The Complete Guide to the Windrow Composting Process
In waste management, the windrow composting process plays a key role in turning organic waste into nutrient-rich compost on a commercial scale. In this method, biosolids are piled, exposed to air and sun, and arranged in windrows. The process includes aeration, drying, sieving, and turning. These steps improve oxygen flow, control odours, and support microbial activity. The windrows are designed for easy turning to ensure microbes get enough oxygen.
Windrow composting Methods/Approaches
There are primarily two methods for windrow composting: aerobic and anaerobic composting.
1) Anaerobic Windrow Composting
A composting process in which the decomposition of materials occurs in the absence of oxygen, carried out by micro-organisms.
2) Aerobic Windrow Composting
In aerated windrow composting approach, air or oxygen is supplied to the composting windrow, either by regular turning or by installing an aeration system consisting of pipes and an air blower beneath the windrow. To improve energy efficiency, aeration can be automated using an aeration control system.
Aerobic composting is further categorized based on the aeration method used in the facility.
Operations/ process overview in windrow composting
windrow composting process on a commercial scale
Step 1
Receive and inspect materials, and reject loads with contaminants, for instance, weeds, chemicals, and general waste. They can be sent to landfills.
Mix inputs and form windrows.
Step 2
Reduce the size by shredding or cutting materials greater than 100mm.
Step 3
Mix input and form windrows with the height 1-3m, and width 2-6m.
Step 4
Composting
42-56 days
Maturation 21-28 days
Inspect and monitor temperature and moisture conditions frequently in these phases of compost production.
Step 5
Screening
Compost Turning Frequency
The optimal frequency depends on the rate of decomposition occurring in the windrow whether it is slow, moderate, or fast. Under normal conditions, turning the compost every 3 to 7 days (rather than daily) is recommended to maintain proper aeration and temperature without excessive heat loss (Awasthi et al., 2014).
Process Duration
Windrow composting process takes about 22 weeks to complete. During this process, the heaps are kept narrow, and the waste material is frequently recirculated for effective results and the removal of pathogens. Food waste is regularly mixed and moved into long composting piles (windrows), each measuring 1–3 meters high and 2–6 meters wide. These compost windrows are continuously monitored to ensure compliance and maintain quality.
Facility space requirements for processing 1 tonne/day
- 1 tonne/day – Requires approximately 450 m² (about the size of 1 basketball court)
- 5 tonnes/day – Requires approximately 1,500 m² (roughly 1 Olympic-sized 50m pool)
- 20 tonnes/day – Requires approximately 6,000 m² (around the size of 1 rugby field)
Additional area is needed for raw material blending, storage, processing, vehicle parking, and final compost storage.
Equipment required for windrow composting
- Compost windrow covers for rain prevention. The recommended covers are semi-permeable that facilitate the air flow but can repel moisture.
- Water supply, hose with flow regulator, sprinkler/irrigator shovels
- Windrow turner
- Aeration control system comprised of fans and pipes
- Carbon dioxide probes
Windrow Composting Temperature Monitoring Requirement
A temperature monitoring system is mandatory, whether you choose the anaerobic or aerobic composting approach.
Why it’s important
Maintaining a certain temperature for a specific duration is essential to achieve hygienization, remove pathogens, and kill weeds in the composting materials. Incomplete or unpasteurized compost, meaning material that does not reach 55°C for at least 3 days—can spread weeds to new areas.
Pathogens present in compost can also pose risks to human health.
Resource: You can read our detail guide how to monitor the compost pile temperature?
Pathogens of concern in composting
- Viruses (e.g., hepatitis, enteric viruses)
- Bacteria (e.g., fecal coliforms, Salmonella spp., Legionella, epidermal and respiratory pathogens)
- Protozoa (e.g., Cryptosporidium, Giardia)
- Helminths (e.g., parasitic worms, tapeworms, roundworms, and flukes)
How to eliminate pathogens from compost?
- Ensure every part of the compost material is pasteurized by maintaining high internal temperatures for the required duration and regularly turning the windrow to eliminate “cold spots.”
- Implement rigorous quality assurance by testing compost for pathogens at the start of processing any new feedstock type, and whenever there are significant changes in feedstock or the process.
- Prevent re-contamination by separating equipment, vehicles, and zones used for raw feedstock from those used for treated compost. Wash all machinery thoroughly between handling untreated and pasteurized materials, and avoid applying leachate to compost that has already undergone heat treatment.
- For compost derived from high-risk sources (such as animal excreta, offal, sewage sludge), conduct frequent pathogen testing to ensure safety before application.
Windrow composting cost
The Secretariat of the Pacific Regional Environmental Programme (SPREP) reported, the capital investment for windrow composting machinery and equipment is approximately €100,000. This estimate excludes costs related to land acquisition and site preparation.
Operational Costs per Tonne
The Secretariat of Pacific Regional Environment Programme also reports that the operating costs for windrow composting typically range between €50 and €100 per tonne of compost produced.
Recommendations for odours management
There is a need to establish provincial composting standards, similar to those in Alberta, where the regulations include contingency response plans to minimize offensive odours.
Favourable conditions for windrow composting
During composting, it is essential to maintain favourable conditions such as light, air, and temperature to ensure sufficient bacteria for the decomposition of organic material. This can be achieved through frequent turning.
References
- https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/windrow-composting
- https://pacwasteplus.org/wp-content/uploads/2022/12/Windrow-Composting-Factsheet-7-1.pdf
