Without of grain of salt
Industrial wastewater is purified in sewage plants, but common salt is not affected. The Re-Salt research project aims to reduce wastewater streams and recover the salt.
What are you going to have for dinner tonight? Pasta perhaps? A heaping spoon full of salt in the cooking water is needed to make it taste right, say 20 grams? If in 10 % of Gemany’s 41 million households someone has the same idea, 82 tons of salt from pasta cooking water will go down the drains tonight. That sounds like a lot, but it is nothing that sewage plants can’t cope with.
Industrial operations deal with salt loads in a different order of magnitude: Covestro alone uses 1.8 million tons of common salt (sodium chloride) worldwide every year for chlor-alkali-electrolysis. With this process, the basic chemicals caustic soda and chlorine are produced.
Covestro has been striving for a long time to recover common salt from plastics manufacturing wastewater. There are some obstacles to overcome that partners from research and industry (Covestro, DECHEMA-Forschungsinstitut, Donau Carbon, EnviroChemie, Solar Spring, Technologiezentrum Wasser, TH Köln, Uni Duisburg) are tackling together in the Re-Salt project. The wastewater contains about 5 % common salt and needs to be concentrated to 25 % to be reused for electrolysis – for comparison: pasta cooking water contains about 1 % salt.
- High-pressure reverse osmosis and membrane distillation processes are developed for the concentration process.
- Sample preparation and analytics are not designed for salt concentrations that high and need to be adapted.
- Organic pollutants need to be removed before the wastewater can be recycled, so as not to damage the electrolysis plant. To achieve this, activated carbon is modified on the surface and polarised electrochemically.
The electrochemistry specialists at DECHEMA Research Institute are responsible for polarising the activated carbon. Adsorbing and desorbing organic molecules by way of electrochemical sorption is the area of expertise of DECHEMA’s researchers. “We have already removed pharma ingredients such as ibuprofen and diclofenac from wastewater. I am positive that the technique will work for the critical organics as well,” explained Dr. Klaus-Michael Mangold, Head of the Electrochemistry Workgroup, adding with a twinkle in his eye “as a zero-liquid discharge solution for dinner, I recommend one-pot-pasta.”
-- MARLENE ETSCHMANN --