Spinning Compost into Gold

Kim A. O'Connell

Good news in one area of the waste business -- for instance ample landfill capacity and the accompanying relatively lower disposal fees -- can spell trouble in another area of the waste business, such as for disposal alternatives like composting. Composting has other competitors for the trash, too.

Florida, for example, has a significant infrastructure and capacity for waste incineration. Therefore, its communities must make greater efforts to encourage composting and to stimulate compost end-markets.

Pioneering Efforts

More than a decade ago, one south Florida community, the Solid Waste Authority (SWA) of Palm Beach County, realized the benefits of diverting organic waste. Responsible for managing and disposing of the solid waste generated by the county's approximately 1.2 million residents, the county began composting in 1991 and opened its current facility in 1994, accepting residential yard waste and sludge from local wastewater treatment facilities.

The county generates in excess of 2.2 million tons of waste, according to a 1995 report. Of that, it accepts about 200,000 tons of yard trimmings collected curbside and 60,000 tons of biosolids collected at wastewater treatment facilities per year.

In recent years, however, the county has had difficulty handling the growing influx of organics in its composting operations. Spreading the material and removing contaminants were particularly labor-intensive, and the facility's grinding and screening system could not always keep up with the material flow. All equipment was mobile and independently operated, which led to operating inefficiency and incompatibility.

“We basically had a hodgepodge of equipment over the years,” says Patrick Byers, SWA assistant director of composting and vegetation services. “It's difficult to purchase mobile equipment that matches each other and that's large enough to do the kind of processing we're talking about. You have to inspect and remove the contamination, you have to dry and grind the material and reduce its size, and you have to have some quality control on screening the material.”

To alleviate the problem, the county began designing and building one of the first integrated stationary woody waste recycling systems in the country.

A One-Stop Shop

The county sees the reason to compost as simple. “You don't want to put sludge and yard waste into a landfill,” says Michael Perrotti, SWA's compost manager. “It takes up 20 to 25 percent of your capacity, and it breaks down so fast that you'd have pockets [in a landfill].” Furthermore, there is plenty of yard waste to be had in south Florida, Perrotti adds. “Everything's growing 12 months of the year.”

In 1991, SWA first began composting with a 30-ton-per-day pilot plant with one material agitator and four composting reactors. So successful was the test that in 1994, the county opened its current facility with nine agitators moving feedstock into 36 compost reactors. The woody waste recycling and composting processes both take place at the 1,400-acre North County Regional Resource Recovery complex.

Yet the work involved a long and inefficient system of spreading out the feedstock, manually removing contamination, stockpiling the material for a four- to six-week drying period, grinding and screening. The SWA soon noted that other recycling facilities were doing things more efficiently.

“We realized that there were options out there,” Byers says. “Through discussions with colleagues in the industry, I realized that there are systems that are integrated that are doing other types of recycling, such as demolition debris recycling. It wasn't too difficult to sit down knowing the processing and pencil out a conceptual idea.”

After bidding out the process of researching, acquiring and installing a new system, the county chose RRT Design and Construction, Melville, N.Y., to evaluate the current operation, provide equipment and construction specifications, estimate costs and develop concept drawings. RRT then chose Continental Biomass Industries (CBI), Newton, N.H., to supply equipment for the all-new system.

“RRT had a lot of experience in materials management for C&D and curbside collected recyclables,” Byers says. “So they were able to take that knowledge and pragmatically apply it to a yard waste situation in south Florida.”

CBI, Byers says, helped the county by custom-building an integrated system with a prescreener, picking station, grinder and starscreen system.

System Savings

In the new system, organic material first enters the process in the prescreener, which acts as a feed hopper and screens out three-inch material, which then can bypass the picking station. The picking station allows workers to remove contamination such as plastic, rock and metal. After foreign objects are picked out, the material moves into the grinder, which is powered by a 1,050-horsepower Caterpillar engine, and then through the multi-deck starscreen, which allows material to waterfall over each of the decks. This helps to separate fine 1-inch material from the “overs” product, which is a boiler fuel that goes to a waste-to-energy plant.

