Bioaugmentation in treatment wetlands: Opportunities, challenges, and safety considerations

Bioaugmentation has been increasingly applied to enhance pollutant removal in treatment wetlands (TWs). However, its wider implementation is still constrained by limited understanding of long-term performance stability and ecological safety. Here, this review synthesizes the current applications of microbial inoculation strategies, highlighting emerging opportunities, key challenges, and critical safety considerations for implementation. The potential avenues toward sustainable bioaugmentation are summarized. These include alternative nitrogen removal processes, multi-pathway elimination of emerging contaminants (ECs), safe detoxification of heavy metals (HMs), and nutrient removal under extreme environmental conditions. Subsequently, key constraints limiting implementation are discussed, including the isolation of indigenous functional microorganisms and the reduced performance stability of inoculants under complex environmental conditions. To address these limitations, approaches such as Raman-activated cell sorting (RACS) and inoculant immobilization have been proposed. Finally, the ecological risks potentially associated with bioaugmentation were evaluated to ensure the safe implementation of microbial inoculation. These risks include disruption of native microbial communities, horizontal transfer of antibiotic resistance genes, and formation of toxic transformation products. Overall, this review provides insights into sustainable, site-specific bioaugmentation strategies in TWs and supports ecological engineering approaches for the remediation of diverse pollutants.