A small-scale low-cost water treatment system for removal of selected heavy metals, bacteria and particles

There is increasing recognition around the world that conventional piped systems are not the only solution for providing safe water. The traditional approach can be complemented by non-networked water supply and treatment systems to complete the service chain across urban, peri-urban, and rural contexts (CAWST 2017a). Colombia, for instance, has new legislation regarding universal access to basic services that recognizes that, to reach full water supply coverage for most vulnerable populations in peri-urban, rural and dispersed areas, centralized and traditional implementation mechanisms, for water quality assurance, are not sufficient. The new legislation prompts government agencies to acknowledge, evaluate and accept alternative, viable, context-appropriate solutions such as low-cost, point-of-use (PoU) water treatment technologies to improve water quality for underserved populations (op cit). Many poor communities, especially in sub-Saharan Africa, are underserved and below the global average for basic access, when it comes to providing people with safe water (WHO 2012). Lack of access can be fatal, particularly for the elderly, young children, pregnant women and people with HIV/AIDS (WHO 2017a). The absence of safe water is among the leading causes of child mortality in poverty stricken communities (WHO 2012). This study was undertaken to develop a low-cost, PoU water treatment system using easily accessible low-cost materials affordable to the poor of developing countries. Two low-cost, Intermittently-operated Slow Sand Filtration (ISSF) systems for PoU water treatment, incorporating granular activated carbon (GAC), non-woven geotextile and filter mats were designed and constructed from easily acquired materials locally available in South Africa.

The aim was to develop a PoU appropriate for low-income settings, and able to significantly remove turbidity and bacteria from water, and appreciably reduce concentrations of selected heavy metals. The system is also expected to treat enough water sufficiently quickly for point-of-use in households or small settings such as schools, etc. It must also be durable, requiring minimal frequency of cleaning and maintenance, easily assembled, low-cost, generally ‘free-standing’, and with little or no plumbing (WHO 2016). The main contaminants addressed in this study were bacteria (E.coli and thermo-tolerant (fecal) coliforms), particles (turbidity or suspended solids), and some heavy metals. While the water treatment focus for PoU applications must always be the microbial aspect (McAllister 2005), disease may also result from consuming water containing toxic levels of elements like arsenic and lead (WHO 2017a).

Many conventional methods exist for removal of heavy metals and other chemical contaminants, bacteria and particles, involving multiple steps such as tower aeration, lime softening and/or coagulation, followed by settlement of the insoluble precipitates, and rapid filtration and disinfection (Mcghee 1991; de Moel et al. 2007; WHO 2017a). In addition, high-tech water treatment technologies such as ultrafiltration, nanofiltration, ion exchange, flotation, ozonation, ultraviolet disinfection and reverse osmosis can treat various types of contaminated water (Peavy et al. 1986; Mcghee 1991; WHO 2017a). However, most of these are too expensive and fail to meet the specific needs of poor communities (McAllister 2005). Therefore, other small-scale, low-cost technologies are required. In this study, two low-cost filtration systems incorporating alternating layers of sand, gravel, GAC and non-woven geotextile with filter mats placed on filter surfaces, were investigated to assess their effectiveness in removing bacteria, particles and selected metals (arsenic, cadmium, lead, iron and manganese).

Bacterial removal was considered because infectious diseases caused by bacteriological agents are by far the most common and widespread health risk associated with drinking-water (McAllister 2005; WHO 2017a). Fecal coliforms and E.coli were used as indicator organisms, as their presence in water signals the presence of fecal contamination, and potentially, pathogens. The presence of coliform bacteria may indicate the presence of other pathogens that can lead to severe and sometimes life-threatening water borne diseases such as cholera, typhoid, dysentery, diarrhea, infectious hepatitis and giardiasis (de Moel et al. 2007; Ritter 2010; WHO 2017a).

