page_title: Vermifilter
section_title: Secondary treatment
hierarchical_section_title: Vermifilter / Process types / Secondary treatment
caption_attribution_description: English: Domestic vermifilter with dripping application of wastewater.
context_page_description: A vermifilter is an aerobic treatment system, consisting of a biological reactor containing media that filters organic material from wastewater. The media also provides a habitat for aerobic bacteria and composting earthworms that produce humus. The "trickling action" of the wastewater through the media dissolves oxygen into the wastewater. This is an important feature because bacteria and worms that rapidly decompose organic substances need oxygen to survive. Wastewater is purified by removing pathogens and oxygen demand.
  Vermifilters are most commonly used for sewage treatment and for agro-industrial wastewater treatment. Treatment can take place in either large centralized systems or by smaller on-site sewage treatment. Vermifilters are also used if wastewater requires treatment before it can be safely discharged into 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. In this case, the treated effluent is disposed of to either surface or subsurface leach fields. Solid material is retained, de-watered and digested by bacteria and earthworms.
context_section_description: Secondary and tertiary treatment vermifilters can be underneath the primary vermifilter in a single tower but are typically single reactors, where several reactors can be chained in series as sequential vermifilters. Drainage within the reactor is provided by filter media packed according to the hydraulic conductivity and permeability of each material that is present within the vermifilter. The filter packing retains the solid particles present in the effluent wastewater, increases the hydraulic retention time and also provides a suitable habitat for sustaining a population of composting earthworms. This population requires adequate moisture levels within the filter media, but also adequate drainage and oxygen levels.
  Sprinklers or drippers can be used in secondary and tertiary treatment vermifilter reactors (see image).
  Hydraulic factors (hydraulic retention time, hydraulic loading rate and organic loading rate) and biological factors (earthworm numbers, levels of biofilm) can influence treatment efficiency.
caption: Secondary treatment domestic vermifilter for wastewater showing drippers
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