Insights

How better H2S control may limit GHG emissions in the wastewater industry

In this insights post, we discover how improved monitoring and control of hydrogen sulfide (H2S) can benefit to not only solve odor and corrosion related issues but also help reduce methane (CH4) emissions in the wastewater industry – a challenge that is much greater than expected according to recent studies.

Author: Peter Madsen | Published on 25 Jul 2024 | 5 min read

Introduction

Recent studies show that methane emissions from the wastewater industry are nearly double previous estimates (Zondlo et al., 2023). That is an issue because methane is a potent greenhouse gas (GHG) with a global warming potential almost 30 times greater than CO2. This underscores the urgent need for enhanced monitoring and mitigation strategies across the industry to reduce methane emissions and better align with UN Sustainable Development Goals for climate action.

As cities continue to urbanize and develop net-zero plans, they can’t ignore the liquid wastewater treatment sector: Mark Zondlo, 2023

Methane emissions from wastewater are twice as high as expected

Methane is a potent greenhouse gas with a global warming potential of 29.8, meaning it causes almost 30 times more global warming over 100 years than an equal amount of carbon dioxide. In 2022, methane accounted for 12% of all GHG emissions in the U.S. (U.S. Environmental Protection Agency, 2023). Major sources of methane emissions include energy production, agriculture, waste handling and landfills.

Methane (CH4) is produced in anaerobic conditions in wastewater systems, including in force mains, in anaerobic digesters, and in sludge handling areas via methanogenic archaea whereby organic matter decomposes in the absence of oxygen. Similarly, hydrogen sulfide (H2S) is produced by sulfate-reducing bacteria that reduce sulfate to sulfide using organic matter or hydrogen. Both gases are thus prevalent in the same anaerobic environments in the wastewater industry. If H2S emissions are detected at the end of force mains, it is a strong indication that methane emissions could also be present, as both gases are produced under similar conditions (Parker & Walton, 2023).

The great challenge is that methane and H2S emissions, despite being highly unwanted gases, typically are not measured regularly. This lack of monitoring means that many utilities may be unaware of the full extent of their greenhouse gas emissions.

Two recent studies from Princeton University researchers utilized direct measurements and machine learning to assess methane emissions in the wastewater industry (Zondlo et al., 2023). One study performed on-site methane emissions measurements at 63 wastewater treatment plants across the U.S., while another analyzed literature data from methane monitoring studies worldwide. These studies found that methane emissions were nearly double the current estimates set by the The Intergovernmental Panel on Climate Change (IPCC), highlighting the need for improved monitoring and mitigation (Zondlo et al., 2023).

H2S and CH4 mitigation strategies

Effective mitigation strategies are essential for reducing both H2S and CH4 emissions in the wastewater industry and a litterature review by Parker and Walton (2023) outlines several practical methods that can be used to address both types of emissions at the same time.

Nitrate Addition: Nitrate serves as an alternative electron acceptor, which inhibits the activity of the sulfate-reducing bacteria responsible for H2S production. This, in turn, limits the conditions favorable for methanogens that produce methane. By promoting these microbial processes, nitrate addition can thus mitigate both H2S and CH4 emissions.

Iron Compounds: Iron salts, such as ferric chloride or ferrous sulfate, can effectively control H2S by precipitating sulfide as insoluble iron sulfide. This reduction in H2S can also indirectly impact CH4 production, as both gases are produced under similar anaerobic conditions. The presence of iron creates a more aerobic environment that is less conducive to CH4 generation.

Calcium Nitrate: Calcium nitrate can be used similarly to other nitrate compounds to reduce the production of H2S and CH4. It is particularly effective in environments where the addition of other nitrate forms might be less practical.

Biofilm Shocking: This method involves the intermittent dosing of chemicals to disrupt biofilm formation and activity, thereby reducing the production of both H2S and CH4.

Implementing these strategies requires accurate monitoring to optimize the dosage and application of these compounds. Advanced H2S sensors can provide real-time data, enabling proactive management and rapid response to changing conditions. This not only helps in reducing emissions but also ensures compliance with environmental regulations and contributes to sustainability goals.

References

  • Zondlo, M., et al. (2023). “Underestimation of Sector-Wide Methane Emissions from United States Wastewater Treatment.” Environmental Science & Technology
  • Parker, W. J., & Walton, J. R. (2023). “A literature-based comparison of embodied GHG emissions of forced main sewer additives with potential reductions in methane generation.” Water Practice & Technology, Vol 18 No 12, 3387. DOI: 10.2166/wpt.2023.219
  • U.S. Environmental Protection Agency (2023) – Overview of Greenhouse Gases. epa.com
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