Impacts and Mitigation of Treatment Plants and Landfills Methane Emissions

Methane is a more potent heat-trapping gas than carbon dioxide, around 80 times more powerful. Though it does not stay as long in the atmosphere as carbon dioxide, emissions are more than 80 times more potent than carbon dioxide to cause damage to our climate. 

Between the two GHGs, carbon dioxide stays longer (between 20-200 years) in the atmosphere than methane (around 12 years); however, comparing one tonne of each gas in twenty years, methane’s heat-trapping effects are 86 times more potent (Economist, 2021).

Experts agree that if methane emissions are halved in the next 30 years, it can cut back 0.18°C off the global temperature by 2050. Scientists estimate that between 550m and 880m tonnes of methane were released annually between 2008 and 2017, and 60% is due to three types of human activities: farming, burning fossil fuels, and landfills and sewage-treatment plants—each accounting for a third of total emissions.

This article focuses on landfill and sewage-treatment plants’ methane emissions, how plants manage them, and what approaches or technology they use to reduce them. The implications these changes will have in sewer treatments worldwide.

A study by Liu et al., Methane emissions from sewers, find that sewer systems emit significant amounts of methane; however, according to researchers, no large methane sinks or methanotrophic activities—a biochemical process that breaks down methane—exist in sewer plants to date.

Methane emissions would occur in gravity sewers, pumping stations, and inlets of wastewater treatment plants. However, the amounts of methane produced are affected by several factors, like wastewater retention time, volume-to-area ratio, temperature, and organic matter concentration in sewers.

Due to methanogens’ sensitivity to environmental conditions, most of the chemicals applied to control sulphide in sewers also suppress methane production, a finding that the study investigates for possible methane mitigation. The study also looked at methane production, quantification, and modelling in wastewater treatment plants.

A study by Nisbet et al. says that technical developments make quantifying methane emissions from landfills and sewage facilities easier. Fast-growing cities in developing and tropical countries, with their poorly regulated landfill areas and sewage plants, are increasingly becoming hotspots for methane emissions. However, cost-effective methods are available to mitigate methane emissions.

According to the study, the initial step to mitigate methane emissions is to locate the leaks or emissions. The easiest way to find leaks is from “tractable emissions”, referring to apparent locations or methane emissions sources of methane emissions such as the gas industry, urban wastewater and sewage, landfills, underground coal mines, etc. Improvements in using drone systems (AUV), which are cost-effective, are increasingly used to detect leaks or identify “super emitters”.  

According to the study, when leaks are located, they are easily quantifiable and can be stopped quickly, cheaply, and even profitably.

Reducing methane emissions from urban wastewater and sewage poses some challenges as well. Biogas extraction can still produce leaks and drains susceptible to a methane explosion. Methane production in the sewage can deplete biodegradable chemical oxygen demands, detrimental to wastewater treatment processes.

Methane removal from pipes running from buildings to wastewater treatment plants can be done by installing small bioreactors along the sewer’s length and harvesting methane-rich air above the sewage for soil oxidation.

Other techniques used to reduce methane emissions in wastewater treatment plants are submerged underwater bioreactors, which halve methane emissions. Floating bioreactors on wastewater settling pools in agricultural settings can oxidate 67% of methane, and the technology can be applied in urban wastewater treatments.

Other methane mitigation methods include sponge reactors for anaerobic sludge effluents and blanket reactors for anaerobic sludge that can remove up to 50% methane. Generally, methane removal in wastewater treatment plants is inexpensive and self-financing because of methane’s potential to be converted to energy.

Landfills in large urban areas are enormous sources of methane emissions. Still, they can be easily mitigated through capture and piping or adding a thick soil cover to host methanotrophic bacteria. Bacterial methane oxidation is a low-cost mitigation option for developing countries. Researchers also suggest the viability of methane oxidation in oil walls and sanitary landfills in Alberta, Canada, and that it can be enhanced by adding biochar.

Soil oxidation works as a passive bio-cover system and has a high mitigation efficiency of up to 80%. One can enhance mitigation efficiency by adding local compost materials like garden and kitchen waste. Even in freezing conditions, methane consumption in landfills continues due to its endemic exothermic state.

In some developed nations, particularly in Europe, landfill emissions are now heavily regulated and not a problem compared to developing countries, except for California. California’s landfills are a source of significant methane emissions in the state, accounting for 41% of its total methane emissions.

Landfills in developing countries are typically uncontrolled, poorly managed, and susceptible to burning. Burning a widespread landfill can emit enormous amounts of methane and harmful air pollution.

A solution to capture methane emissions from landfills is to cover them with a geomembrane and fit them with gas capture piping that can deliver gas to power electricity generators. However, as a warning, anaerobic biodigesters can become a source of methane emissions if not managed carefully.

If methane cannot be harvested and converted to power, biofiltration can be a removal solution. However, these methods require ongoing investment, commitment, and management to maintain pipe integrity to avoid fractures and leakages.

The study also presents mitigation solutions for other methane sources, such as deep coal, open-cast coal, agriculture, and biomass burning in the tropics. It also discusses “intractable emissions”, or tricky ones from moving animals and food production—emissions that are not easily stopped. Researchers describe existing methods to quantify and locate these methane emissions.

As the studies have shown, several methane mitigation solutions and technologies are available and being implemented worldwide, ranging from low-cost, nature-based solutions to oxidate methane and those designed to capture methane for fuel.

Thankfully, technologies are available, continuously improved, and scaled up to detect methane leaks. Detecting and quantifying methane leaks is the first and critical step in methane emissions mitigation.

To read the studies mentioned in this article, click the links below: