Valorization of petroleum refinery oily sludge using Perionyx excavatus: Insight from ecological functional dynamics...

The growing accumulation of petroleum refinery oily sludge (OS) is a major environmental concern, necessitating sustainable, eco-friendly management strategies. Vermicomposting is a sustainable approach for waste management, however, potential application of this technique in OS management is still limited. This study investigated the vermiconversion potential of cow dung (CD) amended OS by employing Perionyx excavatus. During the study gradient concentrations of OS and CD in the range of 10-100 % were maintained in the substrate mixtures. The vermicomposting potential was assessed in terms of earthworm's survival metrics, ecological functionality, nutrients parameters and compost quality of the final product. The crude OS was lethal to Perionyx excavatus however, the incorporation of the CD significantly enhanced the total cocoon production (6.67 ± 1.15 to 71.33 ± 9.29), growth rate (-2.14 to 2.08 mg wt worm^-1day^-1) and the survival percentage (46.67 to 100 %) of the earthworm. Additionally, the physicochemical parameters such as pH, EC, C/N and TOC shifted towards maturity ranges besides enhancement in nutrient budget (17.91-219.41 %). The beneficial bacterial count (1.09 to 4.08 folds) and enzyme activities (1.02 to 3.08 folds) showed significant enhancement in the substrate mixture demonstrating the strong ecological functionality of Perionyx excavatus in transforming OS + CD substrate mixtures. The seed germination index (>80 %), potential ecological risk index (<150 %), and compost quality index (>2) showed field application potential of the vermicomposting outputs. Multivariate statistical analysis using Pearson correlation, PCA and CCA demonstrates a synergistic interaction between different dimensional parameters of vermicomposting processes. The findings clearly revealed that CD addition to OS helps in toxicity mitigation and bioconversion into a nutrient-rich compost suitable for safe agricultural application. Besides, the study also proposes a strategy for preliminary screening method to formulate a standardized substrate mixture that optimizes growth of Perionyx excavatus for efficient vermicomposting based remediation.