Study On Nitrogen Removal From Typical Iron Industrial Wastewater By Combined Technology Of Nitrification And Denitrification

This study proposed a combination technology of heterotrophic denitrificationautotrophic nitrification-sulfur autotrophic denitrification for nitrogen removal of a low concentration nitrogenous wastewater in the steel industry.In this study,the start-up process was finished by simulated wastewater in three groups of reactors.Then,the potential influencing factors of heterotrophic denitrification and autotrophic nitrification were analyzed.The three-stage connection was used to complete the reactor operation.The feasibility of the method was proved.On the basis of stable operation,the degradation kinetics of each reactor matrix was analyzed.In this study,the heterotrophic denitrification reactor was successfully started by activated sludge and denitrifying sludge.During this process,the HRT was maintained at 4 hours,and the removal rate of nitrate was over 80%over 24 days,and the effluent nitrate was maintained at 2 mg/L.This study explored factors that may have an impact on denitrification at different influent concentrations.For the C/N ratio,the removal effect of nitrate increased with the increase of C/N ratio,but under the conditions of medium concentration and high concentration,the excessive C/N ratio shows inhibition of nitrate removal.For HRT,it showed a rapid decrease of the removal rate in the short-term shortening,and can be recovered after long-term operation.For COD type,methanol had the least help for denitrification,and glucose and sodium acetate were similar.For influent ammonia,the inhibition of occurred when influent nitrate concentration was high.During the operation,the reactor load was increased by shortening the HRT,and the maximum influent load of the reactor was achieved.During the reduction of HRT from 4 hours to 2 hours and to 1 hour,the effluent nitrate could recover to below 5 mg/L after a short-term increase.When the HRT was shortened to 0.5 hours,the effluent nitrate was maintained at 9 mg/L.In order to reduce the load of the sulfur autotrophic denitrification section,the HRT was selected to be maintained at 1 hour,and the effluent nitrogen and nitrogen were reduced to less than 5 mg/L.Based on the stable operation,the matrix degradation kinetics model of the denitrification reactor was established.After heterotrophic denitrification,the study successfully started the autotrophic nitrification reactor by inoculating aerobic activated sludge.During this process,the HRT was maintained at 4 hours.After 25 days,the ammonia removal rate was over 90%,and the effluent ammonia nitrogen was maintained at about 1 mg/L.This study also explored factors that may have an impact on nitrification at different influent concentrations.For HRT,the rapid decrease of removal rate was shown in the short-term shortening.It could be recovered under low-concentration and medium-concentration influent conditions after long-term operation.However,the effluent quality was reduced after HRT was reduced to 1 hour under high concentration.Effluent ammonia was maintained at 20 mg/L and could not be recovered.For COD concentration,the ammonia nitrogen removal performance decreased rapidly with the increase of influent COD concentration under three concentrations.For COD type,methanol had the least inhibition of nitrification,while the inhibition of sodium acetate effect was the most serious.For influent nitrate,no inhibition of ammonia removal was observed under the three influent conditions.During the operation,the reactor load was increased by shortening the HRT.The maximum influent load of the reactor was obtained under the premise of ensuring the quality of the effluent.During the reduction of HRT from 4 hours to 2 hours and to 1 hour,the effluent ammonia could recover to less than 1 mg/L after a short-term rise.When the HRT was shortened to 0.5 hours,the effluent ammonia rapidly rose to above 20 mg/L and could not be recovered in a short time.In order to ensure the lowest possible ammonia nitrogen concentration in the effluent,the HRT is adjusted back to 1 hour,and the effluent ammonia was maintained below 1 mg/L.On the basis of stable operation,a matrix degradation kinetics model of autotrophic nitrification reactor was established.After the completion of the nitrification section,the sulfur autotrophic denitrification reactor was successfully started by inoculating the activated sludge onto the surface of sulfur.During this process,HRT was maintained for 4 hours.After 7 days,the removal rate of nitrate increased from 76%to 94%,and the effluent nitrate was maintained at about 1mg/L.During the operation,the reactor load was increased by shortening the HRT,and the maximum influent load of the reactor was achieved.During the reduction of HRT from 4 hours to 2 hours and to 1 hour,the effluent nitrate increased to about 13 mg/L in short term.When HRT was adjusted back to 2 hours,the effluent nitrate was rapidly reduced and maintained at 4 mg/L.For rapid denitrification,the HRT was adjusted back and maintained at 1 hour and the effluent nitrate was maintained below 15 mg/L,ensuring that the total effluent nitrogen is not higher than 20 mg/L.The feasibility of this combination technology was verified after this operation process.Based on the stable operation,the matrix degradation kinetics model of the denitrification reactor was established.