Experimental Study On Treatment Of Medium And Low Concentration Ammonia Nitrogen Wastewater By One-Stage Sequencing Batch PN-A Process

In recent years,one-stage short-cut nitrification-anaerobic ammonia oxidation process has attracted wide attention from scholars at home and abroad because of its high efficiency and low consumption.This process has been successfully applied to the treatment of wastewater with high ammonia nitrogen concentration,but the treatment of medium and low concentration wastewater mostly stays in the laboratory or pilot-scale stage,and there are few reports on practical engineering application.Further research is needed to realize the wide application of short-cut nitrification-anaerobic ammonia oxidation process with medium and low ammonia nitrogen concentration.In this experiment,Sequencing Batch Reactor was used to culture the coupled sludge,and anaerobic ammonium oxidation granular sludge with high efficiency was inoculated in the reactor with medium and low concentration short-cut nitrification to form AOB and Anammox bacteria coupling system,which maintained the stability of the system.According to the operation mode of complete nitrification-high load short-cut nitrification-medium and low load short-cut nitrification-one-stage short-cut nitrification-anaerobic ammonium oxidation start-up,one-stage short-cut nitrification can be started quickly and run stably for 90 days.The main conclusions are as follows:(1)At the start-up stage of nitrification reactor,2.5 L suspended plastic filler was added.After 7 days of operation,the nitrification reaction was successfully started.The influent NH4+-N concentration was 100 mg/L,the temperature was 30～32℃,and the HRT was kept at 6 h.The ammonia nitrogen removal effect was better,and the removal rate of NH4+-N quickly increased to 99%,and the ammonia nitrogen removal load was 0.2 kgN/(m3·d).The effluent NO3--N concentration is between 20～30 mg/L,and the nitrite accumulation rate is low,which indicates that NOB in the reactor still has high activity.It is necessary to continue to inhibit the growth of NOB in the subsequent operation process,so as to facilitate the realization of the coupling reaction of short-cut nitrification and anaerobic ammonia oxidation.At this stage,the dissolved oxygen concentration is higher,resulting in higher NOB activity in the reactor.In the follow-up experiment,the consumption rate of dissolved oxygen will be increased by increasing the load of influent ammonia nitrogen.Under the same oxygenation capacity,the concentration of dissolved oxygen can be reduced and the inhibition of NOB can be improved.(2)After the nitrification reactor was successfully started,the HRT of the reactor was kept unchanged,and the ammonia nitrogen concentration in the influent increased in gradient.At the start-up stage of high-concentration short-cut nitrification reactor,the short-cut nitrification rate was 77.31%and the ammonia nitrogen removal rate was stable at about 90%under the condition of influent ammonia nitrogen load of 1.9 kgN/(m3·d).Most of the sludge is flocculent,the flocculent sludge is less granular,the sludge particles are smaller,and the flocculent sludge is highly irregular,and it is dark brown.The size distribution of sludge has no obvious regularity,ranging from sludge flocs with the smallest size of 0.35～1.5 μm to microbial aggregates with the largest size of about 250 μm.However,the influent ammonia nitrogen concentration is high(952.87 mg/L),and the dissolved oxygen concentration is also high,which can not meet the start-up of sh ort-cut nitrification-anaerobic ammonia oxidation reactor under the condition of medium and low concentration.It is necessary to realize short-cut nitrification and further reduce dissolved oxygen concentration under the condition of medium and low concentration,so as to meet the need of start-up of short-cut nitrification-anaerobic ammonia oxidation coupling reactor.(3)At the start-up stage of the medium-low concentration short-cut nitrification reactor,0.5 L floc sludge with high concentration short-cut nitrification was inoculated from the nitrification reactor,and 700mL suspended plastic filler was added.After 60 days’ operation,the short-cut nitrification was carried out under the condition that the influent NH4+-N concentration was at least 112.01 mg/L,and the short-cut nitrification rate was 79.78%,and the influent ammonia nitrogen load was 224.02 gN/(m3·d).Under the condition of dissolved oxygen concentration of 0.8 mg/L,ammonia nitrogen removal load of about 0.45 kgN/(m3·d)can still be realized.The activity of AOB increased to 1.643 kgN/(m3·dMLVSS),while the activity of NOB remained stable at 0.0712 kgN/(m3·dMLVSS)～0.0833 kgN/(m3·dMLVSS).The activity of AOB is far greater than that of NOB,and the activity of NOB bacteria is inhibited.The reactor already has the conditions to start a one-stage short-cut nitrification-anaerobic ammonia oxidation coupling reactor at medium and low concentration.The MLSS,MLVSS,MLVSS/MLSS are 1.31 g/L,0.59 g/L and 0.45 at the initial stage of start-up and 1.33 g/L,0.71 g/L and 0.53 at the end of operation.(4)In the start-up and operation stage of the coupling reactor of short-cut nitrification and anaerobic ammonia oxidation with medium and low concentration,0.2 L anaerobic ammonia oxidation granular sludge was inoculated in the short-cut nitrification reactor at the initial stage of start-up,and the ammonia nitrogen removal rate fluctuated greatly,which may be due to the change of the culture environment of inoculated sludge,and the short-cut nitrification reaction was severely inhibited under the conditions of low dissolved oxygen and low influent substrate concentration,and the activities of AOB and AnAOB could not be fully utilized.After increasing the dissolved oxygen in the coupled reactor,the activity of nitrifying bacteria recovered rapidly.After 110 days of operation,the short-cut nitrification-anaerobic ammonia oxidation was carried out under the condition of influent concentration of about 100 mg/L and HRT of 8 h,and the influent ammonia nitrogen load was 120～160 gN/(m3·d),which realized the short-cut nitrification-anaerobic ammonia oxidation under the condition of medium and low concentration.With the continuous reduction of dissolved oxygen concentration,the ammonia nitrogen removal rate of about 93%can still be achieved under the condition of dissolved oxygen concentration of 0.22 mg/L,and the TN removal rate slowly increases to about 80%,with the synergistic effect of short-cut nitrification and anaerobic ammonia oxidation;The activities of AOB,NOB,DNB and AnAOB were 1.216 kgN/(m3·dMLVSS),0.0714 kgN/(m3·dMLVSS),0.0756 kgN/(m3·dMLVSS)and 0.4032 kgN/(m3·dMLVSS),respectively,and AnAOB showed activity only under anoxic condition,but not under aerobic condition.The reactor successfully realized the start-up of short-cut nitrification-anaerobic ammonia oxidation coupling reactor under the condition of medium and low concentration.At the initial start-up stage of the coupled reactor,MLSS was 1.33 g/L,MLVSS was 0.71 g/L,MLVSS/MLSS was 0.53,and the final sludge concentration in the reactor was 2.09 g/L,MLVSS was 1.51 g/L,MLVSS/MLSS was 0.72,so the biomass in the reactor increased.