Establishing goals for your separation efforts can help you maximize the volume and the value of your diversion program.

By Lynn Merrill

Tightening the Strategy
A Positive Sort of a Different Color
Designing for Strategic Diversion

When material recovery facilities (MRFs) first became an important component of the integrated waste system, system designers weren’t sure how they could achieve the separation of the various components of the material stream. Commodity handling systems that move loose materials worked on the premise that the material was generally a uniform size, weight, and shape. It then became rather straightforward to design systems that would move and segregate these items into measurable quantities for use in the manufacturing process.

But when full-scale recycling programs came around, suddenly system designers were faced with having to deal with a material stream that changed its weight, volume, and physical configuration every minute. Out of this literal mixed bag of commodities, the system was expected to pull various uniform materials out for remanufacturing. These materials have to then be to a certain standard or tolerance in order to be marketable to an end user, such as a paper mill or a glass plant.

One solution was to segregate materials at the curb, presorting the material stream in order to minimize contamination and maximize resale value. This preprocessing strategy resulted in lower volumes of recovered materials, but the recovered materials were of higher value. Since the mandated goal was to maximize diversion, such programs were limited in their ability to achieve the volumes needed to meet the 25-50% diversion goals mandated. Additionally, the time and cost of having to separate materials on-route pushed the industry toward more commingled programs, forcing the separation and high-grading to occur inside a central facility.

As volumes increased from blue bag and barrel programs, the levels of contamination and the need to move materials quickly increased as well. Simultaneously, the markets for these materials became saturated and quality-control standards increased, while prices paid per ton decreased. Early separation-system strategies, including such concepts as positive- or negative-sorts, began to emerge. But it became apparent that a simple magnet to remove ferrous materials and a lot of people trying to pick materials off a moving belt could be problematic and costly as well.

The hope for handling the higher volumes of materials while maximizing the quality and value of materials separated at the lowest possible operating cost hung on the idea of automated separation equipment. Machines that could color separate glass or identify various plastics could further increase diversion levels while reducing the number of manual laborers sorting through the stream. The number of new MRFs capable of handling volumes in the 1,500- to 2,000-tpd range increased nationwide.

After over a decade of rapid development, it appears that quantum leaps in separation technologies have diminished and that the rapid construction of new separation facilities has ebbed. Most facilities are now looking at retrofitting proven technology back into lines that were first designed in the early to mid-1990s. They’re looking for systems that are reliable, durable, and can reduce operating costs further while improving the separation capability and quality of materials.

Tightening the Strategy

Many companies offering separation equipment report that the number of orders for equipment has diminished and customers are looking for equipment that will last longer with fewer maintenance headaches. "On rotary screens in general, what we have done in the last couple of years is offered screen plates that provide longer wear life," states Dave Schellberg, assistant sales manager at McLanahan Corporation in Hollidaysburg, PA, a manufacturer of rotary screens. "We’re probably among the most expensive rotary screens an engineering firm or the end user may consider. But that higher price comes into longevity, continued high availability, and lower maintenance in comparison to some of the competitive units that we’ve seen out there. "

Schellberg doesn’t see the construction of new facilities occurring as they did up to five years ago. "I don’t know if there are any big plants that have been built in the last few years," he observes. "I was talking to some other people that used to work for resource recovery engineering firms; they don’t anymore because landfilling has been made more available and cheaper. Unless it’s environmentally mandated by municipalities or states, it’s hard to justify the capital cost of a large MRF. We haven’t had many leads for large trommel screens for a couple of years like we did in the early and mid-1990s."

Helping a customer get the right equipment requires a comprehensive look at the facility, recommends Al Gedgaudas, manager of resource recovery equipment at Eriez Magnetics in Erie, PA, a manufacturer of systems designed to remove ferrous and nonferrous metals from the commingled stream. "We try to get comprehensive information," he says when recommending equipment to a customer. "We have data sheets for our field people and we usually make a visit to make sure nothing has been missed or that the person we’re in contact with may have forgotten to tell us something important."

