dc.description.abstract | Since nitrogen pollutants in water are one of the most concerned pollutants at present, their excessive discharge will cause pollution to the environment and even harm the human. In addition, the government attaches great importance to environmental protection regulations, discharge standards use higher standards for discharge water quality control. Since the heterotrophic denitrification bacteria are mostly used for denitrification in wastewater treatment plant, but need to add additional organic carbon source to have better denitrification effect when treating inorganic wastewater. Therefore, autotrophic denitrification bacteria have been developed for denitrification, which have advantages such as no need to add additional organic matter and lower sludge production.
In this study, thiosulfate was used as the inorganic electron donor in the sulfur autotrophic denitrification (SADN) system, and find the most suitable S/N ratio, also compare the effects of different pH values and dissolved oxygen concentrations in SADN. The results shown that when the S/N ratio = 2.19, the autotrophic denitrification sludge have enough electron donors to do the denitrification reaction, and there will be no accumulation of intermediate products; when the S/N ratio = 1.88, the nitrate in autotrophic denitrification will be preferentially reduced, lead to the nitrite will be accumulation. In addition, the autotrophic denitrification sludge domesticated in this study was mainly composed of Sulfurimonas and Thiobacillus, which accounted for more than half of the total.
The effect of pH in autotrophic denitrification reveal that denitrification rate reaches maximum at pH = 7, and between pH = 6 ~ 8, nitrate can be completely removed without intermediate product accumulation, and the average specific denitrification rate (SDNR) at this time is 7.69 mg NO3--N/g VSS*hr; when pH < 6 or > 8, the denitrification efficiency restricted, the specific denitrification rates were 1.66 and 4.12 mg NO3--N/g VSS*hr at pH = 5 and 9, respectively. Moreover, most of the nitrate was reduced to nitrite and accumulated.
The effect of dissolved oxygen concentration, shown that when the system is in anoxic stage (DO = 0 mg/L), the denitrification rate reaches the best performance and can completely denitrify. Under microaerobic conditions (DO = 1 mg/L), although nitrate is completely reduced at the end of the reaction, most of it is accumulated to nitrite. However, denitrification was severely inhibited under aerobic conditions (DO = 3 mg/L).
Keyword: autotrophic denitrification, reduced inorganic sulfur compounds, S/N ratio, pH, dissolved oxygen | en_US |