Study On Two-stage MBBR Partial Nitrification-Anammox Treatment For Thermal Hydrolysis Anaerobic Digester Effluent

The composition of residual sludge in urban sewage treatment plants is complex,which contains a lot of organic matter,bacteria,virus and so on,which must be properly disposed.The thermal hydrolysis process followed by anaerobic digestion（THP-AD）is considered to be one of the most economical and effective technologies for sludge treatment and disposal.However,thermal hydrolysis anaerobic digester effluent was produced during the process of THP-AD which has the characteristics of high ammonia concentrations（500～2000 mg/L）,high COD concentrations（1000～3000 mg/L）,low biodegradable organic matter concentrations and low COD/N.How to treat it efficiently is very important to reduce the nitrogen load and denitrification effect of municipal wastewater treatment plant.This study focused on the two-stage PN/A biofilm（MBBR）process for the treatment of sludge thermal hydrolysis anaerobic digester effluent.AOB and Anammox bacteria were cultured respectively to form a two-stage PN/A process to treat the actual sludge thermal hydrolysis anaerobic digester effluent.The denitrification effect and influencing factors of the two-stage PN/A treatment of the thermal hydrolysis anaerobic digester effluent were studied,and the functional microbial community structure on the biofilm was analyzed.The main conclusions are as follows:（1）Under the dual inhibition of FA and FNA,stable partial nitrification was achieved after 90 days.Nitrite accumulation rate reached 92.64%,the activity of AOB increased to6578.78 mg NH₄⁺-N/（m²·d）,NOB was successfully inhibited,and the ratio of NO₂^--N_eff/NH₄⁺-N_eff was 1.23.The results of high-throughput sequencing and FISH showed that Nitrosomonas,possibly a functional bacterium for the partial nitrification process,was dominant on the genus level after enrichment culture,which verified the successful initiation of the partial nitrification process from the perspective of molecular biology.（2）After 180 days of enrichment culture,Anammox reactor was successfully started up.The nitrogen load of MBBR reached 13875 mg N/（m²·d）,and the total nitrogen removal rate reached 85.44%.The activity of anammox bacteria in the biofilm increased from 231.56 mg NH₄⁺-N/（m²·d）to 6588.12 mg NH₄⁺-N/（m²·d）,and the anammox bacteria with Ca.Brocadia as the dominant bacteria were enriched successfully.（3）The PN and Anammox reactors were coupled and successfully started,and artificial water was replaced with sludge thermal hydrolysis anaerobic digester effluent with a gradient of 30%,65%and 100%respectively.The actual sludge thermal hydrolysis anaerobic digester effluent was treated with a two-stage MBBR nitrification and Anammox process.The biodegradable organics in the influent were mainly removed in the partial nitrite section（accounting for 86%of the total removal rate）,and only a small part of them entered the anaerobic ammonium oxidation reactor（accounting for 14%of the total removal rate）,thus ensuring the stable operation of the anaerobic ammonium oxidation reactor.The total influent load of the PN/A system was 4572.9 mg N/（m²·d）,and the average removal rate of TN was 77.91%.（4）Controlling the concentration of FA in the partial nitrification is the key factor to MBBR two-stage partial nitrification-Anammox process for the treatment of sludge thermal hydrolysis anaerobic digester effluent.Compared with the intermittent influent,the continuous influent method can more effectively control the FA concentration within the appropriate range.When the average concentration of FA is 8.78 mg/L,it is more conducive to the stable operation of the partial nitrification and the ratio of NO₂^--N_eff/NH₄⁺-N_eff can be stabilized in the range of 1～1.3:1,so as to ensure the normal operation of the Anammox reactor.（5）The residual COD in the sludge thermal hydrolysis anaerobic digester effluent led to the massive proliferation of heterotrophic bacteria,which reduced the proportion of AOB and anammox bacteria in the biofilm.Nitrosomonas decreased from 20.09%to7.84%,Brocadia decreased from 11.02%to 4.59%,and the activity of AOB decreased from 6578.78 mg NH₄⁺-N/（m²·d）to 5405.89 mg NH₄⁺-N/（m²·d）,the activity of anammox bacteria decreased from 6588.12 to 3964.77 mg NH₄⁺-N/（m²·d）.