Zanker Recycling installed a shredder from SSI Shredding Systems to reduce the size of bulky waste items and residuals from its recycling lines.

Shredders in the waste and recycling industries are usually used to reduce the size of material for easier transport by rail, truck or ship. At Zanker Recycling, San Jose, California, easier transport is only one reason the company installed its shredder.

The shredder breaks up material, allowing the fines to be made into alternative daily cover (ADC) for a local landfill. It also allows Zanker to increase its diversion rates.

“It’s a combination of things that goes into the shredder,” Michael Gross, director of sustainability at Zanker, says. “It’s loads of what we call trash that are so marginal they aren’t worth sorting. They may have a 20 to 25 percent recycling rate.”

Gross says bulky items picked up from residential curbs, such as furniture, mattresses and white goods, and residuals from other recycling lines also go into the shredder.

“A construction waste line may have a beautiful piece of lumber that’s painted. We can’t pull that piece of lumber off for biomass, so it falls off the end of the conveyor,” Gross says. “We weight it in as outbound on our construction line, and it’s weighted as inbound on [this line].”


Zanker Recycling started in 1985 as a landfill when the city of San Jose required it to divert 25 percent of its material. “We found out a lot of materials can be recycled,” Gross says.

Gross claims Zanker started one of the first wood, concrete and demolition recycling facilities in the U.S.

Today, Zanker employs 230 people and has two recycling locations in San Jose and Sacramento, California, along with a composting facility near Gilroy, California. Seven lines are registered or certified with the Recycling Certification Institute (RCI), Sacramento.

In May 2017, Zanker started its demolition materials (DM) reduction line. Gross says the DM reduction line allows Zanker to “go after items that no one really goes after” to find materials that could be recycled.

“My Sheetrock recycling operation has minimal contamination. We’re already pulling out the metal and garbage. In the garbage there’s a lot of lumber, but not enough to justify a stockpile. So, we’ll take that pile, weigh it out of the Sheetrock operation and then inbound it at the DM line,” Gross says.

Between the line’s start and December 2017, it processed 69,000 tons per day. The wood processed in the line is made into mulch and the concrete is made into base rock. Copper wire, ferrous, nonferrous metals and beverage containers are also collected from the line, creating a 54.92 percent diversion rate.

The shredder allows Zanker to increase its diversion rates by allowing it to remove recyclables it may have previously missed.


The bulky items and residuals are loaded into an all-electric Pri-max PR6600 shredder from SSI Shredding Systems, Wilsonville, Oregon. The shredder breaks down the material to 14-inch minus. Gross says Zanker chose that size to make a manageable material that can serve double duty as a recyclable material and ADC.

“After the material is shredded and gone through the sort line and is either ADC or comes off as waste, it’s so easy to manage,” he says. “It’s easy to pick up and handle. The handling of the material is made a lot safer, which all rolls down to the bottom line—if you have a good, safe operation, you’re probably doing pretty good financially.”

The shredder processes 90 tons of materials per hour. Once shredded, the material is conveyed under a magnet to remove ferrous metals and then dropped into a SST 1025 trommel screen from Doppstadt, Rockville, Maryland.

The first section of the trommel screen removes 1-inch-minus fines, which are conveyed under another magnet to remove more metals. The remaining 1-inch-minus material is stockpiled and shipped as ADC. The second section of trommel screens removes the 4-inch-minus fines, which are processed through an Air Knife separator from General Kinematics, Crystal Lake, Illinois. The Air Knife removes any remaining fines less than 1-inch minus before heavy items, such as glass, metals, wood and stones, are removed from lighter items, such as paper, plastic and insulation.

The heavy items are conveyed under another magnet and then stockpiled for ADC. The light materials are conveyed to a bunker until they are shipped to a landfill. The remaining materials larger than 4 inches are conveyed to a sort line where wood, concrete, metals and brick are removed. The sorted materials are sent to other recyclers for processing, and residuals from the sort line are directed to the on-site landfill or transported to the Marina Landfill in Monterey County.

The ADC is used at the New Vienna Landfill, which is owned and operated by Republic Services, Phoenix. Gross says the relationship between Zanker and the landfill has lasted for eight years. “Even if the recycling credit goes away, we’re still going to be producing it,” he says.

According to Gross, the main goal of the DM reduction line is to divert more material rather than create ADC. The ADC is created because, Gross says, “there’s nothing else I can do with it.

“When we were making the DM plant, our original diversion number was 35 percent, so we were surprised to see how high our number was and the metal in our loads,” Gross says. “You don’t think about where you find metal in things—little brackets that hold together Ikea furniture, a table that has metal legs. It’s amazing to find all this stuff.”

Bulky items, such as furniture, mattresses and white goods, and residuals are broken down to 14-inch minus at Zanker’s DM reduction line.


The relationship between SSI and Zanker has grown over time, Gross says, starting with meetups at conferences. “I’ve known Terri [Ward of SSI] for years, I’ve been on the board of the CDRA [Construction & Demolition Recycling Association] for a long time. She was a member and would come to conferences, and we would talk about shredders,” he says.

Zanker used a shredder in 1989 for its demolition processing facility, and Gross says it had consistent issues with breaking down. While looking for a shredder to place on the DM line, he says Zanker demoed a few and chose SSI.

“The stuff we’re dealing with is hard,” he says. “Bulky items are hard.”

Zanker looked at four different shredders before deciding on SSI’s Pri-max PR6600. It chose this model because, Gross says, a company in the Bay Area was using the same size shredder. “We asked if we could lease it for a month and they said no, but we went on a few trips and we just saw how durable it was,” Gross says. “The proof was in the pudding from the competitors to the customers.”

To keep its shredder durable, Gross says maintenance is key. “You have daily preventative maintenance where you’re blowing stuff off, cleaning filters, greasing certain components. You do that after so many hours in one day,” he says. “Once per week, we hard-face.”

With hard-facing, a maintenance person welds metal to certain parts of the machine to either increase its wear resistance or restore a worn-down surface.

Gross says the only issue with the shredder was a hydraulic motor going out. The motor was not manufactured by SSI and was replaced in a day. “When you do startup, you expect stuff is going to happen because guess what happens? Stuff happens.”

The author is assistant editor of Waste Today and can be reached at