Removal of turbidity was considered for aesthetic reasons because water that is aesthetically unappealing can lead to water use from sources that, while aesthetically more acceptable, may not be safe (WHO 2017a). There is a common perception that clear water is equivalent to safe water (Kotlarz et al. 2009). This view maybe somewhat justifiable, since pathogens are often attached or adherent to suspended particles (e.g. clay and silts) in water (CAWST 2011; WHO 2017a). According to WHO (2017b), the presence of particles can also indicate the presence of hazardous chemical and microbial contaminants, and increase chlorine demand. Reduced chlorine demand allows lower chlorine dosage (Kotlarz et al. 2009), which could increase taste acceptability and reduce water treatment costs. Apart from interfering with chlorination effectiveness, elevated particle concentrations in drinking water may produce disinfection byproducts (DBPs); the desired maximum particulate level for this purpose is 1.0 nephelometric turbidity units (NTU). Kotlarz et al. (2009) showed that free chlorine residual was maintained at a significantly higher level in water passed through a sand filter before chlorination than in unfiltered water.

To enhance bacterial and particulate removal, filter mats (three geotextile layers each 0.60 cm thick) were employed, to augment mechanical trapping and support bio-layer growth. This was supplemented by sizing the fine sand layer according to recommendations by CAWST (2011) and Parsons & Jefferson (2006), with an effective particle size of 0.1 to 0.2 mm and uniformity coefficient of 1.5 to 2.5, giving a more tightly packed sand layer and, thus, more effective bacterial and particulate removal. This is expected to enhance surface straining and biological removal of contaminants, in addition to adsorption and natural bacterial death, which occur within the sand body.

An attempt was also made to enhance the systems' effectiveness in removing iron, manganese and other heavy metals. GAC was included mainly for this purpose, in addition to removal of color, taste and organic pollutants (McAllister 2005; WHO 2017a). Not all filters can remove heavy metals or other toxins from water, but incorporating GAC or bone charcoal, where appropriate, may help (Mihelcic et al. 2009). In regions where such contaminants are present in water, their removal is a good idea. The toxic elements considered were arsenic (As), cadmium (Cd) and lead (Pb), which are amongst the most common environmental pollutants (Turkez et al. 2012). According to Llobet et al. (2003) these metals have no beneficial effects in humans and there is no known homeostatic mechanism for them. They are toxic and, when present in water supplies anywhere, require continued attention (Okun & Ernst 1987). It is noted, however, that inclusion of the metals in this study does not imply that all will necessarily be present or that other metals, not addressed, will always be absent.

Arsenic is highly poisonous and occurs naturally in many groundwaters, as well as some surface water sources. South Africa, where this research was done, is known to be affected by arsenic in drinking water (Mihelcic et al. 2009; CAWST 2011). According to Ahmed (2008), high arsenic doses are fatal immediately. Long-term consumption of arsenic in drinking water is often associated with increased risk of chronic diseases such as skin bulges (keratosis) on palms and feet, and cancer of the skin, lungs, bladder and kidney (WHO 2017a).

Cadmium is classified as a human carcinogen known to cause deleterious effects to health and bone demineralization, either through direct bone damage or via renal dysfunction (Renu & Singh 2017). According to WHO (2017a), the kidney is the main target organ for cadmium toxicity, where it accumulates and has a long biological half-life of 10 to 35 years, in humans.

Lead is found in many water supplies across the world, and is particularly important because it is highly toxic and has been shown to cause neurological damage in children, leading to intellectual and psychological impairment, even at extremely low exposures (Okun & Ernst 1987; Renu & Singh 2017). It is also associated with reduced fertility, impaired fetal development, impaired kidney function and increased blood pressure (WHO 2017a).

