Comparative assessment of heavy metals content during the composting and vermicomposting of Municipal Solid Waste employing Eudrilus eugeniae

- Vermicompost of organic MSW contained lesser amount of metals than its compost.
- The concentration of metals increased in earthworms' tissue after vermicomposting.
- The decrease in Cr, Cu, Co, Zn and Ni during vermicomposting was due to earthworms.
- Eudrilus eugeniae was exceptionally proficient in Cd bioaccumulation.
- Higher BCFs indicated the potential of using Eudrilus eugeniae in vermicomposting.

This study was undertaken to have comparative assessment of heavy metals content during composting and vermicomposting processing of Municipal Solid Waste (MSW). Six scenarios were set up in which three experiments were for composting (controls) denoted as S1 for food waste, S2 for paper waste and S3 for yard waste and the corresponding replicates for vermicomposting processes were S4, S5 and S6. Vermicomposting caused significant reduction in Cd (43.3-73.5%), Cr (11.3-52.8%), Cu (18.9-62.5%), Co (21.4-47.6%), Zn (34.6%) and Ni (19.9-49.6%) compared to composting which showed a progressive increase. Addition of worms did not show any effect on Fe and Mn, most probably from the genesis of organic-bound complexes. The efficacy of utilizing Eudrilus eugeniae was indicated by the high values of bioconcentration factors (BCFs) which were in the order of Cd > Ni > Cu > Co > Cr > Zn and the increase amount of these metals in the earthworms' tissue after the vermicomposting processes. Different values of BCFs were obtained for different heavy metals and this accounted that earthworms exert different metabolic mechanisms. Regression analysis of the reduction percentages (R) in relation to BCF showed that RCdtot.S6, RCrtot.S5 and RCutot.S6 were significantly correlated with BCFCd.S6, BCFCr.S5 and BCFCu.S6 respectively. Thus, in comparison to simple composting processes, data analysis suggested the feasibility of inoculating E. eugeniae to MSW in order to mitigate the content of toxic heavy metals.