|Written by Greg Ruland|
|Tuesday, 29 November 2011 00:00|
There are many ways to describe what the Cottonwood Wastewater Reclamation Plant processes, but city workers call the end product “biosolids.”
Farms across the state call it fertilizer.
Utilities Administrative Manager Roger Biggs calls it Play-Doh and produces a sealed plastic baggie containing a clump of the thick, dark mud to prove his point.
It moves between the fingers like Play-Doh. It smells like fresh-turned sod.
It grows nonfood crops in abundance, like at a farm in Camp Verde and another in Buckeye, Biggs said.
It is, in fact, the B-grade product of the city’s primary reclamation plant, located at the 1100 block of West Mingus Avenue.
But does “poo” by any other name smell just as sweet?
Not really. What comes into the plant and what goes out are two significantly different materials, each with their own distinct aroma.
What comes in from five sewage lift stations around the city amounts to about a 1.5 million gallons per day of wastewater from every sink, toilet and drain of nearly 5,000 customers.
When it arrives, the sewage is stirred and kept in holding tanks where natural processes break it down. Insects play a key role, Wastewater Superintendent Debbie Reitkreutz said.
Next, the chocolate-colored slurry is spun through a centrifuge where treated liquid, or effluent, is separated from treated biosolids.
The centrifuge machine is located on a second story of a building with a 20-yard container, positioned on rails for ease of movement, located directly below it. “Dewatered” sludge falls from the centrifuge directly into the container, Reitkreutz said.
Finally, the effluent is pumped to irrigate about 80 acres of city-owned land and most of the biosolids are trucked to private nonfood farms as fertilizer, she said.
In 2010, for example, D&K Farming Enterprises applied 1,261 tons of biosolids to land and carted only 210 tons to Waste Management’s Grey Wolf Landfill, according to city records.
Responsibility for trucking the city’s biosolids this year again went to D&K Farming Enterprises, which has operated under contract with the city for the past three years.
D&K’s bid to do the work — a charge of $55 per ton for landfill loads and $53 per ton for loads applied to the land — was accepted by unanimous vote of City Council on Nov. 15. D&K’s was lowest of the two bids offered.
The contract, which expires in October 2012, can be renewed twice for one additional year. The contract includes a 3 percent increase in the per-ton rate for each year it is in effect.
The mud-like B-grade biosolids Biggs displayed during a tour Thursday, Nov. 17, represent a very small percentage of the plant’s total output compared to the A-grade effluent it pumps, he said.
It is nevertheless a significant amount. D&K could be called on to cart as much as 40 tons of biosolids from the site per day, according to the contract.
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