Eco-friendly Degradation of Tannery Sludge with Coir Pith and Nava Rasa Karaisal

The disposal of tannery sludge (TNS) without treatment causes severe toxic metal contamination in the ecosystem and food chain. Hence, eco-friendly solid waste management is essentially needed for the tanneries. The aim of this study was to degrade the raw TNS into composted sludge using coir pith (CP) as an adsorbent for organic compounds and other pollutants and Nava Rasa Karaisal (NRK) as a consortium of microorganisms. The TNS treated with CP and NRK showed decolorization and a reduction in pH. After the treatment, the electrical conductivity decreased from 24.7 to 6.31 μS/cm; total dissolved solids (28.4 ppm), salinity (21.2 ppm) and dissolved oxygen (7.5 mg/L) in the untreated TNS were reduced to 10.9 ppm, 4.9 ppm, and 4.6 mg/L in the TNS+CP+NRK treatment, respectively. SEM analysis showed small, smooth-walled structures on the surface of composted TNS compared to rough textures on the untreated TNS. Energy-dispersive spectroscopy analysis showed a higher number of elements in NRK (16) than in untreated sludge (8). Four different bacteria and six fungi were dominant in the treated tannery waste. The effect of different dilutions (12.5%, 25%, 50%, 75%, and 100%) of treated TNS on seed germination of Vigna radiata L. was carried out to check the feasibility of using the treated TNS for plant irrigation and growth. The results showed maximum growth at lower concentrations (12.5% and 25%). The results indicated that TNS treatment using CP and NRK is a potential eco-friendly approach to remediating the sludge waste.