​Wastewater treatment captures CO2 and produces energy

Engineers at the University of Colorado Boulder have developed a wastewater treatment that captures CO2, produces energy, and could help reduce rising acidity in the oceans.

Rotork at Dutch water treatment plant
Rotork at Amsterdam water treatment plant

According to the research, published recently in the journal Environmental Science and Technology, Microbial Electrolytic Carbon Capture (MECC) involves an electrochemical reaction that absorbs more CO2 than it releases, creating a source of renewable energy in the form of hydrogen gas at the same time.

“This energy-positive, carbon-negative method could potentially contain huge benefits for a number of emission-heavy industries,” said Zhiyong Jason Ren, an associate professor of civil, environmental, and architectural engineering at CU-Boulder and senior author of the study.

Traditional wastewater treatment contributes to CO2 emissions through both the decomposition of organic material, and the fossil fuels burned to power energy-intensive treatment machinery.

MECC uses the natural conductivity of saline wastewater to facilitate an electrochemical reaction designed to absorb CO2 from water and air. According to the team at CU-Boulder, the process transforms the CO2 into stable mineral carbonates and bicarbonates. These can then be used as raw materials in the construction industry, a chemical buffer in the wastewater treatment cycle itself, or to reduce acidity downstream of the process such as in the ocean. 

Rising acidity in the oceans is a threat to marine life, particularly shellfish and coral.
Rising acidity in the oceans is a threat to marine life, particularly shellfish and coral.

Ocean absorption of CO2 increases acidity and is a long-term threat to marine life. The researchers claim that the dissolved carbonates and bicarbonates produced via MECC could help chemically counter these effects.

“This treatment system generates alkalinity through electrochemical means and we could potentially use that to help offset the effects of ocean acidification,” said Greg Rau, a senior researcher at the Institute of Marine Sciences at the University of California Santa Cruz and a co-author of the study. “This is one of several environmentally-friendly things this technology does.”

The research raises hopes that wastewater could be treated on site rather than via the costly disposal methods currently used. However, further work is required to optimise the system as well as assess its scalability, according to the team.

“The results should be viewed as a proof-of-concept with promising implications for a wide range of industries,” said Ren.