• Energy Research

The effect of electrostatic fields on the bioelectrochemical removal of ammonium and nitrite from nitrogen-rich wastewater was investigated at strengths ranging from 0.2 to 0.67 V/cm in bioelectrochemical anaerobic batch reactors. The electrostatic field enriched the bulk solution with electroactive bacteria, including ammonium oxidizing exoelectrogens (AOE) and denitritating electrotrophs (DNE). The electroactive bacteria removed ammonium and nitrite simultaneously with alkalinity consumption through biological direct interspecies electron transfer (DIET) in the bulk solution. However, the total nitrogen (ammonium and nitrite) removal rate increased from 106.1 to 166.3 mg N/g volatile suspended solids (VSS).d as the electrostatic field strength increased from 0.2 to 0.67 V/cm. In the cyclic voltammogram, the redox peaks corresponding to the activities of AOE and DNE increased as the strength of the electrostatic field increased. Based on the microbial taxonomic profiling, the dominant genera involved in the bioelectrochemical nitrogen removal were identified as Pseudomonas, Petrimonas, DQ677001_g, Thiopseudomonas, Lentimicrobium, and Porphyromonadaceae_uc. This suggests that the electrostatic field of 0.67 V/cm significantly improves the bioelectrochemical nitrogen removal by enriching the bulk solution with AOE and DNE and promoting the biological DIET between them.

Gradient-porous copper foam electrodes were applied to alleviate the adverse effects of the uneven current distribution of electrodes along the electrolyte flow direction in thermally regenerative ammonia-based batteries (TRABs). The results indicated that gradient-porous copper foam with a decreasing pore size (TRAB-LMS) provided the most uniform current distribution and generated the highest power density (15.5 W/m2), total charge (1800 C) and energy density (1224 W h/m3). With the increase in flow rate, the power density of the TRAB-LMS increased considerably within a certain range and then decreased slightly, with the optimal flowrate at 15 mL/min. Under the optimal flow rate, the performance of TRAB-LMS increased when the ammonia concentration rose from 0.5 to 2 M (1 M=1 mol L−1); however, it decreased slightly when the ammonia concentration further increased to 3 M. The slight decrease in the cathode potential suggested that the flow and ammonia concentration beyond the optional values facilitated not only the transfer of ammonia into the porous anode, but also the crossover of ammonia from the anode to the cathode.

An urgent demand for recycling spent lithium-ion batteries (LIBs) is expected in the forthcoming years due to the rapid growth of electrical vehicles (EV). To address these issues, various technologies such as the pyrometallurgical and hydrometallurgical method, as well as the newly developed in-situ roasting reduction (in-situ RR) method were proposed in recent studies. This article firstly provides a brief review on these emerging approaches. Based on the overview, a life cycle impact of these methods for recovering major component from one functional unit (FU) of 1 t spent EV LIBs was estimated. Our results showed that in-situ RR exhibited the lowest energy consumption and greenhouse gas (GHG) emissions of 4833 MJ FU−1 and 1525 kg CO2-eq FU−1, respectively, which only accounts for ~23% and ~64% of those for the hydrometallurgical method with citric acid leaching. The H2O2 production in the regeneration phase mainly contributed the overall impact for in-situ RR. The transportation distance for spent EV LIBs created a great hurdle to the reduction of the life cycle impact if the feedstock was transported by a 3.5–7.5 t lorry. We therefore suggest further optimization of the spatial distribution of the recycling facilities and reduction in the utilization of chemicals.

Abstract An easy two-stage approach was proposed to prepare microencapsulated phase-change materials (MEPCMs) with n-heptadecane as the core and hexanediol diacrylate (HDDA) polymer as the shell in a co-flowing microfluidic device. The micromorphology and chemical compositions of the MEPCMs were investigated by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The results showed that the shell of HDDA polymer was successfully fabricated upon n-heptadecane core. The obtained MEPCMs had regular spherical shape, smooth surface, and uniform particle size. The coefficient of variation in size was within the 2% limit. The thermal energy storage properties of the MEPCMs were investigated by differential scanning calorimetry. The results revealed that the MEPCMs with HDDA shell had good phase-change performance, high thermal-storage capability. The thermogravimetric analysis and thermal cycling test consisted with 100 heating/cooling processes were conducted to investigate the thermal stability of the MEPCMs. The results showed that the HDDA shell of MEPCMs was able to provide good protection for the core material of n-heptadecane. The excellent thermal stability of the MEPMCs was confirmed by the absence of n-heptadecane leakage. These advantageous properties make the MEPCMs with HDDA shell potential materials for thermal energy storage applications.

