Cathodic biofouling control by microbial separators in air-breathing microbial fuel cells

High H2O2 production in membrane-free electrolyzer via anodic bubble shielding towards robust rural disinfection

Hydrogen peroxide (H2O2) can be sustainably synthesized through the electrochemical oxygen reduction reaction in a dual-chamber water electrolyzer separated by expensive ion exchange (IX) membranes. The development of an IX membrane-free electrolyzer has been limited by direct anodic degradation of the produced H2O2. Here, we devise a bubble shielding strategy by using a low-cost polytetrafluoroethylene hydrophobic porous layer (HPL) on the anode that enables numerous sites for anodically generated oxygen bubbles and significantly suppresses H2O2 degradation in the electrolyte. The H2O2 production increases by ~600% compared to that using non-bubble shielded anode. A high H2O2 concentration of 10.05 ± 0.05 g L-1 at 40 mA cm-2 can be obtained with both HPL-coated anode and cathode. A solar-driven disinfection device equipped with HPL-coated electrodes achieves >99.9% E. coli inactivation within 60 min. This innovative approach for achieving high electrochemical H2O2 concentrations in IX membrane-free electrolyzers more generally provides insights for fine tuning three-phase interfaces and could be applicable to other reactions pathways in electrochemical applications.

Selection and optimization of biofilm carriers as high-effective microbial separator in microbial fuel cells

Four biofilm carriers including pyrite, manganese ore, ceramsite, and polyurethane sponge were used to construct microbial separators (MSs), while their performance in dual-chamber microbial fuel cells (MFCs) was evaluated. Polyurethane sponge and pyrite were superior biofilm carriers for MSs. The dense biofilm on the polyurethane sponge provides MS with optimal barrier capacity against dissolved oxygen and chemical oxygen demand. Pyrite's unique redox activity enhances proton transfer in MS and reduces ohmic resistance in MFC. The optimal thicknesses of polyurethane sponge MS and pyrite MS were 1.20 and 1.80 cm, and the maximum power densities of MFCs equipped with these two MSs were 14.62 and 11.21 W/m3. Using MSs as separators can significantly lower MFC manufacturing costs, particularly with polyurethane sponge MS at 3.52 $/m2. Additionally, MSs demonstrated good regenerability. These results indicated that MSs based on pyrite and polyurethane sponge have the potential to be high-effective separators for MFC scale-up.

Sorting Out the Latest Advances in Separators and Pilot-Scale Microbial Electrochemical Systems for Wastewater Treatment: Concomitant Development, Practical Application, and Future Perspective

To date, dozens of pilot-scale microbial fuel cell (MFC) devices have been successfully developed worldwide for treating various types of wastewater. The availability and configurations of separators are determining factors for the economic feasibility, efficiency, sustainability, and operability of these devices. Thus, the concomitant advances between the separators and pilot-scale MFC configurations deserve further clarification. The analysis of separator configurations has shown that their evolution proceeds as follows: from ion-selective to ion-non-selective, from nonpermeable to permeable, and from abiotic to biotic. Meanwhile, their cost is decreasing and their availability is increasing. Notably, the novel MFCs configured with biotic separators are superior to those configured with abiotic separators in terms of wastewater treatment efficiency and capital cost. Herein, a highly comprehensive review of pilot-scale MFCs (>100 L) has been conducted, and we conclude that the intensive stack of the liquid cathode configuration is more advantageous when wastewater treatment is the highest priority. The use of permeable biotic separators ensures hydrodynamic continuity within the MFCs and simplifies reactor configuration and operation. In addition, a systemic comparison is conducted between pilot-scale MFC devices and conventional decentralized wastewater treatment processes. MFCs showed comparable cost, higher efficiency, long-term stability, and significant superiority in carbon emission reduction. The development of separators has greatly contributed to the availability and usability of MFCs, which will play an important role in various wastewater treatment scenarios in the future.

