Kill two birds with one stone – due apology to animal lovers – the humble author has no inclination to kill “birds” – merely trying to cite a real-world example of, as the Cambridge Dictionary says, achieving two things (solving two problems) in a single action. This is essentially what thermophilic composting does.
Problem No. 1
Related to public health and hygiene – release of unprocessed municipal waste, livestock manure and agro-industrial waste to the environment poses imminent risks of spreading animal and plant pathogens. It is absolutely imperative that such pathogens are eliminated prior to the release of the waste.
Problem No. 2
Related to soil and agriculture – nutrients that are provided to the soil by inorganic fertilizers are immediately available to plants leading to improved plant growth and crop production. Nevertheless, inorganic fertilizers neither improves soil health nor replace organic matter that is lost during cultivation. Instead, their continuous use results in long-term damage to the soil.
So, where is the stone that can hit the two problems simultaneously? – Composting
What is composting?
Essentially, composting is the controlled aerobic biological decomposition (involving free oxygen) or degradation and conversion of solid organic material into a crumbly, dark, humus-like substance – the resulting product is called compost. The term “aerobic” implies that the process is occurring in the presence of oxygen.
A heap of organic material contains within itself billions of microorganisms – actinomycetes, bacteria and fungi. Therefore, biodegradation of organic material in the heap occurs naturally in the environment. Nevertheless, in order to enhance the efficiency, the process needs to be controlled or “engineered”.
is composting process thermophilic?
Chemical reactions in the compost pile releases heat to the surroundings – the process is therefore exothermic. A generic composting process is characterized by four main phases:
I (the initial phase) – said to be mesophilic – degradation of organic matter starts – lasting for 24 to 72 hours – rapid increase in temperature 10-42 °C.
II (thermophilic phase) – temperatures between 45 and 70 °C – lasting from several days to several weeks.
III (mesophilic II phase) – also called the maturation phase – temperatures decrease between 65 and 50 °C – lasting for 1-2 months.
IV (curing phase) – temperature decreases between 50 and 20 °C – lasts for 1-4 months – organic matter produced stabilizes.
Two kinds of microorganisms in action
Two kinds of microorganisms are active in the different phases:
Mesophilic – organisms which grow between temperatures 20 and 45 °C with an optimum growth temperature in the range 30-39 °C.
Thermophilic – organisms thriving at high temperatures between 40 and 120 °C. Many thermophiles are archaea, some of them are bacteria and fungi.
Most of the biodegradative activities are carried out at the thermophilic phase by thermophilic microorganisms – hence the process is sometime referred to as thermophilic composting. Thermophilic microorganisms (or thermophiles) produce and secrete a wide spectrum of thermostable enzymes (thermozymes), such as protases, cellulases, hemicellulases and lignin modifying enzymes, which are the key factors driving the composting process.
So, we have found the STONE for both the problems:
Composting sanitizes the pathogens contained in the waste material, since these pathogens cannot withstand the high temperatures of the thermophilic phase.
The final stable product, called compost, is a sustainable soil improver – it improves the physico-chemical characteristics of the soil and, in many cases, can be used as an alternative to inorganic fertilizer.
Food an Agriculture Organization (FAO) of the United Nations recommends improving the fertility of soils through the application of high-quality compost. Instead of burning the crop residues after harvest, they can be used for compost production.