Public agencies refine grinding strategies

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Courtesy of BioCycle Magazine

From coast to coast, municipal agencies operate yard trimmings composting facilities. In many cases, they are on the front line when storms hit that leave downed trees and branches in their wake, opening their gates to a flow of feedstocks of all shapes and sizes. On the other end of the processing chain, these facilities are refining their capabilities to transform the incoming wood, storm debris and yard trimmings into high quality mulch and compost products. This article highlights facilities in Pennsylvania and California.

Allentown, Pennsylvania

In late October 2011, Lehigh County, Pennsylvania, like many surrounding regions, had a Halloween trick played on them. A snowstorm dropped a significant amount of wet heavy snow, which built up on trees that had not yet dropped their leaves. The result was many downed trees and branches, along with lengthy power outages. One year later, on October 29, Hurricane Sandy hit, once again causing major tree damage in the region.

The net effect on the City of Allentown, Pennsylvania’s leaf and yard trimmings facility was, and still is, a huge backlog of unprocessed debris, including trees with massive roots, and piles and piles of leaves. “We exhausted the capacity of local farms to take our leaves for mulching, and have quite an accumulation of single ground mulch from wood that we did process,” explains Eric Trobetsky, Operations Manager for the City of Allentown, who oversees the municipal yard trimmings and wood processing facility. “We used to take material to the Lehigh County composting facility for processing, but since it was privatized, there is a fee to tip there.”

In the spring of 2011, Allentown purchased a Vermeer tub grinder with the capacity to “process stumps the size of a Volkswagen Beetle,” says Trobetsky. “We were fortunate to already have that when the freak snowstorm hit in the fall of 2011.” The grinder is rated to process 300 cubic yards (cy) in an 8-hour day, but throughput varies with the size of the material It is equipped with a shield that covers half of the grinding drum. “That is essential for worker safety because when the machine is running, material can fly out of one side of the drum,” he adds. “The shield is placed on that side so that anything coming out is caught. Also, it is easy to do maintenance on the grinder due to the way the tub opens and tilts to a 90° angle. We can access the cutters and tips easily.”

The city makes the grinder available to other municipalities that also are struggling to process stockpiled storm debris. “We need to get an annual permit from the Pennsylvania Department of Transportation to transport it because it is too large to move under a regular license,” explains Trobetsky. “We ask that they pay the costs of an operator to be there for 8 hours and the wear parts to run the machine.”

He estimates about 80 tractor-trailer loads worth of single ground mulch are on site that need to be screened prior to sale. The city of Allentown is working with American Biosoils & Compost (ABC) to process the mulch. ABC is a joint venture between Two Particular Acres, a composting facility in Royersford, Pennsylvania, and the H&K Group, a quarry company that sells stone, sand, gravel and landscape products. ABC is developing a number of composting sites at H&K Group quarries, in part to process source separated organics from Weis Markets (see “Trimming Costs With Composting,” January 2013). The company has lent the city of Allentown a screen plant, and in turn purchases the mulch for a reduced price.

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