BDSALgreenH2

Hydrogen is considered a key energy carrier in Germany's future energy transformation. However, hydrogen is only green if the energy required for its production is also green energy, i.e. generated by wind or sun. As these resources at the DE site do not cover the energy requirements for reverse osmosis and electrolysis, there are already plans to import some of the hydrogen required from countries such as Australia. The current project aims to show that it is possible to reduce the energy required for the production of ultrapure water (by reverse osmosis) by at least 80% with the help of pre-desalination. This should make it possible to produce more ultrapure water locally with existing capacities of green electricity than currently calculated.

The reverse osmosis (RO) plant, which today supplies around 70 % of all desalinated water, consumes over 4 kWh/m³ for the desalination of full-strength saltwater. Compared to saltwater desalination, brackish water desalination requires less energy in the range of 0.5-2.5 kWh/m³. This is due to the lower salt content, which makes it possible to apply a lower pressure and achieve a much higher water recovery. The energy requirement for technical desalination using reverse osmosis therefore increases with the salt content. 

In previous studies, we have already been able to show on a laboratory scale that biological desalination can reduce the salt content by around 90% (from 35g/L to less than 4g/L). The current project aims to demonstrate that the reduction in salinity also contributes to a reduction in the energy costs of the reverse osmosis required in the final step. Similarly, this reduction in energy consumption leads to significant savings in greenhouse gas emissions. The project can be an opportunity for the development of local hydrogen production in the Northwest Lower Saxony region; due to its coastal location, this region has the possibility to use salt- and brackish water instead of fresh water for hydrogen production. At the same time, large amounts of green electricity are already being produced locally, which is available for the production of ultrapure water.

Based on the results of this project, it will be calculated whether biological desalination can be implemented and established on an industrial scale in order to provide the required quantities of pre-desalinated water to achieve the hydrogen targets. Apart from the validation of biological desalination on a pilot plant scale (the aim is to produce 3-4 m³ of low-salt water (< 4g/L) per week), markets for the microalgae biomass produced are to be explored. The microalgae biomass produced can also contribute to improving sustainability, for example by being used as a substitute for mineral fertilizers (potential areas of application: lawn and cereal fertilizers) where the expected salt content can be tolerated.