Depending on the application, metal separation equipment can run as high as $100,000. "When you start to get into the higher-priced equipment, we will have a factory person come out and visit," states Gedgaudas. "You try to make sure that everybody has a good feeling and that you have got the best equipment for what the customer wants to do. Sometimes what the customer anticipates something will do doesn’t always work out that way. The more everybody is on the same channel in the beginning, the better off it works."

Sizing the equipment to meet the present and future demand is also important, especially on metal separation equipment, says Gedgaudas. "The most valuable commodity in a MRF plant is the aluminum used in beverage containers. An eddy-current separator is the most expensive thing you can buy. Usually that is put in as close to the end of the line as possible, and you try to do a lot of screening and sizing so you limit the tonnage to that [piece of equipment]. You can get by with the right-size or smaller-size machine."

The belt width of the feed line can determine the quality and quantity of recovery of all commodities. If the belt is too small, the burden depth of the material coming across the line increases, leaving items buried. If the belt is too wide, the pickers are unable to comfortably reach all parts of the feed line and materials toward the center will be missed, thus affecting recovery rates.

While the early heydays of touted automation–with machines that can successfully pick off PET or green glass–haven’t fully been realized yet, that doesn’t mean that you shouldn’t continue to look at ways to reduce the manual side of the facility through automated features or systems. "Anything you can do to automate helps your profit line because the machine is always working, it typically doesn’t make mistakes, and you can reallocate the people who are doing that job to other things," says Gedgaudas.

The cost-effectiveness of these automated sorting systems has to be evaluated in order to ensure that the incremental improvement in recovery rates, quality of materials recovered, and value received is offset by the capital costs and maintenance costs. A machine that’s dedicated to color-sorting glass or segregating PET from HDPE can only perform that function and could be idled if market conditions changed. With manual separation systems involving pickers, reprogramming is as simple as saying, "Today you’re going to remove mixed office paper."

Nonengineering issues can affect selecting the right separation or volume reduction equipment, says Jerry Mishler, technical sales with SSI Shredding Systems in Wilsonville, OR. "We are providing equipment for a specific purpose, and we will give users and operators all the data we have from previous installations to evaluate and see if they need volume reduction. They obviously make the decision of whether that is going to be cost-effective. We aren’t told many times of all the factors involved in those decisions. In some cases you know the actual cost effectiveness when you look at the numbers on the surface; it doesn’t look like it would pay for itself. But there are other reasons. Maybe it’s impossible to site a new landfill in a reasonable time period, so they are going to use one of our machines to get more time to make that decision. We don’t always see those factors."

A Positive Sort of a Different Color

At the Mirror Nova Scotia Ltd. landfill in Lakeside, NS, separation technology takes a different turn. Because of various environmental concerns, the company separates organic materials out of the wastestream and sends these organics to a composting operation in order to reduce odors before they are landfilled.

"The reason this facility is in place came about from a public consultation process in order to site a new landfill," says Stephen Copp, landfill manager. "The problems they had with the last municipally run landfill–odors, sea gulls, and environmental impairment–the new landfill would not be able to have these things at all. We’re a private company that performed a public/private partnership with the municipality of Halifax to guarantee that these requirements would be met. We take in about 550 tons a day, and we don’t recover any organics. Instead it all ends up in the landfill."

The municipality operates a successful blue-bag program, as well as a green-cart program that recovers yardwaste. These materials are then sent to various separation programs. The remaining fraction of wastes is delivered to the Mirror Nova Scotia plant. Here the waste is processed through a trommel screen, recovering a smaller-size fraction that consists of 80% plastics and papers. "There is only 5% to 10% of the wastestream that we receive that is organic," says Copp. The plant has bag breakers and shredders and does recovery of some recyclables that don’t make it into the blue-bag program. "This facility reduces the amount of materials coming in the front door by about 20% overall."

