THE EFFECTS OF NITRATE AND DO ON THE NITRATE UTILIZATION EFFICIENCY IN AEROBIC AND ANOXIC BIOREMEDIATION PROCESSES

摘要

This study focused on the nitrate utilization efficiency for toluene removal under different operating conditions. The nitrate utilization efficiency is defined as the ratio of the total amount of toluene removed to the total amount of nitrate consumed. The experiment was conducted with a series of batch reactors. The batch reactors were seeded with both aerobic toluene degraders and denitrifying bacteria and contained both nitrate and dissolved oxygen as electron acceptors. The experimental results indicated that toluene could be effectively removed under the aerobic or anoxic conditions, as soon as oxygen or nitrate was sufficiently supplied. The nitrate utilization efficiency in the obligate anoxic condition was only 0.22 mg-toluene/mg-nitrate, lower than that calculated from the theoretical stoichiometry equation, 0.26 mg-toluene/mg-nitrate. The results showed that toluene could be simultaneously removed by both aerobic toluene degraders and denitrifying bacteria in reactors containing both nitrate and limited oxygen. Also, nitrate utilization efficiency was relatively better in reactors containing both nitrate and limited oxygen compared to that in reactors containing nitrate alone. When the initial dissolved oxygen concentrations increased from 4.6 to 12.3 mg/L, the overall and anoxic nitrate utilization efficiencies increased from 0.31 and 0.3 to 0.51 and 0.47 mg-toluene/mg-nitrate, respectively. However, a further increase in dissolved oxygen concentration did not increase the nitrate utilization efficiency, because of the formation of a highly oxidized environment inhibiting the activity of denitrifying bacteria.