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AWA to start feeding digester food

Authority began process with sludge about two months ago

It could take up to a year before the newly built $35 million anaerobic digester at the Altoona Water Authority’s Westerly Sewer Treatment Plant becomes “revenue neutral.”

A long operational ramp-up is required, according to Aiden Murphy, director of performance assurance for Energy Systems Group, which built the digester and has guaranteed revenue neutrality long-term.

The authority began feeding the digester about two months ago with sludge from the plant and within days will start feeding it “high-strength” food waste that is far more potent in producing biogas to heat the digester and eventually a dryer that will transform biosolids from the plant and from client sewer utilities into innocuous Class A mulch.

The operational ramp-up needs to be slow and deliberate as the processes in the digester take hold.

In anaerobic digestion, bacteria break down organic matter in a sealed tank, producing biogas with a high methane content and “digestate,” which has both a solid and a liquid component, according to an Environmental Protection Agency web page.

Plant operators feed materials into the digester in a prescribed sequence, little by little, testing and evaluating, making sure that what is happening is “stable,” according to Murphy.

It started with the plant’s sludge, which was then supplemented with sludge brought in from client sewer plants, he said.

After the food waste from the first vendor comes at the end of this week, food waste from a second vendor will arrive in early to mid-January, Murphy said.

The effort will involve tinkering with what the plant accepts and with the blending and feed rates of material, Murphy said.

The judgment involved has been honed by training the plant crew has received, he said.

A boiler fired with commercial natural gas has been heating the digester, but eventually, the digester will produce enough biogas to enable workers to switch to the biogas boiler, Murphy said.

Later, there should be enough biogas to fire the dryer, which will process the authority’s own biosolids and biosolids for client treatment plants.

The authority has continued for now to spread its Class B solids on the fields of three farms.

The number of farmers willing to accept those solids has dwindled, as regulations on the material have tightened.

Mirror Staff Writer William Kibler is at 814-949-7038.

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