The material starts on the tipping floor, where inerts and large bulky items are pulled out and sent directly to the landfill via rolloff bins, accounting for 20% of the material received by the front-end processor. The remaining 80% are delivered onto a conveyor belt to a presort station where it is inspected prior to going to the bag breaker. Once the bags are ripped open, the material goes to the trommel screen, where materials 2 in. or less in diameter fall through and are directed toward the composting facility. "Anything that falls through the back end of the tube, which has 6-inch holes, goes through to another sorting station, where they look for hazardous materials," explains Copp. "They run it through a magnet, and it goes through a shredder to bring it down to a 2-inch nominal size. All that material goes to the compost facility too."

Materials that pass through the trommel screen come out the back end. "It’s where we do a final check for organics to make sure all are out of the waste," says Copp. "We pull out pop bottles, cardboard, and paper and do a check for hazardous wastes. Anything that doesn’t get pulled off goes into a truck and straight down to the landfill. We probably remove 20 to 30 tons of recyclables–paper and cardboard–a week. We are going to probably hit 6,000 tons of metals taken out of the garbage this year." For Halifax as a whole, the city achieved a 55% diversion rate.

Designing for Strategic Diversion

Many lessons have been learned in the design and placement of equipment in a MRF over the last decade. One of the most critical lessons is that there needs to be a great deal of flexibility built into the system in order to meet changing markets for materials and for handling increased tonnage. "Experience shows that we have to design the system with flexibility," says David Chon, president of David Chon Associates in Towson, MD. Chon’s experience dates back to 1974 in the design of waste handling systems, starting with the refuse-derived fuels market.

According to Chon, you should design your system with room to grow, for the placement of new equipment and for ensuring that the materials are metered properly so that they flow through the system without overloading. "The market changes quite often, so you have to put enough flexibility to change your system around so you can meet the market demand," he says.

Chon looks for proven technology in designing a system. "That means someone out there is using it and it works. A lot of times when you design the system, the salesman comes in and tells you how good their machine is. You need to study it carefully. There are no shortcuts. If you buy the cheap equipment to satisfy your budget, then you have to pay for it later anyway. I call it the ‘fast food’ philosophy. I worked on one project [where], systemwise, it was a good design, but selection of equipment was so poor, it bankrupted eventually."

Using mechanical systems makes the most sense. "I always believed mechanical systems are more dependable than manual systems," says Chon. "You don’t have legal disputes, vacations, sick leave, late to work, or increases in salaries." Chon recalls the conversion of a manual aluminum picking system to automation in one facility. "We had 20 people on each of three lines, and we cannot pick enough aluminum to justify that. When I put in the eddy-current demonstration unit in this system, it worked so well we made money. After one month they ordered two more systems and they’re making tons of aluminum. On the same token they now have one person to pick out the contaminants, and the quality is such that they get a good price. Manual systems are good for small facilities, but for the larger systems you should try looking into mechanical systems so you use less manpower. You use manual operations to pull out contaminants so that you increase the product quality so you can increase the revenue."

At the RSW Recycling facility in Reno, NV, Recycling Manager Kevin Reilly is looking at the conversion of a curbside-sorting program with a simple hand-sort system to something bigger. "We process about 35 tons per day of residential materials and 65 tons per day of commercial at our Sparks facility," he says. "Curbside we color sort the glass; commingle the plastic, tin, and aluminum; and commingle the newspapers and magazines. These are put into separate compartments in the truck, which are dumped into different areas [of the facility] for sorting. Most of it is run over a single belt and is hand-sorted except for the steel cans, which are done by a magnet."

The 12-year-old facility has served the company well, but the company is just beginning to explore converting its curbside program. "We’re going to a single stream, providing one container to the customer," Reilly says. "Commingle everything and separate it at the facility."

Reilly cautions that the planning is still in the infancy stage and they’re really not sure how it will all be accomplished. But he already knows that it will mean a major remodeling of the separation systems, and he already has advise for those facing a similar task: "Spend some time investigating it before you spend the money. Visit facilities and then try to design something that is going to fit your program."

Lynn Merrill is director of public services for the City of San Bernardino, CA.