Quantifying the biofilm effects on phosphorus adsorption of sediment

Purpose Sediment is a good substrate for microorganism colonization in aqueous environments. The secretion of metabolic products by microorganism induces biofilm growth on sediment surfaces, which further affects their interaction with pollutants and exerts important impacts on aqueous ecosystems. In this study, the effects of biofilm on the phosphorus (P) adsorption of sediment were quantified. Methods A specially designed cylinder was used for biofilm cultivation with different original sediment sizes (0.02–0.05, 0.05–0.1, and 0.1–0.2 mm) and under different hydrodynamic conditions (flow velocities of 0.1, 0.15, and 0.2 m s −1 ), and their kinetic and equilibrium P adsorption characteristics were experimentally explored. Then, an expression of P adsorption by bio-sediment was derived through incorporating the amount of biomass into the modified Langmuir isotherm. Results The adsorption kinetic process of bio-sediment was best described by the pseudo-second-order model. The P adsorption capacity increased with the increasing biofilm cultivation period (i.e., an approximate increase of an order of magnitude), which increased quickly in the first few weeks due to the rapid biofilm growth and then tended to be stable due to the gradually stabilization of biofilm growth. More biomass accumulated on the surface of finer sediment after biofilm growth leading to a greater P adsorption capacity, while the difference in P adsorption was not so obvious for bio-sediment formed under different flow velocities. Conclusion The P adsorption of sediment was significantly enhanced after biofilm growth, and the derived model could reasonably predict the adsorption characteristics of bio-sediment, verifying the possibility to consider the biomass into adsorption isotherms. Further studies considering the structure and components of biofilm need to be conducted in the future.