Modular BioSand Water Filter [Download a PDF Copy]
In October (2010), I have built a modular biosand filter made from 2-gallon
white plastic paint buckets. The buckets are made of food-grade (number 2)
polyethylene plastic and are the same buckets you can find at most hardware
stores worldwide. Figure 1 shows a photograph and Figure 2 shows a drawing
of the prototype filter. I believe this modular water filter meets the critical
design requirements of the biosand filters developed by the CAWST. The
basic difference is the modular design breaks up the normal single column
biosand filter into three or more stacked 2-gallon sections or modules. The top
2-gallon module forms the biological zone where pathogens are removed by
the biolayer (or schmutzedecke). The subsequent middle and bottom modules
form the non-biological zone(s) where mechanical trapping and adsorption play
a major role in removing any remaining contaminants, pathogens and parasites.
In this design, the 2-gallon modules are stacked one on top and inside the other
forming a stable filter column. The siphon tubing is used to assist the first
water connection between the top 2-gallon filter - that includes the biolayer -
and the middle 2-gallon filter. The siphon tubing is wrapped in a way that
allows water to flow down the stack while maintaining enough standing water
to nourish the biolayer. The middle filter has a small drainage hole at its base
to complete the water flow to the bottom filter that includes the outlet tube.
Finally, a larger 5-gallon bucket may be used to store treated water. The
5-gallon bucket may be used as the container that kits all the parts and tools
used to assemble the modular filter.
Please be aware, this is a pre-filter tool. Treat filtered water with
sunlight, heat or chlorine before final storage and consumption - as I
describe elsewhere on my website.
Below, I have included detailed assembly instructions. First, familiarize yourself
with the general principles of a biosand filter - I will only touch upon the sticky
parts of my modular variant - Please refer to my drawing .
In my modular design, you are using four buckets in a stack. The most top bucket
is for feeding water (slowly) to the other three. The (top) BioSand Filter bucket
uses siphon pressure and gravity to deliver the water to the middle Sand Filter
bucket. From the middle, gravity (alone) moves the water to the bottom Sand Filter.
Gravity pressure from the stack forces water to flow from the bottom Sand Filter
bucket tube or faucet.
1.) Care needs to be taken to make the BioSand Filter bucket - first. Prepare a 1/2-inch
diameter hole for the tubing to come out the side. Make it 1-inch down from the top
of the bucket. Begin with one length of tubing (about 32-inches) that runs from the
INSIDE bottom and out the hole. Use waterproof foil tape to seal the area were the
tube comes out. A proper gasket or food safe putty are other way to form a seal.
Do the best you can. Add your clean sand, pebbles and rocks as shown. Add water
to the bucket and test the siphon. A proper siphon maintains about a 2-inch of
standing water at all times. Check for leaks and seal as needed.
2.) Prepare the other two Sand Filter buckets. Make a small drainage hole at the
bottom of the middle Sand Filter bucket. Add sand, pebbles, rocks and tubing as s
hown. Stack the two Sand Filter buckets together.
3.) Stack the BioSand Filter bucket on top of the two Sand Filter buckets. Wrap
the remaining OUTSIDE tubing section down and along the bucket. You insert
the end into the narrow gap between the two buckets. Cut off any extra tubing.
The main advantages of the modular biosand water filter design include:
1. Low cost - less than $20 for everything (including tools, sand, pebbles, etc).
2. Available - uses ordinary components that may be obtained worldwide.
3. Lightweight - plastic body weights a few pounds. Filled with sand, each
2-gallon module weights ~23-lbs. The complete filter with three modules filled
with sand and gravel weights less than 75-lbs - compared to over 200-lbs for
an empty concrete biosand filter.
4. Portable - all parts and tools fit inside a 5-gallon bucket (kit) that a child
can carry and transport.
5. Durable - heavy duty plastic won't corrode, crack or break under normal use.
6. Easy to assemble - one able-bodied person + 30 minutes.
7. Easy to maintain - no breakable or moving parts to wear out. Needs periodic
simple cleaning. Modular design assists trouble-shooting.
8. Sustainable - simple technology and made mostly of sand.
9. Modular design - 2-gallon biosand filters may be prepared prior to adding
other sand filters in the stack. Water filter stacks may be customized according
to local water conditions - adding or deleting 2-gallon sand filters. In some cases,
activated carbon modules and other filter materials may be added to improve
removal of heavy metals and known chemical contaminants.
Figure 1. Modular BioSand Water Filter (prototype).
Figure 2. Drawing - Click to Enlarge.