Relative effectiveness of Eisenia fetida and Eudrillus eugeniae in vermiremoval of heavy metals (Cd & Cr) from sewage sludge

Abstract

Sewage sludge represents a significant environmental challenge, necessitating sustainable management practices. The predominant disposal method typically involves agricultural and forestry applications; however, this approach carries inherent risks of soil and groundwater contamination with heavy metals. Vermiremediation has emerged as an effective and environmentally friendly bioremediation strategy, capable of pre-treating sewage sludge prior to its integration into agricultural systems. Nevertheless, it is critical to optimize bioremediation strategies, particularly regarding species selection, to enhance outcomes. This study assessed the vermiremoval efficiency of cadmium (Cd) and chromium (Cr) by two earthworm species, Eisenia fetida and Eudrilus eugeniae, over a 60-day experimental period under controlled conditions. Sewage sludge combined with cow dung was treated within plastic microcosms (three replicates per species), and metal concentrations in both the sewage sludge and earthworm tissues were quantified at the 0th, 20th, 40th, and 60th days of the study. The bioaccumulation factor (BAF) and remediation efficiency (RE) were computed. Repeated measures ANOVA indicated a significant difference between the species in terms of their vermiremoval and metal uptake efficiencies over time. Eudrilus eugeniae demonstrated a superior capacity for the removal of Cd (F = 17.311, p < 0.001, η² = 0.812) and accumulation of Cd (F = 8.930, p = 0.002, η² = 0.690) and Cr (F = 28.85, p < 0.001, η² = 0.880) compared to Eisenia fetida. Furthermore, Eudrilus eugeniae exhibited significantly higher RE for both Cd (F = 137.4, p < 0.001, η² = 0.920) and Cr (F = 27.35, p < 0.001, η² = 0.690) relative to Eisenia fetida. Temporal factors also significantly influenced RE for Cd (F = 575.14, p < 0.001, η² = 0.990) and Cr (F = 7732.94, p < 0.001, η² = 0.990). The BAF for Eudrilus eugeniae was significantly higher for both Cd (F = 44.75, p < 0.001, η² = 0.790) and Cr (F = 183, p < 0.001, η² = 0.940) in comparison to Eisenia. fetida. The findings underscore the species-specific efficiencies in metal uptake, suggesting that Eudrilus eugeniae offers a distinct advantage over Eisenia fetida for vermiremediation in tropical and subtropical environments.