Water Treatment, Carbon Balance

We used to trade one pollution for another. To prevent water pollution, most water treatment plants release carbon dioxide and nitrous oxide (both are greenhouse gasses) to power or as a byproduct of cleaning wastewater. That’s changing—water treatment plants around the world are retooling themselves to fit a circular economy. One of the leaders, BIOFOS, just hit the carbon neutral milestone a year ahead of schedule.

BIOFOS Lynetten water treatment facility, photographed in 2018. Photo credit: Nordic Innovation on Flickr (CC BY 2.0).

BIOFOS, Denmark’s largest water treatment utility, has tackled their emissions from both ends: directly cutting emissions and by recapturing energy to use in green electricity or heating systems.

About half of the greenhouse gas emissions from BIOFOS’s water treatment is nitrous oxide. This greenhouse gas is a byproduct of water treatment processes. While projects search for alternative processes, BIOFOS has pulled all the stops to cut their carbon dioxide emissions. One such effort: 2 out of 3 BIOFOS plants have been converted to “bottom aeration”, with the 3rd plant expected to refit next year. Aeration encourages microbial growth, which helps remove dissolved metals and gasses from wastewater. Bottom aeration is much more energy-efficient than other methods to achieve this step and implementing it has reduced the carbon emissions of the Avedøre and Lynetten treatment plants.

BIOFOS has also made strides to recover energy and resources from the water treatment process. Heat capture systems drive district heating, while the carbon-rich ‘sludge’ is converted into biogas. BIOFOS began selling more energy than they bought to operate back in 2014, and since then they have also begun recovering phosphorus and metals from the sludge. After everything extractable has been retrieved, some of the sludge is incinerated and recycled as a building material.

By slashing emissions and recovering energy, BIOFOS’s three wastewater treatment plants now displace more greenhouse gas emissions than they emit. But that’s not the end: BIOFOS still plan to implement bottom aeration in their Damhusåen facility and are continuing research to curb the byproduct nitrous oxide. It’s a lot of work to refit old plants, research new treatment processes, and find uses for byproducts, but these water treatment plants show us all that work is worth it. Clean water is essential to human life and a healthy environment, and now we have the technology and the know-how to clean water without dirtying the sky.