RaHa – Rainwater Harvesting – Earth Dams (Silanga)


RaHa Clean Close water is plenty from silangas.

road RaHa

RaHa installs filters in the silanga dikes and supplies corresponding tanks villagers around the silangas. When it rains, the villagers connect the tanks to the filter outlets.

franc tanks

This is a special rainwater filter for installation within standard manhole shafts or plastic shafts. Each of such filters is suitable for a silanga.

road raha1

The cleaned water has such an excellent water quality that it can be discharged directly into the tanks, sometimes through storm water treatment. The filter function is an up-flow process and this allows for a design with a minimal height difference between the inlet and outlet.

In the filter shaft the rainwater is cleaned by basic operation of the following processes: Sedimentation, Adsorption, Filtration, and Chemical Precipitation. Incoming rainwater is led down to the basal section of the filter shaft. A hydrodynamic separator built in the base section promotes particulate sedimentation. The water is led into this separator tangentially and generates a radial flow pattern.

Particles settle into the silt trap located below the separation chamber. Above the separation chamber are 4 filter elements, occupying the full shaft width such that all water must flow up through the filter. The Siltation of this filter is slow due to the upwards flow, and the fact that the filter is below the water level. The filter is easily exchanged.

The system is maintained once a year.

Function Principles:

1. The rainwater from the connected area is fed into the basal section of the filter housing. The angled inlet generates a radial flow pattern.

2. The hydrodynamic separator converts turbulent waters into a radial laminar flow pattern, generating particle sedimentation, particularly of the sand fraction.

3. This takes place over an inlet to the lower section of the filter shaft. The sediment is retained in a silt trap chamber below the separator. The silt trap needs to be emptied out at intervals.

4. In the central section of the filter housing is the actual filter. The filter element filters out the fine materials in an up-flow process and dissolved materials are precipitated and adsorbed. The filter can be backwashed. When exhausted the filter is easily exchanged.

5. The filter element is easily pulled up via the shaft opening.

6. Above the filter element is the clean water. It passes via an oil separator and then flows via the outlet into tanks beside the silangas.


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