More than 30 percent of greenhouse gas emissions are from coal-fired power plants – more than all the vehicles on the road or, for that matter, any other industry. To reduce carbon emissions, the 

Environmental Protection Agency (EPA) has finalized the Clean Power Plan (CPP), a new rule that limits carbon emissions from power plants for the first time. The lengthy and complex plan establishes guidelines for states to regulate greenhouse gas emissions from existing fossil fuel-based electric generation units.

The CPP establishes targets to reduce carbon emissions for each state resulting in 32 percent total emissions reductions by 2030, which is below 2005 emissions levels. The targets range from 7 percent for Connecticut to 48 percent for South Dakota. States have different targets based on each state’s particular set of existing resources. These include the mix of coal and oil plants as well as their existing renewable energy infrastructure. States can achieve their goals through a variety of options that include shifting towards renewable energy, improving energy efficiency and switching to natural gas and nuclear power. 

Renewable energy offers numerous benefits while also delivering carbon emissions reductions. However, some renewables like wind and solar are intermittent, meaning they cannot be used around the clock. The sun does not shine at night and the wind does not always blow. So until we can store sunlight and wind energy – an issue that engineers are working on – a reliable baseload fuel is needed for our energy needs. In the meantime, other renewable sources such as landfills can produce reliable energy at all times. Landfills generate gas from waste decomposition. This gas can be captured and converted into energy that is available 24 hours a day.

Mostly Methane

When waste is buried in a landfill, microorganisms decompose the organic materials and generate a landfill gas byproduct. Landfill gas is largely made up of methane and carbon dioxide; this accounts for about 99 percent of the landfill gas. The remaining 1 percent are non-methane organic compounds. 

Methane is itself a powerful greenhouse gas, and as a result landfills are subject to the Clean Air Act to control air emissions. Traditionally, landfill gas was flared to destroy the methane and other components of the gas. However, methane is also the ingredient in natural gas and can be used as a fuel, thereby taking a potential greenhouse gas and converting it into a fuel while simultaneously avoiding the extraction of other fossil fuels. 

Landfill gas can be extracted from the landfill by exerting a vacuum on horizontal or vertical wells located in the waste. Once the gas is extracted, it flows through a series of lateral and header pipes to a central location where it can be directed to either a flare or converted into energy. Energy uses for landfill gas can be varied – including everything from direct on-site generation of electricity to compressed natural gas for vehicle fuel, to piping offsite for use in turbines that take advantage of both electricity and heat from the gas.

Because this is an active biological process where microbes are actively consuming the organics and emitting the gaseous byproducts, landfill gas generation varies by site based on a number of different factors. These include everything from the quantity of material to the types of wastes received, to the temperature and moisture of the facility. Engineers use models to predict the quantity of landfill gas and from there determine whether it is feasible to convert the landfill gas to energy.

Currently, landfill gas-to-energy facilities produce over 2,000 MW of energy. However, new project development has been moderated by lower natural gas prices and limited tax credits. Depending on the technology selected, the beneficial-use projects can be costly to construct. Project feasibility is determined based on project development costs including operational costs versus the long-term revenues anticipated from the sale of the energy. 

Besides the infrastructure needed to convert the gas to energy, utilizing the landfill gas generally requires some pre-treatment as well. This treatment can include removal of excess liquid, filtration to remove particulates and compression of the landfill gas. The pre-treatment equipment increases the costs associated with project development. Cheap natural gas has hindered the potential project revenues, jeopardizing the viability of new projects. 

It is anticipated that the CPP could spark new project development. Increased demand for dependable renewable energy sources might lead developers to prioritize landfill gas projects. Plus, capacity for new projects exists. According to EPA’s Landfill Methane Outreach Program, 440 landfills could serve as candidates for project development, resulting in approximately 855 MW of additional renewable energy capacity. Development of new landfill gas energy projects can help achieve the objectives of the CPP – that is, provide cleaner air and reduce greenhouse gas emissions that cause climate change.

Anne Germain, P.E., BCEE, is director of waste and recycling technology for National Waste & Recycling Association.