Restaurants and kitchens release large amounts of wastewater into the environment on a daily basis. Upstream anaerobic sludge bed system (UASB) can be effective in the treatment of this type of wastewater due to its advantages. In this method, granulated sludge, large molecules of oil, fat and detergents in wastewater are converted to biogas under anaerobic conditions. Therefore, the performance of the UASB in removing of COD and fat from wastewater of restaurant was investigated with 1925 and 225 mg/lit, respectively, COD and fat was investigated. The results show that the UASB wastewater treatment system is able to remove 78% of wastewater COD at temperature of 25 ℃ and a hydraulic residence time of nine hours. In addition, the effect of temperature and hydraulic residence time on the performance of the UASB system was investigated. The results show that with increasing temperature, the percentage of COD removal first increases and then decreases, so that at 40 ℃, 84% of COD wastewater is removed. Also, by increasing the hydraulic retention time to one day, the highest percentage of COD removal, i.e., 92.5%, was obtained at 40 ℃. The optimal treatment conditions for this type of wastewater in the UASB system, are this condition, and also the UASB system can be removed fat and nitrate 96.5 and 90%, respectively. In addition, the performance of the activated sludge aerobic treatment system was investigated and the results show the maximum removal of COD is 53.5%
