Groundwater ammonia pollution is well investigated worldwide as well as in Viet Nam. The products of its conversion process, namely nitrite and nitrate, cause the toxicity of ammonia in water. In addition, the existence of ammonia in water causes the modification of water taste and smell, increases the risk of heterotrophic and contagious microorganism presence. Biofilm technique has been being applied to treat the ammonia in the groundwater recently. In this present study, fixed‐bed biofiltration technique was implemented to remove the ammonia at high concentration of 20‐50 mgN/L. The results indicated that the effluent reached the standard of domestic and drinking water quality (the ammonia concentration < 3 mgN/L) at all investigated ammonia concentrations. The specific nitrification rate of the microbial carrier used reached the maximum value of about 3.76 kgN.m‐3.day‐1 with the hydraulic retention time lower than 0.4 h and feed ammonia concentration of about 50 mgN/L. The biomass density in biofiltration column before experimental implementation was about 1000 mg/L.

In order to determine the ammonium treating efficiency, several factors were investigated, including: carrier size and dimension, the volume of carrier, ammonium concentration… which impact on nitrification rate by two (02) techniques: moving and fixed bed microbial film. The results indicated that with moving bed microbial film technique, the best size and dimension of carrier is a cube with 1x1x1 cm, the content of carrier is of 20% in volume. However, fixed bed microbial film technique is favored by the cube of 2x2x2 cm carrier, the content of 50% in volume.