Treat wastewater in an environmentally sustainable way with worms

Vermifiltration is a non-sewered sanitation technology that uses a symbiotic relationship between Eisenia Fetida earthworms and microorganisms to treat wastewater. The earthworms not only break down organic matter, which is then more easily available to the microorganisms, but they also aerate the vermifilter via their burrowing activity and this stimulates bacterial productivity. This technique has various advantages: it is low-cost and robust, requires minimal to no energy use and can be built with local, easily available materials (compost, biochar, gravels, sand, etc.). Additionally, treated wastewater can be used to close water and resource loops. 

Vermifiltration has been implemented on a full-scale in various countries, including China, Germany, France, India, Rwanda, the USA and Switzerland. One example in Switzerland is the vermifiltration installation at the housing cooperative, Equilibre, in Geneva, which treats wastewater from 100 habitants. Despite growing implementation, an optimised design model for building and operating vermifiltration has not yet been scientifically defined. Additionally, as the majority of the scientific research remains at a laboratory scale, the effects of both scaling-up and the long-term use on the treatment efficiency of vermifiltration is lacking. The lack of scientific knowledge is a barrier which impedes vermifiltration from being used more widely in Switzerland and globally. 

Developing scientific standards

The University of Geneva and the Management of Excreta, Wastewater and Sludge research group at the aquatic research institute Eawag have begun a four-year research project in February 2022. The first step was a study that evaluated the treatment performance of a full-scale vermifilter at the housing cooperative Equilibre in Geneva. Study results show that the effluent quality remains stable even with varying hourly hydraulic loading rates and with seasonal temperature changes. In addition, it was observed that the vermifilter buffers outdoor temperatures, which may explain how it can function well despite the colder climate observed in winter.

The next steps in the ongoing research include analysing greenhouse gas emissions, micropollutant treatment, nitrogen and phosphorus fates and the use of the effluent for irrigation. The results of this study aim to better understand the overall treatment mechanisms that are taking place during vermifiltration. These results are necessary in creating an optimised design model, as well as for ensuring treatment efficiency of future installations. Vermifiltration could be a boon for municipalities because it offers a low-cost, sustainable wastewater treatment system.