SHORT COMMUNICATION: Use of calcium sulphate dihydrate (CaSO4•2H2O) as an alternative to the conventional use of aluminium sulphate in the primary treatment of wastewater

Abstract

The application of calcium sulphate dihydrate (CaSO 4·2H2O) as a coagulant-flocculant alternative to the conventional use of aluminium sulphate in the primary treatment of wastewater was evaluated using a jar test apparatus. Samples from the State Water Commission (CEA) in Queretaro, México, were collected for the experiments. Turbidity and pH were measured before and after applying the calcium sulphate dihydrate (CaSO 4·2H2O). Turbidity readings obtained for the doses of 4 g·ℓ-1 of aluminium sulphate varied from 3.91 to 3.87. The corresponding water pH was 3.90, giving the water an acidic character. Use of aluminium sulphate in the clarification of wastewater, thus, has financial and environmental implications due to the need to raise the pH of the treated water to 6.5–8.5, the recommended optimum interval for the physical-chemical-biological removal of pollutants. By contrast, calcium sulphate di-hydrate (CaSO 4·2H2O) (gypsum) doses of 1, 1.5 and 2 g·ℓ-1 resulted in a pH of between 7.04 and 7.51 repeatedly.

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