Further Treatment of Oil-Containing Wastewater in the Buffer Pond of the Chernikovsk Oil Refinery

N. I. Alekseeva

From the Republican Sanitary and Epidemiological Station of the Bashkir ASSR

At existing oil refineries, the principal treatment facilities remain oil traps and earthen settling ponds that capture only floating oil. Dissolved and emulsified oil is not captured by these facilities and passes entirely into receiving waters. Consequently, the Belaya River in Bashkiria, as well as other rivers receiving refinery effluent, continues to be polluted with oil.

Through an extensive program of measures, Bashkir oil workers have achieved a marked improvement in the treatment of oil-containing wastewater while minimizing the total quantity of wastewater discharged into receiving waters. As a result, the sanitary condition of the Belaya River has improved over the past two years, but the river remains excessively polluted. In places its surface is covered by a continuous layer of petroleum products; the water smells and tastes of kerosene and carbolic acid (oil and phenols); and the shoreline vegetation, riverbed, and banks are contaminated with fuel oil over a considerable distance.

In our view, the results we have obtained from the further treatment of wastewater in the buffer pond being constructed at the Chernikovsk oil refinery are encouraging, and we consider it necessary to share these preliminary data.

The original design provided for a pond with a capacity of 5 million m³, in which wastewater would settle for 10 days. The designer subsequently reduced the pond capacity to 1 million m³ without consulting the State Sanitary Inspectorate, citing research institute data demonstrating only under laboratory conditions that settling wastewater in ponds for more than 2 days was ineffective.

By November 1957, the facilities required for the refinery’s startup were ready, but the full complex of treatment facilities had not been completed, and we did not authorize the refinery to begin operation. The refinery management subsequently proposed a plan, agreed upon with the State Sanitary Inspectorate, under which the refinery’s wastewater would be accumulated in the buffer pond without discharge into the Belaya River until construction of the full treatment complex was complete. Construction of the buffer pond had been completed, except for the oil-recovery installations. The relatively large capacity of the pond and the comparatively small volume of wastewater—80–100 m³ per day during the first months—made it possible to accumulate the wastewater there. Wastewater has now been accumulating in the pond for a year without being discharged into receiving waters. Of course, some of the wastewater evaporates and some seeps into the ground, since the pond is unlined, which, incidentally, is one of the major sanitary shortcomings of the design.

We were unable to assess the effects of seepage into the ground because the test pits for collecting water samples had not yet been completed.

Thus, favorable conditions arose for observing the processes of further wastewater treatment in the buffer pond during prolonged retention.

The buffer pond is located on the right bank of the Belaya River, 3–4 km from the water, in an area not subject to flooding. The pond is 1,000 m long, 250 m wide, and 4 m deep, with a capacity of 1 million m³. The pond is unlined; only the embankment is—

…lined with rubble stone. The pond consists of two sections; the effluent enters the first section, from which it can be discharged into the second.

Filling the pond with wastewater began during the cold season, in November 1957. At first, only the first section was filled, over a period of 1½–2 months. During the first few months, the incoming wastewater contained as much as 280–600 mg/L of petroleum products, and a thick oil film soon appeared on the pond surface because it could not be pumped off: the oil-recovery installations had not yet been completed. During this period, the pond operated as an ordinary earthen settling basin, and the effluent escaping through leaks in the stoplogs—discharge into the river having been prohibited by the State Sanitary Inspectorate—contained up to 70 mg/L of petroleum products. The color, transparency, oxidizability, and other characteristics of the wastewater remained entirely unchanged (see table).

The transparency of the wastewater entering and leaving the pond was 3–5 cm (by Snellen’s method), and an oil film rated at 4–5 points persisted in the second section as well.

Beginning in early May, the wastewater was discharged into the second section, where it remained for approximately 6 months before being released into the Belaya River. With the onset of warm, sunny days, the volume of incoming effluent increased at the same time, reaching 500 m³/h, while its petroleum-product content decreased. The wastewater in the pond changed from dark brown to pale yellow, its transparency increased from 3–5 to 16 cm, and the amount of petroleum products decreased. The oil film began to disappear, and the oxidizability of the effluent fell sharply.

Subsequently, in July–August, the degree of treatment of wastewater entering the second section of the pond improved somewhat further and became nearly stable (see table).

In the second section, the oil film disappeared completely; only isolated iridescent patches could be observed in windy weather.

Bottom-dwelling life appeared in the second section of the pond in the form of fouling organisms and various larvae. A rich bacterial flora was also present: more than 100 million bacteria per milliliter of water. These were mainly non-spore-forming types (Pseudomonas—fluorescent bacteria), as well as phenol- and hydrocarbon-degrading, denitrifying, cellulose-degrading, and sulfur-reducing forms.

It should be noted that a small amount of fecal and domestic wastewater entered the pond along with the industrial wastewater.

The marked improvement in the physicochemical properties of the wastewater, together with the presence of biological life in the second section of the pond, suggests that, during prolonged retention in this section, not only mechanical settling but also biological polishing of the wastewater takes place.

The results obtained, however, are achievable only at a ratio of effluent volume to pond capacity such as that at the Chernikovsk oil refinery. If wastewater from the entire group of Ufa plants were to enter this pond, as envisaged by the project, biological processes in the second section would, of course, cease or be substantially weakened, and the pond would operate like the ordinary earthen basins used for additional settling that are now found at almost all plants. In March–May 1959, as the volume of effluent increased, its degree of treatment declined somewhat, to 10–12 mg/L; the spring flood period may have been a contributing factor.

Conclusions and recommendations

1. The buffer pond at the Chernikovsk oil refinery provides a good degree of wastewater treatment, provided that the effluent remains in it for a prolonged period (5–6 months).

Results of laboratory analyses of wastewater from the buffer pond of the Chernikovsk oil refinery

There was no discharge into the river.

1. Throughout the observation period, the first section of the pond functioned as a simple settling basin of the earthen-pit type, since the oil-recovery installations had not been completed and there was no means of removing the oil that floated to the surface.

Effective treatment of the wastewater in the second section of the pond results not only from further mechanical clarification but also from biological processes.

1. The buffer pond we studied could have operated even more effectively if major design shortcomings had been remedied: oil enters the second section through the bottom outlet; operation of the oil-recovery installations is not automated; and no provision has been made for collecting floating oil or for lining the pond to prevent groundwater contamination.

2. To ensure the normal and efficient operation of buffer ponds, they must not be overloaded with wastewater when production is expanded.

3. After treatment in the buffer pond, the wastewater requires only odor removal by 100-fold dilution, which the Belaya River can provide.

Received March 5, 1959.