Slow Sand Filtration Workshop - PowerPoint PPT Presentation

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Slow Sand Filtration Workshop

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Slow Sand Filtration Workshop Saturday 31 January 2009 Tufts University Anderson Hall, Nelson Auditorium 200 College Ave Medford, MA 02155 Prototype Construction ... – PowerPoint PPT presentation

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Title: Slow Sand Filtration Workshop


1
Slow Sand Filtration Workshop
  • Saturday 31 January 2009
  • Tufts University
  • Anderson Hall, Nelson Auditorium
  • 200 College Ave
  • Medford, MA 02155

2
Agenda
  • Presentation
  • Workshop objectives
  • Introduction to Tufts EWB
  • Global role of sand filtration
  • Slow sand filter technology
  • Filter construction and maintenance
  • Break
  • Prototype build session
  • Discussion
  • Successes and obstacles with the technology

3
Workshop Objectives
  • Learn about slow sand filtration technology
  • Learn how to design, construct and maintain slow
    sand filters
  • Collaborate on future project work and workshops
  • Discuss ideas and share helpful tips

4
Tufts University Engineers Without Borders
5
History
  • Four projects
  • Tibet (2005)
  • Latrines
  • Ecuador (2006-2008)
  • Green House, BioGas Systems, Water Quality
  • El Salvador (2006-Present)
  • Water Distribution and Quality
  • Haiti (2008-Present)
  • Assessing (Latrines, Water Accessibility, Market
    Construction)

6
El Salvador
  • Arada Vieja
  • Located south of capital of San Salvador
  • Population 120
  • Assessment trip in July of 2006 resulted in a
    need for filtered water

7
Slow Sand Filtration
  • Successive trips dedicated to building filtration
    system
  • January 2007 Began construction
  • July 2007 and January 2008 Finished construction
    and conducted water quality tests
  • January 2009 Follow up trip

8
System Profile
Sand Filtration System
125
100
75
Elevation
Spring Box
50
Intermediate Tank
25
Hydraulic Ram Pump
300
150
600
450
900
750
3000
1050
Distance
9
Water Quality Tests Jan. 2008
  • Tested for bacteria and E. coli at key locations
  • Spring box
  • Intermediate tank
  • Filters
  • Dirty and clean spigots

10
Sand Filter Prototypes
  • Started after Summer 2006 assessment trip
  • Provides hands on experience with the technology
  • Gives insight into the construction process
  • Assesses the effectiveness of the filters

11
Prototype Water Quality Testing
  • Test water before and after filtration
  • Test water for
  • Turbidity
  • Total coliform
  • E. Coli

12
Prototype Test Results
E. coli Results
Full removal of E. coli bacteria
13
El Salvador Project Future
  • Arada Vieja Project
  • Expect 1-2 more trips for further water quality
    testing and community health surveys
  • Porvenir Project
  • Assessment trip January 2009
  • Small community with water access and quality
    problems
  • Assessing feasibility of slow sand filtration

14
TuftsEWB_at_gmail.com
15
The Global Role of Sand Filtration
16
The Global Role of Sand Filtration
  • Small scale micro-enterprise projects
  • Africa, Latin America, Asia
  • Large scale
  • Springfield, MA
  • Paris, France
  • London, England
  • Antwerp, Belgium

17
The Global Role of Sand Filtration
  • Emergency and disaster relief
  • Pilot project by Medair in Darfur starting in
    2003
  • Provided clean water to 7,500-10,000 people in
    the region

18
Past, Present and Future EWB Projects
  • Utah State University in Mexico
  • San Francisco Professionals Chapter in Fiji
  • University of Maryland, College Park in Ecuador
  • Lafayette College in Honduras
  • New Jersey Institute of Technology in Milot,
    Haiti
  • Hope College in Nkuv, Cameroon
  • University of Colorado at Boulder in Muramba,
    Rwanda

19
Slow Sand Filter Technology
20
Slow Sand Filtration The Basics
  • Oldest form of water treatment
  • Used to treat surface and ground water
  • Improves physical, chemical and bacteriological
    quality of water
  • Transportation, attachment and purification

21
Slow Sand Filter Physical Setup
Source Oasis Design (2006)
22
How It Works
  • Standing water
  • Heavy particles settle
  • Light particles coalesce
  • Algae grows release of oxygen
  • Biofilm (Schmutzdecke)
  • Forms within 10-20 days of consistent flow
  • Made up of algae, bacteria, fungi and other
    microorganisms
  • Feeds on dead algae and live bacteria in the
    water
  • Strains suspended particles
  • Color removal
  • Breakdown of nitrogen compounds

