GreenYes Archives

[GreenYes Home] - [Thread Index] - [Date Index]
[Date Prev] - [Date Next] - [Thread Prev] - [Thread Next]


[greenyes] Re: Methane Not CO2 Key to Last Global Warming


John Reindl asks with regard to the article that I posted yesterday on the subject that Methane Not CO2 Key to Last Global Warming:


"This is an interesting article. Does anyone have some numbers -- with
documentation -- on how much methane would be released from bio-reactor
landfills, and what percentage of the US greenhouse gases this would
represent?

John Reindl"
This is a vital question. The first thing to note is that there are NO measurements of uncontrolled air emissions (of which methane constitute approximately half) from either the current generation of dry tomb landfills or the proposed next generation of bioreactors. Unlike factories which release pollutants out of a smokestack or outfall where measurements can be readily undertaken, gas is released both across 100-500 acres, and also laterally migrating through the soil when the top of the landfill is capped with a low permeable cover.

By way of background, today's modern landfills, because of their size and barriers for the finite period of time until they fail, keep out oxygen as well as leachate in. Sixty percent of our trash is organic material (unrecycled paper, food scraps and greenwastes) that decomposes in the presence of water. In the resulting oxygen-starved (or anaerobic) conditions of these modern landfills, methane is created during anaerobic decomposition that otherwise would never have existed. Methane is considered to have 21 times or more of the warming potential as CO2.

For that reason today's landfills, designed with barriers intended to isolate the waste from liquids, are one of the largest contributors to climate change, after combustion of coal and oil. The exact or even approximate amount of that contribution is controversial because emissions occur over a five hundred acre working face that are not directly measurable, and the effectiveness of the gas collection piping systems used to abate these emissions is very hard to establish. Using arbitrary assumptions without any factual basis, EPA says today's dry tomb landfills contribute 4% of manmade greenhouse gases (which, by itself, is not good). We say that there is no evidence to support a figure lower than 20%. But, resolving that is not what is needed to know for this case, which is how the change from dry tomb landfills to bioreactor landfills makes things substantially worse, and especially so in the near term.

Because of critics, the industry is being forced to acknowledge that so-called dry tomb landfills are fatally flawed, merely postponing, not preventing, pollution until the time the liners "eventually fail" (EPA's own words), they are attempting to propose another landfill-type solution to the probem. That is the bioreactor, in which liquids are deliberately introduced --instead of being kept out -- in an attempt to accelerate decomposition and better stabilize the site before it is closed. Liquifying a manmade mountain to accelerate decomposition, which is what bioreactors do has its own enormous complications, more prominently, the prospect of catastrophic sideslope failure. But, equally intimindating is the implications for increased uncontrolled emissions of methane.

To recognize why, Here what is needed to understand how these gas collection systems work. Simply, perforated pipes run through the waste mass connected to a vacuum system that sucks gas out from the trash which generates it. One of their weak links is the fact that the negative pressures used to draw the landfill gases reach not only outward into the waste but upward to the surface, where they draw air. When more than 5% oxygen mixes with methane, explosive conditions are created, and consequently, the systems have to be ramped down when that happens to prevent fires.

Thus, until the landfill cell tops out and is closed with a synthetic gas impermeable cover to keep out air infiltration, landfill gas collection systems are only of marginal utility.

With that background, then the conditions of bioreactors can be brought back into the picture in two salient particulars. First, as part of the on-the-cheap philosophy going into developing a design protocol for bioreactors to insure that they remain cheaper than sustainable diversion approaches, in order to recover valuable air space released from rapid decomposition (and minimize overall costs), bioreactors generally do not install the final cap for 10-15 years. Second, however, by accelerating decomposition, bioreactors compress most of the methane production to those same early years when there is no essential cap for gas collection to work. In addition, there are several other complications of pulling gas from a waste mass undergoing rapid differential settlement, but let's pass by that for now.

On top of that, and distinct from the delayed cover flaw, the rapid differential settlement that is part of accelerating decomposition in a heterogeneous waste mass creates further impediments to gas collection. The rigid vertical pipes used in dry tomb designs would tilt and fail under those conditions, and so flexible horizontal tubing is often resorted to. In addition to their inability to hold a strong vacuum like rigid pipes, they will tend to dip when laid over soft spots, and thence flood out, making that line inoperative or nearly so.

Thus, most methane generated by bioreactors, and very much more than in dry tomb landfills and especially so in the near term, will be released uncontrolled into the atmosphere.

The industry attempts to paper over this fact by pointing to the fact that bioreactors have been measured to capture 74% more gas per ton of waste in place than dry tomb landfills in the early years. But, they deliberately ignore the fact that they are also producing far more gas in the early years, some studies indicate as much as 10 times more.

Bottom line is that bioreactors are a major climate change issue that the protagonists in the global warming debate have failed to recognize, and one that will lead to massive volumes of additional warming gases not presently occurring if this rule, which permits states to issue bioreactor permits without any substantive limitation, is not reversed.

How much so remains to be quantified. There are infra-red and laser scanning technologies being developed, but not yet applied.

What we can see from this discussion, however, is that, until we have hard data, the structure of on-the-cheap bioreactors in which the final cover is delayed for a very long time to save money is such that near term releases will be substantially greater.

I'd be very interested if one of the landfill companies monitoring this listserve would respond so that we could engender a constructive dialog to hone in on the true state of affairs.

Peter



[GreenYes Home] - [Date Index] - [Thread Index]
[Date Prev] - [Date Next] - [Thread Prev] - [Thread Next]