Renewable energy source, such as food waste (FW), has drawn great attention globally due to the energy crisis and the environmental problem. Anaerobic digestion (AD) mediated by novel microbial consortia is widely used to convert FW to clean energy. Despite of the considerable progress on food waste and FWAD optimization condition in recent years, a comprehensive and predictive understanding of FWAD microbial consortia is absent and therefore represents a major research challenge in FWAD. The review begins with a global view on the FWAD status and is followed by an overview of the role of AD key conditions’ association with microbial community variation during the three main energy substances (hydrogen, organic acids, and methane) production by FWAD. The following topic is the historical understanding of the FWAD microorganism through the development of molecular biotechnology, from classic strain isolation to low-throughput sequencing technologies, to high-throughput sequencing technologies, and to the combination of high-throughput sequencing and isotope tracing. Finally, the integration of multi-omics for better understanding of the microbial community activity and the synthetic biology for the manipulation of the functioning microbial consortia during the FWAD process are proposed. Understanding microbial consortia in FWAD helps us to better manage the global renewable energy source.
In this paper, the dynamical behaviors of the FitzHugh–Nagumo (FHN) system with a memory trace, which has time-fractional derivatives, are investigated. For the case of a classical order, the constant input current can change the stability of the equilibrium point in a single FHN unit, and the equilibrium is unstable in a certain range of the current. A decrease of the order of the time-fractional derivative may lead to a linear reduction of the range and the appearance of a solution of mixed-mode oscillations, which consist of subthreshold small-amplitude oscillation and suprathreshold large-amplitude oscillation. In the parameter space of the input current and the fractional order, the region of existing the mixed-mode oscillation is linearly widened when the fractional order moves toward its small value. If a suprathreshold perturbation is periodically applied, there exist some obvious bands, on which the excited period is locked to the perturbation period according to some rational ratios. As a result, the bands can be narrowed by decreasing the value of fractional order and their location has a slight drift toward the small value of the perturbation period. In addition, the properties of solitary traveling waves and wave train solutions are also studied in the one-dimensional space. It is illustrated that the traveling pulse is wider for a smaller value of fractional order, and its velocity is larger. Further, some relations of wave trains have a great change when the value of the fractional order is changed.
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