Advanced Nitrogen and Phosphorus Removal of Three-dimensional Biofilm-electrode Reactor With Sulfur/Sponge Iron Mixed Fillers

In order to strengthen the efficiency of the advanced nitrogen and phosphorus removal process of three-dimensional biofilm-electrode reactor(3DBER)and improve the quality of secondary effluent from wastewater treatment plant, a three-dimensional biofilm-electrode reactor with sulfur/sponge iron mixed fillers (3DBER-S-Fe) composite denitrification and phosphorus removal process was constructed using sulfur/sponge iron mixed fillers, studies were conducted under different ρ(C)/ ρ(N), I and hydraulic retention time (HRT) conditions to explore the effects on the performance of advanced removal of nitrogen and phosphorus. Finally, biofilms were taken from the fillers and cathode to build the bacterial 16S rRNA gene clone library by adopting the high-throughput sequencing technologies. Results show that under the condition of ρ(C)/ ρ(N)=2, I=150mA and HRT=4h, the total nitrogen (TN) and total phosphorus (TP) removal rate of 3DBER-S-Fe can reach to 85.59% and 97.43% respectively. Furthermore, the removal efficiency of nitrogen and phosphorus is strengthened by properly increasing anyone of the three conditions. The largest proportion is Thiobacillus bacteria that can use elemental sulfur as its electron donor which separately accounts for 40.62% and 44.75% of the bacterial community on the fillers and cathode, and the proportion of Rhodocyclaceae bacteria which can use elemental hydrogen as its electron donor reaches more on the latter. Therefore, the result of high nitrogen removal efficiency of the 3DBER-S-Fe mainly depends on the interaction of hydrogen autotrophic denitrification and sulfur autotrophic denitrification, and the process of hydrogen autotrophic denitrification mainly occurrs on the cathode.