Archive for June, 2013
TweetIntroduction Oceans contain over 97.2% of the planet’s water. Because of the high salinity of ocean water and the significant costs associated with seawater desalination most of the global water supply has traditionally come from fresh water sources – groundwater aquifers, rivers and lakes. Today, however, changing climate patterns combined with population growth pressures and […]
Oceans contain over 97.2% of the planet’s water. Because of the high salinity of ocean water and the significant costs associated with seawater desalination most of the global water supply has traditionally come from fresh water sources – groundwater aquifers, rivers and lakes. Today, however, changing climate patterns combined with population growth pressures and limited availability of new and inexpensive fresh water supplies are shifting the water industry’s attention: in an emerging trend, the world is reaching to the ocean for fresh water.
Until recently, desalination was limited to desert-climate dominated regions. Technological advances and an associated decrease in water production costs over the past decade have expanded its use in coastal areas traditionally supplied with fresh water resources. Today, desalination plants provide approximately 1% of the world’s drinking water supply and the commissioned and installed desalination capacity has been increasing exponentially over the past 10 years.
Higher Productivity Membrane Elements
A key factor that has contributed to the dramatic decrease of seawater desalination costs over the past 10 years is the advancement of the SWRO membrane technology. Today’s high-productivity membrane elements are designed with several features that yield more fresh water per membrane element than any time in the recent history of this technology: higher surface area, enhanced permeability and denser membrane packing. Increasing active membrane leaf surface area and permeability allows it to gain significant productivity using the same size (diameter) membrane element. Active surface area of the membrane elements is typically increased by membrane production process automation, by denser membrane leaf packing and by adding membrane leaves within the same element.
The total active surface area in a membrane element is also be increased by increasing membrane size/diameter. Although 8-inch SWRO membrane elements are still the “standard” size most widely used in full-scale applications, larger 16-inch and 18-inch size SWRO membrane elements have become commercially available over the past three years and have already found full-scale implementation in several SWRO projects worldwide (Bergman & Lozier, 2010).
In the second half of the 1990s, the typical 8-inch SWRO membrane element had a standard productivity of 5,000 to 6,000 gallons per day (gpd) at salt rejection of 99.6%. In 2003, several membrane manufacturers introduced high-productivity seawater membrane elements that are capable of producing 7,500 gpd at salt rejection of 99.75%. Just one year later, even higher productivity (9,000 gpd at 99.7% rejection) seawater membrane elements were released on the market. Over the past three years SWRO membrane elements combining productivity of 10,000 to 12,000 gpd and high-salinity rejection have become commercially available and are now gaining wider project implementation.
The newest membrane elements provide flexibility and choice and allow users to trade productivity and pressure/power costs. The same water product quality goals can be achieved in one of two general approaches: (1) reducing the system footprint/construction costs by designing the system at higher productivity, or (2) reducing the system’s overall power demand by using more membrane elements, designing the system at lower flux and recovery, and taking advantage of newest energy recovery technologies which further minimize energy use if the system is operated at lower (35% to 45%) recoveries.
Innovative hybrid membrane configuration combining SWRO elements of different productivity and rejection within the same vessel which are sequenced to optimize the use of energy introduced with the feed water to the desalination vessels is also finding wider implementation. In addition, a number of novel membrane SWRO train configurations have been developed over the past five years aiming to gain optimum energy use and to reduce capital costs for production of high-quality desalinated water.
Design and Equipment Enhancements for Lower Energy Use
Energy is one of the largest expenditures associated with seawater desalination. Figure 1 shows a distribution of the energy use within a typical seawater desalination plant. As shown on this figure, the SWRO system typically uses over 70% of the total plant energy.
Figure 1 – Energy Use Breakdown of Typical SWRO Desalination Plant
Increased High Pressure Pump Efficiency
One approach for reducing total RO system energy use which is widely applied throughout the desalination industry today is to incorporate larger, higher efficiency centrifugal pumps which serve multiple RO trains. This trend stems from the fact that the efficiency of multistage centrifugal pumps increases with their size (pumping capacity). For example, under a typical configuration where individual pump is dedicated to each desalination plant RO train, high pressure pump efficiency is usually in a range of 80% to 83%. However, if the RO system configuration is such that a single high pressure pump is designed to service two RO trains of the same size, the efficiency of the high pressure pumps could be increased to up to 85%.
Proven design that takes this principle to the practical limit of centrifugal pump efficiency (≈ 90%) is implemented at the 86 MGD Ashkelon seawater desalination plant in Israel, where two duty horizontally split high pressure pumps are designed to deliver feed seawater to 16 SWRO trains at guaranteed long term efficiency of 88%. Continuous plant operational track record over the past 5 years shows that the actual efficiency level of these pumps under this configuration is close to 90%.
A current trend for smaller desalination facilities (plants with fresh water production capacity of 250,000 gpd or less) is touse positive displacement (multiple-piston)high-pressure pumps and energy recovery devices, which often are combined into a single unit. These systems are configured to take advantage of the high efficiency of the positive displacement technology which practically can reach 94% to 97%.
