Integral approach for phytoremediation process: lessons learned

MERINI, LJ; GIULIETTI, AM

Chania

Conferencia; 5th European Bioremediation Conference; 2011

Department of Environmental Engineering - Technical University of Crete

Research on phytoremediation has gained interest during the last two decades, in correlation with the success of experimental studies carried out in the lab and greenhouse. Although mineralization of organics can be achieved into some plants tissues, it has been recognized that combination of vegetal and microbial metabolic activities is the most efficient strategy for a successful remediation. In this way, most scientific research is currently focused on microbe-assisted phytoremediation of organic environmental contaminants. Despite the promising results obtained at lab scale, they are not in correlation with the number of successful projects carried out at field scale. When the lab data is intended to be scaled up, researchers face a whole new universe to cope with. When field scale phytoremediation processes are boarded, performing of lab scale experiments is essential to obtain criteria and application tools. During lab scale performance of the mentioned assays, it is necessary to hold a global vision about the complexity and dynamism of the events taking part in the phytoremediation process. In the “isolate to study” process, phytoremediation has been dissected in such a way that reports assessing the integrated action of the plant, soil (mineral and organic fractions), microfauna, bacteria, fungus and the contaminant (often complex and heterogeneous) are scarce. In this context, the selection and design of the experimental system are critical. Among the most commonly used, the following systems can be mentioned rising complexity order: in vitro cell cultures, in vitro organ cultures (stems and hairy roots), hydroponics and microcosms. It is important to point out that microcosms are not commercially available and its design has to be customized case by case. In a first stage, it is necessary to consider the soil physico-chemical and textural characteristics, since they condition the selection of the analytical methods for monitoring the decontamination process, among other aspects. From the analytical point of view, it is also important to consider both, the special characteristics of the ongoing process and the requirements of the new environmental paradigms. In many cases, it may be necessary to develop analytical technics which implies the use of environmental friendly chemicals. In a second stage, the selection and management of the biological agents (plants and microorganisms) are the main aspects to be considered. It is important to understand that the sole presence of plants, independently of their remediation capacity per se, is an advantage since they generate a microenvironment favorable for microbial activity (rizospheric effect) and usually reduce horizontal (run-off) and vertical (leaching) migration of the contaminant. Besides, the esthetic value and public acceptance of plants presence is an additional unscientific advantage. In addition, when biological agents are selected, flora, microorganisms and microfauna naturally selected by the contamination event or autochthonous organisms are preferred. In a third stage, the scale up to field scale requires the use of heavy duty machinery and dealing with large amounts of soil which implies engineering knowledge. On the other hand, although the comparative low cost is one of the main advantages of phytoremediation, field scale projects involve large budgets. So, boarding a full scale phytoremediation project necessarily implies an interdisciplinary approach, which include from chemistry, biochemistry and agronomy to engineering, legislation, ethic and economy. Finally, although phytoremediation ought to be an essentially interdisciplinary technology, the successful combination of the different involved areas is probably the most challenging objective.