What is the problem with traditional SANITATION systems?
Traditional onsite sanitation systems, such as pit latrines and septic tanks, require frequent emptying which can be problematic in some scenarios. Emptying should ideally be carried out by a vacuum pump truck, but this can be costly and streets in urban settlements are often too narrow to accommodate such large vehicles. As a result, approximately 200 million latrines are manually emptied each year by workers who descend into the pits to remove the harmful waste by hand. Once removed, whether by hand or by pumping, the sludge is often dumped into the immediate environment, releasing the pathogens that were previously contained within the pit or tank.
What is worm-based sanitation?
Worm-based sanitation uses composting worms to process and digest human faeces, converting it into carbon dioxide, water, ammonia, and vermicompost (worm faeces). Composting worms can be used onsite at a household scale, in the form of a vermifilter toilet (also known as a tiger worm toilet or tiger toilet), or on a larger scale to treat faecal sludge and sewage.
Household Scale
To the user, vermifilter toilets look the same as a traditional pit latrines. The difference is the composting worms living in the pit, or vermifilter. Vermicompost builds up more slowly than sludge in traditional pit latrines because solids are digested by the composting worms. The result is a smaller system, which requires less frequent emptying. A vermifilter typically requires emptying once every 3 - 5 years, whereas a traditional pit latrine may need emptying multiple times a year, depending on size and use. When vermifilters do require emptying, vermicompost is easier to remove than sludge, as it is more dry, and it can usually be buried onsite without further treatment.
Large Scale Systems
Composting worms can also be used to treat much larger volumes, such as faecal sludge from traditional onsite sanitiation systems and sewage. The sewage treatment plant (STP) shown in the first image below, can treat up to 500,000 litres of sewage per day.
Can you use any worms?
Composting worms being farmed in India.
There are several species of worm that are suitable for worm-based sanitation systems. Red Tiger Worms (Eisenia fetida or its close relative Eisena andreil) are commonly used, which is why vermifilter toilets are also known as tiger worm toilets or tiger toilets. The African Nightcrawler (Eudrilus eugeniae) and the Indian Blue (Perionyx excavatus) are also widely used, however if a worm can be confirmed as composting then it is likely to be suitable for worm-based sanitation.
Are there other benefits?
The design and construction of vermifilters can be adapted to suit the local environment and available resources. The materials and construction costs are similar to traditional pit latrines, however because they require less frequent emptying and no additional treatment, the maintenance costs are much lower over the lifetime of the toilet.
As the process to break down the waste is aerobic, vermifilter toilets are less smelly and have fewer flies than traditional pit latrines. This can help with promoting use, and fewer flies means fewer vectors for disease.
Frequent removal and transport of sludge from traditional pit latrines to treatment facilities results in carbon emissions, as vermicompost from vermifilter toilets can be buried onsite it doesn’t require any transport. The aerobic process in worm-based sanitation systems also produces less methane than traditional pit latrines.
The liquid effluent produced by vermifilter toilets has been used as a soil conditioner to help with crop growth. Vermicompost can be used in a similar way, although the volume produced on a household scale is unlikely to be sufficient for this purpose. Large scale systems, in particular faecal sludge treatment plants, may be able to incorporate selling vermicompost as soil conditioner into the business model of the plant, to offset some operational and maintenance cost. However this requires further investigation to demonstrate safe handling and determine viability, as discussed on our research questions page.