Enhancement of anaerobic digestion of high salinity food waste by magnetite and potassium ions: Digestor performance, microbial and metabolomic analyses.

The study investigated the effectiveness of magnetite and potassium ions (K+) in enhancing anaerobic digestion of high salinity food waste. Results indicated that both magnetite and K+ improved anaerobic digestion in high-salt environments, and their combination yielded even better results. The combination of magnetite and K+ promoted microorganism activity, and resulted in increased abundance of DMER64, Halobacteria and Methanosaeta. Metabolomic analysis revealed that magnetite mainly influenced quorum sensing, while K+ mainly stimulated the synthesis of compatible solutes, aiding in maintaining osmotic balance. The combined additives regulated pathways such as ATP binding cassette transport, methane metabolism, and inhibitory substance metabolism, enabling cells to resist environmental stress and maintain normal metabolic activity. Overall, this study demonstrated the potential of magnetite and K+ to enhance food waste anaerobic digestion in high salt conditions and provided valuable insights into the molecular mechanism.

Enhancement of denitrification in biofilters by immobilized biochar under low-temperature stress.

Efficient removal of nitrate under low temperature is challenging because of the reduction of the microbial activity. This study successfully explored the promotion on the performance of denitrification utilizing the immobilized biochar in biofilters under low temperature (6 ± 2 °C). The results showed that the immobilized biochar increased the denitrification rate by 76.8% and decreased the nitrous oxide emissions by 82.5%. Mechanistic studies revealed that the immobilized biochar increased the activities of the denitrifying enzymes and three enzymes involved in glycolysis. Furthermore, the immobilized biochar elevated the activity of the electron transport system by 31.8%. Finally, structural equation model explained that the increase of nitrate reductase activity was a crucial factor to enhance the total nitrogen removal efficiency in biofilters with immobilized biochar. Overall, the use of immobilized biochar can be a novel strategy to enhance nitrogen removal and reduce greenhouse gas emissions in biofilters under low temperature.

Impact of biochar on greenhouse gas emissions from constructed wetlands under various influent chemical oxygen demand to nitrogen ratios.

Biochar is widely used for nutrient removal in constructed wetlands (CWs); however, its influence on greenhouse gas (GHG) emissions from CWs remains unclear. Here, biochar was used to mitigate the global warming potential (GWP) from CWs and promote the removal of contaminants from simulated domestic wastewater under different influent chemical oxygen demand to nitrogen ratios (COD/N = 3, 6, 9, 12). Results demonstrated that biochar could improve the removal of COD, NH4+- N, and TN. The average N2O and CO2 fluxes were significantly lower and CH4 fluxes were higher in biochar-added CWs than those in none-biochar CWs. Biochar reduced GWP values of N2O and CH4 from 18.5% to 24.0%. N2O fluxes and GWP decreased, while CH4 and CO2 fluxes increased as COD/N ratios increased. Additionally, biochar increased the abundance of Geobacter and denitrifiers such as Hydrogenophaga. Overall, biochar could not only promote the removal of nutrients but also mitigate GWP in CWs.