Investigating the impact of inoculum source on anaerobic digestion of various species of marine macroalgae

This study investigated the intrinsic biodegradation potential of marine organic sediment for effective biogas production from various species of marine macroalgae and non-marine biomass. Biogas production potential tests were carried out on three species of seaweed harvested from the west coasts of Scotland, Laminaria digitata, Fucus serratus, and Saccharina latissima, and on a non-marine cellulose biomass seeded with uncultivated and unadapted anoxic marine sediments. As a comparison, the same experiments were repeated using the same substrates but seeded with active mesophilic anaerobically digested sewage sludge. For the cultures seeded with anoxic marine sediments, the highest methane yield was observed in both L. digitata and S. latissima cultures while F. serratus and cellulose, cultures performed relatively poorly. For those seeded with digested sludge, all cultures performed relatively well, except F. serratus. These results show that marine sediments can be effective inoculum for seaweeds digestion. Phylogenetic analyses of the methanogenic community in both sources of inoculum showed that the methanogen community within the sediment and sludge seeded cultures were different. Each culture was dominated by methanogenic populations suitable for the utilisation of the specific biomass derivatives and environmental conditions. For instance, members of the genus Methanosaeta which, dominated sludge seeded cultures were not detected in the sediment seeded cultures. A similar occurrence was observed for the genus Methanofollis which was only detected in the sediment seeded cultures. Hence, in areas where seaweed forms part of a co-digestion with non-marine biomass, start-up using a mixture of anoxic marine sediments and digested wastewater sludge has the potential to provide greater process stability and robustness than using either as sole inoculum

The biogeographical distribution of closely related freshwater sediment bacteria is determined by environmental selection

The role of environmental selection in governing the structure of communities of freshwater sulfur bacteria (Achromatium spp) was experimentally tested by mixing sediments from two geographically separated lakes (Rydal Water (RY) and Hell Kettles (HK)) that harboured Achromatium spp. Community profiles of Achromatium spp in sediment microcosms at day 0 and after 60 days were compared to determine whether initial Achromatium community composition or subsequent selection by the sediment environment had greater influence in dictating the final Achromatium community structure. It was found that Achromatium spp from the HK community became established in mixed sediments at the expense of members of the RY community. This selection for the HK Achromatium community was more pronounced when sediment composition was manipulated to resemble HK sediments. Our findings definitively demonstrate that environmental selection is the primary determinant of Achromatium community structure in these sediments

Identification of putative methylotrophic and hydrogenotrophic methanogens within sedimenting material and copepod faecal pellets

In the present study, sedimenting particulate material and faecal pellets from natural and laboratory-reared copepods were examined for the presence of methanogenic Archaea. 16S rRNA gene sequences closely related to Methanogenium, Methanobacterium and Methanolobus spp. were detected, indicating the potential for different methanogenic metabolisms (hydrogenotrophic and methylotrophic methanogenesis) in these samples. The present study represents the first 16S rRNA gene-based identification of methanogens in copepod faecal pellets and importantly the first reported 16S rRNA-based occurrence of potentially hydrogenotrophic methanogens from marine particulate material, where it was previously thought that methylotrophic methanogens dominated methanogenesis. Anaerobic incubation experiments using sedimenting particulate material and copepod faecal pellets demonstrated active methane production and indicated that the associated methanogenic community was viable under the conditions tested