An aging materials-recycling facility is like an aging car in many ways. It may cost more to run and to repair than a newer model, may not perform as well, lack today’s advanced convenience features, and look old (which could become an issue with the neighbors).

By George Leposky

A material recovery facility (MRF) built a decade or so ago may suffer from one or more of the following shortcomings: design flaws that detract from the facility’s performance, measured against today’s standards and even, in some cases, against the designer’s original projections; deterioration of the physical plant and equipment over time; and inadequate capacity to accommodate an increasing volume of solid waste being generated in the facility’s service area.

When your car gets too old to tolerate, you trade it in on a newer model. Replacing an aging MRF should be an equally intuitive decision. But the cost of building a new MRF from scratch and finding a site where the neighbors won’t object to its presence can be daunting. Instead of trying to surmount those obstacles, some public and private solid waste managers are finding ingenious ways to extend the life and improve the performance of existing MRFs.

According to Christian LaPointe at Machinex Industries of -Plessisville, QB, “As a result of increased tonnage, more MRFs are now looking into the effectiveness of their processes (less than 500 MRFs are processing most of the current MSW recycled in the US). Better engineered processes and maximum quality throughput are standing as ‘standard operation’ in our industry today.

Existing processing facilities are already embracing conversion plans from multisorts to one-stream operation. Single-stream plants shouldn’t stand still either, since new mechanical screen performance and latest technological innovations—such as optical recognition equipment—are available.”

Following are three case studies of existing MRFS that have gained a new lease on life at a fraction of the cost of new construction.

Rebuilding in Rockland County
Rockland County, NY, was in the midst of a growth spurt when its Solid Waste Management Authority (SWMA) began building a MRF in 1995, using technology from Macpresse International Srl, an Italian firm represented in the US by Sierra International Machinery LLC, in Bakersfield, CA.

Located across the Hudson River from Westchester County and just north of the New Jersey state line, Rockland County experienced an 8.8% increase in population in the 1990s, from 265,475 in 1990 to 286,753 in 2000. Three years later, the 2,000-square-mile county’s population was estimated at 292,989, up an additional 2.2% from 2000.

The MRF, however, was not keeping pace. Its design had some inherent deficiencies.

The container line’s long, low-tech infeed conveyor was relatively narrow by today’s standards, with a 30-inch magnet to capture ferrous metals; everything else required manual sorting.

The plastic extracted from the waste stream was dropped into collection bins, then fed in batches, 300 to 400 pounds at a time, to an open-ended single-ram baler. Once baled, the plastic had to be tied with additional straps to hold the bales together.

The same baler also was being used for paper, which it handled more effectively. But, because the facility had only one baler, it couldn’t process paper and plastic simultaneously. Everything had to be batched, which slowed down the operation.

In addition, the equipment suffered from serious reliability problems. Parts would jam and break. Material with good market quality was hard to produce because the bales varied widely in weight, and because the facility couldn’t effectively remove the trash—paper, plastic bags, large pieces of plastic, and non-recyclable metal—that came to the facility commingled with the bottles and cans being recycled.

In 2004, the SWMA sought bids to rebuild the MRF and privatize its operation. The winning bidder was a partnership consisting of RRT Design & Construction of Melville, NY, an engineering and construction firm that specializes in recycling and solid waste processing facilities; and Hudson Baylor Corp. of Newburgh, NY. RRT redesigned, overhauled, and rebuilt the plant, then trained Hudson Baylor to run it for the next 10 years.

“We took the plant to 12 tons an hour—nearly three times the throughput,” says Nathiel Egosi, RRT’s president. “We shut it down for six weeks, removed more than three-quarters of the equipment, and rebuilt it according to a more efficient and functional design.”

During the six-week shutdown period, some materials were recycled through a transfer station RRT designed and built for the SWMA in 2001. That facility includes a sorting line with a cross-belt, overhead self-cleaning electromagnet from Dings Co. Magnetic Group in Milwaukee, WI. The electromagnet automatically removes all ferrous metals from the waste stream. Because the transfer station was available, Hudson could retain its 12-person staff, continue some processing of materials, and stockpile the rest until the MRF resumed operation.

