Effect of humic acid on phenanthrene removal by constructed wetlands using birnessite as a substrate

The binding of polycyclic aromatic hydrocarbons (PAHs) to humic acid (HA) can boost the complexation-flocculation process and promote pollutant oxidation through the role of HA as an electron shuttle. HA-coated biochar (BA) was added to study the effects of HA on phenanthrene (PHE) removal by constructed wetlands (CWs) using birnessite as a substrate. HA reduced the average PHE concentration of effluent by 26.58% due to its role as a complexing agent, based on Fourier-transform infrared spectroscopy analysis. For CWs with birnessite, the PHE removal performance was further enhanced due to the role of electron shuttles. X-ray photoelectron spectroscopy and illumina high-throughput analysis revealed an enhanced Mn-Fe cycle. The total relative proportions of Mn-oxidizing bacteria and iron-oxidizing bacteria in VFBCW-HA/BA were 2.33 and 5.50 times as high as those in VFBCW-BA and VFCW-HA/BA. Humic acid also accelerated the biodegradation of PAHs and the quantity of PAH degradative bacteria in VFBCW-HA/BA was 6.29 times greater than in VFBCW-BA.