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6CCVD Research

Treatment of hydrothermal carbonization process water by electrochemical oxidation - Assessment of process performance

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-11-13
JournalEnvironmental Research
AuthorsJudith Gonzålez-Arias, M.A. de la Rubia, M.E. Sånchez, Xiomar Gómez, Jorge Cara-Jiménez
InstitutionsUniversidad AutĂłnoma de Madrid, Universidad de LeĂłn
Citations21
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study investigates the feasibility and performance of Electrochemical Oxidation (EO) using a Boron Doped Diamond (BDD) anode for treating highly contaminated process water (PW) derived from the hydrothermal carbonization (HTC) of olive tree pruning.

  • Core Achievement: EO successfully removed complex organic matter from HTC process water, validating BDD technology for this challenging waste stream.
  • Efficiency Boost: The addition of supporting electrolytes (Na2SO4 or NaCl) was crucial, increasing Total Organic Carbon (TOC) removal efficiency to 30-40%, compared to only 17% in the control experiment (without conductivity adjustment).
  • Pollutant Degradation: Almost all initial chemical species identified via GC-MS were partially or totally removed after 300 minutes of EO treatment, confirming high mineralization capability.
  • VFA Reduction: The reduction in TOC and Chemical Oxygen Demand (COD) was corroborated by a corresponding decrease in Volatile Fatty Acids (VFAs), indicating effective breakdown of primary organic pollutants.
  • Cost Challenge: The process suffers from high Specific Energy Consumption (SEC), leading to significant treatment costs ranging from 1 to 45 €/kg CODremoved, highlighting the need for energy optimization or valuable chemical recovery.
  • Future Pathway: The work suggests EO as a promising step toward the sustainable utilization and valorization of HTC liquid byproducts within a circular economy framework.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Feedstock SourceOlive tree pruning PWN/ALiquid effluent from HTC (250 °C, 3 h)
Anode MaterialBoron Doped Diamond (BDD)N/ABi-polar operation mode
Cell Volume75mLCommercial flow cell
Electrode Area (Effective)42cm2Distance between electrodes: 5 mm
Applied Voltage25VConstant across all tests
Current Density Range1.38 to 11.79mA/cm2Dependent on conductivity and time
Initial COD (PWraw)19.73g/LHigh organic load
Initial TOC (PWraw)7.11g/LHigh organic load
Control Conductivity (A)1.44mS/cm2Without electrolyte addition
Na2SO4 Conductivity (B)10.90mS/cm2Supporting electrolyte added (~10 g/L)
NaCl Conductivity (C)15.80mS/cm2Supporting electrolyte added (~10 g/L)
Max TOC Removal (B/C)40%Achieved with supporting electrolytes (300 min)
Max TOC Removal (Control A)17%Without conductivity adjustment (300 min)
SEC Range3.68 to 156.89kWh/kg CODremovedHighly dependent on time and electrolyte
Cost Range1 to 44.56€/kg CODremovedBased on Spanish 2022 electricity price (0.284 €/kWh)

Key Methodologies

Section titled “Key Methodologies”
  1. Feedstock Generation (HTC): Olive tree pruning was processed via Hydrothermal Carbonization (HTC) at 250 °C for 3 hours (1/20 biomass/water ratio) to generate the highly contaminated Process Water (PW).
  2. EO Reactor Setup: Electrochemical oxidation was performed in a 75 mL batch cell utilizing a commercial BDD anode and cathode system (42 cm2 effective area) at a constant potential of 25 V.
  3. Electrolyte Conditions: Three distinct conditions were tested to assess the role of conductivity:
    • A (Control): Raw stored PW (low conductivity).
    • B (Na2SO4): Conductivity adjusted to 10 mS/cm2 using Na2SO4.
    • C (NaCl): Conductivity adjusted to 5 mS/cm2 using NaCl.
  4. Kinetic Assessment: Experiments were run for four reaction times (30, 60, 150, and 300 minutes) to evaluate the effect of duration on organic matter removal and byproduct formation.
  5. Performance Metrics: Process performance was quantified using standard wastewater metrics: Total Organic Carbon (TOC), Chemical Oxygen Demand (COD), and Volatile Fatty Acids (VFAs).
  6. Chemical Analysis: Gas Chromatography/Ion Trap Mass Spectrometry (GC-MS) was employed to identify and track the removal or generation of specific chemical species (phenols, furans, acids) before and after EO treatment.

Commercial Applications

Section titled “Commercial Applications”

The findings support the application of BDD-based Electrochemical Oxidation in several high-load waste management sectors:

  • Industrial Wastewater Treatment: Direct application for treating complex, recalcitrant liquid effluents from biomass conversion technologies (HTC, pyrolysis, torrefaction) where high COD and diverse organic species are present.
  • BDD Electrode Technology: Reinforces the commercial viability of BDD anodes for Advanced Oxidation Processes (AOPs) due to their superior ability to generate highly reactive hydroxyl radicals (·OH) and achieve high mineralization rates, even in low-conductivity solutions (when supplemented).
  • Circular Economy Integration: Provides a necessary treatment step for HTC process water, enabling the full valorization of agricultural waste (olive pruning) and reducing the environmental burden of the liquid byproduct.
  • Chemical Recovery: The identification of generated intermediate compounds (e.g., 1,3,5-Benzenetriol, Eucalyptol) suggests a potential strategy to integrate EO with downstream separation processes to recover valuable chemicals, thereby offsetting the high Specific Energy Consumption (SEC) costs.
  • Pharmaceutical and Complex Pollutant Remediation: The demonstrated effectiveness of BDD-EO in degrading complex aromatic rings and heterocyclic compounds is directly transferable to treating pharmaceutical or dye-contaminated industrial streams.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2022 - A comprehensive review on current technologies for removal of endocrine disrupting chemicals from wastewaters [Crossref]
  2. 2012 - Electrochemical oxidation of succinic acid in aqueous solutions using boron doped diamond anodes [Crossref]
  3. 2015 - Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods. An updated review [Crossref]
  4. 2009 - Electro-Fenton process and related electrochemical technologies based on Fenton’s reaction chemistry [Crossref]
  5. 2005 - Electrochemical oxidation of phenolic wastes with boron-doped diamond anodes
  6. 2021 - Electrochemical oxidation of organic pollutants in low conductive solutions
  7. 2021 - Electrochemically generated sulfate radicals by boron doped diamond and its environmental applications [Crossref]
  8. 2010 - Removal of acid green dye 50 from wastewater by anodic oxidation and electrocoagulation-A comparative study [Crossref]
  9. 2019 - Performance of electrochemical processes in the treatment of reverse osmosis concentrates of sanitary landfill leachate [Crossref]

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