Changes to the MRF included

• Removing all of the conveyor belts used for sorting glass. “The decision was made to no longer sort glass by color,” Egosi says. “Now all glass is broken by a glass-breaker screen. Then it goes to a pulverizer, made by Andela Products Ltd., of Richfield Springs, NY, that produces an aggregate material less than three-eighths of an inch in size. It’s free of contaminants and suitable for use in various civil-engineering applications, including road construction, pipe bedding, and filtration. It’s basically gravel. The county is using the material on its own roads and other construction projects, and is looking for other markets.”
• Replacing the old 30-inch-wide infeed conveyors with new 48-inch-wide conveyors—giving sorters more room to remove trash and other foreign matter
• Installing a second baler. The new baler, from Marathon Equipment Co. of Vernon, AL, is dedicated to baling aluminum and steel cans, and plastic. It makes plastic bales that weigh over 1,000 pounds. “Now the paper baler can concentrate on just doing paper, and the container baler does just containers,” Egosi says. “We retain the ability to bale containers with the old baler if the new one goes down. We modified the other side of the plastic storage bins, reversing the slope of the floor by welding in new plates. Now the bins can discharge either way—to the old baler, or to the new baler via a new conveyor we installed underneath the sorting platform. It runs parallel to the bins above the floor, carrying the product to the new baler. We lost some bale storage because the additional equipment took up room, but whatever space we lost on the floor we gained back because the bales are much denser.”
• Adding a stationary compactor for trash. Before, trash was accumulated in small hoppers and baled. Now it is compacted and stored in a compactor box similar to those used by supermarkets. A truck collects the box and takes it to the transfer station, where the trash is loaded onto trailers and hauled to the landfill.
• Modifying the building so the new equipment would fit and function. The walls of the building were opened to put some equipment outside because it wouldn’t all fit inside, and conveyors were installed to bring materials back into the building.
• Upgrading the electrical and fire-sprinkler services.
• Relocating the stairs.
• Refurbishing and relocating the eddy current separator, a pneumatic device that blows aluminum and plastic from the sorting area into the bins.
• Repairing the worn-out tipping floor.

PHOTO: ATHENS SERVICES

The $2 million project was awarded as a lump-sum contract with a fixed schedule. “We started in July of 2004,” Egosi says, “with design, engineering, fabrication, and shipping of equipment, and preparatory work. Everything was at the site before the six-week shutdown began on January 13, 2005. The plant was back online by the end of February. We spent March and April debugging and training the operators.”

The retrofit concluded on time and in budget, and is meeting performance expectations with total separation of the container- and paper-baling systems, and with consistently higher container bale weights.

In retrospect, Egosi says, he would have preferred to do the work at a different time of year. “Winter is a slow period for the county, with fewer recyclables, but it was very inconvenient for us because of snow all over the equipment. Snow even came into the building. We used tarps and heaters inside, but half the equipment was being installed outside. Millwrights won’t walk or work on steel when it rains or snows because of the danger of slipping and falling. If we were shut down during the week, we had to work weekends. We dealt with it.”

Floor Fixing in Phoenix
The 27th Avenue Solid Waste Transfer Station in Phoenix, AZ, was built in 1995 with a second-level tipping floor consisting of a concrete slab reinforced with trap rock topping. Seven years of wear and tear from heavy garbage trucks and front-end-loader bucket drops seriously damaged the surface. Six separate areas totaling 12,000 square feet needed repair—60% of the total floor area of 20,000 square feet.

PHOTO: ATHENS SERVICES

City officials considered replacing the entire floor, including the rebar, or covering the existing floor with a topping containing iron filings. Ultimately they opted for an emery topping, Emerytop 400 from L&M Construction Chemicals Inc., of Omaha, NB.

“Emery is more durable,” says Philip A. Smith, P.E., L&M’s vice president, technical director, and resident engineer. “This particular formulation is internally sealed against aggressive chemical activity when it’s put down, so it doesn’t get into the pore structure of the cement. It’s more resistant than iron topping to ionization from garbage leachate that could penetrate through the topping and attack the rebar.”

Also, Smith says, metallic toppings have problems with rust, and with delamination due to drying shrinkage. “Emery doesn’t rust,” he says, “and we’ve been able to control drying shrinkage. Our procedure holds the material stable for bonding to occur.”

Emery is an aggregate mixture of corundum (a natural form of aluminum oxide) and magnetite, which has a high iron-oxide content. Mixed with sodium silicate, emery makes carborundum stones for sharpening knives. L&M’s Emerytop 400, a proprietary cement paste containing a mixture of polyhedral isostructural emery aggregate and several other ingredients, “contains one of the purest forms of emery on earth,” Smith says. “It contains at least 58% aluminum oxide and 25% iron oxide. We bring it into the country from Turkey and crush it.”

With the hardness of aluminum and the toughness and malleability of iron, emery is twice as abrasion-resistant as metal. On the Mohs scale---a logarithmic measure of mineral hardness, diamonds are rated highest at 10. L&M’s emery aggregates score close to 9, iron just 4 to 5. “An Emerytop 400 floor supports up to 10,000 pounds per square inch, whereas normal concrete supports only 4,000 to 5,000 pounds per square inch,” Smith says.

Truesdell Corp. of Phoenix served as contractor for this project; L&M provided materials and technical expertise. The work spanned six weekends, from close of business on Friday to the start of the Monday day shift. During these weekends, the transfer station remained in operation, but processed a reduced volume consisting solely of residential solid waste.

