU may be safe for drinking, but the visible cloudiness has a negative impact on consumer acceptability.

Irrespective of treatment and filtration, the other physico-chemical quality parameters including TDS, conductivity, BOD, COD, metal and heavy metal content was found within the recommended level except for pH. The pH of cotton sari filtered water was 9.9; this might be due to the addition of 0.01% scallop powder (Table 3). On the other hand, bio-sand filtration showed acceptable pH levels (7.3–7.6) over sari filtered water (9.8–9.9). When MOSP was added to the water the resulting pH was recorded as 9.8–9.9. This water passes through sand, charcoal and gravel and comes into contact with organic matter, and the presence of charcoal may absorb some color and stone might add some minerals to the water and consequently, the pH was reduced to neutral. In contrast, the sari filter does not have these materials and thereby retains the higher pH. When sari filtered water was treated with MOSP followed by second filtration with bio-sand filtration, the pH was found to be within acceptable limits. All these experiments demonstrated that bio-sand filtration is a better choice than the sari filter in converting surface water to clean water.

In addition, the aesthetic characteristics including bad color, taste and odor of water do not pose any health concerns to the people. However, clean water with a good taste and odor is always more acceptable to the consumer. The dead pathogens and dirt particles impart typically unpleasing taste, color and odor to the water and removing these tastes and odorants from the water will improve its aesthetic qualities considerably. The sand, charcoal and gravels used in bio-sand filtration reduced bad odor and taste and improved the appearance of the water. They also filtered out the microbial contaminants.

Access to clean water is a basic human right for everyone in the world and is a prerequisite for sanitation and health improvement. Water contamination is posing serious health problems in every developing nation. Considering the global statistics, around 135 million people will die from water-related diseases by 2020 if no requisite actions are taken. In order to improve the clean water situation, use of surface water from rivers is a better choice than withdrawal of excessive ground water. In Bangladesh, tube wells became a solution, but soon turned out to be a menace as they were contaminated with arsenic in many areas. Cities and towns are supplied with expensive large scale water treatment plants but this is not viable for the majority of the population in Bangladesh who live in isolated villages. A similar situation exists in most of the low resource countries of the world. Therefore, in this study, simple and inexpensive domestic scale technology for drinking water was developed for the rural population using locally available materials.

The Moringa oleifera Lam (Moringaceae) is a highly valued plant, distributed in the tropical and subtropical regions. It has an impressive range of medicinal uses with high nutritional value. The seed kernel of this plant has a considerable amount of low molecular weight and water soluble proteins. These proteins are characterized as positively charged in solution. After adding to water, the positively charged proteins primarily magnetize negatively charged particles (clay, silt bacteria, and other toxic particles). As a result, large flocs are formed by continuous agitation. Thus, the flocs are removed by settling or filtration (Aho & Lagasi 2012). The seed also serves as an antimicrobial agent as it contains a few antibiotics such as benzyl iso-thiocyanate and benzyl glucosinolate. These antimicrobial peptides either disrupt cell membrane or inhibit essential enzymes (Mangale et al. 2012). According to Ali et al. (2009), Moringa seed showed high coagulation activity in highly turbid water and vice versa. Water treated with Moringa seed showed decreased turbidity, total hardness, acidity, alkalinity and chloride concentration (Mangale et al. 2012). In addition, Moringa seed has not been found to contain any toxicity or cause any health risk to date (Mangale et al. 2012; Eze & Ananso 2014). This information is in agreement with the results obtained in this study.

On the other hand, scallop shell powder is known as the commercial waste product of scallop. The main component of scallop shells is calcium carbonate (CaCO₃), which is converted to calcium oxide (CaO) when heated (Zaman et al. 2012). Heated scallop shell powder possesses broad antimicrobial action against the vegetative cells of bacteria, spores, and fungi (Sawai et al. 1999, 2001, 2003). Scallop powder is applied to fresh vegetables and processed foods to reduce the number of viable bacterial cells. The Japan Ministry of Health and Welfare and FDA approved this heated shell powder as calcinated calcium for washing fresh fruits and vegetables and are thus used as an antimicrobial agent in this study.

Furthermore, activated carbon works via a process called adsorption, whereby pollutant molecules in the water are trapped inside the pore structure of the carbon substrate (Desilva 2000). Active charcoal carbon filters are most effective at removing chlorine, sediment, volatile organic compounds (VOCs), taste and odor from water (Taraba et al. 1990).

Sand filtration of drinking water has been practiced since the early 19th century and various scales of slow sand filters have been widely used to treat water at the community, and sometimes local or household, level (Droste & McJunkin 1982; Cairncross & Feachem 1983; Chowdhuri & Sattar 1990; Logsdon 1990; Palmateer et al. 1999). Bio-sand filters have been shown to remove 90–99% of pathogens found in water. The filter has been tested by various government, research, and health institutions, as well as by non-governmental agencies in both laboratory and field settings (Duke et al. 2006; Stauber et al. 2006; Ngai et al. 2007). A modified bio-sand filtration was found to be effective in removing both pathogens and heavy metal from source water (Muhammad et al. 1997; Ngai et al. 2007). On the other hand, the bio-sand filter designed in this study was appropriate for household use and contains a bed of about 12 cm of fine sand supported by charcoal and a gravel layer incorporated into a plastic pipe and a flow rate of about 0.1 m/hour. However, in the bio-sand filtration process, the accumulation of particles occurs within the top few centimetres of sand and can be cleaned manually or hydraulically by opposite direction or replaced on a regular but usually infrequent basis. Thus, additional spare PVC pipe could be provided to each household for obtaining a continuous supply of clean water.

Surface water treated with MOSP followed by natural bio-sand filtration was found to produce clean water. The bacteriological and physico-chemical quality parameters of this water showed non-significant differences in quality parameters recommended by EPA and BSTI. Moreover, the treated water stored for 6 months at room temperature did not deteriorate in quality, indicating the usefulness of this technology in clean water scarcity areas of the world, because the ingredients used are readily available, inexpensive, user friendly and natural. Therefore, despite many similar water purification systems available commercially, this new method would be the most simple, inexpensive and ecofriendly.

This work has been partially financed by the Japan International Cooperation Agency project entitled ‘Survey on securing drinking water using natural ingredient during a flood (SME Partnership Promotion)’. The authors would also like to thank the ORPCE Tokyo office for providing scallop powder and Engr Md. Mofizur Rahman, CARS, DU for designing a household filter to successfully complete this work.