Research On Highly-efficient Partial Denitrification Coupling With Anammox

The partial denitrification-anammox process is one of the hot topics in the field of wastewater biological nitrogen removal with great engineering application prospects.The main objective of this paper is to obtain the optimum sludge source for fast start-up and maintaince of partial denitrification under low temperature,and then to study the feasibility of hydroxylamine（NH₂OH）to enhance the partial denitrification activity and nitrite accumulation performance.Finally,through the comparison of NH₂OH dosing to realize the rapid start-up of single-stage partial denitrification-anammox system.Single-stage partial denitrification-anammox has achieved the high efficiency and stable simultaneous removal of ammonia and nitrate,which provided a new idea for its effective treatment of municipal wastewater and industrial nitrate wastewater.Specific results are as follows:1.Rapid start-up and efficient and stable operation of partial denitrification（NO₃^--N→NO₂^--N）reactor provided flexible NO₂^--N substrate for anammox reaction,which was an important prerequisite for simultaneous NH₄⁺-N and NO₃^--N treatment of actual wastewater.To explore the feasibility of rapid start-up of partial denitrification and stable accumulation of NO₂^--N in different waste sludge sources,three identical SBR reactors（S1,S2 and S3）were inoculated respectively:sludge discharging from laboratory municipal wastewater denitrifying phosphorus removal system,surplus sludge from municipal wastewater treatment plant,and river sediment sludge.The characteristics of partial denitrification start-up and NO₂^--N accumulation were compared,and the partial denitrification activity of the system or NO₃^--N→NO₂^--N transformation performance were investigated,analyzing the characteristics of the functional bacteria genera of the reactor from the perspective of microbiology.Results indicated that all three SBR partial denitrification reactors could be launched successfully in 6～9 d with sodium acetate as the sole carbon source,high p H（9.0±0.1）and COD/NO₃^--N ratio（3.0～3.5）.The average NO₃^--N→NO₂^--N transformation ratio of the system was S1>S2>S3（75.92%>73.36%>69.90%）.At the same time,it was found that S1and S2 had different degree of partial denitrification performance deterioration trend under continuous low temperature（14.8℃）,but S3 could maintain good NO₂^--N accumulation performance.High throughput sequencing showed that Proteobacteria and Bacteroidetes were dominant in partial denitrification system,and the abundance of Thauera was significantly different in the three PD reactors:S3>S1>S2（25.09%>4.71%>3.60%）,indicating that S3 had stable and efficient NO₂^--N accumulation performance and high abundance Thauera might play a significant role in maintaining low temperature partial denitrification activity.2.The partial denitrification sludge of S3 reactor obtained in the first part of the study was taken as the research object.However,the sludge was stored in 4℃refrigerator for 6months.After the recovery of operation,it was found that the biological activity and nitrite accumulation performance were low.Therefore,the effect of NH₂OH addition on the performance recovery of partial denitrification sludge was investigated.Hydroxylamine（NH₂OH）can significantly promote reaction rate and enhance biomass activity of anammox as an important intermediate metabolite.However,comprehensive insights into nitrite（NO₂^--N）production performance response of partial denitrification（PD）sludge to NH₂OH addition still be lacking,which is considered to be extremely vital for the coupled PD and anammox system.This experiment was the first time to elucidate the changes of NO₂^--N accumulation performance of partial denitrification sludge under the condition of initial0～50 mg/L NH₂OH.Results indicated that NH₂OH addition was demonstrated as a feasible strategy for enhancing NO₂^--N accumulation of PD biomass,facilitating the maximum increase of NO₃^--N to NO₂^--N transformation ratio（NTR）to 80.47±2.82%,leading to the 2.56 times NO₂^--N than those of control group.And the momentary inhibitory effect on NO₃^--N reduction process attributed by high-level NH₂OH concentration（35～50 mg/L）was also observed.These investigations were further identified by enzymatic assays,in which the activity of NO₃^--N reductase was largely improved while NO₂^--N reductase was partially inhibited under low-dose of NH₂OH,whereas both of them were reduced when high NH₂OH present.Further,results of q PCR revealed the evident upregulated functional genes membrane-bound nitrate reductase（nar G）,which was mainly related to NO₃^--N→NO₂^--N denitrification reduction process.Besides,NH₂OH addition contributed to the increasing secretion of extracellular polymeric substances（EPS）content also proteins（PN）/polysaccharides（PS）ratios in EPS,implying the potential involvement of maintaining the stability of PD aggregates.3.DEnitrifying AMmonium OXidation（DEAMOX）process integrated partial denitrification（PD）and anammox in a single-tank has attracted extensive attention as a promising alternative in wastewater biological treatment.However,the major potential issues for unimplemented DEAMOX system were overlong start-up and unstable operation when suffered the load shock and ambient temperature.Therefore,referring to the optimal NH₂OH concentration（10 mg/L）obtained in the second part,the effects of hydroxylamine（NH₂OH）addition（HA）and bioaugmentation（BA）strategies on the room temperature start-up and stability of the system were investigated in two mainstream DEAMOX sequencing batch reactors（SBR,R1 and R2）.Results suggested that,during 340 days operation,R2 received 10 mg/L HA and 1:25（anammox/PD,v/v）BA ratio could achieve desirable nitrogen removal efficiency（NRE）of97.22%within 145 days.Which was compared to R1 under higher BA ratio of 1:12.5 but without HA obtained a little lower NRE（90.86%）after 184 days of operation.The anammox contributed a significant proportion to nitrogen removal in both SBRs.Additional batch trials revealed that HA contributed to efficient PD with nitrate（NO₃^--N）-nitrite（NO₂^--N）transformation ratio（NTR）reached 98.64%at C/NO₃^--N ratio of 2.6 in R2,while R1 related to lower NTR（94.2%）required C/NO₃^--N ratio of 3.0.Notably,the performance restored quickly in R1 with a low effluent total nitrogen of 4.21 mg/L despite nitrogen loading rate greater than 0.15 kg N/m³/d and temperature decreased to 14.6℃,which was mostly ascribed to the activation of anammox consortia by NH₂OH addition.Quantitative microbial analysis revealed that abundant NO₃^--N reductase（nar G）supported a high NO₃^--N reduction rate and functional genes hzs A and hdh were extensively detected as the representative of high anammox activity.Heterotrophic denitrifying bacteria Thauera,Denitratisoma,and unclassified f Comamonadaceae dominated NO₂^--N accumulation.Candidatus Brocadia as the dominant anammox specie,and its relative abundance maintained stable during DEAMOX overlong term operation process.