Class A Biosolids Saving City Time and Money

Jan. 28, 2002

Reclassifying Forest City, N.C.’s Biosolids Program

In addition to treating wastewater, Forest City, N.C.’s wastewater treatment plant (WWTP) used to recycle and store biosolids, a byproduct of the wastewater treatment process. After treatment, the Class B biosolids were hauled to neighboring farms at a cost to the city and distributed over pastureland.

During the rainy winter season, however, the city often had to store the biosolids for weeks on end, which posed a two-fold problem: limited long-term municipal storage space, and fecal coliform counts that steadily increased during prolonged storage and exceeded the U.S. Environmental Protection Agency’s Class B biosolids limits.

Seeking an alternative method for handling and storing its biosolids, the city consulted USFilter in May 1997.

USFilter supplied the city with its Dragon Dryer™ indirect rotating chamber (IRC), an automated heat drying system that produces Class A biosolids. The Dragon Dryer™ IRC, engineered by USFilter’s Davis Products of Thomasville, Ga., safely dries biosolids and decreases their volume by 75 percent or more. In addition to minimizing the biosolids’ sheer volume, this increasingly popular method of indirect heat drying also eliminates harmful bacteria and produces a higher quality product.

Forest City previously produced Class B biosolids, which have less stringent standards for treatment but contain various amounts of pathogens. (These pathogens are generally reduced and diluted by spreading the material and exposing it to natural sunlight, wind and soil microbes.) For the city to achieve Class A biosolids certification, bacteria would need to be removed from the biosolids before they left the facility.

Operating at temperatures of around 212°F, the indirect heat of the Dragon Dryer™ IRC kills pathogens found in the biosolids during the drying process. Consequently, the Dragon Dryer™ IRC produces Class A biosolids, which meet and exceed the EPA’s standards for pathogen-free material and vector attraction.

The single-pass dryer produces biosolids in granule sizes perfect for use as a fertilizer and capable of being stored in the facility’s 6,000 cubic foot storage silo.

Prior to installing the dryer, the city was storing its biosolids in roll-off containers all over its property. Today, the city can safely store 30-days worth of processed biosolids in one silo for up to four weeks. The Forest City Dragon Dryer™ IRC has the capacity to dry up to 62 wet tons of biosolids every 24 hours.

Now more efficient than ever, Forest City’s WWTP is producing Class A biosolids that are used as fertilizer for agriculture and residential lawns or gardens. Farmers now drive to the plant, place their trucks under the silo and load the dried biosolids for a $20 fee, totally eliminating the city’s transportation liability and cost.

USFilter’s Dragon Dryer™ IRC has allowed Forest City, N.C. to upgrade the type of biosolids produced, benefiting the local environment and solving the municipal WWTP’s biosolids storage problem.

Susan McCorvey

USFilter’s Davis Products

Phone: (229) 227-8741

Fax: (229) 228-0312

Email: [email protected]