Vermifilter
A vermifilter (also vermi-digester or lumbrifilter) 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 purify the wastewater by removing pathogens and oxygen demand.
Solid material (such as fecal matter and toilet paper) is retained, de-watered and digested by bacteria and earthworms into humus that is integrated into the filtration media.
The liquid passes through the filtration media where the attached aerobic microorganisms biodegrade pathogens and other organic compounds, resulting in treated wastewater.
Alternative terms used to describe the vermifiltration process include aerobic biodigester, biological filter with earthworms, or wet vermicomposting.
Vermifiltration was first advocated by researchers at the University of Chile in 1992 as a low-cost sustainable technology suitable for decentralised sewage treatment in rural areas.
As a result of oxidation reactions, biodegradation and microbial stimulation by enzymatic action, organic matter decomposition and pathogen destruction occurs in the vermifilter.
In a study where municipal wastewater was treated in a vermifilter, removal ratios for biochemical oxygen demand (BOD5) were 90%, chemical oxygen demand (COD) 85%, total suspended solids (TSS) 98%, ammonia nitrogen 75% and fecal coliforms eliminated to a level that meets World Health Organisation guidelines for safe re-use in crops.
Twin-chamber parallel reactors offer the advantage of being able to allow one to rest, while the other is active, in order to facilitate hygienic removal of humus with reduced pathogen levels.
Seasonal and environmental factors (such as temperature) and variable influent volumes can cause buildup of solid waste as a pile.
Primary treatment of wet mixed blackwater can also include greywater containing food solids, grease and other biodegradable waste.
Because liquid effluent is discharged almost immediately on entering the digester, little dissolved oxygen is consumed by the wastewater through the filtration stage.
[9] The liquid effluent is either discharged directly to a drain field or undergoes secondary treatment before being used for surface or subsurface irrigation of agricultural soil.
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.
The filter media has the dual purpose of retaining the solid organic material, while also providing a habitat suitable for sustaining a population of composting worms.
Common filter packing materials include sawdust,[12][13] wood chips, coir, bark, peat, and straw for the organic layer.
[14] Materials with low granulometry (small particles) and large surface area may improve the performance of the vermifilter but impede its drainage.
In principle, provided the environment is aerobic, the longer the wastewater remains inside the filter, the greater the BOD5 and COD removal efficiency will be, but at the expense of hydraulic loading.
[21] The hydraulic loading rate is an essential design parameter, consisting of the volume of wastewater that a vermifilter can reasonably treat in a given amount of time.
