Several factors control the success of the vermicomposting process.
Temperature
Different species of worms have varying temperature preferences and tolerances. To ensure optimal performance and timely production of a stable product, it is crucial to maintain a temperature range of 20 – 25°C. When temperatures drop, the food consumption of earthworms declines, and the composting time increases. If temperatures fall below 10°C, the worms become inactive.
With increasing temperature, the reproduction rates of earthworms decline, and extended exposure to temperatures above 35°C can lead to the death of worms. This is especially a risk for larger-scale systems which can have heat-retentive properties, as composting can take place, heating up the worm bins.
If a worm system is kept outside, it should be placed in a sheltered position away from direct sunlight and insulated against frost in winter.
Moisture
Moisture content plays a crucial role in successful vermicomposting. Both earthworms and microorganisms rely on water availability to carry out their metabolic processes. If the moisture level is too low, their activity will decrease significantly. Conversely, if the moisture level exceeds 90%, anaerobic decomposition may occur, leading to worm death due to drowning and suffocation. The ideal moisture content range for vermicomposting is between 60 and 80%.
Air
Adequate aeration needs to be ensured as earthworms thrive in well-ventilated environments. An unhealthy worm bin potentially caused by anaerobic conditions will have foul odours (smell of ammonia) and cause the death of worms. Oxygen can be provided by air holes in the bin, the occasional stirring of bin contents, and the removal of some bin contents if they become too deep or too wet.
pH
Composting worms thrive in a pH range between 6 and 7. It’s important to note that worms are sensitive to acidity or alkalinity, and therefore, they cannot survive in piles with a pH lower than 5 or greater than 9. As the pH level increases or decreases, the metabolism and breeding of earthworms decline, which affects the bioconversion rates.
The Carbon-to-Nitrogen (C:N) Ratio
The C:N ratio is an important factor in the growth and reproduction of earthworms. When the feed material has a high C:N ratio, the earthworms consume it at a faster rate, which in turn accelerates their growth and reproduction. However, if the C:N ratio is too high or too low, it can have an adverse effect on their growth and reproduction. Also, substrates with a low carbon/nitrogen ratio are better for older earthworms, whereas a high carbon/nitrogen ratio is suitable for the growth of small or young earthworms. Although the optimal C:N ratio for earthworms in vermicomposting with faecal solids is still being studied, researchers have suggested that efficient vermicomposting can be achieved within the C:N ratio range of 20:1 to 25:1.
Further, worms are highly sensitive to ammonia. It has been found that ammonia concentrations lower than 1 mg/L can lead to increased worm mortality.
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