The treatment method, known as microbial electrolytic carbon capture (MECC), purifies wastewater by using an electrochemical reaction that absorbs more CO2 than it releases while creating renewable energy in the process.
“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 new study, which was recently published in the journal Environmental Science and Technology.
Wastewater treatment typically produces CO2 emissions in two ways: the fossil fuels burned to power the machinery, and the decomposition of organic material within the wastewater itself. Plus, existing wastewater treatment technologies consume high amounts of energy. Public utilities in the US treat an estimated 12 trillion gallons of municipal wastewater each year and consume about 3 percent of the nation’s grid energy.
Existing carbon capture technologies are energy-intensive and often entail costly transportation and storage procedures. MECC uses the natural conductivity of saline wastewater to facilitate an electrochemical reaction that is designed to absorb CO2 from both the water and the air. The process transforms CO2 into stable mineral carbonates and bicarbonates that can be used as raw materials by the construction industry, used as a chemical buffer in the wastewater treatment cycle itself or used to counter acidity downstream from the process such as in the ocean.
The reaction also yields excess hydrogen gas, which can be stored and harnessed as energy in a fuel cell.
The findings offer the possibility that wastewater could be treated effectively on-site without the risks or costs typically associated with disposal. Further research is needed to determine the optimal MECC system design and assess the potential for scalability.
A carbon-negative wastewater treatment system could benefit power companies, the authors say, as the EPA’s Clean Power Plan requires power plants to comply with reduced CO2 emission levels.