Similarities and differences between aerobic composting and anaerobic composting in solid waste treatment

There are many kinds of composting systems used to treat municipal solid waste. According to the way of biological fermentation, it can be divided into aerobic composting and anaerobic composting.

1. Aerobic composting. Aerobic decomposition generally occurs in the presence of oxygen and water, and its formation process is as follows:

Organic matter+aerobic bacteria+oxygen+water → carbon dioxide+water (in vapor state)+nitrate+sulfate+oxide.

No harmful substances are produced during this reaction. Although it is tasteless without biodegradation, the odor produced by aerobic fermentation after proper treatment is very small. Compared with the traditional sanitary landfill, it shortens the anaerobic digestion process from several years to less than 20 days. Aerobic composting has the characteristics of controllable process, simple operation, fast degradation, good resource effect, ability to treat mixed environmental protection garbage and low operating cost. According to the oxygen supply mode and logistics mode of composting, the domestic waste composting systems commonly used abroad at present can be divided into the following categories.

① Natural ventilation static composting. This is the simplest composting method, which is to pile the prepared materials on a piece of ground about 2 meters high. The shape of the pile is generally long, and it can also be piled into other shapes according to the site conditions. This composting method is very similar to natural stacking in the open air. The reactor is often under pressure, and the outside air cannot diffuse into the reactor, which makes it anaerobic, with strong smell, insufficient fermentation and long fermentation period.

② Forced ventilation static composting. In order to overcome the shortcoming of insufficient oxygen supply in naturally ventilated static composting piles, ventilation pipes or tanks are generally arranged at the bottom of the pile along the length direction, and forced ventilation is carried out by high pressure according to the fermentation condition of the pile. Because the oxygen demand and water content of the pile can be controlled to a certain extent by controlling the amount of air blast, the fermentation period is obviously shorter than that of natural ventilation static composting.

(3) Mechanical stacking of strip compost, that is, stacking compost materials into strips by mechanical means. The cross section of the material pile is stepped, about 2 meters high and 4 meters wide. The length of the material pile depends on the site. Promoting the contact between the pile and the air through mechanical rotation is called mechanical rotation strip composting.

④ Closed mechanized composting. The main technological process of the method is that compostable garbage after mixed garbage treatment enters a special fermentation workshop, and the garbage is turned over by a special dumper to facilitate aerobic fermentation of the garbage, and the garbage after full aerobic fermentation is screened as required.

2. Anaerobic composting.

Anaerobic composting of organic waste is an anaerobic digestion technology, which uses microorganisms to quickly convert organic matter in waste into methane and ammonia under anaerobic conditions. Anaerobic process generally occurs under anoxia, and its formation process is as follows:

Organic matter+anaerobic bacteria+carbon dioxide+water → gaseous methane (biogas)+ammonia+final product.

The products after anaerobic decomposition contain a large number of thermophilic bacteria, which will cause serious pollution to the environment. It obviously contains organic fatty acids, acetaldehyde, mercaptan (alcohol smell), and hydrogen sulfide gas is also mixed with some compounds and some harmful mixtures. For example, hydrogen sulfide, a highly active and deadly gas, can quickly combine with some waste organic substances to form a black and odorous mixture.