Contrasting fate and binding behavior of Mn and Cu with dissolved organic matter during in situ remediation using multicomponent capping in malodorous black water

Abstract

The common use of peroxides in the remediation of malodorous black water may lead to the activation of heavy metals in sediment when eliminating black and odorous substances. The mechanisms of heavy metal interactions with dissolved organic matter (DOM) in response to in situ capping have not been elucidated, but this information could guide the optimization of capping materials. We developed a capping material consisting of hydrothermally carbonized sediment (HCS), hydrated magnesium carbonate (HMC) and sodium percarbonate (SPC) and used microcosm experiments to investigate the dynamics of Mn and Cu at the sediment–water interface in malodorous black water. The results showed that HCS, HMC and SPC contributed multiple functions of mechanical protection, chemical isolation and oxygen provision to the new caps. HMC promoted the conversion of Mn/Cu into carbonate minerals. The optimal mass proportions were 25 % HCS, 60 % HMC and 15 % SPC based on the mixture design. In situ capping altered the fate and transformation of metals in the sediment-overlying water profile in the short term through Mn immobilization and Cu activation. The complexation of Cu(II) ions was significantly stronger than that of Mn(II) ions. In situ capping had a significant effect on the order of complexation of different fluorescent DOM molecules with Mn(II)/Cu(II) ions: microbial byproducts and fulvic acid-like components were preferentially complexed with Cu(II) ions after capping, while phenolic and humic acid-like components preferentially interacted with Mn(II) ions. Humic-like components bound to Cu were affected the most by capping treatment, whereas protein-like components were relatively weakly affected. Our study provides valuable knowledge on the impact of in situ capping on DOM–metal complexes.