Experimental Study On Treatment Of Sludge Anaerobic Digester Liquor By Two-stage PN/A Biofilter Reactor

The digester liquor produced by anaerobic digestion of sludge has the characteristics of high ammonia nitrogen and low carbon-nitrogen ratio,so its efficient treatment is of great significance to reduce the nitrogen load of municipal sewage treatment plant and enhance its nitrogen removal efficiency.In this study,the simulated sludge digester liquor was treated by two-stage partial nitritation-anammox process.Using the continuous flow biological filter reactor（CBFR）as the experimental device,the start-up and stable operation of partial nitritation were realized in PN-CBFR,and then the efficient nitrogen removal was realized in two anammox reactors.The effects of substrate concentration,nitrogen load and influent substrate ratio on the nitrogen removal performance of ANAMMOX were explored in HL-CAFR,while the inhibition of higher substrate concentration on the nitrogen removal performance of ANAMMOX was explored in HC-CAFR.The main results and conclusions of this paper are as follows:（1）When the ratio of COD to TN was kept at 0.5 and the concentration of NH₄⁺-N increased gradually from 600±10 mg/L to 1000±10 mg/L,the nitrogen loading rate（NLR）was increased from 0.60±0.02 kg N/（m³·d）to 1.0±0.02 kg N/（m³·d）in PN-CBFR.In the stable period,the effluent ratio of NO₂^--N/NH₄⁺-N was kept between1.08 and 1.25,the average nitrite accumulation rate（NAR）reached 96.00%,and the COD removal rate was 89.07%,implying that it could meet the requirements of influent nitrogen matrix for subsequent anammox.（2）The concentrations of free ammonia（FA）and free nitrous acid（FNA）in each operation stage were higher than the inhibition threshold of NOB,so it could effectively inhibit NOB,but did not affect the activity of AOB in PN-CBFR.The results of high throughput sequencing showed that Nitrosomonas was the dominant species of AOB in PN-CBFR,and no NOB-related strains were detected.There were also a variety of denitrifying bacteria and anaerobes in the system,which also played an important role in the nitrogen-carbon cycle.（3）When the influent NH₄⁺-N and NO₂^--N were 250±10 mg/L and 275±10 mg/L,respectively,and HRT was kept only 2 hours,the NLR reached 6.30±0.10 kg N/（m³·d）in the HL-CAFR,and the average TN removal rate in the stable period was 81.76%.The results showed that the anammox bacteria enriched and cultured by biological filter column had strong resistance to the changes of external environment（substrate,load）,and the HL-CAFR system was relatively robust.（4）More than 75%of the nitrogen removal in HL-CAFR occurred in the 0～20 cm section.At the end of the experiment,the determination results of microbial aggregates showed that the biomass,SAA and EPS contents of biofilm and granular sludge in the0～20 cm section were significantly higher than those in the 20～47 cm section,which proved that the 0～20 cm section was the main functional area.The results of high-throughput sequencing showed that unclassified＿Candidatus Brocadiaceae and Candidatus Kuenenia were the main anammox bacteria detected at the genus level,and their relative abundances in biomass of 0～20 cm and 20～47 cm were more than 50%and 40%,respectively.（5）When the influent NH₄⁺-N and NO₂^--N concentrations were both 300±10mg/L,and NLR was 1.80±0.02 kg N/（m³·d）in HC-CAFR,the anammox bacteria were seriously inhibited.The average removal rate of TN was 82.24%after 98 days of biological acclimation when the concentration of TN was kept constant and the ratio of influent NH₄⁺-N:NO₂^--N was 1:1.1.（6）When the average influent FA and FNA concentrations of HC-CAFR were15.98 mg/L and 43.82 ug/L,respectively,the inhibition threshold of FA and FNA on anammox bacteria were exceeded in most literature,but the TN removal rate of the reactor remained above 80%,indicating the strong resistance and adaptability of biofilm and granular sludge to higher substrate concentration.（7）Haldane model can well describe the inhibition kinetics of NH₄⁺-N and NO₂^--N on anammox in HC-CAFR.When NH₄⁺-N was used as inhibitor,the maximum NH₄⁺-N removal rate q_maxwas 29.28 mg N/（g VSS·d）,the ammonia-nitrogen half-saturation constant Ks was 10.79 mg/L,and the inhibition constant K_i was 4408.64 mg/L.When NO₂^--N was used as inhibitor,the maximum NO₂^--N removal rate q_max was 29.00mg N/（g VSS·d）,the nitrite half-saturation constant Ks was 9.54 mg/L,and the inhibition constant K_i was 2350.00 mg/L.