Treatment of Produced Water Using a Pilot-Scale Advanced Electrochemical Oxidation Unit

At a Glance

Metadata	Details
Publication Date	2025-03-12
Journal	Molecules
Authors	Bassam Tawabini, Abdullah A. Basaleh
Institutions	King Fahd University of Petroleum and Minerals
Citations	2
Analysis	Full AI Review Included

Executive Summary

This study successfully optimized the treatment of high-salinity synthetic Produced Water (PW) using a pilot-scale Advanced Electrochemical Oxidation (EO) system featuring a Boron-Doped Diamond (BDD) anode.

Core Technology: A pilot-scale electrochemical treatment system (ETS) utilized a BDD anode and a carbon-PTFE Gas Diffusion Electrode (GDE) cathode for efficient organic pollutant degradation.
Feedstock Challenge: Synthetic PW simulated real-world effluent, characterized by high Total Dissolved Solids (TDS 16,200 mg/L) and a moderate Total Organic Carbon (TOC 250 mg/L) load.
Optimization Results: Response Surface Methodology (RSM) confirmed that electric current density and initial pH were the most significant factors influencing TOC removal efficiency. Airflow had a statistically insignificant impact.
Peak Performance: A maximum TOC removal efficiency of 84% was achieved within 4 hours (240 minutes) of electrooxidation.
Optimal Conditions: The best performance was obtained at the highest tested levels: 200 mA/cm² current density, pH 12, and 2 NL/min airflow.
Kinetic Behavior: The degradation kinetics shifted from pseudo-second-order (mass transfer limited) at low current densities to pseudo-first-order (reaction limited by TOC concentration) at high current densities and high pH.
Value Proposition: The results confirm the substantial potential of BDD-based EO systems for large-scale, robust treatment of complex, high-salsalinity industrial wastewater.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Boron-Doped Diamond (BDD)	N/A	Electrochemical Cell
Cathode Material	Carbon-PTFE	GDE	Electrochemical Cell
Effective Electrode Area	0.01	m²	Electro MP Cell
Maximum Current Supply	22	A	DC Power Source
Maximum Voltage Supply	70	V	DC Power Source
Initial TOC Concentration	250 ± 30	mg/L	Synthetic Produced Water (PW)
Initial TDS Concentration	16,200 ± 400	mg/L	Synthetic Produced Water (PW)
Initial Conductivity	24,320 ± 300	µS/cm	Synthetic Produced Water (PW)
Optimal Current Density (C)	200	mA/cm²	Maximum TOC removal
Optimal pH (B)	12	N/A	Maximum TOC removal
Optimal Airflow (A)	2	NL/min	Maximum TOC removal
Maximum TOC Removal	84	%	Achieved in 240 min at optimal conditions
Optimal Reaction Time	240 (4)	min (h)	Time for 84% TOC removal
RSM Model F-Value	8.37	N/A	Indicates model significance (p-value 0.0057)
RSM Adjusted R²	0.6482	N/A	Model Fit
Current Density Range Tested	50 to 200	mA/cm²	Independent variable C
pH Range Tested	2 to 12	N/A	Independent variable B
Airflow Range Tested	0 to 4	NL/min	Independent variable A

