Vermifilter

A vermifilter (also called vermi-digester or many other names) is an aerobic treatment system comprising a passive biological reactor that removes organic matter, pathogens and oxygen demand from wastewater. This is achieved via media that filters organic material from the wastewater and provides a habitat for composting earthworms that produce humus. The trickling action through the media also oxygenates the wastewater.

Vermifilters are most commonly used for sewage treatment (either at a centralized level or in an on-site sewage treatment facility) and for agro-industrial wastewater treatment. Applications include those where wastewater quality requires improvement before discharging to the environment.

Vermifilters can be used for primary, secondary and tertiary treatment of blackwater and greywater. On-site systems can treat influent from flush toilets, where the treated effluent is disposed of to either surface or subsurface leach fields. These systems may be called "vermifilter toilets". Solid material (such as fecal matter and toilet paper) is retained, de-watered and digested by bacteria and earthworms and converted into humus in the primary process. The liquid fraction passes through filtration media on which microorganisms are attached, where secondary treatment occurs, mostly by retention of organic compounds that undergo biodegradation, but also by increasing dissolved oxygen in the water.

Vermifilters are a low cost aerobic wastewater treatment option. Vermifilters are usually a "passive" wastewater treatment system which means little if any energy is required for their operation. Pumps are only required if gravity flow is not possible. They can also have a high level of treatment efficiency with a relatively low space requirement.

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