The increasing amount of industry in the world and the consequent production of waste and wastewater treatment is a problem that needs to be solved sistematically. Therefore, the aim of this study was to investigate the effectiveness of iron chloride and polyacrylamide (PAM) in coagulation and flocculation processes, to determine optimal dosages and to find out the influence of pH value and temperature of water medium on sedimentation processes. The examination was carried out on sample of wastewater from oil rafinery in Urinje using JAR test. The optimal dosage of iron chloride and polyacrylamide has been established by measuring the settling velocity of formed flocs.By comparing the results of settling velocity in dependence on addition of 0,90, 1,35 and 1,80 ml of iron chloride, it was concluded that 1,35 ml is the optimal dose of iron chloride. Among the samples in which was added 10, 15 and 20 ml of polyacrylamide, the best results were achieved at 15 ml of PAM.The pH value was regulated by the addition of 0, 0,25, 0,50 and 1,0 ml of nitric acid. Results showed that sedimentation processes are slowed down by lowering the pH value. Dependence of settling velocity of formed flocs on temperatures of 22 ℃ and 4 ℃ was also investigated and it was shown that low temperature does not improve sedimentation processes. The quality of wastewater was determined by measuring turbidity with measuring cylinder and secchi disk. Turbidity of untreated wastewater was 151,86 NTU. After treatment,almost all samples were completly transparent. However, in two samples treated on temperature of 4 ℃ cloudliness wasn't completly reduced which is probably due to innapropriate dosage of treating chemicals whose effectiveness is further reduced at low temperatures. Optimization of physicochemical parameters is nessesary, daily but also a powerful tool in real wastewater treatment.