Iron and manganese removal were considered mainly for aesthetic reasons because these metals affect the acceptability of water. They occur naturally in ground- and surface- waters, in places where the rocks and sediments are high in iron and/or manganese (CAWST 2017b). Drinking water containing high concentrations of iron may not make people sick, but it affects the taste and gives it a reddish cast (CAWST 2017b). This makes the water less appealing to drink and can lead to indirect health impacts, if users lose confidence in treated water and either drink less, or opt for aesthetically better alternatives – i.e., without iron and/or manganese effects – that could be more harmful to health (CAWST 2017b; WHO 2017b). Since the raw water used in this study was collected from a point in the stream with noticeable mixing and turbulence, it was assumed that the iron and manganese were mainly in their oxidized forms.

Two small-scale, low-cost, sand filtration systems incorporating GAC, non-woven geotextile and filter mats for removal of selected heavy metals, bacteria and particles from water were designed, constructed, and evaluated for this study. They were exposed to a single surface water source for five months and three weeks, a period that covered seasonal variations in raw water quality, as it ran from winter through spring to summer.

The research was conducted in the Water Quality Laboratory of the Department of Civil Engineering at Stellenbosch University in Cape Town, South Africa. Raw surface water samples were obtained from Kromrivier stream, at 33°55′34.68″S and 18°51′40.56″E, next to the bridge between Ryneveld Street and Kromrivier Road, Stellenbosch, South Africa.

Two small-scale, low-cost ISSF systems were evaluated for heavy metal, bacterial and particulate removal when exposed to surface water from 19 June to 8 December 2017. Both systems comprised columns 60 cm tall and of 10.5 cm internal diameter, and made of transparent Plexiglass. 1 mm perforated diffusers were fabricated for uniform and gentle water distribution onto the filter surface, and to prevent the schmutzdecke from being disturbed.

A 10 cm gravity water head was provided above the filter systems to drive water slowly through the filter media. The lower the gravity head, the less the pressure and the slower the flow rate, resulting in higher particulate and bacterial removal. The two ISSFs for PoU application were constructed with alternating filter media layers consisting of sand, gravel, GAC and geotextile. The main aspects included were: (i) filter mats (non-woven synthetic fabric) placed on the sand surface (ii) GAC layered within ISSF-1, and (iii) non-woven synthetic fabric layered within ISSF-2.

It is noted here that this research is ongoing and is expected to have two major phases. The phase, discussed in this paper, focused on evaluating the contaminant removal performance – i.e., their effectiveness – and assessed the potential for improvement. The next expected phase will involve constructing improved versions, and assessing their performance against an ordinary ISSF system having no GAC or geotextile, and, at the same time, duplicates of the two systems but without allowance for bio-layer growth. Construction of full-scale units is also anticipated, to check whether scale affects contaminant removal significantly. In the anticipated second phase units, there will also be a (standard) mechanism to maintain the recommended 5 cm standing water level automatically on the filter surface (CAWST 2011) and thus preserve the microbial community by preventing the bio-layer from drying out. In this phase, the standing water level was maintained manually to the labeled mark, which was rather laborious.

System 1 (ISSF-1) incorporated GAC and system 2 (ISSF-2) non-woven geotextile layered within the filter media. Both had geotextile filter mats on top of the filter surface to offer some form of bacterial and particle removal, thereby serving as a pretreatment step. The mats are expected to provide longer filter run times and a simpler filter cleaning method than with ordinary ISSF systems. In this case, cleaning only involves the removal and cleaning of the filter mats. The GAC in ISSF-1 is expected to improve system adsorption capacity and help with metal removal. Table 1 highlights the key filter materials, from top to bottom, in both systems. The silica sand and gravel were polished and graded at the University of Stellenbosch's Civil Engineering Geotechnics Laboratory. Fabrication was done in the Hydraulics Laboratory, and the systems were assembled and tested in the Water Quality Laboratory.

