Editorial for the Special Issue “Novel Electrochemical Technologies for Energy Applications and Wastewater Treatment”

1. Introduction

Global population growth, combined with the energy-intensive demands of modern lifestyles, has led to a significant increase in energy demand, accompanied by the ongoing environmental burden due to the dependence on fossil fuels [1,2]. In this context, the development of environmentally friendly and efficient technologies is becoming an imperative need, both for meeting energy needs and for water decontamination [3]. Electrochemical technology is emerging as a key pillar towards this direction [4,5].

The present Special Issue focuses on innovative electrochemical technologies with dual applications, i.e., energy production and wastewater treatment. Research interest has particularly focused on new approaches, such as microbial fuel cells (MFCs) utilizing organic waste as a substrate for the bioelectrochemical degradation of pollutants, while simultaneously producing electricity. In addition, advanced methods such as electrochemical oxidation, the use of ultrasound assistance or 3D electrodes enhance the management of difficult pollutants, including pharmaceutical residues and heavy metals.

In the context of this effort, the recent publications included in the issue present important developments in areas such as the use of rice and sugarcane waste in MFCs, the degradation of hydroquinone and anastrozole, the removal of toxic metals through biofilms, as well as the enhancement of electrochemical activity through composite materials and intermittent ultrasonic action. The abovementioned developments highlight the potential of electro-biochemical technologies as tools for environmental protection and the transition towards green energy.

These developments not only highlight the flexibility of electrochemistry, but also its adaptability to real-world conditions where pollutants, water-matrix complexity and energy efficiency are critical factors. Integrating waste-to-energy strategies with novel electrochemical systems opens up new horizons for circular economy applications, offering sustainable alternatives to conventional treatment methods. As research continues to improve electrode materials, microbial consortia and system configurations, the role of electrochemistry-based technologies in addressing global environmental and energy challenges is expected to become even more important.

2. Overview of Published Articles

The work of Torlaema et al. [6] presents the combined utilization of rice waste as an organic substrate for the degradation of hydroquinone via a MFC. With 29 d of operation and an external resistance of 1000 Ω, a maximum voltage of 168 mV and 68% degradation of the pollutant were achieved, confirming the role of specific bacterial strains (Lacticaseibacillus sp., Pediococcus sp., Secundilactobacillus sp.) in electricity generation and biodegradation.

In the study by Dhawle et al. [7], the anodic electrochemical oxidation of the pharmaceutical contaminant anastrozole (ANZ) via a boron-doped diamond (BDD) electrode is examined. The removal of the contaminant (82.4%) was achieved within 90 min, while the effects of pH, current density, presence of chlorides and composition of the aqueous matrix were evaluated, demonstrating the potential of e-AOPs in the treatment of recalcitrant micropollutants.

Another work, by Ahmad et al. [8], explores the improvement of MFC performance through the use of novel anode materials, specifically graphene-zinc oxide (GO-ZnO) composite anodes. The examined systems achieved a power density of 1.05 mW/m² and efficient metal ion precipitation (Cd²⁺, Cr³⁺, Pb²⁺, Ni²⁺), highlighting the influence of the electrode material on electron transport and overall energy and detergent performance, where they were found to operate effectively for 30 d.

In the same context, the study by Aleid et al. [9] utilizes waste sugarcane extract as an organic substrate in MFC for the removal of Pb²⁺ and Hg²⁺ ions. With a maximum current density of 86.84 mA/m² and removal efficiencies of 82% and 74.85% for Pb²⁺ and Hg²⁺, respectively, the work highlights the value of biomass residues as viable substrates for enhancing electro-generation and bacterial activity.

Finally, the work of Long et al. [10] examines an alternative optimization strategy for non-aqueous redox flow batteries (Fe/V RFBs) using deep eutectic solvents (DES) and ultrasonic assistance. Through intermittent application of ultrasound, a reduction in energy consumption by ~50% is achieved while maintaining high electrochemical efficiency. The study highlights the significance of sonoelectrochemistry for mass transport optimization in systems with high viscosity.

3. Challenges and Perspectives

The papers collected in this Special Issue highlight the rapid development of electrochemical technologies as an innovative and promising approach to achieve sustainable decontamination and simultaneous energy recovery. The utilization of agricultural and industrial waste as organic substrates highlights the possibility of applying electro-assisted technologies at a local and decentralized level, enhancing the circular economy. At the same time, progress in the design of functional electrode materials, especially using nanostructured or composite materials [11], improves electrochemical performance, while opening prospects for increased stability and lifetime of the systems. In addition, the integration of physicochemical methods, such as ultrasonic assistance, could significantly improve mass transfer and reduce energy consumption, making the integrated systems more efficient and environmentally friendly. Non-aqueous electrolytes, such as deep eutectic solvents, appear as novel alternative electrolytes for high-energy-density applications, while the targeted exploitation of microbial communities, adapted to specific pollutants, is an emerging research field.

However, challenges remain, thus limiting the commercial deployment of these technologies. The scaling of MFC systems remains limited, mainly due to low power density and variability in microbial activity. Furthermore, the application of electrochemical technologies to real and complex waste streams requires further research to maintain efficiency under uncontrolled conditions, where the toxicity strongly depends on the operating conditions and electrolytes used. Cost management, selection of sustainable materials and energy balancing of processes are issues that need to be addressed in order to achieve the functional and environmental integration of these technologies.

Overall, the studies in the issue reinforce the belief that the convergence of electrochemistry with biotechnology and environmental engineering can offer clean, efficient and flexible solutions with a significant contribution to the transition towards a sustainable and green society. However, significant efforts are needed to overcome the barriers to implementation. These efforts must be at the interface of materials science, biology, electrochemistry and environmental and process engineering.