Key Takeaways & Executive Findings
- •• • The PPy-PPCH3BO3-CC anode, derived from pomelo peel biochar activated with H3BO3 and modified with polypyrrole, achieved a charge transfer resistance (Rct) of 12.82 Ω, a 74.64% reduction compared to the unactivated PPy-PPC-CC electrode, and delivered a maximum power density of 478.03 mW·m−2, a 79.71% improvement, underscoring its potential for cost-effective, high-performance MFC anodes. • • Addition of Scutellaria baicalensis extract as a natural electron mediator increased the maximum output voltage to (637±10) mV, power density to 586.68 mW·m−2, and Coulombic efficiency to (66.94±1.02)%, representing respective enhancements of 7.06%, 22.63%, and 21.95% over the control, while also prolonging high-voltage output duration, indicating superior electron shuttle capability. • • In the combined system treating methyl orange wastewater, the maximum output voltage was (587±10) mV, power density 423.12 mW·m−2, Coulombic efficiency (57.85±1.06)%, and decolorization rate (95.86±1.12)%, with a 9.11%, 36.86%, 26.78%, and 5.63% improvement over the control, respectively, and a significantly reduced internal resistance of 7.15 Ω, demonstrating synergistic enhancement of electricity generation and dye degradation. • • The use of pomelo peel, an abundant agricultural waste, as a precursor for high-performance biochar anodes, combined with plant-derived EMs, offers a sustainable and low-cost strategy to overcome the bottlenecks of expensive anode materials and synthetic mediators, aligning with green chemistry principles and circular economy goals.
Abstract
To enhance the electricity generation and decolorization efficiency of bioelectrochemical systems (BES) for azo dye wastewater, this study introduced pomelo peel biochar as anode material and flavonoid-rich Chinese herbal medicines as electron mediators (EMs) into microbial fuel cells (MFCs). The anodes were prepared by chemical activation with KOH, ZnCl2, and H3BO3, followed by polypyrrole (PPy) modification. Among the modified anodes, PPy-PPCH3BO3-CC exhibited the best electrochemical performance. The EMs were derived from aqueous extracts of Scutellaria baicalensis (Huangqin), Ginkgo biloba leaves, and Pueraria lobata (Gegen). The extract from Scutellaria baicalensis showed the highest electron transfer capability. In the MFC system equipped with the optimal anode and Scutellaria baicalensis extract, the maximum output voltage reached (587±10) mV, power density increased to 423.12 mW·m−2, Coulombic efficiency was (57.85±1.06)%, COD removal efficiency was (77.45±0.92)%, charge transfer resistance (Rct) decreased to 7.15 Ω, and methyl orange decolorization rate reached (95.86±1.12)%. These results were significantly superior to the control group, demonstrating that natural source materials can effectively enhance the performance of BES for methyl orange wastewater treatment.
1. Introduction
Bioelectrochemical systems, particularly microbial fuel cells (MFCs), have attracted considerable attention for their dual functionality in wastewater treatment and energy recovery. However, their practical application is hindered by insufficient power output and high operational costs, primarily due to limited electron transfer capability of anode materials and slow microbe-electrode electron transfer kinetics. Conventional carbon-based anodes, such as carbon fiber, are expensive and their production may cause environmental pollution. To address these challenges, researchers have explored two main strategies: developing high-conductivity modified anodes and introducing exogenous electron mediators (EMs) to facilitate electron shuttling. While synthetic and biosynthetic EMs are effective, they often suffer from high production costs and potential secondary pollution. Therefore, there is a pressing need for green, economical, and naturally derived materials that can enhance MFC performance without compromising environmental sustainability.
This study introduces a novel approach by utilizing pomelo peel, an abundant agricultural waste, as a precursor for biochar anodes, and flavonoid-rich Chinese herbal medicines (Scutellaria baicalensis, Ginkgo biloba, and Pueraria lobata) as natural EMs. The pomelo peel biochar was chemically activated with KOH, ZnCl2, and H3BO3, and further modified with polypyrrole to enhance its electrochemical properties. The herbal extracts were evaluated for their electron transfer capabilities. The optimal combination was then applied to treat methyl orange (MO), a model azo dye, in MFCs. This integrated strategy aims to simultaneously improve electricity generation and dye decolorization efficiency, offering a cost-effective and environmentally friendly solution for azo dye wastewater treatment, thereby addressing the key bottlenecks of current MFC technologies.
