UH Mānoa tackles wastewater emissions with $2M grant

Developing innovative technology aimed at reducing greenhouse gas emissions from wastewater treatment facilities is the focus of a new University of Hawaiʻi at Mānoa project.

The research team—including Zhiyue Wang, assistant professor in the Department of Civil, Environmental and Construction Engineering and the Water Resources Research Center, and Tao Yan, professor in the Department of Civil, Environmental and Construction Engineering and director of the Water Resources Research Center—aims to investigate a new process that could significantly decrease the environmental impact of traditional nitrogen removal methods in wastewater treatment. Removing nitrogen from wastewater is crucial because excess nitrogen can cause harmful algae blooms in lakes and oceans, while conventional treatment processes release a significant amount of greenhouse gasses that contribute to climate change.

This effort is supported by a $1,994,225 grant from the US Department of Energy, awarded to Kennedy Jenks, a water and environmental engineering and environmental sciences firm. The UH team will work with Jenks and the City and County of Honolulu to run pilot-scale testing at the Waiʻanae wastewater treatment facility starting 2025.

“This research is particularly crucial for Hawaiʻi, where our unique island ecosystem demands innovative solutions to protect our environment and manage our resources sustainably,” Wang said. “By developing technology that can reduce greenhouse gas emissions from wastewater treatment while potentially increasing energy recovery, we’re not only addressing global climate concerns but also working towards greater energy independence for our island communities.”

At the heart of this project is the development of the Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) process. This approach focuses on converting ammonia, a common component in wastewater, into nitrous oxide. Nitrous oxide can then be burned alongside biogas, improving overall energy efficiency at treatment facilities. Recovery of nitrous oxide, 300 times more potent than carbon dioxide, can greatly reduce its release into the atmosphere as well.

Researchers aim to achieve an 80% nitrogen removal rate and a 60% nitrous oxide conversion rate through this method. If successful, this technology could reduce greenhouse gas emissions from nitrogen removal processes by 50% or more. This project aligns with the US Department of Energy’s goals for decarbonization in the water treatment sector.

It also addresses challenges associated with co-digestion, a common practice in wastewater treatment where additional organic waste is added to improve biogas production. While beneficial, co-digestion can lead to increased ammonia levels, which contribute to greenhouse gas emissions. The CANDO process offers a potential solution by converting this excess ammonia into a usable energy source.

Researchers believe this technology could be integrated into existing wastewater treatment facilities, providing both environmental and economic benefits. The project team estimates that implementing CANDO could increase energy generation from co-digestion by 5% through nitrous oxide recovery.