Enhanced removal of COD and color from landfill leachate in a sequential bioreactor

•Leachate was treated by a sequential process involving bacterial and fungal sp.•The process was optimized by Box–Behnken design and response surface methodology.•Optimized conditions showed enhanced removal of COD (76.9%) and color (45.4%).•Sequential treatment by the strains led to significant reduction in genotoxicity.

In the present study, a sequential treatment process was carried out using a fungal sp. (Phanerochaete sp.) followed by a bacterial sp. (Pseudomonas sp.) for the degradation and detoxification of contaminants in landfill leachate. The process was optimized using Box–Behnken design (BBD) and response surface methodology (RSM) for three variables (C source, N source and duration), while monitoring two responses (% COD and color removal). After treatment in a bioreactor under optimized conditions, enhanced removal of COD (76.9%) and color (45.4%) was observed. Further, GC–MS analysis of metabolites detected at different stages of treatment showed formation of degradation products of lignin and polycyclic aromatic compounds. Treatment efficiency was finally evaluated by the alkaline comet assay in HepG2 human hepato-carcinoma cells. The results indicated no statistically significant DNA damage at the end of the treatment, making the effluent suitable to be discharged conforming to the safety standards.