UV/chlorine oxidation of the phosphonate antiscalant 1-Hydroxyethane-1, 1-diphosphonic acid (HEDP) used for reverse osmosis processes: Organic phosphorus removal and scale inhibition properties changes
2019
Huang, Nan | Wang, Wen-Long | Xu, Zi-Bin | Wu, Qian-Yuan | Hu, Hong-Ying
Reverse osmosis (RO) technology plays an increasingly important role in municipal wastewater reclamation. However, the antiscalants used in RO systems showed adverse effects to the ecosystem: impending the removal of hardness from RO concentrates; inducing phosphorus pollution in receiving water; enhancing the trace metal migration in the environment. In this study, UV/chlorine advanced oxidation process was used to oxidize a typical phosphoric antiscalant (1-Hydroxyethane-1, 1-diphosphonic Acid, HEDP). UV/chlorine showed significant synergetic effects on HEDP degradation compared to UV irradiation or chlorination alone. Compared to UV/H₂O₂ oxidation, UV/chlorine process is more efficient for HEDP transformation with chlorine dosages ranging from 0.1 to 0.4 mmoL/L. Chorine dosage showed dual effects on HEDP oxidation by UV/chlorine: the increasing trend of transformation efficiency of HEDP got slower with increasing chlorine dosage. The transformation efficiency of HEDP by UV/chlorine oxidation decreased from 39% to 14% with pH increasing from 4.5 to 9.0, likely due to the higher quantum yields and lower radical quenching rates of HOCl than those of OCl⁻. The transformation efficiency of HEDP decreased 14% and 42% with 30 mM of chloride and bicarbonate, respectively. The presence of nitrate promoted the oxidation of HEDP by UV/chlorine: the transformation efficiency increased 5% and 83% with the presence of 5 mM and 30 mM nitrate, respectively. Based on the static scale inhibition tests, UV/chlorine oxidation is effective at removing the scale inhibition ability of HEDP. During UV/chlorine process, the maximum scale inhibition ratio decreased from 66% to 34% as the removal of phosphonate ligand from HEDP increased to 80%.
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