Species-specific vermicomposting of dairy processing sludge: optimized pre-composting, comparative earthworm performance, and life cycle assessment

In this study, vermistabilization of dairy processing sludge (DPS) was performed by mixing with cattle dung (CD) in 1:1 ratio and subjecting it to varying pre-composting periods of 7 days to 35 days for the three earthworm species, Eisenia fetida (E.F), Eudrilus eugeniae (E.E), and Perionyx excavatus (P.E). Pre-composting times of 3 weeks (DPS_21E.F), 2 weeks (DPS_14E.E), and 3 weeks (DPS_21P.E) gave optimal results for all three earthworms’ growth, reproduction, and composting efficiency in terms of total Kjeldahl nitrogen, total available phosphorus, and total potassium for the three species. E.F was found to have the most effective soil-builder capacity, which contributed to a higher seed germination index, 193% for Vigna radiata (mung bean), 197% for Raphanus sativus (radish), and 193% for Cucurbita pepo (pumpkin). LCA showed that vermicompost treatments resulted in climate change impacts of approximately 265, 272, and 276 kg CO₂-eq for E.F, E.E, and P.E, respectively, compared to approximately 415 kg CO₂-eq for synthetic urea. Terrestrial acidification impacts ranged from approximately 10.86–10.90 kg SO₂-eq for vermicompost treatments, whereas the urea system exhibited the highest impact at approximately 11.03 kg SO₂-eq, with additional contributions from natural gas–based fertilizer production.

Graphical abstract