Ozone/Carbon Odor Control on Wastewater Facility – Case Study
- No significant degradation of carbon after 4 years (biofilm not present)
- 86% to 95% odor reduction at stack outlet
- Significant capital/maintenance cost reductions
- Maintenance vs. biofilters or scrubbers significantly reduced
- Operating costs lower than biofilters, scrubbers
- 84% H2S reduction
For the last 4 years we’ve been monitoring an Envron wastewater odor control installation using a combination of Ozone as the initial oxidizer with a carbon scrubber prior to release to atmosphere. The system was installed summer of 2014 and results are 86 to 95% odor reduction at the stack outlet with minimal degradation of the carbon. (See Case Study below).
Ozone is the fastest acting oxidizer that is commercially available. Ozone systems provide consistent oxidizer output for rapid destruction of long-chain organic (odorous) compounds. The Ozone system at this facility provides initial oxidation of the odorous compounds. The carbon scrubber acts as a second barrier to remove any residual odors and is also used to destroy residual ozone (exothermic reaction). Static mixers ensure entrainment of the ozone with the odorous compounds.
A carbon bed provides the “scrubbing” of the Ozone/gas mix. Unlike a traditional stand-alone carbon scrubber there has been no biofilm formation on the carbon. In a moist organic-rich airstream a biofilm is usually expected. While carbon suppliers generally consider the carbon “depleted” when odor control drops off, the carbon in this case has not exhibited degradation after 4 years of operation.
We attribute this to the effects of ozone in inhibiting biogrowth in the carbon. We have seen the same biofilm inhibition in other Envron odor control installations. For example at an installation at AFB International where traditional chemical scrubbers were converted to Ozone. Ozone effectively penetrated the existing biofilm and the biofilm then sloughed off the packing bed substrate.
Since no biofilm has been observed at this wastewater site and since the carbon remains effective, it appears the carbon is being “maintained” by the ozone.
ADVANTAGES of CARBON/OZONE
The carbon/ozone system provides a “synergistic” set of advantages. No biofilm development means the carbon has not needed to be regenerated after 4 years of use. As well, no degradation of the carbon due to the ozone has been observed even though the reaction is exothermic. Carbon is “regenerated” by heating, which would also remove any biofilm from the carbon. Regeneration has not been needed at this facility.
As an added benefit the carbon provides destruction of any excess ozone which would meet even the most stringent ozone emission regulations. This means that higher initial dosages of ozone can be designed into the system for a more thorough and rapid destruction of long-chain (odorous) compounds. This is also beneficial for fluctuating odor levels.
OZONE ADVANTAGES vs. SCRUBBERS and BIOFILTERS
Contacting/Retention times are reduced and system footprints are much smaller. This makes the system ideal for applications where space for the contacting/retention system is tight or limited. Traditional chemical based scrubbers can be replaced with Ozone in air, eliminating water disposal issues.
Envron Ozone systems are usually distributed (depending on site requirements) meaning that routine maintenance on a single generator/oxygen concentrator can be performed while the rest of the system is running. In the unlikely event of a single generator/concentrator failure, the rest of the system is running and the carbon provides a secondary barrier for odors.
Routine maintenance for both the carbon scrubber and Ozone system can be scheduled providing adequate lead time for personnel deployment. Management by emergency is not required.
OZONE/CARBON vs BIOFILTERS
Ozone/carbon offers a much smaller footprint than traditional biofilters. On a retrofit contacting/retention systems can be roof-mounted or on the ground. Alternately, the existing building ventilation system can be enlarged. With new construction, the contacting/retention system can be built into the building ventilation system. Because any excess ozone is being removed by the carbon, Ozone generation can be increased allowing more ozone to be available for fluctuating odor levels.
Biofilters require a precise operating environment (temperature, moisture) to remain effective. In the case of weather fluctuations, a biofilter’s effectiveness may be compromised and the biofilter may have to “recover” by rebuilding the biofilm. Ozone/Carbon systems are mechanical and do not require a “break-in” or “recovery” period.
Sewage Pump Station – Case Study
Wastewater flow: 400 m3/day – Please note – systems can be scaled up or down depending on site requirements.
Sewage type: sanitary
Flow Type: gravitational
Chimney gas flow: 1,100 M3/hr (650 CFM) – Please note systems are scalable. Envron systems have been sized to 150,000 M3/hr (88,000 CFM)
- Self-contained Oxygen Concentrator provides 95% pure oxygen to the ozone generator
- Envron ozone generator provides Ozone to the contacting/retention system.
- 21ZX control sensor, the sensor measures ozone concentrations in the range of 10/0.01 ppm, and will be calibrated annually.
- Contacting/Retention provided by HDPE Rotomold tanks.
- Carbon Scrubber – 3 second Empty Bed
Odor sampling was done by an accredited laboratory according to European standard- EN13725.
Sample 1 (low odors)
No. of units odor treatment facility entrance: 8661 odor units / cubic meter of air
No. of units odor treatment facility exit 455 odor units / cubic meter of air.
Percent reduction: 95%
Sample 2 (peak odors)
No. of units odor treatment facility entrance: 46,400 odor units / cubic meter of air
No. of units odor treatment facility exit: 6,500 odor units / cubic meter of air.
Percent reduction: 86%
The concentration of hydrogen sulfide treatment facility entrance: 6 mg / m³ air
The concentration of hydrogen sulfide treatment facility exit: 0.962 mg / m³ air
Percent reduction: 84%