Fast digester start-up under mesophilic conditions using thermophilic inoculum

The paper deals with fast procedures adopted for starting-up anaerobic digesters treating biological wastes. In particular, results related to the behaviour of a digester treating sewage sludge with a fast start-up (in 22 days) and using a thermophilic inoculum are presented and compared with those related to a passage from mesophilic to thermophilic temperatures (from 37 to 55°C, in 31 days) and to a direct re-start-up under thermophilic conditions (27 days). In the latter cases, the organic fraction of municipal solid wastes was digested. Main findings concern: the identification of two retention times as the necessary period for reaching the first steady-state condition; the usefulness of performing a real time process monitoring the observation that thermophilic inoculum allows better digester performances in the first start-up period, a finding however, that requires more experimental work.