Selenium removal by clam shells and gravels amended with cattail and reed litter

Increasing selenium (Se) levels in aquatic environments raise concerns all over the world. This study investigated effects of organic amendments (cattail and reed litter) and porous media (gravels and clam shells) on Se removal efficiency of horizontal subsurface flow constructed wetlands. Our results show clam shells reduced Se (by mass) up to 2.4-fold faster than gravels within 19 days. Using clam shells as the sole substrate, 96.3% removal efficiency was obtained for cattail litter as an amendment, compared to 88.7% for reed litter over 10 days, although the latter released carbon and nitrogen at least 1.4-fold faster than the former. Meanwhile, speciation analysis suggests Se0 (~75%) and organo-Se (~94%) dominated the biofilms on shells and plant litter, respectively, as substrates. Overall, this study suggests clam shells and cattail litter as an effective medium and carbon source, respectively, can enhance microbial Se removal without posing risks to wildlife health. [Display omitted] •Reed litter released C and N much faster than cattail litter during decomposition.•Clam shells reduced Se (by mass) up to 2.4-fold faster than gravels.•Se decreased by 96 and 89% for shells amended with cattail and reed, respectively.•As a carbon source and medium, reed reduced Se ~1.5-fold faster than cattail in 48 h.•Se0 and organo-Se dominated biofilms on shells and litter, respectively, as media.