Cold-Weather Composting: Challenges and Innovative Solutions for Year-Round Operations

Ice-covered compost pile at Lorass Disposal in Canada, featuring SG Bunker® with GORE® Cover.

Municipalities and industrial composting operators in cold regions understand that maintaining compost at a high temperature throughout the winter is no small feat. Freezing temperatures, snow, and bitter winds can all jeopardize the delicate biological process of composting. Yet with the right technology and design strategies, successful year-round composting in sub-Arctic and other cold climates is not only possible but proven. This article examines the primary challenges of cold-weather composting and the innovative solutions, such as the SG Bunker® System, that enable continuous, compliant operations even in the depths of winter.

Challenges of Composting in Cold Climates

Cold climates present several challenges that can hinder the composting process. In regions with long, harsh winters (from temperate zones up to sub-Arctic areas), compost site operators must contend with:

• Frigid Temperatures: Sub-freezing weather dramatically slows microbial activity, extending the time needed for decomposition. If internal pile temperatures drop too low, composting can come to a halt. Operators must prevent the compost from freezing solid, as dormant microbes will not break down the material until warmth returns.

• Snow and Ice: Heavy snowfall can bury compost piles or add excess moisture as it melts, potentially compromising the composting process. Snowmelt and rain can waterlog compost heaps, driving out air and creating anaerobic (oxygen-poor) conditions. This slows decomposition further and can cause foul odors or leachate runoff. Ice buildup may also impede equipment and handling.

• High Winds and Heat Loss: Winter winds whip away rising hot air from the pile, making it harder for microbes to retain the heat they generate. Wind chill on exposed piles can cool the surface and edges, causing core temperature loss. Wind can also unexpectedly dry out piles on cold, low-humidity days, upsetting the moisture balance required for composting.

• Seasonal Feedstock Variation: The quantity and type of feedstocks can vary significantly in cold regions due to seasonal fluctuations. For example, a leaf and yard debris surge in autumn may be followed by very little fresh green material in mid-winter. Managing a seasonal imbalance in carbon vs. nitrogen inputs and storing materials until they can be processed is often necessary. Additionally, frozen or compacted feedstocks, such as clumped biosolids or food waste, can be challenging to mix and handle.

• Water Management: Cold weather complicates leachate and stormwater management. Liquids can freeze in collection tanks or pipes. Conversely, piles kept outdoors face an influx of snow and rain, as noted. Ensuring that process water (leachate) is collected and treated, and that stormwater is diverted, requires careful design of pads and drainage systems. Any water retained in the pile (or added) must be monitored, as too little moisture will halt microbial activity, while too much will create anaerobic zones. Finding the right balance is more challenging in winter, when evaporation is low and freezing is a risk.

• Post-Processing Difficulties: Even once the active composting phase is complete, cold weather can create challenges in curing, screening, and storage. Piles in curing or storage may re-freeze, making it difficult to screen out contaminants or achieve a fine, finished product until thawed. Storing finished compost outdoors in winter might require tarps or covered sheds to prevent the product from crusting with ice or getting overly wet. If screening equipment or conveyors are exposed, they may require heating or de-icing to operate reliably in sub-zero conditions.

Each of these challenges can slow down the composting process or increase operational costs in winter. Historically, many open-air compost windrows in cold climates mainly went dormant in winter, accumulating material to be composted later in spring. However, modern composting technology provides methods to keep the process active year-round, even in cold weather.

Technology Solutions for Cold-Weather Composting

Advances in composting systems have made it feasible to maintain efficient composting even in winter. A combination of process control, physical covers or enclosures, and heat management is key. Here are some of the technology-based solutions enabling cold-climate composting today:

Covered, Aerated Static Pile (ASP) Systems: Unlike traditional open windrows, covered ASP systems insulate and actively aerate the compost pile. The SG Advanced Composting approach integrates the GORE Cover, which maintains the elevated temperatures necessary for pathogen kill, even in freezing weather. The cover keeps snow off the pile and prevents excessive drying or wetting, buffering the compost from the external climate.

• Meanwhile, blower-driven aeration pipes beneath the pile supply oxygen and remove excess moisture and CO₂, generating thermal energy through microbial respiration. The result is a self-heating, well-insulated compost process.

• SG Compost Control System: The entire process is managed by the Compost Control System, which adjusts airflow based on temperature and oxygen feedback, ensuring the microbes stay within their optimal range. The pile generates heat to sustain the process by keeping the biology active. The integrated controls and aeration also mean operators don’t need to turn the piles, as in windrow composting, which limits the exposure of hot compost to the frigid air.

