When OLR was increased from 16 to 24 g COD/L. d. on 188 day the biogas production decreased from 37.1 to 25.71 L/d. Gao et al.,reported that volumetric biogas production increased with increasing OLR but afterwards began to decrease due to deterioration of COD removal efficiency during treatment of distiller’s grains wastewater in UASB reactor