Overview

Cary is the first in the region to build and operate equipment that dries wastewater treatment sludge into BB-sized fertilizer pellets. This provides an environmentally-safe alternative to the increasingly impractical method of trucking sludge away and spraying it on farmland.

The drying equipment is able to handle more sludge than Cary's wastewater treatment plants produce right now. The Town is planning to accept sludge from nearby towns, providing a regional solution for an important waste management issue. The waste generated by a typical family in a year will produce about 100 pounds of fertilizer.

Enviro Gems

The Town of Cary will market its round fertilizer pellets under the name Cary Enviro Gems. The name was selected from among more than 60 ideas submitted by Town employees during an internal naming contest.

Cary Enviro Gems are being sold wholesale to distributors for approximately $15 to $20 per ton, depending on market conditions. The Town sold the first 50 tons of Cary Enviro Gems to a Georgia-based fertilizer blender in February 2006.

Location - South Cary Water Reclamation Facility, one of two wastewater treatment plants in Cary. (Sludge from the North Cary plant will also be dried there.)

More on Why

Like many other towns, Cary used to hire companies to spray sludge on numerous pieces of farmland in the vicinity. However, this means hauling sludge by tractor-trailer as much as 60 miles. With development in the area, finding suitable land for disposal will become increasingly difficult. Some also question whether land application is the best environmental solution for the treatment byproduct.

North Carolina has strict rules getting rid of sludge and limiting exposure. Sometimes it goes into landfills, taking up valuable disposal space. Drying sludge into pellets decreases the volume to a small fraction of the original amount while producing a safe and useful landscaping product.

The Scoop on Sludge

Sludge is the residue of biological wastewater treatment and is referred to in the treatment industry as bio-solids. It contains the remains of organisms that digest solids left over after water in sewage has been removed, treated and either released into creeks or reused. Even so, sludge is almost entirely water.

At the South Cary plant, sludge is pumped from settling basins into a machine with porous belts that allow some of the liquid to drain off as it moves across the belts. Then thickening sludge drops into a hopper for pumping into storage tanks where biological decomposition continues.

Spin Cycle

With the new process, sludge in the holding tanks - still a soupy consistency - will move through a centrifuge. It throws off much more of the liquid, taking the sludge from 97 percent water to 80 percent water.

Into the Dryer

This is the final stage, where the sludge turns into tiny, round pellets that can be used as a fertilizer or soil amendment. This converts sludge into a product that the public can use. The pellets are stored in a silo until sold.

To Learn More

Robert Paul Bonné
Utilities Director
Town of Cary
Public Works and Utilities Department
PO Box 8005
Cary, NC 27512
(919) 469-4303