... And Sewage, Too

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.... And Sewage, Too By ROSE GEORGE

Leeds, England - ON several quiet streets in Sheffield, a northern English city

an hour from here, are street lamps that look like ordinary gas lamps, but do

not burn ordinary gas. Instead, their light comes from gas released from the

sewers that run beneath them. Thus, they are both relics of the past, when gas

lamps lighted our streets, and of the future, when excrement and wastewater will

again be seen as a resource, not a waste.

" Wastewater " has always been recognized to have some value. In 1860, as

waterborne sewer systems were becoming the norm, an alderman named Mechi told

Farmer's Magazine that " if the money value of our sewers could be shown to the

British farmer in bright and glittering heaps of sovereigns, he would gasp at

the enormous wealth, and make great efforts to obtain the treasure. " Mechi was

talking about the fertilizing nutrients in human " waste, " which he thought were

needlessly ruined by mixing excrement with water, but he might also have been

talking about its wasted energy potential.

Sludge, the solids that remain after sewage has been cleaned into effluent, has

a high B.T.U. content (a measurement of fuel's energy); it burns efficiently and

well. Other aspects of wastewater treatment can also reap energy: anaerobic

digestion (whereby bacteria munch on the organic contents) produces methane,

which with turbines can become combined heat or power. Microbial fuel cells can

use bacteria to get electricity from sewage, while gasification, a

high-temperature process, can reap fuel-ready gas from sludge.

When it comes to harnessing energy from wastewater treatment, it sounds as if we

are spoiled for choice. Then you look at the numbers. Of the 16,000 wastewater

treatment plants in the United States, about 1,000 process enough gallons (five

million daily) to be able to generate cost-effective energy using anaerobic

digestion. Yet only 544 use anaerobic digestion, and only 106 of those do

anything more with the gas produced than to flare it.

If those 544 treatment plants generated energy from their sewage, the E.P.A.

concluded in a 2007 report, they could provide 340 megawatts of electricity

(enough to power 340,000 homes), and offset 2.3 million tons of carbon dioxide

that would be produced through traditional electricity generation. In the effort

to reduce greenhouse gases, the E.P.A. said, this would be equivalent to

planting 640,000 acres of forest or taking some 430,000 cars off the road.

Gasification, like anaerobic digestion, is an age-old process. It used to supply

gas lamps in some American towns, too, before piped gas became the norm. The

process — a thermal conversion at high temperatures — could probably be done in

a garbage can. But the utilities haven't been eager to push the technology. The

sewage treatment process — essentially, filter, settle, digest — hasn't changed

much since the early 1900s, because it works. And drying out sludge enough to

make it burnable takes money and energy. Pilot projects may take several years

to pay for themselves, which can clash with short-term budget cycles.

Other factors may force the industry's hand. It takes considerable energy to

clean sewage, and energy costs have risen along with global temperatures. Now

isolated pioneers are showing how investing in " waste " can pay off: London's

Thames Water utility now generates 14 percent of the power it needs from burning

sludge or methane, saving $23 million a year in electricity bills.

Also, it's green to burn the brown stuff. Resource recovery from wastewater

counts as renewable energy, which makes sense: we're hardly likely to stop

providing the raw material anytime soon. So why continue to flush away a

resource whose value, even under the dim light of a sewer gas lamp, should be

blindingly obvious?

Rose is the author of " The Big Necessity: The Unmentionable World of

Human Waste and Why It Matters. "

http://www.nytimes.com/2010/04/28/opinion/28george.html

Author website with book reviews

http://rosegeorge.com/site/books/the-big-necessity/

THE BIG NECESSITY: The Unmentionable World of Human Waste and Why It Matters. By

Rose .

Takes aim at a taboo subject, revealing everything that matters about how

people do, and don't, deal with their own bodily waste. The author takes you

from the deep underground sewers of Paris, London, and New York to an Indian

slum where ten toilets are shared by 60,000 people. 288 pages. Published by

Metropolitan.

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