Loading authentic research manuscript (Pages 1–5)...
WANG Xinyao, WANG Haiman, WANG Guiqiang, ZHANG Shuyue (2026). Enhanced Performance of Bioelectrochemical Systems Using Natural Source Materials for Methyl Orange Wastewater Treatment. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202509019
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the long-term stability of the PPy-PPCH3BO3-CC anode under continuous operation, and how does it compare to conventional carbon cloth anodes in terms of fouling and performance degradation?
The study reports that the PPy-PPCH3BO3-CC anode achieved a low charge transfer resistance (Rct) of 12.82 Ω and maintained high performance during the experimental period. However, long-term stability data beyond the reported operational timeframe are not provided. Conventional carbon cloth anodes typically suffer from biofilm fouling and performance decline over extended operation. The polypyrrole modification and biochar structure may offer improved resistance to fouling due to enhanced surface properties, but further long-term studies are required to confirm this advantage.
What is the cost-effectiveness of using pomelo peel biochar and herbal extracts compared to commercial anode materials and synthetic electron mediators?
Pomelo peel is an abundant agricultural waste with minimal cost, and its conversion to biochar involves simple chemical activation and pyrolysis steps. In contrast, commercial carbon fiber anodes are expensive. The herbal extracts, particularly from Scutellaria baicalensis, are derived from readily available plant materials, offering a low-cost alternative to synthetic mediators like neutral red or anthraquinone-2,6-disulfonate. The study demonstrates significant performance enhancements, suggesting that the cost-benefit ratio is favorable, though a detailed economic analysis is not provided.
How does the addition of Scutellaria baicalensis extract affect the microbial community structure and activity in the MFC anode biofilm?
The study focuses on electrochemical performance and does not include microbial community analysis. However, the enhanced Coulombic efficiency and reduced internal resistance suggest improved electron transfer, possibly due to the flavonoid compounds acting as redox mediators that facilitate interaction between microbes and the anode. Future studies should investigate the microbial community dynamics to understand the mechanistic basis of the observed improvements.
What is the scalability potential of this approach for industrial-scale treatment of azo dye wastewater, considering factors such as reactor design, mass transfer, and continuous operation?
The study was conducted in a laboratory-scale H-type MFC with a working volume of 100 mL. Scaling up to industrial levels would require addressing challenges such as electrode surface area, reactor configuration (e.g., flat-plate or tubular designs), and hydraulic retention times. The use of low-cost materials and natural EMs is advantageous for scale-up, but pilot-scale studies are necessary to evaluate performance under real-world conditions, including variable wastewater composition and flow rates.
What are the specific mechanisms by which flavonoids in Scutellaria baicalensis enhance electron transfer in MFCs, and are there any potential side effects or degradation products?
Flavonoids possess redox-active moieties that can undergo reversible oxidation-reduction reactions, enabling them to act as electron shuttles between microbial cells and the anode. The study observed a significant reduction in charge transfer resistance (Rct) to 7.15 Ω, indicating improved interfacial electron transfer. The degradation products of flavonoids in MFC environments are not characterized, but they are likely biodegradable and non-toxic, given the natural origin. Further research is needed to identify any intermediate compounds and assess their environmental impact.
Related Chinese Research & Cross-Citations
Analysis of National and Local Policies for Medical Waste Treatment and Disposal in China
The escalating generation of medical waste, driven by healthcare expansion and frequent medical activities, poses significant environmental and public health risks. Under the framework of ecological civilization, China is developing a comprehensive policy system for medical waste treatment and disposal, yet the current framework remains nascent and exhibits inconsistencies between national and local policies. This study systematically analyzes the status of national and local policies from 2003 to 2024, collecting 413 policy documents (166 from national ministries and 247 from provincial governments). The analysis examines temporal evolution, regional distribution, and policy focus, alongside the influence of medical waste output, treatment technologies, facility infrastructure, and major epidemic responses. Findings reveal distinct policy phases: initial self-disposal, exploratory management, foundational system building, and rapid development. Regional disparities are pronounced, with eastern coastal areas showing more advanced policies due to greater technical and financial resources. The surge in medical waste, particularly during the COVID-19 pandemic, underscores the need for enhanced regulatory guidance. Non-incineration technologies are gaining traction for their environmental and cost benefits, and facility coverage has improved but remains uneven. The study proposes five policy principles to foster technological innovation and industrial upgrading, ensuring safe medical waste management and environmental protection.
