Enhanced Short-cut Denitrification By Fe^?0?-activated Carbon And Its Influencing Factors

A lab-scale SBR inoculated with normal activated sludge and fed with synthetic wastewater was examined for the denitrification using nitrite as electron acceptor system startup.Fe^?0?-activated carbon was used to enhance nitrogen removal in the absence of organic carbon,and the influence of the Fe/C mass ratio and initial pH value on the nitrogen removal efficiency and N₂O emission during denitrification were explored.The results obtained were as follows:?1?A lab-scale SBR with activated sludge was used,by increasing the influent nitrite concentration of the SBR(from 30 mg·L^-1 to 180 mg·L^-1),the effluent nitrite concentration was near 0 mg·L^-1,the denitrification rate of 99% in SBR.Thus nitrite denitrifition of nitrite wastewater was successfully induced.By scanning electron microscopy,the change of sludge form: the inoculated sludge appear wadding,complex structures and plenty of microorganisms.After the startup,sludge was comprised of dominant bacteria.?2?The feasibility of using Fe^?0?-activated carbon to enhance biological shortcut denitrification was studied under the condition of inorganic and low carbon nitrogen ratio?C/N=1:1?.Results showed that:In an inorganic environment,the nitrite removal efficiency increased from 7.4% to 31.1% when the Fe^?0?-activated carbon was used to enhance short-cut denitrification.Compared with the addition of Fe^?0?,the ammonia nitrogen produced in the process of metal corrosion is reduced.Under low carbon nitrogen ratio,The addition of Fe^?0?-activated carbon increased the removal rate of nitrite with only adding denitrifying sludge from 45.6% to 76.5%.Therefore,the Fe^?0?-activated carbon can be used to enhance the short-cut denitrification and improve the nitrogenremoval efficiency.?3?The results of batch experiments showed that the ratio of Fe/C could affect the denitrification rate and N₂O release in both inorganic and low carbon nitrogen ratio?C/N=1:1?.In the inorganic,When the Fe/C mass ratio was reduced from 1:1 to 2:1and 1:2,the denitrification rate and nitrite removal efficiency first increased and then decreased.When the iron carbon ratio was 1:1,denitrification rate and nitrite removal efficiency reached the maximum of 5.58 mg??g?h?^-1 and 41.1%,and 0.1 mg of nitrous oxide was emitted.Under the low carbon nitrogen ratio,When the Fe/C mass ratio was reduced from 1:1 to 2:1 and 1:2,the denitrification rate and nitrite removal efficiency first increased and then decreased.When the iron carbon ratio was 1:1,denitrification rate and nitrite removal efficiency reached the maximum of 4.11 mg??g?h?^-1 and 47.1%.?4?The results of batch experiments showed that the pH could affect the denitrification rate and N₂O release in both inorganic and low carbon nitrogen ratio?C/N=1:1?.In the inorganic,When the pH value was increased from 6 to 9,the denitrification rate decreased from 7.39 to 5.96 mg??g?h?^-1,and the nitrous oxide emission decreased from 0.19 to 0.12 mg.Under the low carbon nitrogen ratio,When the pH value was increased from 6 to 9,denitrification rate and nitrite removal rate increased first and then decreased.Fe^?0?-activated carbon-activated sludge system denitrification rate and nitrite nitrogen removal rate at pH value was 7.5 reached the maximum was 4.64 mg??g?h?^-1 and 50.0%,and the pH value has little effect on N₂O release.?5?The effect of inorganic ions on the nitrogen removal efficiency and ammonia nitrogen content of the composite system was studied.The results showed that: The nitrogen removal rate increased with the increase of the concentration of ferrous ions in the composite system.When the concentration of ferrous ions was 150 mg?L^-1,nitrite removal rate was 59.3%,ammonia generation rate is 13.8%.The nitrogen removal efficiency decreased with the increase of the concentration of sulfate ion,and the ammonia nitrogen production rate decreased.When the concentration of sulfate ion is90 mg?L^-1,the nitrite removal rate was 14.1%,ammonia generation rate is 1.4%.When the increase of the concentration of ammonium ion,the nitrite removal rate of the composite system decreased,and the ammonia nitrogen production rate decreased.When the ammonium ion concentration of 150 mg?L^-1,the nitrite removal rate was37.7%,ammonia generation rate is 1.1%.