Finding, Gathering, and Treating Water Luke Miller Lindsay Ellis Abby Krich Xinning Zhang

Introduction Water sources Water collection Water treatment Development vs. Relief

Water Sources Groundwater (wells and springs) Surface water (fresh) Rainwater Other options

Groundwater (Wells and Springs) Requires least input Energy efficient Clean Inexpensive If ground sources are available, make use and/or make extreme efforts to not contaminate

Groundwater: Wells Requires pumping Minimum of 50’ deep and 200’ from surface water to avoid contamination Test drilling should be done to determine probable well productivity, depth, spacing, water quality, and location

Hand Pumped Well

Spring Water Collection -most reliable source of natural filtered water in rural areas -If flow is less than 15 L/min a reservoir is not required -If storage is planned, the top of the storage tank must be below the eye of the spring for gravity feed.

Spring Box If the slope is very steep or the spring has a large flow, if may be necessary to build a spring box. Normally the spring box is less than one meter by one meter.

Surface Water (Fresh) Many sites have an abundance Rivers Lakes Streams Should be used only when groundwater is not available

Surfacewater Concerns Must investigate Drainage areas Rainfall, runoff, evaporation Sanitary survey Reservoir necessity Downstream effects

Surfacewater Problems Factors that can block intake Floating Debris Suspended Solids Bed load

Stream Intake and Settlement Stream intake and settlement in small mountain streams in Seychelles (UNESCO, 1991).

Tilted Perforated Plate

Vertical Perforated Plate

Rainwater Should be a last-resort method Requires extra construction of complex rain catchment devices Roofs should also be made of material that will not contaminate the water (no metal, shingles, etc.) Water supplies are limited and unpredictable

Rainwater Catchment System Catching clean rain water is one of the most common and oldest methods for collecting safe drinking water.

Other Options If all else fails, freshwater can be extracted from seawater, brackish water, or water vapor in the air Methods include reverse osmosis, electrodialysis, distillation, and vapor compression All are complex, costly, difficult to operate and maintain, and present disposal problems Let’s stay away from these

SLOW SAND FILTRATION A LOW TECH SOLUTION TO WATER TREATMENT

HISTORY At the beginning of the 19 th century, a Scotsman named John Gibb developed a way to provide clean water for his bleachery. Gibb built a built a water treatment plant that utilized the slow sand filtration technique, which is now regarded the oldest type of municipal water filtration.

Possibilities Slow sand filters continue to provide a cheap and relatively easy way for obtaining potable water. They may be a suitable water treatment choice for rural communities.

How the filter works Raw water percolates very slowly through the bed of uniformly porous sand. As raw water filters down the bed, a layer of microorganisms begins to form in the tops few millimeters of the filter. In a mature filter, this rich, sticky, mat-like biological layer is called a Schmutzedecke. The microorganisms break down and feed off of organic matter in the water. Inorganic particles are trapped in this layer as well, possibly by adsorption.

A combination of physico-chemical and biological mechanisms are involved in the filtration process. Biological mechanisms are not yet fully understood. Depending on the raw water quality, cleaning of the filter bed will be necessary after a few weeks or months to prevent clogging. This is done by scraping off only the top inch.

Capacity The capacity of a slow sand filter depends mainly on the filter surface. The recommendations are in the range of 100 to 300 L per m 2 and hour m 2 (25 – 75 gal/sq. yd. per hour).

Figure 1. Typical cross section of a slow sand filter.

Advantages There is a minimal amount of maintenance work (most time consuming is scraping off the top layer). COST of materials and operation. Materials can be found locally. No known negative impacts to the environment, as of yet. Energy consumption is low. No pre-treatment chemicals are needed.

Disadvantages Need a lot of land and filtration materials to produce significant amounts of treated water. Raw water turbidities need to be low so that the filters are not clogged too quickly. Filters treat cold water less effectively due a smaller population of microorganisms. Raw water needs to contain nutrient content for the Schmutzedecke to form. Organic chemicals are not completely removed.

Table 1. Typical Treatment Performance of Conventional Slow Sand Filters Water Quality Paramenter Removal Capacity Turbidity<1.0 NTUU Coliforms1-3 log units Enteric Viruses2-4 log units Giardia Cysts2-4+log units Crptosporidium Oocysts >4 log units Dissolved Organic Carbon <15-25% Biodegradable Dissolved Organic Carbon <50%

Table 1. Continued Water Quality Paramenter Removal Capacity Trihalomethane Precursors <20-30% Heavy Metals: Zinc, Copper, Cadmium, Lead >95-99% Iron, Manganese>67% Arsenic<47%

Conclusions Slow sand filtration is a practical and low cost method for treating water. Slow sand filters are easy to construct and require a minimum amount of maintenance.

References ures/BNP__Features__Item/0,3643,76891,00.html ures/BNP__Features__Item/0,3643,76891,00.html wiesbaden.de/fag/bio/pf/pfSFengl14.html wiesbaden.de/fag/bio/pf/pfSFengl14.html wtprimer/slowsand/slowsand.html wtprimer/slowsand/slowsand.html ilter.htm ilter.htm

Instructions for building a slow sand filter: er/slow_sand_filter.htm

Development rather than relief  Relief  Immediate but temporary help for times of disaster  Easier, so you can help more people  Development  Slower, but lasting  Concerned not so with helping people have more, but helping them be more  Long-term goal of sustainability