Top Photo: Courtesy of Rotochopper

Taylor Nathe

In an ideal world, organic feedstocks would arrive clean, consistent, and ready to process. But for today’s organics recyclers, that’s rarely the case.

Instead, incoming material streams are increasingly mixed with plastics, metals, packaging, and other non-organic contaminants. Food waste often arrives bagged or boxed. Yard waste can include rocks, wire, and construction debris. Municipal organics programs — while expanding rapidly — introduce even further variability into the feedstock mix.

The result is a growing operational challenge: How does an organics recycler process contaminated organics efficiently without sacrificing uptime, safety, or end product quality?

For many operations, the answer lies in a smarter system design — specifically, a two-step workflow that combines shredding with high-efficiency grinding.

The Reality of Contaminated Organics

Contamination in organic streams is not a temporary issue — it’s a long-term trend that BioCycle has been covering since the 1980s.

As municipalities push toward zero-waste goals and expand food scrap collection, the volume of organics increases — but so does the level of contamination. Even with strong education and sorting programs, non-organic materials inevitably make their way into the stream.

Operators are left balancing competing priorities:

• Maintain high throughput
• Protect equipment from damage
• Produce a consistent, marketable end product
• Keep labor and maintenance costs under control

It is common practice at composting facilities to size-reduce an incoming organics stream with grinders, especially when food waste is co-collected curbside with yard waste. Trying to accomplish all of this with a grinder alone often leads to compromises.

High-speed grinders are engineered for production and particle size control — but they are not designed to absorb the full impact of contaminated feedstock. Incorporating shredding into the process helps manage contamination before it reaches downstream equipment.

When contaminants enter the grinding chamber, they cause:

• Excessive wear on teeth and screens
• Unexpected downtime for repairs or cleanout
• Safety risks from thrown objects or equipment failure
• Inconsistent material output

As contamination increases, these risks — and the associated costs — scale with it.

A Rotochopper shredder equipped with a cross-belt magnet removing metal contaminants.

Step 1: Shredding to Control Contamination

Shredders like the Rotochopper 75 and 95 are built to do what grinders shouldn’t: handle tough, unpredictable, and contaminated material. A piece of metal through a high-speed grinder can take a rotor out of commission — and take a profitable day with it.

A shredder works differently. High torque and low speed let it accept material in whatever form it arrives — bagged waste, packaged material, mixed loads, metal included — and work through it without the violent impact dynamic that destroys grinder rotors. This is especially valuable in applications like C&D waste recycling, where mixed and unpredictable material streams are the norm.

Where metal would stop a high-speed grinder cold, a shredder can process it through its rotors — and the cross-belt magnet pulls it out of the material stream before it ever reaches the grinder.

The shredders can be configured with:

• A hydraulically adjustable cross-belt magnet to remove ferrous metals from the material stream
• Metal detection and auto-reverse to catch what the magnet misses
• Multiple rotor configurations — including waste wood fine, waste wood rough, and C&D/MSW — can be selected based on feedstock and processing goals. Fine rotors deliver uniform output, rough rotors handle coarse material and contaminants, and C&D/MSW rotors are built for mixed waste and aggressive intake. Rotor configurations can be changed on the shredder to match different materials, providing flexibility as needs evolve.

By the time material reaches the grinder, the things that would damage it are already gone.

Step 2: Grinding for Precision and Marketability

Once feedstock has been preprocessed and conditioned, a Rotochopper horizontal grinder — whether an L II, B-66, FP-66, or EC-366 — can operate at its full potential. 

Horizontal grinders are designed to:

• Produce a consistent, uniform particle size
• Deliver high throughput rates
• Create end products tailored to specific applications

When fed clean, controlled material, grinders perform efficiently and with less wear. Operators can dial in screen sizes and rotor configurations to achieve target specifications — whether for composting, soil blends, or other markets.

This same principle applies in high-variability environments like disaster debris cleanup, where controlling feedstock before grinding is critical to maintaining safe and consistent production.

This is where the shredder + grinder workflow creates a clear division of labor:

• The shredder manages variability and risk
• The grinder delivers precision and final product quality

A Rotochopper diesel horizontal grinder processing pre-shredded material.

Why This Workflow Works

1. Protects Equipment and Increases Uptime: Preprocessing with a shredder keeps damaging contaminants out of the grinding chamber. That means longer life on wear parts, fewer surprise shutdowns, and additional hours producing material instead of clearing jams.

“Shredding before we grind allows us to process material that we couldn’t otherwise accept,” explains Max Dunham at Dunham Brothers in Lakeville, Minnesota. “Big pallets and spools with lots of metal in them would be impossible without the shredder in front of the grinder.” 

2. Expands Acceptable Feedstocks: With a shredder in place, operations can confidently accept challenging material streams, including bagged or packaged food waste, contaminated yard waste, municipal organics with unknown inputs, and mixed debris streams containing organic fractions. This flexibility opens the door to new revenue opportunities.

3. Better Product at Lower Cost: Consistent feedstock going into the grinder means consistent output coming out. Fewer repairs, less downtime, and efficient processing all drive down cost per ton.

4. System Built to Match Incoming Material: No two feedstock streams are exactly alike, and contamination levels change with every load. The right system accounts for that — not by working harder, but by dividing the work between equipment designed for each stage.

Rotochopper’s 75, 85, and 95 shredders handle the unpredictable front end — breaking down contaminated material, removing ferrous metals, and conditioning feedstock for consistent downstream processing. Paired with Rotochopper horizontal grinders in diesel or electric configurations, the result is a system built to produce uniform, marketable end products from the kind of material that used to threaten shutting down operations. 

Turning Contaminated Organics into Opportunity

Contaminated feedstock isn’t going away. If anything, it will continue to increase as more communities invest in organics diversion programs.

For operators, this presents a choice: treat contamination as a limitation — or design a system that can handle it.

A shredder and grinder workflow allows organics recycling facilities to take on challenging material without compromising performance. Instead of rejecting loads or risking equipment damage, contaminated organics can be processed efficiently, turning them into a consistent, valuable end product.

In a competitive market, that capability can be the difference between reacting to problems and capitalizing on opportunity.

This article was produced as sponsored content in partnership with Rotochopper and tailored for BioCycle’s audience. Because Rotochopper sells factory-direct, our team can help you design a shredder and grinder workflow sized to your feedstock, your throughput targets, and your site. Call 320-875-9950 or visit rotochopper.com/contact.