County refits compost plant
New Jersey’s Cape May County has achieved remarkable success with its new sludge composting facility. The facility handles virtually all the sludge from the county’s four wastewater treatment plants, producing 20 dry tons of compost daily. The final product is nutrient-rich, pathogen-free and odorless.
Buyers are primarily golf courses, nurseries, public works facilities and the New Jersey Department of Transportation, which uses the compost for roadside restoration projects to enrich the coastal county’s dry, nutrient-poor soil.
Ironically, it was that sandy, highly-abrasive soil that, upon finding its way into the sludge, accelerated wear on the conveyer belt drag chains in the old composting facility, resulting in very high maintenance expenses.
In 1987, Cape May County Municipal Utilities Authority started looking for alternatives, including “sandwich” style conveyor designs. The authority hired CH2M Hill of Englewood, Colo., which then brought in a conveyor specialist subcontractor, Wolf Associates, to examine all the available options.
Eventually, the facility purchased two sandwich-type conveyors (HACs) from Continental Conveyor, Winfield, Ala.
Initial installation began in August 1990. To keep costs down, operations personnel elected to assemble the new system themselves. “We shut down in April to do all the work, and it only took about two weeks,” says County Municipal Utilities Authority Engineering Manager Manley Solheim. “Of course, in the meantime, we had to pay to take all the sludge elsewhere, so length of downtime was really important.
“The cost of the project with the authority work force serving as a construction contractor was about $763,000, or a savings of about $860,000 when compared with the general contractor’s bid,” Solheim says.
In the HACs, the sludge and sawdust “raw feed” are dropped separately on the conveyor belt from two live-bottom hoppers, then conveyed 30 feet straight up to two mixers in an adjacent room. There, pug mill mixers thoroughly mix the sludge with sawdust, as well as some recycled compost.
The mixed material is conveyed by the second HAC up to an outside shuttle conveyor that takes the material to one of two reactors for in-vessel material at a rate of approximately 44 tons per hour and a belt speed of 250 feet per minute.
“I think the consideration of in-vessel sludge composting as a viable sludge treatment alternative will increase in the coming years,” Solheim says. “In fact, there have been a number similar projects begun since ours started up.”