Cambridge, Ohio retrofitted a portion of its vacuum assisted drying beds into a covered composting facility, processing about 300 dry tons/year of biosolids and wood chips.
Like many small communities in an agricultural area, the City of Cambridge, Ohio (pop. 14,000) managed biosolids generated by its 2.25 mgd Water Pollution Control Center (WPCC) via land application on farm fields. “Then around 2000, our equipment started getting old and failing, and at the time, we didn’t have the budget to buy new machines,” recalls Chris Jamiel, superintendent of the Cambridge WPCC. “We stopped the agricultural program and ended up sending the biosolids to the landfill.”
Hauling and disposal fees were between $50,000 and $100,000/year, and Lou Thornton, Cambridge’s environmental compliance and safety manager, was looking for a more sustainable alternative. He began exploring the option of composting biosolids with green waste, and toured a variety of facilities to see what would work best for Cambridge. “We had stopped using the vacuum assisted drying beds that were in a greenhouse structure, so that area was available for composting,” says Jamiel. “Lou decided that given that space, windrow composting would work out best.”
The city had been struggling with removing solids throughout the treatment facility and reviewed various treatment options. It experimented with a dewatering tube system that resulted in 8 to 10 percent solids, and ultimately opted to install a rotary fan press that produces 19 to 22 percent solids. “We were paying to haul a lot of liquid, and the higher solids content is much more conducive to composting,” he notes. The rotary fan press has been operating since 2010.