[Effect of suspended sediment on the transformation of organic nitrogen]

Microcosm experiments have been carried out to study the effects of suspended sediment on the transformation of organic nitrogen contaminants under different conditions, including with and without spiking bacteria to the water-sediment system. When with the natural water and sediment as cultivation media and without spiking bacteria to the water system, the presence of sediment could stimulate the transformation of organic nitrogen, and the transformation rates were correlated well with the sediment concentration. When the initial concentration of organic nitrogen in the water system was 5 mg/L, and the suspended sediment content were 0, 5 and 10 g/L, the first-order transformation rate constants of organic nitrogen were 0.286,0.333 and 0.538 d(-1), respectively; the nitrification rate constants (K4) were 0.001 8, 0.003 8 and 0.0050 L x (d x micromol)(-1), respectively, when fitting the nitrification process with the Logistic kinetics. When spiking the water systems with the same initial bacteria density, the first-order transformation rate constants of organic nitrogen and nitrification rate constants (K4) increased with the sediment content. With the natural water and sediment as cultivation media, the mechanism regarding the effects of suspended sediment on organic nitrogen transformation includes the following aspects: (1) The initial amount of bacteria increased with the sediment content in the water system. (2) The growth of bacteria was promoted by the sediments, and bacteria tended to attach to the sediment. In addition, most of organic nitrogen was attached to the sediment phase and the transformation of organic nitrogen in the water system mainly occurred at the sediment/water interface. (3) The presence of sediment increased the contact chances between bacteria and organic nitrogen, thus stimulated the transformation of organic nitrogen contaminants.