Bioremediation of an Agricultural Heavy Soil Polluted with Lindane: Comparison of Anaerobic and Aerobic Slurry Bioreactors

摘要

Slurry bioreactor is an ad situ and ex situ technology that can be used for bioremediation of problematic sites (when the less expensive natural attenuation or stimulated in situ bioremediation are not feasible), such as those characterized by soils with high contents of clay and organic matter, by pollutants that are recalcitrant, toxic, and display hysteretic behavior, or when bioremediation should be accomplished in short times under the pressure and monitoring of environmental agencies and regulators. Lindane or γ-hexachloro-cyclohexane (HCH) is a toxic and recalcitrant chlorinated insec- ticide widely used in developing countries, particularly in Mexico. The purpose of this research was to evaluate the effect of electron acceptor and supplementation of degrad- able organic co-substrate sucrose on lindane removal from a clayish agricultural soil with high levels of organic matter, using batch slurry bioreactors. A simple 3x2 factorial ex- periment was carried out with factor electron acceptor at three levels (aerobic, methanogenic and sulfate-reducing SB, i.e., A-SB, M-SB and SR-SB, respectively) and factor sucrose concentration at 0 a 1 g/L. An agricultural, mineral clayish soil with 8% organic matter and 100 mg/kg lindane was treated in lab scale SBs. SBs were inoculated with biomass previously acclimated to lindane in suspended-growth, liquid phase, con- tinuous bioreactors. Abiotic control SBs (sterilized soil and inocula) and biotic control SBs (non-inoculated, non-sterilized soil) were also run. No general trends were observed for the two factors since their interaction was very strong. In this way, for SB without sucrose, lindane efficiency removals followed this order: A > SR M (86, 82 and 41%, respectively). In the case of SB supplemented with sucrose, the efficiencies were SR > A M (88, 77 and 47%, respectively). Our hypothe- sis that sucrose co-substrate would improve lindane removals was just true for sulphate- reducing SBs. Unexpectedly, A-SB without sucrose outcompeted the units with sucrose (86 and 77%, respectively). Lindaneclastic bacterial counts were in the order of 8 (log CFU) for A-SB independ- ently of sucrose or no sucrose addition, 6.5 (log UFC) in M-SB, and 7 (log CFU) in SR- SB. Biotic control A-SBs, M-SRs and SR-SBs exhibited reductions of lindane in the or- der of 60% suggesting that the soil native microflora itself had a significant capacity for degrading or transforming lindane. This is consistent with lindaneclastic bacterial counts around 6.7, 5.0 and 5.5 (log CFU) in the aerobic, methanogenic and sulfate-reducing bi- otic controls, respectively. Inoculation with acclimated biomass seemed to increase lindane removals by an absolute 20% (relative 30%). On the other hand, removals of lin- dane in abiotic control SBs were very low, with an average of 11%. The excellent and moderate performance of SR- and M-SBs, points out to a promising alternative for the application of anaerobic SB to the bioremediation of heavy soils polluted with lindane.