densities vary between 10 g l−1 and 40 g l−1 of filter packing material. an abundance of earthworms improves treatment efficiency, in particular bod5, tss and nh4+ removal. this is because earthworms release organic matter into the filter media and stimulate nitrogen mineralization. earthworm castings may have substances which contribute to higher bod5 removal. operation and maintenance a vermifilter has low mechanical and manual maintenance requirements, and, where gravity operated, requires no energy input. recirculation, if required for improved effluent quality, would require a pump. occasional topping up of organic materials may be required as these decompose and reduce in volume. the volume of worm castings increases only slowly and occasionally vermicompost needs to be removed from the vermifilter. solids accumulate on the surface of the organic filter media (or filter packing). the liquid fraction drains through the medium into the sump or equaliser and is either discharged from the reactor or recirculated to the top for further treatment. wastewater is discharged to the surface of the filter material by direct application or by sprinklers, drippers or tricklers. examples construction of primary and secondary domestic vermifilters from readily available materials a household pour-flush toilet, with combined primary vermifiltration and direct effluent infiltration into the soil below, is called the "tiger toilet" and has been tested by bear valley ventures and primove infrastructure development consultants in rural india. unlike a pit latrine , it was found that there was virtually no accumulation of fecal material over a one-year period. in the effluent, there was a 99% reduction in fecal coliforms . user satisfaction is high, driven mainly by a lack of odour. this system is now being marketed commercially in india, where over 2000 of these toilets and treatment systems had been sold and installed by may 2017. "tiger worm toilets" are also being promoted by oxfam as a sanitation solution in refugee camps, slums and peri-urban areas in africa, for example in liberia. low-flush vermifilter toilet systems with direct subsoil soakage are being marketed in ghana and other african countries by the ghana sustainable aid project (gsap) with support by providence college in the u.s. and the university of ghana. biofilcom is a company active in ghana which is marketing the process under the name of "biofil digester". in australia and new zealand, there are numerous suppliers offering vermifilter systems for domestic greywater and/or blackwater treatment, with primary treated effluent disposal to subsurface leach fields. examples include wormfarm, zenplumb, naturalflow, swwsnz and autoflow.