Experimental Study On The Treatment Of Low Nitrogen Wastewater By BFR Centered With Anammox

In order to explore the operation characteristics of anammox biofilter reactor（BFR）in the treatment of low nitrogen wastewater,the partial denitrification-anammox（PD-A）integrated in one reactor and in two-stage biofilter reactors were used to treat the secondary effluent of sewage treatment plant in laboratory scale.In this paper,the impact resistance,nitrogen removal performance,population migration and niche differentiation of anammox bacteria enriched under the gravity flow of laboratory-scale BFR in the treatment of low nitrogen wastewater were discussed.Then,the integrated BFR coupled with PD-A was used to mix the secondary effluent of urban sewage treatment plant with a small amount of raw water.NH₄⁺and COD in the raw water and NO₃^-in the secondary effluent were used to realize the partial denitrification in the integrated BFR to accumulate NO₂^-and use it as the anammox substrate to remove NH₄⁺in the influent to explore the nitrogen removal performance of the integrated BFR at low substrate concentration.Finally,the anammox biofilter（A-BFR section）and the partial denitrification biofilter（PD-BFR section）were started simultaneously to explore the nitrogen removal performance of anammox and the ability of partial denitrification to accumulate nitrite at low nitrogen concentration.This paper could provide data and theoretical support for PD-A process in deep nitrogen removal of sewage.The main results and conclusions of this study are as follows:（1）Under continuous gravity flow,the spontaneous chemotaxis of anammox bacteria in BFR led to the regional distribution of microbial community.The anammox activity and relative abundance of the main functional area were 40.80 mg-N/（g VSS·day）and 38.20%,respectively.The biomass in BFR was distributed according to the gradient of hydraulic process and the biomass of the main functional area accounted for 42.03%of the total biomass of the whole reactor.（2）Due to the synergistic effect of complex biological communities,the redistribution and reconstruction of anaerobic bacteria enhanced the denitrification effect and impact resistance of BFR.Under the conditions of influent TN of 100.36 mg/L,HRT of 3 h and 25℃,the TN removal rate was more than 90%,and the maximum value reached 98.94%.After an idle period of 42 days and 52 days,the nitrogen removal performance of BFR was restored on the 2nd and 4th days,and the TN removal rates were83.84%and 86.52%,respectively.（3）The integrated PDA-BFR can achieve deep denitrification under the conditions of influent TN of 33.43 mg/L,HRT of 1.5 h,25℃,and COD/NO₃^--N of 2.5.The average effluent TN concentration was 9.42 mg/L during stable operation.The highest biomass concentration in the 75-100 cm section of the reactor reached 16.11 g/L,and sufficient biomass maintenance was critical to the denitrification performance of the integrated PD-A-BFR system.In addition,the EPS and three-dimensional fluorescence results of biomass showed that microorganisms produced more proteins at low nitrogen concentrations.All biofilm TB-EPS contained protein-like substances.The production of protein-like substances was conducive to the formation of biofilms,which could protect microorganisms and improve nitrogen removal efficiency.（4）In the two-stage PD-A biofilter reactor,A-BFR can achieve efficient removal of low nitrogen concentration under the conditions of 25℃,influent 15 mg/L NH₄⁺-N and15 mg/L NO₂^--N,respectively.The average total nitrogen removal rate reached 83.74%.The long-term and batch experiments of PD-BFR showed that pH was an important factor affecting the PD process.Nitrite could be accumulated to the maximum at pH 8.7,but the denitrification process in BFR was severely inhibited due to the low substrate concentration,which eventually led to the difficulty to accumulate nitrite for the substrate supply of A-BFR section.