Sulphate removal by forward osmosis and hollow fibre immersion modules
Background:
One of the long-term consequences of opencast lignite mining in Germany is the extensive iron and sulfate contamination of ground and surface waters. While iron pollution can be substantially reduced by mine water treatment plants and other measures, no large-scale solutions have yet been pursued to reduce sulfate pollution.
Although various processes for sulfate removal exist (e.g. ettringite precipitation, nanofiltration + precipitation, microbiological sulfate reduction), they have various disadvantages (expensive, generation of large amounts of sludge, very high space requirements).
In the overall SULFAMOS project, a process engineering solution is to be developed which, in addition to reducing the sulfate load, also includes the production of valuable materials in the form of gypsum for the building materials industry.
The process engineering solution combines the process stages of forward osmosis and precipitation. Compared to pressure-driven reverse osmosis, forward osmosis offers energy-saving potential and significantly better scaling behavior on the membrane surface.
By operating the demonstrator plant to be realized in the project at different model sites, it is ensured that the developed technology can be flexibly applied and adapted to different water compositions.
Aims:
In the SULFAMOS project, various objectives are being pursued on both the material and the process side.
For the process step of forward osmosis, the focus is on the development of a new type of hollow fiber membrane with a robust outer coating. With this new type of membrane, the development of an immersion module for these membranes will be carried out. These submersible modules will be installed in a process combination of membrane module and precipitation module, which allows a continuous operation of the whole plant without blocking of the membranes, in demonstrator size. Based on this demonstration plant, the processes will be tested in the field at different model sites with different water compositions and the products water and gypsum will be qualified with regard to their possible applications.
The main objective of the SULFAMOS project is to develop and demonstrate a process based on continuous forward osmosis to deplete sulfate from wastewater, surface water and groundwater so that they can be used as irrigation and drinking water. The second main objective is to make the sulfate precipitated in the form of gypsum usable as a raw material.
