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).