Improved Energy Recovery
Advances in the technology and equipment allowing the recovery and reuse of the energy applied for seawater desalination have resulted in a reduction of 80% of the energy used for water production over the last 20 years. Today, the energy needed to produce fresh water from seawater for one household per year (~2,000 kW/yr) is less than that used by the same household’s refrigerator.
While five years ago, the majority of the existing seawater desalination plants used Pelton Wheel-based technology to recover energy from the SWRO concentrate, today the pressure exchanger-based energy recovery systems dominate in most desalination facility designs. The key feature of this technology is that the energy of the SWRO system concentrate is directly applied to pistons that pump intake seawater into the system. Pressure-exchanger technology typically yields 5% to 15% higher energy recovery savings than the Pelton-Wheel-based systems.
Figure 2 depicts the configuration of a typical pressure exchanger-based energy recovery system. After membrane separation, most of the energy applied for desalination is contained in the concentrated stream (brine) that also contains the salts removed from the seawater. This energy-bearing stream (shown with red arrows on Figure 2) is applied to the back side of pistons of cylindrical isobaric chambers, also known as pressure exchangers (shown as yellow cylinders on Figure 2). These pistons pump approximately 45% to 50% of the total volume of seawater fed into the RO membranes for salt separation. Since a small amount of energy (4 to 6%) is lost during the energy transfer from the concentrate to the feed water, this energy is added back to feed flow by small booster pumps to cover for the energy loss. The remainder (45% to 50%) of the feed flow is handled by high-pressure centrifugal pumps. Harnessing, transferring and reusing the energy applied for salt separation at very high efficiency (94% to 96%) by the pressure exchangers allows a dramatic reduction of the overall amount of electric power used for seawater desalination.In most applications, a separate energy recovery system is dedicated to each individual SWRO train. However, some recent designs include configurations where two or more RO trains are serviced by a single energy recovery unit.
Figure 2 – Pressure Exchanger Energy Recovery System
While the quest to lower energy use continues, there are physical limitations to how low the energy demand could go using RO desalination. The main limiting factors are the osmotic pressure that would need to be overcome to separate the salts from the seawater and the amount of water that could be recovered from a cubic meter of seawater before the membrane separation process is hindered by salt scaling on the membrane surface and the service systems. This theoretical limit for the entire seawater desalination plant is approximately 4.5 kWh/kgal.
Seawater Desalination Cost Trends
Advances in seawater RO desalination technology during the past two decades, combined with transition to construction of large capacity plants, and enhanced competition by using the Build-Own-Operate-Transfer (BOOT) method of project delivery have resulted in an overall downward cost trend. While the costs of production of desalinated water have benefited from the most recent advances in desalination technology, the cost spread among individual desalination projects observed over the past three years is fairly significant.
Most recently commissioned large seawater desalination projects worldwide produce desalinated water at an all-inclusive cost of US$3.0 to US$5.5/kgal. However, the traditionally active desalination markets in Israel and Northern Africa (i.e., Algeria) have yielded desalination projects with exceptionally low water production costs (110 MGD SWRO Plant in Sorek, Israel – US$2.00/kgal; 87 MGD Hadera Desalination Plant, Israel – US$2.27/kgal; 132 MGD Magtaa SWRO Plant in Algeria – US$2.12/kgal).
On the other end of the cost spectrum, some of the most recent seawater desalination projects in Australia had been associated with the highest desalination costs observed over the past 10 years – i.e., the Gold Coast SWRO Plant in Queensland at US$10.95/kgal; the Sydney Water Desalination Plant at US$8.67/kgal; and the Melbourne’s Victorian Desalination Plant at US$9.54/kgal.
While this extreme cost disparity has a number of site-specific reasons, the key differences associated with the lowest and highest-cost projects are related to five main factors: (1) desalination site location; (2) environmental considerations; (3) phasing strategy; (4) labor market pressures; (5) method of project delivery and risk allocation between owner and private contractor responsible for project implementation.
The desalination projects with highest and lowest costs have a very distinctive difference in terms of project phasing strategy. While the large high-cost projects incorporate single intake and discharge tunnel structures built for the ultimate desalination plant capacity (which often equals two times the capacity of the first project phase), the desalination projects on the low end of the cost spectrum use multi-pipe intake systems constructed mainly from high density polyethylene (HDPE) that have capacity commensurate with the production capacity of the desalination plant. Additional multiple intake pipes and structures are installed as needed at the time of plant expansion for these facilities.
While the single-phase construction of desalination plant intake and outfall structures dramatically reduces the environmental and public controversy associated with the plant capacity expansion at a later date, this “ease-of-implementation” benefit typically comes with an overall cost penalty. The notion that the larger costs associated with building complex intake and outfall concrete tunnels in one phase will somehow be offset by economies of scale usually does not yield the expected overall project cost savings. The main reason is the fact that the cost of 100 linear feet of deep concrete intake or discharge tunnel is over four times higher than the cost of the same capacity intake or discharge constructed from multiple HDPE pipes located on the ocean bottom, while the economy of scale from one-stage construction is usually less than 30%.
Labor market differences can have a profound impact on the cost of construction of desalination projects. The overlapping schedules of the series of large desalination projects in Australia have created temporary shortage of skilled labor, which in turn has resulted in a significant increase in unit labor costs. Since labor expenditures are usually 30% to 50% of the total desalination plant construction costs, a unit labor rate increase of 20% to as high as up to 100%, could trigger sometimes unexpected and not frequently observed project cost increases.