Figure 1 shows schematic diagrams of the systems. Each was provided with a tap for collecting treated water. GAC was purchased from a local pet shop in Stellenbosch making it relatively affordable and easy to obtain. Clean quarry sand was used in the study to ensure purity, with no fines, organics or pathogens, as recommended by CAWST (2011). The GAC was placed below the sand to inhibit particle clogging of the GAC, and also because it is recommended that the GAC not be used as a primary layer or filter (McAllister 2005). It was also done on the assumption that this arrangement allows less contaminated water to pass through the GAC layer for removal of color, taste, some organics, certain pesticides and other micro-pollutants (Kawamura 2000; McAllister 2005) with less interference from particulate matter. In addition, it has been indicated by others (Siabi 2003; Mihelcic et al. 2009), that GAC can be used for removal of species like arsenic, iron and manganese.

In an ISSF system raw water flows downwards by gravity, and pathogens and turbidity are removed by mechanical trapping primarily in the top few centimeters of the filter media (CAWST 2011; WHO 2017a). ISSF filter systems are operated intermittently as water becomes available, unlike ordinary slow sand filters, which are continuous filtration systems where water flows through at a slow but continuous rate (Manz 2004; CAWST 2017a). A bio-layer, commonly known as the ‘schmutzdecke’, develops on the filter surface and helps in pathogen removal due to predation of pathogens by organisms living within it (CAWST 2011; WHO 2017a). Pathogens also die naturally deeper within the filter depth as oxygen, light and food become too scarce to sustain microbial life – most organic material is trapped on the filter surface. ISSFs are most effective in treating low-turbidity water or water that has been treated partially (WHO 2017a). When clogging occurs – i.e., when there is little or no flow – the top few centimeters of sand containing the accumulated solids are normally scraped off and replaced (CAWST 2011; WHO 2017a). ISSFs can remove algae and microorganisms, including protozoa, bacteria, helminths, and, if coupled with pretreatment, can reduce turbidity from very high levels (Manz 2004; WHO 2017a). Hence, filter mats were included to serve as a pretreatment to enhance performance, minimize clogging and reduce scraping requirements. Another removal mechanism by ISSFs is adsorption (or attachment), whereby pathogens and particles are adsorbed, or become attached to filter media. It was with respect to this aspect that GAC was included in ISSF-1, to augment adsorption capacity.

A household version of ISSF systems, normally called a biosand filter (BSF), was originally developed by Dr. David Manz, University of Calgary, in 1991 and has been further developed by CAWST to the current version 10 (Manz 2004; CAWST 2011). In 2012, Samaritan's Purse Canada and Clear Cambodia, used slow sand filtration and BSF principles to develop an ISSF system appropriate for institutional scale use, such as that of health centers, to improve water quality in rural schools in Cambodia, and included a float valve to control water level, filter hydraulic loading rate and flow rate (CAWST 2017a). The name commonly applied to this institutional-scale ISSF is ‘school biosand filter’ (sBSF). WHO refer to the BSF system as the ‘household-level intermittently-operated slow sand filtration (hISSF)’ (WHO 2017a). The filtration principle, and key contaminant removal mechanisms such as trapping, predation, absorption and natural bacterial death are the same. Both versions are primarily intended for bacteriological water quality improvement, although modifications can be made to allow removal of other impurities, e.g., arsenic (NE-WTTAC 2014). Some literature shows that both versions remove bacteria successfully (Manz 2004; CAWST 2011; CAWST 2017a). While others report that the filters remove fewer bacteria, particularly in field settings, and their filtrate does not consistently meet potable water guidelines in removing bacteria and other pathogens (Nemade et al. 2009; Stubbe et al. 2016).

ISSF-1 and ISSF-2 were designed to include materials highlighted earlier, to try to enhance performance so that a single system is expected to improve water quality with respect to bacteria, particulates and selected metals, thus increasing health benefits and filter run times, while reducing cleaning problems. In this context, some modifications to the hISSF system have been reported, focusing on improvements in the water's microbiological quality. For example, researchers at Massachusetts Institute of Technology have added a layer of sand above the diffuser basin, to provide a second biolayer (NE-WTTAC 2014). The TivaWater system, promoted in some African countries, is a lighter and more compact version of the BSF that includes integrated storage for filtered water (NE-WTTAC 2014). No literature on the performance impact of these modifications is available.

