Biosolids Composting O Control: Managing Odors from Processing Through Curing Odor
Biosolids composting gives wastewater treatment facilities an opportunity to turn organic material into a useful end product, but the process can also create challenging odor conditions. Material handling, changing biological activity, moisture, temperature and aeration can all influence when odors develop and how noticeable they become beyond the facility.
Effective biosolids composting odor control starts with understanding where those emissions are coming from and how operating conditions are affecting them. Simply treating the air without understanding the process may address part of the problem while leaving the primary odor source unchanged.
At Webster Environmental Associates, Inc. (WEA), we help facilities evaluate odor at the source and develop control strategies based on actual site conditions rather than applying the same solution to every composting operation.
Why Biosolids Composting Can Create Odor Problems
Composting depends on biological activity. As microorganisms break down organic material, conditions inside the composting process continually change. If areas become poorly aerated or anaerobic, stronger odor compounds may develop.
Biosolids themselves can also arrive at the composting process with an existing odor load. Storage time, dewatering, handling methods and upstream wastewater treatment conditions can influence the characteristics of the material entering the composting operation.
Once composting begins, odor can potentially be released during several stages, including:
- Biosolids receiving and storage
- Mixing biosolids with amendment materials
- Active composting
- Aeration and pile turning
- Material transfer
- Curing
- Finished compost storage and handling
Weather can add another variable. Warmer temperatures can increase biological activity, while wind and atmospheric conditions affect how emissions travel beyond facility boundaries. WEA’s broader odor-control work accounts for environmental and operational factors because odor generation and off-site impact can change considerably with site conditions.
Finding the Actual Source Before Choosing a Solution
When complaints occur, the strongest-smelling location inside the facility is not automatically the source creating the greatest off-site impact.
A comprehensive odor evaluation can include source sampling, chemical analysis and dispersion modeling to determine which processes are contributing most significantly to the problem. WEA has used this type of approach at wastewater facilities to characterize odors, prioritize sources and evaluate mitigation alternatives rather than relying solely on perception.
For a biosolids composting operation, that information can help answer important questions. Is odor primarily being generated during receiving? Does turning create short periods of high emissions? Are curing or storage areas contributing more than expected? Are operating conditions creating an avoidable odor problem?
Those answers provide a much stronger foundation for selecting an odor control strategy.
Containment and Air Collection
In some composting applications, controlling where odorous air travels is an important part of the solution.
Covers, enclosures and properly designed ventilation can capture emissions before they disperse through the facility or into the surrounding community. Captured air can then be routed to an appropriate treatment system.
WEA evaluates airflow, emissions and the physical characteristics of a facility when determining how containment should fit into an overall odor-control design.
The goal is not necessarily to enclose every process. It is to identify where containment provides enough benefit to justify the additional infrastructure and treatment requirements.
Biofiltration for Composting Odors
Biofiltration can be particularly useful for treating large volumes of odorous air containing biodegradable compounds.
A biofilter routes contaminated air through porous media that supports naturally occurring microorganisms. Those microorganisms biologically oxidize odor compounds as the air moves through the media. Maintaining proper moisture and pH is important for keeping the biological population healthy and the system operating effectively.
Biofilters are commonly associated with wastewater and composting applications because they can provide biological treatment without the ongoing chemical requirements associated with some other technologies. However, they require appropriate loading conditions, adequate space and proper operation.
That is why choosing biofiltration should follow an evaluation of the actual air stream rather than simply assuming that a biological process requires a biological odor-control system.
When Other Odor Control Technologies Make Sense
Not every biosolids composting facility will have the same emissions profile.
Depending on contaminant concentrations, airflow and variability, other technologies may be appropriate. WEA’s odor-control toolbox includes chemical scrubbers, activated carbon systems, biotrickling filters, covers, enclosures and ductwork, among other approaches.
In some situations, a combination of technologies may provide better performance than relying on a single treatment method.
This is also where WEA’s independence from odor-control manufacturers is important. The company does not represent a particular equipment manufacturer, allowing recommendations to be based on the facility’s actual needs rather than a predetermined technology.
Odor Control Should Include the Composting Process
Equipment is only part of biosolids composting odor control.
Operational conditions should also be evaluated. Aeration, moisture, material handling, residence time and the condition of incoming biosolids can all influence odor generation. Finding opportunities to prevent or reduce odor formation at the source can reduce the burden placed on downstream air-treatment equipment.
This creates a more complete strategy:
Identify the source. Reduce odor generation where practical. Capture emissions where necessary. Treat the remaining odorous air with the appropriate technology.
That approach can also help facilities avoid spending money treating air from areas that are not actually driving their odor problem.
Building an Odor Control Strategy Around the Facility
Composting operations vary in layout, capacity, feed material, surrounding development and community sensitivity. An odor control system that works well at one facility may be unnecessarily expensive or ineffective at another.
WEA approaches odor control by collecting data, evaluating alternatives and designing around the individual facility. The firm has decades of specialized odor-control experience and has completed hundreds of projects involving municipal and industrial odor challenges.
For facilities dealing with recurring complaints, planning a composting expansion or evaluating an aging odor-control system, the first step should be understanding the problem before selecting the equipment.
Effective biosolids composting odor control is ultimately about controlling odor from the process to the property line, with a strategy designed around how the facility actually operates.