How to monitor compost windrows?
When you monitor compost windrows or piles, you can see what’s happening inside and keep the compost conditions optimal. For example, checking the temperature tells you when it’s time to turn the pile. Windrow monitoring is also a compliance mechanism with regulatory agencies. For that reason, compost monitoring sheets are important tools that help you:
- Record data accurately
- Understand any challenges that come up.
- Fix problems when needed
- Keep track of pile activity for regulatory review and windrow compost process validation
In this article, you’ll learn how to:
Pathogens removal process monitoring
Monitor compost temperature
Monitor compost moisture
Check compost pile structure
Monitor compost odors
Compost process validation monitoring
To ensure compost is valid for sale, all critical control parameters such as temperature, moisture, oxygen levels, turning frequency, maturation, materials ratios, and retention time must be monitored and recorded. Requirements vary by country and certification system; for example, BGK in Germany, the PAS 100 in the UK, and EU or US regional guidelines.
Proper log sheets must follow local regulatory and certification standards, as they are essential for showing compliance during audits and verifying compost safety and quality.
Compost pathogens removal process monitoring
Pathogen removal in compost occurs during the thermophilic phase, where temperatures of 55–65°C (131–149°F) are maintained to destroy harmful microorganisms. Compost windrow sanitization is achieved by maintaining ≥55°C (≥131°F) for at least 3 days in in-vessel systems or ≥55°C (≥131°F) for at least 15 days with regular turning in windrow systems.
At this stage, monitor the temperature regularly and record the readings in a log sheet for compliance verification. This is the most critical phase of the entire composting process, as it determines both the quality of the compost and its approval for sale in the market.
Windrow compost monitoring systems such as Periskop simplify this process by providing continuous temperature data that can be accessed remotely, eliminating the need for frequent site visits and enabling the download of compliance reports for the entire composting cycle.
How do you monitor the temperature of compost windrows?
You should measure the temperature from the centre of the windrow. For example, if your windrow is 4 meters wide, use a probe that is 2 meters long. The temperature does not remain constant over time. Usually, it rises at first, stays high for several weeks or months, and then slowly drops back to normal. That’s why Periskop smart probes or compost thermometers with spikes up to 2 meters long work well for commercial composting.
Why monitor compost temperature?
Checking the temperature gives you helpful information, like:
- Is decomposition happening as it should?
- Why isn’t the pile getting hot?
- Are the probes working properly?
- When should you turn the compost?
For example, if the pile temperature is between 40°C and 50°C (104°F to 122°F), it indicates a good carbon-to-nitrogen balance and active microbes.
How to fix temperature problems
If the compost pile gets too hot
- Turn the pile more often to let out extra heat.
- Add more browns, which are carbon-rich materials.
If the compost pile is too cold
- Add water to help the microbes work better.
- Mix or aerate the pile to give it more oxygen.
Microbes create heat as they break down the compost.
What is the ideal temperature range for composting?
The best temperature range for breaking down organic matter and pathogen removal is 32°C to 60°C (90°F to 140°F).
- If it’s below 32°C (90°F), decomposition slows down. Sanitization will not be achieved.
- If it’s above 60°C (140°F), microbes start to die.
Temperature can tell you even more about your compost.
Temperature can also show if there’s enough moisture in the compost windrow. Low temperatures might mean the microbes aren’t very active, possibly because there isn’t enough moisture for them to grow and decompose. Conversely, high temperatures can indicate that microbes are working hard. But if it stays too hot for too long, too much moisture can evaporate, slowing microbes and causing the temperature to drop suddenly.
How can you check the moisture content in a compost windrow?
- Check moisture using your senses
- If water drips out when you squeeze the compost, the moisture content is too high—about 70%.
- If the compost glistens between your knuckles, the moisture content is probably around 65%.
- If the compost holds its shape when squeezed but does not fall apart, the moisture is between 50% and 65%.
- Using smell to check moisture
If you notice strong or unpleasant smells, it could mean:
- Excess moisture
- Poor aeration/oxygen
You can fix these problems by turning the pile, adjusting the moisture, or improving airflow.
What is the best moisture level for a compost windrow?
Aim for a moisture content between 60% and 65%.
When should you turn the compost pile?
After about three days, when the first stage of decomposition is done, the pile’s temperature will start to drop.
This is a good time to turn the pile to:
This is a good time to turn the pile to:
- Reactivate microbial activity
- Supply oxygen through aeration
If the pile reaches 60°C (140°F), turn it to prevent overheating. High temperatures can:
- Kill beneficial microbes
- Cause spontaneous combustion
- Lead to regulatory violations
At what temperature can a compost pile catch fire?
If the temperature goes above 70°C (158°F), spontaneous combustion or a compost heap fire can occur. This is dangerous, can create smoke, and may cause legal or compliance problems at the composting site.
Pile structure monitoring
Pile structure is the overall shape of the compost pile. A good structure helps the pile maintain its shape and airflow. It depends on how the pile is built, the recipe used, and the particle size and density of materials. Poor structure can make the pile too dense, cause it to slump, and lead to anaerobic conditions.
Tools required for pile structure monitoring
Hands and Eyes
Monitoring log
How to monitor compost pile structure
- Look at the overall shape of the compost pile. If the windrow is slumping or cannot hold a triangular or rounded shape, the structure may be poor.
- During the moisture squeeze test, check how dense the compost feels. Look for a mix of particle sizes (from about 1 inch down). Wood materials help improve the structure.
- Check for surface crust on the pile, as this can reduce airflow.
- Advanced field or lab tests are usually not needed unless there is an ongoing problem.
Record your observations about pile structure in a monitoring log and keep the records on file.
How to fix the compost pile structure
A poor pile structure usually indicates that the compost recipe needs adjustment or that the materials were not mixed well. Dense or slumping piles reduce oxygen in the core.
To fix this:
- Add bulking materials like wood chips or bark (5–10% of the mix) and reshape the pile.
- If piles are very tall (over 8 feet), consider making smaller piles.
- Note that piles naturally shrink as composting progresses. This is normal, not slumping.
- If the surface crusts, turn the pile to mix crusted material and restore airflow.
- When building or turning piles, try to avoid compacting the material.
Compost pile odor monitoring
Compost odor is an important indicator of a compost pile’s internal dynamics.
Why do compost windrows and feedstock produce odors?
Odors result from microbial activity in compost piles. They also indicate that the compost pile needs attention. Most odors suggest one of three conditions: the pile is low in carbon, low in oxygen (often due to high moisture), or too dense. These conditions are usually related and often occur together. Compost odors develop from the release of volatile organic acids (VOAs) and other chemical compounds, such as ammonia and sulfur dioxide.
How to monitor compost odors
Smelling the pile while working around or turning it is a common practice among compost producers. If odors are distinct, strong, and or present even when the pile has not been agitated, they typically indicate a problem and should be addressed. Common compost odors include ammonia and sulfides, which create a “rotting garbage” smell. Compost piles can exhibit a range of odors depending on their condition.
How to prevent compost odors
Carbon-based materials (such as activated carbon, compost, or biochar) help reduce odors by supporting microbes that break down odor-causing compounds. They also improve aeration and help control excess moisture in the pile. Adequate carbon levels prevent excessive nitrogen volatilization, which is associated with many compost odors. Carbon also provides binding sites for odorous compounds, allowing them to be captured and metabolized before being released into the surrounding environment. For dense piles, adding bulking materials such as wood chips or bark or increasing the frequency of turning can help improve oxygen levels.