Without exception, the lowest cost desalination projects to date have been delivered under turnkey BOOT contracts where private sector developers share risks with the public sector based to their ability to control and mitigate the respective project related risks.
On the other hand, the most costly desalination projects worldwide have been completed under an “alliance”[(a type of design-build-operate (DBO)] model where the public utility retains the ownership over the project assets but expects the DBO team to take practically all project-related risks. In this case, DBO contractors take upon project risks over which they have limited or no control, by delivering very conservative designs, incorporating high contingency margins in the price of their construction, operation and maintenance services, and by insuring these project risks at very high premiums. As a result, the projects delivered under such structure carry very high contingencies and upfront insurance and performance security payments which ultimately reflect on the overall increase of the cost of water production.
While under a typical BOOT project, the insurance and contingency costs are usually well below 20% of the total capital costs, projects with disproportionate transfer of risk to the private contractor result in built-in insurance and contingency premiums which exceed well over 30% of the total project capital costs. As a result, most often benefits gained from using state-of-the-art technologies, equipment and design, are negated by overly burdensome insurance and contingency expenditures and high cost of project funding.
Seawater Desalination Challenges in US
Water Production Costs
Currently, the cost of desalinating seawater in the US is relatively high compared to that of traditional low-cost water sources (groundwater and river water) and to production costs for water reclamation and reuse for irrigation and industrial use. Indeed, the cost of traditional local groundwater water supplies in some parts of the US are as low as US$0.50/kgal to US$0.90/kgal. However, the quantity of such low-cost sources in coastal urban centers of California, Texas, Florida, South Carolina and other parts of the US exposed to recent long-term drought pressures is very limited.
The generally lower costs for production of reclaimed water and for implementation of water conservation measures have often been used as an argument against the wider use of seawater desalination. This argument however, is fatally flawed by the fact that water conservation and reuse do not create new sources of drinking water – they are merely a rational tool to maximize the beneficial use of the available water supply resources. Under conditions of prolonged drought when the available water resources cannot be replenished at the rate of their use, aggressive reuse and conservation can help but may not completely alleviate the need for new water resources and water rationing.
Typically, seawater desalination cost benefits extend beyond the production of new water supplies. If seawater desalination is replacing the use of over-pumped coastal or inland groundwater aquifers, or is eliminating further stress on environmentally sensitive estuary and river habitats, than the higher costs of this water supply alternative would also be offset by its environmental benefits. Similarly, seawater desalination provides additional benefits in the time of drought where traditional water supplies may not be reliable and their scarcity may increase their otherwise relatively low costs.
Salt separation from seawater requires a significant amount of energy to overcome the naturally occurring osmotic pressure exerted on the reverse osmosis membranes. This in turns makes seawater desalination several times more energy intensive than conventional treatment of fresh water resources. Table 1 presents the energy use associated with various water supply alternatives. The table does not incorporate the costs associated with raw water treatment and product water delivery.
Table 1 – Energy Use of Various Water Supply Alternatives
While energy use for seawater desalination is projected to decrease by 10 to 20 % in the next 5 years as a result of technological advances discussed previously, the total energy demand for conventional water treatment would likely increase by 15 to 20 % in the same time frame because of the energy demand associated with the additional treatment (such as micro- or ultra-filtration, ozonation, UV disinfection, etc.) which would be needed in order to meet the most recent regulatory requirements for production of safe drinking water in the USA.
A number of the seawater desalination projects under consideration in California and Florida are proposed to be collocated with power generation plants which currently use seawater for production of electricity. Under the collocation configuration the desalination plant does not have a separate intake and discharge to the ocean and both the desalination plant intake and desalination plant discharge are connected to the exiting power plant discharge outfall or canal.
Collocation yields a number of benefits mainly because it avoids construction and permits for new intake and concentrate discharge facilities, and because of the energy cost savings associated with the desalination of warmer source water. However this intake configuration alternative has been considered undesirable by some environmental groups due to the potential loss of marine organisms caused by the impingement of marine organisms against the screens of the power plant intake and their entrainment inside the power plant conveyance and cooling system and subsequently inside the desalination plant.
Based on recently introduced regulatory requirements, the 21 once-through cooling plants along the California coast are required to prepare comprehensive plans for discontinuation of their use of open intakes and switching to air-cooling towers or to water close-circulation cooling towers in order to reduce impingement and entrainment of marine organisms.
Opponents of collocated seawater desalination plants have often present the argument that if the power plant changes its cooling system in the future, seawater desalination under collocated configuration at the particular location would no longer be available. This argument however, is unfounded in reality, because even if the host power plants abandon once-through cooling in the future, the desalination projects will still retain the main cost-benefits of collocation – avoidance of the need to construct a new intake and outfall. The cost savings from the use of the existing power plant intake and outfall facilities would be over 25%, resulting in a significant net benefit with or without the power plant in operation.
Recent studies of wedge-wire screens in Santa Cruz, California indicate that this type of open intake may prove to be a viable alternative for dramatic reduction in impingement and entrainment of marine organisms. Typically, wedge-wire screens are designed to be placed in a water body where significant prevailing ambient cross flow current velocities (³ 1 ft/s) exist. This cross high flow velocity allows organisms that would otherwise be impinged on the wedge-wire intake to be carried away with the flow.
