Waste Stream to Revenue Stream

A regional composting facility helps a Texas city and water district deal with waste management issues and create highly successful commercial products
Waste Stream to Revenue Stream
Shredded brush flies off the conveyor belt of the chipper (Vermeer.)

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The City of Killeen, Texas, and the Bell CountyWater Control & Improvement District No. 1 have turned biosolids from three wastewater treatment plants into a source of revenue with a composting facility that opened last summer.

The district’s Regional Compost Facility went into operation in August 2011 after navigating the state’s rigorous permitting process. Water district general manager Jerry Atkinson foresees a market that will consume all of the composted material produced out of biosolids from Killeen (population 128,000) and the U.S. Army’s Fort Hood (30,000). “We anticipate we’ll sell every bit of the product we have,” he says.

Most will be sold to contractors for seeding on Texas Department of Transportation highway rights-of-way after construction projects. Local landscaping contractors are also included in the marketing plan, and the district will reserve about 20 percent of the material for sale to local residents, who will have their choice of compost ($10 per cubic yard), chipped brush for mulch ($8), or a custom blend of compost with sand, clay and silt branded BioLoam ($13).

The district will also sell compost to wholesalers under a request for proposal (RFP) process. Wholesalers will be allowed to set up operations to package the material on site.

 

Big step forward

Composting is a major advance from the district’s previous practice of land-applying Class B biosolids on cropland and ranchland. Composting helped solve two problems: The district needed a new beneficial use for its biosolids after a land application agreement fell through, and Killeen was spending about $150,000 a year stacking and hauling brush to landfills.

In 2006, the Bell County WCID No. 1 began research on building a compost site to turn the biosolids and brush piles into a rich soil supplement — and ease the pressure on both entities’ budgets. Atkinson estimated that the two could save more than $200,000 per year.

After initiating talks with the city, the district in 2007 leased 20 acres of land Killeen had available at its waste transfer station, where brush was being stacked before being hauled to landfills. The key was to develop the compost facility without adding debt.

“We were worried about whether we had enough available funds to do this without borrowing any money,” Atkinson says. When the recession hit in 2008, he noticed that as large private building projects slowed and public entities began to tighten their belts, the demand for new construction dipped and costs began falling.

“I told the board, ‘Why don’t we go out for bids and see what we get back?’” he recalls. With a design from the Lockwood, Andrews & Newman engineering firm in hand, the district put the project out for bids.

The board was pleased when the low bids came in at $2 million for a 1,600-square-foot administration building, site preparation, and the primary composting area – a 13-acre concrete pad where biosolids would be mixed with wood chips and yard waste and windrowed. The composting equipment added $1.6 million, for a total of $3.6 million, well within budget.

 

Heavy volume

Site preparation was an important part of construction. The district contracted for tests to make sure the soil could support the compost facility and the product that would be piled on it. Planners also had to slope the site so that all runoff could be steered to three retention ponds on the property. A 1-acre pond at the front of the facility enhances its appearance, as does a functional windmill used to aerate the pond. Besides protecting the surrounding watershed from runoff, the ponds supply water for hydrating the windrows when needed.

The compost facility handles all biosolids from the district’s treatment plants. Two (the 38th Street Plants) are conventional aeration facilities built side by side and permitted for 18 mgd and 6 mgd maximum flow. The newest plant, commissioned in 2007, is a 6 mgd facility that serves the southern part of Killeen and is one of the state’s largest sequencing batch reactors. In recent years, in a prolonged drought, the three plants have generated an average of 190,000 cubic yards per year of Class B biosolids. “In wetter years, it will be more,” says Atkinson.

 

Certified quality

The district took steps to ensure acceptance of its product. After it was certified bacteria-free, the district was listed on the state DOT website as an approved compost vendor. The district also joined the U.S. Composting Council (USCC), and its compost has received the organization’s Seal of Testing Assurance (STA) certification.

Certification requires the district to have its products analyzed at least every 60 days at an approved testing facility. Samples must be tested for pH, soluble salts, nutrient content (total N, P2O5, K2O, calcium and magnesium), moisture content, organic matter content, bioassay, stability, particle size, pathogens, and trace metals.

