Study On Purification Of Low Temperature River Water By Nitrogen Removal Functional Psychrotrophs

Surface water pollution has been a serious problem for a long time in China,biological treatment is commonly used for river water remediation.However,purification efficiency would decrease in cold seasons because of the slow microbial metabolism and low enzyme activity at a low temperature.Therefore,this paper enriched and screened the indigenous psychrotrophs in the river,obtained the nitrogen removal functional psychrotrophs,and explored its enhancement methods to further improve the nitrogen removal performance of the bacteria at low temperatures,then carried out a pilot test to prove its engineering application possibility.In this study,the nitrification and denitrification medium was used alternately to screen and domesticate the nitrogen removal functional psychrotrophs from low-temperature river water.In the enrichment medium and simulated river water medium,the psychrotrophs can effectively remove nitrogen at 8℃both.The results of high-throughput sequencing showed that the typical denitrification phylum（Proteobacteria,Firmicutes and Bacteroidetes）accounted for 95.93%of the domesticated psychrotrophs.The nitrogen removal efficiencies,microorganism community activity and community density of the psychrotrophs under low temperature were evidently better than that of the ordinary temperature nitrogen removal functional microorganisms.Adding zero-valent sponge iron,bio-energizer and immobilizing the nitrogen removal functional psychrotrophs could enhance the purification effect of COD_Crand nitrogen by the psychrotrophs at low temperatures.Under the aerobic condition of8℃,the three strengthening methods could remove 51.48%,47.16%and 59.06%of COD_Cr;62.32%,59.81%and 78.07%of NH₄⁺-N;18.20%,12.84%and 20.74%of NO₃^--N;then 43.57%,41.80%and 55.96%of TN,respectively.Among the three strengthening methods,the immobilization of microorganisms can obviously improve the denitrification performance of psychrotrophs.The activity of microbial community on the biochar carrier and the zeolite carrier was not much different,the community composition on the two carriers were also not significantly different,but the TN removal efficiencies of immobilized microorganisms prepared by zeolite carrier is slightly higher than that of biochar carrier.Results of the pilot experiments showed,the three methods which were in-situ immobilized microorganisms,pre-immobilized microorganisms with low-temperature acclimation and pre-immobilized microorganisms coupled with bio-energizer could effectively improve the purification of river water under natural low temperature conditions of 10～16℃.At stationary condition,the removal efficiencies of COD,NH₄⁺-N,NO₃^--N and TN increased from 21.3%,37.2%,8.5%and 6.9%to72.3%～77.9%,48.6%～62.7%,35.3%～42.3%and 26.2%～31.9%,respectively.COD removal under 2～3 cm/s flow rates was obviously better than that under static conditions,and the removal efficiency of TN at 2 cm/s flow rate was the highest.