This document discusses biological sand filtration for water treatment. It describes the basic components of a sand filter, including the schmutzdecke layer, sand layer, optional activated carbon, gravel layer, and output. The schmutzdecke is an important biological layer that traps and breaks down pathogens through bacteria, fungi, and other microorganisms. The sand provides substrate for the biofilm, while the gravel and output layers allow treated water to flow out. Regular maintenance like replacing sand is needed to keep the filter functioning properly. Water testing helps determine the effectiveness of treatment and safety for consumption.

1. Biological Filtration
Sand Filters 101

2. What is a Biological Filter
● Mechanical trapping of particles and pathogens
● Predation of pathogens by organisms living in the filter
● Adsorption where organisms clump together and bind to
the sand layer
● Natural deaths where pathogens finish their life cycle
and cease multiplying

3. Basic Sand Filter Parts
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Input
Schmutzdecke
Sand Layer
Activated Carbon (optional)
Gravel Layer
Output

5. Schmutzdecke!
This is the active biological layer at the top of
the sand filter. It does the work by trapping and
breaking down pathogens.
● Bacteria, fungi, rotifers, algae,and protozoa
● Do keep it.
● Don’t disturb it - slow flow...

6. Sand!
● Provides a substrate for the biofilm layer
● Use different particle sizes
● Needs to be exchanged periodically

7. Activated Carbon- What is it?
This is highly porous charcoal. It is useful
because it can bind chemical impurities
through adsorption.
The contaminants are locked up, but the carbon
needs to be changed out periodically, in order
to remain effective.

8. Gravel Layer
This layer keeps the sand in the filter, and
allows the water to come out - slowly…

9. Outflow and Storage
http://www.surferswithoutborders.org/

10. Other Sand Filter Plans…
● Surfers Without Borders Slow_Sand_Filter
● CAWST Biosand Filter
● National Drinking Water Clearing House Slow Sand Filter

11. Sunlight
Ultraviolet light is pretty good at killing
pathogens,
but takes time, and is not guaranteed.

12. Water Testing
How safe is this water…?

13. Water Testing
The most basic test - sight and smell...

14. Water Quality Measures
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Turbidity
TDS - Total Dissolved Solids
Ph Level - Neutral is best
Nitrates
Fecal Coliform
Biochemical Oxygen Demand
Phosphorous

15. Testing for Everything…?
It’s difficult to test for everything for a number
of reasons:
● Cost - Example Price List Water and
Wastewater
● Technology ● Identification Know your source!

16. Streamer
http://nationalatlas.gov/streamer/

17. Commercial Tests
Home test kits range between $9 and $40 for a
single use.
Commercial lab kits cost more
(~$1000), and will not test for
everything...

18. Emergency Preparedness
How to be ready

19. How Much Water Do I Need?
● Minimum: One gallon of water / a person /a
day
● Hot outside? - double that - two gallons / day
● Consider how long it will be before another
source of water becomes available (keep at
least three days worth).

20. How Should I Store It?
● Keep it in a cool, dark place.
● Keep the water sterile (covered and sealed).
● Replace it every six months.

21. Purifying Water In a Pinch
1.
2.
3.
4.
5.
Boiling…(160 degrees for 30 minutes)
Bleach… (~two drops per a quart)
Iodine Tablets…(usually two tablets / quart)
Solar Stills…
Portable Water Filters...

22. Food!
Don’t forget about food - you need at least three
days / person in your household.
● Dry or canned goods keep best.
● Avoid salty foods if water is an issue.

23. Other Things to Consider...
The best resource in an emergency is
community.
Charleston Rain Catchers
http://tinyurl.com/l5am32d (Facebook Group)

24. Resources
Appropriate Technology, Development Wiki - http://tinyurl.com/k3yytyl
EPA Guide to Home Water Testing http://tinyurl.com/kfrnuur
Filter Design and Construction - http://tinyurl.com/nxdubq5
How to Filter Water with a Sand Filter - http://tinyurl.com/885u3pr
Iodine Tablets - http://tinyurl.com/kfwx8t4
Water Emergency Preparation - Ready.gov/water
Water for the World - http://www.lifewater.org/resources/rws3/rws3c3.pdf