Dual-Media Filtration for Treatment of Refinery Waste Water

Abstract

Abstract Waste water from refinery process units contains entrained oil and suspended solids which must be removed prior to discharge of the water. Primary gravity separation by an API separator reduces the oil and suspended solids concentrations. However, further treatment is usually required to make the water amenable to secondary treatment. Filtration is one of several processes which can be used in this service. Pilot studies were made on site at an Imperial Oil refinery. The filter media consisted of a 2 ft. depth of anthracite on top of a 1 ft. depth of sand. The filtration rate was varied and the filter was operated downflow with gravity flow. The average oil and suspended solids reductions were 75% and 55%, respectively. Run lengths of 15 to 40 hours were observed (depending upon feed quality) before backwashing was required and the amount of backwash water was 1 to 2 vol % of the water filtered. Based on these pilot data, a dual-media filter was constructed at an Imperial Oil refinery to treat 6,000 US gal/min. Data from the first year of operation show a very good agreement with the design values. The average percentage reductions of oil and suspended solids were 79% and 54%, respectively. The average effluent oil concentration is less than the design target. The filtration cycle length is 13 hours due to a slightly higher suspended solids in the feed than expected. No deterioration of the filter media has been observed with time. The backwash is treated by chemical flocculation to reduce its volume and the sludge is disposed of by incineration.