The City of Warren (OH) Water Pollution Control is using a dry lime additive with a high calcium carbonate concentration. Their Natures Blend Processing Facility started marketing its lime biosolids in 1998. Including startup-related capital costs, the city saved $323,000 in costs that year from 1997 by avoiding disposal costs and getting paid for their biosolids, Superintendent Tom Angelo said.
The 14 mgd Warren wastewater treatment plant generates about 50-60 wet tons of sludge per day, but the processing facility has a capacity of 240 wet tons. This extra capacity is intended to accommodate biosolids from other wastewater treatment plants that have contracted with Natures Blend Processing Facility.
"We already have a customer base thats over 700 people," Angelo said. Their customers include home gardeners, landscapers, farmers and golf courses.
Before the lime facility was in use, 1997 biosolids disposal costs were $375,000 to $425,000 per year.
Using contracts with neighboring municipalities and bulk sales of Natures Blend at $3.49 per cubic yard, the city paid for all costs related to treating and marketing the biosolids. In fact, Angelo reports a profit of about $35,000 for 1998.
The Warren facility was able to go from a regulated product to a Class A exceptional quality biosolids. Equipment purchases included two Ashbrook belt filter presses, Serpentix conveyors, and an RDP lime stabilization/pasteurization system. The stabilization system uses electrical heat and lime.
"(The RDP system) uses both electrical heat and lime to generate the heat. We dont use as much lime because we actually preheat the cake with electrical heat," Angelo said.
The electrical heat allows operators to use only about 30-35 percent lime on a dry weight basis. That figure would be 80 percent or more without the electrical heat.
From the stabilization system, the biosolids go through a sifting machine into storage, where they are dispensed in bulk form or packaged in bags, as Angelo hopes to do this spring.
The stabilized biosolids have high sulphur and calcium carbonate levels, which Angelo says helps "buffer" the pH and protect plants, as well as discourage fungal diseases such as powdery mildew. The lime-stabilized, Class A product has a relatively stable pH of about 11.5. The potting soil mix to be marketed in the spring will have a pH of 7.
This year, the facility will begin bagging potting soil and lawn fertilizer. "Were hoping to move about 50,000-60,000 bags in the spring, just in our very first year out. So were hoping to generate an additional $200,000 in revenue just from bag sales," Angelo said.