Technological solutions to landfill management: Towards recovery of biomethane and carbon neutrality

Inadequate landfill management poses risks to the environment and human health, necessitating action. Poorly designed and operated landfills release harmful gases, contaminate water, and deplete resources. Aligning landfill management with the Sustainable Development Goals (SDGs) reveals its crucial role in achieving various targets. Urgent transformation of landfill practices is necessary to address challenges like climate change, carbon neutrality, food security, and resource recovery. The scientific community recognizes landfill management's impact on climate change, evidenced by in over 191 published articles (1998-2023). This article presents emerging solutions for sustainable landfill management, including physico-chemical, oxidation, and biological treatments. Each technology is evaluated for practical applications. The article emphasizes landfill management's global significance in pursuing carbon neutrality, prioritizing resource recovery over end-of-pipe treatments. It is important to note that minimizing water, chemical, and energy inputs in nutrient recovery is crucial for achieving carbon neutrality by 2050. Water reuse, energy recovery, and material selection during manufacturing are vital. The potential of water technologies for recovering macro-nutrients from landfill leachate is explored, considering feasibility factors. Integrated waste management approaches, such as recycling and composting, reduce waste and minimize environmental impact. It is conclusively evident that the water technologies not only facilitate the purification of leachate but also enable the recovery of valuable substances such as ammonium, heavy metals, nutrients, and salts. This recovery process holds economic benefits, while the conversion of CH4 and hydrogen into bioenergy and power generation through microbial fuel cells further enhances its potential. Future research should focus on sustainable and cost-effective treatment technologies for landfill leachate. Improving landfill management can mitigate the adverse environmental and health effects of inadequate waste disposal.

Insight into the Pseudocapacitive Behavior of Electroactive Biofilms in Response to Dynamic-Controlled Electron Transfer and Metabolism Kinetics for Current Generation in Water Treatment

Electroactive biofilms (EBs) engage in complex electron transfer and storage processes involving intracellular and extracellular mediators with temporary electron storage capabilities. Consequently, electroactive biofilms exhibit pseudocapacitive behaviors during substrate degradation processes. However, comprehensive systematic research in this area has been lacking. This study demonstrated that the pseudocapacitive property was an intrinsic characteristic of EBs. This property represents dynamic-controlled electron transfer and is critical in current generation, unlike noncapacitive responses. Nontransient charge and discharge experiments revealed a correlation between capacitive charge accumulation and current generation in EBs. Additionally, analysis of substrate degradation suggested that the maximum power density (Pmax) changed with the kinetic constants of COD degradation, with pseudocapacitances of EBs directly proportional to Pmax. The interaction networks of key latent variables were evaluated through partial least-squares path modeling analysis. The results indicated that cytochrome c was closely associated with the formation of pseudocapacitance in EBs. In conclusion, pseudocapacitance can be considered a valuable indicator for assessing the complex electron transfer behavior of EBs. Pseudocapacitive biofilms have the potential to efficiently regulate biological reactions and serve as a promising carbon-neutral and renewable strategy for energy generation and storage. An in-depth understanding of the intrinsic property of pseudocapacitive behavior in EBs can undoubtedly advance the development of this concept in the future.

PCL/PEO Polymer Membrane Prevents Biofouling in Wearable Detection Sensors

Technological advances in biosensing offer extraordinary opportunities to transfer technologies from a laboratory setting to clinical point-of-care applications. Recent developments in the field have focused on electrochemical and optical biosensing platforms. Unfortunately, these platforms offer relatively poor sensitivity for most of the clinically relevant targets that can be measured on the skin. In addition, the non-specific adsorption of biomolecules (biofouling) has proven to be a limiting factor compromising the longevity and performance of these detection systems. Research from our laboratory seeks to capitalize on analyte selective properties of biomaterials to achieve enhanced analyte adsorption, enrichment, and detection. Our goal is to develop a functional membrane integrated into a microfluidic sampling interface and an electrochemical sensing unit. The membrane was manufactured from a blend of Polycaprolactone (PCL) and Polyethylene oxide (PEO) through a solvent casting evaporation method. A microfluidic flow cell was developed with a micropore array that allows liquid to exit from all pores simultaneously, thereby imitating human perspiration. The electrochemical sensing unit consisted of planar gold electrodes for the monitoring of nonspecific adsorption of proteins utilizing Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The solvent casting evaporation technique proved to be an effective method to produce membranes with the desired physical properties (surface properties and wettability profile) and a highly porous and interconnected structure. Permeability data from the membrane sandwiched in the flow cell showed excellent permeation and media transfer efficiency with uniform pore activation for both active and passive sweat rates. Biofouling experiments exhibited a decrease in the extent of biofouling of electrodes protected with the PCL/PEO membrane, corroborating the capacity of our material to mitigate the effects of biofouling.

