Biosand Filter Construction Guide Copy

Biosand Filter Construction GuideEngineers Without Borders at the University of Wisconsin Madison

Muramba, RwandaSupplemental Report • Rwanda Team • January 27, 2008

EWB-UW • Rwanda Team • www.ewbuw.org/donate

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Table of Contents

Science Behind the Filter! 2

The Layers of the Filter 2

Filter Construction! 3

Step 1: Container Determination - Blue Plastic Drum 3

Step 2: Sand and Gravel Procurement - Go Local 3

Step 3: Sand and Gravel Purification - A Time-Intensive Step 4

Step 4: Container Faucet and Plumbing - A Simple On/Off Switch 5

Step 5: Diffusion Plate Creation - A Elementary Sift 6

Step 6: Filter Placement and Final Setup Instructions - A Heavy Drum 7

Step 7: Initial Priming and Flushing of System - Forward To Cleaner Water 7

Budget! 9

Biosand Filter Budget 9

Bibliography 10

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Science Behind the FilterThe biosand filter technology is a simple and effective technology that can be implemented with a

small budget. Our group decided to pursue further research into this appropriate design solu-

tion.

The Layers of the Filter

! The first layer is biologically the most important. In only a couple of centimeters of wa-

ter, a diverse feeding sequence will emerge known as the schmutzdeke or more simply, the bio-

logical layer. The sand layer filters out 95 to 99% of organic contaminates including bacteria,

viruses, protozoa, worms, and particles. 1 These organic contaminates stay in this water layer

above the sand layer. A natural food chain

will emerge within this layer. As more wa-

ter is strained through, the filter will be-

come more effective in killing off harmful

contaminates. This biological layer does

the work in removing these contaminates

while the sand and gravel layers will per-

form more aesthetic work on the water.

These two layers will deodorize, refresh,

and clean the water making it more enjoy-

able to drink. 2

EWB-UW • Rwanda Team • www.ewbuw.org 2

Figure 1 - To the right is the basic

design our team used in the field

to build a biosand filer.

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Filter ConstructionOne Design Among Many

EWB-UW spent much time researching possible biosand filter designs. Our design shows only

one representation of many. Scores of factors molded the final design into what it became in the

field. Below step-by-step instructions are given for our filter design. It is hoped that future

groups will experiment with the design in order to find the easiest to build and most efficient fil-

ter possible.

Step 1: Container Determination - Blue Plastic Drum

! For ease of construction, purchase, and transport, a blue, plastic, 250 liter drum was

chosen as the vessel that would later be used construct the filter. Unlike concrete vessel designs,

a plastic drum like this does not need to be built. For our short time in Muramba, this proved to

be essential. These drums

are readily available in Ki-

gali. They cost about $100,

but are lighter and easier to

transport than concrete.

The plastic is sturdy enough

to withstand transport along

a rocky road and movement

in working with it, but soft

enough to not be a burden

when the time comes to drill

a hole through its side.

Step 2: Sand and Gravel Procurement - Go Local

! The EWB-UW Rwanda team collaboratively works with the vocational school in Mu-

ramba, Rwanda on most projects. Their expertise with construction in Muramba is quite good.

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Figure 2 - One 250 liter drum





When we work with them, Innocent Kambande acts as a sort of “construction manager” and

main contact while the work is in progress.

! We discussed our projects in detail with Innocent. He placed the order for materials that

would be needed during construction. Sand and gravel were on that list, and were later collected

from a small quarry near Muramba. Local resources like this are essential to appropriate devel-

opment increasing the chances of continued, local biosand filter construction.

Step 3: Sand and Gravel Purification - A Time-Intensive Step

! The sand and gravel that are entered into the container must be relatively pure. If they

are not, the filter will work mechanically, but not very effectively. Make sure to clean the sand and

gravel. This process seems simple, but can be quite daunting.

! Our group knew that the sand and gravel must be cleaned, but did not understand the

time commitment that would be required to achieve this. Numerous hours were spent at a con-

tinuously running tap, trying to purify the sand. In the end, the sand could be called clean, but a

better way to clean the sand should be researched.

! The method we used involved a bucket, the polluted sand, and a local tap (known to be E.

coli negative). The sand was placed in the bucket and then positioned under the tap which filled it

with water. About three times as much water than sand was in the bucket by the end. Next, the

water and sand were spun around by hand effectively separating dirt and grime. While the mix-

ture was still spinning, the top layer (mostly water since the heavier sand would fall immediately)



Figure 3 - Examples of gravel and sand.





would be poured out. This had to be done fifteen to twenty times per bucket. A volume of sand

equating to about 200 liters must also be cleaned for this design. This proved to be a very ineffi-

cient process. But, this process provides future groups a focus for research: find a way to clean

sand better.

Step 4: Container Faucet and Plumbing - A Simple On/Off Switch

! The only part that can move on the filter is the simple tear-drop shaped valve used as a

faucet. The simplistic design relies on water pressure to allow the water to “run” when the valve

is opened by the user.

