Study The Removal Of Sulfur Autotrophic Denitrification For Simulation Groundwater Nitrate

In the recent years, nitrate pollution in groundwater was more and more increasing.One of the most effective way to remove nitrate pollution is biological denitrification.Using the autotrophic denitrification technology to remove nitrate in groundwater hasbeen a popular topic. But the disadvantages such as high concentration of effluent sulfate,more start-up time, poor adaptability of temperature and so on restricted the application ofthis technology. In this research, the fixed reactor was packed with the3:1rate of sulfurand quartz sand. Artificial nitrate wastewater was used to study the effect of concentrationof nitrate, hydraulic retention time, temperature, pH to the denitrifying rate. This studyexplored the autotrophic denitrification possibility of groundwater, and analyzed therelationship of flora structure change and denitrification rate. in the reactor Finally, batchexperiments of sulfur autotrophic denitrification was carried out to analyze ORP changesduring the denitrification process.First, start-up process of the fixed bed reactor has been discussed. The experimentresults showed that start-up time of the fixed bed reactor was about15d. Thedenitrification rate reached20.51mgN/(L·h). Sulfate concentration in the effluent wasconsistent with the theoretical value, effluent pH was6.5~7, ORP was about50mV. Andthere was no air bubbles jam because of high porosity during the denitrification process.After the reactor successfully domesticated, microbial community structure was observedby FISH technology. The results suggested that the relative abundance of Thiobacillusdenitrificans at the bottom, middle and upper reactor was0.165%,0.210%and0.280%,respectively. SEM showed that microbial species in sludge at the bottom are moreabundant than that of the upper. The inflow nitrate concentration should be less than300mg/L at HRT of8.4h. The best HRT was2.5h when nitrate nitrogen was70mg/L. Theoptimizedtemperature and pH was30℃and7, respectively.To test the low-temperature (10℃) adaptation of sulfur autotrophic denitrification,the simultaneous study of heterotrophic and sulfur autotrophic denitrification wasconducted to control the effluent sulfate concentration. The result showed that the reactorstarted about30d, the average denitrification rate was17mgN/(L·h). The sulfateconcentration was effective controlled and stayed under250mg/L by controling the rate ofheterotrophic and sulfur autotrophic denitrification bacteria. The ORP in autotrophic denitrification process was between0~50mVand the ORP ofheterotrophic denitrifying was around-350mV. Knee point of ORP was seen in the ORPdiagram when Sulfur autotrophic denitrification finished at different initial nitrateconcentration and different temperatures.In a world, this study completed the theory of sulfur autotrophic denitrification, andprovided an effective method to the groundwater denitration and provided moretheoretical and technical supports.