Following on from the successful pilot plant trials, permission was granted by the Malawian authorities to carry out full scale trials on the existing water treatment works at Thyolo in southern Malawi. The works treats on average 60m3/hr using alum or synthetic polyelectrolytes as coagulants (depending on availablity). Coagulant is drip fed into the incoming raw water with rapid mixing being achieved by flow over a 'V'-notch weir.The works comprises 2 upflow reactor clarifiers followed by rapid gravity filters. The water is chlorinated and held in a contact tank prior to distribution. At the time of the full scale trials the works was in a state of disrepair with both impeller drives on the upflow clarifiers out of use. The original coagulant dosing pumps had long since ceased to operate.

The following sequence of photographs details the main parts of the Thyolo treatment works.

General view of the works. The two blue tanks in the foreground are the reactor clarifiers.

The two reactor clarifiers - the inoperable impeller drives are evident.

Rapid gravity sand filters.

Preparation of seed solutions for full scale trials

M.oleifera seed for the trials was obtained from villagers in the Nsanje region of southern Malawi where the tree grows extensively. Seed processing was carried out on site by the wives of the workers on the main works. The seeds were dehusked then ground to a fine powder using a traditional pestle and mortar. The powdered seed was then passed through a maize sieve prior to use. Coagulant preparation followed that used during the pilot plant trials i.e. a paste was made of the seed powder and water prior to dilution to the required concentration. The seed solutions themselves were then sieved prior to dosing.

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Dehusking of the seeds - only
the kernel is used to obtain the coagulant

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Seed kernels pounded in a
traditional maize pestle and mortar

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Pounded seed is passed through a maize sieve to obtain a fine powder

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Sieved seed ready for solution preparation

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A paste is made of the seed powder and
water prior to dilution to required concentration

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Seed solution ready for dosing