| With the develop of industry, a lot of sewage riched in nitrogen and phosphorus discharge into natural water in rivers and lakes and cause water eutrophication seriously. Therefore, people pay more attention to the biological nutrient removal technology work very well in nitrogen and phosphorus removal at the same time with low cost, high efficiency, carbon source saving sludge yield reducing. However, recent studies found that denitrifying phosphorus removal process produced large amount of N2O. Acetate and propionate are the most common carbon sources in the sewage, and influent carbon source in sewage treatment plant changes with time. Therefore the study on N2O emission under different carbon sources of denitrifying phosphorus removal process has important significance.The objective of this paper was to evaluate the pollutants removal and N2O emission under different carbon source conditions in an anaerobic/anoxic/aerobic denitrifying phosphorus removal system. Firstly, long-term experiment was researched using acetate, aceate and propionate mixture, propionate as carbon sources, to evaluate the changes in the pollutants removal. Then, N2O emissions were obtained when the three-systems were at stable conditions to study the effects of carbon sources on denitrifying phosphorus removal. Afterwards, the sludge morphology and colony structure were studied by using scanning electron microscope and PCR-DGGE molecular biology technique, analyzing the relationship between sludge micro environment and the effect of treatment of sewage. The main conclusions of this paper are as follows:Pollutants removal efficiencies were different significantly in the denitrifing phosphorus systems by using different carbon sources. COD removal efficiencies of three systems were similar and high above87%. However, the presence of propionate reduced the total nitrogen removal efficiency. Total nitrogen removal efficiencies in acetate and propionate systems were average at71.39%and42.35%, respectively. Anaerobic phosphorus release in propionate system was much higher than that in acetate and mixed acid systems, and the carbon source of propionate improved the total phosphorus removal efficiency. Using acetace as carbon source, the total phosphorus removal efficiency is only87.23%, however, when using propionic as carbon source the total phosphorus removal efficiency increased to88.94%. Nitrite accumulation of acetate system was obvious, resulting in nitrite concentration was up to22.08mg/L. However, propionate system did not produce nitrite. Denitrification process in propionate system was not complete, resulting in higher effluent nitrate concentrations.Changes in carbon sources made large differences in the release of N2O in denitrifying phosphorus removal systems. N2O production in acetate system was much higher than that of mixed and propionate systems. The concentration of N2O production in acetate system was3.3mg/L, while the propionate system did not produce N2O. Therefore, propionate has obvious advantages to reduce N2O production in denitrificing phosphorus system. Moreover, different carbon sources could affect the number and types of PHA synthesis. When using acetate as carbon source, PHA synthesis was the highest, and when using propionic as carbon source PHA synthesis was the lest. The less quantity of PHA in propionate system could lead to the denitrification process conducting incompletly. When use mixed acid and propionate as carbon sources increasing of content of PHV and PH2MV in PHA synthesis anaerobicly help to reduce the production of N2O.The observation of microbes in sewage sludge found that, cocci were the dominant bacteria in sludge microorganisms when using acetate as carbon source. Using propionate as carbon source, most sludge bacteria were bacillus bacteria, indicating that propionate system could rich in more denitrifying bacteria. According to the PCR-DGGE results, carbon sources could cause the different of whole bacteria species and denitrifying bacteria species. Data implied that the mixed acid system had the highest diversity of whole bacteria species, while the propionate system had the highest diversity of nitrifying bacteria. Meanwhile, the dominant strains of each system were quite different. These changed the course of operation processes from the aspect of nature of biological wastewater treatment, thereby enabling the system’s treatment effect and the amount of N2O produced a difference. |
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