Although solid magnesia serves as a reservoir for Mg2þ ions, continuous NH4þ and PO34 consumption leads to decreasing pre- cipitation rates. Thus, the system reaches an equilibrium state with a very steady pH. Unlike the results for molar ratios 0.5 and 0.75, experiments conducted at molar ratio 1 show a subsequent increase in pH. This increase is related to an excess of MgO and Mg(OH)2, because the precipitation of struvite is too low to consume further Mg2þ ions, and the remaining magnesia particles start to dissolve again and release OH into the system. As a consequence, higher final pH values lead to lower struvite solubility (Ohlinger et al., 1998) and higher phosphorous recovery rates. Maximum pH and SI values, as well as the reaction kinetics (Quintana et al., 2005), increase with the amount of MgO introduced to the system. Wu et al. (2005) reported similar pH and phosphorous recovery behavior with the use of Mg (OH) as a precursor.
2
MgCl2 experiments performed at a molar ratio of 0.5 and 0.75
Although solid magnesia serves as a reservoir for Mg2þ ions, continuous NH4þ and PO34 consumption leads to decreasing pre- cipitation rates. Thus, the system reaches an equilibrium state with a very steady pH. Unlike the results for molar ratios 0.5 and 0.75, experiments conducted at molar ratio 1 show a subsequent increase in pH. This increase is related to an excess of MgO and Mg(OH)2, because the precipitation of struvite is too low to consume further Mg2þ ions, and the remaining magnesia particles start to dissolve again and release OH into the system. As a consequence, higher final pH values lead to lower struvite solubility (Ohlinger et al., 1998) and higher phosphorous recovery rates. Maximum pH and SI values, as well as the reaction kinetics (Quintana et al., 2005), increase with the amount of MgO introduced to the system. Wu et al. (2005) reported similar pH and phosphorous recovery behavior with the use of Mg (OH) as a precursor.2MgCl2 experiments performed at a molar ratio of 0.5 and 0.75
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