Studies on Remediation of DDT-Contaminated Soil and Dechlorination of DDT

Biodegradation of DDT using multi-species mixtures: From genome-mining prediction to practical assessment

DDT (dichlorodiphenyltrichloroethane) is a commonly used insecticide that is recalcitrant and highly stable in the environment. Currently, DDT residue contamination, especially in agricultural soil, is still a concern in many countries, threatening human health and the environment. Among the approaches to resolve such an issue, novel biodegradation-based methods are now preferred to physicochemical methods, due to the sustainability and the effectiveness of the former. In this study, we explored the possibility of building mixed microbial cultures that can offer improved DDT-degrading efficiencies and be more environmentally transilient, based on genome annotation using the KEGG database and prediction of interactions between single strains using the obtained metabolic maps. We then proposed 10 potential DDT-degrading mixed cultures of different strain combinations and evaluated their DDT degradation performances in liquid, semi-solid and solid media. The results demonstrated the superiority of the mixtures over the single strains in terms of degrading DDT, particularly in a semi-solid medium, with up to 40-50% more efficiency. Not only did the mixed cultures degrade DDT more efficiently, but they also adapted to broader spectra of environmental conditions. The three best DDT-degrading and transilient mixtures were selected, and it turned out that their component strains seemed to have more metabolic interactions than those in the other mixtures. Thus, our study demonstrates the effectiveness of exploiting genome-mining techniques and the use of constructed mixed cultures in improving biodegradation.

The influence of small-scale interlayer heterogeneity on DDT removal efficiency for flushing technology

With an aim to investigate the influence of small-scale interlayer heterogeneity on DDT removal efficiency, batch test including surfactant-stabilized foam flushing and solution flushing were carried out. Two man-made heterogeneous patterns consisting of coarse and fine quartz sand were designed to reveal the influencing mechanism. Moreover, the removal mechanism and the corresponding contribution by foam flushing were quantitatively studied. Compared with surfactant solution flushing, the DDT removal efficiency by surfactant-stabilized foam flushing increased by 9.47% and 11.28% under heterogeneous patterns 1 and 2, respectively. The DDT removal contributions of improving sweep efficiency for heterogeneous patterns 1 and 2 by foam flushing were 40.82% and 45.98%, and the contribution of dissolving capacity were 59.18% and 54.02%, respectively. The dissolving capacity of DDT played a major role in DDT removal efficiency by foam flushing under laboratory conditions. And the DDT removal contribution of significant improving sweep efficiency was higher than that of removal decline caused by weak solubilizing ability of foam film compared with solution flushing. The obtained results indicated that the difference of DDT removal efficiency by foam flushing was decreased under two different heterogeneous patterns with the increase of the contribution of improving foam flushing sweep efficiency. It suggested that foam flushing can reduce the disturbance from interlayer heterogeneity in remediating DDT contaminated heterogeneous medium.

The reaction mechanism for highly effective hydrodechlorination of p-chlorophenol over a Pd/CNTs catalyst

Different mass-transfer mechanisms of CNTs and AC for the HDC of p-CP.

Evaluation of foam surfactant for foam-flushing technique in remediation of DDT-contaminated soil using data envelopment analysis method

With an aim to select the most appropriate foaming surfactant for remediation of DDT-contaminated soil by foam-flushing technique, the performances of nonionic and anionic surfactant in several aspects were observed in this study. SDS had the best foam static characteristic among the four experimental surfactants. The solubilizing ability for DDT followed the order of Tween80 > TX100 > SDS > Brij35. The adsorption loss of SDS onto soil was the lowest. The order of desorption efficiency for DDT followed as TX-100 > Tween80 > Brij35 > SDS. Based on these experimental investigations, the overall performances of foaming surfactants were evaluated by data envelopment analysis method. The results indicated that SDS was the optimal alternative for remediation of DDT-contaminated soil by foam-flushing technique. This conclusion was reached with the consideration of the cost, foam static characteristic, surfactant adsorption loss, solubilizing ability, and desorption efficiency of surfactant for DDT.