• Integrated Heat Recovery: Beyond simply retaining heat, some facilities capture and reuse the heat generated by composting. One innovative feature that SG and others have employed is an in-floor heating system built into the compost pad. For instance, pipes or tubing (e.g., filled with water or glycol) can be embedded in the concrete pad beneath the piles. As the compost above reaches thermophilic temperatures (often 55–65°C or 130–150°F), that heat transfers into the fluid in the pipes. The warmed fluid is then circulated to heat on-site buildings and garages or preheat incoming air or feedstocks. This not only puts waste heat to good use but also cools the pile if it risks overheating, providing an additional layer of process control. In cold climates, the heat generated by recovered compost can offset facility heating costs. A great example is a Washington State compost facility that installed 5,000 feet of tubing in its ASP pad and now heats its office and shop entirely using compost waste heat. SG’s bunker systems can include such heat recovery infrastructure from the start. While not every site will implement full heat capture, having an insulated pad and walls helps retain pile warmth. Some operators also redirect the warm exhaust air from the compost blower system into greenhouses or buildings in winter. These approaches harness the compost’s natural exothermic process as a benefit rather than a waste, enabling facilities to thrive in low temperatures.

• Operational Adaptations: Technology aside, successful cold-weather composting also involves procedural strategies. Managing feedstock throughput is critical – e.g., processing autumn leaves promptly (or mixing them with high-nitrogen waste) so they don’t become an insulating “cold cap” on piles in winter. Other tactics include staging feedstocks in a warmed building or grinding frozen bulking agents. Covering curing piles with insulating layers, such as a layer of finished compost or a tarp, can help preserve heat. When the weather is extreme, operators might adjust aeration rates (slower airflow to retain heat longer in a pile) or extend the active composting phase by a couple of weeks to meet pathogen-kill criteria. The flexibility of modern control systems enables more effortless adjustment of these parameters in response to changing ambient conditions.

In short, composting systems can maintain thermophilic conditions year-round through the use of covers, aeration, enclosure, and effective heat management. Organizations like Sustainable Generation® have tested and validated these technologies in the world’s harshest climates.

Design Recommendations for Winter Composting Success

Drawing from decades of such experience, engineers have developed a set of best practices for designing composting facilities in cold climates. Some key design recommendations include:

• Integrate Heat Recovery: If possible, build the composting pad with an embedded heating loop system (e.g., pipes under or through the floor) to capture heat from the compost mass. This can be used to warm buildings or preheat incoming air, and it also helps moderate pile temperatures. Even if a complete heat reuse system isn’t initially within the budget, having the infrastructure in place allows for future upgrades as needs grow. At a minimum, an insulated concrete pad will retain heat more effectively than bare ground, and a heat recovery system can be a thoughtful addition to enhance winter performance and energy efficiency.

• Enclose and Protect Critical Equipment: Plan to keep blowers, controls, and other sensitive equipment out of the elements to prevent damage. For example, SG’s cold-climate bunker designs often place the aeration blowers and control units behind a push wall or inside a small, insulated room. This ensures that valves and electronics are protected from direct snow or freezing rain. It also makes maintenance easier in winter, as operators can service equipment in a sheltered space. Likewise, having an enclosed receiving bay means trucks can tip waste without snow blowing in, and loaders can work the feedstock piles without battling ice. Protecting these system parts from the weather greatly increases reliability when temperatures drop.

• Plan for Leachate and Stormwater in Design: Since winter will pose challenges to your water management, design your site with separate pathways for leachate and clean stormwater. This might include sloped pads that drain leachate to a sump (kept warm or agitated to prevent freezing) and outer diversion channels to carry rain and snowmelt away from the compost area. Covered systems naturally help by keeping precipitation off the piles, but any liquids that collect need a freeze-resistant handling system. Insulated pipes, heat tracing, or storing leachate in a heated tank are all strategies to consider. Good drainage and liquid control will prevent winter ice hazards and ensure regulatory compliance with water quality​standards.

• Allow Flexible Process Control: Finally, choose composting technology that allows operators to adjust to winter conditions. This means robust aeration controls (with the ability to adjust airflow rates, switch between positive and negative aeration, etc.), temperature monitoring throughout the pile, and the ability to recirculate air or exhaust heat as needed. Automation can be set to maintain target temperatures. Still, staff should be ready to intervene during extreme cold snaps (for instance, temporarily recirculating warm air into the pile or adding extra insulation on top of the cover). The system should also be designed with surplus capacity – winter decomposition might be slower, so having additional curing space or a slightly longer retention time in the design will provide a buffer when everything slows down in January. It is designed for the worst-case winter scenario, not just average conditions.

By following these recommendations – insulating and enclosing the process, reclaiming heat, weather-proofing equipment, and building in process adaptability – municipalities and operators can set themselves up for composting success even in cold climates. Sustainable Generation’s evolution of the SG Bunker® System reflects these best practices: early systems started as open covered piles, and over time, they added heated pads, integrated covers, and complete enclosures to become more winter resilient. Today’s designs build upon lessons learned and continue to demonstrate reliable performance.

Conclusion

Composting in cold weather can be challenging, but it can be overcome with the right tools and planning. By understanding the unique challenges that freezing temperatures present – and leveraging modern solutions such as advanced covers, aeration control, heat recovery, and insulated enclosures – operators in sub-Arctic and temperate regions can keep their organic waste recycling programs running 365 days a year. Over 3.5 million tons of organic waste are now processed annually using covered ASP technology, much of it in climates once deemed too cold for year-round composting. The benefits are clear: municipalities can divert waste from landfills year-round, meet regulatory requirements for pathogen killing (even in winter), and produce high-quality compost for soil restoration.