Advanced hybrid electro-oxidation & O3 technology for water reuse in the fruit and vegetable process industry.

Sonia Sanchis,Pedro Gomez,Javier Pinedo,Julia Garcia-Montaño,Jose Guillermo Berlanga,Javier Donato,David Gali,Vicent Sala

doi:10.2166/wst.2021.297

Abstract

Alternative sanitising agents are required in the fruit and vegetable processing industry, capable of effectively disinfecting both the product and the washing water to increase its reuse, while not producing harmful by-products like chlorine-based agents. In the present work, electro-oxidation (EO) and ozone are proposed for vegetable process water reuse, being optimised for their individual and combined application. The application of hybrid electro-oxidation and ozone achieved 7 log reduction after 15 min of treatment in batch using boron-doped diamond (BDD) as anode material, showing important synergistic effects when compared with the individual treatments. When the process was applied in continuous mode, up to 6 log reduction of total bacteria was achieved using EO alone with Ru as the anode and stainless steel as the cathode, under 11 mA/cm2 of current density, a cell retention time of 12 s and no addition of chemical reagents (electrolyte). Under these conditions, the absence of microorganisms in water was maintained for more than 24 h, no harmful by-products (chlorate, bromate) were detected and no damage to lettuce seeds were observed when evaluating water reuse potential.

Highlights

In the fruit and vegetable process industry, washing is designed to remove dirt, pesticide residues and microorganisms responsible for quality loss
Disinfection capacity increased up to 6 log after 60 min of treatment under the mentioned conditions It is important to consider that using low current densities avoids the appearance of dangerous disinfection by-products (DBPs) such as perchlorate and trihalomethanes (Cano et al 2012), so current densities above 29 mA/cm2 were avoided in the present work, and DBPs were analysed once the technology was totally optimised, ensuring their absence in the treated water
Water conductivity highly affects the EO process: treating water with 100 μS/cm instead of 550 μS/cm caused an increase in voltage from 40 to 75 V and a decrease of almost 2 log in disinfection capacity This observation corresponds to previous recommendations which suggest that electro-oxidation leads to better disinfection yields and lower electricity consumption when treating waters that have moderate to high conductivity (Hand & Cusick 2021)

Summary

Introduction

In the fruit and vegetable process industry, washing is designed to remove dirt, pesticide residues and microorganisms responsible for quality loss. Important in the fruit and vegetable process industry to clean and hygienise, removing soil and debris, but especially to avoid cross-contamination between clean and contaminated product. Chlorinated agents are used worldwide for disinfecting water and wastewater, due to their ease of use and relative low cost. Hyperchlorination of water with high total organic carbon (TOC) content may produce unacceptably high levels of disinfection by-products (DBPs) such as trihalomethanes. EO is an effective, environmentally sustainable, and versatile technology based on the electro-generation of high reactive species (·OH, H2O2, O3, chloride-derived species, etc.) with high oxidation potentials (2.08 eV for O3 and 2.8 eV for ·OH) compared to hypochlorite (1.48 eV), resulting in promising technologies for disinfection (Barrera-Diaz et al 2014)

Methods

Results

Conclusion