The use of micro-algae to purify grey water and remove most energy of the organic compounds of interest is a promising lead in the circular economy. Batiactu is the point with Christine Grimault, the deputy director general of Ennesys, a French company that works on systems combining digester and bacterial photobioréacteur algal.
Micro-algae have been tested for capture of carbon dioxide at the outlet of chimneys of cement plants. But this is not the track followed by Ennesys, a company which is registered in a logic of circular economy-where the organic wastes become resources to be valued in pond culture-specific. Christine Grimault, who has just returned from Abu Dhabi where a facility has been in operation for ten months, explains : “We have done 5 years of R&D : the tubular system works perfectly. The model installed in the stud farm private in the United Arab Emirates allows you to purify water from the cleaning of the stables and treat the organic waste from the site to produce fertiliser, high value-added“. In the middle of the desert, the installation Freewaterbox will reduce water consumption, improve crop yields and even get (a little) energy.
Dirty water + waste + cocktail algae/bacteria = clean water + biogas + fertilizer
But how does the installation ? The gray water is first filtered by a membrane. A part is oriented to a digester bacteria which are added to organic waste. In addition to the production of biogas and compost, the system produces a liquid this time entrusted to the micro-algae that will nourish and which will be regularly harvested. For 50 cubic metres of dirty water introduced 500 kg of waste, the system separates 49 m3 of purified water, 150 m3 of biogas (energy), 80 kg of compost (solid) and 600 liters of makes bio-stimulating algal (liquid). The deputy director, said : “It was clean water but that is not considered safe to drink. However, it is possible to irrigate and water crops with. On the other hand, it recovers energy that is capable of autoalimenter the system, including its pumps and circulation. Finally, we get two types of fertilizer : compost 100 % organic, very rich, and makes bio-stimulating algal capable of improving the crop yields of +45 to +55 %“. What to do grow sugar cane in the desert.
Schematic diagram of Freewaterbox © Ennesys
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A dozen strains of algae have been selected for their resistance to extreme temperatures (between -7 °C and +45 °C), their ability of quick fixing (nitrogen, potassium, phosphate, heavy metals, CO2, etc.) and their potential for growth. Christine Grimault, explains : “We are targeting many markets : that of field crops, vegetables, fruit and grain, but also livestock production and food processing in the broad sense (factories of beverages, breweries, dairies, canneries, etc). One of the hotels and holiday villages in remote sites, typically on an island. As well as college campuses and eco-districts“. The system Freewaterbox has been chosen to equip the future campus Mohammed VI of Laayoune in Morocco, in a project designed by Anthony Béchu. In Defence, it is the “City of Innovation, Culture and Entrepreneurship” of Heinrich von Sponeck, which will be equipped with a solution in the façade, however devoid of the aspect of biogas production.
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