Water Science & Technology Vol 54 No 5 pp 227–234 © IWA Publishing 2006 doi:10.2166/wst.2006.566

The effects of a polyacrylamide-derived water treatment residue on the hydraulic conductivity, water retention and evaporation of four contrasting South African soils and implications for land disposal

M. Moodley^* and J.C. Hughes^**

Water treatment residue (WTR), a by-product from the production of potable water, was traditionally disposed of to landfill but there is growing interest in applying this waste to land as an alternative disposal option. Because WTR consists mainly of flocculated fine silt and clay, there is concern that should the residue decompose back to its original constituents, there is an adverse risk for soil water storage and transmission properties of soil. In a laboratory study, four different soil types were amended with a polyacrylamide WTR at rates ranging from 0 to 1,280 Mg ha^-1. The treatments were evaluated for changes in water retention, hydraulic conductivity and evaporation. The results showed that WTR decreased bulk density and evaporation and actually increased hydraulic conductivity and water retention, mainly because of the sustained performance of the polymer in binding the silt and clay into gravel-sized aggregates. Such changes were, however, only significant at the 1,280 Mg ha^-1 application rate. Therefore, very large amounts of WTR would have to be applied in order to markedly change these inherent physical properties of the soils. In view of this finding, the land treatment of WTR appears possible.

Keywords: Evaporation; hydraulic conductivity; soil physical properties; water retention; water treatment residue

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