The Memphis, Tennessee suburb of Collierville operates the Shelton Road Wastewater Treatment Plant, a 3.5-million-gallon-per-day (MGD) treatment facility. The treated wastewater is discharged to the nearby Wolf River, while the biosolids are disposed of in a Class I municipal solid waste landfill operated by Republic Services in Shelby County. With a goal of optimizing the treatment plant’s solids processing, the Town of Collierville, Tennessee, called on Gresham Smith to study the existing operations, evaluate alternatives, and design a solution that would add redundancy, meet future capacity needs and reduce disposal costs.


Town of Collierville


Collierville, TN

Project Type




3.5 MGD

treatment capacity


new screw press units


under project budget

A Two-Story Problem

Prior to the expansion project, the plant’s solids handling system relied on a 45,000-gallon gravity thickener tank and a two-belt filter press for solids thickening and dewatering. The equipment was located in a two-story sludge dewatering building, which was originally designed in 1978 and situated adjacent to the plant’s chlorine building. The belt filter press was located on the second floor, and the roll-off dumpster was located on the first floor, causing two operational issues: solids were not evenly distributed into the dumpster, requiring operators to manually adjust the dumpster location or take the solids by hand. Additionally, trucks had difficulty accessing the building.

Assessing the Alternatives

After examining the plant’s current equipment and solids thickening and dewatering processes, the team evaluated multiple new technologies—three thickening systems and four dewatering systems—and weighed them against a set of evaluation criteria. The equipment needed to add system redundancy, increase capacity to accommodate future population growth, reduce waste volume to save on disposal costs, increase operational efficiencies for plant operators, and work within the existing footprint. The team also assessed up-front and life cycle costs, maintenance requirements and odor control requirements.


Right-Sized Recommendations

After review, Gresham Smith recommended keeping the gravity thickener tank operational and installing two screw press units. This solution offered redundancy while creating flexibility for future capacity and minimized the necessary footprint at the best price. During the project’s subsequent design phase, Gresham Smith was able to utilize the existing sludge dewatering building—with structural reinforcement on the second floor—for both new screw press dewatering units, saving on construction costs. The design also included a new adjacent metal building to house the disposal dumpster, which provided much needed space for trucks and operators.

A Sustainable Solution

After implementing the improvements, the treatment plant is now producing a higher-quality material, which could be turned into a Class A residual, such as fertilizer, should the Town decide against landfill disposal in the future. Additionally, the new equipment has increased the solids concentration, resulting in less landfill disposal costs to the Town.

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Justin Avent, P.E., ENV SP
Justin Avent, P.E., ENV SP
Senior Water Resources Engineer