Low cost drinking water treatment using indigenous materials for remote communities in developing countries

Groundwater in many remote areas in developing countries was polluted with various harmful contaminants such as heavy metals and fluoride. The existence of these contaminants in polluted groundwater usually exceeds the standard limit recommended by the World Health Organisation (WHO) for drinking water quality. The primary objective of this study was to examine the use of indigenous natural products that are locally available, non-toxic, easy to prepare and biodegradable. It was expected that natural material can be an alternative to the expensive and harmful chemicals used for drinking water treatment. Based on previous studies, Moringa oleifera (Moringa seeds), Cicer arietinum (chickpeas), Musa Cavendish (banana peel), Cocos nucifera (coconut's solid endosperm) and Lentinus edodes (Shiitake mushroom) were selected as natural water purification agents to examine their potential of removing various contaminants from polluted groundwater. However, it is important to realise that the effectiveness of each biomass tends to vary, depending on the contaminant. For this study, coagulation was selected as the key treatment process due to its practicality and simplicity to be used by non-skilled remote communities with small-scale water treatment systems. This research focused on groundwater as it is a major source of drinking water supply especially for many remote areas in the developing countries such as Pakistan, India, Sri Lanka and Bangladesh. It was documented in the literature that arsenic (As) and fluoride were the most concerned water contaminants due to their excessive level in groundwater, followed by other heavy metals such as lead (Pb), nickel (Ni) and cadmium (Cd). These harmful chemicals will lead to long-term effects on human health. Turbidity is generally not an issue for groundwater quality because the underground water has been filtered through the natural soil filtration system. Only in certain cases, groundwater was found turbid and aesthetically unpleasant due to the improper groundwater abstraction. In this study, the effectiveness of plant-based materials for the removal of low concentrations of As, Pb, Cd, Ni, fluoride and turbidity were investigated. Batch tests with individual biomass and their combinations were conducted at a pH of 7. Synthetic groundwater samples with known concentration of As, Pb, Ni, Cd, fluoride and turbidity was prepared, each with different biomass dosages ranging from 100 mg/L to 600 mg/L and different biomass dosing methods (single, combination and sequential manners) were attempted. Based on the preliminary screening, Moringa oleifera (MO) and Musa cavendish (MC) have been chosen to be used for the study based on their efficiency in removing target contaminants. The optimum efficiency was achieved by using combination of MO and MC (MO+MC), which dosed either in a mixing or in a sequential manner. The optimum biomass dosage was 200 mg/L for the individual biomass and 200:200 mg/L for the combined biomass. Unlike chemical coagulants such as alum, natural materials did not significantly affect the pH of water during treatment. Treatment tests were also conducted on actual groundwater samples to verify the applicability of the studied treatment process on actual applications. The results suggested that the MO+MC was capable of treating actual groundwater samples to meet the required WHO standards. Characterisation study of the combined biomass (MO+MC) before and after the treatment process was conducted using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) in order to determine the possible mechanisms behind the removal of each contaminant. Based on the FTIR spectral analysis, carboxylic acids, primary and secondary amines as well as carbonyl (amides) were identified as the dominant functional groups in MO, MC and MO+MC which were favoured during the adsorption of the contaminants. SEM exhibited that there was an abundant availability of porous and irregular surfaces which provide binding sites that facilitate the accumulation of target contaminants on the biomass. On the other hand, through EDX analysis, EDX spectra of the contaminant-loaded biomass (after treatment) exhibited specific feature (element) which corresponded to the presence of the target contaminants through adsorption. It was revealed that adsorption (chemisorption and physisorption) was the main mechanism for the removal of target contaminants besides ion exchange and surface complexation. Therefore, existing adsorption models were evaluated by fitting the experimental adsorption data of single-contaminant and multi-contaminant elements to predict the treated groundwater quality. Based on the results, most of the experimental adsorption data provided an agreement with the Freundlich model, which was then selected to predict the final groundwater quality. Variations of input water quality were generated using a simple Monte Carlo simulation method (random number generation) to simulate the actual groundwater quality. These water quality samples were subjected to the selected treatment process. The probability of the groundwater quality (after the treatment with MO, MC and MO+MC) complied with WHO standards were also predicted. The results showed that 94% and 91% from 1000 samples of groundwater contaminated with Pb were complied with WHO standards after treated using MO and MO+MC respectively. Furthermore, 98% and 84% from 1000 samples of groundwater contaminated with Ni and Cd, respectively, complied with WHO standards. At the final stage of the research, cost estimation of the proposed treatment method (MO and MC dosed in a mixing manner) was carried out. It was assumed that there would be no cost incurred on the natural materials of biomass as they would be freely available in the selected countries. The only cost that might be incurred during the treatment process was the investment on raw groundwater storage, coagulation reactor and sand filter containers, grinder as well as the siever. The contaminant-loaded biomass was managed using native earthworms called Perionyx excavatus which was previously reported capable of converting arsenic from plant available form to plant unavailable form. Therefore, after cost estimation analysis, it appears that the proposed treatment would be economically feasible to the remote communities in the developing countries. To sum up, this research had demonstrated that tropical plant-based materials had the potential in removing target contaminants from contaminated groundwater to meet WHO standards for drinking water. The understanding of the whole process was essential in developing an operational scale decentralised treatment system in the future.