Analysis of the Hysteresis of Lindane in a Soil Rich in Organic Matter Using Poggi´s Differential Coefficient of Hysteresis (Paper L-41)

The aim of this work is to present a critical review on slurry bioreactors (SB) and their application to bioremediation of soils and sediments polluted with recalcitrant and toxic compounds. The scope of the review encompasses the following subjects: (1) process fundamentals of SB and analysis of advantages and disadvantages; (2) the most recent applications of SB to lab scale and commercial scale soil bioremediation, with a focus on pesticides, explosives, polinuclear aromatic hydrocarbons, and chlorinated organic pollutants; (3) trends on the use of surfactants to improve availability of contaminants and supplementation with degradable carbon sources to enhance cometabolism of pollutants; (4) recent findings on the utilization of electron acceptors other than oxygen; (5) bioaugmentation and advances made on characterization of microbial communities of SB; (6) developments on ecotoxicity assays aimed at evaluating bioremediation efficiency of the process. From this review it can be concluded that SB 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 regulatiors. SB technology allows for the convenient manipulation and control of several environmental parameters that could lead to enhanced and faster treatment of polluted soils: nutrient N, P and organic carbon source (biostimulation), inocula (bioaugmentation), increased availability of pollutants by use of surfactants or inducing biosurfactant production inside the SB, etc. An interesting emerging area is the use of SB with simultaneous electron acceptors, which has demonstrated its usefulness for the bioremediation of soils polluted with hydrocarbons and some organochlorinated compounds. Characterization studies of microbial communities of SB are still in the early stages, in spite of their significance for improving reactor operation and design optimization; so far SB are still modelled as “black boxes”. We have identified the following niches of research needs for SB in the near and mid term future, inter alia: (1) application of SB with sequential and simultaneous electron acceptors to soils polluted with contaminants other than hydrocarbons (i.e., pesticides, explosives, etc.), (2) evaluation of the technical feasibility of triphasic SB that use innocuous solvents to help desorbing pollutants strongly attached to soils, and in turn, to enhance their biodegradation, (3) gaining deeper insight of microbial communities present in SB with the intensified application of molecular biology tools such as PCRDGGE, PCR-TGGE, ARDRA, etc., (iv) development of more representative ecotoxicological assays, more complex however more informative than the mere uni-species bioassays or battery of uni-species tests (for instance, microcosm and mesocosms bioassays) to better assess the effectiveness of a given bioremediation process.