M.oleifera in water treatment

General

The use of natural materials of plant origin to clarify turbid surface waters is not a new idea. Sanskrit writings in India dating from several centuries BC make reference to seeds of the tree Strychnos potatorum as a clarifier, Peruvian texts from the 16th and 17th centuries detail the use by sailors of powdered, roasted grains of Zea mays as a means of settling impurities. More recently, Chilean folklore texts from the 19th century refer to water clarification using the sap from the 'tuna' cactus (Opuntia fiscus indica). However, of all the plant materials that have been investigated over the years, the seeds from M.oleifera have been shown to be one of the most effective as a primary coagulant for water treatment.

The traditional use of the M.oleifera seeds for domestic household water treatment has been limited to certain rural areas in the Sudan. Village women collecting their water from the River Nile would place powdered seeds in a small cloth bag to which a thread is attached. This would then be swirled around in the turbid water. Water soluble proteins released from the powdered seeds, attach themselves to, and bind between, the suspended particles forming larger, agglomerated solids. These flocculated solids would then be allowed to settle prior to boiling and subsequent consumption of the water.

Since the early 1970's a number of studies have been carried out to determine the effectiveness of the seeds for the treatment of surface water at individual household level. Utilising artificially prepared turbid water and naturally turbid raw waters, laboratory investigations have confirmed the seeds to highly effective in the removal of suspended solids from waters containing medium to high initial turbidities. At low turbidities, as may be experienced during the dry season, the seeds are less effective although their performance is very much dependant on the raw water to be treated. Work is currently underway at the University of Leicester examining the potential of utilising the seeds within a contact flocculation filtration process for the treatment of low turbidity water. Preliminary results have demonstrated some considerable success.

The majority of the early work has been carried out with a view to establishing the viability of using the seeds within household water treatment practices. Following success in the laboratory, the Environmental Engineering Group extended its activities to an evaluation of the seeds effectiveness on continuous flow systems. Pilot plant trials and full scale trials carried out in Malawi in collaboration with the Polytechnic of Malawi (contacts) demonstrated that the seeds could be used effectively on continuous flow systems producing treated water quality similar to that of aluminium sulphate.

The active fraction of the seeds has received much interest. Investigations by Professor Tauscher at the University of Karlsruhe, Germany, have revealed that the coagulant properties of the seeds are due to a series of low molecular weight cationic proteins. Under current CEC funding, attempts to isolate and characterise these active proteins are continuing.

The potential toxicity of the seeds has been considered in two major studies. The conclusions of both were that the doses typically used for water treatment posed no serious threat to human health. Further details of these studies may be found in the articles by Berger et al.,1984 and Grabow et al.,1985, detailed in the selected reading list below.

Waste minimisation is a major concern of the whole Moringa concept. To this end work is being carried out by Mr.McConnachie at the University of Edinburgh, Scotland, to evaluate the feasibility of producing a low cost activated carbon from the seed shells. A single stage steam pyrolysis process has been shown to yield an activated carbon with treatment performance as efficient as commercially available carbons. Funded by the ODA, this work is a collaborative venture with the Polytechnic of Malawi and is continuing.


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Selected reading list

Berger,M.R., Habs,M., Jahn,S.A.A. and Schmahl,D. 1984, Toxicological assessment of seeds from Moringa oleifera and Moringa stenopetala, two highly efficient primary coagulants for domestic water treatment of tropical raw waters. East African Medical Journal, 61 pp712-716.

Folkard,G.K., Sutherland,J.P. and Grant,W.D., 1993. Natural coagulants at pilot scale; In: Pickford,J., ed. Water, Environment and Management: Proc. of the 18th WEDC Conference, Kathmandu, Nepal, 30 Aug.-3 Sept.1992. Loughborough University Press, pp51-54.