Each system was charged with at least 7.5 liters of water per day, fed in by pouring onto the filter surface to provide a maximum water head of 10 cm. Because the column reservoirs could not handle the full charge volume, they were filled to capacity and water was added when the head was low enough to accommodate more. The flow rate was measured using a 2 L jar and stopwatch at the fastest flow point in the filter, as this determines possible detachment of microbes and particles attached to filter media, and their subsequent flushing into the filtered water (NE-WTTAC 2014). The systems' initial flow rates were between 8 and 15 L/h, to ensure adequate empty-bed contact time (EBCT) for the GAC, and longer contact times between raw water and the bio-layer during the filtration run period. Flow rate was measured over the study period and decreased gradually with time, as expected. As the flowrate decreased the treated water quality improved, especially after filter ripening, for both systems, and particularly in terms of bacterial and particulate removal. The filters were not cleaned during the study, in order to reach the lowest possible flow rate. Initial observed flow rates were 10.08 and 9.97 L/h for ISSF-1 and ISSF-2, respectively, and 6.34 and 6.13 L/h at the study end. In other words, the two systems where still yielding appreciable volumes of treated water at the end of the study.

To ensure that the source water was contaminated, raw water samples were collected and tested for two weeks before evaluation tests commenced. In both weeks more than 500 CFU/100 ml of fecal coliforms and more than 400 CFU/100 ml of E.coli were recorded. TSS and turbidity were consistently above 14 mg/l and 10 NTU, respectively. The concentrations of indicator bacteria (fecal coliforms and E.coli), particles (TSS and turbidity) and metals (arsenic, cadmium, lead, iron and manganese) were determined before and after treatment by each filter system. Other parameters measured were pH, dissolved oxygen (DO), electrical conductivity (EC) and total dissolved solids (TDS). The two system models were flushed with potable tap water prior to use until the discharge was clear, to remove impurities.

Treated water was collected daily for physico-chemical tests and fortnightly for bacteriological tests, and only in the last two months for metal species. Tests for E.coli and fecal coliforms were done by Water Analytical Laboratory (WALAB) accredited to the South African National Accreditation System (SANAS), No: T0375 for microbiological analysis, whereas the metals were determined by the Central Analytical Facilities (CAF) of Stellenbosch university. The CAF operates state of the art equipment and provides analytical services to the Stellenbosch University research community and the rest of the South African research and development sector. Physico-chemical tests were done in the Water Quality Laboratory at Stellenbosch University. All tests were carried out in accordance with the Standard Methods for the Examination of Water and Wastewater (APHA/AWWA/WEF 2012).

• C_o = concentration of contaminant in untreated water

• C_e = concentration of contaminant in treated water

The untreated river water was characterized initially and on each sampling day over the study period for the selected contaminants. Raw water quality was then compared to the South African National Standards (SANS) 241 and WHO guidelines for potable water – see Table 2. In addition to the high particulate and iron contents, the raw water was highly contaminated with E.coli and thermo-tolerant (fecal) coliforms.

The results (Figures 2 and 3) show that ISSF-1 and ISSF-2 were both significantly effective in bacterial removal, and recorded respective E.coli removal ranges of 87.3 to 99.9% and 84.1 to 100%, as well as achieving fecal coliform removal of 88.5 to 99.9% and 85.0 to 99.8%. The average E.coli removal rates (95% for ISSF-1 and 94% for ISSF-2) are slightly higher than those typically reported for ISSFs, e.g. 90% (WHO 2017a).

