ANAEROBIC EXPANDED-BED LABORATORY DIGESTER FOR THE TREATMENT OF SWINESLURRIES - COD REMOVAL AND METHANE GENERATION

The performances of a digester, fed with swine slurries, under differe nt COD specific load rates (2.1-30.3 Kg/m(3) . d) and HRT (60-14 h) du ring start-up and steady-state periods were evaluated. The reactor (6. 01 useful volume, 100 cm height, 0.2-12 cm diameter) was filled at 20% (v/v) with marl sand (30/60 mesh) selected among four different mater ials, after preliminary tests carried out in batch. The expansion of t he granular bed up to 30% of useful the volume was obtained recycling the slurries with a peristaltic pump. During the experimental trial, C OD influent increased from 5.4 Kg/m(3) to 17.7 Kg/m(3), while HRT decr eased from 60 to 14 h. COD remotion, CH4 yield and coenzyme F-420 cont ent in biofilm attached to inert matrices were monitored. The best res ults in COD remotion (72%) were obtained with a specific load of 6.2 K g COD/m(3).d and the higest specific methane production (0.2 m(3)/Kg C OD rem.) with a specific load of 2.2 KgCOD/m(3).d. The digester contin ued to run also when HRT was rapidly reduced but went through serious difficulties when specific load was increased up to 70.8 KgCOD/m(3).d.