Valorisation of Dairy STP Sludge: Effects of Sludge based Compost on Early Plant Growth Assessed Through Phytotoxicity Assays

This study evaluates the quality of dairy waste compost by assessing its effect on monocot and dicot seed germination using the tray method. Compost samples were mixed with soil in varying ratios, and germination rate, root, and shoot lengths of Vigna radiata (green gram) and Triticum aestivum (wheat) were recorded. The compost was produced using a Smartenviro Systems drum composter containing 40 kg of dairy sludge and 10 kg of sawdust as a bulking agent. Composting was carried out for 12–15 days at 45–55°C under thermophilic conditions, with daily drum rotation using a 0.5 HP geared motor for uniform aeration and mixing. The sawdust improved the C: N balance, enhancing organic matter degradation and yielding stable, odor-free compost. The automated, enclosed design minimized labor and leachate loss. Germination assays indicated that the compost-soil mixtures were non-phytotoxic and promoted early plant growth. Pathogen analysis confirmed the absence of Salmonella spp. and Staphylococcus aureus; however, detectable Escherichia coli and elevated chromium (Cr) levels above regulatory limits indicate incomplete sanitization and highlight the need for additional stabilization or post-treatment before unrestricted agricultural application. Overall, the results demonstrate the potential of controlled compost-soil blending for sustainable dairy waste management, while emphasizing the importance of further treatment to ensure microbiological and chemical safety.