Influence of the pretreatment of activated sludge in the aerobic digester as inoculum on rapid anammox enrichment

This study aims to determine a shorter start-up period for the anaerobic ammonium oxidation (anammox) reaction which is one of the main obstacles in the application of anammox technology. The results obtained from the two identical laboratory-scale upflow packed bed reactors (R1 and R2) were compared whether the pretreatment of the activated sludge as inoculum plays an important role in the rapid enrichment of anammox bacteria. Pretreatment consists of aerobic digestion and continuous washing of the reactor. Both reactors were fed with synthetic wastewater during 192 d. Anammox activities evaluated by mass balances based on ammonium, nitrite, and nitrate analysis and nitrogen removal rate (NRR). The results demonstrated that the R1 reactor was successfully enriched on day 112 and had an NRR of 30 gN/m3 d. By contrast, it took 58 d to enrich the R2 reactor (48.5 gN/m3 d). It is possible to enrich anammox bacteria within 58 d by applying activated sludge pretreatment to shorten the period for the removal of unwanted organisms and their lysed cell debris.