Collection System: 0.04 MGD
Hydrogen Sulfide in Wastewater Collection Systems
Hydrogen sulfide (H₂S) is a corrosive and potentially hazardous gas that can accumulate in wastewater collection systems.
H₂S is commonly produced when sulfate-reducing bacteria (SRB) break down organic material under anaerobic, or oxygen-limited, conditions.
Hydrogen sulfide generation can be especially problematic for wastewater utilities operating in warm climates, where higher temperatures can accelerate biological activity and oxygen consumption.
Why Warm Temperatures Increase H₂S Production
As wastewater temperatures rise, dissolved oxygen can be consumed more rapidly within collection lines.
When oxygen levels become depleted, anaerobic conditions may develop. These conditions create a favorable environment for sulfate-reducing bacteria and can increase sulfide production.
Long sewer retention times, high organic loading, and limited wastewater movement can further contribute to H₂S formation.
Why Wastewater Utilities Manage Hydrogen Sulfide
Controlling hydrogen sulfide is important because excessive H₂S can create several operational and safety concerns, including:
- Strong sewer odors
- Corrosion of pipes and infrastructure
- Damage to pumps and treatment equipment
- Reduced collection system reliability
- Potential health and safety risks for wastewater workers
For these reasons, wastewater utilities actively monitor and manage hydrogen sulfide emissions in sewer collection systems to protect infrastructure, improve working conditions, and reduce odor complaints.
Figure 1. Sulfide transformations in a gravity collection systems (Apgar & Witherspoon 2008).
Using Bioaugmentation to Reduce Hydrogen Sulfide
Bioaugmentation can be used as part of a strategy to reduce hydrogen sulfide (H₂S) formation in wastewater collection systems.
By introducing concentrated populations of organotrophic bacteria into collection infrastructure, operators can help promote microbial competition for available organic substrates. This may limit conditions that favor sulfate-reducing bacteria (SRB), which are responsible for producing hydrogen sulfide under anaerobic conditions.
The following case study describes the use of BioLynceus® ProBiotic Scrubber® OCC (PBOCC) to reduce H₂S concentrations and odors in a municipal wastewater collection system.
H₂S Problems in a 0.04 MGD Collection System
A municipality in New Mexico was experiencing elevated hydrogen sulfide concentrations within its wastewater collection infrastructure.
The gravity collection system averaged approximately 0.04 MGD and discharged wastewater to a larger utility for treatment.
The greatest H₂S accumulation occurred within the system's force main.
Vapor measurements at the force main outfall averaged approximately 150 parts per million (ppm). To meet the city's ordinance, H₂S concentrations in the pipe headspace needed to average 5 ppm or less.
Because the force main exceeded the city's H₂S limit and generated noticeable odors, wastewater management needed a treatment strategy to reduce sulfide formation.
Treating H₂S with ProBiotic Scrubber® OCC
BioLynceus® recommended a bioaugmentation program using ProBiotic Scrubber® OCC (PBOCC).
Daily applications of PBOCC were introduced at the lift station upstream of the force main.
The treatment added a diverse population of organotrophic bacteria designed to support biological activity within the collection system and reduce conditions that favor excessive sulfate-reducing bacteria.
H₂S Reduced Within 60 Days
PBOCC was applied for approximately two months, from March through April, until stable results were achieved.
During the treatment period, average daily air temperatures ranged from approximately 50°F to 70°F.
Within 60 days, H₂S concentrations measured at the force main outfall decreased to below the city's ordinance limit.
Wastewater staff also reported a noticeable reduction in odors. The smell from the force main changed from a strong, pungent odor to a more earthy smell.
Reduced FOG and Lift Station Maintenance
The treatment program also produced an additional operational benefit.
Operators observed less fats, oils, and grease (FOG) accumulation in the lift station where PBOCC was dosed.
The reduced grease buildup lowered cleaning and maintenance requirements within the wet well.
Improved H₂S Control and Odor Management
Throughout the treatment program, the wastewater utility observed:
- Lower hydrogen sulfide concentrations
- Reduced sewer odors
- H₂S levels brought below the city's ordinance limit
- Reduced FOG accumulation in the lift station
- Lower wet well cleaning and maintenance requirements
Because of the results achieved during the initial treatment period, the city continued applying PBOCC to the wastewater collection system.
Supporting H₂S Control with ProBiotic Scrubber® OCC
BioLynceus® ProBiotic Scrubber® OCC is designed to support hydrogen sulfide reduction, wastewater odor control, microbial balance, and collection system maintenance.
References
- Gerardi, M. (2016). Wastewater Bioaugmentation and Biostimulation. Lancaster, Pennsylvania: DEStech Publications, Inc., pp. 20–21.
Wastewater Bioaugmentation and Biostimulation - Apgar, P.D., & Witherspoon, J. (2008). Minimization of Odors and Corrosion in Collection Systems. IWA Publishing, pp. 7–10.
Minimization of Odors and Corrosion in Collection Systems