5.1 What is vermicomposting, and vermifiltration and how does it work?

Vermiprocesses involve the use of earthworms (vermi-) for specific purposes. Two common vermiculture processes are vermicomposting and vermifiltration. At the centre of these treatment processes are earthworms that actively feed on the organic waste. They ingest the material and break it down through their digestive processes. The earthworms excrete castings, which are nutrient-rich, dark, granular material known as vermicast or worm castings.

The following schema shows different activities and attributes that are facilitated by earthworms.

In addition to digestion, earthworms burrow through the bedding material, creating channels that enhance aeration and water movement in the compost. Also, they introduce beneficial microorganisms into the compost, further aiding the decomposition.

Vermicomposting and vermifiltration can both be implemented on various scales, ranging from small-scale, household systems to larger, community-level or industrial applications.

While both processes have applications in treating human waste, vermifiltration specifically focuses on the filtration and treatment of liquid effluents, while vermicomposting focuses on dewatered sludge or other organic solid wastes. In this sense, the two processes differ in their primary objective.

Vermifiltration is primarily aimed at treating wastewater by removing or reducing pollutants. The result is treated water, and the solid residues/vermicompost, remaining in the filter, are a second output result. Vermicomposting, on the other hand, has the primary goal to convert organic waste into vermicompost which is the only output of the process.

The following schemata show typical set-ups for vermicomposting and vermifiltration. While vermicomposting tanks can be made from local materials such as bricks or concrete, vermifilters require enclosed reactors made from durable materials that eliminate vermin entry, usually plastic or concrete. Vermifilters further require a filter layer made of material such as sawdust, straw, coir, bark mulch or peat.

Besides the outlined difference, the treatment principles are the same. The earthworms are grown within the composting system, and their population is adjusted based on the available feed substrates, eliminating the need for restocking.

The following table summarises the main differences between the two main vermiculture processes.

As the focus of this training is sludge and biosolids management, we will focus on vermicomposting for the remaining lesson.

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