| The tranditional subsurface wastewater infiltration system has a good performance in organic substance and phosphorus removal, however, its capacity and efficiency is still low with regard to nitrogen removal because of the lack of carbon source in denitrification area. The tranditional added carbon sources could not be applied widely because of their kinds of problems. Some studies have found that the refractory fulvic acid was degraded at 1.3m in the deep underground soil infiltration system and it was transformed into protein substances, which led to a promotion of the denitrification process and the denitrification efficiency.In order to find out the degradation mechanism of fulvic acid and its effect on the denitrification process in the deep underground soil infiltration system, some organic glass columns with radius of 0.3m and a height of 2.4m were used in this experiment to stimulate the the deep underground soil infiltration system, and they were filled with soil to a height of 2.0m. The removal efficiencies of kinds of pollutant in the domestic wastewater made by myself would be conducted before and after the addition of fulvic acid which was extracted from the landfill leachate in A shu wei sanitary landfill in Beijing.Before the addition of fulvic acid, the TP?COD?TN and NH4+-N concentrations in the effluent were 0.068mg/L?51.02mg/L?18.26mg/L and 0.68mg/L separately, and the efficiencies were 98.78%?85.47%?66.38% and 97.96% separately. According to the change of nitrogen along the depth of the system, it could be found that the nitrogen was mostly removed by nitration-denitrification process. At 0~0.2m of the top layer, aerobic decomposition of organic matter predominated, and the nitration was restrained. At 0.2~1.1m, the nitration reaction happened, which led to the increase of nitrate concentration and the accompanying increase of TN. At 1.1~2.0m, denitrification reaction predominated and 5.42mg/L nitrogen was removed by this process, which only accounted for 9.98% of the whole removed nitrogen because of the lack of carbon source. According to three-dimensional fluorescence and parallel factor analysis(PARAFAC) method, it has been found that the protein substances decreased and the fulvic acid increased over 1.1m, but only a little fulvic acid was degraded into protein substances at 1.1m, and these protein substances were utilized immediately and the content of protein substances stayed stable afterwards. The result indicated that the denitrification process was limited by the lack of carbon source.After the addition of fulvic acid, the TP?COD?TN and NH4+-N concentrations in the effluent were 0.051mg/L?58.37mg/L?18.15mg/L and 0.49mg/L separately, and the efficiencies were 99.22%?87.41%?74.86% and 98.72% separately. It could be seen that the nitrogen removal efficiency improved apparently, the removal amount increased to 54.04mg/L from the fomer 36.05mg/L The change of nitrogen was similar to the former. At 0~0.2m of the top layer, aerobic decomposition of organic matter predominated, and the nitration was restrained. At 0.2~1.4m, the nitration reaction happened, which led to the increase of nitrate concentration and the accompanying increase of TN. At 1.4~2.0m, denitrification reaction predominated and 7.20mg/L nitrogen was removed by this process, which accounted for 13.32% of the whole removed nitrogen. The removal nitrogen amount and efficiency by denitrification process improved 1.78mg/L and 32.84% separately. According to three-dimensional fluorescence and parallel factor analysis method, it has been found that a part of fulvic acid was degraded into protein substances which could be utilized by microorganism at 1.4m, and these protein substances were utilized immediately. At the same time, the denitrification efficiency and the amount of removed nitrogen increased in the end, which indicated that the fulvic acid can be used as slow-released carbon source in the deep underground soil infiltration system to improve the denitrification process. |
PDF Full Text Request