Once screening is complete, the material is mixed with biosolids from local wastewater treatment plants and mechanically agitated during a minimum 14-day cycle. Compost curing takes place in an IPS system supplied by U.S. Filter, Palm Desert, Calif. Biofilters are designed to help contain odors in the enclosed system.

Then, the resulting compost is delivered back and put through a bivi-Tec wave screen made by Aggregates Equipment Inc., Leola, Pa., and processed into various product grades. The facility currently screens compost from 1/4 inch to 1¼ inches in size.

The new woody waste recycling system went into operation in October 2000, and already is showing efficiency improvements, Byers says. Previously, three loaders and one grapple, each with their own operator, and eight temporary employees were needed to process materials. Now, only one loader and one grapple (with one operator each), as well as four temporary machinery employees are needed. The production capacity of the new system is between 50 and 60 tons per hour of feedstock.

The facility has about seven full-time employees, working 10-hour shifts. The facility is open 10 hours a day, six days a week. And the new design has helped the county achieve a 40 percent savings in operating costs, going from $1.65 million before the new system to about $1 million now. The savings incurred are considered to be enough to recover the capital expense of the new system in five years, Byers predicts.

“We reduced the amount of steps needed to handle the material, and the equipment was matched up in throughput capacity,” he says. The facility also has supplemented its new stationary system with new mobile equipment, including a log loader by John Deere, Moline, Ill., five rubber-tired loaders by Case Equipment, Lexington, Ky., and a telescoping lift by JLG Industries, McConnellsburg, Pa.

After creating the custom integrated processing system for Palm Beach County, CBI started building stationary integrated systems for other customers, too, Byers says.

Spreading it Out

Yet the best composting system in the world can't create viable end-markets for compost. And Palm Beach County recognizes that in south Florida, composting markets are still young and growing.

“It's difficult to market low quality compost in south Florida,” Byers admits. “There are substitutes that you have to compete with, such as Florida peat. The difficulty comes in convincing the customer that compost has better qualities.”

Typically, the agricultural community in Florida is accustomed to growing their products in sand and having to heavily fertilize crops, Byers adds. “A transition to an organic material is fairly expensive for an agricultural operation, so volume markets don't exist very well as far as the agricultural community goes.”

Compost is increasingly being used as a substrate for a soil amendment for various horticultural or landscaping projects, but products are not heavily used in transportation beautification projects, Byers says.

“The state enacted a recycling rule that made it mandatory to recycle, but in the case of organic products, [there aren't] enough teeth in the rule to promote the use of those products by the state,” he says. “So the Department of Transportation has sporadically gotten involved in using the products, but not on such a large scale as other states have.”

The good news, Byers says, is that because Palm Beach County is a resort community, more and more golf clubs are buying compost — a promising trend considering the area has more than 150 golf courses. Additionally, the SWA has one built-in customer — the Palm Beach County government. “We knew we had a lot of uses for it internally,” Byers says. “Obviously our long-term goal is to generate a market that would produce revenue.”

Setting the Standard

Even as it works to stimulate markets for compost, Palm Beach County is continuing to ensure that its facility maintains the highest safety and public health standards. The facility tests for the presence of fecal coliform every week, for example, and routinely sends its employees for additional training. “Nothing leaves this site unless it's tested,” Perrotti says.

The SWA also will continue to upgrade facility equipment as technology advances and compost markets continue to expand. For instance, the SWA recently added more horsepower to the grinder and is looking to add a magnetic device to the system to better ferret out metals.

“We do need to add something to the system to improve the ability to sense metal, such as rebar and axles from cars, which do cause damage to the equipment,” Byers says. “But we can do something about it at a certain point in the flow. You just don't have that ability with the mobile equipment. An integrated system gives you the option of adding these different components and making it efficient.”

In the end, the Solid Waste Authority recognizes that composting is a natural process. “Composting has been around for a very long time,” Perrotti says. Palm Beach County is just helping nature take its course in a more efficient and effective way.

Contributor Kim A. O'Connell is based in Arlington, Va.