Lenoir biosolids facility
Lenoir biosolids facility

City of Lenoir

Biosolids Facility Improvements

When the City of Lenoir’s existing lime stabilization system was out of service and had exceeded its useful life, the City hired McGill to conduct a biosolids study to explore other options; this provided a prime opportunity for the City to explore other methods of handling the treatment and disposal of biosolids produced at the City’s two wastewater treatment plants (WWTPs) and water treatment plant (WTP).

Biosolids is likely a new term to most people. Here are the basics of biosolids (as explained on the Environmental Protection Agency website):

  • Biosolids are a product of the wastewater treatment process
  • When treating wastewater, liquids are separated from solids
  • Those solids are then treated to produce a nutrient-rich product called biosolids
  • The terms “biosolids” and “sewage sludge” or simply “sludge” all refer to the same thing

The Challenge

The City’s previous method for biosolids handling (filter press) resulted in a dewatered sludge, which produced truckloads of biosolids that had to be shipped out every year to local farms or to a landfill. It was costing the City a significant amount of money to regularly transport this large volume of dewatered sludge.

Our Solution

Process alternatives in our study included belt filter press and centrifuge dewatering equipment, as well as thermal dryers, solar drying, lime pasteurization for Class A biosolids, and the disposal of Class B biosolids. Our optimal solution would be less costly and efficiently remove sludge from the waste stream at its WWTP. The study pointed the City towards choosing to install a thermal dryer system to produce class A biosolids.

The project design included:

  • new sludge pumps
  • a belt filter press
  • dewatered solids storage
  • screw conveyors
  • thermal belt dryer system
  • a bucket elevator
  • building improvements
  • biosolids storage area improvements
  • site work
  • piping
  • valves
  • electrical
  • controls
  • supervisory control and data acquisition (SCADA) programming
  • related appurtenances

The Results

The City selected the thermal belt dryer system as the Class A biosolids system. The installation of a thermal dryer not only reduced the volume of biosolids waste, but reduced pathogens and created a Class A compost product that can be used in many applications.

Biosolids leave the aeration tanks as 90% wet, then are reduced to 20% wet after going through the belt filter press, before getting down to only 1% wet when the biosolids come out of the thermal dryer (which significantly decreases the volume of the sludge by removing the water). This is the primary benefit of a thermal dryer, but a secondary benefit is that it kills the pathogens.

Percent wet graphic

This new process alters a waste product from the aeration process into a beneficial reuse as a soil amendment that provides several benefits, including nutrient additions, improved soil structure, and water reuse. Biosolids are rich in nitrogen, phosphorus, potassium, sulfur, magnesium, calcium, copper, and zinc, which are all beneficial elements for plants. Class A biosolids compost produced by the Lenoir WWTP can be bagged and sold as a soil amendment that it is safe to apply to gardens or be used by NCDOT for roadside soil backfill. Utilizing a thermal drying process results in a product that can be sold or used, which is a benefit to the City.

At its permitted capacity, the City would utilize its belt filter press and thermal dryer to reduce approximately 98,000 wet tons of sludge to 1,600 dry tons of compost annually. At current capacity in 2023, the City dewatered 154 million gallons of sludge with an average of 2.05% solids, equivalent to 767 dry tons per year.

Through the implementation of this new system, the City of Lenoir increased annual expenditures for the purchase of natural gas used in the drying process (estimated to be $84,000 per year), but also reduced expenditures associated with hauling the biosolids to local farms (estimated to be $73,000 per year) and operations and maintenance costs (estimated to be $8,000).

After our team completed the biosolids study, the City then retained McGill for the design, permitting, bidding, and construction administration of biosolids facility improvements at its Lower Creek WWTP.

“We were very pleased with the outcome of this project. From the beginning, the staff at McGill worked with us and sought input from City leadership as well as the maintenance staff that would be maintaining the dryer equipment for years to come. The level of evaluation on the front end led us to find a technology and process that best suited our operational needs, in addition to our financial needs. A good team effort led us to a successful project.”

  • Radford Thomas
    Former Director of Public Services at the City of Lenoir

Lenoir biosolids facility


McGill has worked closely with the City Lenoir on this project that turns what is considered a waste product into a product that can be sold, financially benefitting the City.


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Project Services Included:

  • Evaluation
  • Funding
  • Surveying
  • Design
  • Permitting
  • Bidding and award
  • Construction administration
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