“The largest of the six sections was about 2,700 square feet. We did one section each weekend, starting with the smallest and working toward the largest, learning from experience on the smaller ones,” says Ray Hinesly, L&M’s southwest regional sales manager.

PHOTO: ATHENS SERVICES

Preparation of the surface entailed score-sawing the old floor topping to a .75-inch depth, scarifying the surface with hydraulic demolition hammers mounted on small skid-loaders, cleaning the entire floor with water blasters and scabblers, and removing all loose aggregate and topping. In some places, the damaged surface had to be removed down to the rebar. Then the scarified surface was saturated with water.

On Sunday morning, blowers removed any excess water. Then a slurry of L&M Everbond mixed with portland cement was applied as a bonding substrate, and the Emerytop 400 was placed over the wet substrate, consolidated with a vibrating screed, and bull-floated to create a slip-resistant finish. In all, the project consumed seven 40,000-pound truckloads of Emerytop 400—a total of 280,000 pounds.

“This product is so cement-rich that it requires very thorough curing,” Hinesly says. “We used L&M E-Con evaporation retardant during the topping placement, then covered the finished floor with curing mats to make sure the water content stayed in the slab, and water-cured it for a week. After removal of the curing mats, we sprayed an acrylic sealer, L&M Dress & Seal 30, to help the curing process last even longer.”

One challenge the work crew faced was the tight schedule. “The contractor had to get the equipment in, do a lot of scarifying, lay down the topping, and get it ready to cure by Sunday afternoon,” Hinesly says. “They met the schedule each time.”

Heat was another complication. The work was done in summer, when Phoenix regularly experiences daytime high temperatures in excess of 105°F, with very low humidity. “We moved the Emerytop 400 material inside the building Friday night so it wasn’t in direct sun, and did our mixing and pouring early Sunday morning—about 3:00 a.m.—when the temperature was only in the 80s,” Hinesly says.

“We also mixed the material with ice water. We filled a Buffalo—a 700-gallon tank trailer—with ice from a local wholesaler, then brought it to the job and added water immediately prior to mixing. The ice brought the water down to the 40s.”

The projected life of the new flooring is 10 years, but it may last longer. “We’ve had the floor down three years, and it’s still pristine, with no signs of wear whatsoever,” Smith says.

Odor Control in California
Natural ventilation was supposed to contain dust and odors within the 14.5-acre site where Athens Services built its MRF in 1997. It didn’t. Several days a month, on average, wind and weather conditions prompted neighbors to complain about the plant’s aroma.

A privately owned refuse collection and recycling firm based in City of Industry, CA, about 13 miles east of downtown Los Angeles, Athens Services serves about three dozen communities in Los Angeles and Riverside counties. Its MRF is in an industrial area, but nearby to the south are residential and agricultural areas from which the complaints emanate.

“We take all the usual precautions you would in a well-run solid waste facility,” says Duane H. McDonald, Athens’s director of environmental services. “We don’t want people to know we’re here. We don’t want them to smell us or see us. We don’t want to intrude on their activities in any way that isn’t absolutely necessary.

“We keep material moving. We process it quickly, then ship out the recyclables and residue. We keep the facility clean, and contain things as much as possible indoors, but on any given day we were completely at the mercy of weather conditions. The odor of the plant was noticeable if the wind was blowing from the east or northeast through the plant toward this residential neighborhood.”

Fortunately, prevailing winds in the Los Angeles Basin come from the Pacific Ocean to the west, but when the torrid Santa Ana wind blows in from the desert to the east, “it’s hot as well as smelly,” McDonald says. “Easterly winds also occur in the early morning or late evening when the onshore breeze becomes an offshore breeze. This happens more often, but it’s not as strong.”

The MRF is 545 feet long, 210 feet across at its widest point, and about 50 feet tall at its highest point. It encompasses 102,000 square feet, with 52,000 square feet devoted to tipping, transfer, conveyor loading, and bulk material storage; and 48,000 square feet devoted to recovery, baling, and shipping of recyclable materials.

The building has windows about halfway up its sides, and ventilation openings under a skylight at the ridge line of the roof. As air inside the building warms, rises, and flows out the top, cooler air flows in from the sides. This arrangement provides enough ventilation for employee comfort, but falls short of original expectations for dust and odor control.

Company officials knew they had to do something to placate the neighbors, because they want to expand the MRF from its current daily capacity of 1,920 tons to 5,000 tons. The MRF is in an unincorporated area, so the Los Angeles County Department of Regional Planning would have to approve, after public hearings held by the county planning commission. At those hearings, “odor was a major discussion item,” McDonald says.

