| Recently,as the large-scale pig farms of China develop rapidly,the anaerobic digested swine wastewater with low COD/TN(C/N<5)ratio brings increasingly prominent pollution to the environment.Thus,the Ministry of Environmental Protection revised the "livestock and poultry breeding industry pollutant discharge standards"(GB 18596-2001),and the second exposure draft of this standard with more stringent pollutant emission limits was isssued,including COD,NH4+-N,TP,TN,heavy metals and other indicators.In other words,the more stringent standard is another challenge to the original swine wastewater treatment process,in which has the disadvantages of low nitrogen removal rates,high investment and operating cost and poor stability.In order to overcome these inadequacies,an integrated technology(SF AO4)was established for the treatment of the effluent from anaerobic digestion with low C/N ratio,which constituted an influent step feeding unit,a pre-denitrification unit,four micro-aeration anoxic units,a clarifier.Then,the capacity of carbon and nitrogen removal efficiency of this whole process would be assessed.At the same time,the hydraulic retention time(HRT)of SFAO~4 were optimized to improve the efficiency and the stability of nitrogen and carbon removal.In the end,the mechanism of biological denitrification was preliminarily analyzed by means of fluorescence quantitative polymerase chain reaction(PCR).The obtained results can provide technical guidance for the standard revamp and pollution control of large-scale pig farms wastewater treatment technology.The main results of this thesis are summarized as follows:(1)In the SFAO~4 system,partial nitrification and simultaneous nitrification-denitrification can be steadily achieved when DO of micro aeration units were controlled under 0.5 mg/L.Based on the balance of carbon sources and alkalinity,the average C/N ratio of inlet water was greater than 5 in the SFAO~4 system,which led to 94%,96%and 90%removal efficiency of COD,ammonia and TN respectively,and the effluent average COD,NH4+-N and TN concentration were 270 mg/L,30 mg/L and 85 mg/L respectively.The SFAO~4 system enhanced nitrogen characterized by a third micro aeration feeding for swine wastewater rich in organic carbon source,which benefit to denitrification,but it had no significant effect on carbon removal by step-feeding.(2)During 4.5 d HRT,the efficiencies of simultaneous nitrogen and carbon removal were the highest in the SFAO~4 process,and the average removal rate of ammonia,TN and COD were 0.152 kg/(m3·d),0.154 kg/(m3·d)and 1.25 kg/(m3·d)respectively.The removal rate of ammonia,TN and COD were significantly decreasing with declined HRT,the lowest average removal rate of ammonia,TN and COD could be achieved in 4.0 d HRT.For 5.0 d,4.5 d and 4.0 d HRT,the ammonia and TN concentration of the effluent could both meet the second exposure draft of"discharge standard of pollutants for livestock and poultry breeding" in the SFAO~4 process.(3)In the SFAO~4 system,the results of quantitative PCR suggested that the mechanism of microbial denitrification was simultaneous nitrification and denitrification,meanwhile,the anaerobic ammonium oxidation(Anammox)could be also found in the SFAO~4 system,yet with the lowest abundance.The order of the abundance of biological removal of nitrogen was nirS>AOB amoA>nirK>nxrB>hzo>AOA amoA,The nirS played a key role in the removal of nitrogen,and the abundance of ammonia oxidizing bacteria amoA(AOB amoA)was much higher than the abundance of nitrite oxidizing bacteria nxrB(NOB nxrB).In a word,the performance of nitrification and denitrification could be improved in the SFAO~4 system because of enriching the Anammox,AOB,NOB and denitrifier simultaneously by step-feeding.When HRT was 4.5 d,the ratio of nirS/AOB amoA copies of SFAO~4 reactor was the highest,reaching 108.9,so that the denitrification rate was higher than that of nitrification rate,which showed the best denitrification efficiency. |
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