Life Cycle Assessment applied to remediation technologies: methodological and practical issues

At the present day, remediation of polluted groundwater can be performed through various technologies; however, these technologies are often associated with relevant costs (both economic and environmental) and technical issues [1] which in some cases may affect the cost effectiveness and feasibility of remediation itself. This is why efforts in the field of research are being increasingly focused in the development of bioremediation technologies which use the degrading potential of bacteria and microorganisms to remove target pollutants. These technologies require a smaller demand for resources and technical equipment in order to achieve clean up targets compared to traditional systems. The focus of the study was to evaluate, by a comparative Life Cycle Assessment (LCA) approach, the environmental performance of an innovative technology (a modified Permeable Reactive Barrier, PRB), within the framework of EU Minotaurus project, in comparison to a permeable reactive barrier filled with Zero Valent Iron (ZVI) and a Pump and Treat System (PTS) [3]. A few methodological issues showed up during the research. First, a full scale modified PRB had to be designed in order to allow comparison with reference technologies: the new system has been modeled introducing graphite instead of ZVI as a reactive medium. Secondly, Ecoinvent database did not provide a specific item to address the discharge of treated groundwater as surface water in the PTS, thus not allowing the evaluation of the impact resulting from the depletion of a non-renewable (in the short medium term) resource; this issue has been addressed by modeling post treatment water as if it were wastewater with a slight degree of contamination. Finally, a first run of results produced through EDIP/UMIP 97 method showed a particular emphasis on ecological and human toxicity impact categories. According toInternational reference Life Cycle Data System(ILCD [5]) suggestions tohandle with care these categories' scores, another run of results has been produced through IMPACT 2002+ method. A key to the interpretation and comparison of the results obtained by the two methods was provided by the analysis of the results produced in the Global Warming Potential category. The results showed that, for all three systems analyzed, the critical factor is the reactive medium, to which both calculation methods associated the most relevant impacts. The modified PRB [2] showed the best performance, even if its efficiency in remediation process must be tested and backed up by field results. In passive remediation technologies the use of less impactful media turned out to be a key factor in order to improve the overall sustainability of remediation systems, with particular reference to PRB, which showed the poorest performance due to the use of ZVI. The performance of the Pump and Treat system turned out to be closely related to the amount of Granular Activated Carbon (GAC) employed: the sizing applied to this case study kept total environmental score comparable to those of the passive technologies; however, considering the relevant environmental burden of the activated carbon production process, it can be expected a high environmental cost for applications of this technology involving larger volumes of water or longer operation time.