The Influence On Phosphate While Using Fenton-like Oxidation To Remove Trichloroethylene From Groundwater

Trichloroethylene (TCE) is one of contaminants which can cause cancer,malformation and mutation. The widely application, the inappropriate dispose havemade TCE become a common contaminant in soil and groundwater.It is hard for TCEto be absorbed and easier to transport because of its relatively higher density andlower viscosity. With these properties, it can always stay at the bottom of aquifer to beDNAPLs pool(dense non-aqueous phase liquids). DNAPLs is difficult to be clean upand becomes the continuous contamination source.In this paper, we choose one of the In Situ Chemical Oxidation (ISCO) methods,Fenton-like Oxidation, to remove TCE from groundwater. There are two commonoxidation systems for Fenton-like method: siderite catalyzed hydrogen peroxidesystem which is called single oxidation system and siderite catalyzed hydrogenperoxide-sodium persulfate system which is called double oxidation system. Basedon groundwater treatment experience, inorganic ions in waste water always have animpact on the oxidation process of Fenton-like system. Basically, H2PO4-has thelargest impact on Fenton-like system. Therefore, we choose it as the target ion tostudy its influence mechanism on Fenton-like reactions. The main results are asfollows:Phosphate mostly presents as H2PO4-in both Fenton systems. With the increasingof the concentration of phosphate, the removal efficiency of TCE decreases. Whenphosphate concentration reaches100mg/L, the inhibiting effect for TCE removalefficiency stays stable. As for the reason, the surface of siderite seldom absorbsphosphate. This phenomenon is mostly caused by the complexation between iron ionand phosphate.The TCE removal process of Fenton system mainly depends on the free radicalfrom iron ion catalyzing oxidant. The influence of phosphate on single oxidationsystem has two ways: the decreasing amount of free radical when H2PO4-reacts withiron ion; H2PO4-will consume HO which supposed to be used for TCE. As for double oxidation system, there is one other impact besides the two mentioned above.It will decrease the SO4-yield since it decreases the concentration and energy of ironion.Increasing the usage of siderite from0.0229g to0.2290g, the removal efficiencyof TCE will increase from20%to60%then tends to be stable. More siderite willquench the hydroxyl radical. Fe2+and H2PO4-will start catalytic oxidizing reactionafter complexation while Fe3+and H2PO4-cannot. Besides, with the increase oftemperature, the reaction is more spontaneous and the TCE removal efficiencybecomes higher.In both Fenton systems, the chlorine balance increases with time. It can reachhigher than90%after48hours and almost realize dechlorination with no secondarypollution.