Stephanie is a wastewater process engineer with Jacobs Engineering with a focus on collection system odor control. Stephanie has a B.S. in Biosystems Engineering from Purdue University and a M.S. in Environmental Engineering from the University of Illinois at Urbana-Champagne.

• Add Second Speaker

Gabrielle is a civil engineer in Jefferson County's Environmental Services Department. She is a 2018 graduate of Auburn University's with a B.S. in Civil Engineering.

Odor mitigation to prevent neighborhood complaints is a challenge in collection systems. Most odors in wastewater collection systems and treatment plants are due to hydrogen sulfide (H₂S) gas: high H₂S emissions can cause safety issues, corrosion of equipment, and nuisance odors. Jefferson County Environmental Services Department (JCESD) experienced an unusually high number of odor complaints in the vicinity of a chain of six wastewater pump stations in the Hoover area. An odor study was conducted to determine the specific locations of odorous air release, the magnitude and cause of the odor, and to develop recommendations on viable solutions to the problem. This presentation will provide:

• Examine a complete odor control case study at JCESD
• The benefits of using sewer process models for developing odor and corrosion mitigation strategies
• Lessons from the odor control pilot study, focusing on dosing strategies
• A preview of the path from pilot to full scale design implementation

In late 2021, a sampling campaign was conducted by JCESD to understand the wastewater characteristics within their sewer. Three sampling locations, in series, all showed high levels of H₂S gas with peaks ranging from 230 – 330 ppm. The observed concentrations could potentially be dangerous to workers in and around the sewers, and the H₂S concentrations present would lead to corrosion over time if not addressed.

The sewer process model (Mega-WATS) was used to evaluate the system by providing a better understanding of the biological and chemical reactions in the collection system causing odor production to efficiently screen several odor control technologies for JCESD. The Mega-WATS model is currently considered by most to be the most rigorous sewer process model. Once the model was calibrated using data from the sampling campaign, seven different odor and corrosion mitigation strategies were analyzed: five liquid dosing strategies and two vapor phase technologies.

JCESD decided to move forward with piloting chemical dosage of calcium nitrate (Bioxide™) because the modeled chemical dose achieved the same odor control effectiveness as the other chemicals with a lower cost and less hazardous chemical properties. From the pilot study, a steady state chemical dose setpoint of 93 gpd was able to achieve target H₂S concentrations of an average less than 10 ppm and peaks less than 50 ppm at the final discharge manhole.

The results from steady state piloting showed that the study area had significantly higher H₂S values during the evenings than at other times throughout the day, so three diurnal dosing strategies were trialed to see if the same target concentrations could be met with a diurnal dosing strategy as with a steady state strategy. The pilot study showed that diurnal dosing would be successful and allow for an average of 60 gpd to be used, saving 33 gpd compared to the steady state dosage. Following the pilot, JCESD decided to proceed with the design of a chemical feed system to dose Bioxide at a diurnal dose rate.

This study has demonstrated the effectiveness of combining multiple tools when developing odor mitigation strategies such as modeling, operational input from the utility, and piloting.  It illustrated that modeling allowed for timely and cost-effective assessment of multiple alternative analysis for odor mitigation strategies and the piloting allowed for an optimized chemical dosing rate strategy for chemical feed system design.