Some considerations on the factors influencing the composting process

Dear readers, to continue with some aspects related to composting, this publication will describe some factors that influence the process. In this sense, it is necessary to comment that composting is based on a biological process carried out by microorganisms, therefore it is affected by all those factors that influence the growth and activity of these microorganisms, within the main factors that condition the composting process are the type of substrate (waste), aeration or presence of oxygen, moisture content, pH and carbon/nitrogen ratio. These factors condition and determine the development of the process and the obtaining of a quality final product.

The materials or raw materials used for composting determine the quality of the product obtained after the composting process. In addition, their physical characteristics influence the composting process since they can affect the decomposition and the presence of oxygen in the compost pile.

The following are what we consider to be the main characteristics that should be taken into account in the composting process

The ideal particle size according to some bibliographic sources is 2 to 5 cm although the size could be larger which would favor the circulation of oxygen within the compost pile, the greater the porosity of the pile, the greater the aeration and activity of the microorganisms, the smaller the particle size, the pile tends to compact which results in less aeration and therefore less microbial activity, slowing the process.

Composting is a process that requires the presence of oxygen, i.e. an aerobic process, for microorganisms to develop, therefore, aeration is an important factor in the composting process since oxygen is essential for the metabolism of the microorganisms that participate in the decomposition of organic matter. Aeration is influenced by the size of the particles to avoid compaction of the pile as mentioned in the previous section, but in addition to this, it is important to manage the pile by turning the material periodically to improve the entry of air.

To obtain a good quality compost it is important that there is a balanced ratio between both elements. Theoretically, a carbon/nitrogen ratio of 25:1 or 35:1, that is, 25 and 35 atoms of carbon for each atom of nitrogen, but this will vary depending on the raw materials that make up the compost. Prior to the elaboration of the compost, the carbon-nitrogen ratio must be determined, which is fundamental to obtain a good substrate for the development of microorganisms. The optimum carbon-nitrogen ratio can be calculated using a formula proposed by Rynk, et al. (1992); to do this, the percentages of humidity, carbon and nitrogen of each raw material are taken, data that can be collected from the literature, and based on this data the formula gives the amount of each raw material to be used in the preparation of the compost.

It is important to take this parameter into account, especially when the product is to be marketed, because if the ratio is higher than 35, there is not enough nitrogen for the proliferation and development of microorganisms and biological activity will decrease, which will delay the process. In the opposite case, if the value is below 25, the nitrogen will be in excess, possibly generating an unpleasant odor in the mixture due to the loss of ammonia gas.

In the composting process it is important to maintain moisture levels in a range between 40-60% if the moisture content is higher, water will occupy all the pores and therefore the process would become anaerobic (without oxygen), i.e., putrefaction of the organic matter would occur. If the moisture content is too low, the activity of the microorganisms is reduced and the process is slower. Of course, the moisture content will depend on the raw materials used, where the carbon-nitrogen ratio plays an important role, balancing the quantities of raw materials used. To determine the moisture content of the compost manually, a sample is taken by hand and pressed; if a few drops of water appear on the hand, the moisture content is optimal; if, on the other hand, after pressing the material, it does not emit water, it means that it lacks moisture.

As mentioned in one of the previous articles, the temperature of the composted mass reaches temperatures ranging between 10 and 40 °C, this temperature increase is related to the presence of microorganisms, this temperature increases as the days pass until reaching ranges between 40 and 70 °C which is the reflection of biological activity within the ensiled mass, which allows to control pathogens, parasites and weed seeds. The ideal Ph for the process is between 6.5 and 8.0 for the microorganisms to have the ideal conditions.

Dear readers, as can be seen there are some factors that influence the composting process and it is evident that the ideal conditions are sought for the microorganisms that decompose the organic matter, all these elements also influence the natural ecosystems, therefore, depending on the edaphoclimatic conditions (soil and climate) the decomposition of organic matter is done quickly and efficiently. The biotic factor gives us great benefits without incurring great costs, we only need to understand nature and its processes.