Two-stage phyto-microremediation of tannery effluent by Spirodela polyrrhiza (L.) Schleid. and chromium resistant bacteria

•Two-stage tannery effluent treatment by S. polyrrhiza and Cr-resistant bacteria.•It showed reduction of 81.2% COD, 97.3% Cr, 99.3% Cr(VI), 97.0% Pb(II), 95.7% Ni.•High SOD and APX activities were observed in Spirodela exposed to tannery effluent.•After treatment, LC–MS showed conversion of complex compounds into simpler ones. Two-stage sequential treatment of tannery effluent was conducted employing a wetland plant, Spirodela polyrrhiza (L.) Schleid., and chromium (Cr) resistant bacterial strains. The bacterial strains were isolated from Cr-enriched environmental matrices and rhizosphere of Spirodela polyrrhiza. The phyto-rhizoremediation of tannery effluent by Spirodela and its rhizospheric bacteria (Cellulomonas biazotea APBR1-6, Bacillus safensis APBR2-12, Staphylococcus warneri APBR3-5, Microbacterium oleivorans APBR2-6), followed by microremediation by Cr resistant bacteria (Micrococcus luteus APBS5-1, Bacillus pumilus APBS5-2, Bacillus flexus APBE3-1, Virgibacillus sediminis APBS6-1) resulted in reduction of pollution parameters [COD (81.2%), total Cr (97.3%), Cr(VI) (99.3%), Pb(II) (97.0%), Ni (95.7%)]. The LC–MS analysis showed that many pollutants detected in untreated tannery effluent were diminished after bioremediation or long chains of alcohol polyethoxylates viz. C18EO6 in untreated effluent were broken down into smaller unit of alcohol polyethoxylate (+HHO[CH2CH2O]H), indicating that bacteria and Spirodela polyrrhiza, alongwith its rhizospheric associates utilized them as carbon and energy source.