Finding, Gathering, and Finding, Gathering, and Treating WaterTreating Water

Luke Miller

Lindsay Ellis

Abby Krich

Xinning Zhang

IntroductionIntroduction

Water sourcesWater collectionWater treatmentDevelopment vs. Relief

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

SLOW SAND FILTRATIONSLOW SAND FILTRATION

A LOW TECH SOLUTION TO WATER TREATMENT

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

Development rather than reliefDevelopment rather than relief

Relief Immediate but temporary help for times of disaster Easier, so you can help more people

DevelopmentSlower, but lastingConcerned not so with helping people have more, but

helping them be moreLong-term goal of sustainability