ACETYLENE AS A POSSIBLE SUBSTRATE IN THE DENITRIFICATION PROCESS

Abstract

The possible involvement of acetylene (C2H2) as a carbon substrate in the denitrification process was studied in the laboratory with Brookston silty clay. Two experiments of 360 and 600 h durations, respectively, were conducted with saturated soil with or without C substrate (1% wt/wt ground alfalfa) and C2H2 (1.0 kPa) in an He environment. Incomplete reduction of NO3− to N2O and N2 occurred in the absence of both C substrate and C2H2. With C substrate but without C2H2, complete reduction of NO3− to N2 was observed. In the absence of C substrate and in the presence of C2H2, N2O production was higher than in the absence of both C substrate and C2H2 and complete reduction of NO3− to N2O and N2 was observed. With both C substrate and C2H2 added, there was complete conversion of NO3− to N2. A decrease in C2H2 concentration was observed in the absence of C substrate. Production of C2H4 or CO2 did not account for this decrease in C2H2 concentration. When N2O and C2H2 were introduced together into preincubated flasks, N2O concentration showed an initial increase and then a decrease. A decrease in C2H2 concentration was also observed. Again, this decrease was not accounted for by either C2H4 or CO2 production. Increases in the production of N2O and N2 gases and decrease in C2H2 concentration in the absence of C substrate suggested that C2H2 enhanced denitrification. No conclusive data were obtained to suggest that C2H2 acts as a carbon source during denitrification.