From hypertrophic lagoons to bioenergy production

The study of natural environments, together with the knowledge of applied microbial ecology, can drive innovation in bioenergetic applications. Hypertrophic lagoons are characterised by rapid and huge biomass blooms and decomposition. In these salty shallow-water ecosystems the microbial degradation is supported by a chain of electron acceptors, in which oxygen is the first, and sulphate the last and most available one (about 3 g/1). The latter plays a pivotal role in the ecology of these environments. Bacterial sulphate reduction is strongly supported by small molecules produced by microaerophilic fermentation in warm seasons. The same microbial communities and metabolism can support also an effective methanogenesis in different environmental conditions where SO₄ is depleted. A sediment sample collected in an hypertrophic coastal lake in Central Italy demonstrated a high hydrogen production capability in laboratory tests. The bacterial community was characterised by molecular techniques, after 210 h of acclimatisation in a Continuous Stirred Tank Reactor (CSTR), while producing high rate and yield of hydrogen in stable conditions. The selected inoculum, F₂₁₀, was successfully tested for hydrogen production on different kinds of organic wastes. Further, batch experimental trials in which F₂₁₀ was added to a methanogens community showed an increase in the efficiency of methane production.