Anaerobic expanded-bed laboratory digester for the treatment of swine slurries : COD removal and methane generation

The performances of a digester, fed with swine slurries, under different COD specific load rates (2.1-30.3 Kg/m(3) . d) and HRT (60-14 h) during 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 materials, after preliminary tests carried out in batch. The expansion of the granular bed up to 30% of useful the volume was obtained recycling the slurries with a peristaltic pump. During the experimental trial, COD influent increased from 5.4 Kg/m(3) to 17.7 Kg/m(3), while HRT decreased from 60 to 14 h. COD remotion, CH4 yield and coenzyme F-420 content in biofilm attached to inert matrices were monitored. The best results in COD remotion (72%) were obtained with a specific load of 6.2 Kg COD/m(3).d and the higest specific methane production (0.2 m(3)/Kg COD rem.) with a specific load of 2.2 KgCOD/m(3).d. The digester continued 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.