Highly efficient removal of phosphonates by ferrate-induced oxidation coupled with in situ coagulation

Efficient Treatment of Phosphonate-Laden Wastewater by CaO2/UV: Partial Oxidation, Complexation, and Coprecipitation

“…The spectrum of P 2p can be fitted by two peaks at 133.0 and 133.9 eV, corresponding to the PO 4 3− and C−P, respectively. 32 This means that both P i and P o are present in the precipitates. 48 The spectrum of O 1s could be divided into two peaks: CO 3 2− (531.0 eV) and PO 4 3− (531.8 eV).…”

“…This is due to the complexation of NTMP with Ca 2+ , which results in less free Ca 2+ , hindering the formation and precipitation of Ca-phosphate and the associated coprecipitation of NTMP and its degradation products. 32 In the CaO 2 / UV system, dosing with 1.5 mM CaO 2 typically releases at least 1.5 mM Ca 2+ . Indeed, when 2.0 mM Ca 2+ was dosed, the total P removal efficiency reached 54.2% after 4 h of treatment.…”

“…DTPMP has the highest molecular weight and is more prone to coprecipitation among the five phosphonates. 32 The simplest phosphonate, PBTC, with the same P o concentration, should have the most robust antiprecipitation ability because it contains three extra −COOH groups, which could strongly bind with Ca 2+ even after the C-PO(OH) 2 group is broken. In addition, the bulk pH is much lower than the rest of the phosphonates after dosing CaO 2 (Figure 5c).…”

“…The varied conversion efficiency of P o to P i among the five phosphonates is linked with their unique molecular structures, which results in different reactivity with hydroxyl radicals generated in the CaO 2 /UV system. 30,32 Figure 5b shows the conversion efficiency of P o to P i is in the order of NTMP It is important to note that different phosphonates and their degradation products exhibit distinct antiprecipitation properties and thus affect the availability of free Ca 2+ . In the CaO 2 /UV system, the overall removal trend of TP reflects the reactivity of phosphonates with radicals, the evolution of the antiprecipitation ability of parent phosphonates, and their degradation products.…”

“…24,25 In particular, for ironbased AOPs, pH adjustment is enough to induce iron phosphate formation after treatment. 10,29,31,32 Generally, AOPs involve the addition of oxidants, i.e., ozone, persulfate, or H 2 O 2 , and activators, such as transition metal catalysts and UV irradiation. Of note, Sun et al reported that some phosphonates could be selectively degraded with lightmediated charge transfer without dosing oxidants.…”