Smarter sprinkling using subsurface water storage, combined with iron removal

In the Netherlands groundwater is extracted for applications in the agricultural, industrial and drinking water sectors. At the same time there is an urgent need to render water consumption more sustainable. In this context a great deal is expected from the possibilities presented for the subsurface storage of excess precipitation. But the frequent presence of dissolved iron in our groundwater and the subsurface can cause problems for both direct groundwater extraction and for subsurface water storage. Extraction wells and irrigation facilities can become clogged, crops can become discoloured, and the iron can be toxic for livestock, and can have negative consequences for water quality and soil fertility. This project is studying the extent to which subsurface iron removal might provide possible solutions to these problems.

Technology

The extraction of groundwater for the provision of drinking water has for many years included the successful application of the subsurface iron removal technique. This involves the periodic injection of oxygen-rich water into the ground, which causes the in-situ precipitation of ferric hydroxide. During the subsequent extraction, the dissolved iron binds to the ferrous hydroxide. As a result, a multiple of the volume of the injected oxygen-rich water can be extracted, before the iron ‘breaks through’ to the well. Never before has this technique been combined with subsurface water storage. This could create a synergy, which would foster both water supply and quality, as well as address well-clogging problems.

Challenge

This project aims to build experience with subsurface iron removal in subsurface water storage. Research will examine whether the technique is also applicable to groundwater with a more challenging composition than is usually the case in drinking water production. An irregular composition can be prejudicial to subsurface iron removal. The groundwater can for instance contain higher iron concentrations or methane, or have a lower pH. Moreover, rainwater is naturally already relatively acidic. The project will also study how the performance of subsurface iron removal can be maximised, and how the technology can be smartly implemented within the operational management. Pilots will be set up at the sites of two greenhouse horticulturalists and three dairy farmers in the Province of North Brabant.

Solution

The pilot studies will provide the basis for defining the framework conditions for a long-term, stable combination of subsurface water storage and subsurface iron removal, and their implementation for the agricultural sector in North Brabant and elsewhere.

The three basic steps of subsurface iron removal (from left to right): Aeration of a volume of water, injection and extraction of iron-free water.