Cold Can't Stop Alaska Sewage Composting
FAIRBANKS, Alaska Environmental consultant Mike Pollen remembers standing on a pile of sewage sludge composting outside the Fairbanks treatment plant on a November day in 1997. The temperature was 40 degrees below zero but his feet were warm. Then sweaty. Then uncomfortably hot inside his insulated rubber boots.
"They felt like they were going to melt," he said.
He figures there was a 180-degree difference between the compost cooking at his feet and the frosty temperature freezing his head.
Prevailing wisdom said sludge composting wouldn't work north of North Dakota. Pollen, the author of several wastewater system training manuals used in Alaska, remembers turning to a utility official and remarking, "You know what you just did? You just rewrote the textbook."
Over the years, utility officials in the community 120 miles south of the Arctic Circle continued "aerated static pile composting" and now turn waste from 87,000 residents into a product so highly desired they can't make enough to satisfy requests from gardeners and landscapers who want to amend their sub-Arctic soil.
"It's something we think is a big hit," said Dave Dean, support services manager for Utility Services of Alaska.
The compost, cooked in beds bigger than football fields, has the Environmental Protection Agency's highest rating. Cooperative extension officials recommend it for growing vegetables as well as flowers and grass.
The price is right -- just $15 per pickup load or $5 per yard dropped into dump trucks -- and it's free to anyone with a shovel and a trash can.
But merely getting sludge off the premises has been a triumph for the second largest community in Alaska, where winter routinely lasts seven months and the severe cold can make life miserable for microbes.
Sewage sludge is the solid material removed from water that flows into a treatment plant -- 15 gallons at a time from a dishwasher, 31.5 gallons per 6.3-minute shower, 1.5 gallons per flush.
Treatment plants strive to separate solids from liquids, then deal with each separately.
Rich in nutrients, raw sludge also can be filled with dangerous pathogens or heavy metals that must be addressed before it can be applied to fields, burned, or even buried in a landfill.
There are plenty of ways to neutralize human waste but utility companies are constrained by time, space and money.
If they choose a process that's slow, they end up stockpiling sludge, where it's attacked by anaerobic bacteria that produce offensive odors. For many aerobic processes, abundant space is needed, unless a utility has cash for equipment that can speed or automate decomposition.
The Fairbanks plant itself is designed for the cold. It's one of the few in the country that's fully enclosed, allowing treatment in huge tanks all year round. The plant pumps pure oxygen into its digester, speeding the work of helpful bacteria that turn raw sludge into digested sludge.
In the early 1980s, when the EPA enforced new water quality laws, Fairbanks was banned from hauling digested sludge to its landfill. The utility, then owned by the city, instead merely stored it outside the plant.
When the utility ran out of storage space, it built a lagoon with 20-foot high walls. That filled up too, and utility officials launched a half-dozen attempts to address their sludge trove.
A contractor burning pure sludge produced putrid clouds that hung near the ground during winter temperature inversions. Operators tried mixing sludge with lime, which neutralized the pathogens but made a product that had the consistency of toothpaste and wouldn't mix with soil.
Finally, just before the utility was sold to private investors, operators began experiments with composting.
Digested sludge is run through a press to mash out water. Still, the sludge is 80 percent liquid when it's moved outside by conveyor to a dump truck.
That's where Jeff Karrick, one of three full-time compost operators, comes in. Karrick is a master of mega-mixology with a front-end loader, his measuring cup a 4-yard bucket, his "bin" the flat ground outside the plant.
Like any home composter, he mixes digested sludge, a "green" material rich in nitrogen and phosphates, with a carbon source that feeds bacteria, provides bulk to let in air and absorbs moisture from the sludge. The utility uses fresh wood chips obtained from the only sawmill in the Fairbanks North Star Borough, plus partially decomposed wood chips screened from older compost piles.
Karrick dumps 16 yards of used wood chips onto 16 yards of new chips, then adds 14 yards of sludge. With his heavy equipment, he attacks the pile from all sides, lifting, dropping and mixing until the material is homogenous. Then, on top of perforated pipe that delivers air, he stacks the mix against the main pad, creating a massive 9-foot-high sludge and wood chip cake that when completed will be 120 feet wide and 360 feet long.
Operators frost the top and sides with 2 feet of composted material. The topping keeps odors and nasty clouds of blowflies at bay.
"That's our biofilter," Karrick said.
The extra layer is also the key to the success of cold weather composting, said Nora Goldstein, executive editor of BioCycle magazine and a member of the Water Environment Federation, a national nonprofit organization focused on clean water.
In the extreme cold, Goldstein said, bacteria could slow or shut down. That's not bad, unless it forces a utility to stockpile sludge.
"So much of that depends on the composition mix and the insulation of the pile," she said.
Temperature probes detect some cooling in the coldest weather but extra fresh wood chips keep the pile hot enough to let operators add to the pad all winter long -- and never stockpile sludge.
EPA requires the compost to cook at 104 degrees for 14 consecutive days. For three consecutive days, the temperature must reach at least 131 degrees so pathogens will be killed.
The highest temperature recorded in a Fairbanks pile was 206 degrees.
"I'm thinking of digging a hole and dropping a pig in there," Karrick joked.
When the piles attain the required temperatures, the stack -- now just 8 feet fall because of the shrinkage in the composting process -- is run through a screening machine to take out wood chips that didn't process.
EPA allows up to 1,000 fecal coliform bacteria per gram dry weight of compost. Tests of finished compost often don't detect any. Fairbanks has little manufacturing and solids entering the plant contain little heavy metal such as arsenic and lead. The official EPA rating for the compost is "exceptional quality."
The product has been around long enough that most gardeners have overcome their repugnance of using a product made from human waste.
Michele Herbert, land resources agent for the University of Alaska Fairbanks Cooperative Extension Service, recommends the compost to gardeners and has used it herself to grow vegetables, mulch perennial beds and landscape.
"It's crazy, the stuff is so good," she said.
In contrast, the city had to pay more than $400,000 to neutralize and move the 50,000 cubic yards of sludge that had accumulated over 20 years before a solution was found.
Dean, the utility support services manager, said the company is not making money off compost. It charges enough to defray its cost of loading.
But operators are clearly proud that they've solved their sludge problem by taking something nobody wants and turning it into a desirable commodity.
Source: Associated Press