Another Way to Deal with Sludge

With Scott Bradford's experiments with our own sludge in mind, I arranged to tour the Fairbanks Wastewater Treatment plant just before dawn Wednesday. (That was 8 AM here!)

Sludge is what is left after as much water as possible has been extracted from sewage. It has value, if properly treated, as a soil amendment. Treatment requires combining it with sufficient carbon and air so that it heats up thus killing any pathogens. Scott has treated sludge on a small scale producing vital compost. He tests it every which way to confirm that it is free of toxins, and by the way, it smells great.

Fairbanks, according to the plant operator, has the only installation in the state, and maybe the country, that treats 100-foot long windrows of sludge. I had to see it.

Once sufficiently de-watered, the operators use front-end loaders to mix sludge with large wood chips. Next it is laid down in 5-foot high 100-ft. long piles. The pile is fed with as much air as required through a blower system. Temperature probes are inserted. The pile is "done" after it maintains 131-degrees F for 3 consecutive days. There is no external source of heat. Biology does the trick. The piles "work" year round, despite deeply cold Fairbanks winters.

The piles are built on asphalt pads designed to capture any leachate from the "cooking" sludge and direct it back into the plant for treatment. The Fairbanks plant is a secondary treatment plant and delivers its effluent back into the river.

In the spring, gardeners and landscapers arrive with pickups and take away the sludge-turned-compost for $10 a pick-up load. And soon, after the cabbages, carrots and lettuce are harvested and consumed...the process begins all over again.

When this innovation was introduced in the late 90s, Northland Lumber was looking for a way to dispose of its chips and was delighted to deliver chips for free. However, now that the value of the chips is apparent, and the need determined, Northland dedicated equipment and time to harvesting trees just for chips. The treatment plant now buys chips, but in the process a small local industry has been created.

The large chips are screened out of the compost and used by the plant over and over again.

As we examine our own wastewater treatment system, I think a road-trip to Fairbanks might be in order!