Study On Humic Acid Removal In Water By Ultraviolet Activated Peroxy Acid Salts

Humic acid?HA?is a macromolecular organic substance with a complex structure which commonly found in natural water bodies.Higher content will affect the color and odor of the water body,and flow into the food chain will affect human health.Therefore,removing HA can improve water condition and reduce the harmfulness of polluted water.The advanced oxidation processes are widely used to degrade organic pollutants in water due to its high efficiency and low cost.It mainly includes the processes based on sulfate radicals?SO₄^-·?and hydroxyl radicals?·OH?.SO₄^-·has a high redox potential?2.5-3.1 eV?,long life and selectively.SO₄^-·is mainly obtained by activating potassium persulfate?PDS?or potassium persulfate?PMS?.The structure of PMS is asymmetric,so it easier to be actived than PDS.The potential of·OH is 1.7-2.8 eV,·OH can be generated by Fenton process.Because of hydrogen peroxide?H₂O₂?is not easy to store and transport.Recently,sodium percarbonate?SPC?and sodium perborate?SPB?were chosen to be used as substitutes for H₂O₂,they are non-toxic and harmless.UV is a good choice for activating peroxyacids because of its low cost,simple equipment and no further pollution.Therefore,this paper has established four UV-activated peroxy acid systems to reduce HA.The main contents are as follows:Four types of ultraviolet activated potassium persulfate?UV/PDS?,ultraviolet activated potassium persulfate?UV/PMS?,ultraviolet activated sodium percarbonate?UV/SPC?and ultraviolet activated sodium perborate?UV/SPB?were studied The effectiveness and mechanism of the system to remove HA in water.The effects of peroxonate dosage,initial HA concentration and initial pH on HA degradation were investigated,and the best experimental conditions were determined.The effects of common anions(CO₃^2-,HCO₃^-,Cl^-,NO₃^-,SO₄^2-,H₂PO₄^-)on the removal effect of HA were investigated.The mechanism of HA degradation and mineralization was analyzed by ultraviolet-visible spectroscopy?UV-Vis?,total organic carbon analyzer?TOC?,specific ultraviolet absorbance?SUVA?,ultraviolet absorbance,and three-dimensional fluorescence spectroscopy?3D-EEM?.Free radical scavenging experiments determine the active species that play a major role in the system.The best experimental conditions of the four systems are as follows:In the UV/PDS system,under the conditions of a PDS concentration of 3 mmol L^-1,an initial HA concentration of 15 mg L^-1 and an initial pH value of 6,the HA removal rate could reach 94.8%after 180 min.In the UV/PMS system,under the conditions of PMS concentration of 1 mmol L^-1,initial HA concentration of 15 mg L^-1 and initial pH value of3,the removal rate of HA can reach 95.2%after 60 min.In the UV/SPC system,under the conditions of SPC concentration of 0.5 mmol L^-1,initial HA concentration of 10 mg L^-1and initial pH value of 9.9,the HA removal rate can reach 92.1%after 90 minutes.In the UV/SPB system,under the conditions of SPB concentration of 1 mmol L^-1,initial HA concentration of 10 mg L^-1 and initial pH value of 10,the HA removal rate can reach88.8%after 60 minutes.The more complex the water composition,the more it can affect the ability of the system to oxidize and decompose HA.The common CO₃^2-,HCO₃^-and NO₃^-in the water body can inhibit the oxidation ability of the four systems.In addition,H₂PO₄^-also has an inhibitory effect on the UV/PMS system.The active species in UV/PDS and UV/PMS systems are SO₄-·and·OH,the active species in UV/SPC system are CO₃^-·and·OH,and the active species in UV/SPB system are·OH.