A 2-mm cylindrical wedge wire screen intake is also planned to be tested for one year at the West Basin Municipal Water District’s Ocean Water Desalination Demonstration Facility in Redondo Beach. This demonstration facility is currently under operation.
Various sub-surface intake technologies (i.e., beach wells, horizontally directionally drilled and slant wells and innovative infiltration gallery configurations) have been heavily promoted by the California Coastal Commission and local environmental groups as a viable alternative to power plant collocation and construction of new open intakes along the California coast. Ongoing long-term studies of subsurface intakes in Long Beach and Dana Point, California are expected to provide comprehensive data that would allow completing a scientifically-based analysis of the viability and performance benefits of alternative subsurface intakes.
Seawater desalination plants along the US coastline would produce concentrate of salinity that is approximately 1.5 to 2 times higher than the salinity of the ambient seawater (i.e., in a range of 52 ppm to 67 ppm). While most marine organisms can adapt to this increase in salinity, some aquatic species such as abalone, sea urchins, sand dollars, sea bass and top smelt, are less tolerant to high salinity concentrations. Therefore, thorough assessment of the environmental impact of the discharge of concentrate and of any other byproducts of the seawater treatment process is a critical part of the evaluation of project viability.
At seawater desalination projects that are proposed to be collocated with power plants, the desalination plant discharge is planned to be diluted with the cooling water of the power plant to salinity levels that typically do not have significant impact on aquatic life. The magnitude and significance of impact, however, mainly depend on the type of marine organisms inhabiting the area of the discharge and on the hydrodynamic conditions of the ocean in this area, such as currents, tide, wind and wave action, which determine the time of exposure of the marine organisms to various salinity conditions.
Extensive salinity tolerance studies completed over the past several years at the Carlsbad seawater desalination demonstration facility in California indicate that after concentrate dilution with power plant cooling seawater down to 40 ppm or less, the combined discharge does not exhibit chronic toxicity on sensitive test marine species. Recent acute toxicity studies at this facility further show that sensitive marine species can event tolerate salinity of 50 ppm or more over a short period of time (2 days or less).
Some seawater desalination projects are planning to use deep injection wells to discharge the high-salinity seawater concentrate generated during the reverse osmosis separation process. However, the full-scale experience with this concentrate disposal method to date is very limited.
A third disposal alternative, besides injection wells and co-disposal with power plant cooling water, currently under consideration for implementation at a number of seawater desalination projects in the US, is the discharge of the concentrate through existing wastewater treatment plant ocean outfall. International experience with such co-located discharges is fairly limited. However, this technology may have a number of merits similar to these derived from the collocation of desalination and power generation plants.
Proving that concentrate discharge from a seawater desalination plant is environmentally safe requires thorough engineering analysis including: hydrodynamic modeling of the discharge; whole effluent toxicity testing; salinity tolerance analysis of the marine species endogenous to the area of discharge; and reliable intake water quality characterization that provides basis for assessment of concentrate’s make up and compliance with the numeric effluent quality standards applicable to the point of discharge. Comprehensive pilot testing of the proposed seawater desalination system is very beneficial for the project environmental impact analysis.
Summary and Conclusions
Over the past decade seawater desalination has experienced an accelerated growth driven by advances in membrane technology and environmental science. While conventional technologies, such as sedimentation and filtration have seen modest advancement since their initial use for potable water treatment several centuries ago, new more efficient seawater desalination membranes and membrane technologies, and equipment improvements are released every several years. Although, no major technology breakthroughs are expected to bring the cost of seawater desalination further down dramatically in the next several years, the steady trend of reduction of desalinated water production costs coupled with increasing costs of water treatment driven by more stringent regulatory requirements, are expected to accelerate the current trend of increased reliance on the ocean as an attractive and competitive water source. This trend is forecasted to continue in the future and to further establish ocean water desalination as a reliable drought-proof alternative for many coastal communities in the United States and worldwide.
Although seawater desalination projects in the US face a number of environmental challenges, these challenges can be successfully addressed by carefully selecting the project site, by implementing state-of-the art intake and concentrate discharge technologies and by incorporating energy efficient and environmentally sound equipment and systems.
Nikolay Voutchkov, PE, BCEE Water Globe Consulting, LLC, Stamford, CT. Editor of Desalination Technology: Health and Environmental Impacts (2010) IWA Publishing.
Water Desalination and European Research
Nanofiltration for Brackish Desalination
GWI – Global Water Intelligence: Market-leading Analysis of the International Water Industry, 10, pp.9, 2009.
Bergman R.A. and J.C. Lozier.“Large-Diameter Membrane Elements and Their Increasing Global Use”. IDA Journal. pp. 16, First Quarter 2010.
Global Water Intelligence
International Desalination Ascociation
Joseph Cotruvo, Nikolay Voutchkov, John Fawell, Pierre Payment, David Cunliffe, Sabine Lattemann Desalination Technology: Health and Environmental Impacts (2010) IWA Publishing.
