The Methane Commonality: Wastewater Treatment and Eutrophication

Eutrophication, the process of excess nutrients entering bodies of water primarily from sewage and agricultural runoff, leads to the overgrowth of algae triggering numerous environmental issues, particularly for fish. When the algae die, they sink to the aquatic floor, and oxygen-consuming bacteria begin decomposition. This occurrence can rapidly consume oxygen, creating hypoxic conditions where bacteria break down organic matter and produce methane as a byproduct instead of CO2, due to the lack of oxygen. Methane is then released into sediment and water, and eventually escapes into the atmosphere as a harmful greenhouse gas (GHG). 

HydroPhos Solutions aims to prevent eutrophication by removing phosphorus from point source water emitters. Wastewater treatment plants are critical for managing excess nutrient content in their effluent, however their operations can come with an unintended consequence - atmospheric methane emissions. So in terms of methane emissions, which is worse: eutrophication or wastewater treatment plants?

HydroPhos Solutions has written deeper dives about the connection between eutrophication and greenhouse gas emissions specifically covering methane, as well as the relationship between climate change and eutrophication. However, we will now focus on GHG emissions from wastewater treatment plant operations. Even though GHG emissions from wastewater make only a small contribution to global anthropogenic GHG emissions, it is still important to discuss their contributions and understand WWTP processes, as atmospheric warming leads to other social and environmental consequences beyond the world of wastewater treatment.  

Looking into the future, numerous macro-level phenomena are expected to exacerbate eutrophication. By 2100, the global population is estimated to reach almost 11 billion people. More people means more water use, sewage, and food, leading to potentially greater nutrient runoff into lakes and rivers. This increase in wastewater and agricultural runoff is expected to cause a 25-200% rise in eutrophication by 2050, with that number potentially doubling or quadrupling by 2100. Additionally, as the planet warms, so will bodies of water, which create ideal conditions for algae to thrive, further increasing methane emissions. Moreover, the surface area of water bodies on Earth is expected to rise, leading to an overall increase in potential methane-emitting waters. According to some estimates, eutrophication-driven lake greening could boost global methane emissions by 30-90% over the next 100 years.

Human activities account for about 60% of today’s methane emissions. Wastewater treatment plants contribute a portion of this through both direct methane release, as well as indirect ways through emitting excess nutrients in nearby water bodies. Between 1990 - 2019, US methane emissions from wastewater treatment jumped from 10% to 14%. With a warming climate and expanding population, the use and importance of WWTPs is expected to grow to maintain clean sources of water and preserve aquatic ecological communities. 

Wastewater treatment involves processing sewage through central facilities using various water purification methods including several stages: 

1. Influent (wastewater entry)

2. Preliminary treatment (removal of large debris)

3. Primary treatment  (sedimentation)

4. Secondary treatment (removal of organic matter)

5. Disinfection (bacteria elimination)

6. Tertiary treatment (removal of heavy metals, toxins and nutrients) *where HydroPhos goes!

The primary sources of methane emissions in wastewater treatment stem from processes with oxygen-free environments, specifically anaerobic treatment, anaerobic sludge digestion, or stabilization ponds during the secondary treatment stage. Annual methane emissions from the US centralized municipal plant sector is estimated to be upwards of 639 thousand metric tons per year. Further, global methane emissions from wastewater are expected to grow by approximately 19 percent between 2010 and 2030. 

So who emits more methane: eutrophication or wastewater treatment plants? It is estimated that a rise in eutrophication will contribute 72.2 to 92.9 million tons of methane per year, far surpassing the municipal wastewater industry’s estimated 640,000 metric tons of methane per year. 92 million metric tons of methane equate over a quarter-trillion gallons of gasoline consumed! In order to prevent further methane emissions (and thus further planetary warming), we must find solutions to prevent and mitigate instances of eutrophication. 

Besides our work, we are luckily  to know of other innovative startups building solutions to address these issues:

Watabat: Revolutionizing water quality management by integrating cutting-edge robotics and AI to provide real-time, accurate monitoring and early warning systems for harmful algal blooms and other water contaminants

Kai Pono: Replacing conventional stormwater drainage with a high-performing filtration system that can be placed in the curb and gutter line to proactively mitigate stormwater pollution

In conclusion, while wastewater treatment plants contribute to methane emissions through operational processes, the far greater threat comes from the unchecked rise of eutrophication from anthropogenic excess nutrient inflow. As population growth and agricultural runoff drive excess phosphorus into bodies of water, the resulting methane emissions from eutrophication could skyrocket, potentially outpacing those from wastewater treatment plants by a vast margin, and preventing eutrophication must be a top priority to mitigate the global rise in methane emissions.