Gassenschmidt, U., Jany, K.D., Tauscher,B. and Niebergall, H. 1995, Isolation and charaterization of a flocculating protein from Moringa oleifera Lam. Biochimica et Biophysica Acta, 1243, pp477-481

Grabow,W.O.K., Slabbert,J.L., Morgan,W.S.G. and Jahn,S.A.A. 1985, Toxicity and mutagenicity evaluation of water coagulated with Moringa oleifera seed preparations using fish, protozoan, bacterial, coliphage, enzyme and Ames Salmonella assays. Water SA, 11 (1) pp9-14.

Gupta,A. and Chaudhuri,M. 1992, Domestic water purification for developing countries. J.Water SRT-Aqua, 41 (5) pp290-298.

Jahn,S.A.A., 1989, Moringa oleifera for food and water purification - selection of clones and growing of annual short stem. Entwicklung + Landlicher Raum, 23 (4) pp22-25.

Jahn,S.A.A. 1986, Proper use of African natural coagulants for rural water supplies. Manual No.191, Pub.: GTZ, Eschborn, Germany.

Jahn,S.A.A., 1989, Simplified water treatment technologies for rural areas, GATE (GTZ), 1, pp37-41.

Jahn,S.A.A. 1981. Traditional water purification in tropical developing countries: existing methods and potential applications. Manual No.117, Pub.: GTZ, Eschborn, Germany

Jahn,S.A.A. 1984, Effectiveness of traditional flocculants as primary coagulants and coagulant aids for the treatment of tropical raw water with more than a thousand-fold fluctuation in turbidity. Water Supply, 2 (3/4) Special Subject pp8-10.

Jahn,S.A.A and Dirar,H. 1979, Studies on natural water coagulants in the Sudan with special reference to Moringa oleifera seeds, Water SA, 5 (2) pp90-97

Madsen,M., Schlundt,J. and El Fadil,O. 1987, Effect of water coagulation by seeds of Moringa oleifera on bacterial concentrations. Journal of Tropical Medicine and Hygiene, 90 pp.101-109.

Sutherland,J.P., Folkard,G.K. and Grant,W.D., 1990. Natural coagulants for appropriate water treatment: a novel approach, Waterlines, April, 8 (4), pp30-32.

Sutherland,J.P., Folkard, G.K., Mtawali,M.A. and Grant,W.D. Moringa oleifera at pilot/full scale. In: Pickford,J. et al. eds. Water, Sanitation, Environment and Development: Proceedings of the 19th WEDC Conference, Accra, Ghana, Sept.1993. Loughborough University of Technology Press, 1994, pp.109-111.

Tauscher,B., 1994, Water treatment by flocculant compounds of higher plants. Plant Research and Development, 40, pp.56-70


Pilot plant trials

It is now regarded as axiomatic that both water and wastewater technology for developing countries must be no more complex than strictly necessary, be robust and cheap to install and maintain. A prototype treatment works was designed founded on this philosophy. The pilot plant was constructed within the grounds of the Thyolo Water Treatment Works, the works being controlled by the Ministry of Works and Supplies Water Department of the Malawi Government. The system was successfully commissioned during the 1992 rainy season with the source water exhibiting turbidity levels in excess of 400NTU throughout the study period. Solids removal within the plant was consistently above 90% following a gravel bed flocculation stage and plain horizontal flow sedimentation. Subsequent rapid gravity sand filtration gave a final, treated water turbidity generally well below 5NTU. M.oleifera seed dose ranged from 75-250 mg/l depending on the initial raw water turbidity.


Full scale trials

In February 1994, the main Thyolo works was operated using M.oleifera solution as coagulant. The works comprise upflow contact clarifiers followed by rapid gravity filters and chlorinator. The clarifiers are in a state of disrepair with the impeller drives and chemical feed pumps inoperative. Alum solution is introduced into the incoming flow of 60 cubic metres per hour by simple gravity feed. Comparable treatment performance with alum was achieved. Inlet turbidities of 270-380NTU were consistently reduced to below 4NTU. This was the first time that M.oleifera had been successfully used as a primary coagulant at such a scale with the treated water entering supply.


Active coagulant fraction


Activated carbon