Vermicomposting of Dairy Industry Sludge into Bio-manure for Microgreen Cultivation

Abstract

Background: Dairy industry sludge presents a disposal challenge because of its high moisture and organic-matter contents. Methods: This study evaluated the conversion of untreated raw sludge (RS) and biostimulant-amended bio-active sludge (BS) into bio-manure through pre-composting and vermicomposting with Eisenia fetida. Six formulations containing sludge, cow dung, and agro-waste were prepared, and physicochemical changes in pH, moisture, temperature, electrical conductivity, organic matter, organic carbon, and the carbon-to-nitrogen ratio were monitored. Total plate count was also assessed. The resulting vermicomposts were used as stand-alone cultivation media for fenugreek (Trigonella foenum-graecum) microgreens and were compared with chemical and organic controls using germination percentage, germination index, fresh and dry biomass, and seedling vigour index. Results: Both sludge groups showed progressive stabilisation during processing, with final C/N ratios below 15 and electrical conductivity values below 1300 µS/cm. Among the sludge-derived media, BS1 produced the highest germination percentage (80%), germination index (399.09%), fresh biomass (2.30 g), and seedling vigour index (1320). RS2 showed the strongest performance among the raw-sludge formulations, with 75% germination and a seedling vigour index of 847.5. Conclusion: Vermicomposting stabilised dairy sludge and produced material capable of supporting early fenugreek microgreen growth under the evaluated conditions. Further replicated studies are required to confirm microbial safety, heavy-metal content, and performance across crops and cultivation settings.