| Nitrate often contaminated surface water resources due to excessive use of fertilizers and uncontrolled on-land discharges of raw and treated wastewater and can therefore limit the direct use of surface water for drinking water purposes. Many researches on the denitrification of source water had been reported in the last three decades with the increasing nitrogen pollution concerns; biological treatment was the most attractive process to remove nitrogen from surface water sources due to its low cost and high efficient. However, there are still some problems on denitrification of drinking water resources. Firstly, biological nitrogen removal of ectopic widely used in surface water sources has a restriction of biological contact time——an important limiting factor for influencing the removal efficiency of total nitrogen. Secondly, electron donor used to improve the denitrification efficiency can increase water treatment costs and some substrate or its intermediate products of biological oxidation may produce toxic effects on life.In this research, a multifunctional device for water lifting and aeration (WLA) was combined with in-situ biological purification technology (ISBP) for the denitrification of surface water. The main objective of this research was to investigate the key issues of nitrate removal of micro-polluted raw water with the combined system under low temperature, oligotrophic and aerobic condition. Oligotrophic denitrifiers and cold-resistant denitrifiers were cultured for microbial agents, which was the important source of bacteria for in-situ biological inoculation or in-situ bio-contact oxidation system. Both ISBPs were combined with WLA in order to obtain a satisfactory performance on nitrogen and organic matter removal. Properties and experiments of enhanced in-situ biological nitrogen removal of micro-polluted raw water were discussed in this paper. The main results and conclusions of this study are as follows: (1) Domestication, isolation and denitrification properties of oligotrophic aerobic denitrifiers. Oligotrophic denitrifiers strain PY8, DA15 and DF7 was isolated after the acclimatization with low-nutrient medium in order to remove nitrogen desirably under oligotrophic conditions. According to their physiological, biochemical methods and the sequence analysis of 16S rDNA, strain PY8, DA15, DF7 was identified as Rhizobium sp., Arthrobacter sp. and Bacillus sp., respectively. On the base of the isolated strain FY3, FY5 and FY7, oligotrophic denitrifying functional bacteria populations Z4 (PY8, FY3 and FY7) was formulated by niche separation, and all the functional bacteria were studied for nitrogen removal performance. The results showed that all the strains grew slowly, and pH value, temperature, C/N ratio, NaNO3 concentration and inoculum had different effects on denitrification performance of strain PY8, FY3 and FY7. Also, the strain PY8 had a significantly heterotrophic nitrification performance. It was confirmed that the strain PY8, FY3 and FY7 had the capacity of express periplasm nitrate reductase through the PCR reaction, and periplasmic nitrate reductase played an important role in aerobic gentrification.(2) Domestication, isolation and denitrification properties of low-temperature- resistant aerobic denitrifiers. Low-temperature-resistant denitrifying bacteria were isolated by gradually reducing temperature condition, and the strain DW3 was identified as Pseudomonas sp., the strains of DW4, D3 and D4 as Acinetobacter sp., based on biochemical index analysis and 16S rDNA sequence homology analysis. Growth curve and nitrogen removal capacity was investigated for the four strains. The results indicated that in addition to D3 strain, other strains were present a decline phase, and the strains of the denitrification took place in the logarithmic phase. Also, pH value, temperature, C/N ratio and inoculum could influence denitrification performance of low-temperature- resistant denitrifiers. A desirable ammonia removal rate was obtained for the four strains in nitrification medium. D3 and D4 still maintained a certain dehydrogenase activity at 10℃. The results also proved that DW3 and D3 strains had periplasmic nitrate reductase and could realize aerobic denitrification. Low-temperature-resistant and oligotrophic denitrifying functional bacteria groups L1 (PY8, DW3 and D3) and L2 (PY8, DW3 and D4) could were constructed by self-adjustment and eco-recombination for the purpose of denitrification under oligotrophic and low temperature conditions.(3) Properties and efficiency of in-situ biological inoculation nitrogen removal of micro-polluted raw water. Oligotrophic denitrifying functional bacteria populations Z4 as bacteria source was used for in situ biological inoculation technology in small scale tests. The showed that a preferable purification could be presented under 0.1 mg/L inoculating dose, and the removal rate of nitrate, total nitrogen, CODMn and TOC during the entire operation (32 days) could reach 72.3%, 71.3%, 32.3% and 34.8%, respectively. Also, nitrogen removal effects in steady running period could meet the requirements of classⅢof surface water quality according to GB3838-2002. DO, temperature, pH and C/N ratio was important influencing factors for denitrification performance of oligotrophic dominant agents. The cold-resistant and oligotrophic denitrifying functional groups L1 showed a high efficiency for nitrogen removal in low temperature, and the optimum removal rates of nitrate and total nitrogen reached 46% and 53% during 36 days operation.