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TweetJohn Roach, Contributing Writer, NBC News Elevated levels of methane and other stray gases have been found in drinking water near natural gas wells in Pennsylvania’s gas-rich Marcellus shale region, according to new research. In the case of methane, concentrations were six times higher in some drinking water found within one kilometer of drilling operations. […]
John Roach, Contributing Writer, NBC News
Elevated levels of methane and other stray gases have been found in drinking water near natural gas wells in Pennsylvania’s gas-rich Marcellus shale region, according to new research. In the case of methane, concentrations were six times higher in some drinking water found within one kilometer of drilling operations.
TweetAbstract This paper provides a followup on the health impact of providing access to water treatment and flush toilets to region of Honduras. Significant reductions were found in the one-year incidence of positive test results for the three protozoan species tested. This finding combined with the previously reported ethnographic and medical chart review data provides […]
This paper provides a followup on the health impact of providing access to water treatment and flush toilets to region of Honduras. Significant reductions were found in the one-year incidence of positive test results for the three protozoan species tested. This finding combined with the previously reported ethnographic and medical chart review data provides compelling evidence that such interventions significantly reduce the disease load from waterborne pathogens within this population. Furthermore, the finding that initial results are significantly different, even in the initial round of testing, if individuals who are not followed up are eliminated from the analysis has profound methodological implications which warrant further investigation and demonstrates the need for precise definitions of community in future studies.
A key component of the United Nations Millennium Development Goal Number 7 states “halve, by 2015 the proportion of the population (global) without sustainable access to safe drinking water and basic sanitation.” Most waterborne diseases result in diarrhea which continues to be a leading cause of morbidity and mortality worldwide. According to World Health Organization data, using existing technologies approximately ten percent of the worldwide burden of disease would be removed by the water supply, sanitation, hygiene, and management of water resources, making water-related diseases arguably the most manageable set of health problems affecting humans .
A great deal of work has been done attempting to measure the impact of interventions to provide improved water sources at the household level, and less frequently at the community level. The overwhelming majority of these studies have also used either key informant or self-reporting of diarrhea (defined as three or more loose stools per day) as the measure of disease burden [2–4]. Reliance upon such nonobjective measures introduces a host of potentially confounding variables [2, 5, 6] and yet appears to have been used in all of the 2,120 published studies reviewed in a far reaching meta-analysis produced for the World Bank on diarrhea and water interventions . While some of these deficiencies may be reduced by shortening recall time to seventy-two hours or less, potentially profound observer effects remain. Estimates of disease load changes are further impeded by researchers’ concentration on known users of water systems rather than measurements on community disease levels of disease changes regardless of compliance, thus making extrapolations of disease rate changes inappropriate.
In 2006, Water Missions International (WMI) received a grant from the Pentair Foundation to provide improved water source access and toilet systems to all of the people in the district of Colon, Honduras, an area that contains approximately 340,000 people. The goal of 100% coverage utilizes a combination of solutions including home-based filtration systems (provided by a different NGO) for communities with less than 300 people, and a variety of high-capacity treatment systems for larger communities. In the initial phase of the study, all 604 water sources for the control and test communities were tested by pressure filtration methods, and all failed quality testing by being positive for coliform bacterial growth. For all households that lacked adequate sanitation facilities and agreed to assist in installation, sanitary pit latrines with pour-flush toilet (toilets with water traps and no reservoir that are flushed by pouring a bucket of water into the basin) were also provided. Water treatment systems and pour-flush toilets deployed during the present study were developed and manufactured by Water Missions International, a nonprofit organization based in Charleston, SC, that works to provide sustainable water treatment capacities and sanitation facilities for people in developing countries. The technology uses a combination of multimedia, multistage filters, and chlorination to provide treated water for drinking and cooking that meets the most stringent class of WHO drinking water standards as well as passed present US standards from the EPA—specifically, tests on treated water grew no coliform bacteria on repeated, monthly testing during the period of this study. In addition, WMI provides community development programs that include education and microenterprise strategies to assure sustainability of these interventions.
In the baseline study phase of the project, water sources for 613 communities were identified. Various water quality tests were conducted on the community water sources by standard membrane filter test. High counts of coliform bacteria indicative of fecal contamination were found in 100% of the water sources. As previously published , initial stool tests also showed that 29.3% (53 of 181) of the volunteer subjects from the twelve communities that had been randomly selected from the state of Colon carried at least one of the three tested protozoan parasites. Also as reported previously, the prevalence of positive protozoan parasite levels was significantly lower in the intervention groups as compared to the test group. Even greater reductions of disease rates (at least 52%) were noted in the medical chart reviews of visits to the local health facility for diarrhea and dysentery as well as self-reporting of the same diseases via ethnographic interviews. Ethnographic data further suggested widespread acceptance and community-wide reproduction of the awareness of health benefits derived from consuming treated water. The present paper is a followup to that report primarily looking at the development of positive parasite stool tests in the same communities twelve months after the initial round of tests with an expanded study population.