Recovery of electron and carbon source from agricultural waste corncob by microbial electrochemical system to enhance wastewater denitrification

The denitrification process in wastewater treatment plants (WWTPs) is limited by insufficient carbon sources. Agricultural waste corncob was investigated for its feasibility as a low-cost carbon source for efficient denitrification. The results showed that the corncob as the carbon source exhibited a similar denitrification rate (19.01 ± 0.03 gNO₃^--N/m³d) to that of the traditional carbon source sodium acetate (19.13 ± 0.37 gNO₃^--N/m³d). When filling corncob into a microbial electrochemical system (MES) three-dimensional anode, the release of corncob carbon sources was well controlled with an improved denitrification rate (20.73 ± 0.20 gNO₃^--N/m³d). Carbon source and electron recovered from corncob led to autotrophic denitrification and heterotrophic denitrification occurred in the MES cathode, which synergistically improved the denitrification performance of the system. The proposed strategy for enhanced nitrogen removal by autotrophic coupled with heterotrophic denitrification using agricultural waste corncob as the sole carbon source opened up an attractive route for low-cost and safe deep nitrogen removal in WWTPs and resource utilization for agricultural waste corncob.

Enhanced electron recovery by optimizing sandwich structure agricultural waste corncob filled anode in microbial electrochemical system to facilitate wastewater denitrification

Microbial electrochemical system autotrophic denitrification has attracted much attention due to its cost-efficiency and clean advantages. The autotrophic denitrification rate highly depends on the input electrons to the cathode. In this study, agricultural waste corncob was filled into sandwich structure anode as low-cost carbon source for electron production. The COMSOL software was used to guide the construction of sandwich structure anode to control carbon source release and enhance electron collection, including suitable pore size (4 mm) and current collector arrangement (five branches). Optimized sandwich structure anode system with the help of 3D printing obtained a higher denitrification efficiency (21.79 ± 0.22 gNO₃^--N/m³d) than anodic systems without pore and current collector. Statistical analysis showed that enhanced autotrophic denitrification efficiency was the responsible for enhanced denitrification performance of the optimized anode system. This study provides a strategy to improve the autotrophic denitrification performance of the microbial electrochemical system by optimizing the anode structure.

Insights into the Electron Transfer Behaviors of a Biocathode Regulated by Cathode Potentials in Microbial Electrosynthesis Cells for Biogas Upgrading

Bioelectrochemical-based biogas upgrading is a promising technology for the storage of renewable energy and reduction of the global greenhouse gas emissions. Understanding the electron transfer behavior between the electrodes and biofilm is crucial for the development of this technology. Herein, the electron transfer pathway of the biofilm and its catalytic capability that responded to the cathode potential during the electromethanogenesis process were investigated. The result suggested that the dominant electron transfer pathway shifted from a direct (DET) to indirect (IDET) way when decreasing the cathode potential from -0.8 V (Bio-0.8 V) to -1.0 V (Bio-1.0 V) referred to Ag/AgCl. More IDET-related redox substances and high content of hydrogenotrophic methanogens (91.9%) were observed at Bio-1.0 V, while more DET-related redox substances and methanogens (82.3%) were detected at Bio-0.8 V. H₂, as an important electron mediator, contributed to the electromethanogenesis up to 72.9% of total CH₄ yield at Bio-1.0 V but only ∼17.3% at Bio-0.8 V. Much higher biogas upgrading performance in terms of CH₄ production rate, final CH₄ content, and carbon conversion rate was obtained with Bio-1.0 V. This study provides insight into the electron transfer pathway in the mixed culture constructed biofilm for biogas upgrading.