Aerated Static Pile Composting
Composting is a good way to recycle organic waste and produce compost for use on farms. The process involves four basic steps: aeration, temperature, moisture and turning.
To aerate a compost pile, air is introduced through perforated pipes under the compost. This is called aerated static pile (ASP) composting.
Aerated static pile composting is a type of industrial composting that uses a system of active aeration to supply oxygen and control temperature for the purpose of producing compost. It is a fast method of composting that can produce high-quality organic soil amendments for urban landscaping, farms, and private gardens.
Aeration is essential to the process of composting as it satisfies the oxygen demand from aerobic decomposition (the stoichiometric demand), removes excess moisture, and helps prevent odors. Aeration also helps improve drainage by removing compacted material, preventing thatch buildup, and increasing the contact area between the composting materials and air.
In most cases, aeration systems use perforated pipes laid under the pile that are connected to blowers. Negative air is blown through the pipes and is then biofiltered by a filter made from finished compost.
The aeration pipe system must be designed correctly for efficient air distribution and uniformity of aeration throughout the entire pile. It should also be sized to avoid excess airflow in the pile at any given time.
Depending on the climate where you are composting, aeration may be a necessity to keep the pile from drying out. In hot arid climates, a cover layer of compost on top of the pile may be necessary to retain the moisture in the pile and reduce evaporation. In colder climates, placing the aerated static pile indoors with proper ventilation is sometimes an option.
An aeration system should be controlled with a feedback control strategy that adjusts fan speeds to maintain pile temperatures at a constant level, adjusting speeds as the pile temperature rises and cooling the pile as it falls. In addition, aeration system design should allow for controlling pile oxygen content by adjusting fan speed to keep O2 levels within a desired setpoint.
When using aeration, it is important to make sure that all parts of the pile reach and maintain temperature above 55 degrees for at least 3 days. This will help destroy pathogens, parasites and weed seeds that can be present in the composting material.
The final product, the compost, is then a highly stable, odor-free substance that is ideal for use as a soil additive, fertilizer, or growth medium. Aeration systems are especially helpful in facilities that handle large volumes of manure, yard debris, food scraps and other challenging feedstock materials.
Temperature in aerated static pile composting is an important factor that influences the performance of the system. Proper temperature ranges (up to 135degF) help destroy pathogens, parasites aerated static pile composting and weed seeds, and also promote decomposition of the material. Composting temperatures that drop below this range can cause the breakdown of material to slow down or even stop altogether.
The temperature in aerated static pile composting can be monitored by thermocouples placed inside the pile. These instruments are available from a wide variety of sources and can be used to monitor the temperature over time in large, multi-pile systems or individual compost bins.
Aerated static pile composting is a fast and inexpensive way to produce high quality compost for yard trimmings and other organic wastes. The process can be performed indoors or outdoors and is suitable for a broad range of organic waste, including food scraps, paper products, and sewage sludge.
Regardless of the type of material being composted, aerated static piles must be kept at a consistent temperature to provide optimal conditions for decomposition. This is essential to keep biodegradation rates high and to minimize the possibility of bacterial growth that could inhibit the biological process.
To achieve this goal, aerated static piles must contain a homogeneous mix of waste materials. Layers of grass clippings, straw or other bulking agents will impede uniform airflow throughout the mixture and will create stratification that can obstruct oxygen transfer.
Aerated static piles also need to have a relatively constant moisture content. Low moisture levels prevent adequate oxygenation and encourage the development of anaerobic bacteria. This condition can be counteracted by adding water to the pile during the hot phase.
The optimum composting temperatures in the thermophilic range of 135degF to 160degF are essential for accelerating decomposition and to destroy pathogenic organisms and weed seeds. However, even thermophilic organisms have temperature limits that must be reached before a rapid rate of decomposition can occur.
In aerated static pile composting, fans push or pull air into or out of the composting mass through perforated pipes. These can be rigid or flexible and can be installed in channels, on the top of a floor or included throughout the buildup. Using negative or positive aeration modes in a well-designed piping system will reduce vertical temperature stratification, which is critical to achieving semi-uniform pile temperatures.
The composting process requires a lot of moisture and it’s important to maintain it as much as possible. If the moisture level in the pile drops below 50%, the biological process will stop and the materials will not compost. Moisture also helps keep the microbial populations healthy and ensures that the temperatures in the compost pile stay in a healthy range.
In aerated static pile composting, air is supplied through perforated pipes underneath the materials in the pile. This method is ideal for producing compost quickly. It also reduces odors and makes the composting process less expensive than conventional composting methods.
Aerated static pile composting can be used for small and large quantities of organic waste, including yard trimmings and food scraps. It can produce compost within three to six months and is a good choice for landscapers, farmers or local governments with large quantities of waste.
Moisture is essential for biological oxidation, which is one of the most important factors affecting composting efficiency. Composting systems need to meet a specific moisture requirement, which depends on the type of waste material, the desired compost product, and the capacity of the airflow.
If the composting mix contains too much water, the aerated air will not be able to carry it away from the waste. This may cause it to collapse or block the flow of oxygen into the pile, reducing the effectiveness of the aeration.
To counteract this, a plenum layer is placed on the bottom of the pile, essentially a sheet of material that will gently diffuse the air from the holes in the perforated piping. This enables the pressurized air to be distributed evenly throughout the pile, which prevents it from short-circuiting and drying out different areas of the pile.
This plenum layer is typically made of wood chips to help retain the heat and odors in the pile and to keep airflow consistent. However, this can be done with other materials as well, so long as they are sufficiently porous and breathable.
Aerated static pile composting also uses a blower to provide airflow through the composting material. This can be a simple bounce house type of blower or a more sophisticated system that can control multiple bins and is attached to a timer.
Aerated static pile composting is a good option for farmers, especially in cold climates where outdoor methods might not be possible. It can be used with a negative air system and a biofilter to prevent odors and produce a marketable compost.
It requires no turning and is less physically demanding than traditional composting. It also reduces the amount of land required for the operation.
Turning frequency and total number of turns are determined primarily by moisture content and the structure of the material being composted. If the material decomposes quickly, it may need to be aerated more often than materials that decompose slowly.
In the aerated static pile method, aeration is supplied to the materials using perforated pipes that sit on top of the base materials such as peat moss or compost. These systems can be powered by a blower or by air pressure through the pipes.
A blower forces oxygen through the composting materials, reducing decomposition time and speeding up the composting process. It also helps aerated static pile composting to maintain optimal temperature conditions in the compost to encourage microorganism activity and promote rapid decomposition.
Forced aeration is also more effective at cooling the materials than passively aerated methods. The cooling helps aerobic bacteria to more efficiently bio-oxidize feedstocks, minimizing the production of odorous compounds.
It can also help to maintain the temperature in the core of the pile, where odours tend to be more concentrated. This can be difficult to do with passively aerated methods since the core is not heated and the outside of the pile might be cooler than the core.
This method also requires a lot of monitoring to ensure that the core is always at or near the desired temperature. If the pile gets too cold, it could lose its ability to aerate and could result in odors from anaerobic decomposition.
A number of commercial systems use perforated pipes with a fan that circulates air through the pile. Some systems use positive pressure, where air is pushed through the pile; others use negative pressure, where air is pulled through the pile.