(4) Properties and efficiency of in-situ biological biofilm nitrogen removal of micro-polluted raw water. A rigid suspended packing and a novel suspended packing chosen as biological carriers was applied to in-situ biofilm system. The novel suspended packing was developed for in-situ remediation and could create an appropriate environment for the growth of aerobic, anaerobic and facultative bacteria. Artificially hanged membrane was formed on both carriers with oligotrophic denitrifiers functional groups Z4. The small test results showed that the removal rates of nitrate, total nitrogen and CODMn could reach over 75%, 75% and 25%, respectively, and nitrogen removal effects in steady running period could meet the requirements of classⅢof surface water quality according to GB3838-2002. Temperature, filling ratio of suspended packing and C/N had a certain influence on nitrogen removal efficiency of in-situ biological biofilm system. Oligotrophic bacteria grown at a lower rate and had a greater resistance to external environment, and these properties could provide a better adaptability to poor nutrition environment for them. The adsorption and microbial biofilm formation was a survival strategy in oligotrophic environment.(5) Requirements of mixed aeration technology for in-situ biological inoculation system. Dissolved oxygen concentration could affect denitrification performance of oligotrophic denitrifying functional groups. When the DO concentration greater than 7 mg/L, the denitrification rate was very slow and always maintained a low level. The nitrogen removal rate would increase significantly with the decrease of DO value under condition of DO concentration less than 7 mg/L. These results indicated that aerobic denitrifiers with a higher threshold had a desirable oxygen tolerance. The removal rates of total nitrogen were 91%, 84% and 31% respectively under conditions of DO concentration 3~4 mg/L, 5~6 mg/L and 7~8 mg/L. Both denitrification enzyme and aerobic respiratory system could exist in aerobic denitrifiers, and oxygen was no longer inhibited denitrification enzyme activity and denitrification enzyme generation directly. Periplasmic nitrate reductase subunit gene amplification further explained that aerobic denitrification could occur under high DO concentration condition.(6) Pilot research on combined process of WLA and ISBP. Under the condition of enhanced mixing of water-lifting aeration, a pilot research on ISBP was made for the purpose of pretreatment of micro-polluted raw water. Oligotrophic denitrifying functional groups Z4 as bacterial source constituted combined process of WLA and in-situ biofilm and combined process of WLA and in-situ bio-inoculation. For the combined technology of WLA and in oligotrophic biofilm system, the results showed that removal rates of ammonia, nitrate, total nitrogen and TOC in steady running period ranged from 82%~100%, 62%~79%, 70%~80% and 72%~80%, respectively, under conditions of dissolved oxygen 5~7 mg/L, temperature 10℃~23℃and C/N ratio 1.56 for source water, also the ratio of BOD5 to CODMn was changed from 0.476 to 0.054. Three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy showed that the biogenic dissolved organic matter of raw water had experienced an obvious change during the operation period. As for the combined technology of WLA and oligotrophic bio-inoculation system, removal rates of ammonia, nitrate, total nitrogen, TOC and CODMn in steady running period ranged from 82%~100%, 43%~58%, 63%~70%, 65%~73% and 51%~57% respectively under the same conditions. The PCR-DGGE profiles showed that the microbial populations on the biofilm evolved slowly andα-proteobacterium was the largest fraction. In addition, sequences revealed that strains PY8 and FY3 became the dominant bacteria in the combined system WLA and oligotrophic biofilm, and FY3 and FY7 strain became the dominant bacteria in the combined system WLA and oligotrophic bio-inoculation system. Disinfection tests, biological community structure diversity and acute oral toxicity tests in mice showed that biological agents would not pose a threat to original ecosystems and drinking water. Under conditions of initial temperature of less than 15℃and CODMn/TN of 1.0, cold-resistant and oligotrophic denitrifying functional groups L1 combined with WLA could obtain a desirable denitrification effects during the stable period for more than 50% of nitrate removal rate and 60% of total nitrogen removal rate, and the optimum removal rate for nitrate and total nitrogen was 81% and 84%. Also, the monthly average removal efficiency of TOC、CODMn and BOD5 could reach 63%, 49% and 62%. The experiment results showed that the combined technique of WLA and ISBP was feasible for the denitrification of raw water, and nitrogen removal effects in steady running period could meet the requirements of classⅢof surface water quality according to GB3838-2002. |
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