The Amarillo City Landfill in Texas was recently under fire for its methane gas venting system and emission issues and faces fines if the system is not replaced with a gas collection and control system at a cost of $5.5 million. This recent news has city officials scrambling to fix the venting system that has been used for years.
The city had been allowed to collect and vent the landfill gas to control subsurface lateral migration of landfill gas. But the landfill recently exceeded its emission threshold, which requires it to now collection and control the landfill gas. The city is now also exploring the viability of building a landfill gas to energy project.
“This is a common sequence of events that moves a landfill from venting gas (or not collecting it at all) to active collection and control, and then maybe, if it is feasible, to converting landfill gas into some form of renewable energy,” says Patrick Sullivan, senior vice president of SCS Engineers based in Long Beach, Calif. Once a site is collecting gas, and most likely flaring it, it is determined whether an energy recovery project could be viable. Most landfill owners or operators would like to see energy recovery from landfill gas at their sites, but it is not always feasible in every case due to economics, site constraints, permitting requirements, etc.”
Venting can occur in conjunction with active collection, or a system can be installed on a landfill mass that does not actively “suck” the gas out of the mass, but lets it naturally vent to the atmosphere, according to Anastasia Welch, vice president of SCS Engineers. But venting systems are uncommon because of federal and state regulations that require collection and control of landfill gas.
“Venting is not very common to start with and is mostly utilized at smaller facilities that have not triggered the regulatory need for an active gas collection and control system,” Welch says. “The economics of energy production at smaller landfill make them more difficult to implement, so venting has not likely been significantly impacted by the landfill gas-to-energy market becoming mainstream.”
Matt Stutz, principal for Weaver Consultants Group based in Fort Worth, Texas, says venting systems can still have a place in a landfill's "tool box" in dealing with landfill gas.
“[I]f designed properly, they can be used as an initial phase as a site prepares for an active collection and control system,” Stutz says. “However, given tighter regulations, the need to control odors, and the desire to capture this energy source, the use of a venting system for long term landfill gas control is becoming less common.”
Venting’s effects on the environment is landfill site-specific.
“Methane, although is odorless, it is a greenhouse gas,” says Stutz. “The other trace constituents typically contain odiferous and volatile organic compounds.”
According to Sullivan, when vented, the methane, NMOCs, and other constituents in the landfill gas are emitted into the atmosphere without being controlled.
“This would affect the ambient air quality around the landfill. If the venting is allowed by regulation or permit, this means that the amount of emitted landfill gas is less than the thresholds at which control would be required,” he says.
Managing landfill gas at landfills is comprised of two basic functions: collecting and controlling the emissions of the collected gas.
“If a landfill is required to manage the gas produced within the waste mass, the most common approach is an active system which consists of two parts,” says Welch. “The first part removes the gas from the landfill—literally sucks it out—and the second part controls the gas, either by combustion in a flare, or conversion into some sort of energy production system.”
Landfill gas collection and control systems that actively extract the gas from the waste mass and convey the collected gas through a piping network to a control device is the most common method of control, according to Stutz.
“Although there have been some innovative methods and technologies to different components and the monitoring of a landfill gas collection and control system, the concept and basic design has remained fairly consistent. The most successful and most expensive systems are active landfill gas collection and control systems,” he says.
Sullivan says there is not much in the way of recent innovation when it comes to collecting the gas; however the real innovation comes in designing the collection system in the most effective way possible to optimize gas collection.
“Electricity generation from landfill gas is probably the most successful and commonly used of the innovative ways to control and recover energy from landfill gas,” he says. “Other methods can be successful in case-by-case situations where economics, logistics, and other factors play in their favor.”