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. 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 Agenda

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 150’ 300’ 450’ 600’ 750’ 900’ 1050’ ~3000’ 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@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. 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 The Global Role of Sand Filtration

18. 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 Past, Present and Future EWB Projects

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 Obstacles:Arada 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