Twelve communities from three different categories were randomly selected from the Colon district. Four communities had not yet obtained a water treatment system and were used collectively as the Control Group. Four other communities where water systems (Water Only Group) had been deployed were entered into the study as were four more communities where both water systems and sanitary flush latrines had been installed (Water and Sanitation Group). For both the initial tests in 2009 and the final round of tests in 2010, volunteers were recruited by poster advertising and via community leaders. Methods of recruitment were identical in all communities. All subjects who tested positive for protozoan antigens in either study (2009 or 2010) were treated with an appropriate dose of tinidazole (500 mgs per day for three days for adults with weight adjusted dosing for children). Subjects were directly observed to take the initial dose, which in management of Giardia has been shown to be highly effective without the additional doses. No side effects of treatment were reported. One hundred and sixty-three of the 200 subjects in the final round of testing in 2010 had also participated in the prior studies conducted 12 months earlier.
The effect of previous medical treatment of subjects upon the present study is to provide a population that either tested negative or were given highly effective treatment in 2009—thus providing a subpopulation which was believed to have begun the 12-month test period free of any of the three tested protozoans. The results among the subjects tested both times, therefore, may be regarded as the rates of reinfection over the 12-month period (or a one-year incidence rate) for all three groups.
Recent advances in highly sensitive and specific rapid immunoassays for waterborne parasite diseases have made field testing of individual fecal specimens now possible [9, 10]. These devices test for species-specific antigens of common parasites known to be primarily waterborne. The device chosen for this study tested for three protozoan parasites: Giardia lamblia (now widely known as Giardia intestinalis), Entamoeba histolytica/Entamoeba dispar, and Cryptosporidium parvum antigens. Previous work has shown these tests to have both specificity and sensitivity in excess of 96% for the aforementioned pathogens.
Immunoassay of stool for these waterborne parasites was used as an indicator that the subject had been exposed to waterborne pathogens and was therefore at risk of these and other infectious waterborne illnesses. A separate subset of 163 subjects from the three groups who also gave specimens twelve months earlier was analyzed as a separate subgroup. Given the highly effective cure rates of tinidazole for Giardia and Entameba and the fact that the vast majority of non-immunocompromised subjects will clear Cryptosporidium infections spontaneously, this subset is thought to represent recolonization rates with waterborne protozoan during the year after the initial round of testing and treatment. All specimens were tested within 12 hours of collection using the Triage Micro Parasite Panel manufactured by Biosite Incorporated.
Further information regarding diarrhea and dysentery rates was obtained by reviewing medical records from a public health clinic in a community where a water treatment system had been previously installed. Ethnographic data was collected using a combination of KAP surveys and guided interviews. The medical records review and the majority of the ethnographic data have been previously reported in this journal .
3. Role of the Funding Source and Ethics Review
Water Missions International maintains a country program in Honduras whose staff provided support and significant amount of labor for this project. The study design, collection, and analysis of data and interpretation of the data were the sole responsibility of the author.
Prior to initiation of the study, the Colon Minister of Health and the Institutional Review Board of Water Missions International reviewed and gave approval and consent for the project and study. Consistent with this review, no information from medical chart reviews which could identify subjects of the study was retained outside of the local healthcare facility. Under the supervision of a licensed physician, all individuals in whom potential pathologic parasites were found were given free treatment with regimens previously approved by the Colon Minister of Health. The control communities where no water treatment or sanitation facilities existed were selected from a preexisting construction queue and intervention was not withheld as a result of this study. Verbal consent was obtained and recorded from all subjects.
Age distributions within the three groups are seen in Tables 1 and 2. Gender distribution is seen in Table 3. Parasite test results for the control group compared to the combined water only group and water and sanitation group are seen in Table 4. Giardia and Entameba accounted for all but one positive test in all categories. Giardia accounted for 46% and Entameba 48% of the positive tests while Cryptosporidium remained rare at 6% of the totals.
Table 1: Age distribution of all subjects in all groups.
Table 2: Mean age distribution by group.
Table 3: Gender by intervention group.
Table 4: 2010 data comparing control group to the combination of water only group and water and sanitation group.
Subjects living in communities that did not have access to water systems had significantly higher rates of positive tests than subjects who had either access to water or who had access to water and flush toilets both in the initial survey of 2009 and in the 2010 followup (). These finding are summarized in Figure 1.
In 2009, a comparison of the rate of positive parasite tests appeared to demonstrate that, while access to a water treatment system reduced parasite levels, communities that had both treatment systems and installed flush toilets demonstrated a higher rate of positive parasite tests. These findings show a distinct gender bias toward women and are summarized in Figure 2. Additional ethnographic witnessing suggested that this finding may possibly be explained by the fact that women exclusively cleaned the toilets, often with inadequate supplies and protection. Water Missions International responded to this suggestion with additional training and supplies. In the followup parasite survey of 2010, what had appeared to have been a negative effect of the toilet systems was no longer present, as seen in Figure 2.
A separate analysis of parasite test results including only subjects who were available in both 2009 and 2010 is summarized in Figure 3. Of interest is that the apparent negative effect of the toilets in the 2009 data (Figure 1) completely vanishes when subjects lost to follow up in 2010 are removed from the 2009 analysis.
The present paper is a followup of the research previously reported  and adds support to the conclusion that access to community-based water treatment systems and flush toilets reduced the disease load in this region of Honduras. To our knowledge, these are the first studies to combine self-reported data, medical chart review, and stool immunoassays as an indicator of exposure to potential waterborne pathogens. The triangulation of these methodologies provides powerful support to what are otherwise strongly subjective and questionable measures of disease loads from waterborne pathogens.
