Operational mode and powdered activated carbon promoting syntrophic propionate oxidation during anaerobic digestion of complex organic substances.

Operational mode and powdered activated carbon (PAC) are key factors facilitating microbial syntrophy and interspecies electron transfer during anaerobic digestion, consequently benefiting process stability and efficient methanogenesis. In this study, continuous-flow reactor (CFR) and sequencing batch reactor (SBR), with and without the addition of PAC, respectively, were operated to examine their effects on system performance and methanogenic activity. Based on the cycle-test result, the PAC-amended CFR (CFRPAC) recorded both the highest methane yield (690.1 mL/L) and the maximum CH4 production rate (28.8 mL/(L·h)), while SBRs exhibited slow methanogenic rates. However, activity assays indicated that SBRs were beneficial for organics removal in batch experiments fed with peptone. Taxonomic and functional analysis confirmed that CFRs were optimal for proliferating oligotrophs (e.g., Geobacter) and SBRs were more suitable for copiotrophs (e.g., Desulfobulbus). Metagenomic analysis revealed that CFRs had efficient acetate metabolic pathways from propionate and ethanol, whereas SBRs did not, resulting in the buildup of propionate. Furthermore, Methanobacterium and Methanothrix were acclimated to the different operational conditions, while acetoclastic Methanosarcina and hydrogenotrophic Methanolinea were acclimated in SBRs (5.1-13.4%) and CFRs (0.3-1.7%), respectively. This study confirmed the enhancement of microbial syntrophy by the addition of PAC as well as the acclimation of electroactive bacteria (e.g., Geobacter) with complex organic substances.

Consideration of compound drivers and impacts in the disaster risk reduction cycle.

Consideration of compound drivers and impacts are often missing from applications within the Disaster Risk Reduction (DRR) cycle, leading to poorer understanding of risk and benefits of actions. The need to include compound considerations is known, but lack of guidance is prohibiting practitioners from including these considerations. This article makes a step toward practitioner guidance by providing examples where consideration of compound drivers, hazards, and impacts may affect different application domains within disaster risk management. We discern five DRR categories and provide illustrative examples of studies that highlight the role of "compound thinking" in early warning, emergency response, infrastructure management, long-term planning, and capacity building. We conclude with a number of common elements that may contribute to the development of practical guidelines to develop appropriate applications for risk management.