Chemistry Composting Part 2

Oxygen is an important factor to consider when composting.
Aerobic Composting: An aerobic process in the decomposition of organic materials in the presence of oxygen. Composting can be an aerobic process. As compost is consumed, the carbon to nitrogen ratio goes from 30:1 to 10-15:1. This is because two thirds of the carbon is released as carbon dioxide gas. The carbon is oxidized and carbon dioxide is produced. The remaining third is combined with nitrogen in living cells. The oxidation of carbon is an exothermic process. For every gram of glucose 484-674 kcal of heat are produced. This means that compost heaps can have temperatures above 170 degrees Fahrenheit. The atmosphere is twenty-one percent oxygen, but a compost heap only needs to maintain an oxygen percentage of ten percent to be aerobic. Some compost mixtures naturally maintain healthy oxygen levels by diffusion and convection, while other require active aeration. Blowers or periodic turning and mixing can aerate composts. Compost that is not aerated will become anaerobic. Aerobic composting takes place in bins, pits, or stacking piles.
Anaerobic Composting: Another type of composting is anaerobic- the decomposition of organic matter without the presence of oxygen. Unlike aerobic composting, anaerobic composting is a reduction process. Carbon is reduced to methane gas. Hydrogen sulfide gas is another byproduct of anaerobic composting.
As a result anaerobic composting releases pungent odors. The final product in the reduction process is humus. Some minor aerobic oxidation takes place at the end, but it is negligible. Therefore, anaerobic oxidation releases significantly less heat than aerobic. As a result, pathogens are not destroyed by heat but disappear naturally due to unfavorable condition- a much slower process. Nitrogen is reduced to organic acids and ammonia. Anaerobic compost must sit for up to six months to a year to insure pathogens are no longer present. Anaerobic composting takes place in large well packed stacks. It requires much more water than aerobic so that oxygen cannot penetrate the mixture. When the mixture is eighty to one hundred percent saturated, the organic material becomes suspended in a liquid.
Whether the gardener chooses aerobic or anaerobic composting, there are some basic dos and don’ts of composting. A good balance of green and brown materials will lead to an ideal balance of nitrogen and carbon. However do not include any meats, cooked vegetables, dairy, animal waste, perennial weeds or salad heads.