No abstract

Heterogeneous nucleation refers to precipitation on the surface of nucleating agents such as seed crystals, whereas homogeneous nucleation is precipitation in the absence of available nucleating surfaces. Unlike homogeneous nucleation, heterogeneous nucleation lowers the free energy of crystallization in precipitative water softening processes. To determine the importance of the amount of surface area provided by the nucleating agent, different-sized calcium carbonate seed crystals were added to various hard waters during precipitative softening with caustic soda. Synthetic hard waters (with and without natural organic material) and naturally occurring hard waters were softened to remove dissolved calcium through homogeneous nucleation and heterogeneous nucleation using calcite seed crystals of two sizes. The naturally occurring hard waters were also softened in the presence of softening sludge from selected water softening treatment plants. Study results demonstrated that calcite seed crystals improved the removal of dissolved calcium during precipitative softening and that the optimal seed dose depended on the surface area available for nucleation.ater hardness is defined as the sum of all polyvalent cations present in water (AWWA, 1999), although the hardness of most natural waters is attributable primarily to dissolved calcium and magnesium. Hard water is undesirable for several reasons. Aesthetically, hard water does not lather well and leaves a residue caused by the precipitation reaction between calcium and fatty acids in soap. Similarly, the presence of hardness ions in water can inhibit detergents from interacting with dirt and stains on clothing, thereby hindering laundering processes. Finally, hard water produces scale in hot water pipes and heaters, which reduces the carrying capacity and flow rate in pipes as well as the thermal efficiency of heating elements. To alleviate these problems, water is commonly softened (i.e., calcium and magnesium ions are removed).

If water professionals are to overcome the challenges they face, they must better educate the public about the true value of their water services.

The 2017 State of the Water Industry report highlights opportunities for public involvement that must be meaningful, inclusive, and clearly linked to the decision‐making process.

Our water systems, the cornerstone of modern society, are at risk unless the water industry can secure community support and funding to tackle infrastructure renewal and other critical challenges.