Download PDF Technologies for Clean Water September 1, 2008 Volume 38 Issue 3 The Bridge, Volume 38, Number 2 - Fall 2008. The papers in this issue of The Bridge describe some recent advances in the search for water, in the distribution and treatment of water and wastewater, and in the modeling of complex water systems. Arsenic Filters for Groundwater in Bangladesh: Toward a Sustainable Solution Wednesday, December 3, 2008 Author: Abul Hussam, Sad Ahamed, and Abul K.M. Munir A simple filtration system used in Bangladesh and other countries removes dangerous arsenic from drinking water. The natural presence of arsenic and other toxins in groundwater, the most common source of drinking water, is considered a worldwide public-health crisis and an unprecedented natural disaster. Thirty-five countries around the world have reported adverse health effects from groundwater contaminated by arsenic (Mukherjee et al., 2006). In the Ganga-Meghna-Brahmaputra basin alone, some 500 million inhabitants are at risk from drinking arsenic-contaminated groundwater (Chakraborti et al., 2004). In Bangladesh, an estimated 77 to 95 million people of a total population of 140 million drink groundwater containing more than 50 micrograms per liter (?g/L), that is, 50 parts per billion (ppb) or 0.05 milligrams per liter (mg/L); the maximum contamination level (MCL) according to the Environmental Protection Agency (EPA) standard is 10 ppb. In Bangladesh alone, some 10 million tube-wells are contaminated (Chatterjee et al., 1995; Smith et al., 2000). However, the problem is not confined to Bangladesh. Millions of people in India, Nepal, Cambodia, Vietnam, and even the United States, to name just a few countries, are also vulnerable to the toxic effects of arsenic. FIGURE 1 Arsenicosis patient with hyperkeratosis and cancer on the palm. Drinking arsenic-contaminated water for a long period of time causes serious illnesses, such as hyperkeratosis on the palms or feet; fatigue; and cancer of the bladder, skin, and other organs (Figure 1) (IARC, 2001). In the long term, one in every 10 people with high concentrations of arsenic in their drinking water could die of cancer triggered by arsenic poisoning (Black, 2007). Options for Providing Clean Water The only solution to this crisis is to provide clean, potable water for the masses, water that is free of toxic chemical species and biological pathogens. Safe water options can be classified into three major categories: (1) treating surface water; (2) providing uncontaminated well water; and (3) filtering water. The first option, the treatment of surface water, is used extensively worldwide to ensure that anthropogenic contamination does not degrade water quality. In most developed countries, surface water is extensively treated and filtered before it is piped through an elaborate and expensive network and delivered to consumers. However, in underdeveloped countries such as Bangladesh, where surface water is highly contaminated with pathogenic bacteria and is often not potable, treatment systems are either not available at all or are too expensive for large segments of the population. For these and other reasons, millions of tube-wells were drilled to extract groundwater for drinking in hopes that they would provide uncontaminated water. Unfortunately, 30 to 50 percent of these wells turned out to be contaminated by high levels of arsenic and other toxic species, including pathogens (Islam et al., 2001). Thus the second option, providing uncontaminated well water, is also impractical in many areas. In Bangladesh, even though arsenic-free wells have been painted green to signal that they are safe and people have been strongly encouraged to collect water from these wells, many ignore the warnings for logistical reasons; for example, women must often travel long distances to reach these wells. As sweet water becomes scarcer everywhere, and as potable water supplies become increasingly vulnerable to contamination, the development of affordable water-filtration systems, the third option, is becoming more attractive. Some simple, affordable, sustainable technologies are available for filtering water to remove contaminants. The Grainger Challenge Prize for Sustainability The elimination of arsenic from drinking water, an urgent need for millions of people, was the subject of the inaugural Grainger Prize for Sustainability, which was funded by the Grainger Foundation and administered by the National Academy of Engineering (NAE). The goal of the challenge was to recognize the creators of affordable, reliable, low-maintenance, electricity-free technologies for reducing arsenic in drinking water to an acceptable level for human consumption. In February 2006, NAE announced three winners of the Grainger Prize (NAE, 2007). The first-place was