Biological FiltrationSand Filters 101

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

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

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...

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

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.

Gravel LayerThis layer keeps the sand in the filter, and allows the water to come out - slowly…

Outflow and Storage

http://www.surferswithoutborders.org/

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

Slow Sand Filter

SunlightUltraviolet light is pretty good at killing pathogens,but takes time, and is not guaranteed.

Water TestingHow safe is this water…?

Water TestingThe most basic test - sight and smell...

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

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!

Streamerhttp://nationalatlas.gov/streamer/

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

Emergency PreparednessHow to be ready

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).

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

Purifying Water In a Pinch1. Boiling…(160 degrees for 30 minutes)2. Bleach… (~two drops per a quart)3. Iodine Tablets…(usually two tablets / quart)4. Solar Stills…5. Portable Water Filters...

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.

Other Things to Consider...The best resource in an emergency is community.

Charleston Rain Catchershttp://tinyurl.com/l5am32d (Facebook Group)

ResourcesAppropriate Technology, Development Wiki - http://tinyurl.com/k3yytylEPA Guide to Home Water Testing http://tinyurl.com/kfrnuurFilter Design and Construction - http://tinyurl.com/nxdubq5How to Filter Water with a Sand Filter - http://tinyurl.com/885u3prIodine Tablets - http://tinyurl.com/kfwx8t4Water Emergency Preparation - Ready.gov/water

Water for the World - http://www.lifewater.org/resources/rws3/rws3c3.pdf