Model development of bioelectrochemical systems: A critical review from the perspective of physiochemical principles and mathematical methods

Evaluating advancements and opportunities in electro-assisted biodehalogenation of emerging halogenated contaminants

Electro-assisted biodehalogenation (EASB) as a biostimulation strategy can accelerate the slow attenuation of emerging halogenated contaminants (EHCs) in anaerobic aqueous environments. A timely review is urgent to evaluate the knowledge gaps and potential opportunities, further facilitating its design and application. Till now, EASB achieves promising progress in accelerating biohalogenation rates, promoting the detoxification of EHCs to cope with unfavourable environments and mitigating greenhouse gas emissions. However, EASB of EHCs still faces several knowledge gaps. Exploring crucial microbes and deciphering insights into dehalogenase characteristics and extracellular electron transfer (EET) pathways remain the prominent task for EASB of EHCs. Moreover, microbial ecological relationships and intricate environmental factors affecting performances and applications are largely underexplored. The emergence of emerging tools holds promises for sorting the intricate changes and addressing these knowledge gaps. Judicious use of emerging tools will rejuvenate EASB strategy, from EET to scale-up, to purposefully and effectively address cascading EHCs.

Modeling the effect of external load variations on single, serie and parallel connected microbial fuel cells

This paper presents a microbial fuel cell (MFC) model designed to analyze the effect of the external load on MFC performance. The model takes into account the voltage and the chemical oxygen demand (COD) dependence on the external load. The value of the model parameters were calibrated by means of the voltage relaxation method tests using a controlled load current. Laboratory measurements and MATLAB Simulink model computations were used to validate the proposed model. The tests results demonstrated that the proposed model accurately predicts the voltage and COD evolution during the batch cycle of the MFC. The root mean square error (RMSE) was used to assess the fitting goodness of the model. The RMSE of COD and voltage generation was in all the cases lower than 4%, predicting accurately the behaviour of single MFC as well as MFC connected in series or parallel.

Mechanistic and data-driven modeling of carbon respiration with bio-electrochemical sensors

Bioelectrochemical sensor (BES) technologies have been developed to measure soluble carbon concentrations in wastewater. However, architectures and analytical methods developed in controlled laboratory environments fail to predict BES behavior during field deployments at water resource recovery facilities (WRRFs). Here, we examine the possibilities and obstacles associated with integrating BESs into environmental sensing networks and machine learning algorithms to monitor the biodegradable carbon dynamics and microbial metabolism at WRRFs. This approach highlights the potential of BESs to provide real-time insights into full-scale biodegradable carbon consumption across WRRFs.

Regulating microbial redox reactions towards enhanced removal of refractory organic nitrogen from wastewater

Biotechnology for wastewater treatment is mainstream and effective depending upon microbial redox reactions to eliminate diverse contaminants and ensure aquatic ecological health. However, refractory organic nitrogen compounds (RONCs, e.g., nitro-, azo-, amide-, and N-heterocyclic compounds) with complex structures and high toxicity inhibit microbial metabolic activity and limit the transformation of organic nitrogen to inorganic nitrogen. This will eventually result in non-compliance with nitrogen discharge standards. Numerous efforts suggested that applying exogenous electron donors or acceptors, such as solid electrodes (electrostimulation) and limited oxygen (micro-aeration), could potentially regulate microbial redox reactions and catabolic pathways, and facilitate the biotransformation of RONCs. This review provides comprehensive insights into the microbial regulation mechanisms and applications of electrostimulation and micro-aeration strategies to accelerate the biotransformation of RONCs to organic amine (amination) and inorganic ammonia (ammonification), respectively. Furthermore, a promising approach involving in-situ hybrid anaerobic biological units, coupled with electrostimulation and micro-aeration, is proposed towards engineering applications. Finally, employing cutting-edge methods including multi-omics analysis, data science driven machine learning, technology-economic analysis, and life-cycle assessment would contribute to optimizing the process design and engineering implementation. This review offers a fundamental understanding and inspiration for novel research in the enhanced biotechnology towards RONCs elimination.

