© Jose Gil | Dreamstime.com

In the effort to improve overall recycling or diversion percentages within jurisdictions or municipalities, the dense tonnages associated with construction and demolition (C&D) debris have always been a prime target for recovery.

The common C&D processing equipment of a screen or two and some manual sorters are now including more sophisticated air separation equipment and even infrared (IR) optical units to better separate materials for more recovery or potential new markets.

While the technology is improving to process these C&D materials, most processors within the industry stress the importance of end markets and outlets for the commodities that are targeted for such recovery.

SOPHISTICATED RECOVERY

One of the most sophisticated C&D facilities recently constructed is the Zanker Recycling demolition processing facility in San Jose, California. The system shared the Solid Waste Association of North America’s (SWANA) Gold Award for Recycling Systems in 2016 and is rated for 60 tons per hour (tph) but consistently operates at 75 tph. The facility serves an approximate population of 6 million people in an area with strict recovery regulations regarding all waste.

This system uses three types of screens, four different air classifiers and three separate magnets to achieve a material recovery of over 70 percent. The infeed stream consists mostly of demolition materials from the removal of local houses and businesses. The facility recovers clean fill, metals, concrete and brick and wood as well as using the fines as alternative daily cover (ADC). The results of the first year of operation show the recovery numbers for each of these products, which are displayed in the table on page 35.

While ADC certainly is the largest material recovered, the system was specifically designed to recover clean wood, clean concrete and brick. To achieve this, the stream is screened several times to get an optimal size ratio for the air classifiers, called air drum separators.

The different size streams go to two separate air drum separators that are inline, with the first targeting a clean stream of concrete and brick and the second targeting clean wood. Ferrous items are recovered via magnets and non-ferrous metals are recovered by hand. The wood and the concrete streams have sorters as quality control (QC) to remove unwanted items from the streams such as painted or treated wood.

OPTICS AND SCREENS

Some facilities are also using IR optical technologies to recover wood, similar to those used in recycling processing to recover plastics. Some C&D recovery operations have used optical units for wood recovery, however the results had been mixed as they were not selective enough to get a clean wood stream. Recent upgrades to these units are providing more accurate recovery.

Bauman Enterprises in Cleveland has a recently installed optical unit to eject wood in its C&D plant and Bill Baumann, president of parent company Baumann Enterprises says he has been happy with the results. His system also uses multiple screens to send the right size of material to the optical unit.

The functionality of both air classification units and optical units are very dependent on the sizes of material that are fed to them, with an optimal size ratio—the size of smallest item to the largest item in the stream—that is generally close to 1:4 for air systems and 1:8 for optical units. This may vary depending on the equipment and the type of material but is a good general rule to understand.

Most screening for C&D is done with traditional finger screens, trommels and disc screens. A newer type of disc screen, the Anti-Wrap Screen (AWS) from Van Dyk Recycling Solutions, Stamford, Connecticut, uses large drums with low profile flower type discs located with 6 inches of space between the drums. These are less prone to wrapping materials such as plastic wrapping and tarps.

The screen uses alterations in speeds to change the size of the materials screened out of the stream from approximately 2 inches to 6 inches, depending on rotation speed and material type. In addition to the limited wrapping, the speed variability allows the screen to be used on a wide variety of materials. The AWS screen was first implemented in the U.S. for municipal solid waste systems, but these screens have also been used in C&D applications with reportedly good success.

At the Zanker facility, much of the wood is used as fuel, although the cleanest recovered wood will be further processed into mulch.

The outlets for different types of wood products recovered from C&D seem to be very locally dependent. Dem-Con Cos., Shakopee, Minnesota, focus mostly on wood recovery and try to source its incoming streams accordingly, including pallets and other such items.

Dem-Con has a limited market for mulch, but has a more robust market for animal bedding and fuel for biomass boilers, and have tailored its processing capabilities to match these markets. For instance, animal bedding requires clean, metal-free wood chips without splinters, while their customer requires biomass fuel has a limited size range between ¼ inch to 1 inch. Dem-Con has constructed a much different processing system than the one at Zanker by focusing on the wood chip production, including several grinders and pneumatic conveyors to process and move the wood chips to a covered flatbed outfeed system.

ROBOTICS AND VINYL

One of the most interesting innovations for C&D is the use of robotics systems as sorters. ZenRobotics, Helsinki, Finland, has implemented robotic C&D sort systems in several locations and looks to be part of the future of recycling recovery.

While the current robotic arms are generally slower than human sorters, they are more accurate and do not need as many breaks. Robotic sorters also can handle larger and heavier objects than is considered safe for many human sorters. A system in Japan that uses robotic sorters operates 24 hours a day, which helps make up for the slower throughput the current generation of robots generates.

The technology to recover materials from C&D streams is certainly becoming more sophisticated, enabling better recovery and less necessary labor. The markets for these recovered materials are an important driver for the level of automation that a facility may require, and it is difficult to have one without the other.

It appears that many C&D recovery facility operators throughout the country are adept at finding and providing for current and potential commodity markets within their region. This high-level marketing is very necessary in the C&D recovery business.

With the ever-evolving marketplace and the advent of increasing recycling goals and mandates, constant attention to developing new markets, and protecting your current ones, is paramount. One such market may be vinyl siding. There are regional buyers of clean vinyl siding in many parts of the country, although there are specific requirements for the quality and even the packaging of the siding that need to be taken into consideration.

According to Kevin Reily, president and senior sales manager of Reily Recovery, Haw River, North Carolina, siding baled with horizontal balers tends to pack the material too tight for recovery at the siding processors. Vertical balers are recommended for preparing vinyl siding. The cleanliness of the siding is also important, and while there may not be many siding cleaning systems in the C&D recovery realm yet, if there is a need there will be a solution. The innovative equipment manufacturers have continued to see to that pattern throughout the industry.

As a C&D facility owner, operator or marketer, as new markets emerge and disappear, there is likely a technological solution to help better separate and segregate your materials in a manner that allows you to sell these commodities that would otherwise be wasted in a landfill. This evolving marketplace is why, by necessity, C&D owners and marketers are some of the most creative in the solid waste industry.

A version of this article appeared in the March/April issue of Waste Today, a sister publication of Construction & Demolition Recycling. The author is the senior project engineer for Gershman, Brickner & Bratton Inc., McLean, Virginia, and can be reached at bkelley@gbbinc.com.