Gas from Sewage Sweet for SAWS

Published Date: 
Tue, 10/19/2010

By Colin McDonald

Ameresco LogoMoney is now being made from every aspect of the smelly river of black sewage that flows into the Dos Rios water recycling center.
Today, the San Antonio Water System will celebrate a new plant at the South Side facility that cleans and compresses methane gas that is produced as microbes break down the sewage sludge.

The methane plant is the last of three operations marking a transition for SAWS as Dos Rios goes from a basic sewage treatment plant to a recycling plant that turns the waste from more than 1 million people into commodities.

Dos Rios also sells recycled effluent water to golf courses and the Toyota plant, and it sells bio-solids from the plant as compost to Garden-Ville and New Earth.

“We found we were a lot better at the production than the marketing,” said Robert Yrle, SAWS' director of production and treatment operations, about making partnerships with companies to sell what his plant makes.

The plant's methane used to be burned off with five flares. On a still day, the flames could easily reach 10 feet high. Sometimes the gas would be used to heat boilers that kept digesters at the plant warm.

Now SAWS plans to make about $200,000 a year providing at least 900,000 cubic feet of methane a day to the new plant, which is owned and operated by Massachusetts-based Ameresco. The energy company will sell the treated gas on the open market.

The amount of gas SAWS will provide daily will be enough to heat 3,000 San Antonio homes on an average winter day, according to CPS Energy.

The plant will still have gas left over for the boilers and will occasionally use the flares when gas pressure becomes too great.

By selling the gas instead of burning it, the plant reduces its carbon dioxide emissions by 19,739 tons a year. That's the equivalent of taking 31,261 cars off the road or displacing 396,369 barrels of oil, according to Ameresco.

“And don't forget they were flaring it,” Ameresco Senior Vice President Michael Bakas said. “They were getting nothing.”

While sewage treatment plants across the country have been turning methane gas into heat and electricity for years, San Antonio is one of the first to see its gas sold on the open market.

It can do so because a gas pipeline runs next to the plant. Ameresco plans to make similar plants across the country.

Yrle's next goal is to look at installing solar panels and possibly a small hydropower plant to capture the energy of the treated water that leaves the plant via a 50-foot drop into the San Antonio River.

That water is clean enough for Yrle to drink, and he sees no reason why it can't be tapped for just one more use before being allowed to flow downstream.

From the San Antonio Express-News