Compost in city parks and golf courses saves the money on fertilizer, reduces water usage

Wastewater Superintendent Keelan Yarbrough describes the inner workings of the belt press filter that compresses treated biosolids for composting.

Wastewater Superintendent Keelan Yarbrough describes the inner workings of the belt press filter that compresses treated biosolids for composting.

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Rows of biosolid used to make compost line the ground at the Hilltop Wastewater Treatment Plant north of Kingman.

“I think we’re doing our part to make the city better. This is far better in so many ways that outweigh the negatives.” - Mike Meersman Parks Director

Your feces is making Kingman a prettier place to live – and saves the city money.

The City of Kingman has joined many other cities in using locally made compost in city parks and golf courses. The process is tightly regulated, saves the Parks Department money on fertilizer, reduces water usage and keeps otherwise discarded biosolids out of the Mohave County Landfill, saving the Public Works Department money by avoiding dumping fees.

Concerns were brought to the Daily Miner’s attention over the use of human waste in compost. They were well warranted, but harmless.

Wastewater Superintendent Keelan Yarbrough, Parks Director Mike Meersman and Public Works Director Rob Owen provided a tour of the Hilltop Wastewater Treatment Plant and explained the compost process.

The Cycle of Waste

Both the downtown and hilltop wastewater treatment plants produce biosolids from solid waste (feces, organic matter from garbage disposals) sifted from the nearly 2 million gallons of combined effluent they receive and treat on a daily basis.

The approximately 1.8 million gallons of sewage that pass through the hilltop plant each day are pumped, strained and aerated through a series of filters and tanks. Toward the end of the process, the solid waste, or sludge, is pumped to a separate tank and into a belt press where the sludge is mixed with polymer and squeezed into a thick, mud-like consistency. The biosolids are then trucked to a field at the plant where they sit in piles to dry out and cook off pathogens.

“It’s all about polymer dosage, water dilution and belt tension,” Yarbrough said of making an effective compost.

Biosolid samples are regularly taken to labs in Phoenix and Bullhead City to test for remaining fecal matter or other harmful pathogens. Safety guidelines are set by Arizona Department of Environmental Quality.

“If the samples are over the guideline, we start the process over and resample before we let compost off this facility,” Yarbrough said. “Have we had them not meet the criteria? Yes. We remix and reintegrate them with other biosolids and then resample them.”

Yarbrough did not have an official number on how often the plant has had to remix samples.

When the samples are deemed safe, the biosolids are then mixed with wood chips from local tree trimmings and separated into more piles for further fermentation before being hauled off for use at parks and the golf course.

In 2016, the two treatment plants produced 2,214 dry tons of biosolids. Approximately 380 of those were spread amongst the grass and plants of the 100 acres of city parks and 90 acres of Cerbat Cliffs Golf Course. There are about 4,300 dry tons of biosolids and compost stored at hilltop facility right now.

“The parks have used some, but we’ve produced more,” Yarbrough said.

City Benefits

Meersman said composting is one of the nation’s oldest recyclables and is extremely environmentally friendly, transforming a byproduct into a highly effective fertilizer. He used to use Milorganite, a commercially manufactured fertilizer, but switched to compost when he realized the benefits to the city.

“No mined resources or fossil fuels are used in its production,” Meersman said. “Our city saves tens of thousands of dollars by not having to haul the byproducts from the city’s waste water treatment plant and wood chips to the landfill.”

The Parks Department saves up to $70,000 annually using compost verses industrial fertilizers it would have to purchase. Meersman said they use the compost for its fertility and slow decomposing organic matter, and the compost contains essential plant nutrients the grass uses the nutrients over a longer period of time. Compost contains 85 percent organic matter, which promotes beneficial microbial activity and improves the soil’s ability to grow and nurture grass and plants. Because it doesn’t leach, it is ideal for sandy, rocky soils. 

“With the use of compost from the city’s wastewater treatment plant, we have been able to improve the turf quality substantially,” Meersman said. “The wood chips are slow decomposing organic matter, which are almost nonexistent in the soil in our area. They also hold moisture which works well in the desert.”

Roughly 2,000 tons of biosolids are produced between the two treatment plants each year, which would go to the landfill had the Parks Department opted not to use them. That would take up space and cost money. At the current cost of $34 per ton dumping fee, Yarbrough estimates the city saves about $75,000 annually in landfill tipping fees.

At the plant, the raw biosolids had a slightly unpleasant odor, but nothing overpowering. Once mixed with the tree trimmings, the compost smelled no worse than a bag of fertilizer from Home Depot.

“We feel that the savings from transportation and land fill cost, fertilizer cost savings, improved turf quality, and the positive impact on the environment far outweigh the minor inconvenience of the odor,” Meersman said. “While there is a slight odor to the compost, once it’s applied and watered, in a day or two it’s rarely noticeable.”

Kingman’s budget, parks and residents all come out winners.

“I think we’re doing our part to make the city better,” Meersman said. “This is far better in so many ways that outweigh the negatives.”