MnO2-deposited lignin-based carbon fiber (MnO2-LCF) mats are fabricated for supercapacitor applications. LCF mats are produced from alkali lignin via electrospinning followed by stabilization and carbonization. The carbonization process is carried out at 800, 900, and 1000 °C, and the corresponding mats are denoted as MnO2-LCF-800, MnO2-LCF-900, and MnO2-LCF-1000, respectively. The LCF mats are immersed in a KMnO4 solution at room temperature for 72 h to obtain MnO2-LCF mats. The scanning electron microscopy and X-ray diffraction analysis confirm the deposition of MnO2 on the LCFs. The Brunauer–Emmett–Teller analysis, X-ray spectroscopy, and Raman spectroscopy reveal that MnO2-LCF-800 mat possesses a large number of mesopores and Mn vacancies as compared to MnO2-LCF-900 mat and MnO2-LCF-1000 mat. Consequently, MnO2-LCF-800 mat possesses the best electrochemical properties with a specific capacitance of 131.28 F∙g−1, an energy density of 14.77 Wh∙kg−1, and a power density of 135.01 W∙kg−1 at a specific current of 0.3 A∙g−1. Hence, MnO2-LCF-800 mat shows high potential to be used as a high-performance supercapacitor.

Illustration of the interspecies electron transfer improved by ACET during methanogenesis.

To understand how extracellular polymer substance (EPS) used as an additive promotes methanogenesis, batch tests of methane production potential in anaerobic reactors with the addition of EPS and without EPS (control) were conducted. EPS markedly increased methane production during anaerobic digestion (25.0–36.5%) compared with the control reactor. EPS enriched functional microorganisms, including organisms belonging to the phyla Firmicutes, Actinobacteria, Synergistetes, and Chloroflexi, and optimized the community structure of microorganisms. Among them, 8.86% of the operational taxonomic units were from important hydrolysis and acidification phyla, which may be an important reason for the enhanced methanogenic capacity of anaerobic granular sludge (AnGS). Additionally, EPS increased the number of cytochrome c (c-Cyts) by 15.2–25.0% compared with the control reactor, accelerating the direct interspecies electron transfer between syntrophic bacteria (norank_f__Synergistaceae and Syntrophobacter increased by 58.2–102% and 115–151% compared with the control reactor, respectively) and methanogens (Methanosaeta), thus improving the anaerobic digestion performance. The results were validated by applying 16S function prediction. Interestingly, the average particle size, volatile suspended solids/total suspended solids, and EPS content of AnGS in the EPS reactors were approximately equal to the values in the control reactor during the anaerobic digestion, illustrating that EPS cannot affect the physicochemical properties of AnGS. These results suggest that EPS may be a conductive material in the anaerobic digestion process. Therefore, EPS used as an additive has great potential in the improvement of AD performance.

Basic dyes, which are widely used in industry, can cause serious damage to the environment if they are discharged to waterways. If directly discharged into water, they can cause serious damage to the environment due to their deep color and low degradation rate. The results showed that the average chemical oxygen demand removal rate from the wastewater was greater than 60%, while the methylene blue removal rate was greater than 90%. Anaerobic granular sludge can remove methylene blue and organic matter simultaneously. Candidatus Cloacimonetes was not detected when the methylene blue concentration was 0 mg/L, 2 mg/L, or 4 mg/L. When the methylene blue concentration was 6 mg/L, 8 mg/L, and 10 mg/L, more Candidatus Cloacimonetes was detected in the sludge as the concentration of methylene blue increased. The Candidatus Cloacimonetes content was found to be 1.02%, 1.08%, and 2.11% in these samples, respectively.