Meta-analysis of the removal of trace organic contaminants from constructed wetlands: Conditions, parameters, and mechanisms

Constructed wetlands (CWs) are a promising technique to mitigate trace organic contaminants (TrOCs). The current review used meta-analysis to investigate the TrOC removal in CWs on the basis of 92 selected paper and 2373 observations. The results indicated no regular trend shown for the TrOC removal by using logPow or pKa, whereas TrOCs with molecular weight greater than 358.60 g mol−1 were found generally more recalcitrant than smaller molecules. It was found that solid–water distribution coefficient (logD) can be effective in distinguishing the readily removable TrOCs. Moreover, different patterns of TrOC removal were found correlated with CW conditions (i.e., CW type, CW scale, CW vegetation, and influent type and quality). By quadratic curves fittings, parameters including pH, DO, Eh, TrOC initial concentration, and CW operational time were found to determine the removal efficiency of TrOCs, whereas logD, COD, NH4+-N, and TP were found to be linked to TrOC removal only if the CW conditions were specified. These results also suggested that single factors can hardly determine the fate of TrOCs in CWs. However, some universal patterns could exist for the determination. More attention should be placed in diminishing the scale bias in the future. [Display omitted] •Designs and conditions of CWs were found to determine the fate of TrOCs in CWs.•Conditional parameters included logD, COD, NH4+-N, and TP.•Unconditional parameters included pH, DO, Eh, Ci, and OT.•Parameter logD3.2 was effective in distinguishing readily removable TrOCs in CWs.•A knowledge gap exists between small, lab scale and large, full scale studies.