Study On The Effect And Molecular Ecology Mechanism Of Partial Nitrification Denitration Treatment Of Low C/N Wastewater Based On Chemical Control

In view of the current low C/N characteristics of industrial wastewater and domestic sewage,the denitrification efficiency of traditional biological nitrogen removal process is low due to the lack of influent carbon sources,the equipment and instruments can no longer meet the requirements of the current water discharge standards due to their large floor space and long nitrification start-up time.,so it is necessary to explore new biological denitrification processes.The partial nitrification and denitrification process have become one of the main processes for the treatment of low C/N wastewater due to its simple equipment,low cost,low carbon source consumption,little residual sludge and short reaction time.The enrichment of ammonia oxidizing bacteria?AOB?and the elimination of nitrite oxidizing bacteria?NOB?are the key to the short-range nitrification and denitrification process.However,in practical engineering applications,such as the control of temperature,dissolved oxygen,pH and other technological conditions to achieve the enrichment of AOB and the elimination of NOB is more complex,short-range nitrification and denitrification process has not been widely used.The main purpose of this study is to control the partial nitrification and denitrification by chemical inhibitors to achieve rapid start-up and stable operation.The relationship between nitrification and denitrification functional bacteria during the start-up and operation of partial nitrification and denitrification was elucidated by high-throughput sequencing technology,and the molecular ecological machinery of partial nitrification and denitrification was revealed.In addition,the effects of the three inhibitors in the process of starting and resuming the overall operation are systematically compared and analyzed to explore the best types of inhibitors and make scientific explanations for the engineering application of partial nitrification and denitrification process.Firstly,the optimal dosing concentrations of three inhibitors were determined by inhibitor optimization test:NH₂OH?5 mg/L?,KClO₃?0.5 mM/L?and HCOOH?0.5mM/L?,and the reasonable reaction time was determined to be 8h in this study.Adding inhibitors in the inlet section and acclimating the sludge at 50 mg/L ammonia nitrogen concentration can reach more than 50%NAR in about 15 days.After stable operation,the influent ammonia concentration?150 mg/L?was increased,and the three inhibitors ARE all reached more than 98%after 11 days of operation.The NH₂OH-controlled reactor basically completely removed ammonia nitrogen,with NAR reaching 83.5%,and the addition of KClO₃ and HCOOH both achieved about 75%of NAR.The activity of nitrifying bacteria was calculated by nitrogen conversion.Compared with the control group,the AOB activity increased by 52%and the NOB activity decreased by 34.4%when adding NH₂OH.With the addition of KClO₃,the activity of AOB increased by 21.7%and that of NOB decreased by 38.7%.With the addition of HCOOH,AOB activity increased by 14.1%and NOB activity decreased by 32.5%.Through high-throughput sequencing,it was found that adding inhibitors could effectively inhibit NOB?Nitrospira?and make AOB?Nitrosomonas?occupy a competitive advantage.Compared with the control group,the reactors with added inhibitors all achieved different degree of NOB inhibition.The relative abundance of NOB in NH₂OH,KClO₃ and HCOOH reactors decreased by 1.01,1.01 and 1.05 times,and the AOB increased by 19.23,8.5 and 6.54times,respectively.Moreover,different inhibitors have different influences on microbial community composition.Hydrogenophaga,Thermovirga,and Comamonas were detected only in NH₂OH-acting reactors,and all three genera exhibited degraded organic matter and denitrification.KClO₃ can promote the growth of Streptomyces,which can promote the denitrification.Denitrification of Bradyrhizobium Fusibacter and Thauera were detected in the HCOOH reactor.Then,in this study,the partial nitrification process was destroyed by pH impact?pH=6?,and its rapid recovery ability was explored by adding inhibitors.After 11 days of operation,NH₂OH and KCl O₃ had obvious effects on the recovery of partial nitrification.Among them,KClO₃ has high efficiency for the recovery of short-cut nitrification,achieving more than 95.0%of ARE and more than 84%of NAR.Through the calculation and analysis of nitrification bacteria activity,Compared with the control group,the AOB activity increased by 29.6%and the NOB activity decreased by 45.5%in the reactor with KClO₃ added.High-throughput sequencing showed that after recovery with KClO₃,the relative abundance of AOB increased by 10 times and that of NOB by 1.8 times.KClO₃ can effectively realize the competitive advantage of AOB and effectively inhibit NOB.Finally,this study simulated wastewater to start acclimated denitrification sludge.Two chemical reagents,Fe²⁺and KClO₃,were added to explore the rapid start-up mechanism.After removal of more than 20%of TN,the water from the short-cut nitrification section was used as the denitrification inlet to explore the rapid start-up and stability of partial nitrification and denitrification.After 19 days of operation,TN removal rates were 53.57%and 64.26%,respectively,which were both higher than 35.33%in the control group.KClO₃ and Fe²⁺can promote denitrification process by high throughput sequencing.Among them,adding Fe²⁺could promote the growth of denitrifying microorganisms,and the relative abundance of Thauera increased from 5.56% to 40.72%.