Transformation of nitrogenous compounds in the water-sediment-microbiological system from the Yangtze River

Abstract

The water-sediment-microbiological system was constructed by flow-through technique in the laboratory using the undisturbed sediment cores collected from Nanjing section of Yangtze River to determine nitrification, denitrification and anaerobic ammonium oxidation (anammox) processes of nitrogenous compounds. The nitrification rates ranged from 11.95 to 19.29 μmol N m−2 h−1 in the sediments and the rates of denitrification and anammox ranged from 11.98 to 65.86 μmol N m−2 h−1 and 0.40 to 8.04 μmol N m−2 h−1, respectively. Denitrification dominated nitrogen removal process, especially non-coupling nitrification process. The decrease of total organic carbon (TOC) and electrical conductivity (EC) in sediments increased the activity of ammonia monooxygenase and promoted the rate of nitrification. The denitrification rates were related to NO3−-N concentrations in the overlying water, and TOC, pH and EC affected the activity of the nitrate reductase. The increase of TOC and clay content and the decrease of EC corresponded to the increase of nitrate reductase activity and anaerobic ammonia oxidation rate. The optimum temperature was 35°C for denitrification and 25°C for nitrification. The pH values influenced nitrogen conversion, denitrification occurred more easily in neutral environment, and the nitrogen conversion rates in the light were higher than in the dark.