Water treatment plants are changing in both how they look and how they work.

Our soiled water is definitely promising and full of quality. Until recently, wastewater treatment plants were the end point, the place where untreated water ended its journey. In just a few years, it’s become a source of biofuel and an important part of the energy transition.
The purpose of wastewater treatment plants is to treat used water before releasing it back into nature. The sludge collected during the process can be recycled and used as agricultural fertiliser. With the help of specialised tools, this waste can also be transformed into gas using a process known as methanisation.
The supply is large and is continuously flowing. Strasbourg, Lyon, Grenoble, Nantes, Perpignan, and around ten other cities have already taken the plunge into recycling their biowaste. By 2023, there could be 75 of these sites.
In Grenoble, the biogas generated by the wastewater plant goes into the national GRDF (Gaz Réseau Distribution France) gas network and saves the city over 300,000 euros per year. This is enough to quickly recoup the investments made to produce this biofuel.
In Nantes, biogas heats public buildings, fuels 350 council vehicles and 42 buses, and provides hot water and heating to 2,140 homes.
In Strasbourg, they expect to create 1.6 million m³ of biomethane per year. This purified biogas is put directly into the network and can heat or cool 5,000 homes.

A virtuous cycle

Methanisation works on organic matter. Unlike composting, which is done in the open air, this technology breaks down the waste with micro-organisms in an anaerobic environment, without oxygen. This reaction produces biogas on the one hand, mostly made up of methane, and on the other hand, a residue that can be used for other applications.
Making biogas reduces the amount of sludge produced by wastewater treatment plants by 30–40 %.
In the last ten years, the number of initiatives to develop this biogas resource has increased across France. It is a responsible approach that doesn’t only make good of our wastewater and make us more energetically independent, it also creates a technological ecosystem. Start-ups, researchers, and private investors are all working together to design and implement these innovations that recycle our waste and feed the circular economy.

A production process that produces 14 times less greenhouse gas emissions compared to fossil fuels.

According to GRDF, for an average plant, this biogas could generate 12 million euros in 15 years! The investment needed to produce biogas from the sludge from wastewater treatment plants is paid back in five years on average.
This is just the start of the story. Just 10 % of the actual capacity of the energy potential of wastewater treatment plants is used. To take it further, we need to overcome technological, financial, and regulatory barriers. According to specialists, what could speed up this process is recognising this biogas from wastewater treatment plants as renewable energy in the same way that the electricity produced by solar panels is. Being labelled as “renewable energy” brings many advantages, in particular in terms of tax and investments.
By releasing green energy from grey and black water, treatment plants become part of the virtuous circle of circular ecology.