The previously reported ethnographic data from these communities suggests a high level of understanding of the causes and prevention of diarrhea among the communities studied. The overwhelming majority (130 of 142) of the people interviewed attributed the majority of their diarrheal diseases to water and sanitation issues and improvement of the condition to improved water sources and access to flush toilets. There were also significant signs of a shift of ideations regarding drinking untreated water toward an appreciation of the importance of purified water and prohibitions against drinking untreated water with the addition of water treatment facilities and community education.
Ethnographic data found during this study suggests that, consistent with other similar work, the availability of improved water is felt by its recipients to improve a general sense of health and well-being. High levels of knowledge related to water issues exist in this area of Honduras which could be attributed to many factors including sophisticated public health efforts, high literacy rates comparable to the region, widespread health education in public schools, and the training offered by Water Missions International and other NGOs. Local indigenous belief systems appear uncommonly (mentioned in only 6 of 46 individual interviews and in none of the four focus groups) and for no one were they the basis for a preferred method of treatment.
Immunoassay evidence of decreased prevalence of waterborne parasites strongly supports the contention that community-based water treatment facilities reduce the overall stool parasite load, at least of the three protozoan species tested. Since all subjects who tested positive for either Giardia or Entameba were treated with three doses of tinidazole adjusted for age and weight, the follow-up study of all subjects who submitted stool samples initially is felt to represent the reinfection rates, in essence eliminating concerns regarding residual colonization from exposures that occurred prior to initiation of this study. Previous treatment of subjects who tested positive for any parasite creates the potential for a Hawthorne effect; however, the elevated number of positive tests initially found within the control communities would potentially bias this group more than the test groups and would tend to lessen rather than strengthen the differences found.
Also, as previously reported , when parasite antigens were detected in stool samples of individuals who had access to improved water sources, ethnographic investigation revealed lapses of behavior in spite of the high level of understanding of the risks associated with drinking from untreated sources. Further analysis of the interviews of subjects whose stool was positive for potential waterborne parasites suggests that risk and time management decisions rather than cultural or knowledge-based differences accounted for lapses in behavior and willingness to drink untreated water. Subjects reported that the time required to obtain treated water, sometimes a difference of only a minute or less, was too great to overcome their concerns with potential health risks associated with untreated tap water.
Multiple pathogens and inflammatory conditions cause diarrhea, making monitoring this symptom alone an inexact measure of the disease load related to water quality. Worldwide, the most common causes of diarrhea are viral infections such as the rotavirus, an ubiquitous infection that may be transmitted by personal contact. Food contamination and noninfectious inflammatory diseases add to the diarrhea prevalence. Though not precisely known, the number of diarrhea cases unrelated to waterborne pathogens is likely substantial. This means that the 52% drop in diarrhea rates noted in the previously reported community chart reviews may represent an even greater majority of the cases that could possibly be related to potential water and sanitation issues. This follow-up study strongly supports this finding and suggests that the effect where water treatment systems are maintained may even increase over time.
A comparison of the 2009 parasite test data excluding those lost to follow up a year later was dramatically different from when these individual tests were included (Figure 3). This suggests that the population that was lost to follow up significantly added to the initial rate of positive tests. This phenomenon deserves future scrutiny and incorporation into discussions of the idea of community as a social construct. If community is defined as those present at a given point in time, we see a negative impact from presence of the toilets. When we define community as those who reside in the geographic area for at least one year we find the exact opposite as this apparent negative impact is not detected. As this finding demonstrates, the unit of analysis remains paramount in such studies.
This combination of qualitative data, health records reviews, and immunoassays provides compelling evidence that community-based water treatment facilities with or without providing flush toilets significantly reduced the burden of diseases in the communities of Colon, Honduras. We further validate with objective measures prior work based upon self-reporting of diarrhea rates. Finally, this data suggests that interventions to provide potable water access on a community level when combined with community development efforts and sanitation can play a significant role in the reduction of mortality and morbidity from waterborne diseases and associated comorbidities.
Providing access to water treatment or water treatment and flush toilets significantly reduced the one-year incidence of positive test results for the three protozoan species tested. This finding combined with the previously reported ethnographic and medical chart review data provides compelling evidence that such interventions significantly reduce the disease load from waterborne pathogens within this population. Furthermore, the finding that initial results are significantly different, even in the initial round of testing, if individuals who are not followed up are eliminated from the analysis has profound methodological implications which warrant further investigation.
Adding a temporal definition of community resulted in a completely different finding regarding the impact of supplying flush toilets, demonstrating the need for precise definitions of community in future studies.
The method used here where objective measurements of health effects are coupled with more traditional anthropological tools may serve as a template for future studies in medical anthropology.
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by Jeffery Deal
Health Studies at Water Missions International, 2049 Savannah Highway, Charleston, SC 29407, USA
Received 1 November 2011; Accepted 30 November 2011
Academic Editor: Kaushik Bose
Copyright © 2011 Jeffery Deal. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
TweetMyron L Meters provides introductory as well as professional level material on water quality and water treatment. Did you know that Myron L Meters carries a meter specifically for testing RO systems (see below)? Water purification systems have purified brackish water and sea water for the military, businesses and farms in many different locations on […]
Myron L Meters provides introductory as well as professional level material on water quality and water treatment. Did you know that Myron L Meters carries a meter specifically for testing RO systems (see below)?