! The plumbing of the filter is

made up of one inch PVC, two PVC el-

bows, a tear-drop faucet, glue to hold it all

together, and foam to keep sediment from

clogging the bottom PVC tube. Cut the

PVC into the appropriate lengths. These

lengths will depend on the design of the

filter. Place the PVC into the filter as if

putting together the plumbing to make

sure the tubes fit correctly.

Do not glue the plumbing

together until you are sure everything fits appropriately. With a hole drilling attachment bore a

hole at the height on the drum where the faucet will be. Also, drill holes into the bottom PVC

tube to allow the water to flow out of the filter. Place foam into this bottom tube to prevent debris

from entering. Now, assembly

can take place.

! First, place some gravel

at the bottom of the drum to form

a base for the plumbing to sit on.

This will help keep the filter clear

of debris. The debris can now fall

to the bottom of the drum with-

out interrupting the flow of the



Figure 5 - Bottom segment, elbow, and vertical segment

Figure 6 - Bottom piece with foam





water. Next, assemble the

base PVC tube (with foam),

two elbows, and the vertical

PVC segment. Place this

into the filter and align it to

make sure everything fits.

Remove this assembly from

the filter. Then, take the last

PVC segment and glue it

into place in the wall of the drum. The faucet can then be glued to this. (The glueing steps may

need 24 hours to dry before further construction.) Finally, take the first PVC assembly and glue

it into place onto the last PVC segment and faucet combination. Allow time for the glue to dry

before placing the rest of the gravel and sand.

Step 5: Diffusion Plate Creation - A Elementary Sift

! The diffusion plate protects the biological layer. When water is poured into the filter, it

can disrupt the food chain and biological cycles already present in that top layer. The diffusion

plate can take the disruptive event of water entering the system and disperses it over a larger area.

This is done through the construction of a plane that contains smaller holes for the water to drain

through.



Figure 7 - Wall mounted PVC segment and faucet .

Figure 8- Diffusion plate and three equal length PVC supporting columns.





! In Muramba, our group had to be creative with the tools and materials that we had at

hand. We used the top of one of the 250 liter drums as the diffusion plate. Holes were drilled

across the plate to allow for water flow. The diffusion plate is very simple. The tools that are

needed include a saw for cutting the top of the drum off, and a drill to make the holes.

! The diffusion plate sits atop three small PVC tubes acting as a supporting structure.

These tubes should be placed into the filter first, and then sand should be poured.

! From the pictures of the diffusion plate, it can be seen that the design is not perfect. One

problem is the gap that exists between the plate and the side of the drum. This will not affect the

filter’s performance, but in the perfect case this space would not exist.

Step 6: Filter Placement and Final Setup Instructions - A Heavy Drum

! A filter’s main purpose is to purify water. The filter should be placed near a water source

that is known to be contaminated. Water testing of many sources within an area can help to iden-

tify where a filter will be best suited.

! The individuals who have taken on the project of building a biosand filter should under-

stand that purifying the water must be as easy as possible. Essentially, the filter must be close to

the water source. Water then can be taken from this source, and directly entered into the biosand

filter. It is more likely that individuals will use a system that is close to the source and easy to use.

! After filter construction, the drum will be quite heavy. Too heavy to safely carry or trans-

port by hand. Therefore, the final assembly of the filter should be done at the site determined to

be its final resting place.

Step 7: Initial Priming and Flushing of System - Forward To Cleaner Water

! By this step, the filter should be completely constructed and positioned at the predeter-

mined filter site. Although the sand and gravel have been cleaned, an initial system priming and

flushing must take place.

! For the filter to work correctly and most efficiently, a layer of water must always be pre-

sent on top of the sand layer. This layer should be formed. To do this, take buckets of water and

pour them into the filter. This will prime the filter. It will be filled with water until many centime-

ters of water resides over the sand layer. At this point the faucet can also be tested. The water







pressure will force the water through the pipes and out of the faucet. Notice that the water com-

ing out of the faucet will have a different color. This is due to small sand particles exiting the fil-

ter.

! To evacuate the filter of these particles, the system must be flushed. This is done by tak-

ing additional buckets of water and passing this water through the system. This task should be

done until the water comes out clear.



Figure 9- The final product.





BudgetBiosand Filter Budget

Expense1. Hardware - Sofaru2. Plastic Drums3. Gravel & Sand4. Hardware - CPQ5. PVC6. Material Transportation7. Hardware - Muhirwa

Totals

Rwandan Francs US Dollars23,000 $42.3680,000 $147.335,000 $9.2125,000 $46.043,000 $5.527,500 $13.8121,500 $39.59165,000 $303.86







BIBLIOGRAPHY

1. Manz, David, “Introduction to the BioSand

Water Filter,” http://manzwaterinfo.ca

2. Elliot et al. (2006), “Intermittently oper-

ated, slow sand filtration for point of use

water treatment,” Safe Drinking Water

Symposium, University of North Carolina



http://manzwaterinfo.ca

http://manzwaterinfo.ca





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