RESUMEN
The effect of hydraulic retention time in a range from 1.0-5.5 days was evaluated in a laboratory scale anaerobic fixed bed reactor packed with a hybrid material composed of tire rubber and zeolite. Under these conditions, COD removal efficiencies varied from 28.3% to 82.1%, respectively. Over the more than 6 months of operation, no clogging was observed. The results obtained demonstrated that this type of reactor was capable of operating with dairy waste at a hydraulic retention time 5 times lower than that used in a conventional digester. Based on the laboratory-scale experimental results obtained, a pilot-scale plant was designed. The pilot plant was installed in "Cot de Oreamuno" near the city of Cartago, Costa Rica. Biogas produced in the pilot-scale anaerobic plant was used for the generation of electricity on the farm. In this case, a COD removal efficiency of 63.6% was achieved in the full-scale anaerobic plant at a hydraulic retention time of 3 days, this value being comparable with that obtained at laboratory-scale