removal of oil and grease from the wastewater of railroad repair shop

the purposes of this research have been to determine the wastewater quality of a typical railroad repair workshop and to find a way to reduce the concentrations of present contaminants especially oil and grease. the mean concentrations of oil, cod and ss in the wastewater studied were 287.69, 775.85 and 28723, respectively with average daily discharge to be 30-35 m3. three successive treatment processes were used and the results showed the first stage was gravity flotation with 90 minutes retention time. removal efficiencies achieved for cod, ss and oil were determined 43%, 49.4% and 55.5% respectively. the second stage of treatment was coagulation either lime or ferric chloride could be used for this purpose at phs of 9 and 6. cod and oil removals by lime treatment were 76.6% and 84.4%. the final stage of treatment was daf at 3 atmospheric pressure, by which 92.5%, 89.5%, 89.92% and 88% removals were achieved for oil, ss and cod, respectively.