| The element phosphorus has no substitute in sustaining all life on our planet. Yet today’s phosphorus use patterns have resulted a global environmental epidemic of eutrophication. Simultaneous removing and recovering phosphorous from wastewaters has become one of the global phosphorous resource strategies, which mitigates eutrophication as well as satisfies the necessity for sustainable utilization of phosphorous resource.At present, most of the wastewater contains low phosphorous concentrations. It’s difficult to recover and recycle phosphorous from wastewater in the activated sludge process. According to the above problems, phosphorous bio-accumulation and recovery using the novel continuous alternating anaerobic/aerobic biofilter system were studied in this paper. The major impacting factors of the system were analyzed in order to optimize PAOs enrichment and bio-accumulation in the biomass. Phosphorus recovery as magnesium ammonium phosphate (MAP) from anaerobic released effluents containing high phosphorous concentrations utilized the PAOs enriched biomass to facilitate the formation of high phosphorous recovery liquids. The experiment employed fluorescence in situ hybridization (FISH), chemical equilibrium models and X-ray diffraction(XRD) to analyz the effect of phosphorous Accumulation-Enhancing-Recovery. The main research results are as below:(1)The paper studied the factors of system in order to determine the optimal operating conditions:Backwashing between25d to30d was the key operation to maintain biofilter’s function. With C/P kept at15in the influents, the highest TP removal reached97.4%and the operation pattern saved carbon source at the same time. TP removal of the system could reach to93%when the cycle duration(CD) was kept8.0h(4:4) to maintain the system best function. The hydraulic retention time and inner-loop duration were controlled at1.5h and2.0h respectively to insure that nutrients could be absorbed by biomass and minimize the loss of phosphate during the anaerobic/aerobic transitional period. The anaerobic/aerobic conditions affected the extent of PAO’s P-release and P-uptake.(2) Rapid PAO-enrichment in the biomass and the effects of phosphorus bioaccumulation were studied:The process peroidwas sustained about200days, which was divided into three stages named starting-up phase, optimization phase and recovery phase respectively. In the third phase (phase III), the AABF achieved accelerated PAOs’accumulation and quick increasing of anaerobic released phosphorous concentration(which reached to75mg/L) in the anaerobic effluents of the biofilter. The maximum anaerobic released phosphate related more closely with the total phosphorous content in the biomass, and had relationship with the intracellular phosphorous content. At the same time the concentration of phosphorous and manganese increased simultaneously while that of calcium decreased with the accumulation of PAOs contained biofilm in the biofilter. Carbon source supplement by continuous feeding enhanced phosphorus removal and recovery, and the activity of PAO was strengthened under an average△P/△C of0.26. The FISH detection showed that PAO became the dominant bacteria with the rising proportion. It could be concluded that the cyclical high-concentration carbon source supplement would be beneficial to PAO’s enrichment.(3) Evaluations of phosphorous recovery potentials as MAP from the biofilter’s anaerobic effluents:The phosphorus recovery rate was not high when the initial phosphorus concentration (IPC) was lower than40mg/L, but it reached to82%when the IPC was above80mg/L with the highest removal of98.6%. In order to avoid the influence of Ca2+, the best IPCs were controlled within80-100mg/L. The analysis of the images of precipitated products shown that with IPCs higher than80mg/L, the major structure of precipitated products changed into orthorhombic crystals. And the patterns of XRD showed that the recovery crystal had similar diffraction peaks with struvite, so the recovery products were MAP of high purity. |
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