MESOPHILIC AND THERMOPHILIC BACTERIA IN ANAEROBIC DIGESTION PROCESS

Anaerobic digestion of bioorganic waste is a complex process. Many inhibitors, like accumulation of ammonia and volatile fatty acids, can reduce performances and even prompt process failures. In this contest, temperature and structure of microbial communities in substrate are key parameters that regulate stability and efficiency of the biogas production process. Generally, high temperatures accelerate metabolic rates and, consequently, biochemical processes, decrease degree of pathogen activations, and provide higher degradation rates. Due to a decreased viscosity of the biomass, energy costs for stirring are lower at high thermal conditions. For better biogas production yields, micro-organisms live and act in the biomass under mesophilic or thermophilic conditions, i.e. between 30 °C and 49 °C and between 50 °C and 70 °C, respectively. Typology of microbial population residing in digesters is strongly related to the working temperature range of the digester in the biogas plant. In the present contribution, the microbial dynamics are discussed in the (30 – 70) °C temperature range. Since anaerobic digestion is a multi-stage biochemical process, as four key stages hydrolysis, acidogenesis, acetogenesis and methanogenesis are discussed in relation to the complexity of the microbial communities.