Analysis of the Hysteresis of Lindane in a Soil Rich in Organic Matter Using Poggi\ub4s 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 \u201cblack boxes\u201d. 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

A Minireview on Slurry Bioreactors for Bioremediation of Soils and Sediments (Paper B-33)

Poggi\u2019s differential coefficient of hysteresis (CHPoggi) has been shown to be a useful tool for describing the adsorptive-desorptive behavior of pollutants on solid matrices. The CHPoggi is defined as the ratio of the derivative of the adsorption isotherm to the derivative of the desorption isotherm, both evaluated in a point of interest J in the space q-C of the equilibrium relationship of the pollutant and solid matrix (Poggi-Varaldo et al., 2002, Interciencia 27 (3): 180-185). The aim of this work was to evaluate the adsorptive-desorptive behavior of lindane in an agricultural soil using CHPoggi. In addition, a useful and simple algebraic equation for CHPoggi was obtained for the particular case when the adsorption isotherm is linear and the desorption isotherm follows the equation of Langmuir. The model solid matrix was an agricultural soil, pH 7.1, with low clay and high organic matter contents. The adsorption of lindane onto this soil was described by a linear isotherm given by the equation qa = 3.91*C, whereas the desorption was better described by a Langmuir-like isotherm given by the equation qd = (32.9*C)/(1 + 1.1*C), with q in mg/kg and C in mg/L. Based on the definition of CHPoggi a simple equation was derived, namely, CHPoggi = qmax *b/kl , where qmax = maximum capacity of adsorption of the Langmuir desorption isotherm (mg/kg); b = coefficient of curve growth-shape in the Langmuir desorption isotherm (L/mg); kl = coefficient of the linear adsorption isotherm (L/Kg). The value of Poggi\ub4s coefficient of hysteresis was calculated at the point of interest J (qj = 28.8 mg/kg, Cj = 6 mg/L) using two different methods: first, a numerical method based on the ratio of the tangents to both isotherms in J (as an approximation to the corresponding derivatives), and second, the algebraic equation already given in the above paragraph. The first method yielded CHPoggi = 6.6, whereas the second one gave CHPoggi = 8.4. The agreement between the two methods indicates that the more simple algebraic equation can be used for calculation of CHPoggi whenever the isotherm equations are known. The value of CHPoggi suggests that the hysteresis lindane-soil is moderate