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Large Scale Water Purification


Source: Global Applied Research Network (GARNET)
Moringa Oleifera as a Natural Coagulant

GK Folkard, JP Sutherland, MA Mtawali and WD Grant, University of Leicester, United Kingdom

In many parts of the world river water which can be highly turbid is used for drinking purposes. This turbidity is conventionally removed by treating the water with expensive chemicals, many of which are imported at great expense. This project has investigated the use of crushed seeds from the tree Moringa oleifera as a natural alternative to these conventional chemicals. Results were obtained from a full scale water treatment plant at Thyolo in Southern Malawi which demonstrate that the seeds reduce the turbidity of the raw water by 80 per cent leaving a clear, very low turbidity water.

This applied research project has shown that turbid waters can be clarified to the same degree achieved by imported chemicals by using a natural substance which can be purchased locally from villagers.

Natural coagulants have been used for centuries in traditional water treatment practices throughout certain areas of the developing world.

Although a native species of northern India, the tree is now grown extensively throughout the tropics and is found in many countries of Africa, Asia and South America. Moringa trees have the capacity to grow rapidly from seeds or cuttings, even in poor, marginal soils; require little horticultural attention and are resilient to the effects of extended drought.

For water treatment purposes, the seed pods are allowed to dry naturally on the tree prior to harvesting. After shelving the seeds are crushed and sieved using traditional techniques employed in the production of maize flour. Approximately 50-150 mg of ground seed will be needed to treat a litre of river water, depending on the quantity of suspended matter. A small amount of clean water is then mixed with the crushed seed to form a paste. Dosing is usually according to a 1-3 per cent solution. The crushed seed powder, when added to water, yields water soluble proteins that possess a net positive charge. The solution therefore acts as a natural cationic polyelectrolyte during treatment (Sutherland, J.P., Folkard, G.K. and Grant, W.D., (1990).

Transferring from the individual household to the continuous flow water treatment works has been one of the primary tasks of the University of Leicester's work.
Large scale water treatment works

The University of Leicester's work involved a pilot water treatment works at Thyolo in Southern Malawi, built within the grounds of the main treatment works. The source river used during the research showed turbidity levels in excess of 400 NTU. Solids removal within the plant was above 90 per cent following a gravel bed flocculation stage and plain horizontal flow sedimentation. A last rapid gravity sand filtration gave a final, treated water turbidity measure generally below 5 NTU. Dosing levels of Moringa oleifera seed varied between 75-250 mg depending on initial raw turbidity.

Following the results from the pilot works, permission for full scale trials at the main water treatment plant was subsequently received from the Malawian authorities. The Thyolo works consist of upflow contact clarifiers followed by rapid gravity filters. Soda ash and alum solutions are introduced to the incoming water flow via gravity feed systems at great expense (annually a charge of ?26,000 is made for importing these chemicals from South Africa). Moringa oleifera for the full scale trials were purchased locally from villagers at a fraction of this cost.

The results of two typical trials are given in Figure 1 and Figure 2 below. The works were operated at 60m3/hour with the coagulant solution dosed and monitored using a small centrifugal pump and rotameter respectively. The results of dosing Moringa oleifera seed solution at 75 mg/litre over a seven hour period compares favourably with performance figures for alum dosing at 50mg/litre. Turbidity removal rates are approximately 80 per cent over both trials.

The results from the pilot and full scale trials indicate the viability of Moringa oleifera as a natural coagulant for highly turbid river water. Inlet river turbidities in excess of 270-380 NTU were consistently reduced to below 4 NTU in the finished water.

M.oleifera seed contains 40 per cent by weight of oil, with the remaining presscake containing the active ingredients for natural coagulation. The high market value for the oil make the case for promoting the cultivation of the seed a strong one. The growth of M. oleifera trees by smallholder farmers should be actively promoted as a means of providing vegetables and raw material for oil extraction in addition to a simple, but effective natural coagulant for turbid river water.

Using Moringa oleifera as a replacement coagulant for proprietary coagulants meets the need for water and wastewater technology in developing countries which is simple to use, robust and cheap to both install and maintain.
Further reading:

Folkard, G.K., Sutherland, J.P. and Grant, W.D., 1990. Natural coagulants for appropriate water treatment: a novel approach, Waterlines, April, 8 (4), 30-32

Travis, V.E., Sutherland, J.P., & Folkard, G.K., High Rate Contact Flocculation - Filtration Using Natural Coagulants, First International Conference Environmental Engineering, Vol 2, 47-54, 21-23 Sept 1993, De Montfort University, Leicester, U.K.

Holmes, R.G.H., Folkard, G.K., Travis, V.E., & Sutherland, J.P. Natural Coagulants in Wastewater Treatment, First International Conference Environmental Engineering Vol 2, 47-54, 21-23 Sept 1993, De Montfort University, Leicester, U.K.

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