Composting is a simple, effective and cost-effective way of handling organic waste. But, if you don’t understand the process it will be harder to process your organic waste properly so it turns into compost in an efficient manner.

So, it becomes important that you understand the different phases your organic waste goes through before it turns into usable compost.

In this blog, we will see four different stages of composting and the nitrogen and carbon cycle in each phase of composting.

Stage 1: Mesophilic Stage

This is the first stage of composting and the mesophilic bacteria perform their activity in this phase. These bacterias consume simple sugars and proteins after which they produce carbon dioxide, water and heat. The optimal temperature of this phase is between 20°C to 45°C. During this phase, the compost heats up and the bacteria break down the organic matter.

This mesophilic stage lasts for about five to ten days. Make sure you turn the compost regularly during this phase for proper moisture level and aerating the compost and also the organic matter is evenly exposed to all the bacteria.

Carbon dioxide in Mesophilic Stage

The mesophilic bacteria break down organic materials like proteins and amino acids and while doing this, they release CO2 as the by-product. The amount of CO2 released isn’t very high compared to other stages in the process of composting.

Although the CO2 released is low it’s still important to maintain proper airflow and aerate the compost to allow the organic matter to release CO2 and avoid the buildup of anaerobic conditions.

Nitrogen Cycle in Mesophilic Stage

When mesophilic bacteria break down organic matter, they release ammonium ions(NH4+) which are highly soluble. This is how the nitrogen cycle begins in the Mesophilic Phase. and can leach out of the compost pile if the pile is too wet.

An important thing to know is that if the pile is too wet, the ammonium ions can leach out of the compost pile. So it becomes important to maintain proper moisture levels to prevent the loss of nitrogen from the pile.

Stage 2: Thermophilic Stage

During this stage, thermophilic bacteria come to work and the temperature in this stage lies between 45°C to 70°C because the bacteria works on breaking down more complex compounds like cellulose and lignin. Thermophilic bacteria consume simple sugar and proteins and produce more carbon dioxide, water and heat.

The thermophilic stage lasts for about 4-5 weeks and due to such high temperatures for a long time, the pathogens and weed seeds are killed. It’s not ideal to turn compost for a lot of time during this phase as it will reduce the heat produced inside. However, you should monitor the compost during this phase and make sure that the temperature and moisture levels are optimal for the process to carry on properly.

Carbon dioxide in Thermophilic Stage

Due to the breakdown of more complex substances like cellulose and lignin, the amount of CO2 and heat released in the compost increases. The CO2 levels are way too higher than Mesophilic Stage. It’s very important that you keep your compost well-aerated in this phase.

Nitrogen Cycle in Thermophilic Stage

Cellulose and lignin are very rich in nitrogen and when bacteria break down organic matter, they release ammonia (NH3) and nitrate (NO3-) ions.

Ammonia is a gas, which is lost due to evaporation if the pile isn’t properly managed and nitrate ions are highly soluble and can get washed away if the compost pile is too wet.

To prevent the loss, you have to make sure that you maintain the moisture levels in the compost and aerate the pile regularly.

Stage 3: Cooling Stage

In this stage, the thermophilic bacteria get replaced by mesophilic bacteria which results in a drop in temperature and compost starts to cool down. This stage lasts for about four to five weeks.

During this stage, you should turn the compost more often than in the thermophilic stage to avoid any growth of fungi and other bad bacteria. Also, keep a check on the moisture levels of the compost pile and make sure that it’s not too wet or too dry.

Carbon Dioxide in Cooling Stage

The thermophilic bacteria get replaced by mesophilic bacteria and break down the remaining organic matter and release CO2 in the process. The CO2 production in this phase decreases and the overall temperature of the pile also decreases.

Nitrogen Cycle in the Cooling Stage

Mesophilic bacteria continue to break down the remaining organic materials and release ammonium ions as a byproduct. To prevent the loss of ammonium make sure you turn the pile regularly and maintain good moisture levels in the compost.

Stage 4: Curing Stage

This is the final stage of composting. In this stage, the compost is decomposed and the final product is in front of us. During this phase, you should let the compost sit in proper aerated and moisture conditions for a few months depending on the desired levels of maturity of the compost.

During this phase, make sure you turn the compost regularly and maintain good moisture levels in it to avoid the growth of fungi and other unwanted organisms.

Carbon dioxide in Curing Stage

In this stage, the decomposition is over and compost is maturing hence the release of CO2 in this phase is the lowest of all the phases.

Nitrogen Cycle in Curing Stage

Nitrogen is also produced in this phase as microorganisms continue to break down organic matter and the nitrogen cycle continues but at a very slower rate than the previous stages as the compost is ready and getting matured in this phase.

What we realise


The temperature of the compost pile should be checked regularly and you should also act according to the phase of composting. If the temperature isn’t suitable for the phase of composting it will only slow down the process of composting.


It’s important to maintain good moisture levels in the compost pile. If the compost is too wet, you will lose a lot of nitrogen in the process. If the compost is too dry, it will be hard for the microorganisms to survive

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