| Phosphorus (P) is the direct cause of eutrophication, it is also an indispensible element for life and industry but is with dwindling and nonrenewable resources. The development of wastewater biological P removal-P recovery process has become a research highlight by the experts from all over the world. This research used an alternating anaerobic/aerobic biofilter (AABF) to treat synthetic domestic sewage with low carbon (C) to P ratio (C/P), using periodic carbon source amplification for P recovery can not only improve the efficiency of phosphorous bioaccumulation/harvesting of the biological P removal system, but also can use magnesium potassium phosphate (MPP) crystallization method to recycle a part of P. The main influence factors of biofilter operation were studied to optimize the PAOs enrichment and P bioaccumulation/P removal efficiency; Intracellular storage polymer dyeing, scanning electron microscopy (SEM) observation, fluorescence in situ hybridization (FISH) and real-time quantitative PCR (qPCR) methods were employed to characterize the changes of microbial morphology and composition; and the optimal reaction conditions of MPP crystallization experiment were studied through the mixed wastewater containing P. The main research results are as follows:①The best C/P ratio of the alternating anaerobic/aerobic biofilter used in this experiment was12; the best cycle duration (CD) was8h (3:5); the total phosphorus (TP) removal rate declined gradually with the water temperature rose, TP removal efficiency was highest when the water temperature was10℃; TP removal efficiency was highest when the dissolved oxygen (DO) was2-4mg·L-1; the appropriate backwash intensity and cycle were essential for the normal operation of the biofilter and the optimal backwash cycle for this experiment was30d; through backwash the biofilter could recover to its best processing condition after2-3days; suitable P recovery cycle was very important for the improvement of P removal efficiency and P recovery efficiency in MPP crystallization experiments, the suitable P recovery cycle for this experiment was10d.②Using periodic carbon source amplification would not affect the normal operation of the biofilter, instead it could promote recovering the PAOs ability to accumulate excess P in the later operation, the P removal efficiency of the biofilter was thus improved, especially after three cycles continuous operation of carbon source amplification, P removal efficiency of biofilter maintained above85%, effluent TP concentration maintained about1mg·L-1.③The periodic carbon source amplification could cause great changes to microbial morphology and composition of biofilter, and promote PAOs becoming dominant group. After three times operation of P recovery cycle, the predominant bacterial community members of AABF transferred from β-Proteobacteria to y-Proteobacteria, and the microorganism with polyphosphate-accumulating capacities dominates gradually, especially the Pseudomonas spp. of y-Proteobacteria got constantly increase, and the proportion of PAOs in the biofilm presented great difference with the height of up-flow biofilter.④The optimum pH value of MPP crystallization experiments in this study was10; the P recovery efficiency increased significantly with the initial P concentration increased, when the P concentration reached more than150mg·L-1, the P recovery efficiency could reach95.4%; low initial P concentration mainly generated the Mg3(PO4)2precipitation, high initial P concentration mainly generated the MPP precipitation; in MPP crystallization experiments the optimum rotating speed, reactive crystallization time and settlement time was200r·min"-1,30min and30min, respectively. |
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