Bioelectrochemical reactor to manage anthropogenic sulfate pollution for freshwater ecosystems: Mathematical modeling and experimental validation

Anthropogenic sulfate loading into otherwise low-sulfate freshwater systems can cause significant ecological consequences as a biogeochemical stressor. To address this challenge, in situ bioremediation technologies have been developed to leverage naturally occurring microorganisms that transform sulfate into sulfide rather than implementing resource-intensive physio-chemical processes. However, bioremediation technologies often require the supply of electron donors to facilitate biological sulfate reduction. Bioelectrochemical systems (BES) can be an alternative approach for supplying molecular hydrogen as an electron donor for sulfate-reducing bacteria through water electrolysis. Although the fundamental mechanisms behind BESs have been studied, limited research has evaluated the design and operational parameters of treatment systems when developing BESs on a scale relevant to environmental systems. This study aimed to develop an application-based mathematical model to evaluate the performance of BESs across a range of reactor configurations and operational modes. The model was based on sulfate transformation by hydrogenotrophic sulfate-reducing bacteria coupled with the recovery of solid iron sulfide species formed by the oxidative dissolution of dissolved ferrous iron from a stainless steel anode. Sulfate removal closely corresponded to the rate of electrolytic hydrogen production and hydraulic residence time but was less sensitive to specific microbial rate constants. The mathematical model results were compared to experimental data from a pilot-scale BES tested with nonacidic mine drainage as a case study. The close agreement between the mathematical model and the pilot-scale BES experiment highlights the efficacy of using a mathematical model as a tool to develop a conceptual design of a scaled-up treatment system.

Spatially-assembled binary carbon anode synergizing directional electron transfer and enriched microbe accommodation for wastewater treatment and energy conversion: From simulation to experiments

Bioelectrochemical systems (BESs) hold prospects in wastewater energy and resource recovery. Anode optimization is important for simultaneous enhancement of wastewater energy conversion and effluent quality in BESs. In this study, a multi-physics model coupling fluid flow, organic degradation and electrochemical process was constructed to guide the design and optimization of BES anodes. Based on the multi-physics simulation, spatially-assembled binary carbon anodes composed of three-dimensional carbon mesh skeleton and granular activated carbon were proposed and established. The granular activated carbon conducive to microbe accommodation played a vital role in improving effluent water quality, while the carbon mesh skeleton favoring electron collection and transfer could enhance the bioelectricity output. With an average chemical oxygen demand (COD) removal rate of 0.442 kg m-3 d-1, a maximum power density of 20.6 W m-3 was achieved in the optimized composite anode BES, which was 25% and 154% higher than carbon mesh skeleton BES and granular activated carbon BES. Electroactive bacteria were enriched in composite anodes and performed important functions related to microbial metabolism and energy production. The spatially-assembled binary carbon anode with low carbon mesh packing density was more cost-effective with a daily energy output per anode cost of 221 J d-1 RMB-1. This study not only provides a cost-efficient alternative anode to simultaneously improve organic degradation and power generation performance, but also demonstrates the potential of multi-physics simulation in offering theoretical support and prediction for BES configuration design as well as optimization.

Advances and challenges in biocathode microbial electrolysis cells for chlorinated organic compounds degradation from electroactive perspectives

Microbial electrolysis cell (MEC) is a promising in-situ strategy for chlorinated organic compound (COC) pollution remediation due to its high efficiency, low energy input, and long-term potential. Reductive dechlorination as the most critical step in COC degradation which takes place primarily in the cathode chamber of MECs is a complex biochemical process driven by the behavior of electrons. However, no information is currently available on the internal mechanism of MEC in dechlorination from the perspective of the whole electron transfer procedure and its dependent electrode materials. This review addresses the underlying mechanism of MEC on the fundamental of the generation (electron donor), transmission (transfer pathway), utilization (functional microbiota) and reception (electron acceptor) of electrons in dechlorination. In addition, the vital role of varied cathode materials involved in the entire electron transfer procedure during COC dechlorination is emphasized. Subsequently, suggestions for future research, including model construction, cathode material modification, and expanding the applicability of MECs to removal gaseous COCs have been proposed. This paper enriches the mechanism of COC degradation by MEC, and thus provides the theoretical support for the scale-up bioreactors for efficient COC removal.