Tub grinders help city of bakersfield grow wood waste program

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Courtesy of Morbark, LLC

In its early stages, the wood waste recycling program employed by the Solid Waste Division of Bakersfield’s Dept. of Public Works (DPW) was bare bones at best. Implemented as a means to both lower the volume of material going to landfill and, at the same time, generate a product that could be used by area residents, initial volumes collected and processed were relatively low. Processing was handled by a small, low horsepower grinder that, for the first couple of years, proved adequate. However, as the program matured and volumes increased, it became evident that a larger, more productive grinder was needed. Today the City owns and operates a pair of Morbark 1300 tub grinders and those units have provided the performance needed to meet special needs such as an unexpected uptick in volumes, as well as to grow the program itself.

More Than Just the City
To say that the wood waste recycling program in place is the City of Bakersfield’s is something of a misnomer. According to Kevin Barnes, the DPW’s Solid Waste Director, the area served encompasses far more than just the city itself.

“The program as it exists today serves the residents of the City of Bakersfield as well as all of the unincorporated Kern County immediately surrounding the city. So, given the quarter of a million people living in the city and the 130,000 county residents, our total scope is actually reaching no fewer than 380,000 people.”

Barnes says that the program is geared almost exclusively around a drop-off system, with green waste and wood waste — both natural wood material and clean C & D wood — collected at the nearby Mt. Vernon Greenwaste Facility.

“The overwhelming majority of our material comes from urban sources: mainly tree trimmings or construction wood from remodeling jobs, fence replacements and so on. We do have a collection system in which residents deposit green waste in 64-gallon containers for pickup, but that material — more than 50,000 tons per year of it — goes straight to our composting area. Material that is slated for grinding, however, is collected at Mt. Vernon and sent through a Morbark tub grinder to create the mulch product we need. The end product, three-inch and smaller wood chips, is primarily sold to a huge co-gen plant not far from here for biofuel. Other markets for the material include landscapers and grading companies which find it useful for erosion control. The county finds the material equally valuable for erosion control at its landfill, so we supply them with the mulch they need. And finally, we keep some of the material for our own use. Nothing generated as part of our wood waste program gets left unused.”

Upsizing the Process
Making the move from a small, highly inefficient grinder to a larger one that could help the wood waste program grow was essentially a no-brainer. Deciding which type and model to put to work was a different matter entirely.

“We looked at a broad range of grinders — both tub grinders and the horizontal units available today — and weighed the strengths of each against a list of specifications; price was also a consideration, but performance was the key. Based on those criteria we selected the tub grinder from Morbark and we feel we made the right decision both in manufacturer and in the type of unit we chose. The kind of material we often get in this area essentially took the horizontal grinder out of the equation.”

One such material to which Barnes is referring is the mulberry tree which is seemingly everywhere in the Bakersfield/Kern County region and which produces long, slender branches that have to be almost continually pruned. Seeing people coming to the site with 20-foot trailers full of mulberry branches that have grown up over the summer is not uncommon, he says.

“In our field trials, we found it very cumbersome to get that length of branch — and all the spindly material attached to it — fed into the hopper of a horizontal grinder. And, once in there, we saw the potential for lower production because the branches have a tendency to wrap around a horizontal unit’s rotor. So we opted to stay with the tub-type grinder and the Morbark made the most sense for us based on our criteria.”

A Positive Reaction
Armed with a more powerful grinder, the city’s wood waste program has evolved into a 60,000 tons per year success story. Equally important now, says Barnes, is the program’s ability to react to sudden unforeseen increases in volume.

“This area, though it might seem otherwise, has a seasonality to it. October through January is the pruning season and we see our volumes rise by at least 50%. We are geared up for those volumes and have no problem meeting them. However, occasionally, things happen which we don’t anticipate and which put us to the test. In 1998, for example, a freak snowstorm dumped six inches of snow on Bakersfield area overloading the limbs of trees in the area. The result of that storm was a one-month period in which we went from an average of 2,000 truckloads of wood waste per week to 7,000 truckloads a week. It was chaotic and unbelievably challenging but we proved that we could rise to the occasion. A smaller, less productive grinder would surely not have afforded us the same performance — and the same results.”

Change for the Better
Barnes and his department recently purchased a second Morbark 1300 tub grinder. He says the purchase was based on a routine life-cycle replacement but adds that they now also have a luxury they’ve never had in the past.

“Our studies have found that these units have a five- to seven-year life cycle and we were in our seventh year with the older unit. We felt it was time to bring in another unit which would allow us to rotate the two machines when routine maintenance needs arise. However, having two grinders also opens up a number of additional possibilities for the program. For example, it is now much easier for us to do some auxiliary portable grinding around the area. After Christmas, we have a number of drop-off sites where residents can discard their Christmas trees. We can now easily take one or both of the grinders to the sites and grind the trees onsite.”

According to Barnes, they have been able to initiate a new program with the city’s Parks & Recreation Department. In the past, when that department did their regular tree maintenance they would haul the material to the central processing site. Now, satellite locations set up throughout the area serve as processing sites. Doing so will help spread some of the workload around, reducing the workload on the central site which, he says, is just about at capacity for a single grinder.

“No single piece of equipment can be held responsible or accountable for a program’s success,” he adds. “However, the performance we’ve gotten from the Morbark units has been everything the company promised and then some. More importantly, we’ve gotten excellent support for that equipment and because reducing downtime is as important to us as it is to someone in the private sector, that support weighed heavily on our decision when choosing the second unit. We’re doing things now that, at the program’s outset, we never imagined we’d be doing and we’re seeing new possibilities all the time.

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