Electrochemical Treatment of Effluent for the Removal of Contaminants of Emergent Concern and Culturable Microorganisms

Joana Dionísio,Paula Guedes,Cristiana Gonçalves,Alexandra Ribeiro,Nazaré Couto

doi:10.3390/w13040520

Abstract

The present work aims to study the electrochemical (EC) process applied for the removal of contaminants of emergent concern (CECs) from wastewater after secondary treatment and the effect of the process on the total culturable microorganisms. The EC experiments were performed in a cylindrical open reactor with 500 mL of effluent, and a fixed current density of 8 mA/cm² was applied through mixed metal oxide electrodes. The experiments were conducted in different sets. In the first round (Set 1), the effluent sample was spiked with three CECs (200 ppb each): caffeine (CAF), carbamazepine (CBZ), and oxybenzone (OXY). For the best treatment period, 6 h, electrodegradation rates ranged from 41 ± 7% for CAF to 95 ± 6% for OXY, with an 87% removal of total culturable microorganisms. In the second round (Set 2), aiming to assess EC process efficiency in a more complex CEC mixture, the effluent was spiked with six more CECs (200 ppb each): diclofenac (DCF), triclosan (TCS), bisphenol A (BPA), 17β-estradiol (E2), 17α-ethinylestradiol (EE2), and ibuprofen (IBU), giving a total of nine CECs. In this case, the EC process allowed decreasing the CEC content by 19–100% (below the limit of detection), depending on the effluent samples, and the culturable microorganisms by 99.98% after a 6 h treatment. By contributing to CEC degradation and microorganism removal, the EC process proved to be a viable remediation and disinfection technology for secondary effluent from wastewater treatment plants.

Highlights

Contaminants of emergent concern (CECs) have been found in several aquatic environments, and their ecological and human health impacts are still unknown, in general, their discharge into natural waterbodies is not regulated [1]
A simple electrochemical reactor showed to be a good alternative for the removal of contaminants of emergent concern and microorganisms from real secondary effluents
The experimental work was divided into two major setups, one (Set 1) testing the feasibility of the EC process after 2, 4 and 6 h and one (Set 2) in which different effluent samples were used for the tests and the complexity was increased by increasing the number of CECs from three to nine

Summary

Introduction

Contaminants of emergent concern (CECs) have been found in several aquatic environments, and their ecological and human health impacts are still unknown, in general, their discharge into natural waterbodies is not regulated [1]. Even though new legislation on wastewater reuse was released in May 2020 (on the minimum requirements for water reuse), the European regulation failed to impose a limit on CEC concentration, admitting that such a topic should be reviewed in the future [2]. WWTPs were not designed to remove these recalcitrant substances, which can be found in their effluent, ranging from ng/L up to mg/L [4,6]. Another risk arising from improperly treated wastewater is the possibility of exposure to residual waterborne bacteria and viruses, potential vectors of disease transmission [7]

Methods

Results

Conclusion