Biosolids Management Upgrades: Hominy Creek Wastewater Treatment Facility

Client: City of Wilson
Location: Wilson, NC

The Hominy Creek WWTF is a 16-mgd biological nutrient removal activated sludge wastewater treatment plant that discharges into Contentnea Creek, a tributary stream in the Neuse River Basin watershed. Hazen and Sawyer was selected by the City of Wilson to provide preliminary and detailed design of biosolids management facility upgrades at the Hominy Creek WWTF.

Project Outcomes and Benefits

  • Anaerobic digestion facilities were completely renovated and restored to active service allowing the plant to achieve Class B stabilization without liquid lime addition.
  • Gravity belt thickening facilities were installed to provide enhanced thickening and reduced volumes for waste activated sludge streams.
  • Belt filter press dewatering was installed allowing the facility to migrate from a liquid solids handling program to a less costly dewatered cake solids handling program and provide capability to achieve Class A pathogen reduction via alkaline stabilization.
  • Provided facilities for production of a Class A alkaline pasteurized product using the proprietary RDP EnVESSELâ„¢ Pasteurization Process.
  • Provided a covered dewatered cake storage area to allow facility flexibility in management of residuals dewatering activities independent of land application activities and land application constraints.

Belt Filter Press

Liquid Sludge Holding Tank

Primary Sludge Pump Station

Anaerobic Digesters

Sludge Thickening and Dewatering Building

Hominy Creek Site

Digester Rehab Under Construction

Waste Gas Burners

Prior to upgrades, residuals from the liquid train treatment were alkaline stabilized as a Class B liquid and land applied by a contract operator to agricultural land in the surrounding area. The liquid land application program was subject to seasonal limitations on application causing the plant to have to store liquid sludge for extended periods. Temporary trailer mounted sludge dewatering equipment had been brought to the site by the contract operator to produce a dewatered cake product more amenable to long term storage on existing sludge drying beds. This project included major upgrades to provide a foundation for long-term successful biosolids management. The upgrades to the solids handling facilities included complete anaerobic digester rehabilitation, digester gas handling and treatment, gravity belt thickening, belt filter press dewatering, Class A alkaline stabilization, and covered dewatered cake storage.

The anaerobic digester rehabilitation included replacement of the existing digester covers and replacement of all the mechanical equipment within the existing digester complex, including: heat exchangers, recirculation pumps, transfer pumps, digester mixing pumps, and gas collection and handling equipment. New ancillary facilities including digester gas compression and drying, digester gas fueled hot water boilers, and waste gas flares are also included in the digester rehabilitation work.

A new solids management facility was constructed using pre-cast concrete wall panels that allowed the Contractor to accelerate construction and overall project delivery. The new solids management facility house two three-meter gravity belt thickeners and two two-meter belt filter presses. The solids handling building was also designed to accommodate addition of one, or more, additional belt filter presses or gravity belt thickeners when additional plant capacity is required. The solids handling building also includes feed pumping and chemical preparation facilities for the thickeners and belt filter presses.

Alkaline stabilization equipment is provided in a separate structure located between the solids handling building and the covered cake storage area. The alkaline stabilization process was bid for construction as either a conventional alkaline stabilization system or for the proprietary RDP Technologies En-Vessel Pasteurization Process. Following the bid phase a lifecycle cost analysis was conducted to allow the Owner to select the technology which provided the superior long-term value considering both capital and operating costs. This evaluation demonstrated that the additional capital costs associated with the RDP system would be off-set by reduced annual O&M costs when alkaline stabilization processing exceeds 30 percent of the total annual biosolids production. Based on the superior economics, Hazen and Sawyer recommended additional capital expenditures were warranted for installation of the propriety RDP En-Vessel Process.

For more information on this project, or to discuss a similar project in your area, contact

C. Michael Bullard, P.E. at mbullard@hazenandsawyer.com