The City of Harlan located in Shelby County, Iowa along the West Nishnabotna River, needed a new water treatment plant to replace their existing lime softening plant which had outlived its useful lifespan. To assist in the development of the right solution, Tonka Water was asked to complete a full scale pilot study on their high hardness/high TDS (Total Dissolved Solids) blended well water, so that a cost-effective process could be scaled up to full size utilized in final design.
The chosen process for softening and TDS removal, was a complete Tonka Water integrated system consisting of forced draft aeration, detention, filtration and membrane softening (NF), with integrated controls by Tonka Water. Dual process trains using nanofiltration were provided, consisting of two Flux RO/NF™ skids, each using a 12×6 array NF arrangement.
The Harlan well water chemistry is complex due to a well field consisting of more than twenty low flow wells with widely varying contaminant levels. Treatment begins when the blended raw water is fed through a Tonka Water forced draft aerator prior to detention. Aeration provides initial oxidation of iron and manganese, thus reducing chemical demand. Any remaining iron and manganese is then oxidized chemically prior to being filtered through Tonka Water’s unique high-efficiency OptaCell™ pressure filters with Simul-Wash™. The horizontal pressure filtration effluent is then divided into two streams: one blended stream bypassing the membrane system, and the second stream fed to the Flux RO/NF™ membrane system for more complete hardness and TDS reduction. The membrane bypass stream is then blended back with the aggressive membrane effluent stream to form stable product water for consumption – all guaranteed by Tonka Water.
Tonka Water formulated integrated, seamless controls for the treatment system – from influent to finished water effluent – and guaranteed the results. The combination of aeration, detention, pressure filtration and Nano Filtration allows for a flexible and dependable water treatment system.
|Iron (Fe)||<5.4 mg/L||<0.3 mg/L|
|Manganese (Mn)||<1.2 mg/L||<0.5 mg/L|
|Hardness (CaCO3)||45± mg/L||130± mg/L|