Modern Alchemy: Turning Sewage Into Energy And Money

SAN ANTONIO — The city plans to turn the stench of its residents' waste into sweet green cash and renewable energy.

The San Antonio Water System will sell captured methane gas generated from the utility's treatment of 140,000 tons of biosolids, or sewage, from customers each year.

The city-owned utility's board of trustees approved a contract Tuesday to provide at least 900,000 cubic feet of natural gas daily for the next 20 years to Ameresco Inc., a Framingham, Mass.-based energy services company.

"Treating these biosolids generates an average of 1.5 million cubic feet of gas a day," said Steve Clouse, the water system's chief operating officer. "That's enough gas to fill seven commercial blimps or 1,250 tanker trucks each day."

The utility already sells for reuse a portion of the water that's cleaned at its wastewater treatment plants. It also converts some biosolids into compost that's sold for use in yards and gardens.

"As far as we know, SAWS is the only city in the United States that has completed the renewable recyclable trifecta," Clouse said.

The water system will receive up to $250,000 a year for the methane, which will be drawn from the utility's Dos Rios Water Recycling Center.

Clouse said it will take 18 to 24 months for construction of facilities needed for the contract.

"We're very pleased that we can capture and sell this gas, which is good for San Antonio's air quality and puts this renewable energy resource to work for San Antonio," he said.

Comments

[WolfLarsen]

01:45 AM on 09/15/2008

For years we have been turning our sewage into Republican­s.....it would be nice to turn it into something that will benefit society for a change.

[WilliamGossett]

09:05 PM on 09/14/2008

If the new energy, methane, burns carbon, which it does (chemical structure CH4 --> H2O and CO2), you STILL make greenhouse gas and nitric oxide.

Have to come up with a better solution.

[KillTheMessenger]

12:42 PM on 09/15/2008

Methane is a much stronger greenhouse gas than CO2. Since it is being set free by the garbage dumps anyway, whether we use it or not, capturing the methane and converting it into CO2 is a very significan­t way to curb greenhouse gas emissions. It's not a solution, but it is one necessary step toward a solution.

In any case, we have the solutions. We are just too cheap and too greedy to apply them.

[FearlessFreep]

12:18 AM on 09/16/2008

At least this methane isn't being released into the atmosphere­, where it's one of the most intense greenhouse gases.

[zizyphus]

11:11 AM on 09/13/2008

At the University of Hawaii, sewage sludge has been turned into biochar, a valuable amendment to agricultur­al soil.

I have been watching this Green section, and have not yet seen any articles on Biochar. People should know about this incredible old/new technology for improving soils and sequesteri­ng carbon.

[KillTheMessenger]

08:01 PM on 09/13/2008

You can always count on Americans to do the right thing - after they've tried everything else.

Winston Churchill

Sadly, biochar seems to fall into this category. It will have to wait until we are done trying all the wrong solutions.

[KillTheMessenger]

01:39 PM on 09/12/2008

"That's enough gas to fill seven commercial blimps or 1,250 tanker trucks each day."

1.5 million cubic feet of methane are equivalent to 42500m^3, which at 0.717kg/m^­3 gas density equals a methane mass of no more than 30500kg or little over thirty tons.

A tanker truck carries 9000 gallons of liquid methane. So that makes a load of roughly 9000* 0.00378m^3­*423kg/m^3­=14,390kg or 14 tons.

In other words, it's only 2.1 tanker trucks worth of methane a day, or so. Still not bad. But not nearly as much as the erroneous claim is.

I hope the good man knows the rest of his business better than he does the conversion of gas to liquid transport volumes for methane.

[dadw5boys]

01:38 AM on 09/13/2008

NO ONE CLAIMED TO HAVE THE PROJECT FINISHED THEY ARE JUST STARTING !!!!!

THESE ARE PROJECTION­S!

[KillTheMessenger]

07:58 PM on 09/13/2008

Is that what you said when the math teacher in high school gave you an F for getting all the answers wrong?

A factor of 600 is not a matter of getting a "projectio­n" wrong. It's a matter of not appreciati­ng that methane tanker trucks transport the refrigerat­ed liquid and not the gas under normal conditions­.