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Expert Interviews

Khaled Mahmood Discusses the Benefits of Converting Landfill Gas-Powered Engine Plants to Renewable Natural Gas Facilities

Headshot of Khaled Mahmood

Khaled Mahmood is a registered professional engineer with more than 25 years of experience conducting and managing solid waste and air pollution control permitting and planning engineering projects.

He has extensive expertise with air pollution control and environmental engineering for solid waste and landfill gas-to-energy (LFGTE) facilities. He has conducted air pollution control audits and air emission surveys for industrial and solid waste facilities, including developing compliance strategies to address the impact of regulations on facility operations.

Khaled also has experience performing emissions estimating using U.S. Environmental Protection Agency (EPA) and industry-specific emission factors; regulatory interpretation; New Source Review and Title V permit development; Prevention of Significant Deterioration (PSD) evaluation; and Best Available Control Technology (BACT), air pollution control equipment, and lifecycle analysis.

Khaled holds a Master of Business Administration from Capital University, a Master of Science in environmental engineering from Marshall University, as well as a Bachelor of Science in civil engineering from the University of Minnesota.


Why are clients converting existing landfill gas (LFG)-powered engines to facilities that produce renewable natural gas (RNG)?

Converting an existing LFG-powered engine and turbine plant into an RNG plant helps the environment by significantly reducing emissions, including greenhouse gases (GHG). Facility operators producing electricity from LFG are competing with others generating electricity with natural gas, which typically costs less. If they switch to generating RNG, tax credits from Renewable Identification Numbers (RIN) can provide additional value and make generating RNG more valuable. Also, this type of change reduces the company’s overall carbon footprint and helps achieve environmental sustainability goals.


Can you expand on the benefits of transitioning from electricity production to RNG production?

I see four key benefits to this transition, with the first being the clear environmental benefits from reduced emissions. There will typically be a large reduction in emissions—usually below Title V permitting thresholds—but without limiting production capacity. The LFG treatment system used during RNG processing reduces both the raw LFG’s volatile organic compounds (VOC) and the hydrogen sulfide (H2S) content. Ceasing operation of an LFG-powered engine and turbine plant also reduces methane (CH4), nitrogen oxides (NOx), and carbon monoxide (CO) emissions—hence a boost for GHG CO2e reduction efforts.

A second benefit is increased revenue, as profit increases because RNG has a higher value than electricity. Simply put, pipeline quality RNG offers higher revenue potential than electricity generation. An RNG plant also enhances tradeable RINs credit potential for the facility. In addition, RNG can be used as fuel for vehicles, reciprocating internal combustion engines (RICE) electricity generation, thermal, and other applications.

The third benefit is associated with substantially reduced air permitting requirements when transitioning from electricity production. This can be considerable because permitting is required for each operating engine, and many LFGTE facilities have 20 or more engines. I would estimate that about 75 percent of air permitting requirements will go away when, instead of generating electricity on-site, facilities are simply processing raw LFG to remove impurities and putting it into a pipeline.

The final benefit is reduced routine air quality compliance efforts compared to typical LFGTE facilities. There will be a large reduction in monitoring, testing, recordkeeping, and reporting because facilities may no longer be subject to Title V permit requirements and will not be required to comply with the New Source Performance Standards (NSPS) for RICE.


Can you give us an example of how switching to RNG production has been beneficial?

One interesting example is a project in Michigan where operators found that changing to RNG production greatly reduced pollutants emitted compared to the existing LFGTE facility. This table compares typical yearly pollutant emissions between electricity production and RNG production. For example, the typical yearly emissions of NOx from the LFGTE went from 121.8 tons per year (TPY) to 6.4 TPY when producing RNG, a dramatic change that illustrates why so many of our clients are opting to make the switch.

Pollutant Typical Yearly LFGTE Emission (TPY) Typical RNG Emission (TPY) Net Change (TPY)
NOx 121.8 6.4 -115.4
CO 297.0 31.3 -265.7
SO2 67.0 1.7 -65.3
PM10 13.8 1.6 -12.2
VOC 25.6 0.3 -25.4
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