Study On The Effect Of Sponge Iron Dosage,Carbon Source Concentration And Nitrogen Load On Start Up Of Anammox By Biological Iron Sludge

Anammox has a great prospect but its application in practical wastewater treatment is limited by the long start-up time and incomplete nitrogen removal.In view of the problems existing in the practical application of anammox process,scholars have studied some strengthening approaches.Adding appropriate amount of iron,or adding low concentration of organic carbon source or adjusting and setting appropriate nitrogen load have been proved to have strengthening effects on anammox.However,most of the studies on these three methods focus on the successful start-up of anammox reactors,and there is no systematic study on the three strengthening methods in the start-up process of anammox reaction.Moreover,sponge iron as a high-quality iron source and sodium acetate as a high-efficient carbon source are rarely studied in anammox.Therefore,based on the theory that adding iron,adding organic carbon source and regulating nitrogen load can strengthen anammox reaction,the simulated wastewater prepared according to the concentration ratio of typical substrate in anammox reaction:C（NH₄⁺-N）:C（NO₂^--N）=1.32 was used as the target pollutant,and biological iron sludge with strong microbial diversity was used as the inoculated sludge.The anammox reactors with different sponge iron dosage,different organic carbon source concentration（provided by sodium acetate）and different nitrogen load（controlled by water exchange cycle）were started respectively.Through monitoring the nitrogen concentration in the reactor change,pH value,than anaerobic ammonia oxidation activity and anaerobic ammonia oxidation stoichiometric ratio change,and studied the different sponge iron dosing quantity,different concentration of organic carbon source,nitrogen load of anaerobic ammonia oxidation start and the effects of the nitrogen and nitrogen of sponge iron system mechanism has carried on the preliminary study.so as to provide theoretical basis for the rapid start of anammox and enhanced nitrogen removal.The main results are as follows:（1）In the sponge iron dosage experiment,at the initial stage of the reactor,the sponge iron dosage increased the pH of the reactor.The higher the sponge iron dosage,the higher the pH value of the system,which was not conducive to the growth of anammox bacteria,so the one-time sponge iron dosage may not be conducive to the occurrence of anammox reaction.In terms of the start-up time of the reactor,adding 10g/L,30g/L,60g/L and 90g/L sponge iron into the reactor can inhibit the start-up of the reactor,prolong the start-up time of the reactor,and hinder the improvement of the specific anammox activity,and the higher the adding amount,the stronger the inhibition effect.After the reactor was successfully started,the average total nitrogen removal rate of blank control Fe-0 was 81.97%.However,due to the diversity of iron morphology and microorganisms in Fe-1 system,there were other reactions conducive to TN removal,such as iron-type denitrification and iron-ammoxidation,the average total nitrogen removal rate was 87.54%,and the NO₃^--N accumulation was lower than Fe-0.（2）In the experiment of organic carbon source concentration,from the start-up time of the reactor,adding 7.5,15 and 30mg/L sodium acetate into the influent accelerated the start-up of the reactor and shortened the start-up time of the reactor,mainly shortening the stagnation period and activity promotion period,while adding 60mg/L sodium acetate was due to the high concentration of organic carbon source.The heterotrophic denitrification in the system was too strong,which inhibited the occurrence of anammox reaction,prolonged the start-up time of the reactor,and hindered the improvement of specific anammox activity.After the reactor was successfully started,the average total nitrogen removal rate of C-0 was 81.97%,while the average total nitrogen removal rate of C-1,C-2 and C-3 were 85.10%,89.43%and 90.24%,respectively.The improvement of total nitrogen removal rate of C-1 was mainly attributed to the improvement of ammonia nitrogen removal rate and nitrite removal rate.The increase of total nitrogen removal rate of C-2 and C-3 was mainly due to the increase of nitrite removal rate and the decrease of NO₃^--N generation.It can be seen that adding 7.5mg/L,15mg/L and30mg/L sodium acetate into the influent can improve the denitrification effect of the reactor.TheΔNO₃^--N/ΔNH₄⁺-N values were 0.14 and 0.09,respectively,lower than the theoretical value of 0.26 after C-2 and C-3 were successfully started.It can be seen that adding 15 and30mg/L sodium acetate into the water can reduce the NO₃^--N production in the system.（3）In the nitrogen load series experiments,the N-2 operated under high load had more available substrates for anammox reaction,and the 12h water change cycle made the toxic substances（such as hydrogen sulfide.）generated in the early stage of the reactor discharged quickly,weakened the toxic effect on the system,so the cell lysis period and stagnation period were the shortest.However,when the nitrogen load is too high,a large amount of nitrogen can not be released by anammox reaction,forming air bags in the sludge floc or attached to the surface of the sludge floc,resulting in the reduction of sludge density,poor settlement performance,resulting in floating,serious sludge loss,and longer activity promotion period.The N-3 with the lowest nitrogen load has the longest start-up time due to insufficient substrate concentration and excessive hydrogen sulfide produced in the early system which cannot be discharged in time.After the successful start-up of the reactor,the average removal rate of N-1,N-3 and N-2 total nitrogen was 81.97%,85.77%,and only 75.95%,respectively.Sludge floating loss was the main reason why its nitrogen removal efficiency was lower than other reactors.Although the sludge in the system had higher specific anammox activity,however,low sludge concentration leads to poor denitrification effect.Reactor start-up success after N-2nitrate nitrogen generation than anaerobic ammonia oxidation reaction,the theoretical value and low nitrogen load operation of N-3,nitrate nitrogen generation is higher than the anaerobic ammonia oxidation reaction,the theoretical value,high nitrogen load will help ease the system the accumulation of nitrate nitrogen,make system denitrification more thoroughly,low nitrogen load can lead to excessive nitrate nitrogen generation system.