Kinetic Analysis and Simulation of Pollutant Removal in Sewage Networks
This study investigates pollutant removal characteristics and kinetic behaviors in sewage networks, and analyzes their impact on the carbon-to-nitrogen ratio (C/N, as COD/TN) of influent to wastewater treatment plants. Source water quality sampling at drainage outlets revealed spatial and temporal variations in C/N, with domestic sewage exhibiting higher C/N than industrial sewage, and diurnal peaks reaching 6.92 versus 4.71 during off-peak hours. Using a pilot-scale adjustable sewage network system in Kunshan, experiments were conducted under high (0.491 m·s−1) and low (0.089 m·s−1) flow velocities, monitoring pollutant removal over 144 hours. Pseudo-first-order kinetics were applied to model COD and TN removal. Results showed that COD (including SCOD and PCOD), BOD5, and SS achieved approximately 80% removal within 144 h, with higher removal at low flow velocity. TN, NH3-N, and TP exhibited lower overall removal rates. Kinetic fitting revealed that COD removal rate constants (kCOD) were significantly higher than those for TN (kTN), and both decreased with increasing flow velocity: at low velocity, kCOD=0.0167 h−1 and kTN=0.0029 h−1; at high velocity, kCOD=0.0127 h−1 and kTN=0.0020 h−1. Simulations based on actual source pollutant concentrations indicated that the time for C/N to drop to the denitrification critical value of 4.50 was 12.24 h at high velocity, but shortened to 9.49 h at low velocity. These findings demonstrate that increasing flow velocity effectively retards the decline of C/N. Therefore, regulating network flow velocity to reduce hydraulic retention time is a key strategy for maintaining adequate C/N at the terminal and ensuring denitrification efficiency in wastewater treatment plants.
Preparation of Trimetallic-Carbon Composite Catalysts and Their Application in Catalytic Ozonation of Industrial Wastewater
Advanced oxidation processes (AOPs) are promising for degrading organic pollutants in water treatment. Heterogeneous catalytic ozonation (HCO) has gained attention due to its high oxidation efficiency, strong interference resistance, and low secondary pollution. In this study, a series of trimetallic-carbon composite ozone catalysts were prepared via an organic precursor calcination method using γ-Al2O3 as support. This method enhanced catalytic activity and mechanical strength while overcoming the limitations of carbon materials (low mechanical strength) and metal-based materials (poor mass transfer). The optimized catalyst, CA-FeCoCu, comprising Fe, Co, Cu, carbon, and alumina, exhibited excellent performance in phenol degradation and real industrial wastewater treatment. Characterization revealed that the synergistic effect of trimetals and the introduction of multiple carbon types increased specific surface area and hydroxyl radical (·OH) generation. In a pilot-scale fixed-bed reactor, the CA-FeCoCu/O3 system reduced COD from 120 mg·L−1 to below 40 mg·L−1, with an O3 consumption ratio (O/C) of less than 1, effectively lowering operational costs. This work provides a new strategy for developing efficient and stable heterogeneous O3 catalysts and offers a reference for the practical application of HCO in industrial wastewater treatment.
