| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 98 === The removal of ammonium from the blowdown of wet scrubber was investigated in this study. Both magnesium salt and phosphate salts were added for the precipitation of magnesium ammonium phosphate hexahydrate (Mg NH4 PO4．6H2O, struvite). To recover high concentration of ammonium (NH4+ = 528.17 mg/L) from scrubber blowdown, two sets of chemical, including MgCl2 + K2HPO4 and MgO + 85% H3PO4 were used at the stoichiometric ratio ([Mg2+]:[NH4+]:[PO43-] = 1:1:1) and at different pH ranging from 8 to 9. Experimental results indicated that the optimum removal efficiency of ammonium as struvite was 73.3% at pH 8.5 with the addition of MgCl2 and K2HPO4. Experiments were performed at pH 8.5 by using MgCl2 and K2HPO4 at different molar ratio. Experimental results indicated that the removal efficiency of ammonium reached almost maximum at the stoichiometric ratio of struvite. There was no further effect when molar ratio was higher than stoichiometry. The formation of struvite, as produced under different reaction conditions, were confirmed by FESEM, EDX, XRD and wet chemical analysis. Theoretical equilibria were modeled with PHREEQC and compared with experimental results. Additionally, the effect of iron on struvite precipitation was also investigated by spiking iron to the wastewater. Ammonium removal efficiency was not affected when in the presence of 5-10 mg/L of iron. Experimental results proved that removal of ammonium as struvite from scrubber blowdown is feasible.
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