Triphasic slurry bioreactors for the bioremediation of lindane-impacted soil under aerobic and anaerobic conditions

The objective of this study was two-fold: (i) to evaluate the effect of co-substrate supplementation and possible synergistic effect of the indigenous population and a lindane-acclimated inoculum on the removal of lindane in three-phase, aerobic slurry bioreactors (SB), and (ii) to evaluate the effect final electron acceptor (O₂, CO₂ and SO₄ ^-2, or A, M, and SR, respectively) and supplementation with carbon source (sucrose, 1 and 0 g/L; C or NC, respectively) on the removal of lindane in triphasic lab scale SB. In a first experiment lindane was significantly removed in the first week of operation (55-70%); its reduction further continued at a lower rate. Both factors had a moderately significant effect; on the one hand, sucrose supplementation enhanced the removal of lindane (p < 0.08); on the other hand the indigenous microflora and lindane-acclimated inoculum exhibited some kind of antagonism (p < 0.07), since removals in SB with sterile soil were higher than those with live soil. In a second experiment, there was a significant effect of factor 'electron acceptors' on removal of lindane (p < 0.0001): lindane removal followed the order A > SR > M. Supplementation with sucrose had a significant positive effect (p < 0.004). Main metabolites from lindane degradation were chlorobenzene (CB), 1,2-dichlorobenzene (1,2-DCB) 1,3-dichlorobenzene (1,3-DCB) and 1,2,4- trichlorobenzene (1,2,4-TCB) in aerobic and sulfate reducing slurry bioreactors, only CB and 1,2-DCB were found in methanogenic units. Metabolites were consistent with those reported in aerobic and anaerobic degradation pathways of lindane.