Mass transfer kinetics in ammonium removal during anaerobic ammonium oxidation (anammox) sludge enrichment

Abstract The implementation of anammox technology in various kinds of wastewater has been studied extensively by researchers worldwide. The slow growth rate characteristics of anammox bacteria resulted in the limited availability of inoculum sludge hindering the widespread adoption of anammox technology. Slow-growing bacteria may exhibit different patterns in kinetic mass transfer, leading to varying responses in pollutant degradation processes. Detailed knowledge of pollutant transport by anammox bacteria is scarcely explored. Therefore, the purpose of this study is to validate the applicability of the modified mass transfer models (MMTF) to evaluate the enrichment of anammox sludge and to provide a comprehensive insight into the mechanisms of ammonium substrate transportation to the anammox cells. The highest removal efficiency of the anammox sludge achieved was 84.97%, and the R 2 value proved the applicability of these models. Internal mass transfer (IMT) emerged as the main contributor to global mass transfer (GMT). Therefore, the rate-limiting step in anammox sludge enrichment is governed by the resistance of external mass transfer.