As shown in Figures 2 and 3, bacterial removal became much more pronounced and consistently exceeded 95% after a month's operation, signifying the importance of schmutzdecke growth on systems of this kind. According to CAWST (2011), filter ripening – i.e., schmutzdecke development – which considerably improves bacterial removal, takes about 4 weeks. After filter ripening, the recorded average E.coli contents were 1,233 CFU/100 ml for the raw water, and 6 and 17 CFU/100 ml, respectively, for the treated waters from ISSF-1 and ISSF-2. So both units yielded drinking water of reasonable quality before chlorination. According to various authors (e.g., WHO 1997; Harvey 2007; CAWST 2011), water of this quality may be consumed as it is. This is especially true during emergencies or for those not yet serviced with good quality piped supplies. Even before filter ripening, however, bacterial removal by both systems was high, with ISSF-1 and ISSF-2, respectively, reporting fecal coliform removal of up to 93.6 and 89.1%, and E.coli removal of up to 89.2 and 84.4%. This could be attributed to presence of filter mats on the filter surfaces, and of GAC in ISSF-1 and geotextile layers in ISSF-2.

Both systems can produce relatively high-quality water, and can meet WHO and SANS 241 drinking water guidelines and standards of 0 CFU/100 ml for E.coli and fecal coliforms, if combined with chlorination. This claim was tested on ISSF-1, when its effluent was chlorinated to give 0 CFU/100 ml, using a low chlorine dose (1.875 mg/L) due to the low organic content, as recommended by Kotlarz et al. (2009).

There was substantial particle removal from the raw water by both ISSF-1 and ISSF-2 – see Figures 4 and 5. ISSF-1 was generally better than ISSF-2 for both TSS and turbidity removal, but particulate removal was significant by both. TSS removal was between 88.9 and 100% and 70.0 and 100%, respectively, for ISSF-1 and ISSF-2, whereas turbidity removal was between 87.3 and 100% and 65.8 and 100%. The higher particulate removal by ISSF-1 could be attributed to the presence of the GAC, which, to some extent, increased the filter's adsorption capacity. Although only ISSF-1 consistently met WHO's TSS guideline (0.1 mg-TSS/l) from 17 July to 13 October (Figure 4), both consistently met both the WHO and SANS 241 turbidity guidelines (5 NTU) and removed very large proportions of particulate materials from the raw water, possibly due to the combined effect of the filter mats and bio-layers, coupled with other removal mechanisms.

There was a noticeable difference in particulate removal efficiency between ISSF-1 and ISSF-2 until after 13 October, when both systems began to perform similarly, perhaps indicating that the GAC in ISSF-1 had reached saturation, reducing its effectiveness, and required replacement. In general, the TSS and turbidity removal efficiencies were almost identical for the two systems. Although they cannot be directly correlated, TSS and turbidity are both measures of water clarity, and overlap in the measurement of particles like clay, silt, algae, bacteria, and non-settleable solids (Peavy et al. 1986; Ritter 2010) although they reflect different things (Peavy et al. 1986).

Since both systems can produce clear water, and remove iron and manganese, with significant efficiency – Table 3 – they can improve water security in poor communities, particularly if combined with chlorination to guarantee continued supply of safe water. Both systems are affordable.

Results shown in Table 3 indicate removal of arsenic (up to 30.3%), cadmium (93.9%), lead (63.1%), iron (70.5%) and manganese (94.1%) for ISSF-1, and arsenic (29.3%), cadmium (<LoD), lead (<LoD), iron (92.1%) and manganese (97.7%) for ISSF-2. Iron and manganese removal was substantial by both systems and, since these parameters affect the acceptability of water, their removal is important where they occur. Although ISSF-2 was on average slightly more efficient than ISSF-1 with respect to removing these two species, it did not remove either cadmium or lead.

The slightly better performance of ISSF-2 with respect to iron and manganese probably arose from algal growth observed in the standing water of ISSF-2 (in the last two months of the study), which may have led to increased oxygen release – Figure 7 – and subsequent further oxidation and increased precipitation of the two species, leading to improved capture. Both filter columns were transparent and uncovered, attracting algae and plant growth. ISSF-1 had marginal algal growth as it was more ‘inside’ the laboratory, while ISSF-2 was much closer to the laboratory window and generally recorded higher temperatures.

