Study On The Mechanism Of Characteristic Water Quality Factors Affecting Ammonia Removal By Strain HITLi 7~T At Low Temperature

In most northern China,winter source water has the characteristics of low water temperature and long duration.The research team screened and obtained a low-temperature heterotrophic nitrifying bacterium HITLi 7^T,which can effectively remove ammonia at 2?.The Bio-enhanced Activated Carbon(BEAC)process based on the low-temperature-resistant heterotrophic nitrifying bacteria HITLi 7^Thas been applied to treat actual low-temperature groundwater and surface water,the treatment effect is significantly different.Results found that ammonia removal rate for groundwater was better than that of surface water.Except for temperature effects,both groundwater and surface water lack bioavailable organic carbon,but groundwater is rich in trace elements such as iron and manganese.According to different water sources and water quality,the study of the influence mechanism of organic carbon and trace elements on the removal of low-temperature ammonia by HITLi 7^T,will provide theoretical basis and technical support for the application of BEAC constructed by heterotrophic nitrifying bacteria.Based on the potential of heterotrophic nitrifying bacteria HITLi 7^Tto remove ammonia in low-temperature water,this work systematically studied the mechanism of the growth and ammonia removal by strain HITLi 7^Tat low temperature from the perspectives of ammonia conversion,transcriptome and cold shock protein.The results showed that the strain HITLi 7^Tcould still maintain 72.3%of the utilization rate of NH₄⁺-N of room temperature(20?)at low temperatures(2?),and HITLi 7^Tcould maintain high ammonia metabolic activity at low temperature through some regulatory mechanisms.Element balance analysis found that strain HITLi 7^Thad enhanced dissimilation of carbon and nitrogen sources at low temperature,and the activity of enzymes involved in heterotrophic nitrification and aerobic denitrification was also higher,indicating that strain HITLi 7^Timproved the dissimilation metabolism of nutrients to produce more energy and maintain cell growth and metabolism to adapt to the low temperature condition.Analysis of transcriptome characteristics found that the low temperature adaptation process of strain HITLi 7^Tis complex,involving almost every process of the cell,but mainly by basic metabolic regulation.A large number of genes related to carbohydrate and amino acid metabolism were up-regulated at low temperature,indicating that the basic metabolic activity of HITLi 7^Tat low temperature increased,providing sufficient substrate and energy for rapid growth at low temperature.For the cold shock protein gene of strain HITLi 7^T,the cold shock protein(WP?039620147)encoded by(SE27?RS01265)was analyzed.Results found that the expression level of the protein at 5?15? was significantly higher than that at 25?,indicating that the protein is a cold-adapted protein.Based on this,it could be speculated that when the temperature decreased,strain HITLi 7^Tcould adapt to the low temperature condition by increasing the expression of cold shock protein.In order to analyze the influence of trace elements in groundwater on the removal of ammonia by strain HITLi 7^T,the biomass,DHA activity,extracellular secretions(EPS)amount and composition of strain HITLi 7^Tunder different trace element conditions were analyzed,and results found that iron and manganese can significantly promote ammonia removal by HITLi 7^T.0.12 mg/L Fe and 0.1 mg/L Mn increase the biomass and DHA activity of the strain HITLi 7^Tby about 5 times and 2 times,respectively;iron and manganese can promote the secretion of amino acid extracellular polymer by HITLi 7^T,increases the amount of C=O,C-OH,COC and COOH related to PS and PN,and improve the removal of ammonia through chemical adsorption and biotransformation;BEAC formed in the presence of iron and manganese at 2?,the average removal rate of ammonia can be increased by 1.25 times.In view of the close relationship between the organic carbon and the low temperature adaptation of strain HITLi 7^T,this study focused on organic carbon metabolism characteristics of the strain HITLi 7^Tand the effect on the removal of ammonia.The optimal C/N requirement of strain HITLi 7^Tfor nitrification and denitrification is 3?4,which is far lower than the theoretical critical C/N requirement of most heterotrophic bacteria(C/N=10).The most suitable organic carbon for the growth and metabolism of strain HITLi7^Tis sodium acetate,and sodium carbonate can also be used for autotrophic nitrification.The main reason is that there are some enzymes related to CO₂fixation in the cells of strain HITLi 7^T.The carbon and nitrogen co-metabolism kinetics model were constructed with glucose as the only carbon source,and it was found that the heterotrophic nitrification kinetics of strain HITLi 7^Tconformed to the Contois-Contois model,and the kinetics of denitrification conforms to the Monod-Contois model.And the models are corrected by using temperature,p H,C/N and shaker speed(dissolved oxygen)as environmental factors.Based on the above research,it is proposed to preload the bioavailable organic carbon on activated carbon.It is found that preloading glucose can improve the biomass,biological activity and ammonia removal effect of strain HITLi 7^Ton BEAC.Glucose was used as the activated carbon preloaded carbon to construct the BEAC pilot process.The initial biomass and biological activity on the BEAC were 5.12×10⁸CFU/g-DW C and 3.77 mg TF/L/g-DW C,respectively;the BEAC process was running in different operational conditions,the average ammonia removal,biomass,biological activity and ATP activity of BEAC constructed with pre-loaded glucose are higher than those without pre-loaded glucose.After 95 days of operation,the proportion of dominant bacteria in the microbial structure is higher than that of ordinary BEAC.Food-grade glucose was used for pre-loading applications in the actual water purification plant,with a loaded ammount of 2.5 mg-C/mg-DW C.After artificial immobilization,the number of bacteria formed on BEAC is over 2×10⁶CFU/g-DW C;after 9 days of water flow,ammonia and COD_Mnindexes were lower than 0.5 mg/L and 3.0 mg/L,respectively,confirming that preloaded glucose can be used as a regulation method for the rapid start of the BEAC process.