Food waste impact on dry anaerobic digestion of straw in a novel reactor: Biogas yield, stability, and hydrolysis-methanogenesis processes.

Gradient anaerobic digestion reactor (GADR) can improve substrate utilization efficiency by solving the problem of the "short circuit" of materials. However, the substrate's composition significantly affects the reactor's performance. This study investigated the impact of food waste (FW) levels on corn straw's dry anaerobic digestion (AD) in a novel GADR. The results show that biomethane production can be improved by coupling urban and agricultural solid waste recycling. The mechanism is to increase the hydrolysis and acid production efficiency, and the abundance of enzymes related to methanogenesis. The maximum methane yield (494.2 mL CH4/g VS) and the highest anaerobic biodegradability (85.7 %) were obtained when the FW was added at 60 %. The co-digestion of FW and straw can improve the hydrolysis and acid production efficiency and methane yield, which improves the buffering capacity and stability of the system compared with the single digestion of FW.

[Structure and function of Fenshuijiang Reservoir ecosystem based on the analysis with Ecopath model].

Based on the 2008-2009 survey data of fishery resources and eco-environment of Fenshuijiang Reservoir, a mass balance model for the Reservoir ecosystem was constructed by Ecopath with Ecosim software. The model was composed of 14 functional groups, including silver carp, bighead carp, Hemibarbus maculates, Cutler alburnus, Microlepis and other fishes, Oligochaeta, aquatic insect, zooplankton, phytoplankton, and organic detritus, etc. , being able to better simulate Fenshuijiang Reservoir ecosystem. In this ecosystem, there were five trophic levels (TLs), and the nutrient flow mainly occurred in the first three TLs. Grazing and detritus food chains were the main energy flows in the ecosystem, but the food web was simpler and susceptible to be disturbed by outer environment. The transfer efficiency at lower TLs was relatively low, indicating that the ecosystem had a lower capability in energy utilization, and the excessive stock of nutrients in the ecosystem could lead to eutrophication. The lower connectance index, system omnivory index, Finn' s cycled index, and Finn's mean path length demonstrated that the ecosystem was unstable, while the high ecosystem property indices such as Pp/R and Pp/B showed that the ecosystem was immature and highly productive. It was suggested that Fenshuijiang Reservoir was still a developing new reservoir ecosystem, with a very short history and comparatively high primary productivity.