Remediation of 2,4-dichlorophenol-contaminated groundwater using nano-sized CaO2 in a two-dimensional scale tank

This study evaluates the applicability of nano-sized calcium peroxide (CaO2) as a source of H2O2 to remediate 2,4-dichlorophenol (2,4-DCP) contaminated groundwater via the advanced oxidation process (AOP). First, the effect and mechanism of 2,4-DCP degradation by CaO2 at different Fe concentrations were studied (Fenton reaction). We found that at high Fe concentrations, 2,4-DCP almost completely degrades via primarily the oxidation of .OH within 5 h. At low Fe concentrations, the degradation rate of 2,4-DCP decreased rapidly. The main mechanism was the combined action of .OH and O-2(.-). Without Fe, the 2,4-DCP degradation reached 13.6% in 213 h, primarily via the heterogeneous reaction on the surface of CaO2. Besides, 2,4-DCP degradation was significantly affected by solution pH. When the solution pH was>10, the degradation was almost completely inhibited. Thus, we adopted a two-dimensional water tank experiment to study the remediation efficiency CaO2 on the water sample. We noticed that the degradation took place mainly in regions of pH < 10 (i.e., CaO2 distribution area), both upstream and downstream of the tank. After 28 days of treatment, the average 2,4-DCP degradation level was approximate to 36.5%. Given the inadequacy of the results, we recommend that groundwater remediation using nano CaO2: (1) a buffer solution should be added to retard the rapid increase in pH, and (2) the nano CaO2 should be injected copiously in batches to reduce CaO2 deposition.

Automated summary

This study found that 2,4-DCP degrades rapidly at high Fe concentrations primarily through oxidation by hydroxyl radicals, while at low Fe concentrations, a combination of hydroxyl radicals and superoxide radicals play a role. Additionally, the degradation of 2,4-DCP was significantly affected by solution pH.