Only the Best

The staff in Kelowna, B.C., makes a success of composting with a fine-tuned process and state-of-the-art equipment that supports best management practices

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The City of Kelowna learned a critical lesson about composting: It pays to do things right. A newly upgraded composting facility now yields an extremely high-quality end product prized by landscapers, nurseries and home gardeners.

The product, called Ogogrow, has seen increasing sales every year since it was introduced in 1995. The new facility has significantly enhanced the composting process while eliminating odor issues and improving community relations.

“The community has been very supportive,” says Gordon Light, organics supervisor in Civic Operations, Utility Services. “We are in a geographical area with very little rainfall and poor soils. We make the highest-quality compost possible, and our customers can see the difference our compost has made to their lawns and gardens.”

Down in the valley

Kelowna lies in the Okanagan Valley in south central British Columbia, with mountain ranges on each side. The economy is based mostly on the tree fruit industry and, more recently, vineyards. In addition, the 80-mile-long Okanagan Lake attracts numerous tourists for summer recreation.

The 9.5 mgd (average flow) Kelowna Wastewater Treatment Facility is led by plant supervisor Mike Gosselin, operations foreman Frank Valentim, maintenance foreman Brian McAuley, and instrumentation/electrical foreman Doug Tomlin.

The plant uses a modified Bardenpho process (Ovivo) with three-stage biological nutrient removal. The process consists of two large treatment trains with 14 cells and two smaller trains with seven cells. The wastewater flows through anoxic, anaerobic and aerobic zones that together convert ammonia and nitrate to nitrogen gas.

Effluent from the secondary clarifiers flows by gravity to six cloth media filters (Aqua-Aerobic) that backwash to the headworks. The disinfection system (Trojan Technologies) uses low-pressure, medium-intensity UV radiation. Final effluent is discharged to Lake Okanagan.

Sludge from the primary clarifiers is thickened in one of two circular fermenters. Waste activated sludge from the bioreactor is thickened in three dissolved air flotation (DAF) units.

The thickened sludges are then pumped separately to the dewatering building, where they are blended with polymer and centrifuged into a cake at 18 to 20 percent solids. Bioxide (Siemens Water Technologies) is added to the centrifuged cake before trucking to reduce odor during transportation. The composting facility receives 29,500 wet tons of biosolids per year.

Making progress

Kelowna has composted biosolids for about 30 years, largely because the local geography makes land application impractical. “There are no large farms in the valley,” says Light. “The valley is narrow and densely populated, and land values are high. To find suitable locations for land application, we would have to drive far up into the mountains.”

During the 1980s, the city managed biosolids by combining thickened primary sludge and thickened waste activated sludge in a vault, then trucking it at about 3 percent solids to a holding pond at the local landfill.

The anaerobic composting process used then was inefficient and had odor issues. The biosolids were mixed with hog fuel (wood waste from the forest products industry) and placed into aboveground pits. The biosolids were simply allowed to soak into the woody material. After about a year, the pile was turned and again allowed to sit.

Soon after Light took charge of the process in 1994, the city moved the composting site to a rural location on leased land and switched to an aerated static pile process using positive aeration. The process lacked odor and drainage controls. In 2006, the city created a new composting facility about 18 miles north, owned jointly with the City of Vernon, a community of about 30,000.

“Before we built the new facility, we conducted a value engineering workshop,” says Light. “We invited experts from the industry to Kelowna, spent a whole day with them, and went over more than 100 possible biosolids management technologies. Out of that meeting, we re-confirmed that composting was the best way for us to go here in the Okanagan Valley. It was the most cost-effective, and the compost provided a source of revenue as well as a benefit to the environment.”

The new site receives biosolids from both communities, trucked in by private haulers. Kelowna operates the facility, which uses an extended aerated static pile process with both positive and negative aeration.

“One reason we chose this process is that it’s very compact compared to a turned windrow process,” says Light. “You can do it on a postage stamp.” The facility occupies about 30 acres. The process uses best management practices (BMPs) as outlined in the province’s Organic Matter Recycling Regulation.

Striving for excellence

Light’s staff at the compost facility is led by compost technician Marcia Browne, who is responsible for day-to-day operations, assisted by Level 1 compost technicians Morgan Lewis and Jerremy Kozub. The team also includes equipment operator II Shaun Runnett and loader operators Denis Goulet, Brad Crowell, David Irwin, Shane Prosser, and Art Malieapaard.

The process has seen steady improvement since the move to the new site. Arriving biosolids are emptied into a bunker inside a building. There they are picked up by a front-end loader and placed in a batch mixer with hog fuel and some overs (coarse wood particles) from the final compost screening process.

“We have a specific recipe we follow,” says Light. “The mixers have load scales on them, so everything is measured by weight. We add water as needed.” The mixture is taken outside to an aeration system supplied by Engineered Compost Systems (ECS). The material is placed on two 88- by 610-foot concrete slabs with built-in aeration trenches about 4 inches wide, spaced about 5 feet apart and running the slabs’ full length. Each slab is divided into 18 zones that are individually controlled by an automated process.