The district also must certify that the biosolids going into the compost process comply with all applicable local, state, and federal regulations. The biosolids must maintain a Class B certification from the Texas Commission on Environmental Quality to comply with the STA program. “We’ve maintained that for years,” says Atkinson.

The quality of the biosolids coming out of the district’s treatment plants has presented minimal challenges. There is minimal heavy industry in the district and no food or animal processing facilities.

After the composting process, the material is rated as a Class A product. Besides STA certification, the district is sending its final product to another lab to evaluate its nutritive value. That information is important to commercial and residential customers. “We want to inform them of the nutrient content so they understand the application rates they need with our product,” Atkinson says.

 

Process control

Dewatered biosolids are collected in 25-cubic-yard roll-off containers at the wastewater treatment plants and hauled to the compost site by district employees. The plants produce an average of about 76 tons of material per day at 14 percent solids. Wayne Lovett, district wastewater superintendent, says the compost facility easily keeps up with the plants’ output: “Just as fast as we haul it, they can windrow it.”

At the site, the compost starts as a ratio of one part biosolids to one and a half parts brush. The brush is run through an HG 6000 horizontal grinder (Vermeer) to prepare it for composting. The building of a windrow starts with a bed of chipped brush 18 feet wide and 200 feet long. The first layer is slightly hollowed in the middle to help contain a layer of biosolids.

An operator drives over the two layers with a Wildcat CT718 windrow turner (Vermeer) to mix the two materials. The process continues with alternating layers of brush and biosolids until the windrow reaches a height of seven feet. The rows are seven feet wide at the top. There is enough room in the processing area of the site to build 21 windrows about 15 to 18 feet apart. Lovett estimates the facility will process 100 windrows per year.

Once a new windrow is fully stacked and mixed, it takes about four days for the material to come to a temperature of 130 degrees F as decomposition begins. The optimal temperature range for composting is 130 to 160 degrees F. District employees use probes to take and record the temperatures in all of the active windrows. This is important, Lovett says, because “it has to hold the temperature for 15 days” to eliminate any harmful bacteria.

After the compost has “cooked” for 15 days, it is fed through a Wildcat TR521 trommel screen (Vermeer) to remove pieces larger than 3/8 inch. Finished material is then piled in the curing area of the concrete pad to cool as the decomposition process winds down. Oversize material is returned to the raw brush and processed again to complete its decomposition.

The district estimates it will produce about 26,000 to 30,000 cubic yards of compost per year. After curing, a portion of the compost will be blended with sand, clay and silt from the site to create the BioLoam product.

 

Compost team

The site manager at the compost facility is Matt Atkinson. His staff includes two heavy equipment operators, Isaac Mercado and Anthony Robinson, as well as office worker Tammy Coleman. If business at the compost site gets hectic, two people from the district office have been trained to help with customer service. Jerry Atkinson and Lovett are also available to supplement the crew during busy times.

The facility is open to the public from 8 a.m. to 5 p.m. on Monday, Tuesday, Thursday and Friday and from 8 to noon on Saturday. Commercial trucks that come for loads of compost or BioLoam can drive to a loading area next to the windrows, where the district staff loads them with one of two Volvo front-end loaders, also used to move raw materials and finished product around the site.

Customers with trailers have room to pull in, turn around and back their trailers into the loading area. “We can load all types of equipment,” Lovett says. “And if someone comes in and just wants to get a couple buckets of material, we have a bin where they can fill those.”

The compost facility’s office can take payment by check, credit card or debit card. There is a minimum of $13 per transaction. Although a customer buying compost or BioLoam by the bucket may not take home a full cubic yard, “Compared to buying a bag in the store, they’re still going to save all kinds of money,” Lovett says.

 

Compost showcase

After several months of operation in fall 2011, the compost facility attracted a small crowd of residents to a chilly open house and tour in early December 2011. The facility has been well received, and workers have noted big interest in the BioLoam and regular compost. “It’s been looked at very favorably,” says Atkinson. “It’s been a win-win situation for the district and the city, and the public is impressed at two government entities working so well together.”



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