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Wastewater alkalinity enhancement for carbon emission reduction and marine CO2 removal

  • Author(s): Ming Li, Yuren Chen, Riley Doyle, Jeremy M Testa, Alexandria Gagnon, Charles Bott, Wei-Jun Cai
  • Environmental Research Letters
  • April 1, 2025
Citation: Li, M., Yuren Chen, Riley Doyle, Jeremy M Testa, Alexandria Gagnon, Charles Bott and Wei-Jun Cai. (2025). Wastewater alkalinity enhancement for carbon emission reduction and marine CO2 removal. Environmental Research Letters, 20. https://doi.org/10.1088/1748-9326/adc1e3

Wastewater alkalinity enhancement is a promising approach for ocean alkalinity enhancement due to its potential to deliver strong bases with minimum secondary precipitation and its potential use of the global network of wastewater treatment plants (WWTPs). WWTPs are also significant sources of CO2 due to organic matter oxidation, and integrating alkalinity addition into treatment processes may both reduce in-plant CO2 emissions and increase downstream CO2 uptake. This study presents a modeling framework that combines a modern activated sludge model-based WWTP simulator with an integrated hydrodynamic-biogeochemical-carbonate chemistry model of coastal oceans. We evaluate the effects of adding alkalinity either upstream (UpAdd) of the biological treatment stage or downstream at the discharge location (DnAdd) on WWTP carbon emission reduction and marine CO2 removal. The carbon emission from WWTPs decreases with increasing alkalinity dosage in UpAdd and can be eliminated at a dosage level that is feasible to implement. However, carbon uptake in the surrounding oceanic water is much reduced due to elevated dissolved inorganic carbon in the discharge water. DnAdd does not affect CO2 emissions from WWTPs but enhances carbon uptake in the ocean, with the net oceanic uptake of atmospheric CO2 increasing with increasing dosage level. Across all tested dosage levels, total CO2 removal, including emission reduction at the WWTPs and enhanced carbon uptake in the ocean, is 30% greater in UpAdd than in DnAdd. WWTP treatment tanks have much higher pCO2 than in the ocean, and aeration of process tanks enhances the gas transfer. The upstream alkalinity addition leads to sharp declines in pCO2 in the treatment tanks and large reductions in carbon emission from the WWTPs. These results have implications for developing strategies to reduce global carbon emission and enhance oceanic carbon burial using WWTPs as a delivery mechanism.

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Effects of ocean acidification and temperature on Alaskan crabs

Red King Crab
Image credit: David Csepp, NMFS AKFSC ABL

Long-term declines of red king crab in Bristol Bay, Alaska may be partially attributed to ocean acidification conditions. These impacts may be partially responsible for the fishery closures during the 2021–2022 and 2022–2023 seasons. Researchers found that ocean acidification negatively impacts Alaskan crabs generally by changing physiological processes, decreasing growth, increasing death rates and reducing shell thickness. Funded by the Ocean Acidification Program, scientists at the Alaska Fisheries Science Center continue to investigate the responses of early life history stages and study the potential of various Alaska crabs to acclimate to changing conditions. Results will inform models that will use the parameters studied to predict the effects of future ocean acidification on the populations of red king crab in Bristol Bay as well as on the fisheries that depend on them. Fishery managers will better be able to anticipate and manage stocks if changing ocean chemistry affects stock productivity and thus the maximum sustainable yield.

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Forecasts for Alaska Fisheries

Crab pots and fishing nets in Alaska's Dutch Harbor
Image credit: Michael Theberge

Understanding seasonal changes in ocean acidification in Alaskan waters and the potential impacts to the multi-billion-dollar fishery sector is a main priority. Through work funded by NOAA’s Ocean Acidification Program, the Pacific Marine Environmental Laboratory developed a model capable of depicting past ocean chemistry conditions for the Bering Sea and is now testing the ability of this model to forecast future conditions. This model is being used to develop an ocean acidification indicator provided to fisheries managers in the annual NOAA Eastern Bering Sea Ecosystem Status Report.

ADAPTING TO OCEAN ACIDIFICATION

The NOAA Ocean Acidification Program (OAP) works to prepare society to adapt to the consequences of ocean acidification and conserve marine ecosystems as acidification occurs. Learn more about the human connections and adaptation strategies from these efforts.

Adaptation approaches fostered by the OAP include:

FORECASTING

Using models and research to understand the sensitivity of organisms and ecosystems to ocean acidification to make predictions about the future, allowing communities and industries to prepare

Closeup of oysters cupped in someone's hands

MANAGEMENT

Using these models and predictions as tools to facilitate management strategies that will protect marine resources and communities from future changes

TECHNOLOGY DEVELOPMENT

Developing innovative tools to help monitor ocean acidification and mitigate changing ocean chemistry locally

REDUCING OUR CARBON FOOTPRINT

50 more ways to reduce your carbon footprint >

On the Road

Drive fuel-efficient vehicles or choose public transportation. Choose your bike or walk! Don't sit idle for more than 30 seconds. Keep your tires properly inflated.

With your Food Choices

Eat local- this helps cut down on production and transport! Reduce your meat and dairy. Compost to avoid food waste ending up in the landfill

With your Food Choices

Make energy-efficient choices for your appliances and lighting. Heat and cool efficiently! Change your air filters and program your thermostat, seal and insulate your home, and support clean energy sources

By Reducing Coastal Acidification

Reduce your use of fertilizers, Improve sewage treatment and run off, and Protect and restore coastal habitats

TAKE ACTION WITH YOUR COMMUNITY

You've taken the first step to learn more about ocean acidification - why not spread this knowledge to your community?

Every community has their unique culture, economy and ecology and what’s at stake from ocean acidification may be different depending on where you live.  As a community member, you can take a larger role in educating the public about ocean acidification. Creating awareness is the first step to taking action.  As communities gain traction, neighboring regions that share marine resources can build larger coalitions to address ocean acidification.  Here are some ideas to get started:

  1. Work with informal educators, such as aquarium outreach programs and local non-profits, to teach the public about ocean acidification. Visit our Education & Outreach page to find the newest tools!
  2. Participate in habitat restoration efforts to restore habitats that help mitigate the effects of coastal acidification
  3. Facilitate conversations with local businesses that might be affected by ocean acidification, building a plan for the future.
  4. Partner with local community efforts to mitigate the driver behind ocean acidification  – excess CO2 – such as community supported agriculture, bike & car shares and other public transportation options.
  5. Contact your regional Coastal Acidification Network (CAN) to learn how OA is affecting your region and more ideas about how you can get involved in your community
       More for Taking Community Action