Digester volumes, electrical power and energy productions
were calculated according to Flotats and Sarquella [20]. Table 4
summarizes digester design parameters for conditions of R1 and
R2 with HRTs of 25 and 15 d. Methane calorific value was assumed
to be 8600 kcal m3. Total digester capacities were calculated
including 20% capacity for biogas storage. Co-generation engine
efficiency was considered to be 35% [21] and electrical capacity
would be produced 329 d year1 [22]. Heat energy recovery systems
were supposed to have 55% efficiency. A boiler system with
efficiency of 90% was also considered for covering calorific energy
requirements. Heat energy requirements were based on Bouallagui
et al. [23] considering the temperature difference as the difference
between the temperature of the digestion process and the temperature
of the feed (Table 5). Digester heat losses were assumed to be
10% of total heat requirements.