European refineries separating more oils from wastewater

Although surveyed Western European refinery throughputs increased by more than 10% between 1993 and 1997, the ratio of oil discharged to the amount of oil processed fell.

Total quantity of oil discharged in 1997 is 42% less than that in 1993.

The total volume of effluent discharged from tracked refineries has remained relatively constant. The combination of a reduction of oil discharged and a constant effluent volume suggests that the efficiency of the effluent purification has improved. About 88% of refineries surveyed include biological treatment in their wastewater-treatment facilities.

These are the results of a study by Concawe (Conservation of Clean Air & Water, Europe), Brussels, the oil companies' European organization for environmental and health protection. "Trends in oil discharged with aqueous effluents from oil refineries in Europe" was published in December 1998. The Oslo and Paris Commission, London, also sponsored the survey.

Concawe surveyed countries in the European Union, Norway, Switzerland, and for the first time, Hungary. Responses were received from 105 of the 113 refineries surveyed. For analytical purposes, separate comparisons are made for the 90 refineries that responded both in 1993 and in 1997.

The reported capacities and throughputs of the past and recent surveys are listed in Table 1 [85,947 bytes]. Generally, refinery utilization has gradually increased from 70% in 1978 to 94% in 1998.

Wastewater-treatment systems

Wastewater-treatment systems to separate oil or other contaminants from water may fall into one or more of the following categories:

Gravity separation, which includes API separators, plate interceptors, and tank separation
Advanced treatment, which includes flocculation, air flotation, sedimentation, and filtration
Biological treatment, which includes biofilters, activated sludge, and aerated ponds.

Since the first survey in 1969, refineries have gradually added more effluent-treatment facilities. Refineries with all three types of wastewater-treatment systems are considered the most effective at treating wastes.

In 1969, only 23% of participating refineries in Concawe's survey reported using gravity separation, advanced treatment, and biological treatment. In 1997, 88% of participating refineries used all three types of treatment.

Likewise, the percentage of refineries using only gravity separation decreased drastically from 62% (of 82 refineries) in 1969 to 6% (of 105 refineries) in 1997. Since the 1993 survey, 3 more refineries reported the introduction of biological treatment.

Table 3 [92,002 bytes] illustrates the trend towards biological treatment. Of the 90 refineries that participated in both the 1993 and 1997 surveys, 26 reported making improvements to their effluent-treatment systems since the last survey.

Aqueous effluents

Although the total amount of aqueous effluents has increased since 1993, this increase is mostly attributed to the increase in the number of participating refineries. The ratio of aqueous effluent to the amount of oil processed has remained steady, ranging from 5.4 in 1978, to 4.8 in 1993, and to 4.7 in 1997.

According to Concawe, the significant reduction in the ratio of aqueous effluent to process capacity between 1969 and 1974 was a result of the increased use of air cooling and recirculating cooling water systems, as well as the more extensive reuse of water.

Concawe notes that major reductions in the aqueous effluent discharges between 1974 and 1978 were reported by older refineries constructed on or before 1960. Continual reductions between 1981 and 1990 are a result of plant closures and modifications to cooling systems.

Most of the increase in effluent discharge between 1993 and 1997 is a result of the increased number of refineries reporting discharge quantities. Between 1993 and 1997, effluent discharge increased from 2,670 million metric tons/year (mty) to 2,942 million mty.

Table 2 [61,788 bytes] reports aqueous effluent data collected from the surveys.

Hydrocarbon content

According to the survey, European refineries have systematically reduced the amount of oil discharged with aqueous effluents between 1969 and 1997.

Most refineries used infrared (IR) spectrophotometry to determine the oil content in aqueous effluents. One refiner used an ultraviolet method. Methods varied, however, even among those that used IR spectrophotometry. Refineries used different solvents and wavelengths to determine oil content.

Rather than listing every method used, Concawe presents the measured data as reported. These different test methods should be taken into consideration, however, when evaluating the data.

Comparative data on oil discharged is shown in Fig. 1 [50,722 bytes]. Total oil discharged with aqueous effluents has been reduced drastically since the first survey in 1969. In 1969, Concawe reported 44,000 metric tons (mt) of oil discharged by 73 refineries. In 1997, 105 refineries reported total oil discharges of 1,170 mt, a 97.4% reduction.

The ratio of annual oil discharge to refinery throughput was a high 24 mt/million mt of oil throughput in 1981. In 1997, this ratio was only 1.86 mt/million mt of oil processed.

Other compounds

Concawe's survey for ammonia, sulfides, and phenols is not as comprehensive as that for oil and aqueous effluents.

Concawe has not previously reported these data because not all refineries have reported this information and more importantly, there has been no agreed-upon method of analysis. In particular, ammonia measurements vary in quality.

Table 4 [53,354 bytes] shows the raw data collected in 1993 and 1997 for these compounds. Although there is a decrease in the volume of compounds reported, Concawe warns that caution should be used in interpreting these numbers for the reasons stated above.