[Effects of Nanoscale Zero-valent Iron (nZVI) on Denitrifying Performance of an Upflow Granular Sludge Bed Reactor]

In order to examine the effects of nanoscale zero-valent iron (nZVI) on the performance of denitrifying granular sludge (DGS) in a continuous flow model, the variations of nitrogen removal efficiency in the reactor, sludge morphology, and denitrifying characteristics at different influent nZVI concentrations were investigated in an upflow sludge bed (USB). The results showed that nZVI concentrations lower than 5 mg·L^-1 did not influence the nitrogen removal performance of the reactor significantly, and the activity of DGS was improved slightly. When the influent nZVI concentration was in the range of 5 to 10 mg·L^-1, the DGS could adapt to the biological inhibition of nZVI partially, with the increase of sludge concentration and grain size. However, the higher total iron contents in the sludge resulted in the lower denitrifying activity of the DGS. The removal efficiencies of COD and NO₃^--N in the reactor decreased to 23.3% and 20.3%, respectively, at the influent nZVI concentration of 30 mg·L^-1. Moreover, the DGS was a dark color and of a smaller grain size because of the adsorption of a large amount of nZVI, while the microbe density, such as that of the bacillus species, on the granule surface decreased significantly. In the recovery phase, the nitrogen removal performance of the reactor could almost reach its initial level at nZVI=0 mg·L^-1 during an operation of 20 days due to the fast growth of heterotrophic microbes on the surface of the DGS.