Closed-Loop Energy

This morning I received an emailed press release announcing that the Altamont landfill gas facility in California had been recognized by the state's governor for its achievement in sustainability. What makes this facility unique is that the methane gas generated by the landfill waste is collected and turned into liquefied natural gas (LNG) in a plant run by a joint venture of Waste Management and the North American subsidiary of the Linde Group and then used to power garbage trucks that haul San Francisco's waste to the landfill. That effectively "closes the loop" by turning trash into fuel to collect the trash. It's a clever concept, but I admit to being initially skeptical about the companies' claim that this approach saves 98% of the greenhouse gas emissions from the diesel fuel it replaces. How can that be, when every pound of methane burned in the trucks' engines yields 2.75 pounds of CO2?

The answer to this conundrum lies in the assumptions behind the analysis of the project done by Argonne National Laboratory, which is generally considered the gold standard for lifecycle, or "well-to-wheels" analysis of this kind. Quoting from their report, "At present most of the biomethane generated at U.S. landfills is flared in conjunction with emissions-abatement practices." Since 1996, landfills above a certain threshold have been required to collect methane and other gases produced by the decomposition of refuse and either flare it or put it through a thermal oxidizer to convert the methane to CO2. That's crucial from an emissions perspective, because it reduces the landfill's greenhouse gas emissions by a factor of 21 times versus simple venting. However, the report also states that over 500 projects around the US recover energy from landfill methane, with most either using it to generate power or steam or compressing it and injecting it into natural gas pipelines, where it becomes indistinguishable from the methane produced from natural gas wells. When Argonne confirms that Altamont's LNG emits practically no greenhouse gases, that result is relative to the option of flaring it, not compared to the other uses to which the recovered gas could be put.

The appropriateness of that assumption goes to the heart of the issue of "additionality" that has made the certification of emissions credits so challenging in many cases around the world. In this case, if the Altamont landfill gas in question weren't turned into LNG to fuel San Francisco garbage trucks, would it really be flared or would it be turned into power, as other gas produced at Altamont apparently is? On one level I can't answer that without knowing a lot more about the facility than is provided either on Waste Management's site or in the Argonne analysis. However, it helps to consider that an assessment of any other use of this gas would face the same question; they can't all be compared to each other. There must be a common reference, and going back to flaring, which is the basic standard required under the Landfill Rule of the Clean Air Act, seems the most consistent choice.

With that assumption in hand, and based on Argonne's analysis of the emissions from the different steps involved in producing the LNG, it's perfectly reasonable to claim that at least compared to burning petroleum diesel in Waste Management's trucks, the Altamont LNG is a nearly zero emission fuel. The more interesting question is whether this disposition, with its obvious green PR benefits, is actually the best use of the energy recovered from the landfill. The same Argonne report indicates that the total energy consumption in the landfill gas-LNG-motor fuel pathway is about 8% higher than in the oil well-refinery-motor fuel pathway for diesel fuel. That hints at the possibility that the total emissions reductions from Altamont might be even greater if the gas were used, not to power garbage trucks, but for another purpose, such as generating power to back out electricity imported into the state from coal-burning sources in places like Four Corners, New Mexico. In any case, lest we make the perfect the enemy of the good, what Waste Management and Linde are doing at Altamont is certainly good compared to the default option of flaring all that gas, and the kudos they have received look well deserved.