Biodegradable and compostable differ in two regards, with compostable being the more stringent. Materials and goods that are compostable must biodegrade within a certain time frame and must not leave a toxic residue. So a log is biodegradable, but not compostable because it takes years to fully biodegrade. A cotton textile colored with dyes that contain heavy metals would be biodegradable but not compostable because it leaves a toxic residue (heavy metals).

Time to fully biodegrade is critical to the commercial composter, but usually less important for the home composter who doesn’t usually need the finished compost on a tight time schedule. Items that are biodegradable rather than compostable because they don’t meet timing criteria can often become compostable withe shredding, chipping, grinding, etc. That log could could be made into sawdust which could reasonably go into a compost pile.

On the other hand, there isn’t much you can do about the toxicity of an item. If the item contains potentially toxic or non-biodegradable substances there isn’t much you can do about it. They will be in your compost and if you use that in your vegetable garden, perhaps your food chain too.

PLA is getting a lot of spin from corporate marketing departments that have a lot of money and spin talent. We consumers aren’t all that good at separating the wheat from the chaff, but if we want a better environment, we should start getting environmentally smarter. Here is part of a study that discusses PLA. PLA may sound like the perfect idea and it very well may have niche market applications. Studies have shown that PLA has its own set of problems.

“The conclusions from our analyses were inescapable. The environmental benefit of growing plastic in plants is overshadowed by unjustifiable increases in energy consumption and gas emissions. PLA seems to be the only plant-based plastic that has a chance of becoming competitive in this regard. Though perhaps not as elegant a solution as making PHA in plants, it takes advantage of major factors contributing to an efficient process: low energy requirements and high conversion yields (almost 80 percent of each kilogram of plant sugar used ends up in the final plastic product). But despite the advantages of PLA over other plant-based plastics, its production will inevitably emit more greenhouse gases than do many of its petrochemical counterparts.”

Excerpt from: http://www.mindfully.org/Plastic/Biodegrade/Green-PlasticsAug00.htm

There are basically three types of plastics claiming to be more environmentally friendly; Compostable, Degradable and Biodegradable.
As mentioned, PLA is compostable but only in a commercial facility. PLA doesn’t biodegrade, once it hits a landfill environment it will languish there for a long time.
Degradable plastics such as oxodegradable plastics, break down (degrade) into smaller and smaller pieces until they are too small to see. Degraded polymers don’t biodegrade they just get to small to see and that isn’t good for the environment either.
The third is a biodegradable plastic such as the ENSO Bottle with EcoPure or other plastics with the EcoPure additive. Biodegradable plastic with EcoPure is plastic that has an additive which attracts microbes that consume plastic in an anaerobic or aerobic environment leaving behind biogases and humus.

As you mentioned, most landfills here in the U.S. are the dry tomb type where the trash is compacted and covered limiting oxygen and moisture within the trash. There is however, microbial activity within the anaerobic conditions of a dry tomb landfill which is why the government has mandated that landfill operators capture or burn off the gases produced in a landfill. . Microbes consuming trash in a landfill produce landfill gases (LFG). The good side of LFG’s is that many of these landfill gases are now being captured and used to produce clean energy.

Our company is supporting anew landfill design called “Bioreactor landfills.” Bioreactor landfills are landfills which are designed to enhance microbial action and to capture all the LFG produced. Our company supports recycling and the development of bioreactor landfills. Ultimately, most thing end up in a landfill, biodegradable plastics and bioreactor landfills will be major factor toward improving our environment.
We know there isn’t any one perfect answer, but we are working toward a solution that will help.

Max
http://www.ensobottles.com
“Bottles for a Healthier Earth”