Evaluation of anaerobic digestate as a substrate for vermicomposting

Vermicomposting is an established process to convert organic wastes into vermicastings suitable for plant growth. This research investigated the vermicomposting of anaerobic digestate with four different ratios of sawdust as a bulking material, for 75 days. The optimum proportion of anaerobic digestate to sawdust was identified as 70:30 based on worm growth and reproduction. Vermicomposting process increased the conversion of ammonium into nitrate when compared with control (p = 0.05). Vermicastings produced at the end of this experiment had significantly high N, NO3-N, P and K than the control (p = 0.05). There was significant reduction in pathogen levels by the worms (99%), and also a germination test undertaken showed an 83% increase in radish seed germination after vermicomposting when compared to raw digestate. The results indicated that vermicomposting with Eisenia fetida is a sustainable technology to convert the anaerobic digestate into nutrient-rich, safe to handle vermicastings, which otherwise is a secondary pollutant.