| Wastewater reclamation and reuse are the inevitable way to solve the water crisis. Restricted by the current wastewater treatment technology, the effluent from municipal wastewater treatment plant still contain relatively high concentrations of nitrate and phosphorus, which can cause serious influences to the water environments when used in the aspects of landscape water supplying and groundwater recharging. Therefore, it has become the current hot spots to study the principles of advanced removal of nitrogen and phosphorus for reclaimed water and develop new technologies which can simultaneously remove nitrogen and phosphorus efficiently and cost-effectively.This research were focused on strengthening the efficiencies of advanced removal of nitrogen and phosphorus in the effluent from municipal wastewater treatment plant, In view of the characteristic of low C/N in the effluent, three groups of biological denitrification filter columns which had the same structures by using sponge iron/activated carbon composite fillers, sponge iron/sulfur/activated carbon composite fillers and Three-Dimensional Biofilm-Electrode Reactor with sulfur/sponge iron mixed fillers(3DBER-S-Fe) were run in comparison. Firstly, studies were conducted under different C/N, HRT and I conditions to examine the effects on advanced removal of nitrogen and phosphorus and the removal form of TP in the three groups by using synthetic effluent made from running water and chemicals. And then, correspondingly comparative studies were conducted by using effluent from real municipal wastewater treatment plant, reasons of the disparities in the results were analyzed. At last, the bacterial community composition and the strengthened removing mechanisms of nitrogen and phosphorus were discussed in a micro-level by adopting the Miseq high-throughput sequencing technologies and building the 16 S rRNA bacterial gene clone library. The main results of the research are as follows:Both the sponge iron/sulfur composite fillers and the micro-current could strengthen the removal efficiencies of nitrogen and phosphorus in the low C/N effluent. Under the condition of C/N=2, I=150mA and HRT=4h, the TN and TP removal rates of the 3DBER-S-Fe could reach 85.6% and 97.4% respectively which were significantly higher than the separate systems. What was more, 94.0% of the TP were removed in the form of iron-phosphate precipitation. 3DBER-S-Fe could achieve high removal efficiencies of nitrogen and phosphorus under the conditions of C/N=0, I=0mA and HRT=2h, moreover, the removal efficiencies of nitrogen and phosphorus were strengthened in different degrees by properly increasing anyone of the three conditions. And the systems have better abilities to maintain the pH values between 7.2~8.5.C/N ratio in the effluent from real municipal wastewater treatment plant generally is far below the required theoretical value for denitrifying and most of the CODs in the effluent are difficult to degrade by microorganisms. Both the sponge iron/sulfur composite fillers and the micro-current had an obvious function in promoting the removal efficiencies of nitrogen and phosphorus in the real effluent; the high nitrogen removal efficiencies(95.1%) of the 3DBER-S-Fe mainly depended on the combined actions of hydrogen autotrophic denitrification and sulfur autotrophic denitrification.The Rhodocyclaceae, Thauera, Comamonadaceae and Acidororax bacteria which can use both organic carbon and elemental hydrogen as their electron donor for denitrification totally accounted for 29.47% of the bacterial community in the sponge iron fillers separate system. The proportion of the Thiobacillus bacteria reached 60.47% of the bacterial community in the iron/sulfur composite fillers. The largest proportions were the Thiobacillus bacteria that can use elemental sulfur as their electron donor separately accounted for 40.62% and 44.75% in the bacterial community on the fillers and the cathode, and the proportion of the Rhodocyclaceae bacteria that can use elemental hydrogen as its electron donor apparently reached more on the latter. Therefore, the process of hydrogen autotrophic denitrification mainly occurred on the cathode.This study reinforced the advanced removal efficiencies of nitrogen and phosphorus and further explored the removal mechanisms of the processes. The results are of great significance for improving the status quo of high levels of nitrogen and phosphorus in the effluent from municipal wastewater treatment plant, enhancing the quality of the reclaimed water and promoting the process of turning wastewater into resource. |
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