An AHP-based evaluation system applied for phytoremediation method selection in heavy metal contaminated farmland

Phytoremediation assisted by chemicals is widely applied in heavy metal contaminated farmland remediation. In this study, an effective and comprehensive scoring system was established based on analytic hierarchy process (AHP) assisted by principal component analysis (PCA) and ecological hazard index (EHI). Taking the remediating effect-related characteristics of soil, plant, and microbe into account, the system was designed to encompass 3 criteria containing 9 features and 14 indexes to evaluate the remediating methods. Data of all indexes were then normalized to guarantee their comparability. Afterward, the system was applied in a farmland-remediating case study. Two widely-used methods of phytoremediation, i.e., phytoextraction and phytostabilization, together with 8 chemicals were conducted in the case study to verify the accuracy and feasibility of the evaluation system. Amaranthus hypochondriacus and Jatropha curcas L. were selected as the remediating plants for phytoextraction and phytostabilization, respectively. Urea, potassium sulfate (K2SO4), lime and dolomite were selected to assist phytoremediation. As for the results, applying potassium sulfate (K2SO4) once (EP1) and no amendments applied (SCK) are the best choice for phytoextraction and phytostabilization, respectively. SCK performed better, but with the plants growing, the scores of phytostabilization lessened while phytoextraction elevated. Thus, in the long term, EP1 should be the main remediation method with SCK being the auxiliary one in this farmland. A further endeavor was made to simplify the established system at 3 levels based on 3 principles, i.e., importance, difference, and complexity, to meet the need of different assessments. In conclusion, this comprehensive scoring evaluation system characterized as systematic, accurate, and reasonable could serve as a reference for decision-making of heavy metal contaminated soil remediation.