Fulton County Department of Public Works


Roswell, GA


Wastewater Engineering

Originally constructed in the 1970s and upgraded several times in the years since, Fulton County’s Big Creek Water Reclamation Facility (WRF) is a conventional activated sludge facility with step-feed capabilities and a biological nutrient removal process. In 2017, during its most recent rehabilitation project, Fulton County sought to improve the facility by addressing operational issues, removing hydraulic restrictions that prevented it from passing peak flows and replacing equipment and systems that were nearing the end of their useful life.

The county called on Gresham Smith to design, permit and provide construction services that would improve the biological nutrient removal process, secondary clarifier mechanisms, odor control systems and solids handling capabilities. Through some genuine ingenuity, innovative design and insightful planning, the firm was able to make the necessary upgrades, while also reducing operation and maintenance costs.

in cost savings
MGD peak flow
reduction in chemical usage
Large machines pictured at Big Creek Water Reclamation Facility.

It All Starts With a Model

In 2012, the Big Creek WRF received a new permit, which reduced the phosphorus load-based limit from what was previously allowed, thereby creating a more challenging compliance situation. Gresham Smith performed a Biowin model-based evaluation and hydraulic study to reassess the facility’s various compliance capabilities. The team then used these models to simulate various flow rates and pollutant loading conditions through the existing plant facilities, and design the facility improvements to meet the new phosphorus limits.

Workers clean large aeration basin at Big Creek Water Reclamation Facility.

A Little Cleaning Does the Trick

Due to a lack of screening and grit removal facilities, the aeration basins had accumulated a significant amount of material, leading to capacity and performance issues. The maintenance of plant operations plan specified that each basin be emptied and cleaned to uphold permit compliance.

Plenum suction-style mechanisms pictured at Big Creek Water Reclamation Facility.

Out With the Old, In With the New

Previous computational fluid dynamics modeling and field testing on the secondary clarifiers indicated that the units produced a significant head loss resulting in diminished performance. The model showed that the mixed liquor splitter box weirs resulted in an unequal loading of the clarifiers, and further impacted the aeration basins. We recommended replacing the splitter box gates with upward closing weir gate, and rehabilitating the existing clarifiers with plenum suction style mechanisms that enhance control for balancing flows to each clarifier.

Long piping system pictured at Big Creek Water Reclamation Facility.

Compliance? Check!

With a new permit including more stringent phosphorus limits, reliable RAS pumping capacity and chemical feed facilities are needed to maintain permit compliance and stringent nutrient limits. New ferric chloride, hydrated lime and polymer systems, and increased controls for RAS pumping were designed to provide plant operations staff with flexibility and allow Fulton County to support peak flow and load compliance.

Screw press system pictured at Big Creek Water Reclamation Facility.

A Complete Overhaul

Originally, a plan was made to rehab the existing belt filter presses with in-kind equipment. However, it was determined to be more efficient to design a new screw press system and reconfigure the existing dewatering building. The screw press system reduced plant operation and maintenance costs, as well as alleviated odor complaints. Even better, it reduced overall operation and maintenance costs for the facility.