This study was conducted to investigate the effect of physical and chemical influencing factors on struvite crystallization in treating semiconductor wastewater, in which the high levels of ammonia, phosphate and fluoride are especially presented. The overall goal of this study was accomplished thro...
This study was conducted to investigate the effect of physical and chemical influencing factors on struvite crystallization in treating semiconductor wastewater, in which the high levels of ammonia, phosphate and fluoride are especially presented. The overall goal of this study was accomplished through five specific studies: Effect of mixing on spontaneous struvite precipitation; Characterization of bittern as an alternative to magnesium source; Effect of mixing and impurities(Ca, F) on struvite crystallization; Influence of material type and surface roughness on struvite scale control; Effect of seeding and mixing conditions on struvite scale. The conclusions obtained are as follows. First, mixing energy, i.e., mixing intensity(G) multiplied by mixing duration(td) was elucidated to enhance struvite precipitation and the removal of ammonia and phosphate from semiconductor wastewater. The G·td values, the multiplying value of mixing intensity and mixing duration was a useful parameter to explain the mixing effect in this process, which was to enhance the mass transfer of ammonium ions in the solution inducing the potential of struvite crystallization and growth to increase. Especially at the G·td value over 1x105 the precipitate was close to pure struvite even high level of fluoride as impurity, while insufficient mixing led to the formation of the unexpected precipitates. Second, bittern was found to be an alternative to magnesium ion in order to reduce the cost of chemical(MgCl2) use in the process of struvite crystallization. For inducing effective struvite formation, 1.6 times higher dose of bittern(on molar basis) was required as compared with using MgCl2, and the mixing demand expanded to 4×105. In this process, bittern also acted as coagulant to remove fluoride. Third, the effect of mixing and impurities(Ca, F) on struvite crystallization was investigated by using SEM(scanning electron microscope), EDS(energy dispersive spectrometer), XRD(X-ray diffraction) analyses. From these analyses, the precipitate characteristics and structure of struvite crystal were identified. Forth, surface roughness of material influenced struvite scale formation. The materials selected in this study were FRP(fiber reinforced polymer), acryl, stainless steel, Teflon, synthetic rubber, and natural rubber. With hydrophilic materials(Teflon, synthetic rubber, natural rubber), surface roughness affected struvite scale formation. However this impact was less observed with hydrophobic materials(FRP, acryl). The potential for struvite scale formation was great with the following sequence: stainless steel, synthetic rubber, natural rubber, acryl, FRP, and Teflon. Fifth, seeding and mixing conditions were critical influencing factors to identify struvite scale formation. The pre-formed struvite was selected as seeding material. Seeding effect depended on mixing energy(G·td value). Especially at 5.8×105 or lower, struvite crystallization was much enhanced by seeding. Seeding also saved mixing energy. The mixing demand with seeding was four time less than that without seeding. Finally, the obtained results provide information to improve the practical application of struvite precipitation on the industry. Considering the agricultural use of stuvite, the present study gives feasible information of influence factors on struvite crystallization in order to obtain pure struvite from the stream.
This study was conducted to investigate the effect of physical and chemical influencing factors on struvite crystallization in treating semiconductor wastewater, in which the high levels of ammonia, phosphate and fluoride are especially presented. The overall goal of this study was accomplished through five specific studies: Effect of mixing on spontaneous struvite precipitation; Characterization of bittern as an alternative to magnesium source; Effect of mixing and impurities(Ca, F) on struvite crystallization; Influence of material type and surface roughness on struvite scale control; Effect of seeding and mixing conditions on struvite scale. The conclusions obtained are as follows. First, mixing energy, i.e., mixing intensity(G) multiplied by mixing duration(td) was elucidated to enhance struvite precipitation and the removal of ammonia and phosphate from semiconductor wastewater. The G·td values, the multiplying value of mixing intensity and mixing duration was a useful parameter to explain the mixing effect in this process, which was to enhance the mass transfer of ammonium ions in the solution inducing the potential of struvite crystallization and growth to increase. Especially at the G·td value over 1x105 the precipitate was close to pure struvite even high level of fluoride as impurity, while insufficient mixing led to the formation of the unexpected precipitates. Second, bittern was found to be an alternative to magnesium ion in order to reduce the cost of chemical(MgCl2) use in the process of struvite crystallization. For inducing effective struvite formation, 1.6 times higher dose of bittern(on molar basis) was required as compared with using MgCl2, and the mixing demand expanded to 4×105. In this process, bittern also acted as coagulant to remove fluoride. Third, the effect of mixing and impurities(Ca, F) on struvite crystallization was investigated by using SEM(scanning electron microscope), EDS(energy dispersive spectrometer), XRD(X-ray diffraction) analyses. From these analyses, the precipitate characteristics and structure of struvite crystal were identified. Forth, surface roughness of material influenced struvite scale formation. The materials selected in this study were FRP(fiber reinforced polymer), acryl, stainless steel, Teflon, synthetic rubber, and natural rubber. With hydrophilic materials(Teflon, synthetic rubber, natural rubber), surface roughness affected struvite scale formation. However this impact was less observed with hydrophobic materials(FRP, acryl). The potential for struvite scale formation was great with the following sequence: stainless steel, synthetic rubber, natural rubber, acryl, FRP, and Teflon. Fifth, seeding and mixing conditions were critical influencing factors to identify struvite scale formation. The pre-formed struvite was selected as seeding material. Seeding effect depended on mixing energy(G·td value). Especially at 5.8×105 or lower, struvite crystallization was much enhanced by seeding. Seeding also saved mixing energy. The mixing demand with seeding was four time less than that without seeding. Finally, the obtained results provide information to improve the practical application of struvite precipitation on the industry. Considering the agricultural use of stuvite, the present study gives feasible information of influence factors on struvite crystallization in order to obtain pure struvite from the stream.
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