Water purification systems have purified brackish water and sea water for the military, businesses and farms in many different locations on planet Earth. Reverse osmosis water purification will create clean drinkable water when used on your drinking water.
Reverse osmosis will generally remove salt, manganese, iron, fluoride, lead, and calcium (Binnie et. al., 2002). Most mineral constituents of water are physically larger than water molecules and they are trapped by the semi-permeable membrane and removed from drinking water when filtered through an RO system (AllAboutWater.org, 2004). Meanwhile, consumers are concerned about the removal of minerals from their drinking water.
Reverse Osmosis (RO) removed 90-99.99% of all the contaminants including minerals from the drinking water supply (see Figure 1). RO removes minerals because they have larger molecules than water. The subject of minerals and RO created controversy and disagreement among water and health professionals. The World Health Organization (WHO) made clarification that majority of healthy minerals are needed for human body is from food or dietary supplementary sources and not from drinking tap water. In addition, minerals found in water can be harmful to human health. The evidence is strong that calcium and magnesium are essential elements for human body (WQA, 2011). However, its a weak argument to suggest that we should make up this deficiency through water consumption (WQA, 2011). Tap water presents a variety of inorganic minerals which the human body has difficulty absorbing (Misner, 2004). Their presence is suspect in a wide array of degenerative diseases, such as hardening of the arteries, arthritis, kidney stones, gall stones, glaucoma, cataracts, hearing loss, emphysema, diabetes, and obesity. What minerals are available, especially in “hard” tap water, are poorly absorbed, or rejected by cellular tissue sites, and, if not evacuated, their presence may cause arterial obstruction, and internal damage (Dennison, 193; Muehling, 1994; Banik, 1989).
Figure 1. Reverse Osmosis Membrane (Source:DOI-BUR, 2009)
Organic Minerals vs. Inorganic Minerals
There are two types of minerals in water, organic and inorganic. Human physiology has a biological affinity for organic minerals. Most organic minerals for our body functions come from dietary plant foods (Misner, 2004). A growing plant converts the inorganic minerals from the soils to a useful organic mineral (Misner, 2004). When an organic mineral (from a plant food) enters the stomach it must attach itself to a specific protein-molecule (chelation) in order to be absorbed, then it gains access to the tissue sites where it is needed (Misner, 2004). Once a plant mineral is divested within the body, it is utilized as a coenzyme for composing body fluids, forming blood and bone cells, and the maintaining of healthy nerve transmission (Balch & Balch 1990).
Reverse Osmosis has Little Effect on Water pH
Water pH levels will automatically change when water is ingested and comes into contact with the food in your stomach (Wise, 2011). Even on an empty stomach, your stomach acid alone is already several times more acidic than RO water (pH 6-8) with a pH level of 2 (Wise, 2011). The human body regulates pH levels constantly to find balance and equilibrium (see Figure 2). Therefore under normal conditions it will always maintain a neutral 7.4 pH balance (Wise, 2011). The healthy body is very robust and it will restore homeostatic pH fairly quickly and easily (Wise 2011). Soft drinks and sports drinks typically have a pH level of 2.5, orange juice has a 3 pH and coffee has a 4 pH level and we drink these beverages all the time without problems (Wise, 2011).
Figure 2. Comparison of pH Levels (Source: Wise, 2011)
Water filtered or treated by reverse osmosis is generally pure, clean, and healthy. A reverse osmosis treatment system is currently the only technology that can remove most of the emerging contaminants (i.e., prescription drugs and perchlorate) including other contaminants (i.e., arsenic, cyanide, and fluoride) that are difficult to remove by other treatment methods. No more ingesting of harmful inorganic minerals means the body will no longer be stressed with trying to absorb something that wasn’t supposed to be there in the first place (Wise, 2011). Consumers should not be concerned about the removal of minerals by RO system. As the WHO (2009) and WQA (2011) pointed out, the human body obtains the vast majority of minerals from food or supplements, not from drinking water.
One of the downsides to the reverse osmosis process is that it is so effective in removing particles, it will also remove minerals from your water that may be beneficial. The body needs certain minerals, such as calcium and magnesium, to function properly. In addition, some people believe minerals such as this actually add flavor to the water, so that will be missing if you filter the water. Some find a certain acidic taste to water that has been purified by reverse osmosis. A reverse osmosis system also wastes a certain amount of water. For every gallon of purified water, three or four gallons have to be processed. If water is scarce or expensive in your area, this is a strong consideration.
The Myron L RO-1 was developed years ago specifically for Culligan, and is designed for testing RO systems.
The choice of professionals for years, this compact instrument has been designed specifically to demonstrate and test Point of Use (POU) reverse osmosis or distillation systems. By measuring electrical conductivity, it will quickly determine the parts per million/Total Dissolved Solids (ppm/TDS) of any drinking water.
With a single ‘before and after’ test, this handy device effectively demonstrates how your RO or distillation system eliminates harmful dissolved solids. It will also service test systems, including membrane evaluation programs. Find out more about the RO-1 meter HERE.
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