Removal of Recalcitrant Compounds from Winery Wastewater by Electrochemical Oxidation

At a Glance

Metadata	Details
Publication Date	2022-02-26
Journal	Water
Authors	Ana Baía, Ana Lopes, Maria João Nunes, Lurdes Ciríaco, Maria José Pacheco
Institutions	University of Beira Interior
Citations	11
Analysis	Full AI Review Included

Executive Summary

Core Technology Validation: Electrochemical Oxidation (EO) utilizing a Boron-Doped Diamond (BDD) anode proved highly effective for degrading recalcitrant compounds (Phthalic Acid, Tyrosol, Catechin) in real winery wastewater (WW).
High Removal Efficiency: Optimized treatment (14 h at 300 A m^-2) achieved >99.9% removal of all three target pollutants, reducing the final Chemical Oxygen Demand (COD) by 98.3% (to 97 mg L^-1).
Biodegradability Improvement: The process significantly enhanced the wastewater quality, increasing the biodegradability index (BOD₅/COD) from 0.39 (initial spiked WW) to 0.99 (treated WW).
Pollutant Behavior: Catechin degraded fastest but showed the lowest combustion efficiency (0.74), indicating rapid conversion to intermediate byproducts. Phthalic Acid showed constant combustion efficiency (1.00), suggesting easy mineralization.
Energy Optimization: Operating at the lowest tested current density (300 A m^-2) over a longer duration (14 h) provided the most efficient treatment in terms of applied charge and achieved the lowest specific energy consumption (53 kWh (kg COD)^-1).
Toxicity Reduction: Ecotoxicity towards the model organism Daphnia magna was reduced 1.3-fold, confirming the environmental benefit of the EO process, although non-toxic levels were not fully attained due to persistent short-chain acids.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Boron-Doped Diamond (BDD)	N/A	Electrochemical Cell
Cathode Material	Stainless Steel	N/A	Electrochemical Cell
Immersed Electrode Area	10	cm²	EO Setup
Interelectrode Gap	0.3	cm	EO Setup
Initial Spiked WW COD	5.7 ± 0.1	g L^-1	Before Treatment
Initial Spiked WW BOD₅/COD	0.39	N/A	Low Biodegradability
Optimized Current Density (j)	300	A m^-2	Lowest E_sp, 14 h run
Highest Current Density Tested (j)	900	A m^-2	Fastest removal rate (6 h run)
Optimized Treatment Time	14	h	To meet COD discharge limit
Final COD (14h run)	97 ± 2	mg L^-1	Meets Portuguese limit (150 mg L^-1)
Final BOD₅/COD (14h run)	0.99	N/A	Highly Biodegradable
PhA/T/C Removal (14h run)	>99.9	%	Below detection limit (<0.10 mg L^-1)
Specific Energy Consumption (E_sp)	53	kWh (kg COD)^-1	Optimized 14h run (300 A m^-2)
Electric Energy Consumption (E)	292	kWh m^-3	Optimized 14h run (300 A m^-2)
Phthalic Acid Combustion Efficiency (η_c)	1.00	N/A	Synthetic sample (PhA_1)
Catechin Combustion Efficiency (η_c)	0.74	N/A	Synthetic sample (C_1)
Toxicity Reduction Factor	1.3	fold	Towards Daphnia magna

Key Methodologies

The electrochemical oxidation (EO) experiments were conducted using the following parameters and analytical procedures:

Electrochemical Cell Configuration:
- Undivided cylindrical cell operating in batch mode with 230 mL sample volume.
- Anode: Commercial BDD electrode (10 cm² immersed area).
- Cathode: Stainless steel plate (10 cm² immersed area).
- Mixing: Continuous stirring at 250 rpm.
Wastewater Preparation:
- Real winery wastewater (WW) was collected and characterized (Initial COD: 5.14 g L^-1).
- WW was spiked (fortified) with target recalcitrant compounds (Phthalic Acid, Tyrosol, Catechin) to a concentration of 0.1 g L^-1 each.
Operational Conditions:
- Current Density (j) Study: 300, 500, 700, and 900 A m^-2 were evaluated.
- Supporting Electrolyte: 0.25 g L^-1 Na₂SO₄ was added for runs at j > 300 A m^-2 due to low WW electrical conductivity.
- Optimization Run: 300 A m^-2 without supporting electrolyte, prolonged to 14 h.
Analytical Monitoring:
- Organic Load: Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), and Biochemical Oxygen Demand (BOD₅) were measured periodically.
- Recalcitrant Compounds: High-Performance Liquid Chromatography (HPLC) was used for quantification of PhA, Tyrosol, and Catechin.
- Ecotoxicity: Assessed using the Daphnia magna microbiotest (EC₅₀-48 h) and expressed in Toxicity Units (TU).
- Performance Metrics: Combustion efficiency (η_c) and specific energy consumption (E_sp) were calculated to evaluate mineralization and cost effectiveness.

Commercial Applications

The BDD-based electrochemical oxidation technology demonstrated in this study is highly relevant for industrial wastewater management, particularly in sectors dealing with complex, recalcitrant organic loads:

Winery and Agro-Industrial Effluents: Direct application for treating high-volume, high-salinity WW, ensuring compliance with strict environmental discharge regulations (e.g., meeting COD limits and pH requirements).
Pharmaceutical and Chemical Manufacturing: Use as a tertiary treatment step for streams containing persistent organic pollutants (POPs), such as phenolic compounds (Tyrosol, Catechin) and aromatic acids (Phthalic Acid).
Pre-Treatment for Biological Systems: Implementation upstream of conventional biological wastewater treatment plants (WWTPs) to convert toxic, non-biodegradable components into readily biodegradable intermediates, significantly improving overall system efficiency (BOD₅/COD enhancement).
Advanced Oxidation Processes (AOPs): Integration into industrial AOP trains where the high oxidizing power and stability of BDD anodes are required for complete mineralization, minimizing sludge production compared to chemical methods.
Toxicity Control: Employing EO to reduce the ecotoxicity of industrial discharges, mitigating harmful effects on receiving water bodies and ecosystems.

View Original Abstract

The electro-oxidation of recalcitrant compounds, phthalic acid, tyrosol, and catechin was studied in simulated and real winery wastewater samples using a boron-doped diamond (BDD) anode. In the simulated samples, catechin, although presenting a higher removal rate than that of phthalic acid and tyrosol, attained lower combustion efficiency, indicating that this compound is readily converted into other products rather than being completely oxidized. On the other hand, phthalic acid was easily mineralized. Regarding the electro-oxidation assays performed with the spiked winery wastewater, recalcitrant compounds and overall organic load removal rates increased with applied current density (j), but the removal efficiency of recalcitrant compounds decreased with the increase in j, and the specific energy consumption was significantly raised. The increase in treatment time showed to be a feasible solution for the WW treatment at lower j. After 14 h treatment at 300 A m−2, phthalic acid, tyrosol, and catechin removals above 99.9% were achieved, with a chemical oxygen demand removal of 98.3%. Moreover, the biodegradability index was increased to 0.99, and toxicity towards Daphnia magna was reduced 1.3-fold, showing that the electro-oxidation process using a BDD anode is a feasible solution for the treatment of winery wastewaters, including phthalic acid, tyrosol, and catechin degradation.

Tech Support

Original Source

DOI: https://doi.org/10.3390/w14050750

References

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