An isothermal adsorption model for adsorption of substrates by anammox extracellular polymeric substance proteins: Establishment, verification, and determination of adsorption capacity

Anaerobic ammonium oxidation (Anammox) bacteria (AnAOB) are beneficial for the treatment of NH4+-N and NO2--N simultaneously in sewage waste. These bacteria form particles by secreting or capturing substances such as extracellular polymeric substances (EPS), which adsorb harmful ions with the help of charge adsorption and complexation to protect the growth of AnAOB. However, the substrate also has an electric charge, and the effect of EPS on the adsorption and mass transfer of NH4+-N and NO2--N remains to be elucidated. In this study, we investigated the adsorption effect of EPS from AnAOB on different substrates by using a mathematical model and determined the possible role of EPS in bacterial growth. EPS proteins, which were extracted using the ultrasound method and detected by proteomics, were consistent with the proteins involved in the anammox reaction in cells. The detection models to calculate the adsorption capacity were established in accordance with the dialysis principle. Both the Freundlich model and Langmuir model were used to explain the adsorption of NH4+-N and NO2--N by EPS proteins. Compared with the adsorption of NH4+-N by EPS, that of NO2--N by EPS was well-fitted in the Langmuir model, with relatively high maximum adsorption concentrations.

Automated summary

The study investigated the adsorption effect of EPS from AnAOB on different substrates and found that EPS proteins can effectively adsorb NH4+-N and NO2--N, playing a role in bacterial growth. EPS proteins were consistent with those involved in the anammox reaction in cells, and the Langmuir model showed high maximum adsorption concentrations for NO2--N.