Compost is an organic matter source that has the unique ability to improve the chemical, physical, and biological characteristics of soils or growing media. It contains plant nutrients but is typically not characterized as a fertilizer. According to different raw materials, there are several main compost types, including refuse compost, chicken manure compost and sludge compost, etc. For the sake of generate high quality compost, it’s necessary and important to learn about the influencing factors of composting process and quality, especially in large scale composting sites. So this article will take refuse compost for example to explain and elaborate the key parameters affecting composting process and generated compost quality.
Refuse or Municipal Solid Waste composting, in brief, is the microbial reaction process using microorganism to promote the biodegradable organics in garbage to transform towards stable humus. During this process, the organics in refuse dump make interaction with oxygen and bacteria, releasing carbon dioxide, water and heat, generating humus at the same time. one of the Benefits of MSW compost is that it can be used as soil improvement agent. Waste composting method can not only increasing soil humus and nutrient, but also save large amount of soil resource without secondary pollution.
Parameters Affecting Composting Process & Quality
Microorganism decomposition is the important assurance of composting maturity, so all parameters that influence microorganism activities will affect the effect and quality of generated compost. Due to composting is a complicated biochemical reaction process that can be influenced by many factors, such as carbon nitrogen ratio, moisture, oxygen and aeration interaction, temperature, PH value, raw material size of composting and so on. Let’s discuss the specific affecting factors of composting process so as to control refuse composting process effectively during the actual operation and provide theoretical foundation for improving composting efficiency.
♦ Carbon/Nitrogen ratio:
Among a variety of elements needed by microorganism decomposition, carbon and nitrogen ratio are the most important. Carbon nitrogen ratio is related with compost temperature. If the ratio of material is high, that is, carbon is more while nitrogen element is relatively deficient, bacteria and other microorganism growth will be limited, decomposition rate of organics will be slow and fermentation process will be long. And high carbon nitrogen ratio of raw material will easily lead to high ratio of finished compost that will despoil the nitrogen in soil, making soil fall into nitrogen starvation and then affecting plant growth. However, if carbon nitrogen ratio is too low, especially lower than 20:1, carbon elements available for consumption is lacking while nitrogen element is relative surplus, which makes nitrogen of materials become ammoniacal nitrogen to volatilize, causing fertilizer efficiency lowering due to lots of nitrogen loss. Therefore, in order to make sure microorganism nutrient of organics decomposition balanced, composting carbon nitrogen ratio should satisfy the best ratio(25-35:1) required by microorganism.
lists the Carbon/Nitrogen Ratios of Some Common Organic Materials
Moisture is one of the necessary conditions in composting process and nutrient materials can be absorbed by microorganism only when they are blended in water. The best water content of composting raw materials is usually around 50%-60%. Too low moisture (less than 30%) would affect microorganism activity and make organics hard to decompose while too high would bring down the composting speed and lead to anaerobe decomposition, stench generation and bleeding of nutrient substance.
The moisture of composting material is also closely related to the ventilation capacity of COMPOST TURNER MACHINE and structural strength of compost material. If the water content is over 60%, it will crowd air out, then materials show compact state and compost will develop towards anaerobe direction, at this moment, ventilation should be strengthened. On the contrary, if moisture is less than 20 percents, microorganism will sign off and influence its growth.
♦ Oxygen supply and aeration interaction:
As one of the key parameters of successful composting, the quantity of Oxygen supply and aeration is related to organic content in composting materials, namely, the more organic carbon in the material, the larger oxygen consumption rate. The ideal oxygen concentration is 18%, once less than 18 percents, the micro-organism life activity in composting process will be limited, easily causing stench. In the issue of oxygen supply, the point lies not in whether total oxygen supply is sufficient, but rather in how to ensure oxygen existing constantly without excessive ventilation at the same time. In other words, on the one hand, compost workers should avoid too long time refuse disposal and bad smell caused by inadequate oxygen, on the other hand, they also need to avoid temperature drop of refuse dump and too much energy consumption and running costs caused by superfluous aeration.
Temperature, affecting micro-organism growth, is an important factor for composting to go with a swing. It’s generally acknowledged that the degradation efficiency for organics of thermophilic bacteria is higher than mesophilic bacteria. In the initial stage of composting, its temperature is almost the same with surroundings, after one or two days action of mesophilic bacteria, the composting temperature will reach to 50-65 Celsius, and under this, composting can reach the harmless requirements and kill most of pathogenic bacteria just through 5-6 days. Briefly speaking, too low temperature would greatly extended currying time while too high (over 70 Celsius) may cause adverse impact on composting micro-organism.
♦ pH value:
Generally speaking, the most appropriate pH value for micro-organism is neutral or weak alkali, and too high or too low pH value both can make composting disposal difficult. Besides, pH value also affects the loss of nitrogen, so when pH value is over 7.0, nitrogen will volatilize in the form of ammonia. However, as a significant factor of composting process and quality, pH value ranging from 6.0-7.5 is fit for bacterial development while ranging from 5.5-8.0 is suitable for fungi growth.Particle size of composting raw material
process parameters, acceptable and ideal settings for aerobic composting
♦ Particle size of composting raw material
Because micro-organism proceed activities through organics pellet surface, so lowering size of pellet materials will increase the surface area and promote micro-organism activity and accelerate the composting speed.But on the other hand, too thin materials also prevent the flow of air and reduce oxygen content in composting, then bringing down micro-organism activity speed. Hence, raw material size should be reduced under the premise of air ventilation.
Finished compost should be both stable and mature so that it can safely be packaged and transported and not cause adverse effects during its end us.