| In view of the problem of nitrate pollution in the water,sulfur autotrophic denitrification,as an efficient biological nitrogen removal pathway,can effectively avoid the need of additional carbon source for heterotrophic denitrification.However,the effluent from sulfur autotrophic denitrification contains sulfate and requires additional alkalinity during the process.Studies have shown that addition of carbon source to sulfur autotrophic nitrification system can effectively alleviate the above problems,but mainly focused on the optimization of the operating conditions,there are few studies on reaction mechanism and the microbial community structure and function gene changes.This study through the comparison of performance on sulfur autotrophic and mixtrophic denitrification,preliminary explore the mechanism of mixtrophic denitrification process,and using molecular biology technology to compare the functional gene and the microbial community structures in different reaction systems.The operational efficiency of mixtrophic denitrification was mainly studied through small scale experiments.The results of sulfur autotrophic denitrification and mixtrophic denitrification showed that adding a small amount of carbon source could significantly improve denitrification effect.Compared with the sulfur autotrophic denitrification reactor,the removal rate of NO3--N was increased by 16.2%,29.7% and 37.0%,by adding 1/8,1/4 and 1/2 carbon source(the theoretical carbon source needed to remove the effluent NO3--N)respectively.The results showed that adding carbon source(1/4)could improve the nitrogen removal efficiency in different degree.Based on the operation efficiency of the small scale reactor,the enhancement of carbon source in the mixtrophic denitrification system was analyzed.By comparing the system of autotrophic and heterotrophic denitrification contribution rate,the denitrification efficiency improvement was not only because of heterotrophic denitrification occured,but also improved the system of autotrophic denitrification ability.With the increase of carbon source dosage,heterotrophic contribution rate increased from 1.2% to 9.8%,and the removal amount of NO3--N increased from 21.60 mg/L to 28.64 mg/L.The effect of different time of adding carbon and mixtrophic denitrification efficiency was analyzed.The results showed that adding carbon source at different time could effectively improve the denitrification effect,and the denitrification effect was slightly different at different dosing time.In addition,the results of mixtrophic denitrification peak change of nitrite in the reaction and biomass showed that accelerate the transformation of nitrite nitrogen and increasing the biomass of the system may be the other ways to strengthen the system nitrogen removal.After adding carbon source,the peak value of nitrite decreased by 2.12,2.95 and 0.61 mg/L respectively,and the biomass increased by 5.23,11.31,14.12 nmol P/g,respectively.Microbial samples were collected after stable operation to study the variation of structure and functional gene changes.16 S r DNA high throughput sequencing results showed that the microbial diversity in the mixtrophic was significantly decreased,and the autotrophic and heterotrophic bacteria increased with the increase of carbon source dosage,while the abundance of autotrophic bacteria increased rapidly,and the abundance of heterotrophic bacteria increased slowly,but promotion of autotrophic bacteria domimate in general.Before and after carbon source addition,the relative abundance of typical sulfur autotrophic bacteria increased from 22.1% to 43.9%.Nir S gene and Sox B gene expression analysed by real-time quantitative PCR showed that the carbon source strengthen the cause of denitrification was likely to improve the expression of Nir S gene and Sox B gene.The relative expression of Nir S gene was 4.55,and the relative expression of Sox B gene was 3.95. |
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