Control options for collection system odor

ORP Meters are a low cost way to track anaerobic zones for odor control programs. Photo from Hanna Instruments.

Collection systems with long residence will have anaerobic zones. Under highly negative redox conditions (no oxygen or nitrate/nitrite present), microorganisms that can utilize sulfate and organics as electron acceptors begin to grow on influent organics. We call these organisms sulfate reducing bacteria (SRB) and fermentative bacteria. The SRB are responsible for generation of sulfides and H2S, while the fermentative bacteria produce short chain volatile fatty acids. Both cause odors with the sulfide smelling of rotten eggs and the volatile fatty acids having sharp, rancid odors. I will list the most common control methods used in collection systems.

• Increase pH to neutralize acids and increase sulfide solubility in the water phase.
• Using iron (FeCl) to bind with sulfides
• Adjust redox upward (nitrate, hydrogen peroxides, ozone, oxygen diffusers)
• Sulfide scavengers (such as amine solutions)
• Odor masking agents

Each option has areas where they are most effective. Often it is best to combine technologies to achieve best odor control at the lowest cost. Before undertaking wide scale odor control, you should sample lift stations and lines to isolate the problem areas (use ORP meter), H2S monitors, and finally organic acid analysis. Once the problem areas are mapped, you can evaluate which technology best suits the area.