awarded to the inventor (Abul Hussam) of the SONO filtration system, which is based on a composite-iron matrix (CIM). This system, which has been extensively tested and used in Bangladesh, meets or exceeds local government guidelines for arsenic removal. NAE recognized this innovative technology for its affordability, reliability, ease of maintenance, social acceptability, and environmental friendliness. The second-place award was given to Arup K. SenGupta and his team for a community water-treatment system based on activated alumina. The third-place award was given to Procter & Gamble for its PUR technology, which uses calcium hypochlorite (bleach) to kill a wide range of microbial pathogens and ferric sulfate to remove arsenic through flocculation-precipitation. Arsenic and the Nature of Groundwater Groundwater is a complex matrix in which many chemical species are present. Table 1 shows the compositions of typical groundwater found in Bangladesh. The origin of soluble arsenic in the water is now believed to be the result of the bio-reduction by bacteria of iron-arsenic in the soil (Polizzotto et al., 2005). The groundwater, which has a pH of 6.5 to 7.5, contains inorganic arsenic primarily in two oxidation states, As(III) in H3AsO3 and As(V) in H2AsO4– and HAsO42-. TABLE 1 Water Quality of SONO Filtered Water Compared to EPA, World Health Organization (WHO), and Bangladeshi Standards (1 mg/L = 1000 ?g/L). Empty entries indicate that data were not available. Constituent EPA (MCL) WHO Guideline Bangladeshi Standarda Influent Groundwater SONO Filter Waterb Arsenic (total) – ?g/L 10 10 50 5–4000c 3–30 Arsenic (III) – ?g/L 5–2000d < 5 Iron (total) – mg/L 0.3 0.3 0.3 (1.0) 0.2–20.7 0.19 ? 0.10 pH 6.5–8.5 6.5–8.5 6.5–8.5 6.5–7.5 7.6 ? 0.1 Sodium – mg/L 200 < 20.0 19–25 Calcium – mg/L 75 (200) 120 ? 16 5–87 Manganese – mg/L 0.5 0.1–0.5 0.1 (0.5) 0.04–2.00 0.22 ? 0.12 Aluminum – mg/L 0.05–0.2 0.2 0.1(0.2) 0.015–0.15 0.11 ? 0.02 Barium – mg/L 2.0 0.7 1.0 < 0.30 < 0.082 Chloride – mg/L 250 250 200 (600) 3–12 4.0–20.0 Phosphate – mg/L 6 0.5–50 < 1.5 Sulfate – mg/L 100 0.3–12.0 12 ? 2 Silicate – mg/L 10–26 18 ? 6 aBangladeshi standard values are given as maximum desirable concentration with maximum permissible concentration in parentheses. bSONO filters. ICP multi-element measurements of Cu, Zn, Pb, Cd, Se, Ag, Sb, Cr, Mo, and Ni show concentrations below the EPA and WHO limits at all times. All other measurements show average of semi-continuous measurement of more than 394,000 L of groundwater filtered by us and ETVAM in at least eight different water chemistries in different regions of Bangladesh. Water chemistry parameters were recorded for 23 metals, 9 anions, Eh, pH, Temp, dissolved oxygen, conductivity, and turbidity for hundreds of samples. All prescribed parameters passed the drinking water standards of WHO and Bangladesh. cOne tube-well at Bheramara was found to contain As (total) 4000 ?g/L. The filtered water had 7 ?g/L. This well was later capped by the government. dIn some wells As(III) concentrations exceeded 90 percent of arsenic in all forms. In most groundwater in Bangladesh more than 50 percent of the total arsenic present is in the form of the neutral H3AsO3. The remaining 50 percent is divided equally between two As(V) species (H2AsO4– and HAsO42–). An ideal filter has to remove all three species inexpensively, without chemical pretreatment, without regeneration, without producing toxic wastes, and in the presence of high-soluble iron, calcium, magnesium, phosphate, silicate, and other potentially interfering chemical species. Development of the SONO Filtration System Our work on water filtration began in 1997, about eight years before NAE announced the Grainger Challenge, when we set out to measure and mitigate arsenic levels in drinking water. We first developed a method and protocol for making accurate measurements of trace arsenic in groundwater in Bangladesh (IAEA, 2005; Rasul et al., 2002). Once we were able to measure contamination by arsenic on the ppb level, we were then able to test filtration technologies with groundwater in the field and to ensure quality control in the production of the filters. In our first paper on mitigation technology, published in 2000, we described the distribution of filters and the results in Bangladesh (Khan et al., 2000). FIGURE 2 Schematic illustration of the SONO filter (left) and a filter in use in a village hut (right). The SONO filter (Figure 2), a two-stage, pour-collect filtration system, was developed with Bangladeshi villagers in mind. The top bucket contains the arsenic-scavenging composite-iron matrix (CIM) sandwiched between two layers of sand. The bottom bucket is a simple sand and charcoal filter that cleans the water of residual iron and other impurities that may have drained from