23
How It Works
  • Filter bed
  • Straining of particles
  • Adsorption
  • Biological activity
  • Most activity takes place closer to the top of
    the layer
  • Formation of microorganism layer
  • Gravel
  • Support filter bed
  • Prevent sand particle flow through outlet

24
Advantages of Slow Sand Filtration
  • Unskilled labor to install and maintain
  • Inexpensive
  • Does not require mechanical power
  • Low flow rates
  • Increased time for pathogen removal in biofilm
  • Pathogens not transmitted deeply into layers
  • Biofilm can become better developed
  • Can produce potable water in accordance with EPA
    standards

25
Disadvantages of Slow Sand Filtration
  • Pretreatment required for highly turbid raw water
  • May need disinfection after filtration to meet
    superior water quality standards
  • Requires large surface area
  • Cold temperatures lower filtration efficiency
  • Algae may interfere with operation

26
Design, Construction and Maintenance
27
Basic Design
28
Filter Types
  • Concrete
  • Box or cylinder with outlet embedded in wall
  • Generally cheap
  • Widely used in developing countries
  • Need metal mold for construction- decreases mass
    production
  • Plastic
  • Simple design
  • Mass producible
  • Relatively cheap
  • Durable
  • Lightweight, easy to transport

29
Filter Types
  • Drum Filter
  • Good when cement is difficult to obtain and
    oil/fuel drums are readily available
  • Will need cleaning equipment

Concrete Filter
Drum Filter
30
Considerations for Filter Design
  • High surface area/volume ratio
  • Slow inflow rate
  • 120 L/m2-h or 100-400 L/m2-h
  • Constant or intermittent flow
  • No significant effect on bacterial removal
  • Lower flow rates improve turbidity and color
  • 5 cm head above fine sand layer
  • Clean sand of specific grain sizes

Variable Speed Pump
31
Suggested Grain Sizes
Fine Sand 0.25 0.35 mm 56 - 70 sieve
Coarse Sand 1 1.2 mm 12 - 16 sieve
Gravel 5mm diameter Std. pea gravel, or 3
sieve
32
Cleaning the Sand
  • Method One
  • Sieve sand
  • Put sand in bucket and add clean water
  • Swirl bucket and decant dirtied water
  • Let sand dry
  • Method Two
  • Buy pre-cleaned/pre-sieved sand from distributor

33
Construction
  • Sand Filter Depths
  • Fine sand (.25 - .35 mm effective)
  • 20.5 24 inch depth
  • Coarse sand (1.2 mm effective)
  • At least 2 inch depth
  • Gravel (5 - 15 mm effective)
  • 3 inch depth
  • Outlet Pipe
  • 1 inch pipe diameter
  • 5 cm above fine sand layer
  • Perforated, covered by mesh

34
Prototype Construction
  • General Design
  • - 4 diameter PVC casing
  • - Clear acrylic tube
  • - Piezometers
  • - Outflow tubing
  • - Overflows
  • - Gravel
  • - Coarse Sand
  • - Fine Sand

35
Importance of Backfilling
Air bubbles!
36
Maintenance Performed Every 3-5 Months
  • 1) Remove the lid and the colander/diffuser
    basin.
  • 2) Lower the water level inside the filter by
    using a small cup to scoop out the water that has
    not drained through the outlet pipe.
  • 3) Make a small hole in the sand with the cup.
    Scoop out the water that accumulates in it until
    only wet sand remains.
  • 4) Remove 3 to 5cm of the fine sand layer
  • and set it aside. (After washing and drying in
    the sun, this sand may be reused next time
    maintenance is performed.)

5) Add clean, fine sand from previous
maintenance. Level the surface of the sand. 6)
Reinstall the colander/diffuser basin. 7) Slowly
add water to the filter until water begins to
flow through the outlet pipe again and water is 5
cm above fine sand layer. 8) Again remove the
lid and colander/diffuser basin 9) Level the
surface of the sand again 10) Reinstall the
colander/diffuser basin
37
Schmutzdecke Scraping
38
Questions
39
Break
  • Enjoy refreshments!

40
Discussion
41
Successes and ObstaclesArada Vieja as a Case
Study
42
Successes
  • System requires no electricity
  • Pump is gravity fed
  • Materials can all be found locally except for
    pump
  • Filters succeed in removing E. coli

43
Obstacles to Overcome
  • How long can flow be cut off to filters?
  • Currently 24 hours off, 48 hours on
  • Bacterial growth in clean water storage tank from
    surviving bacteria after filtration
  • No residual disinfection

44
Thank You!
  • EWB - USA
  • Tufts EWB Executive Board
  • Workshop participants

45
References
  • WHO
  • Biosandfilter.org
  • Medair
  • EWB-USA
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