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Polluted river water
River water taken for household use can be full of suspended
matter, particularly in the rainy season. The water carries silt particles, solids, bacteria and other
micro- organisms (some of which can carry disease). It is very important to remove as much as possible of this material before people use the water. Large water
treatment centres do this by adding chemical coagulants to the water. These cause the
particles to stick together (coagulate) and sink. The clean water can then be poured off. The correct chemicals, however, may be
unavailable or too expensive. An alternative is to use a natural coagulant, usually made from plants. In certain parts of the world, this has been done for centuries on a small scale.
Natural coagulants in water treatment
The Environmental Engineering Group at Leicester University, UK,
has been studying the potential use of natural coagulants on a large scale in water treatment works. Their work has looked at the natural coagulation properties of crushed seed of the
Moringa oleifera tree.
This is a native of northern India which is now grown widely through the tropics. It is sometimes known as ‘drumstick’
and ‘horseradish’ Moringa grows rapidly from seed or cuttings, even in poor soils. It needs little care and can survive long
periods of drought. It grows rapidly – growth of up to 4 metres in height, flowering and fruiting were all observed within one year of planting.
Household water treatment
Seed pods should be left to mature on the tree and harvested when dry. The light ‘wings’ and shells of the
seeds are easily removed, leaving the white seed
kernels. These are finely crushed and pounded, using a pestle and mortar. The amount of seed needed to treat
river water depends on how much suspended matter the water contains. Users quickly become familiar with the changing needs of their particular water as the quantity
of sediment changes with the seasons.To treat 20 litres of water (the amount carried in the average large bucket) about 2 grams of
crushed seed is needed (2 level 5ml teaspoons or 2 rounded soda bottle tops). Add a small amount of clean water to the crushed seed to form a paste. Put the paste into a clean bottle
– a soda bottle is ideal. Add a cup (200ml) of clean water and shake for 5 minutes. This action activates the chemicals in the crushed seed.
Filter this solution through white cotton cloth into a 20 litre bucket of river water. The
contents are stirred rapidly for 2 minutes, followed by slow stirring for 10–15 minutes. During this slow mixing period,
the moringa seed binds together (coagulates) the fine particles and bacteria into larger particles which sink
and settle at the bottom of the bucket. After an hour, clear water can be drawn off.
This process will remove 90–99.9% of the bacteria which are attached to the solid particles, as well as clearing
the water. However, some harmful microorganisms still in the water may not be removed, especially if the water is
very badly polluted. For drinking water, further purification is recommended – either by boiling or with
a simple sand filter. The dried seeds (remove discoloured ones) and powder can be stored. However, the paste must be prepared fresh each day.
Large scale water treatment
Trials using moringa seed gave water purification results which were just as good as those obtained with
commercial chemicals – at a fraction
of the cost. 50–150mg of ground seed is needed for 1 litre of water. Simple jar tests will determine how much seed is needed.
Further research are required to obtain a desired result to get a pure drinking water at a low cost.
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Water treatment by plants
