Effect of pre-treatment with humic acids on the activity of nitrifying bacteria in activated sludge

Abstract:

The aim of the present study was to investigate the effect of pre-treatment with humic acids on the activity of nitrifying bacteria (ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB)) in activated sludge processes. Varied concentration of HA (0, 80, 160, 240 mg/L) were applied to pretreat (24 h) three different sludges, including complete nitrification activated sludge with low/high activity (Sc₁/Sc₂), and the partial nitrification activated sludge (Sp). The results showed that the nitrate accumulation rate (R_NA) of Sc₁ increased significantly from 10.73 % to 53.93% after pretreatment with 80 mg/L of HA (50 mg/gMLVSS), simultaneously the ammonia oxidation rates (R_AO) changed insignificantly. In terms of Sc₂, neither the R_AO nor the R_NA changed under each tested condition. For Sp, no NO₃^--N accumulation was observed after the pretrement, which demonstrated that the HA pretreatment did not destruct its partial nitrification performance. In conclusion, HA pretreatment improved the activity of NOB which with low overall nitrification activity, while exhibited insignificant improvement on AOB activity.