User Manual

Where we use filters
• Filters have a huge range of uses at home and in industry. At home we use lter paper for
filtering coffee grains from coffee, and active carbon granules for filtering water, where they
remove chlorine and other chemicals from tap water. Filter paper and active carbon are used
in machines to clean water, fuel, oil and air before they are needed, and in gas masks to
remove dust and dangerous gases from air.
• Sand lters are used mainly for cleaning water before and after we drink it. The type of sand
filter in this kit is called a fast sand filter, as water trickles quickly through it. It removes solid
particles, such as grit, from water. Slow sand filters are deep layers of fine sand. As water
trickles through a slow sand filter, a layer of micro-organisms forms slime on the top. These
organisms use particles in the water as food, so cleaning the water.
Fun facts
• Sand lters clean the water in sh tanks and swimming pools, and water from sinks and
baths (called grey water) so that it can be used to water gardens.
• Active carbon is very porous - water ows easily through the granules because they are full
of holes.
• A one-gram piece of active carbon has a surface area of about 500 square metres - the same
as a basketball court.
• Active carbon is sometimes fed to people who have been poisoned because it traps the
poison in their stomachs.
• Filter paper is used in paper chromatography, which is a way of separating materials
dissolved in a liquid.
How it works
Each section of the filter column removes particles from the water, purifying it. The different
filters remove particles of different sizes. The grains of sand and gravel have small spaces
between them. These allow water to pass through, but trap particles in the water. The carbon
granules are made from a material called active carbon. Chemicals in the water cling to the
surface of the carbon and are removed from the water. This process is called adsorption. The
filter paper has tiny holes between its fibres. Water can trickle through the holes, but particles
larger than the holes are trapped. It is particularly effective in filtering oil. The filter column
demonstrates the principles used at water purification plants, which supply drinking water to
households. At a water purification plant the filtering process is more advanced and chemicals
are added to the water to ensure the water is safe for drinking.
Cleaning the filter material and filter column
Always clean the filtering materials and the filter sections when you finish with them, or
when you want to filter a new mixture. The sand, gravel and active carbon can all be cleaned
and reused. Simply place each material into small glass (don’t mix the materials). Fill the
glass with clean water, add a drop of detergent and stir gently. Let the material settle to the
bottom and then carefully pour away the water. Then rinse the material once or twice with
clean water. Also rinse out the filter sections with clean water. When the materials are clean,
pour them back into their filter sections (remember to put the sand and active carbon into the
sections with two open arches in their plugs). When your filter materials have been used a few
times, you may need to replace them with the spare supplies included in this kit. When you
run out of the spares, you can buy more in most aquarium shops. Fine sand from a beach and
gravels from a garden could also be used, but rinse them thoroughly before use. You could
use tissue paper instead of filter paper.
Trouble shooting
If you find the filtered water not clear or clean:
• Try re-ltering the water. The lter column is only small and may not clean the water
completely in one pass through, especially if your water is particularly “dirty” or “oily”.
• Check that the water is not running through the lter sections too quickly. If it is, try
pressing the filter sections together more tightly, and even sealing around the joins with sticky
tape. This will prevent air leaking into the filter sections, allowing the water to flow downwards
slower.
• Make sure you have put the sand and active carbon into the lter sections that contains the
plugs with two open arches. The “dirty water” needs to flow slower in these two sections.
• You may need to clean or replace the lter materials with the spare supplies included in
this kit (see above).
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