finding, gathering, and treating water luke miller lindsay ellis abby krich xinning zhang
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Finding, Gathering, and Finding, Gathering, and Treating WaterTreating Water
Luke Miller
Lindsay Ellis
Abby Krich
Xinning Zhang
Water SourcesWater Sources
Groundwater (wells and springs)Surface water (fresh)RainwaterOther options
Groundwater (Wells and Springs)Groundwater (Wells and Springs)
Requires least inputEnergy efficientCleanInexpensive
If ground sources are available, make use and/or make extreme efforts to not contaminate
Groundwater: WellsGroundwater: Wells
Requires pumpingMinimum of 50’ deep and 200’ from
surface water to avoid contaminationTest drilling should be done to determine
probable well productivity, depth, spacing, water quality, and location
Hand Pumped WellHand Pumped Well
http://www.unep.or.jp/ietc/Publications/TechPublications/TechPub-8a/instream.asp
Spring Water CollectionSpring 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 BoxSpring BoxIf 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)Surface Water (Fresh)
Many sites have an abundanceRiversLakesStreams
Should be used only when groundwater is not available
Surfacewater ConcernsSurfacewater Concerns
Must investigateDrainage areasRainfall, runoff, evaporationSanitary surveyReservoir necessityDownstream effects
Surfacewater ProblemsSurfacewater Problems
Factors that can block intakeFloating DebrisSuspended SolidsBed load
Stream Intake and SettlementStream Intake and Settlement
Stream intake and settlement in small mountain streams in Seychelles (UNESCO, 1991).
http://www.unep.or.jp/ietc/Publications/TechPublications/TechPub-8d/instream.asp
Tilted Perforated PlateTilted Perforated Plate
http://www.lboro.ac.uk/departments/cv/wedc/papers/22/groupd/prakke.pdf
Vertical Perforated PlateVertical Perforated Plate
http://www.lboro.ac.uk/departments/cv/wedc/papers/22/groupd/prakke.pdf
RainwaterRainwater
Should be a last-resort methodRequires extra construction of complex rain
catchment devicesRoofs should also be made of material that
will not contaminate the water (no metal, shingles, etc.)
Water supplies are limited and unpredictable
Rainwater Catchment SystemRainwater Catchment System
Catching clean rain water is one of the most common and oldest methods for collecting safe drinking water.
Other OptionsOther 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
HISTORYHISTORY
At the beginning of the 19th 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.
PossibilitiesPossibilities
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 worksHow 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.
CapacityCapacity
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 m2 and hour m2 (25 – 75 gal/sq. yd. per hour).
Figure 1. Typical cross section of a slow sand filter.Figure 1. Typical cross section of a slow sand filter.
AdvantagesAdvantages
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.
DisadvantagesDisadvantages 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 Table 1. Typical Treatment Performance of Conventional Slow Sand FiltersConventional Slow Sand Filters
Water Quality Paramenter
Removal Capacity
Turbidity <1.0 NTUU
Coliforms 1-3 log units
Enteric Viruses 2-4 log units
Giardia Cysts 2-4+log units
Crptosporidium Oocysts
>4 log units
Dissolved Organic Carbon
<15-25%
Biodegradable Dissolved Organic Carbon
<50%
Table 1. ContinuedTable 1. ContinuedWater Quality Paramenter
Removal Capacity
Trihalomethane Precursors
<20-30%
Heavy Metals: Zinc, Copper, Cadmium, Lead
>95-99%
Iron, Manganese >67%
Arsenic <47%
ConclusionsConclusions 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.
ReferencesReferences
http://www.drilleronline.com/CDA/ArticleInformation/features/BNP__Features__Item/0,3643,76891,00.html
http://www.mnd.fh-wiesbaden.de/fag/bio/pf/pfSFengl14.html
http://www.cee.vt.edu/program_areas/environmental/teach/wtprimer/slowsand/slowsand.html
http://www.refugeecamp.org/learnmore/water/slow_sand_filter.htm
www.sungravity.com www.nps.gov/dsc/dsgncnstr/gpsd/toc.html
Instructions for building a slow Instructions for building a slow sand filter:sand filter:
http://www.refugeecamp.org/learnmore/water/slow_sand_filter.htm