Biological nitrogen removal by nitrification-denitrification in constructed rapid infiltration land system to treat municipal wastewater

Constructed Rapid Infiltration (CRI) was a promising option for wastewater land treatment due to the high performance in contamination removal and low operation and maintenance costs. The biodegradation and adsorption played an important role in contamination removal in the system. In this study, attention was given to the mechanism of nitrogen removal in the CRI system. A pilot-scale Constructed Rapid Infiltration (CRI) system was used for treatment municipal sewage with influent flow rate at 1.2 m d(-1) at the wet-to-dry ratio at 1:6. The removal efficiency of CODcr, NH3-N and TP were up to 82, 94 and 85%, respectively, after 30 days start-up stage. The distribution of microorganisms showed that the amount of aerobic bacteria was two classes higher than that of actinomyces, fungi and anaerobic bacteria in the infiltration tank in the system. The experiment was carried out to study the biological nitrogen removal in the nitrification and denitrification processes. The concentration change of TOC, NH3-N, NO2--N and NO3--N in the system with biofilm carrier materials and aseptic group were compared in the nitrification and denitrification processes. The results showed that activity of nitrification-denitrification is the main affecting factor to removal efficiency of nitrate nitrogen. The removal of ammonia nitrogen by biodegradation was 83.8% of the total removal efficiency. The transforming efficiency of nitrate nitrogen was 33.24% in denitrification process. In the whole reaction time, denitrification was relatively weak; optimizing the denitrification process will be helpful for improving removal efficiency of nitrogen in CRI system.