Moringa oleifera as a natural coagulant

The authors gratefully acknowledge the financial support of the Overseas Development Administration

Natural coagulants at pilot scale

Crushed seeds of the tree Moringa oleifera Lam. (M.oleifera) are a viable alternative to aluminium sulphate as a coagulant for water treatment applications in the developing world. Supporting cases, in both technical and economic terms are presented based on a recently completed field study in Malawi. A pilot scale treatment works operating at a flow rate of 16.51 min-1 reduced raw water turbidity from 1000 NTU to below 1 NTU (header/ mixer tank, gravel bed flocculator, sedimentation tank and rapid gravity filter). The filter was operated as a contact flocculator -filter during periods of low raw water turbidity. 20 NTU inlet values were reduced to below 1 NTU with this treatment unit. Successful M.oleifera plantation trials are briefly reported as is an economic analysis of establishing M.oleifera as a 'coagulant crop' in the Malawi context

Natural coagulants in water clarification

Powdered seed suspensions of the Moringa oleifera tree have proved effective as a primary coagulant to clarify a stable kao­linite suspension. Acting as a cationic polyelectrolyte optimum minimum dosage to achieve maximum turbidity removal have been determined over a range of initial turbidity values (50-550NTU). The weight ratio of seed dosage to clay concentration appears in­dependent of initial clay concentration. A field usable dissolved air flotation system has been developed. This technique, when applied to a kaolinite/bentonite model sus­pension, produced clear water in minutes as opposed to hours for conventional sedimenta­tion. Topics for further investigation are outlined

Moringa oleifera at pilot/full scale

Crushed seeds of the tree Moringa oleifera Lam. (M.oleifera) are a viable replacement coagulant for proprietary chemi­cals such as aluminium sulphate (alum) in developing countries. The tree is a multi-provider that grows pantropically and its distribution in Africa and various vernacular names are noted. This paper presents results from pilot scale treatment trials carried out at Thyolo in southern Malawi early in 1993. The pilot works utilised for the study, situated on the site of an existing Ministry of Works operated treatment plant, comprises a header/flash mixing tank, gravel bed flocculators, plain horizontal flow sedimentation tank and a rapid gravity filter. The system has a nominal flow rate of I m3/hr. Inlet raw water turbidities were maintained at around 400 NTU throughout the six week study. Over 90% removal of turbidity was achieved by effective floe formation and sedimentation. Floe carry over was subsequently removed in the filter producing a final water consistently less than the WHO guideline value of 5 NTU. Results from full scale trials on the existing Ministry of Works operated treatment plant are also presented. Alum, the normal coagulant used, was replaced with M.oleifera seed solution and comparable performance was observed. This is the first time that M.oleifera has been used as a primary coagulant at this scale (flow rate 16 m3/hr)