Vermifiltration as a mainstream sanitation option
IWBSA wishes to engage with organisations who are actively involved in funding and designing large scale sanitation programmes. These could include programmes delivering improved sanitation to rural and peri-urban households as well as the delivery of improved, innovative treatment systems for urban communities. IWBSA wishes to begin a dialogue with such agencies in order to understand better the criteria governing the selection of appropriate technologies for such programmes, and to share the latest understanding of the potential of vermifiltration to fulfil them.
If you represent an organisation considering such a programme please get in touch with us through the website.
Applications of vermifiltration
The IWBSA, through the work of its member organisation, has been bringing together a compelling body of evidence to support the application of vermifiltration to global sanitation challenges. In particular, we see two key roles for vermifiltration-based systems:
(i) as a low-cost, low-emission, low-maintenance, user-friendly form of safely managed on-site sanitation for rural and peri-urban areas
(ii) as a low-cost, low-emission, low-maintenance wastewater and faecal sludge treatment solution at any scale for urban areas, with potential for significant resource recovery
Why consider vermifilter toilets for decentralised, on-site sanitation?
The full benefit of sanitation provision will only be obtained if the toilet to be used is safely managed. If not, the risk of disease still exists. There are few good options for safely-managed sanitation for low-income consumers at present. Septic tanks are often unaffordable and pit latrines are only considered to be safely managed if emptying services are available and affordable. Often this is not the case and as a result users are faced with the anxiety of what to do when the latrine is full.
Vermifilter toilets - known as Tiger Toilets or Tiger Worm Toilets - are designed to address this concern and meet the criterion for safely managed sanitation, namely waste “ can be treated and disposed of in situ”.
These toilets incorporate a vermifilter digester which removes solid faecal waste rapidly and completely, turning it into small amounts of vermicompost, which accumulates very slowly (emptying frequency estimated every 5-8 years). The liquid effluent is sufficiently well treated to be safely discharged into the surrounding soil. Also, when the Tiger Worm Toilet eventually needs emptying, it is a much safer process to do so compared to pit latrines, due to the relatively low pathogen content of vermicompost compared to the faecal sludge in pit latrines; that said, although vermicompost must still be handled with care, especially in regions where helminth infections are prevalent.
For the users, this removes the anxiety over filling and encourages use, which is vital to obtain the health benefits of sanitation. Faecal removal is cued by the absence of odour, which is greatly valued by the families who use it. The price of vermifilter toilets is comparable to pit latrines so they bring safely managed sanitation within reach of those who could not afford other options.
There is growing awareness of the contribution of conventional decentralised systems such as septic tanks and pit latrines to global warming as a result of the emission of greenhouse gases such as methane linked to anaerobic decomposition processes. Vermifilter toilets offer a route to drastically reduce greenhouse gas emissions as decomposition is aerobic, leading to carbon dioxide emission, which is 25 x less potent in terms of warming.
Are vermifilter toilets ready for scale?
A range of designs are available using readily available materials. The evidence for technical performance is well established and published in peer-reviewed journals. The feedback from users has been evaluated in several countries, most recently in India in a large study using the SanQoL index after prolonged use:vermifilter toilets scored 0.94/1, strongly supporting the expansion of their installation globally.
Worm supply has been shown not be a limiting factor. Construction is straightforward, well within the scope of local masons, and surveys of quality of construction suggest that there are few issues related to the digester. We are also actively pursuing routes to standardise and simplify the installation process in order to facilitate scaling.
Why consider vermifiltration for centralised wastewater and faecal sludge treatment?
Conventional aerobic wastewater treatment plants are energy-intensive because of the need to pump air through the treatment beds. This makes them increasingly expensive to operate and unattractive as investments.
In contrast, wastewater can be treated passively by vermifiltration with much lower energy requirements as it simply passes through treatment beds by gravity. Again, this a route to lower carbon emissions compared with conventional treatments.
Likewise, faecal sludge management is a growing issue in many countries due to inadequate facilities. Using the same modular principles faecal sludge treatment plants incorporating vermifilters have been successfully demonstrated in India and Rwanda, and offers the same advantages of lower energy use and running costs.
These plants also offer the potential for resource recovery in the form of vermicompost, sales of which could offset operating and maintenance costs.
How scalable is vermifiltration for centralised wastewater and faecal sludge treatment?
Treatment can be scaled to cope with any volume of wastewater simply as it is a modular array of vermifilters with each module receiving a defined amount each day. Treatment plants can range in size from individual households through to apartment blocks through to whole communities, up to 500,000 litres/day at present.
With respect to faecal sludge treatment, plants are currently being operated at a capacity of 10,000 litres/day.