the first bucket. This design was selected for production after extensive experiments with alternative designs. Details of the materials, design, and function of the filter in the field, with extensive test data for other filter systems, have been reported elsewhere (Hussam and Munir, 2007). Table 1 compares the quality of SONO-filtered water to acceptable water-quality standards. The SONO filter can produce 20 to 60 liters of potable water per hour for at least five years of normal use for about $40 per filter. The SONO filter, and its predecessor the 3-Kolshi filter (the round clay pitcher shown in Figure 2) satisfied many of the design requirements tested in various stages of the Environmental Technology Verification for Arsenic Mitigation (ETVAM) Program, which was conducted by the Bangladeshi government to screen commercial filters (Alauddin et al., 2001). We realized from the beginning that the fastest way to test filter performance was to use real groundwater containing varied concentrations of arsenic, iron, and other inorganic species and to compare the results of filtering with potable water-quality parameters. The filtration efficiency of SONO was also compared in ETVAM field tests to filters using activated alumina, cerium hydroxide ion-exchange resin, and microfine iron oxide-based filters (BCSIR, 2003). The Search for Active Materials: From Zero-Valent Iron to a Composite-Iron Matrix Significant research has been done on the development of adsorbents and other materials for removing arsenic and other toxic species from water. A large number of adsorbents have been studied: oxides of granular metals, such as amorphous iron hydroxide (Pierce and Moore, 1982), hydrous ferric oxide (HFO) (Wilkie and Hering, 1996), granular ferric hydroxide (Driehaus et al., 1998), ferrihydrite (Raven et al., 1998), red mud (Altundogan et al., 2002), activated alumina (Lin and Wu, 2001; Rosenblum and Clifford, 1984; Singh et al., 2001), iron oxide-coated polymeric materials (Katso-yiannis and Zouboulis, 2002), iron oxide-coated sand (Thirunavukkarasu et al., 2003), Fe(III)–Si binary oxide (Zeng, 2004), iron oxide-impregnated acti-vated alumina (Kuriakose et al., 2004), blast furnace slug (Kanel et al., 2006), iron-cerium bimetal oxide (Dou et al., 2006), iron-coated sponge (Nguyen et al., 2006), nanoscale zero-valent iron (Kanel et al., 2005; Lien and Wilkin, 2005; Yuan and Lien, 2006), sulfate-modified iron-oxide coated sand (Vaishya and Gupta, 2006), HFO incorporated into naturally occurring porous diatomite (Jang et al., 2006), crystalline HFO (Manna et al., 2003), crystalline hydrous titanium oxide (Manna et al., 2004a), granular hydrous zircon-ium oxide (Manna et al., 2004b), and iron(III)-tin(IV) binary mixed oxide (Ghosh et al., 2006). Except for the classic method based on precipitation-coagulation of toxic impurities by flocculent iron-hydroxide precipitate, most of these studies were confined to determining removal capacity and kinetics. None of these materials was extensively tested in the field or passed through rigorous environmental technology verifications. It must be noted that the development, fabrication, in-field testing, production and distribution, user acceptability, maintenance, and sustenance of any of these technologies is very complex and time consuming, even for a very simple system such as ours. Zero-valent iron has been used in the past to mitigate chlorinated hydrocarbons, arsenic, and other toxic species in the environment. The list of materials above shows that iron is the key component of many of them. However, iron-based technologies are subject to many problems: uncontrolled leaching and rusting, which can clog the filter media and filter outlets and render the filter useless; low capacity for arsenic removal; inability to remove As(III) species; and the complexity of regenerating and reusing the material in household filtration systems. In our research, we invented a technique for processing easily available surplus iron into composite-iron granules (CIGs) and then into a composite-iron matrix (CIM). CIM is different from granular metal oxides in that the active medium is made from composite-iron granules into a solid, porous matrix by in situ processing inside the filter. The “sandwich” of sand layers facilitates compaction, controls flow dispersion, controls pore formation, and reduces the production of fine particles. Thus this configuration has a low probability of clogging and a high probability of long-lasting field use without compromising water quality. The active material in the SONO filter removes inorganic arsenic species quantitatively by generating new complexation sites on CIM by in situ iron oxidation and surface-chemical reactions (Hussam and Munir, 2007). These reactions take place quickly for both