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SUSTAINABLE COMMUNITY DEVELOPMENT – WATER SLOW-SAND FILTRATION
Impact/Purpose:
The proposed research project question is: “How can a Slow-Sand water purification system be improved to meet the needs of a small community?” A major issue that persists in underdeveloped areas is both water quality and quantity. There have been point-of-use water purification systems developed that can provide for particulate removal, bacteria destruction, or both. However, large-scale community systems have remained too expensive for underdeveloped communities. This project has three goals: 1) perform research and development tasks that would increase the throughput of the slow-sand technology; 2) design the research outcome into a total community system design that would be applicable to a wide variety of communities; 3) develop an educational strategy that would provide for indigenous community integration, maintenance, and sustainability.
Description:
Site Survey: When this project was developed, the village of Santa Cruz, Baja Verapaz, Guatemala was chosen as a target community for initial development and target implementation. The research team of six students and advisor traveled to the village in early August 2007 for a site survey. Shortly after arriving at the village, we were provided a written report from Plan Guatemala that provided valuable data. A water collection and distribution system was built for the village some years ago using United Nations funding. The storage tank has a storage capacity of 46.2 cubic meters. The vertical drop from the mountain catchment area to the holding tank is 520 feet. This creates a significant hydraulic energy source that is currently unused. Local data and testing showed that their water contains bacteria and is unfit for human consumption.
The team also evaluated the local technical skills and available resources. The local construction consisted of concrete, concrete block, wood and corrugated metal. Sand was found in abundance. These items are directly compatible with the chosen slow-sand filter. Even though the area is tropical in latitudinal location, the mountains create a cooler environment and the August water temperature at the source was measured at 16 degrees Celsius. This temperature will be colder in the winter months and therefore biological/algae growth will be slower than originally expected. Electricity was found to exist at almost every home in the village. Power was limited as there was a single 110-volt line, 15-amp service. The electrical service also demonstrated a fees collection system as each home pays a very low flat rate to maintain this service for their community and home.
Slow-sand Filter: The JBU filter system began with creating a water collection system that closely simulated the environment at Santa Cruz. A water run-off creek runs through our campus and adjacent to our research lab. An analysis of our operating conditions showed that our lab set-up had harsher environmental constraints than those in Guatemala (GUA). Water source turbidity in GUA was less than 5 NTU (nephelometric turbidity units). JBU source was 10-30 NTU. Water temperature was 16 degrees C. in GUA and 8-12 degrees C. at JBU. Growth of the Schmutzdecke was slower than anticipated, but does take place even in this colder environment.
For outcome evaluation, the team chose to use measurement techniques that could be easily transferred into impoverished communities. For measuring the turbidity of the water, a simple graduated cylinder was used. The turbidity tube uses the correlation between visibility and turbidity to approximate a turbidity level. A marker is placed at the bottom of the tube and fluid poured into the tube until the marker can no longer be seen due to the “cloudiness” of the water. This height correlates to a known turbidity value. Though this measuring technique is very basic, it does represent a technology that is readily transferred as an appropriate process to communities like Santa Cruz.
For bacteria analysis, Hach’s PathoScreen™ test was used. The testing has two process to determine presence/absence (P/A) and most probable number (MPN). The technique is well-suited for monitoring drinking water systems in developing tropical countries and remote field locations. The World Health Organization looks to this type of testing for impoverished communities with the criteria that no bacteria colonies be distinguishable after 48 hours of P/A incubation. As the Schmutzdecke was developing in our laboratory system, measureable reductions in bacteria were noted. Bacterial levels reached acceptable levels as the depth of the biological layer reached 7.5 cm. and the flow rate reduced to about one gallon/minute/square meter. All source samples indicated significant bacteria within 24 hours of incubation while outputs began to show no bacteria in medium at 72 hours.
Augmentation System: As a result of the site survey, it was apparent that there were augmentation opportunities. As noted earlier, the current delivery pipe from the catchment point to the holding tank has significant hydraulic energy due to the vertical drop. This information provided opportunity to considered power generation techniques, adding external purification devices, and injection of additives for purification.
To provide water purification, the electrical energy must be converted into an energy source that would kill bacteria. In a short trip outside of Santa Cruz, the project team observed UV lighting being used for purification. Materials are available. Minimal training would be needed for operation and maintenance. A quick analysis shows that fast filtration to remove solid particulates combined with UV light could provide for safe drinking water. The creek water was first run through a sediment filter to remove particulates. The next task was to characterize a UV system at various flow rates ranging from 50% of manufacturer’s ratings to 150%. The bacteria were effectively eliminated even at 150% of rating. We now have data from both the sand filter and the UV system that show encouraging promise for integrating the two approaches during Phase II.
Filter Cleaning: The final element of Phase I research is the slow-sand filter maintenance. The slow-sand filtration system requires continual maintenance for sustained operation. If the biological layer is not trimmed/scrubbed on a regular basis, the system flow will reduce, which negates any improvements in the flow achieved by this project. Two issues arise from this requirement: 1) the need for someone willing to accept the maintenance responsibility and 2) environmentally-friendly disposal of the trimmings. To solve both of these problems, the project team considered both technical issues and a partnership with Students in Free Enterprise (SIFE), an NGO, for implementation considerations.
From the technical side, the basic task removes a layer of sand and Schmutzdecke from the top of the filter, separates the sand and the biological material, places the sand back in the filter and looks for an environmentally friendly and economic way of disposing the biological waste product. During Phase I, system operation required the removal of the biological layer after three months of operation. Approximately 2 cm of this layer was removed yielding just over 24 pounds of sand and with about 9% by-product by weight. The sand was separates from any nutrients using a simple wire screen and shaking. Recovered nutrients were available for usage in micro-enterprise development.
The technical team has partnered with Students in Free Enterprise (SIFE) at John Brown University. SIFE has five active teams working on multi-year projects in Central America. Members of the research team are also members of SIFE. The primary consideration for Santa Cruz is to use the system trimmings as fertilizer in local gardens. With per capita income in many of these communities of only $70-80 per month, a small business can have significant incentive and impact on the local economy.