| Nitrogen pollution exists widely in various water bodies,and is one of the main causes of water eutrophication,which has a great impact on water ecology and human health.Biological method is the most widely used nitrogen removal method at this stage.Among them,heterotrophic nitrification-aerobic denitrification bacteria can complete the nitrification and denitrification processes in the same reactor to achieve high-efficiency decarbonization and nitrogen removal,providing a new idea for biological denitrification.In this study,aiming to achieve deep denitrification of high NH4+-N wastewater,the HN-AD strain Acinetobacter sp.Z1 was isolated and screened from the digestive juice of pig farms,and its molecular identification and morphological characterization were carried out,the results showed that the bacteria had high nitrogen removal performance;The optimal conditions for growth and denitrification of strain Z1 were investigated by single-factor experiment and response surface method;the ammoniation,heterotrophic nitrification and aerobic denitrification capacity of Z1 were investigated when single nitrogen source and mixed nitrogen source were used as nutrient substrates;In addition,the aerobic-anaerobic baffled bioreactor（AOBR）was bioenhanced with Z1 as exogenous bacteria,and evaluated its purification effect on actual high ammonia nitrogen wastewater,in order to provide some theoretical guidance for future engineering applications.The specific contents and conclusions of this study are as follows:（1）Identification of strain Z1.A strain of heterotrophic nitrification-aerobic denitrification bacteria was isolated and purified from the digestive juices of pig farms by selective medium,and its morphological observation and molecular identification were carried out.The colony morphology was dumbbell-shaped and milky white,which was gram-negative bacteria.The 16S r RNA sequences were aligned by BLAST and the MEGA software was used to construct a phylogenetic tree,the results showed that the similarity between this strain and Acinetobacter sp.was over 99%,and it was identified as belonging to the genus Acinetobacter sp.and named as Acinetobacter sp.Z1.（2）Physiological factor optimization.Through single factor experiments,the effects of different carbon sources,initial NH4+-N concentration,C/N,p H,temperature,salinity and dissolved oxygen on the growth and denitrification of Z1 were investigated.The results showed that the optimal conditions for denitrification of strain Z1 were as follows:the carbon source is sodium acetate,the initial NH4+-N concentration is less than 300 mg/L,C/N=12,p H is about 8.0,temperature is 30 oC,salinity is 0 and DO is about 5.41 mg/L,under these conditions,strain Z1 can reduce NH4+-N with an initial concentration of 150.12 mg/L and NO3--N with an initial concentration of 155.50 mg/L to 3.07 mg/L and 5.14 mg/L,respectively,and the removal rates of NH4+-N and NO3--N reached 97.95%and 96.69%,respectively.At the same time,the response surface method was further used to optimize the influencing factors（shaking speed,C/N,initial p H and salinity）in the heterotrophic nitrification process of strain Z1,the Box-Behnken design experiment was used to analyze the effects of each variable and its interaction on the removal of NH4+-N by Z1.The optimal value after RSM analysis was optimized:0%Na Cl concentration,p H=7.95,shaking speed of 160.93 rpm and C/N=12.06,the removal rate of NH4+-N was 92.37%.（3）HN-AD ability evaluation.Strain Z1 can utilize various forms of nitrogen sources to complete the process of heterotrophic nitrification-aerobic denitrification.When（NH4）2SO4 was used as the sole nitrogen source for 36 h,the content of NH4+-N decreased from 135 mg/L to 2.75 mg/L,and the removal rate reached 97.8%;When Na NO2 or KNO3 were used as the only nitrogen source to investigate the aerobic denitrification performance of strain Z1,the average removal rates of nitrite and nitrate were 95.3%and 86.8%,respectively,and the average degradation rates of organic carbon source were 82.4%and 86.8%,respectively;When using（NH4）2SO4 and KNO3as mixed nitrogen sources to investigate its HN-AD performance,the strain preferentially utilizes NH4+-N,and the removal rates of NH4+-N and NO3--N in the whole reaction process reach 97.8%and 94.3%,respectively,the average removal rates were 1.88 and 1.92 mg·L-1·h-1,respectively,and the removal rate of COD also reached86.2%;Besides,in addition to the above typical inorganic nitrogen sources,this study also used organic nitrogen CO（NH2）2-N as the only nitrogen source of strain Z1.After36 h,urea nitrogen was removed by 98.2%,and the average removal rate was as high as 4.02 mg·L-1·h-1.Compared with inorganic nitrogen sources,CO（NH2）2-N is more likely to be the preferential substrate for Z1.No matter which nitrogen source was used as the substrate,the presence of NH2OH and the accumulation of nitrite were not detected in the whole reaction process.At the same time,N2 accounted for 64.70%of the final product of nitrogen conversion in Z1,and only 27.56%of the initial nitrogen source was converted into intracellular nitrogen,indicating that Z1 can be well used in the treatment of actual wastewater treatment.（4）Bioaugmentation of AOBR by strain Z1.Under the optimal operating parameters,the removal rates of COD,NH4+-N and TN of the actual swine wastewater after the AOBR was stable were 52.86%,54.70%and 52.20%,respectively.After adding exogenous HN-AD bacteria Z1 in the aerobic chamber,the treatment efficiency of effluent COD,NH4+-N and TN increased to 65.75%,68.11%and 63.04%,respectively,which were 12.89%,13.41%and 10.84%higher than the unstrengthened reactor.The results of community structure change and functional annotation showed that there were a large number of microorganisms and functional genes related to nitrogen removal in the four chambers of the AOBR,and the nitrogen metabolism pathway map confirmed that there were abundant nitrogen metabolism pathways in different chambers of the reactor.In this experiment,HN-AD bacteria were screened from swine wastewater and their growth characteristics and nitrogen removal performance were studied,then,it was combined as a bio-enhancement method with AOBR for wastewater treatment,aiming to provide some technical reference for the engineering application of HN-AD bacteria. |