As(III) and As(V) (Figure 3). FIGURE 3 Figure showing that CIM can remove both As(V) and As(III) species from water almost completely within five minutes of contact. The two-stage filter system also increases the amount of arsenic removed through flocculation and the precipitation of naturally occurring iron.The theoretical life span of a filter (for a 10 ppb breakthrough) could range from 5 to 200 years, depending on model assumptions. Experimental filters installed in the field at different times have functioned for three to six years in Bangladesh without breakthroughs, even with high-soluble iron (21 mg/L in one case), high phosphate content (50 mg/L), and varied water chemistries (Hussam and Munir, 2007). Management of Spent Materials Spent materials from all filtration technologies, including the SONO filter, are contaminated with high concentrations of toxicants. Thus the process and complexity of waste disposal affect their technical viability, cost, and social acceptability. At present, the only way to identify toxic waste is to leach the solid material, under simulated conditions, to determine if the levels of toxic species released into the environment exceed regulatory limits. In our case, the measurements on used sand and CIM, by total available leaching protocol (TALP), showed that the spent material was completely nontoxic, less than 5 ?g/L of arsenic in all forms; this is 100 times lower than the EPA limit (NAE, 2006). The procedure was repeated, with similar results, using Bangladeshi rainwater (adjusted to pH7) to test the system with the primary mode of transport of water-soluble species during the rainy season. Similar results were obtained by ETVAM with the backwash of filter waste using EPA’s toxicity characterization leaching procedure (TCLP). Arsenic species in the used sand and CIM are present in oxidized form and firmly bound with insoluble-solid CIM, similar to a self-contained, naturally occurring compound in the Earth’s crust. Thus disposing of them is almost like putting soil on soil. Most important, in NAE’s tests, the used CIM was characterized as “undetectable and nonhazardous (limit 0.50 mg/L)” by the TCLP (NAE, 2006). The EPA recommended limit for the land disposal of arsenic is 2 kilograms per hectare per year. This corresponds to arsenic from 10 million liters of water with a concentration of 200 mg/L (Khan, 2007). By this standard, the spent media from household filters used for 274 years at 100 liters per day could be disposed of on four square meters of land. Thus this iron-based arsenic filtration system appears to be benign and safe in terms of waste disposal. Technology Use, Distribution, Cost, and Social Acceptance At the time of the writing of this article, about 90,000 filters had been distributed in more than 18 districts throughout Bangladesh and Nepal. The large-scale procurement of the apparatus was primarily funded through local nongovernmental organizations (NGOs), local governments, and international institutions (e.g., UNICEF). The filters were transported on flatbed trucks and distributed in villages by flatbed rickshaws. Two other popular modes of transport are shown in Figures 4a and 4b. FIGURE 4 a. SONO filters being transported by boat in Bangladesh. b. SONO filters transported by oxcart in Nepal. At a cost of $35 to $40 for five years (the equivalent of the one-month income of a village laborer in Bangladesh), SONO is one of the most affordable water filters being used in that country. The system is made even more affordable by monthly payment schedules available through the NGOs that distribute the filters. Because the filters do not require chemicals or consumables, the estimated operating cost is no more than $10 for five years (if the flow controller needs replacement). One unit can meet the needs of two families for drinking and cooking water for at least five years. Following simple instructions and at no cost, the user can set up the system in 20 minutes. Potable water is collected within two to three hours (the first two batches must be discarded), and most people like the taste of the soft water. Our experience shows that water collection and maintenance of the SONO filter are done mostly by women, who like the system because they do not have to walk the distance to and from the closest arsenic-free well. People who drank the filtered water for two years showed some improvement in arsenical melanosis and reported a general sense of well-being and improvement in health. Because the filter has a flow rate of 20 liters per hour, it produces enough water for drinking and cooking, of course, but also for other purposes, such as cleaning and washing cooking utensils. In fact, we found no social or cultural stigma associated with the dissemination or use of the filter. Filters have