Design and operation guidelines for municipal sized surface water limestone contactors

Treatment technologies and know-how to address soft water problems of aggression and corrosion via conventional stabilisation using lime and carbon dioxide are readily available for larger water supply systems and areas close to technical support centres. However, treatment technologies and know-how for small-scale and/or remote rural application are not as readily available. Accordingly, CSIR conducted research into the use of limestone for stabilisation purposes, which culminated in the development and implementation of small and medium scale (municipal size) limestone contactors. To date, approximately 14 municipal size limestone contactor systems have been installed in South Africa with treatment capacity ranging from 2 Ml/d to 18 Ml/d, with a 50 Ml/d limestone contactor system currently under construction in the Free State province. However, the medium-term performance efficiency of these units in negating soft water problems has not been thoroughly documented. Furthermore, nearly all of the operational municipal systems in South Africa have been designed by CSIR, using process design and operating guidelines developed by CSIR. Accordingly, Water Research Commission funded studies for the documentation of both limestone contactor performance, and transfer of process design and operating guidelines into the broader water treatment community. This paper will review the performance of operational municipal limestone contactors in South Africa, and present CSIR limestone contactor process design and operating guidelines.