Impacts of mixing on foaming, methane production, stratification and microbial community in full-scale anaerobic co-digestion process

© 2019 Elsevier Ltd This study investigated the impact of mixing on key factors including foaming, substrate stratification, methane production and microbial community in three full scale anaerobic digesters. Digester foaming was observed at one plant that co-digested sewage sludge and food waste, and was operated without mixing. The lack of mixing led to uneven distribution of total chemical oxygen demand (tCOD) and volatile solid (VS) as well as methane production within the digester. 16S rRNA gene-based community analysis clearly differentiated the microbial community from the top and bottom. By contrast, foaming and substrate stratification were not observed at the other two plants with internal circulation mixing. The abundance of methanogens (Methanomicrobia) at the top was about four times higher than at the bottom, correlating to much higher methane production from the top verified by ex-situ biomethane assay, causing foaming. This result is consistent with foaming potential assessment of digestate samples from the digester

Application of a novel molecular technique to characterise the effect of settling on microbial community composition of activated sludge

© 2019 Elsevier Ltd Activated sludge (AS) and return activated sludge (RAS) microbial communities from three full-scale municipal wastewater treatment plants (denoted plant A, B and C) were compared to assess the impact of sludge settling (i.e. gravity thickening in the clarifier) and profile microorganisms responsible for nutrient removal and reactor foaming. The results show that all three plants were dominated with microbes in the phyla of Proteobacteria, Bacteroidetes, Verrucomicrobia, Actinobacteria, Chloroflexi, Firmicutes, Nitrospirae, Spirochaetae, Acidobacteria and Saccharibacteria. AS and RAS shared above 80% similarity in the microbial community composition, indicating that sludge thickening does not significantly alter the microbial composition. Autotrophic and heterotrophic nitrifiers were present in the AS. However, the abundance of autotrophic nitrifiers was significantly lower than that of the heterotrophic nitrifiers. Thus, ammonium removal at these plants was achieved mostly by heterotrophic nitrification. Microbes that can cause foaming were at 3.2% abundance, and this result is well corroborated with occasional aerobic biological reactor foaming. By contrast, these microbes were not abundant (<2.1%) at plant A and C, where aerobic biological reactor foaming has not been reported

Automatic multicast IPsec by using a proactive IPsec discovery protocol and a group key management

Internet protocol based networking is gaining ground in armed forces, leading to a concept described by the NATO as network centric capabilities (NCC). The goal is to enable state-of-the-art, affordable and powerful electronic information services to the troops. A tighter connection of the forces is expected to further enhance the joined strike capabilities. Providing secure information exchange within groups of armed forces is one aspect of the NCC concept. Such group communication is enabled by the multicast feature of the IP technology. Security requirements are met by using the IP security (IPsec) architecture. IPsec enables secure communication between secure private networks via an unsecured public text network. While secure unicast transmission with IPsec is common, only few achievements have been made to secure multicast transmissions. The protection of multicast data traffic of a group in an automated way is described in this document. We utilize an automatic detection of IPsec devices and an efficient key management protocol to reach our aim