Study On Cold-adapted Mechanism Of Acinetobacter HITLi 7~T And Ammonium Removal From Drinking Water At Low Temperature By Functional Bacterial Community

In cold region,low temperature period is long,and water quality of source water changes with the seasons.Parts of the water quality in low temperature period have these characteristics: high ammonium concentration and poor biochemical characteristics.Low temperature inhibits autotrophic nitrifiers,which naturally enriched in normal biological activated carbon(BAC),from removing ammonium.Heterotrophic nitrification bacteria can use organic carbon for nitrification.In comparison with autotrophic nitrifiers,heterotrophic nitrification bacterium's growth rate is higher,and its tolerance ability to change of temperature is stronger.Thus,heterotrophic nitrification bacteria are more suitable to treat source water in cold region.Biologically enhanced activated carbon(BEAC)process can combine adsorption function by active carbon with biodegradation function by dominant bacterium community.The study on cold-adapted mechanism of Acinetobacter sp.HITLi 7T,and ammonium removal from drinking water at low temperature by functional bacterial community,has important theoretical significance.In this paper,the cold-adapted mechanism of the low-temperature heterotrophic nitrification bacterium HITLi 7T was studied in terms of gene characteristics,gene expression,and fatty acid in biofilm.The results showed that the cellular and metabolic pathways in the functional classification of the Acinetobacter sp.HITLi 7T were dominant in biological pathways.The cell and cell fractions were the main components of the cytology module.The binding and catalytic activity played an important role in molecular function.These could help the strain HITLi 7T to keep the fluidity and stability of the cell membrane,and maintain a high metabolic substrate binding capacity and catalytic activity at low temperature.The genome of the strain HITLi 7T contained 9 kinds of cold adapted enzymes and 10 cold shock protein gene modules.The strain HITLi 7T could adapt to the low temperature environment through cold shock protein expression and enzyme-catalyzed biological metabolism.The succinate dehydrogenase,ATP synthase,and S-adenosylmethionine synthase related to the electron transfer of the bacterial respiratory chain in the strain HITLi 7T could be overexpressed at 2 °C.Simultaneously,strain HITLi 7T could induce some proteins with biological protein synthesis function at 2 °C,including transcription-related DNA-directed RNA polymerase,translation-related elongation factors-Tu and elongation factor-G,and protein folding-related Chaperone protein.In addition,the strain HITLi 7T could maintain cell membrane fluidity and stability by regulating the ratio of unsaturated fatty acids and the length of fatty acid chains at 2 °C.Therefore,the strain HITLi 7T could adapt to low temperature of 2 °C mainly through the increase of the concentration of the cold adapted enzyme,the expression of the cold shock protein,the regulation of metabolic pathways,and the ratio of unsaturated fatty acids and the length of the fatty acid chain on the biofilm.Based on the water quality characteristics of the Songhua River,a functional bacterial community was established mainly using the strain HITLi 7T,which accounts for 80% of the total bacteria.The ammonium removal efficiency at low temperature by the functional bacterial community and the biological stability of the strain HITLi 7T were studied using the bench-scale and pilot-scale BEAC process platform.The results showed that under the conditions of constant water temperature 2 °C and influent ammonium concentration of 0.55 mg/L ~1.74 mg/L,the ammonium removal amount of the bench-scale BEAC process was 2.3~3.3 times of that the common granular activated carbon(GAC)process,the DOC removal rate of the bench-scale BEAC process increased by 18.0±7.8% compared with GAC process,and there was no nitrite accumulation.The results indicated that the BEAC process based on the strain HITLi 7T had obvious advantages over the normal GAC process in ammonium and organic pollutants removal,and control effect of nitrite.The pilot-scale BEAC process based on the strain HITLi 7T had been operating for 506 days under conditions of varying water temperature(0.9 °C ~26.1 °C).The removal ratios of ammonium and DOC were 42.0 ± 28.5 % and 29.0 ± 19.1 %,respectively.When the influent C/N ratio was greater than the optimal C/N ratio(10)of the strain HITLi 7T,the pilot-scale BEAC process had higher ammonium removal ratios.Although the diversity of microorganisms in the pilot-scale BEAC process was more abundant with the increase of the operation time,the strain HITLi 7Tcould maintain stable state in the long-term operation(at least 500 days)under the fluctuation of water temperature,and could co-exist with other indigenous bacteria and formed a relatively stable microbial community structure.Therefore,the strain HITLi 7T played a key role in ammonium removal from source water at low temperature(0 °C ~2 °C)in the BEAC process,and could maintained long-term stability,both in terms of the ammonium removal characteristics and microorganisms' dynamic characteristics.The poor biodegradability of the actual water quality limits the ability of the strain HITLi 7T to remove ammonium at low temperatures.In addition,organic carbon sources can be involved in the synthesis of protein in bacteria and the regulation of metabolic pathways,in line with the cold-adapted mechanism of the strain HITLi 7T.Therefore,it is feasible to increase the biodegradable dissolved organic carbon(BDOC)concentration in the system to promote the ammonium removal efficiency by the strain HITLi 7T at low temperature.Three regulatory methods,including preloading carbon source onto activated carbon,addition of carbon source in influent and ozone oxidation process,were conducted to enhance the ammonium removal of the BEAC process at low temperature.The results showed that the initial biomass and microbial activity on the BEAC increased by 2.4-fold and 2.0-fold when glucose was preloaded onto activated carbon with the value of 9.9 mg C/g-dry weight activated carbon.Thereby,the ammonium removal amount of BEAC with pre-loaded glucose(0.99 mg/L)was 4.5 times higher than that of BEAC without pre-loaded carbon(0.18 mg/L).Furthermore,the ammonium removal of the pilot-scale BEAC process increased by 95 % and the organic pollutants removal was also improved with the addition of glucose in influent(optimal dosage Cplus/N=0.5).After the start-up of ozone oxidation process(ozone dosage: 1.3 mg/L),the ammonium removal of the pilot-scale BEAC process increased by 82 %.The three control methods all could increase the microbial activity and biomass by increasing the BDOC concentration,thereby improved the ammonium removal efficiency of the process system during the low temperature period.