“We considered a number of possible solutions. One that immediately came to mind was a better enclosure for our tipping floor. The north side is completely open for trucks to back in to dump their loads, but right now we don’t have space to install a proper enclosure and still leave room for our trucks to maneuver.

“We considered putting in a forced-air exhaust system, but we were concerned that we might end up discharging more air that has odor in it. How would we filter it to remove the odor? We have limited space. Our 14.5-acre site includes the MRF, company headquarters, truck maintenance facilities, and parking for employees and a portion of our truck fleet. Where would we put the fans, how effective would the filtering be, how long would it take to get the system designed and installed, and what kind of noise issues would such a system create?

“We were looking for a solution that would be effective, something we could implement in the short term, that wouldn’t take a great deal of time to construct or require permits to change the building’s footprint.”

From industry colleagues, McDonald learned of other MRFs and transfer stations in the Los Angeles area that had installed fog-nozzle systems from the MicroCool Division of AxAir Nortec Ltd., in Thousand Palms, CA. MicroCool began in 1981 by building low-pressure mister systems, operating at a pressure of 60 to 80 pounds per square inch, for hotels and restaurants in and around Palm Springs, CA. The firm later expanded into high-pressure industrial applications with “flash evaporation” fog systems operating at 1,000 pounds per square inch, says Craig Littleton, MicroCool’s operations manager.

The Athens MRF installed such a system, with nozzles sized so the water droplets they emit are the ideal size to coalesce and drop back to the floor.

City water for the system flows into a small accumulator tank to even out pressure on the inlet side of a high-pressure, low-volume pump. After the water leaves the pump, an injector adds an odor-neutralizing chemical in a concentration of one part chemical per 500 parts water. Then the water moves to a series of electrically controlled valves that send it flowing through a half-mile of pipe to nozzles in five zones set up inside the MRF.

• The transfer area, where a higher concentration of nozzles was installed because dust suppression is a priority.
• The tipping area at the north end, for odor control.
• The materials recovery area at the south end, for odor suppression. Nozzles around the periphery of the building and at the ridge line of roof help to prevent odor from escaping as air flows through those openings.
• The interior of the materials recovery area, for employee cooling along the sorting lines. Tap water without the odor neutralizer is used in this area.
• A small stand-alone line—at the north end where construction and demolition materials are sorted—for odor suppression and dust control.

The odor neutralizer comes in 55-gallon drums. It’s an enzyme preparation that interacts with odor-causing organic compounds and turns them into odorless byproducts. “We’ve tried several products for odor control,” McDonald says. “Until recently we were using EcoCare 250, manufactured by Nature Plus Inc., of Stratford, CT. We just switched to No Scent Odor Neutralizer #10410, made by Odor Control Co. of Scottsdale, AZ.”

PHOTO: ATHENS SERVICES

The system cost about $100,000 in MicroCool hardware. “We estimate that recently we have been spending about $4,500 a month on water, odor neutralizer, and maintenance of the system, which includes monthly maintenance of the pumps and cleaning the nozzles,” McDonald says.

Installation began in November 2003 and was completed in April 2004. McDonald says it didn’t disrupt the MRF’s operations. “MicroCool arranged to work in operational areas of the plant primarily on weekends, when we don’t do material recovery. We implemented the system in phases, beginning in December of 2003, and prioritized it so the odor-control portions of the system would be installed first.”

In fall 2004, Athens purchased and installed a weather station from Davis Instruments Corp., in Hayward, CA, on the roof of the building. Innovative Automation Systems/Hertlein Industries Inc., of Orange, CA, linked the weather station’s output to the MRF’s existing computer, and modified the software to run the fogging system. A software algorithm ratchets up the level of fogging operation based on temperature and wind direction.

“Under normal wind conditions, we operate just the periphery nozzles,” McDonald says. “When the wind shifts to a trouble direction, going straight toward the residential neighborhood, or if the temperature goes above a certain critical point on hot Santa Ana days, we’ve got everything going.”

The weather station and computer automation cost another $20,000, McDonald reports. “Without them,” he estimates, “we probably would incur another $2,000 per month in odor-neutralizer costs, so the system automation and weather station should pay for themselves in less than a year.”

The fogging system isn’t the final solution, McDonald concedes. When the MRF expands, its tipping floor will add 30,000 square feet and another 45,000 square feet will be devoted to material recovery. As the MRF grows, some other activities on the site will have to be relocated. The additional elbow room will allow Athens to enclose the tipping floor so it’s less exposed to wind and weather, and to install a forced-air ventilation and filtration system that will complement the fogging system.

Meanwhile, complaints from the neighbors have decreased significantly. “The fogging system has gone a long way toward making us as unnoticeable as possible to the surrounding area,” McDonald says.

George Leposky is a science and technology writer based in Miami, FL.

MSW - September/October 2005