been installed in hundreds of schools, and many children carry home bottles of filtered water at the end of the school day. The SONO filter requires no special maintenance, except for the replacement of the upper sand layers when the apparent flow rate decreases. Experiments show that the flow rate may decrease 20 to 30 percent per year as a result of the formation and deposition of natural HFO in the sand layers if the groundwater has high iron content (more than 5 mg/L). The presence of soluble iron and the formation of HFO precipitate are common problems in all filtration technologies. Other Benefits Tube-wells were drilled to extract groundwater so that people would not have to drink surface water contaminated with pathogenic bacteria. However, pathogenic bacteria are still present in drinking water because of unhygienic handling and because many shallow tube-wells are located near unsanitary latrines and ponds (Islam et al., 2001). Tests for bacteria from 264 filters showed that 248 of them had no thermo-tolerant coliform (ttc) in 100 milliliters (mL) of water; 16 had 2 ttc/100 mL (VERC, 2007). Pouring five liters of hot water into each bucket every month has been shown to kill all pathogenic bacteria and to eliminate the coliform count. In places where coliform counts are high, this protocol can be followed once a week. We have no record of diarrhea or other waterborne diseases from drinking SONO-filtered water. Thus it appears that the SONO filtration system, per se, does not foster pathogenic bacteria. Except for basic training in hygiene, no special skills are required to maintain the filter, which will produce potable water for at least five years (the time span of our continuing test results). The active media does not require any backwashing or chemical regeneration. The actual life span of the filter will be determined by the life span of the experimental filters running in the field. Except for manufacturing defects, mechanical damage due to mishandling, transportation, or natural disasters (e.g., flooding), none of the filters has shown the maximum contamination level (50 ppb) breakthrough so far. Our experience in Bangladesh shows that careful filter distribution and initial setup appear to be the most challenging tasks for large-scale distribution of the technology. The SONO filter is now manufactured by an NGO (Manob Sakti Unnyan Kendro-MSUK in Kushtia, Bangladesh) from indigenous materials in batches of 200 to 500 units. All of the materials are available almost anywhere in the world, except for CIM, which can be produced under licensing agreement or imported from the manufacturer. The latter is the preferred method for production in Nepal and India. We estimate that about one million people have already benefited directly from the filtration system. In addition, many people, the authors included, use SONO-filtered water for drinking and cooking. In some places, the filtration system has been scaled up by connecting units in parallel for use by small communities. Sustainability through Integrated Programs The sustainability of even a simple technology like SONO requires more than its production and distribution. In most underdeveloped countries, the production and distribution of services to meet humanitarian needs require funding from NGOs and financial subsidies from foreign-aid organizations. But sustainability will require commercialization through further product development. The filter by itself will not solve the water crisis in Bangladesh. The arsenic crisis will require a sustainable, progressive, integrated program to address the overriding issues of sanitation, education, training and motivation, medical care for arsenicosis patients, social mobilization, the empowerment of women through mothers clubs, and so on (Figure 5). Most NGOs recognize this need and are trying to set up intensive training and cultural programs to motivate people to drink arsenic-free water. FIGURE 5 Diagram of an integrated arsenic-mitigation program. Outlook for the Future It is now clear that in Bangladesh and many other countries neither the surface water nor the groundwater is potable without treatment and/or filtration. Thus it appears that the development of low-cost filters is one of the best ways to solve the point-of-use drinking-water crisis for Bangladesh and many other countries. 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About the Author:Abul Hussam is professor of chemistry and director of the Center for Clean Water and Sustainable Technologies at George Mason University, Fairfax, Virginia. Sad Ahamed is a post-doctoral research fellow in the Center for Clean Water and Sustainable Technologies at George Mason University. Abul K.M. Munir is general secretary of Manob Sakti Unnayan Kendro (MSUK), Kustia, Bangladesh.