Key Methodologies

Synthetic PW Synthesis: Brine was prepared by dissolving salts (including NaCl, Na₂SO₄, CaCl₂, MgCl₂) and phenol in deionized water to achieve a TDS of 16,200 mg/L.
Oil Emulsion Preparation: A mixture of three crude oil types (730 mg total) and Sodium Dodecyl Sulfate (SDS) surfactant (150 mg) was prepared, maintaining a 5:1 oil-surfactant weight ratio.
Emulsion Stabilization: The mixture was agitated at 1000 rpm for 30 minutes, followed by 30 minutes of sonication to stabilize the oil-in-water emulsion.
Sample Preparation: After 4 hours of settling to remove free oil, the aqueous layer was collected, adjusted to 2.5 L, and characterized (Initial TOC 250 mg/L).
Pilot System Operation: The Electrochemical Treatment System (ETS) utilized a BDD anode and a GDE cathode (0.01 m² effective area) in a batch recirculation mode.
Recirculation Rate: The PW sample (2.5 L) was continuously circulated through the cell at a constant flow rate of 0.2 m³/h.
Optimization Design: Response Surface Methodology (RSM) using a Box-Behnken Design (BBD) was employed to optimize the three independent variables: Current Density (50-200 mA/cm²), Initial pH (2-12), and Airflow Rate (0-4 NL/min).
Kinetic Analysis: Experimental data were fitted to pseudo-first-order and pseudo-second-order kinetic models to determine the rate-limiting steps under varying current and pH conditions.

Commercial Applications

The BDD-based electrochemical oxidation technology demonstrated in this pilot study is highly relevant for industries generating complex, high-salinity organic wastewater.

Oil and Gas Production: Essential for treating Produced Water (PW), the largest waste stream in the sector, enabling compliance with discharge regulations or facilitating water reuse for fracking and injection.
Petrochemical and Refining: Used for the robust degradation of toxic, non-biodegradable compounds (e.g., phenols, BTEX, COD) found in refinery effluents, where conventional methods are ineffective.
Industrial Brine Management: Applicable to any industrial process generating high-TDS wastewater (e.g., desalination reject brine, mining effluent) contaminated with persistent organic pollutants.
Water Reclamation: Serves as an effective pre-treatment step for membrane processes (like Reverse Osmosis) by significantly reducing the organic load and fouling potential of the feed water.
Advanced Oxidation Systems: Deployment in municipal or industrial facilities requiring high-efficiency, chemical-free oxidation for complete mineralization of trace contaminants (e.g., pharmaceuticals, pesticides, dyes).

View Original Abstract

The main goal of this study is to optimize the treatment of produced water (PW) using a pilot-scale advanced electrochemical oxidation unit. The electro-cell is outfitted with a boron-doped diamond BDD anode and gas diffusion (GDE) cathode. Synthetic PW was prepared in the laboratory following a protocol designed to closely replicate the characteristics of real PW. The PW used in this study had a total dissolved solids (TDS) concentration of 16,000 mg/L and a total organic carbon (TOC) concentration of 250 mg/L. The effect of various electrooxidation parameters on the reduction in TOC was investigated including pH (2-12), electric current (I) (50-200 mA/cm2), and airflow rate (0-4 NL/min). Response surface method RSM with a Box-Behnken design at a confidence level of 95 percent was employed to analyze the impact of the above factors, with TOC removal used as a response variable. The results revealed that the TOC level decreased by 84% from 250 to 40 mg/L in 4 h, current density of 200 mA/cm2, pH of 12, and airflow rate 2 (NL/min). The investigation verified the influential role of diverse operational factors in the treatment process. RSM showed that reducing the airflow rate and increasing pH levels and electric current significantly enhanced the TOC removal. The obtained results demonstrated profound TOC removal, confirming the substantial potential of treating PW using the electrochemical method.

Tech Support

Original Source

DOI: https://doi.org/10.3390/molecules30061272

References

2017 - Microbial distribution and variation in produced water from separators to storage tanks of shale gas wells in Sichuan Basin, China
2017 - An overview on exploration and environmental impact of unconventional gas sources and treatment options for produced water [Crossref]
2019 - Produced water characteristics, treatment and reuse: A review [Crossref]
2023 - A review of waste management approaches to maximise sustainable value of waste from the oil and gas industry and potential for the State of Qatar [Crossref]
2023 - Produced Water Treatment: Review of Technological Advancement in Hydrocarbon Recovery Processes, Well Stimulation, and Permanent Disposal Wells
2024 - Comprehensive insights into the impact of oil pollution on the environment