Some people have recently been upset by my strong promotion of waste-to-energy as a better solution to waste disposal than a landfill. While they acknowledge the nastiness of the methane that emanates from a landfill, they also see a lot of very nasty stuff being produced when trash is burned. And their argument is correct. If the trash is simply burned, whether in a furnace or in the open air, lots of bad stuff is produced in the process. The safety of waste-to-energy depends on how we handle those compounds.

The study of waste-to-energy starts with a landfill. As things (mostly the organics) decompose, they create a lot of methane gas, which is 28 times as bad as CO2 for the environment. There is no way to stop that from happening, except to stop putting organics into the landfill in the first place. Even if we managed to stop that today, what’s already there will be a problem for decades to come.

The simplest way to deal with that gas is to collect it in underground pipes and burn the gas. That turns the methane into CO2. Not good, but 1/28 as bad as the original methane. This is what Casella does at its landfill in Old Town, and what Brunswick will be doing with our now-closed (but much, much smaller) landfill.

The next step up the ladder is to collect the gas, clean out some residual solids, and burn it in a generator to make electricity. This is the approach taken by Waste Management Systems at its landfill in Norridgewock. That works well, but is highly inefficient, and it depends on how clean the gas is before it’s burned. Approximately 2500 Metric Tons of waste per day nets about 3.2MW of electricity.

The next step up is to make the process more efficient by burning the trash directly, and using the heat to produce electricity, which is the process to which we usually refer when we talk of waste-to-energy. The key is to clean the exhaust so no bad materials are sent out of the stack from the furnace. If that step is not taken (or not done well), then there is little or no environmental gain from the burning, and that’s where the critics see the problems.

I explored that question with ecomaine to see just how they protect their exhaust gasses and ensure that nothing but water vapor escapes from their stacks. They shared a list with me of nine compounds for which they scrub the exhaust using four different scientifically proven scrubbing techniques to clean out the contaminants, (also available for review on their website).

Several processes are then employed to neutralize them so that the ash that remains is completely non-hazardous. This neutralized “fly ash” is then mixed with the “bottom ash” from the burning, and moved to ecomaine’s own ashfill. The testing records show that only a very tiny proportion of the levels of these contaminants allowed by the EPA are to be found in the ash or the exhaust gasses. What comes out is some of the cleanest air (and cleanest ash) in Portland.

The Recycle Bin is a weekly column on what to recycle, what not to recycle, and why, in Brunswick. The public is encouraged to submit questions by email to [email protected] Harry Hopcroft is a member of the Brunswick Recycling and Sustainability Committee.

Comments are not available on this story.

filed under: