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CLEARGREENTM MAINSTREAM

Until very recently, the essential function of wastewater treatment plants (WWTP) was to depollute wastewater, so that purified water could be returned to the natural environment in the cleanest possible state. But the processes used to achieve this objective consume huge amounts of energy. Today, one of the main challenges is to transform WWTPs into genuine positive-energy factories. This is one of the goals that SUEZ is pursuing by developing biofactories 1 . They are infrastructures capable of radically improving their energy balance by saving energy and producing biogas from the organic matter contained in wastewater.

To achieve the greatest energy-savings, it is necessary to tackle the main problem: the first stage in the treatment of nitrogenous pollution (nitrification). This biological process is essential to meet environmental standards, but it requires a lot of oxygen and therefore a lot of energy. The second stage of conventional nitrogen treatment consumes large quantities of organic carbon. This over-consumption of carbon reduces

the quantity of available digestible organic matter used in the anaerobic digestion process to produce biogas.

The Cleargreen™ Mainstream process developed by SUEZ breaks away from this model. Thanks to this technology, WWTPs can halve their energy consumption and, most importantly, produce more energy than they consume.

Cleargreen™ Mainstream is a two-stage process. The first stage or the nitrate shunt 2 limits the action of the bacteria responsible for conventional nitrification, which consume a great deal of oxygen. The second stage completes the elimination of the nitrogenous pollution by converting it into simple gaseous nitrogen. This phase uses so-called Anammox bacteria that do not need any organic carbon 3 , which consequently remains available to produce biogas. The secret of the process lies in the control of the bacterial populations involved.

The Cleargreen™ process has been patented. It increases methane production by 33%1 and reduces net energy consumption by 50%. In the meantime, it remains below the nitrogen discharge thresholds in the treated water required by the strictest standards2.

After numerous test of the process, success is on the way. This solution that ushers WWTP into the era of the circular economy, by transforming it into genuine biofactory that produces resources and energy. As well as producing energy, SUEZ biofactories are also centres producing resources (water, nutrients, biosolids), whose environmental impact (noise, odours, landscape integration) has been minimised.

SOLUTION Nr. 6

are you ready to use the power of bacteria to create biofactories producing green energy?

suez.com 1 - The main component of biogas. 2 - Often between 10 and 15 mg/L.