Upflow anaerobic packed bed (UAPB) reactor is an upflow fixed film packed bed bioreactor that is used for rapid biotransformation of organic matter to methane. In this study, biofilm was established on seashell, packed in an UAPB bioreactor. The start-up duration for the bioreactor was 3 to 5 days while the major problem associated with normal UASB reactors is long start-up. The reactor was operated at room temperature (25 °C) with various HRT of τ = 6, 9, 10, 13, 16, 20 and 24 h. The organic loading was gradually increased from 1.6 to 9.9 g L-1 h-1 COD. The UAPB reactor was continuously operated for 65 d. The treatment of high organic load dairy wastewater at HRT of 6 h was conducted. Maximum biogas production of 12.4 L h-1 (6.57 mol h-1) was achieved. At HRT of 16 h, a 94.5 % of COD removal was obtained. Methane yield of 0.12 g CH4 per g lactose at the highest OLR was achieved
