Wastewater Treatment Plants Emit More Greenhouse Gas Than Previously Thought

A new study reveals that levels of greenhouse gases being emitted by wastewater treatment plants are higher the previous estimates.

The study, published in the journal Environmental Science and Technology, showed that carbon emissions from petroleum products treated in wastewater plants could increase the estimate of total greenhouse gas emissions from 12 to 23 percent.

According to a press release by the American Chemical Society, previous carbon dioxide estimates by the Intergovernmental Panel on Climate Change (IPCC) did not include carbon emissions from wastewater treatment plants. The neglect of carbon emissions from wastewater plants was based on the assumption that wastewater largely contains and releases carbon from non-petroleum products, such as human waste.

However, researchers investigating the fossil-related carbon content of municipal and industrial wastewaters at various points in the treatment process found that relevant amounts of petroleum products, such as synthetic chemicals from detergents, wash into wastewater and can eventually add to total greenhouse gas emissions. Additionally, the researchers discovered that the fossil content at different treatment points within wastewater treatment plants could amount to 28 percent in primary influent and showed varying distribution leaving different unit operations.

While carbon was not included in the estimates, IPCC take into account other greenhouse gases emitted by wastewater treatment plants, including, methane and nitrous oxide. With the addition of carbon from treatment plants, previous estimates of the total greenhouse gas emissions of wastewater treatment plants could increase by 12 to 23 percent.

With their findings, the researchers are recommending the addition of wastewater treatment plants to the climate action plans of the government to curb emissions from this source. Furthermore, the researchers found that treating wastewater sludge could offer an opportunity to reduce the fossil carbon emissions from treatment plants, noting that on-site carbon sequestration run on renewable energy could also lower these plants' impact.