Effect of C/N ratio on the bioregeneration of biological activated carbon

Abstract

To obtain insight into the role of biological activated carbon (BAC) in the operation of the denitrification process using external carbon source, the effect of C/N ratio on bioregeneration of BAC was investigated using a fluidized bed reactor. The C/N ratio was controlled by the semi-continuous mode in which NO3-N was continuously supplied to each column. The supply of sucrose as a sole organic carbon was controlled during the experimental period. The BAC under steady state of the continuous experiments was supplied to the semi-continuous experiment. The organic carbon was supplied to each column for 20 minutes in all semi-batch experiments, but the intervals were varied from 8 to 24 hours. The influent organic carbon concentrations were controlled to maintain the average C/N ratio at 7.06 for all semi-batch experiments. In the semi-continuous experiment, the five columns have achieved an average denitrification efficiency ranging from 71% to 99%, though the influent C/N ratios were varied from 0 to 508. This is due to the adsorption and desorption capacities of BAC. BAC plays a role as a storage tank for the residual sucrose using its micropore during the time when sucrose was supplied, and BAC supplied the sucrose to the denitrifying bacteria as a carbon source so as to keep high nitrogen removal rate when sucrose was not fed to the columns. These results suggest that bioregeneration may be influenced by the C/N ratio in the environment around BAC.