Differentiated Characteristics of Suspended Particulate Matter and Their Effects on Water Quality in the Middle and East Routes of the South-to-North Water Diversion Project
This study investigates the spatiotemporal differentiation of suspended particulate matter (SPM) characteristics, sources, and their impacts on water quality between the Middle Route (closed artificial channel) and East Route (open natural water system) of the South-to-North Water Diversion Project. Thirty sampling sites (13 on the Middle Route, 17 on the East Route) were established, and samples were collected during dry and wet seasons. Water quality parameters and SPM characteristics were analyzed, including particle size distribution, total suspended solids (TSS), chlorophyll a, and stable carbon and nitrogen isotopes. Results show that the Middle Route maintains good and stable water quality, with SPM dominated by coarse particles (>63 μm, 61.43%–94.68%), total phosphorus (TP) <0.01 mg·L−1, and a significant positive correlation between chlorophyll a and coarse particles (r=0.60), indicating algal aggregation dominates particle formation. In contrast, the East Route exhibits high and fluctuating nitrogen and phosphorus concentrations, with SPM dominated by fine particles (<20 μm, 51.26%–88.61%), TP ranging from 0.03 to 1.11 mg·L−1, and a positive correlation with fine particles, suggesting significant external inputs. Carbon and nitrogen isotope analysis reveals that Middle Route SPM primarily originates from autochthonous algae (contribution >46.75%), while East Route SPM is influenced by both terrestrial C3 plants and algae. The distinct engineering and management approaches of the two routes lead to significant differences in SPM characteristics and sources, thereby affecting water quality dynamics. The Middle Route requires an 'algal reduction and hydrodynamic optimization' strategy to control algal-derived coarse particle deposition, whereas the East Route benefits from 'retention-sedimentation and wetland purification' to reduce external fine particles and pollutant inputs. This research provides theoretical support and practical guidance for differentiated SPM management in long-distance water diversion systems.
Combined Ozone Micro-Nano Bubble Oxidation and Powdered Activated Carbon Adsorption for Removal of Taste and Odor Compounds from Drinking Water
Algal-derived taste and odor compounds (2-methylisoborneol, 2-MIB, and geosmin, GSM) in drinking water sources are poorly removed by conventional treatment. This study systematically evaluated the standalone and combined performance of ozone micro-nano bubbles (O3-MNBs) oxidation and powdered activated carbon (PAC) adsorption for removing 2-MIB, GSM, and algal cells from source water. Results showed that O3-MNBs pre-oxidation achieved >97.5% removal of odorants at 400 ng·L−1 and 67.2% algal cell removal within 30 min. When applied as a deep treatment stage, the degradation rate constant (k) was 10.1%–25.6% higher than in pre-oxidation due to lower background matrix interference. Both pre-oxidation and deep treatment reduced effluent concentrations of 2-MIB and GSM to below 10 ng·L−1, with oxidation kinetics fitting pseudo-first-order models (R²>0.95). PAC adsorption of both compounds followed pseudo-second-order kinetics (R²>0.99), with GSM equilibrium adsorption capacity approximately 20.0% higher than that of 2-MIB. In pure water, adsorption capacity increased by >10.0% compared to raw water. Based on kinetic models, a quantitative prediction method was established for O3-MNBs oxidation and PAC adsorption processes, aiming to achieve efficient odorant removal and cost optimization, providing theoretical support for advanced drinking water purification and smart water plant construction.
Pulsed Electric Field Enhancement of Nitrogen Removal Performance and Microbial Community Structure Response in Anammox Granular Sludge
This study investigated the effects of a ring-shaped pulsed electric field (PEF) (1.5 V, 4 h on-time per cycle) on nitrogen removal performance and microbial community structure of anammox granular sludge (AnGS). Two anaerobic sequencing batch reactors (R1 control, R2 with PEF) were operated under stepwise increasing nitrogen loading rates (NLR). At NLR below 1,155 mg·(L·d)−1, R2 exhibited total nitrogen removal efficiency (TRE) 7.5%–17.0% higher than R1, with biomass, specific anammox activity (SAA), and extracellular polymeric substances (EPS) increased by 5%–7%, 21%–71%, and 54%–77%, respectively. However, at NLR above 1,320 mg·(L·d)−1, the toxic effect of nitrite dominated, and PEF enhancement diminished or even reversed to inhibition. Microbial community analysis revealed that at low-to-moderate NLR, PEF increased the relative abundance of Planctomycetes and key anammox bacteria (Candidatus Brocadia and Candidatus Jettenia), along with enhanced community richness (Chao1) and diversity (Shannon/Simpson indices). At high NLR, PEF decreased microbial richness compared to R1. Principal component analysis and redundancy analysis indicated that PEF was the key factor driving community differences at low-to-moderate NLR, whereas nitrite concentration became the dominant factor at high NLR. This study provides theoretical support for enhancing the resilience and engineering application of anammox processes.