The trenches are covered by stainless steel covers perforated with thousands of quarter-inch air holes. “We supply a soft flow of air, at a pressure of perhaps 2 inches of water column,” says Light. “If you blow air too hard, you tend to channelize it — the air finds the quickest route through the pile, and you don’t get the most thorough aeration.”

For the first few years, while the final compost product was well received in the market, the process was not achieving BMPs, mainly because the active compost area was too small. “We weren’t keeping the product on air long enough, and our piles were too high because we were trying to compensate for lack of aeration floor area,” says Light.

“The taller piles caused compaction. In addition, we needed a better watering system to maintain biofilter moisture; and we needed an insulating layer over the tops of the piles. An expansion completed in 2010 resolved those issues: It tripled the aeration space and improved the watering system. The upgrade enabled an increase in aeration days to 21, from 10 to 14 days previously.”

Approaching the ideal

In the current process, the initial mix is covered with mature compost (or overs) to provide a biofilter (while the system is in positive aeration mode) and an insulating layer to keep surface temperatures hot. “Bacteria in that layer consume the odorous gases — mercaptans and sulfides — as they pass through,” Light says. “Maintaining that layer in a proper biological state is the key to odor control.”

Primary composting proceeds for 21 days with alternating positive and negative airflow through the piles. “We have the ability to blow air into the pile from below and draw air in from above,” says Light. “The air in this region is very dry, and if we only blow air in from below, the pile can dry out. Also, in winter, the blown-in air can cool the area where the air is introduced.

“With positive and negative airflow, each time the cycle goes into a positive mode, the heat and moisture go up in the pile. In the negative mode, the heat and moisture go down. So with our process, we’re moving air up and down through the piles many times a day. It’s a far superior system.”

After 21 days of aeration, the piles are torn down and the material is repiled on another section of aerated floor to compost for an additional 31 days (secondary composting phase). That material is then screened to one-half-inch particles and put in rows for final curing. Each windrow is tested for fecal coliform and salmonella in accord with the Organic Matter Recycling Regulation.

The resulting approved biosolids compost product is sold to bulk buyers, including landscapers, nurseries and value-added customers. “To control odors at our compost facility we first monitor odor levels on site,” says Light. “Then through odor modeling equipment, we can determine the strength and direction of odors.” The facility uses the OdoWatch system from Odotech.

Building the brand

When Kelowna began marketing Ogogrow, the product had a negative perception. The anaerobic process had created a low-quality product that contained objectionable items like condoms and tampon applicators that did not break down in the composting process. While the city improved its process, Light attended conventions held by the Northwest Biosolids Management Association and learned how to approach marketing.

“We decided to go with a gatekeeper program,” says Light. “We solicited support from specific people in provincial Ministry of Environment and Ministry of Health, and with local nurseries. We spent time with them to explain our program and answer their questions about the product’s safety and efficacy. Then I began marketing the product, first by taking it out in a little pickup truck to landscapers and nurseries and finding out what they would like to see in a final product.”

Light went on local radio programs to promote Ogogrow, and when people called with questions, he not only answered but also referred them to the gatekeepers. “People might call in and say, ‘It sounds like a good idea, but is it safe?’” Light recalls.

“I would reply that we were doing everything in accord with the provincial regulations, but they didn’t have to believe me — if they had concerns about health and safety, they could contact this person at the Public Health Office.

“You know what? Our gatekeepers never got any calls. It was a very good way to introduce the product. I always stressed the process, because it’s the process that makes the product safe. We maintained a positive outlook and kept our messages clearly in mind, and the program went off without a hitch.”

Pleasing customers

As soon as prospective customers saw the quality of the product, the tiny loads Light took out on his marketing missions turned into large and repeated orders. The material is sold on a graduated pricing schedule, ranging from $19.50 per cubic yard for the first 50 yards ordered, to $7.75 per yard for at least 5,000 yards per year.

The vast majority is sold in bulk to landscapers and nurseries. About half of all the compost goes to one customer, Lake Country Compost Distributors, which reprocesses it to create higher-value products sold under the Nature’s Gold brand.

Some compost is trucked to a local landfill where consumers can buy it in bags supplied by the city. “We don’t want to become a big retail outlet because we’re in business with many other companies that also sell the material on the retail market,” Light says. As of November 2010, the city was expecting as much as $600,000 in compost revenue for the year.

“We have an incredible market, and we have a hard time keeping up with demand,” Light says. “When customers describe the product, we hear words like ‘amazing’ and ‘unbelievable.’ We get only a couple of complaints per year, usually associated with weed seeds. We believe the more fertile soil created by the product leads to the germination of weed seeds from other sources.”

Besides marketing Ogogrow as a fertilizer, Kelowna uses it in its water conservation program. The material is top-dressed to residential lawns at a reduced price, and it decreases the water consumed for irrigation.

Light advises communities considering composting to do their homework. “The best advice I can give is to make sure you have done a thorough site evaluation, including odor modeling,” he says. “Make the highest possible quality product, and try to have a continuous supply.”



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