AWA focusing on sludge dryer
Authority would be ‘getting ahead of the curve’ with digester project
The Altoona Water Authority’s proposed anaerobic digester project at the Westerly Sewer Treatment Plant has many potential benefits, but the one that some officials think is most important was not part of the original idea.
From the beginning, officials discussed charging to accept food processing waste and other organic materials, then using that waste, along with the sewage the plant ordinarily treats, to produce methane gas, which in turn could heat the buildings of the plant and generate electricity to run equipment — with excess gas and electricity being sold to their respective outside markets.
Those early discussions, however, didn’t include the idea of using the gas to run a dryer that could transform the heavily regulated Class B sludge currently produced by the plant to virtually unregulated, safe, Class A sludge, staff engineer Mike Sinisi said after a meeting Thursday at which the board received a project update.
Transforming that sludge from Class B to Class A is probably the most attractive feature of the project, because disposing of Class B sludge is becoming increasingly problematic, according to Sinisi and others at the authority.
Farmers now accept Class B sludge for spreading on their fields as fertilizer, but the state Department of Environmental Protection restricts how much can be spread and when, while fewer and fewer farmers remain willing to let it happen, said engineer Jim Balliet of Gwin Dobson & Foreman.
Those DEP restrictions are expected to tighten further, officials said.
Municipalities as close as Centre and Clearfield counties, and especially in eastern Pennsylvania, have begun to prohibit Class B application through zoning, and there have been proposals to legislate against it statewide, said solicitor David Gaines.
If the authority can’t spread the sludge on farms, landfills are an option, but that is also getting more difficult, and at $90 a ton for now, it would be three times the cost of farm application, Balliet said.
“In 10 years, it may almost become mandatory to (produce) Class A,” Gaines said.
Sludge is “a long-term concern,” said authority consulting engineer Mark Glenn of Gwin Dobson & Foreman.
It’s such a problem that the solution offered by the digester overshadows the other benefits of the project, according to Glenn.
Thus, the authority should look at the project, to which the authority has not yet committed, as “purpose-built, not speculative” — the purpose being to provide a solution to the sludge problem, Glenn said.
By going forward, the authority would be “getting ahead of the curve,” Gwin said.
The project, which would be done under a program of the Pennsylvania Sustainable Energy Fund, could cost up to $29 million, yet pay for itself in no more than 13 years, according to savings and revenue calculations by the firm tentatively chosen for the project, Energy Systems Group, which must guarantee the authority will at least break even over a 20-year payback.
Any revenue generated would simply be a bonus, according to Glenn.
Other authority officials might be focused more on the revenue potential, and that’s fine, Sinisi said.
The virtual “pasteurization” of the sludge by heating and drying also reduces its volume by 75 percent, so that 6,000 wet tons of Class B becomes 1,500 tons of Class A, Balliet said.
“It’s easier to get rid of, and there’s a lot less of it,” Balliet said.
Class A sludge is so innocuous that the authority could give it away or even sell it as mulch or soil amendment to homeowners, officials said.
Authority officials talked about a sludge dryer years ago, but decided then that buying the gas to operate it made constructing one unfeasible, Sinisi said.
Producing the gas from incoming sewage and “high-strength organic waste” solves that feasibility problem, he said.
The project will require the transformation of Westerly from an aerobic digester plant to an anaerobic one.
Authority engineers considered constructing an anaerobic digester when the Westerly and Easterly plants were renovated starting about 10 years ago, but aerobic digesters are simpler and served the purpose of those renovations, which was to reduce nitrogen and phosphorus in the effluent in order comply with stricter DEP regulations, Sinisi said.
Last month, ESG submitted a “preliminary audit” for the project, which the authority has been reviewing so it can determine whether to authorize an “investment-grade audit” — which would mean a commitment of authority funds for the first time, though not a commitment to actually do the project.
Board authorization could occur next month or even earlier, if a special meeting is warranted, officials said.
Project design could be done in the fall, permits obtained in spring, followed by a contract with ESG — and full commitment to the project, Balliet said.
If the project is ultimately constructed, it would require additional personnel to operate the plant, Sinisi said.
Mirror Staff Writer William Kibler is at 949-7038.