The aerated static pile method takes the piped aeration system a step further, using a blower to supply air to the composting materials. The blower provides direct control of the process and allows larger piles. No turning or agitation of the materials occurs once the pile is formed. When the pile has been formed properly and where the air supply is sufficient and the distribution uniform, the active composting period is completed in about three to five weeks.

With the aerated static pile technique, the raw material mixture is piled over a base of wood chips, chopped straw or other very porous materia. The porous base material contains a perforated aeration pipe. The pipe is connected to a blower, which either pulls or pushes air through the pile.

The initial height of the piles should be about 150-245 cm high, depending on: material porosity, weather conditions, and the reach of the equipment used to build the pile. Extra height is advantageous in the wintertime as it helps retain heat. It may be necessary to top off the pile with 15 cm of finished compost or bulking agent. The layer of finished compost protects the surface of the pile from drying, insulates it from heat loss, discourages flies, and filters ammonia and potential odours generated within the pile.

There are two common forms of aerated static piles: individual piles and extended piles. Individual piles are long triangular piles with a width (about 300-490 cm, not including the cover) equal to about twice the height of the pile. The aeration pipe runs lengthways beneath the ridge of the pile. Individual piles hold a single large batch of material or a few batches of roughly the same recipe and age (e.g. within three days). Individual piles are practical where raw materials are available for composting at intervals rather than continuously.

As the pile does not receive additional turnings, the selection and initial mixing of raw materials are critical to avoiding poor air distribution and uneven composting. The pile also needs a good structure in order to maintain porosity throughout the entire composting period. This generally requires a stiff bulking agent such as straw or wood chips. Wood chips are often used for composting sewage sludge by this method. Because of their large size, wood chips pass through the process only partially composted. They are usually screened from the finished compost and reused as bulking agents for another two or three cycles. As straw decomposes during the composting period, a pile with straw as an amendment can lose structure gradually. This is compensated partially by the drying that takes place as composting proceeds. Other possible bulking agents and amendments for static pile composting include: recycled compost, peat moss, corn cobs, crop residues, bark, leaves, shellfish shells, waste paper, and shredded tyres. Uncomposted material such as shredded tyres and mollusc shells must be screened from the compost and reused. To obtain good air distribution, manure or sludge must be blended thoroughly with the bulking agent before the pile is established.

The required air flow rates and the choice of blowers and aeration pipe depend on how aeration is managed, i.e. how the blower is controlled. The blower can be run continuously or intermittently. In the latter case, the control mechanism can be a programmed time clock or a temperature sensor.

The air flow rates are based on the dry weight of the primary raw material, such as sludge or manure. They should take into account the presence of typical amendments such as wood chips, straw, and compost. In practice, it may be necessary to adjust the timer cycle, pile size, and blower to suit the specific conditions and materials.

For static pile composting, the air can be supplied in two ways: a suction system with the air drawn through the pile; or a pressure system with the blower pushing the air into the pile. Suction draws air into the pile from the outer surface and collects it in the aeration pipe. As the exhaust air is contained in the discharge pipe, it can be filtered easily if odours occur during the composting process.

With positive pressure aeration, the exhaust air leaves the compost pile over the entire pile surface. Therefore, it is difficult to collect the air for odour treatment. Where better odour control is desired, a thicker outer layer of compost can be used. Pressure aeration provides better air flow than suction aeration, largely because of the lack of an odour filter. The lower pressure loss results in greater air flow at the same blower power. Therefore, pressure systems can be more effective at cooling the pile and they are preferred where temperature control is the overriding concern.

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