Equally, the better removal of the other metals by ISSF-1 could be attributed to adsorption by the GAC layer, although the effect was minimal due to their low concentrations in the raw water. Use of water with relatively higher/synthetic concentrations of the metals concerned is proposed for testing water treatment systems such as these. According to Mihelcic et al. (2009), activated carbon adsorption is a proven process used to remove metals like arsenic and could be feasible for use by poor communities. Better technologies exist but are too costly or still being developed.

ISSF-2 recorded higher cadmium and lead concentrations in its effluent than were found in the raw water influent (entries marked ** in Table 3). It is not clear whether these metals leached from the filter media – e.g., with initial capture and subsequent release.

Although the DO level in the ISSF-1 effluent was low most of the time (Figure 7), both systems consistently met the SANS 241 and WHO guidelines in terms of TDS and conductivity – see Table 1. Their effect on water quality was marginal, however, with respect to these parameters (Figures 8 and 9).

Effluent pH values from the two systems (Figure 6) were generally above the WHO guidelines but within the SANS 241 limits. The high pH values recorded by both systems contributed somehow to the removal of iron and manganese. Tyrrel (1997) says that iron and manganese can be removed by raising the pH of the water, leading to the formation of insoluble metal precipitates that can be removed by filtration. In addition, de Moel et al. (2007) report that the oxidation and hydrolysis rates of iron and manganese depend on the pH – i.e., at low pH the rate of reaction for iron and manganese removal processes is slower than at high pH (Mcghee 1991; de Moel et al. 2007). Thus, de Moel et al. recommend that, when treating water with low pH for iron and manganese, aeration is used to remove much of the carbon dioxide, so that a higher pH is achieved.

As the raw water for this study was collected from a point where there was noticeable mixing and turbulence, it was assumed that the iron and manganese were sufficiently aerated and mainly in oxidized form. This may be supported by the raw water DO levels recorded, which exceeded 8.30 mg/l throughout the trials. The higher DO concentrations recorded by ISSF-2 (Figure 7), started around 15 September and could have been caused by the algal growth observed – algal blooms were seen then in the raw water source and subsequently in ISSF-2. ISSF-1 had marginal algal growth as it was more ‘inside’ the laboratory, while ISSF-2 was much closer to the laboratory window and generally recorded higher temperatures. It was also observed (Figures 8 and 9) that both the EC and TDS concentration of raw water dropped significantly from around 29 September, as did those of the treated effluent. This is likely due to the onset of summer, with reduced dissolved pollutant loads – the latter arising mainly from stormwater inflows. (The study area normally experiences winter rains from around June to September of each year, while very little or no rain is expected at other times.)

Both ISSF-1 and ISSF-2 can meet basic water needs of about 7.5 to 15 liters/capita/day (THE SPHERE PROJECT 2011). They will be particularly useful for poor communities and in emergencies. The systems can treat poor-quality water sufficiently well to produce relatively safe water. Both can improve water security affordably in poor communities, especially with respect to bacterial counts and acceptability aspects (turbidity, suspended solids, iron and manganese).

Bacterial removal efficiency was substantial, and it may be possible to reduce pathogenic loads below infectious levels so that human health is no longer endangered. However, to guarantee the continued supply of water meeting the SANS 241 standards and WHO guidelines for drinking water, supplementary treatment by chlorination is recommended.

The inclusion of filter mats, GAC and geotextiles in both systems is a small-scale, low-cost option for high quality filtration, possibly improving PoU treatment efficiency in underserved communities and minimizing cleaning problems.

System costs are approximately US$24 for ISSF-1 and US$20 for ISSF-2. They are easy to fabricate, assemble, operate and maintain. They could be very useful in homes, small communities, schools, refugee camps, prisons, markets, and/or health centers, where there is no access to safe drinking water sources, and, perhaps even more, where surface water is abundant or there are unprotected water wells.

Low-cost PoU water treatment systems may often offer advantages over networked water supply and treatment systems, by minimizing the risk of contamination between the source and the point-of-use.