Design of Watertight Barriers for Retention Ponds of Cyanide Using Sludge from Water Purification Station (Ziga)

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Résumé

In a context of sustainable development and use of eco- materials, it was examined the possibility of using sewage sludgefrom the water treatment plant of Ziga as an inorganic support to achieve sealing barr iers that can withstand high stresses toovercome any weaknesses of the geological barrier (called passive barrier). The station Ziga that potabilises the water from the riverNakambé is located 45 km north east of Ou agadougou. Some experiments on the rheology of sludge from Ziga as well as thefiltration of the mixture Ziga’s sludge and clays from Nouna, Zo rgho and Ticare, three regions of Burkina Faso, were conducted.These studies demonstrated the complex hydro-mechanical behavior of Ziga’s slurries: Newtonian fluid thixotropic threshold forsolids contents less than 16.5 wt% and non-Newtonian for higher values. Sludge from the water treatment station Ziga have ahydraulic conductivity of 10-8 m/s. The results are below regulatory requirements. However, the permeability can be reduced toachieve the value of 10-9 m/s in particular by adding the clay from Zorgho or Nouna to mixtures of Ziga’s sludge and neutral leachate,typically mineral water. Beside neutral leachate, two types of leachate were used. One type is composed of acid leachate and theother type is basic. It was shown that th e limewater solutions cause deterioration of the seal probably due to the presence ofhydroxide ions.

Mots-clés

Ziga’s sludge, watertight barriers, leachates, hydraulic conductivity, filtration, rheology.