Biofilter Odour Sampling: The Role of the Sheet Cover Method
Many industrial processes generate odours. For example, wastewater treatment, composting, rendering, agriculture and food processing. In these sectors, effective odour control is essential. It supports regulatory compliance and helps protect local communities. One widely used solution is the biofilter. Biofilters remove odorous compounds from an air stream using a combination of physical, chemical and biological processes. Once in place, it is important to conduct ongoing biofilter odour sampling to assess performance and compliance. One method to do this is the sheet cover method. This enables the collection of representative odour samples from biofilters under controlled conditions.
How Biofilters Work
The biofilter consists of a bed or filter medium, typically composed of organic materials. It provides a suitable environment for the growth of micro-organisms. For example, bacteria and fungi.
The odorous air stream is introduced to the biofilter through an inlet system. This ensures even distribution across the filter medium. As the odorous air passes through, micro-organisms break down the odorous compounds through biological degradation.
To remain effective, biofilters need careful operational control. Operators must maintain appropriate moisture levels, usually through irrigation. They must also ensure a balanced nutrient supply to support microbial activity.
The odorous air must spend a specific period of time (about 60 seconds, known as the ‘residence time’) within the biofilter. This maximises the biological degradation process. At the end of the process, the treated air has reduced odour concentrations. It is released into the atmosphere directly or through stacks.
Monitoring and maintaining your biofilter is essential to prevent a decline in performance. Regular checks should include moisture control, nutrient balance and replacement or replenishment of the filter media. Biofilter odour sampling is an important part of this maintenance cycle.
Why Biofilter Odour Sampling is Important
By conducting periodic biofilter odour sampling, you can:
Evaluate Performance
Sampling before and after treatment, and at periodic intervals, provides insights into how effectively the biofilter is reducing odorous emissions.
Demonstrate Compliance
You can use odour sampling data to demonstrate that your facility complies with the odour limits outlined in your operating permit.
Identify Operational Issues
Where odour issues persist, sampling helps pinpoint the problem and guide troubleshooting measures.
The Sheet Cover Method
Biofilters often require sampling across a large surface area. As a result, a specific technique called the Sheet Cover Method is used. This involves covering the biofilter surface with a thin polymer film (the ‘sheet’), and securing it to prevent leakage of odorous air from the edges. We then create a single outlet opening, large enough to ensure adequate back pressure beneath the sheet. This allows us to collect odour samples without dilution from wind and weather conditions.
The method is also referred to as the sheet method or full cover method. It is just one of a range of odour sampling methods available for different applications.
When to Use the Sheet Cover Method
Typically, we use the sheet cover method to sample odour emissions from biofilters and other large surface sources where wind and atmospheric conditions can affect sample quality. The method helps ensure representative samples that accurately reflect biofilter emissions and are suitable for odour measurement by dynamic olfactometry.
The table below summarises some of the challenges associated with biofilter odour sampling and how the sheet cover method helps overcome them.
| Challenge When Sampling Biofilters | How the Sheet Cover Method Helps |
|---|---|
| Large surface area | Enables sampling across a defined area of the biofilter surface. |
| Wind interference | Prevents dilution by external air movement. |
| Changing weather conditions | Creates more controlled sampling conditions. |
| Representative sampling | Enables collection of samples that better reflect actual emissions. |
Silsoe Odours is UKAS accredited for conducting biofilter odour sampling using this method, as outlined in the European odour standard EN 13725:2022.
Specialists in Biofilter Odour Sampling
Effective odour control is essential for industries that generate emissions. Biofilters provide a highly effective treatment solution. But, you must verify performance to ensure ongoing compliance and efficiency.
Biofilter odour sampling provides a robust way to assess system performance. The sheet cover method enables accurate sampling from large surface areas under controlled conditions.
To learn more about biofilter odour sampling or the sheet cover method, contact our specialist team.
Call: 01525 860222
Follow: LinkedIn | X (Twitter) | Facebook
Published June 2023. Last updated June 2026.
