Aerated Static Pile Composting

Aerated static pile composting, or ASP, is an effective method to accelerate and manage the composting process with much lower risk of foul odors. It also is an ideal system for colder climates, where year-round composting may be difficult or impossible.

In aerated static pile composting, organic waste is mixed into a large pile and then aerated through the addition of bulking agents such as wood chips or shredded newspaper. The air flow is controlled by pipes that deliver or draw the air into or out of the piles.

Aeration

Aeration in composting is the process by which air is circulated through the waste pile to satisfy the stoichiometric demand of oxygen to aerobic decomposition; remove excess heat; and control moisture. This is important to the microbial population, which needs constant access to oxygen for a rapid and complete decomposition of organic material.

Aerated static pile composting (ASP) is a mechanically aerated method that was originally developed for composting biosolids in North America. It has recently been utilized for a variety of other feedstocks, including compostable municipal solid wastes.

The aeration process used in aerated static pile composting relies on the mechanical transfer of air from an external source into the waste. The aeration is typically delivered through fan blades that sit on top of the composting mass. The fans are controlled by a timer or manual switch to ensure the appropriate amount of air is supplied at all times, and that the system does not overheat.

There are a number of different types of aeration systems, and the choice will depend on what kind of composting operation is being operated. Some systems simply operate on positive pressure, meaning that they push air into the compost pile through a pump. Others pull air through the compost pile using a blower or fans.

Many aerated static pile composting systems also incorporate a cover layer to help reduce odors and regulate air emissions. The cover consists of compost that is stable and is highly effective at retaining nitrogen. The microbes that live under the cover will aerated static pile composting destroy any odorous compounds from the compost mix as they decompose it.

This is a valuable tool for controlling air emissions, as some local air quality districts require that all composting operations be covered in order to meet their emissions reduction mandates. The compost cover is also a thermal blanket that helps the raw materials reach temperatures adequate to destroy pathogens, parasites and weed seeds (131°F for at least 3 days).

Aerated static pile composting is a beneficial method of composting for a variety of facilities. The process is relatively inexpensive to implement, especially compared with other composting methods, and it produces compost relatively quickly. It is suitable for a large variety of feedstocks, including yard trimmings, food scraps and compostable municipal solid waste.

Temperature Control

Aerated static pile composting is a method for processing large volumes of wet materials like sludge, manure or bio-solids. These systems are also used to compost municipal solid waste (MSW) and yard trimmings. They offer process control for rapid biodegradation and work well for facilities processing wet materials and large volumes of feedstocks.

Aeration is needed to satisfy the stoichiometric demand for oxygen in aerobic decomposition, remove excess moisture and heat, and keep temperatures within a target range. The total oxygen demand for each dry weight of compost depends on the stoichiometric demands for the organic decay (oxidation of carbon) and nitrification processes. The total stoichiometric demand for each feedstock in a compost mix is then summed to calculate the airflow rate needed to maintain temperature at 131degF and microbial oxygen levels above 12%.

During aerobic decomposition, the microbes in the pore spaces of the material absorb oxygen, dissolving it into the liquid film surrounding the particles. However, the solubility of oxygen in this film decreases with increasing temperature. This is called Henry’s Law and inhibits bio-oxidation as temperature increases.

As a result, the rate of heat generation in a composting cycle is very variable and changes as different groups of microbes become active or inhibited. Having a smart aeration system that intelligently controls airflow to maintain temperatures inside the target range allows for maximum composting efficiency.

The airflow rates required to maintain these targets vary depending on the size and construction of the facility and the amount of feedstock in the pile. In a small facility, airflow rates may be as low as 10cfm/cy of pile volume, while in an industrial system the airflow rate can exceed 1000cfm/cy of pile volume.

To achieve these rates, airflow is delivered through a fan attached to rigid or flexible perforated piping that runs through the compost mass. The piping can be installed in channels or on top of the pile, or it can be included throughout the buildup phase.

The piping system is typically controlled by a computer and includes a control manifold that branches for the purpose of feeding individual bins or piles. The piping must be designed carefully to ensure even distribution of air in the entire pile.

Energy Efficiency

Aerated static pile (ASP) composting uses forced aeration and air flow to promote heat-stable microbial populations in composted waste. This method can be used to recycle a wide variety of food waste and other organic materials. Aerated systems typically use computerized monitoring to control the rate and schedule of air delivery. In larger systems, perforated piping and fans deliver the air to composting bins or piles. The piping often branches at several points to feed many bins or piles at the same time.

Aeration is an important part of composting, because the microbial populations in a pile need air to operate at peak efficiency to reduce pathogens and increase the temperature of the compost. Without aeration, compost piles can become very hot and burn the materials that have been added to them. The aeration system also can help control moisture levels in the compost.

In addition to controlling temperatures, aerated static pile composting can be an excellent way to conserve energy. The heat released by the composting process can be recovered for space heating or other energy uses.

This technique can be applied in a wide range of facilities, including indoor or outdoor windrow composting, tunnel composting, and fully enclosed in-vessel composting. It is also a good option for large food processing plants, which often have significant volumes of feedstocks that need to be composted quickly.

The energy recovery rate from aerated static pile composting is much higher than that of other composting technologies, due to the ability of the process to produce large amounts of heat in the form of water vapor. This enables heat exchange to be achieved directly between the heated vapor and a cold liquid source, thereby recovering heat for localized space heating needs.

Another advantage to the aerated static pile system is that it doesn’t require the physical turning that other composting techniques require. aerated static pile composting However, it does require careful monitoring to ensure that the outside of the pile heats up as much as the core of the pile. In extremely cold weather, it may be necessary to place the aerated piles indoors with proper ventilation.

No Physical Turning

Aerated static pile composting is a type of composting that uses air circulation to speed up the decomposition process. Compost materials are piled on ridged or flexible perforated pipes that connect to fans, which circulate oxygen through the pile. Positive pressure systems use a fan to push air into the pile, while negative pressure systems pull air through the compost. This method is primarily used in larger operations because it allows for large-scale composting and is more energy efficient than other methods.

This method of composting is particularly effective at composting low-moisture feedstocks, such as yard trimmings and municipal solid waste. It does not work well for animal by-products and grease from food processing industries. It also does not work as well with odor-producing material such as sawdust.

It is important to note that while this method of composting does not require physical turning, it still requires a lot of monitoring. It is important to ensure that the inside of the compost pile heats up as much as the outside, and that all the layers in the pile are evenly aerated.

One way to reduce odors from aerated static pile composting is to cover the pile with a fabric bio-layer. This will help to keep the temperature of the composted material at a higher level, which will aid in the reduction of pathogens that can make the material stink.

However, this can be a difficult process and can add to an already labor-intensive operation. It is difficult to seal the cover around the pile without the need for specialized sealing equipment and it can be hard to reseal the cover once a new layer of compost has been applied.

Another approach to odor control is to cover the compost pile with an insulative bio-layer. This helps to raise the temperature of the material and therefore help it to pass the EPA-validated time/temperature pathogen reduction requirements.

This method of composting is a great choice for farms, schools, or other organizations that need to process large amounts of organic waste on a regular basis. It is also useful for colder climates where it is not possible to compost year-round outdoors.