For the past 30 years, Penobscot Energy Recovery Co. has been crunching, grinding, shredding and burning all types of waste material, then quietly making electricity to be put back into the grid. The operation is not an easy one, and it involves big heavy machines, conveyors, magnets and furnaces that run at 1,600 degrees.

As part of Orrington's annual Old Home Week celebration, PERC offered plant tours July 21 that show how waste is converted to electricity within the massive complex.

Maintenance Supervisor Matt Albert explained to visitors that when garbage is burned, it makes steam that powers a turbine and then ultimately creates electricity — a chemical-to-electrical conversion.

But how, logistically, does this happen?

Trash is unloaded and piled high in one area of the complex where large loaders collect and dump the waste into a new grinding machine known as "The Terminator." The Komptech 6000 is a slow-speed grinder that can handle all kinds of waste and turn it into smaller, more manageable material.

From this large grinding room, the material is placed on a conveyor that moves the waste to another grinding and shredding station where metals are magnetically separated, and then to another grinding and shredding station, each one making the material smaller.

After the waste resembles the consistency of crushed leaves, the material is transferred through a conveyor to the furnaces, where it is burned and the heat creates steam.

On this day, one boiler was down for maintenance so the plant was at half-capacity, or producing only 10.2 MW per hour, Albert said.

The equivalent, he said, would be similar to "powering about 8,000 average homes."

PERC has signed contracts with 43 towns for their municipal solid waste, according to Ted O'Meara, who handles corporate communications and public affairs for the company.

Another nine towns send their municipal solid waste to PERC under contracts with private waste haulers.

In addition, there are towns that send their oversize bulky waste — things like carpet, tires, shingles and brush that aren’t part of regular municipal solid waste — and demolition waste to PERC. The company also has contracts with several private haulers for commercial waste.

According to its website, PERC is developing new options for the future that will help reduce waste and increase recycling.