The Sucking Sound? Just A Little Biogas
by April Streeter, Gothenburg, Sweden on 11. 2.07
This nifty little shed on a suburban street in Gothenburg, Sweden is filled with microbes busily eating household garbage in a pilot project to dry up compost before it's turned into methane at the local biogas plant.
Brainchild of Lars Smedlund, the Somnus Hus is a system that helps remove 75 percent of the moisture, and most of the odor from compostable food waste. About 180 families in a condominium complex in the pilot will share the shed and deposit their paper bags with food scraps into the green shute (each family has a key to the shute). After the scraps are shredded, moisture is sucked away via a wet filter system filled with odor-eating bacteria. In 4-5 days the scraps resemble finely-chopped wood chips (photo after the jump).
Unlike other compost systems, which are subject to rot when too wet, the Somnus system is designed to control the humidity and smell, and the smaller resulting volume of compost only requires a pick-up once or twice a year, versus the once a week or every two weeks for food compost collection systems such as San Francisco's.
Even better, the dried-up compost can be redistributed in community gardens, or it can be collected by what Smedlund described as 'sucking cars' (industrial vacuum trucks) where it is then deposited as raw material at the local biogas plant - at least in places like Gothenburg where there actually are 'local biogas plants.'
By Smedlund's reckoning, each bag of household food scraps can make enough methane to drive a car 3.2 kilometers. If only Volvo hadn't killed their bi-fuel methane model last year!
Smedlund says each shed uses about 6,500 kWh of electricity per year - about the same as a TV on stand-by. The Gothenburg pilot will last 1.5 years. ::Via Smedlund.se
6500 Kwh of power from a TV on standby? Can that be true? That's more than my entire house's electricity consumpution for a year. Just wondering.
"... each shed uses about 6,500 kWh of electricity per year - about the same as a TV on stand-by ..."
Actually that would be for all the TVs in the complex of 180 units, assuming each had only one TV. 8760 hours per year x 4 Watts per TV x 180 units = roughly 6,300 kWh (or 6,300,000 Wh).
This is about the same as the total energy used per year for 1 efficient European home (about 17.5 kWh per day).
I do like the idea and wish that we could do something like that here. I set up a pilot composting program for the Whole Foods stores in the Balt - DC area in 2000-2001 and the moisture content of the waste was the biggest issue (weight, fouling/health concern, mess). An efficient moisture removal system would have greatly helped. (they cancelled the program due to above concerns)
Lew
The 6500kWh is compensated for by reduction of transport movements and also by the potential energy in the biomass (the articles on the website speak of 450.000kWh per 200 households (= 1 unit) per year). I think the transport energy use is far more than the 6500kWh (26x reduction!)
Apparently the author of this post gravely mistunderstands the basics of anaerobic digestion (the process where biomethane is generated), or she/he is all too uncritical of the information provided by the technology developer (a technology yet in a pilot stage, by the looks of it).
Dry compost, aerobic decomposition will not generate biogas/methane if done properly.
Jeffrey, the two processes are separate... The drying is done at the point of collection (with as little decomposition as possible) and the anaerobic decomposition is done in the local biogas plant. Perhaps your conclusion was drawn too soon?