Slasorb : Wastewater treatment using a by-product of the steel industry

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In september 2008, a European initiative called Slasorb was launched, to treat wastewater through an original process : the removal of phosphates using a by-product of the steel industry called 'slag'.

"Large quantities of phosphorus are present in human effluent, with less significant amounts in detergents, according to Florent Chazarenc, lecturer and researcher in the Energy systems and environment department at the Ecole des Mines de Nantes, who started and managed the project. In wastewater treatment plants designed to deal with towns with a population of more than 20,000, wastewater is treated by injecting iron or aluminium salts, however these methods are much more expensive when used in smaller plants." Hence the idea of using slag from the steel industry – a method which has already been used  on the other side of the Atlantic, and which Florent Chazarenc was able to see for himself in Canada, where he spent five years working on the subject.


In 2008, Florent Chazarenc set up a group to address the issue in Europe. He built a consortium which included Arcelor-Mittal, the world's number one steel company, and a number of SME's such as Akut, a company which works in wastewater treatment, and Epur Nature, specialised in reed bed filters, as well as three laboratories : the Ecole des Mines-Armines, coordinaters of the project, and two German laboratories, FeHS and ArGe-HK. The Slasorb project (which comes from 'using SLAg as SORBent to remove phosphorus from wastewater'), had a budget of a little over a million euros. The project was launched in July 2009, for an initial period of 36 months - extended for a further six months.

"The removal of phosphorus from waste water has become a major issue a result of increasingly strict regulations in Europe, according to Florent Chazarenc. We are ahead of new regulations. Slasorb provides a method which is effective and  inexpensive, and uses a an indusrial by-product : slag. The end product is a phosphate residue, which can then be used as fertilizer in agriculture."


Landing the first client


First of all, the consortium carried out laboratory trials, using 60 litre tanks, before moving onto tests on approximately 6 cubic metres."We were able to show that it was possible to obtain good results, and that there were absolutely no risks" said Florent Chazarenc.The next stage consisted of field trials, using several thousand cubic metres. In order to do this, Slasorb planned to set up the trials on -site, at a steel mill.

Today, the European project has come to an end. Florent Chazarenc however is undeterred : he is still working on the process, in the hope of convincing that first client to take the plunge. One idea would be for the team to work with a local council for example, to build a water treatment plant, and to split the costs. Florent Chazarenc is also in touch with other laboratories at the Ecoles des Mines in Alès  and Albi. "I really think that next year will see us land first customer, in France, Luxembourg or in Germany, says Florent Chazarenc. After that, the idea will catch on very quickly."

Florent Chazarenc is also working with the Polytechnique de Montréal, as an associate professor. Meanwhile, his team is working on how to increase the phosphorus removal rate of slag ( by 4 or 5 times the present rate) using mineral compounds. In other words, they are definitely not short of projects and ideas.

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