Abstract The anode material plays a significant role in determining the performance of microbial fuel cells (MFCs). In this study, the bamboo charcoal tube is proposed as a novel anode substrate by carbonizing the natural bamboo. Its surface functional groups, biocompatibility and internal resistance are thoroughly investigated. Performance of the MFCs with a conventional graphite tube anode and a bamboo charcoal tube anode is also compared. The results indicate that the tubular bamboo charcoal anode exhibits advantages over the graphite tube anode in terms of rougher surface, superior biocompatibility and smaller total internal resistance. Moreover, the X-ray photoelectron spectroscopy (XPS) analysis for the bamboo charcoal reveals that the introduced C–N bonds facilitate the electron transfer between the biofilm and electrodes. As a result, the MFC with a bamboo charcoal tube anode achieves a 50% improvement in the maximum power density over the graphite tube case. Furthermore, scale-up of the bamboo charcoal tube anode is demonstrated by employing a bundle of tubular bamboo charcoal to reach higher power output.

A self-recirculation electrolyte system driven by air bubble buoyancy force is proposed for unbuffered microbial fuel cells (MFC) in this study. It was demonstrated that the electrolyte recirculation rate increased with the aeration rate in a certain range. Compared with buffer condition, buffer-less condition resulted in a 10%∼20% lower voltage (14.2% lower maximum power density) but a 9.1% higher Coulombic efficiency (CE) at an aeration rate of 92.0ml/min. Under buffer-less condition, increasing the aeration rate resulted in a higher voltage output, a higher COD removal, and a higher CE due to the enhanced proton transfer and increased oxygen for cathode reaction. However, an extra high aeration rate induced a rapid deterioration of anode performance due to the excessive oxygen transfer into anode. This study demonstrates that the self-recirculation electrolyte system could be helpful for future unbuffered MFC designs.

Abstract Microbial electrosynthesis systems are a novel device for simultaneous CO2 reduction and CH4 production, and the CH4-producing biocathode in this system is the key component. This work presents a mathematical model to insight into the process of CH4 production on the biocathode. The model couples bioelectrochemical reaction, charge balance, mass transfer, dissolution of gaseous CO2 and interconversion of hydrated CO2, H2CO3, HCO3− and CO32−. To our knowledge, this is the first theoretical report for CH4-producing biocathodes in microbial electrosynthesis systems. This model is capable of predicting the response of CH4-producing biocathodes with operating time under various conditions and describing the effects of different parameters on CH4 production. The results suggest that the most important processes which influence the performance of biocathodes are the interconversions of hydrated CO2, H2CO3 and HCO3−.

A laminar-flow controlled microfluidic microbial fuel cell (MMFC) is considered as a promising approach to be a bio-electrochemical system (BES). But poor bacterial colonization and low power generation are two severe bottlenecks to restrict its development. In this study, we reported a MMFC with multiple anolyte inlets (MMFC-MI) to enhance the biofilm formation and promote the power density of MMFCs. Voltage profiles during the inoculation process demonstrated MMFC-MI had a faster start-up process than the conventional microfluidic microbial fuel cell with one inlet (MMFC-OI). Meanwhile, benefited from the periodical replenishment of boundary layer near the electrode, a more densely-packed bacterial aggregation was observed along the flow direction and also the substantially low internal resistance for MMFC-MI. Most importantly, the output power density of MMFC-MI was the highest value among the reported µl-scale MFCs to our best knowledge. The presented MMFC-MI appears promising for bio-chip technology and extends the scope of microfluidic energy.