Research on the application of the PN/A process in projects of sludge-digestion liquid treatment by thermal hydrolysis
The partial nitrification-anaerobic ammonium oxidation(PN/A)process was successfully launched in a sewage treatment plant in Beijing for the treatment of sludge-digestion liquid treatment by thermal hydrolysis.The optimal operation conditions were proposed based on the project commissioning.Specifically,the PN/A system could be quickly initiated when the proportion of biofilm-inoculated carrier was 18%of the total carrier and the relative abundance of anaerobic ammonium oxidation bacteria(AnAOB)on the biofilm reached 6.8%.The designed water treatment capacity could be achieved within 3months,where the total nitrogen removal load was 0.26kg/(m³·d)and the total nitrogen removal efficiency reached 80%.Quantitative PCR and high-throughput sequencing analysis showed that different spatial distribution characteristics of AOB and AnAOB abundance,and proportions of both ammonia oxidizing bacteria(AOB)and AnAOB increased steadily during the commissioning;and the respective abundance of AOB in flocs and AnAOB on the biofilm reached the magnitude of 1011 and 1012 after 3 months of cultivation.Data from practical operation demonstrated that the sidestream treatment system has a positive impact on the mainstream,where a 2.9 mg/L decrease of the total nitrogen was observed with the influent for a sewage treatment plant of 40×104t/d.At the last running stage of the project,an insufficient supply of free ammonia(FA)was observed in the anoxic zone of the reaction tank,which resulted in the unstable performance of the PN/A system.However,the system could be quickly restored by controlling the FA concentration at the beginning and end of the reaction tank and the remaining ammonia nitrogen concentration.
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