The removal efficiency of aqueous humic acids by a single-stage activated sludge process and a two-stage activated sludge process was studied using synthetic wastewater,and the removal mechanism was explored by testing the element composition of the sludge,relative content of humic acids in sludge,sludge activity and the molecular weight distribution of humic acids in influent and effluent.

Experimental results showed that when COD concentration in influent was between 280～320 mg/L,gas to liquid ratio was 3:1 and HRT was 10h,the removal efficiency was the best,with average removal efficiency of COD,NH4+-N,TN and SS as 92.