Experimental Evaluation of Ascaris Egg Survival During Vermicomposting of Faeces

Abstract

Tiger worm toilets (TWTs) are a form of non-sewered sanitation that uses composting worms, such as Eisenia fetida (tiger worms), to convert human waste into vermicompost. Previous studies have shown low concentrations of faecal coliforms in vermicompost. However, this is the first study to assess whether TWT-produced vermicompost contains surviving parasitic helminth eggs. To evaluate this, six laboratory-scale biodigesters, replicating the tiger worm loadings and bedding layer types in a TWT, and three control units (the same setup without tiger worms) were fed identically with pig faeces spiked with a known concentration of Ascaris eggs for four weeks. After this time, the pig faeces in the biodigesters had been transformed into vermicompost, whereas the pig faeces in the control units remained unchanged. A standard multiple-straining method was then used to analyse and count Ascaris eggs in the coir, gravel, and end products of both biodigesters and control units. Findings revealed that the tiger worms did not degrade the Ascaris eggs, and viability analysis confirmed that the eggs that were present in the vermicompost remained viable. In the biodigesters, most Ascaris eggs were found in the coir layer (48–72% of the total eggs), whereas in the control units, they were primarily concentrated in the pig faeces layer at the top (71–74% of the total eggs). Eggs were also detected in the gravel and effluent of biodigesters, but not in that of the control units, likely due to the tiger worms’ movement between layers of the biodigester. There was a significant difference in egg distribution across biodigester layers (p = 0.03), indicating that some layers consistently retain higher Ascaris egg concentrations. This study, therefore, indicates that TWT end products, including vermicompost and effluent, are not considered safe for agricultural use, as per World Health Organization guidelines. Therefore, these products require safe disposal or further treatment before use, particularly in settings with a high prevalence of ascariasis.