Dealing with our trash

There's a promising six-part series on the Science Channel called Ecopolis, that attempts to point a new forward as cities try to manage problems like food production, water access, transportation, waste management and energy. The show will run through 20 possible solutions, gauging their ability to reduce the carbon footprint of a future megacity.

A recent episode focuses on how to deal with waste, looking at four examples that could help.

TRASH TO ISLANDS

Densely populated Singapore is known for its spotlessly clean atmosphere. (Spitting out your chewing gum on a city street will get you fined.) But the city has to do something with all the trash that is picked up. City planners want to reduce physical waste to 10% of current levels. Their solution is to burn the trash in super-efficient incinerators.

But what to do with the highly toxic leftover ash? Since it has to go somewhere, it was decided to use the detritus to build an island not far offshore.

Singapore uses impermeable membranes to contain the ash, and manages the mixture by adding plant material to rehabilitate the materials. Mindful that toxins could seep out, designers planted mangrove trees, a very senstive plant that acts like a canary in a coal mine. If the mangroves start to die, there is a problem.

City planners hope this solution takes care of Singapore's waste needs until 2040. Carbon footprint reduction potential: 3%.

PLASMA GASIFICATION

Because incineration has harmful byproducts, some are turning to vaporization as an alternative. The hope is that energy and materials can be recovered from waste.

Plasma gasification mimics conditions on the sun, reducing compounds to their basic scientific elements. This method is already in use to deal with radioactive wastes. But how to put this expensive process to work for everyday garbage?

First, garbage is fed into a superhot (1,600 degrees Fahrenheit) chamber that reduces the waste to tiny particles. Then, the particles are put into a plasma chamber (1,800 degrees) that blasts the waste, turning it into energy.

The plant in Wiltshire, England, run by Advanced Plasma Power, runs on a gasplasma process. It's estimated such a process could generate five times more power than it takes to run, with nearly zero emissions. Carbon footprint reduction potential: 3%.

BIOCHAR

Let's begin by looking back at the example of how ancient Amazonian civilizations turned barren soil into rich growing material, burning organic material and mixing the char into the soil. The secret of charcoal lies in its honeycomb-like molecular structure, which gives microbes a good place to grow.

BEST Energies is developing a product called Biochar, turning organic waste from cities and farms into both fertilizer and green energy. Volatile gas byproducts are burned by slow pyrolisis to create electricity. The Australian company's leftover char material locks in carbon. After mixing it into the soil, it improves the soil, boosting agricultural yields by 50% in some cases.

The key? How much carbon dioxide is released from the char into the atmosphere? If the technology adversely affected global warming, the benefits might be negated. Early results are promising. Carbon footprint reduction potential: 21%

HEAT FROM HUMAN WASTE

Each day the average American flushes away 100 gallons of liquid and solid waste. Because it holds heat, an average 50 degrees, the waste holds energy potential.

In 2010, Vancouver, British Columbia, will host the Winter Olympics. The city hopes to capture heat from sewage to keep Olympic Village warm.

One example is already in use. In Oslo, Norway, lukewarm sewage is run through a heating plant to keep the city warm. In the sewage heat exchanger, a liquid refrigerant absorbs heat from the sewage, creating gas under extreme pressure, raising the temperature to 150 degrees. The superheated gas runs over a separate pipe, heating the water inside. A network of insulated pipes delivers the heat.

Oslo's sewage can heat up to 4,000 homes yearround, and the pipe grid warms more than 400,000 square feet of sidewalk, melting hazardous snow and ice.

Using Oslo's example, Vancouver hopes to keep Olympians warm. Potential carbon footprint reduction: less than 1%.