The Importance of Methane Monitoring for a Wastewater Treatment Plant

 In a wastewater treatment facility, one of the key parts for a safety plan is to reduce the risks to workers and the immediate environment of hazardous gases. Sewage naturally gives off methane gas and hydrogen sulfide that can be detected through a “rotten egg” smell. Early warning devices and gas detection equipment for methane monitoring can help provide more time in remedial and preventive action. Methane monitoring can also be used as part of a total integrated monitoring system and safety plan for a wastewater treatment facility.

Methane emissions in a wastewater treatment plants

During the process of wastewater treatment, a plant emits greenhouse gases like carbon dioxide, methane and nitrous oxide. Carbon dioxide is released from combustion of fossil fuel that is required in the operation of the wastewater treatment plant. It is also produced directly during the respiration of organic matter. Nitrous oxide is expected to be emitted during biological nitrogen removal from wastewater through nitrification and subsequent denitrification processes. Methane has a global warming potential and it is formed in the sewer system and in those parts of the wastewater treatment plant where anaerobic conditions prevail. However, even with methane monitoring, less attention is provided to methane since most of the concern is on nitrous oxide emissions. Overall methane emissions cause slightly larger greenhouse gas footprints than carbon dioxide emissions from a wastewater treatment plant. 

Why it is important to monitor, measure and dispose of methane and other digester gases

Digester gases pose plant safety concerns and odor issues in the immediate environment and have been cause for many complaints from residents. Digester gas which is 60% to 65% methane is a by-product of the wastewater treatment system and a greenhouse gas that stays in the atmosphere for approximately 9 to 15 years. However, methane digester gas with proper treatment can be used in an internal combustion engine to drive a generator, fuel boilers or generate electricity for plant use. Properly measuring, monitoring and utilizing the methane by-product as an energy resource can provide a win-win solution for the wastewater treatment plant and the community as a whole. However, accurate methane monitoring and measurement is critical to the process of harvesting it as fuel gas and will continue to require the attention of plant engineers at the wastewater treatment plants.

The advantages of methane for energy efficiency programs

  • Residents of a municipality are benefited by lower sewer rates while providing renewable electric energy
  • Methane gas which is collected from digester gases can fuel two continuously running generators that can each produce up to 2235 kilowatts of electricity or a total of approximately 4.5 megawatts.
  • Using whatever methane is produced onsite, the wastewater treatment plant not only becomes self-sufficient in terms of energy but the facility is also able to sell excess power generated to the local energy grid.
  • Not only is power consumption dramatically reduced but it conserves natural resources and the savings are passed along to the taxpayers.
  • Utilizing one source of fuel generates two forms of energy: electricity and heat. 

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