food waste causing methane?

I've been researching food waste lately, and I didn't understand something.  I knew you all would.

I read in a New York Times article that, among the many problems we already know about food waste, food waste in landfills is creating methane gases.  Of course, one MAJOR solution would be to compost this.  But here's my question, revealing just how little I know about science: why would food waste in a landfill create methane gases, and composting not?  What's the connection (or lack of connection) there?

Original article: http://www.nytimes.com/2015/02/26/us/food-waste-is-becoming-serious-economic-and-environmental-issue-report-says.html?_r=0

Methane gas is a product of anaerobic decomposition, which is the process in a landfill. Often when we talk about composting, we're talking about an aerobic process.

aerobic - air loving invisible beasties (bacteria and others)
anaerobic - non-air-loving invisible beasties.

Example: Sourdough is aerobic fermentation.  Sauerkraut is anaerobic fermentation.

The gas that is produced from them is (oversimplifying) fermentation farts.  There is a scientific way of explaining it, but really all one needs to know is that the bacteria eats up the food and produces gas.  When I produce gas, it's a fart.  So I call them fermentation farts.  Different kinds of invisible beasties produce different kinds of gas and this very loosely goes by whether they are air-loving or non-air-loving.  


Composting, except for bokashi which is partly done in an anaerobic environment, is usually exposed to the air.

The landfill is usually sealed off from the air, by all the garbage and in some cases deliberately to prevent bad smells.  This produces an environment which is anaerobic and produces different gases than normal composting.

Thanks; such a simple answer I'm fairly embarrassed I didn't think of it myself...but I guess I know nothing about landfill conditions.  In Europe, trash is separated prodigiously and composted or processed accordingly.  In Northern Montana, our landfill was just a series of piles, and the Birds of Prey helped speed the process along.  I hadn't really thought of it as being fully anaerobic in that context but I can see how that must be the norm in other places.

I did a farm tour of a farm digester one time and that was enlightening.

The guy was saying that his 1200 cow dairy farm would only produce 250,000 KW's running on cow manure, so he licensed his farm as a municipal dump and can now accept food scraps from a special trash disposal company. Doing so jumped his output from a measly 250,000 KWs to a megawatt. The triple jump in power is simple to understand, the cows had already extracted 3/4 of the methane by burping and farting, and so for manure, very little was left.

As for how his operation worked, he said it was simple. It was like a cows digestive system with a hose plugged to an engine that tuned a generator.