In fact, the NaOH pyrogenation process cannotentirely avoid the formation of the byproducts [e.g., Mg3(PO4)2 and Mg2P2O7]. Through the analysis of published literatures, it was found that the large consumption of NaOH and the formation of byproducts may be the main obstacles to the further development of struvite recycling technology. To avoid the formation of Mg2P2O7 in the pyrogenation of struvite, Huang et al. (2014) proposed the chlorination decomposition process of struvite, and found that the main components of the decomposition process were newberyite,
dissolved HPO4 2−and Mg2+, and magnesium phosphate (MP).Although this process well resolved the problem ofthe formation of Mg2P2O7, unfortunately, it only reduced a small amount of the struvite precipitation cost (34%) due to the large consumption of sodium hypochlorous. As for how to reduce the consumption of NaOH, to the best of our knowledge, there is no study dealing with this problem. On the basis of our previous investigations and the summary of the published literatures, we found that the reported struvite recycling technologies were significantly affected by the habitual thinking of researchers. They commonly considered that only when struvite was decomposed to MgHPO4, MgNaPO4, or dissolved magnesiumand phosphate salts,the recycling could be well accomplished. To the best of our knowledge, there was few investigation
focused on the feasibility of using MP as the active component of the struvite pyrolysate for the formation of struvite. Indeed, under identical reaction conditions, Mg3(PO4)2 has a low capacity for the removal of TAN compared to MgHPO4 and MgNaPO4. However, there was no detailed investigation data demonstrating the capacity of Mg3(PO4)2 for the removal of TAN under different reaction conditions. Therefore, in this study, we proposed a novel recycling process of struvite, which was achieved by pyrolyzing struvite to Mg3(PO4)2. The main objective of this study was to investigate the simultaneous removal of TAN and PT from swine wastewater by the proposed struvite recycling process. Owing to the presence of some organicmatter inswine wastewater,the influence of organicmatter on the crystallization of struvite was first studied by using simulated swine wastewater. Second, the investigations were focused on the performance of MP as the phosphate and magnesium sources of struvite precipitation. Third, to effectively reduce the cost of struvite precipitation, natural brucite mineral was used as the alkali reagent for the pyrogenation of struvite at different Mg(OH)2:NH4 + molar ratios and pyrogenation times, and then the obtained pyrolysate was recycled for the simultaneous removal of TAN and PT from swine wastewater. Lastly, the economic evaluation of the proposed recycling process was undertaken.
In fact, the NaOH pyrogenation process cannotentirely avoid the formation of the byproducts [e.g., Mg3(PO4)2 and Mg2P2O7]. Through the analysis of published literatures, it was found that the large consumption of NaOH and the formation of byproducts may be the main obstacles to the further development of struvite recycling technology. To avoid the formation of Mg2P2O7 in the pyrogenation of struvite, Huang et al. (2014) proposed the chlorination decomposition process of struvite, and found that the main components of the decomposition process were newberyite,dissolved HPO4 2−and Mg2+, and magnesium phosphate (MP).Although this process well resolved the problem ofthe formation of Mg2P2O7, unfortunately, it only reduced a small amount of the struvite precipitation cost (34%) due to the large consumption of sodium hypochlorous. As for how to reduce the consumption of NaOH, to the best of our knowledge, there is no study dealing with this problem. On the basis of our previous investigations and the summary of the published literatures, we found that the reported struvite recycling technologies were significantly affected by the habitual thinking of researchers. They commonly considered that only when struvite was decomposed to MgHPO4, MgNaPO4, or dissolved magnesiumand phosphate salts,the recycling could be well accomplished. To the best of our knowledge, there was few investigationfocused on the feasibility of using MP as the active component of the struvite pyrolysate for the formation of struvite. Indeed, under identical reaction conditions, Mg3(PO4)2 has a low capacity for the removal of TAN compared to MgHPO4 and MgNaPO4. However, there was no detailed investigation data demonstrating the capacity of Mg3(PO4)2 for the removal of TAN under different reaction conditions. Therefore, in this study, we proposed a novel recycling process of struvite, which was achieved by pyrolyzing struvite to Mg3(PO4)2. The main objective of this study was to investigate the simultaneous removal of TAN and PT from swine wastewater by the proposed struvite recycling process. Owing to the presence of some organicmatter inswine wastewater,the influence of organicmatter on the crystallization of struvite was first studied by using simulated swine wastewater. Second, the investigations were focused on the performance of MP as the phosphate and magnesium sources of struvite precipitation. Third, to effectively reduce the cost of struvite precipitation, natural brucite mineral was used as the alkali reagent for the pyrogenation of struvite at different Mg(OH)2:NH4 + molar ratios and pyrogenation times, and then the obtained pyrolysate was recycled for the simultaneous removal of TAN and PT from swine wastewater. Lastly, the economic evaluation of the proposed recycling process was undertaken.
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