5.5 How to design the vermicomposting process

Vermicomposting reactors can be constructed using local materials such as bricks or concrete. To achieve the optimal performance, the following design criteria are suggested:

Some general set-up considerations are as follows:

• Wormbeds: Since the worms are surface dwellers, and since it is crucial to maintain aerobic conditions and moderate temperatures in the substrate, the vermicomposting beds must be shallow.
• Shelter: Structural facilities must protect against extremes of cold, heat, drought and moisture, all of which can cause loss of activity, migration or death of the worms.
• Sludge conveyance: Depending on the nature of the sludge feed, sludge can be moved and distributed by manual, mechanical or hydraulic means.
• Bed harvesting: The collection of worms and castings can be accomplished by manual or mechanical means or by use of mobile equipment.
• Separation of products: Cylindrical rotating screens are commonly used for mechanical separation of worms and castings.

In the previous lesson on composting, the methodology of determining the ideal mixture concerning moisture content was introduced. The same steps apply to the case of vermicomposting.

How many worms are necessary?

The required quantity of worms can be estimated by applying the following formula:

Where,

Exercise

Assuming we want to process 5 m³ of dewatered faecal sludge (TS 30%) daily with a density of 1,050 kg/m³, the optimal feeding rate of 1 kg _feed/kg _worms/d. Please calculate the quantity of worms required.

Solution: