Monday, March 12, 2007

The Future of Energy....Trash?

An article in the Wilmington Star News a few weeks ago has me thinking. The article noted that the county landfill was planning to increase its height from 70 feet to 140 feet tall. That’s about 14 stories high! The reasoning, of course, is that land is limited and permits for new locations are difficult to obtain. The story went on to say that residents generate about 1.6 tons of garbage per person per year.

Based on my experience, this sad story is probably typical of the country. And, trash has negative implications beyond land and permits. When concentrated and compacted, as is typical of today’s landfill, trash slowly decomposes and generates into, among other things, methane, a main component of natural gas which is over 20 times more potent as a greenhouse gas than carbon dioxide, which is usually the poster boy for greenhouse gas in our atmosphere. And there is potential for other pollution through leaching or out gassing of various dangerous compounds, not to mention potential smell and disease issues.

But, trash also has significant energy content. So, I put pencil to paper to calculate what the potential contribution to our energy equation might be if we put trash to work. Wood/paper or plastics make up the majority of this trash. Wood/paper typically has an energy content of 5-7,000 btu/lb, while plastics typically have an energy content of 15-20,000 btu/lb. If we assume an average 10,000 btu/lb, the energy content of trash generated by the US is approximately equivalent to 45% of the total oil production in the US, or about 10% of OPEC oil production.

Since this seems high enough to get almost anyone’s attention, let’s talk about the possibilities. As with many alternative energy issues, the starting point seems to be a discussion about large concentrated processing vs. individual use.

For individuals, the only practical use seems to be burning for hot water supplies. Since hot water use and trash accumulation are both pretty near continuous and the energy content in trash is fairly nearly matched to heating demand for household hot water, this seems a pretty good match. And, it would fairly easy to build a trash based water heater from brick in your backyard. The problem here, especially for a typical subdivision, lies in potential odors and pollutants. Pollution control, though possible, is probably outside the capabilities of most homeowners. For rural folks, this option has feet, since they generally have no trash pickup and often burn their trash in any case. A trash burner can also be supplemented with wood, leaves, pruning debris and other biofuels.

For larger, industrial, processes, a number of options exist. Incineration is one which I believe is viable, assuming proper planning and design to minimize pollution and process upsets. Heating, by plasma arc and other processes to vaporize the trash into combustible gases is another process which has been used. Another approach which has been successfully used is to drill into the landfill and capture/produce the methane as the trash naturally decomposes-slow, but perhaps effective over the long run.

As with most alternative energy sources, the recent high prices are making various approaches more viable. This one could be more viable than most, since by helping solve the longstanding trash accumulation problem, you can effectively kill two birds with one stone. And, this one is sustainable, since trash generation is increasing.