Biogas upgrading performance and underlying mechanism in microbial electrolysis cell and anaerobic digestion integrated system.

The productivity and efficiency of two-chamber microbial electrolysis cell and anaerobic digestion integrated system (MEC-AD) were promoted by a complex of anaerobic granular sludge and iron oxides (Fe-AnGS) as inoculum. Results showed that MEC-AD with Fe-AnGS achieved biogas upgrading with a 23%-29% increase in the energy recovery rate of external circuit current and a 26%-31% decrease in volatile fatty acids. The energy recovery rate of MEC-AD remained at 52%-57%, indicating a stable operation performance. The selectively enriched methanogens and electroactive bacteria resulted in dominant hydrogenotrophic and acetoclastic methanogenesis in the cathode and anode chambers. Mechanistic analysis revealed that MEC-AD with Fe-AnGS led to specifically upregulated enzymes related to energy metabolism and electron transfer. Fe-AnGS as inoculum could improve the long-term operation performance of MEC-AD. Consequently, this study provides an efficient strategy for biogas upgrading in MEC-AD.

Enhancing CH4 production in microbial electrolysis cells: Optimizing electric field via carbon cathode resistivity.

Microbial electrolysis cells (MECs) are increasingly recognized as a promising technology for converting CO2 to CH4, offering the dual benefits of energy recovery from organic wastewater and CO2 emission reduction. A critical aspect of this technology is the enhancement of the electron-accepting capacity of the methanogenic biocathode to improve CH4 production efficiency. This study demonstrates that adjusting the cathode resistivity is an effective way to control the electric field intensity, thereby enhancing the electron accepting capacity and CH4 production. By maintaining the electric field intensity within approximately 8.50-10.83 mV·cm-1, the CH4 yield was observed to increase by up to two-fold. The improvement in CH4 production under optimized electric field conditions was attributed to the enhancement of the direct accepting capacity of the biocathode. This enhancement was primarily due to an increase in the relative abundance of Methanosaeta by approximately 10 % and an up to 83.78 % rise in the electron-accepting capacity of the extracellular polymeric substance. These insights offer a new perspective on the operation of methanogenic biocathodes and propose a novel biocathode construction methodology based on these findings, thus contributing to the enhancement of MEC efficiency.

Succession of the microbial community during the process of mechanical and biological pretreatment coupled with a bio-filter for removal of VOCs derived from domestic waste: a field study.

Changes in the microbial community can not only reflect the efficiency of waste disposal, but also reveal the effect of odor control during the treatment process. This study aimed to evaluate the removal efficiency of volatile organic compounds (VOCs) by the process of mechanical and biological pretreatment (MBP) coupled with a bio-filter (BF). An interesting phenomenon was found that the VOCs were effectively reduced through the MBP process. To understand the removal mechanism of VOCs, the abundance and diversity of microbial bacteria and fungi in the biological dehydration (BD) process, biological fermentation process, and BF process were explored. The abundance and diversity of microbes in the BF were relatively high, of which the bacteria such as Lactobacillus, Bacillus and Candida were the dominant species for VOCs treatment. The proposed technical process and the positive effects observed in this study indicate that it could be applied to the control of VOCs in the treatment of domestic waste.

Kinetic Study on the Preparation of Fumaric Acid from Maleic Acid by Batch Noncatalytic Isomerization.

In recent years, the increase in demand for fumaric acid from industry has resulted in an increased need for a high-selectivity process for the conversion of maleic acid to fumaric acid. A highly selective conversion of fumaric acid was achieved without a catalyst by a simple one-step hydrothermal reaction. In addition, the competitive conversion of maleic acid, fumaric acid, and malic acid was first systematically investigated in detail without using a catalyst. The products were characterized by X-ray diffraction and Fourier transform infrared, which demonstrated that the product was fumaric acid. The highly selective conversion of fumaric acid was achieved, and the yield of fumaric acid could reach 92%. Furthermore, a reaction kinetic model was put forward to study the competitive transformation process. The kinetic model predictions were found to agree well with the experimental data. The kinetic parameters were used to explain the changes in the content of every substance at different reaction temperatures and reaction times. In addition, the initial maleic acid concentration in the reaction was also considered as an influencing factor. These results can facilitate the conditional control and product control of industrial processes for the production of fumaric acid or malic acid using latter without a catalyst.