Make a Solar Pasteurizer
Pasteurization is a process involving heating liquids rapidly to kill harmful organisms. Interestingly, the liquid does not have to be heated to boiling point for pasteurization to occur.
You need to work in a small group to build a solar pasteurizer. It must be made from recycled materials and water should be heated to a temperature of 70°C for 15 minutes to be considered a successful pasteurizer.
- Clear plastic drinking bottle (at least 1 or 1.5 litres)
- An aluminium can (375 ml)
- Black paint
- Cardboard box (or a large piece of thick cardboard) and a 3 cm square piece of cardboard
- Aluminium foil
- Scissors and/or craft knife
Constructing the Solar Pasteurizer
Step 1 Paint the can black and set aside to dry.
Step 2 Cut the top off the drink bottle. Ensure that the bottle is cut at the widest point to allow the aluminium can to be fitted inside it.
Step 3 Cut three or more tabs (slits) in the top section of the bottle.
Step 4 Pierce a hole in the centre of the 3 cm square piece of cardboard and insert a thermometer through the hole—the cardboard should sit firmly around the thermometer.
- Fill the can with water and place the thermometer into the can—the cardboard should rest on the top of the can and the thermometer should stick out enough to be read easily.
- Place the can inside the bottle and put the top section back on the bottle using the tabs (slits) to hold it in place.
- Place the solar pasteurizer in a sunny position and record the temperature at regular intervals (on Table 1).
- If the pasteurizer is not reaching the required temperature (70°C for 15 minutes) follow the additional steps below.
- Make a solar reflector out of the cardboard box (or thick cardboard).
- Cover the reflector in aluminium foil.
- If you do not want to make the reflector you can simply cover one side of the bottle with foil.
Step 8 Locate the reflector and pasteurizer in full sun. For maximum effectiveness make sure the shadow of the pasteurizer appears in the centre of the back panel. Rotate the reflector gently to keep the shadow in this position.
Step 9 Record the temperature at regular intervals (on Table 2).