Tufts Engineers Without Borders Slow Sand Filtration Workshop

Tufts Engineers Without Borders Slow Sand Filtration Workshop Saturday 31 January 2009 Tufts University Anderson Hall, Nelson Auditorium 200 College Ave Medford, MA 02155 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Tufts University Engineers Without Borders Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders History • Four projects – Tibet (2005) • Latrines – Ecuador (2006 2008) • Green House, Bio. Gas Systems, Water Quality – El Salvador (2006 -Present) • Water Distribution and Quality – Haiti (2008 Present) • Assessing (Latrines, Water Accessibility, Market Construction) Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders System Profile Sand Filtration System 125’ Elevation 100’ 75’ Spring Box 50’ Intermediate Tank 25’ Hydraulic Ram Pump 150’ 300’ 450’ 600’ Distance 750’ Tufts EWB Slow Sand Filtration Workshop, 31 January 2009 900’ 1050 ’ ~3000’

Tufts Engineers Without Borders Water Quality Tests – Jan. 2008 • Tested for bacteria and E. coli at key locations Spring box Intermediate tank Filters Dirty and clean spigots Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Prototype Water Quality Testing • Test water before and after filtration • Test water for Turbidity Total coliform E. Coli Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Prototype Test Results E. coli Results Full removal of E. coli bacteria Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Tufts. EWB@gmail. com Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders The Global Role of Sand Filtration Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Slow Sand Filter Technology Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Slow Sand Filter: Physical Setup Source: Oasis Design (2006) Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Design, Construction and Maintenance Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Basic Design Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Filter Types • Drum Filter • Good when cement is difficult to obtain and oil/fuel drums are readily available – Will need cleaning equipment Drum Filter Concrete Filter Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Considerations for Filter Design • High surface area/volume ratio • Slow inflow rate – 120 L/m 2 h or 100 400 L/m 2 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Suggested Grain Sizes Fine Sand 0. 25 – 0. 35 mm ~#56 - #70 sieve Coarse Sand ~ 1 – 1. 2 mm ~#12 - #16 sieve Gravel ~ 5 mm diameter Std. pea gravel, or # 3 sieve Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Construction Sand Filter Depths • Fine sand (. 25 -. 35 mm effective) • • Coarse sand (1. 2 mm effective) • • At least 2 inch depth Gravel (5 - 15 mm effective) • • 20. 5 – 24 inch depth 3 inch depth Outlet Pipe • 1 inch pipe diameter • 5 cm above fine sand layer • Perforated, covered by mesh Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Prototype Construction • General Design 4” diameter PVC casing Clear acrylic tube Piezometers Outflow tubing Overflows Gravel Coarse Sand Fine Sand Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Importance of Backfilling Air bubbles! Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Maintenance Performed Every 3 -5 Months 1) Remove the lid and the colander/diffuser basin. 5) Add clean, fine sand from previous maintenance. Level the surface of the sand. 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. 6) Reinstall the colander/diffuser basin. 3) Make a small hole in the sand with the cup. Scoop out the water that accumulates in it until only wet sand remains. 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. 4) Remove 3 to 5 cm 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. ) 8) Again remove the lid and colander/diffuser basin 9) Level the surface of the sand again 10) Reinstall the colander/diffuser basin Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Schmutzdecke Scraping Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Questions Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Break Enjoy refreshments! Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Discussion Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Successes and Obstacles: Arada Vieja as a Case Study Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Successes • System requires no electricity – Pump is gravity fed • Materials can all be found locally except for pump • Filters succeed in removing E. coli Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders 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 Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders Thank You! • EWB USA • Tufts EWB Executive Board • Workshop participants Tufts EWB Slow Sand Filtration Workshop, 31 January 2009

Tufts Engineers Without Borders References • WHO • Biosandfilter. org • Medair • EWB-USA Tufts EWB Slow Sand Filtration Workshop, 31 January 2009