Keep it Fresh! Field test results of the fresh keeper concept

Ate T. Oosterhof1 and Klaasjan J. Raat2

1Vitens Water Supply Company, PO Box 1090 NL-8200 BB Lelystad, the Netherlands, ate.oosterhof@vitens.nl
 2KWR Watercycle Research Institute, Nieuwegein, the Netherlands

In the Northern part of the Netherlands, a number of fresh water wells are threatened by salinization through the upconing of brackish water. Further salinization of these wells can be prevented by intercepting the upconing brackish groundwater. This concept is called the fresh keeper. The extracted brackish groundwater can be treated by reverse osmosis (RO), rendering a permeate (to be used for drinking water) and a concentrate. Disposal of the saline concentrate is a serious problem at inland productions sites, for which deep well injection into a deeper, brackish aquifer seems the best solution.

A field pilot has started in 2009 at the abandoned well field Noardburgum. The fresh keeper concept, anaerobic RO installation and injection of concentrate are all combined. A single well with two extraction filters is used to extract 50 m³/h fresh water (60-80m depth) and 50m³/h brackish water (130-150m depth). The brackish flow is used to feed the RO installation which operates with a 50% recovery. The permeate (25m³/h) and the abstracted fresh water are transported to the drinking water production plant for further treatment. The concentrate is injected into a confined aquifer at 180m depth.

The source and target aquifers and the RO installation are closely monitored for changes in water flow, hydraulic heads, water quality and performance. The fresh keeper concept operates as intended: the fresh-brackish water interface remained stable and the salinity of the abstracted brackish water even decreased in the first months of operation. Mineral oversaturation of the concentrate did not lead to membrane fouling or injection well clogging by mineral precipitation. Simultaneous abstraction and injection did not lead to short-circuiting of the injected water between target and source aquifer. The results show that the fresh keeper concept works in practice, being successful in stopping further salinization of a fresh water well.