Nitrifying biomass on ring-shaped carriers was modified to nitritating one in a relatively short period of time （37 days） by limiting the air supply, changing the aeration regime, shortening the hydraulic retention ...Nitrifying biomass on ring-shaped carriers was modified to nitritating one in a relatively short period of time （37 days） by limiting the air supply, changing the aeration regime, shortening the hydraulic retention time and increasing free ammonia （FA） concentration in the moving-bed biofilm reactor （MBBR）. The most efficient strategy for the development and maintenance of nitritating biofilm was found to be the inhibition of nitrifying activity by higher FA concentrations （up to 6.5 mg/L） in the process. Reject water from sludge treatment from the Tallinn Wastewater Treatment Plant was used as substrate in the MBBR. The performance of high-surfaced biocarriers taken from the nitritating activity MBBR was further studied in batch tests to investigate nitritation and nitrification kinetics with various FA concentrations and temperatures. The maximum nitrite accumulation ratio （96.6%） expressed as the percentage of NO 2 ？ -N/NOx ？ -N was achieved for FA concentration of 70 mg/L at 36°C. Under the same conditions the specific nitrite oxidation rate achieved was 30 times lower than the specific nitrite formation rate. It was demonstrated that in the biofilm system, inhibition by FA combined with the optimization of the main control parameters is a good strategy to achieve nitritating activity and suppress nitrification.展开更多
Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction(ORR)in alkaline media is important for fuel cell applications.Herein,we report a simple and effectiv...Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction(ORR)in alkaline media is important for fuel cell applications.Herein,we report a simple and effective synthesis of transition-metal-doped zeolitic imidazolate framework-8(ZIF-8)and carbon nanotube(CNT)composite catalysts(ZIF-8@CNT)prepared via high-temperature pyrolysis at 900℃.The catalysts were characterized using different physicochemical techniques and employed as cathode materials in anion exchange membrane fuel cells(AEMFC).The prepared metal-free(ZNT-900),single-metal-doped(Fe-ZNT-900,Co-ZNT-900)and binary-metal-doped(Fe_(1)Co_(1)-ZNT-900,Fe_(1)Co_(2)-ZNT-900)catalysts had a sufficient amount of N-doping with the presence of FeCo moieties in the carbon skeleton of the latter two materials.N_(2) adsorption–desorption isotherms showed that all the prepared catalysts possess a sufficient Brunauer–Emmett–Teller surface area with more micropores present in ZNT-900,while a combined micro–mesoporous structure was obtained for transition-metal-doped catalysts.Binary-metal-doped catalysts showed the highest number of ORR-active sites(pyridinic-N,pyrrolic-N,graphitic-N,M–Nx)and exhibited a half-wave potential(E_(1/2))of 0.846 and 0.847 V vs.RHE for Fe_(1)Co_(1)-ZNT-900 and Fe_(1)Co_(2)-ZNT-900,respectively,which surpassed that of the commercial Pt/C catalyst(E_(1/2)=0.834 V).In H_(2)–O_(2) AEMFCs,the Fe_(1)Co_(2)-ZNT-900 catalyst delivered a maximum power density(P_(max))of 0.171 W cm^(-2) and current density at 0.5 V(j_(0.5))of 0.326 A cm^(-2),which is very close to that of the Pt/C catalyst(P_(max)=0.215 W cm^(-2) and j_(0.5)=0.359 A cm^(-2)).The prepared ZIF-8@CNT catalysts showed remarkable electrocatalytic ORR activity in 0.1 M KOH solution and fuel cell performance comparable to that of the benchmark Pt/C catalyst.展开更多
基金supported by the Estonian Environmental Investment Center Program "Treatment of Nitrogen- rich Wastewaters (SLOTI08262)"a target-financed project of the Estonian Ministry of Education and Research NoSF0180135s08, named "Processes in macro-and microheterogeneous and nanoscale systems and related technological applications"
文摘Nitrifying biomass on ring-shaped carriers was modified to nitritating one in a relatively short period of time （37 days） by limiting the air supply, changing the aeration regime, shortening the hydraulic retention time and increasing free ammonia （FA） concentration in the moving-bed biofilm reactor （MBBR）. The most efficient strategy for the development and maintenance of nitritating biofilm was found to be the inhibition of nitrifying activity by higher FA concentrations （up to 6.5 mg/L） in the process. Reject water from sludge treatment from the Tallinn Wastewater Treatment Plant was used as substrate in the MBBR. The performance of high-surfaced biocarriers taken from the nitritating activity MBBR was further studied in batch tests to investigate nitritation and nitrification kinetics with various FA concentrations and temperatures. The maximum nitrite accumulation ratio （96.6%） expressed as the percentage of NO 2 ？ -N/NOx ？ -N was achieved for FA concentration of 70 mg/L at 36°C. Under the same conditions the specific nitrite oxidation rate achieved was 30 times lower than the specific nitrite formation rate. It was demonstrated that in the biofilm system, inhibition by FA combined with the optimization of the main control parameters is a good strategy to achieve nitritating activity and suppress nitrification.
基金The present work was financially supported by the Estonian Research Council(grants PRG723,PRG4 and PRG1509).
文摘Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction(ORR)in alkaline media is important for fuel cell applications.Herein,we report a simple and effective synthesis of transition-metal-doped zeolitic imidazolate framework-8(ZIF-8)and carbon nanotube(CNT)composite catalysts(ZIF-8@CNT)prepared via high-temperature pyrolysis at 900℃.The catalysts were characterized using different physicochemical techniques and employed as cathode materials in anion exchange membrane fuel cells(AEMFC).The prepared metal-free(ZNT-900),single-metal-doped(Fe-ZNT-900,Co-ZNT-900)and binary-metal-doped(Fe_(1)Co_(1)-ZNT-900,Fe_(1)Co_(2)-ZNT-900)catalysts had a sufficient amount of N-doping with the presence of FeCo moieties in the carbon skeleton of the latter two materials.N_(2) adsorption–desorption isotherms showed that all the prepared catalysts possess a sufficient Brunauer–Emmett–Teller surface area with more micropores present in ZNT-900,while a combined micro–mesoporous structure was obtained for transition-metal-doped catalysts.Binary-metal-doped catalysts showed the highest number of ORR-active sites(pyridinic-N,pyrrolic-N,graphitic-N,M–Nx)and exhibited a half-wave potential(E_(1/2))of 0.846 and 0.847 V vs.RHE for Fe_(1)Co_(1)-ZNT-900 and Fe_(1)Co_(2)-ZNT-900,respectively,which surpassed that of the commercial Pt/C catalyst(E_(1/2)=0.834 V).In H_(2)–O_(2) AEMFCs,the Fe_(1)Co_(2)-ZNT-900 catalyst delivered a maximum power density(P_(max))of 0.171 W cm^(-2) and current density at 0.5 V(j_(0.5))of 0.326 A cm^(-2),which is very close to that of the Pt/C catalyst(P_(max)=0.215 W cm^(-2) and j_(0.5)=0.359 A cm^(-2)).The prepared ZIF-8@CNT catalysts showed remarkable electrocatalytic ORR activity in 0.1 M KOH solution and fuel cell performance comparable to that of the benchmark Pt/C catalyst.
