Electrolytic circulation well drives chemical oxidation of TCE in a simulated aquife

doi:10.13745/j.esf.sf.2021.2.1

Abstract

Abstract:

Traditional groundwater remediation by in-situ chemical oxidation has the problem of short transport distance and low utilization efficiency for oxidants. In this study, a two-well groundwater circulation mode was applied to enhance mass transfer; and electrolysis in the injection well was utilized to generate O₂ and H₂ in-situ. In order to use Fe(Ⅱ) in sediments for TCE degradation, ethylenediamine tetraacetic acid (EDTA) was added to chelate Fe(Ⅱ) and increase •OH production. The system performance was evaluated in a two-dimensional sandy tank filled with interlayers of sand and clay. The current was set to 0.2 A and the flow rate was 72 cm/d. Results from a 9-day experiment showed that 3 mg/L TCE was degraded down to 1 mg/L (67% removal). Addition of 0.5 mmol/L EDTA before electrolysis increased the dissolved Fe(Ⅱ) concentration in the aquifer from 0-2 mg/L to 4-14 mg/L after a day of hydraulic circulation, with the higher concentrations around clay fillings. During electrolysis, groundwater circulation promoted the effective contacts and reactions of O₂, Fe(Ⅱ)-EDTA and TCE for TCE degradation. In the early stage, the rates of Fe(Ⅱ) oxidation and TCE degradation were slower around clay fillings than in other areas, but the gap gradually decreased in the later stage. Adding acetate upon completion of electrolysis promoted Fe cycling and utilization in the aquifer. This remediation process improved the oxidant transport distance through groundwater circulation and the oxidant utilization efficiency through use of relatively stable O₂and Fe(Ⅱ)-EDTA from aquifer, demonstrating its potential application in the remediation of organic pollution in groundwater.

Key words: electrochemistry, circulation well, chemical oxidation, ferrous iron, trichloroethylene

CLC Number:

X523
X505

LIU Yang, XIE Wenjing, ZHENG Yunsong, ZHANG Yaoqiang, CAI Qizheng, YUAN Songhu. Electrolytic circulation well drives chemical oxidation of TCE in a simulated aquife[J]. Earth Science Frontiers, 2021, 28(5): 197-207.

Figures/Tables 8

Fig.1 Schematic diagram of two-dimensional sand tank experiment

Fig.2 Variations of DO (a), dissolved Fe(Ⅱ) (b) and TCE (c) concentrations during dynamic operation

Fig.3 Variations of EDTA (a) and total dissolved Fe (b) concentrations during dynamic operation

Fig.4 Temporospatial variations of dissolved Fe(Ⅱ) concentration during the second EGCW treatment

Fig.5 Temporospatial variations of TCE concentration during the second EGCW treatment

Fig.6 Temporal profile of TCE degradation (a), and variations of EDTA (b) and dissolved Fe(Ⅱ) and total dissolved Fe (c) concentrations in static system

Fig.7 Schematic diagram of TCE degradation mechanism in tank system

Fig.8 Variations of DH (a) and N O 3 - and N O 2 - (b) concentrations during dynamic operation

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