Ecological problems of utilization of waste activated sludge of saratov refinery and ways to solve them

Abstract

The ecological problems of the Saratov Refinery (SarNPZ) associated with utilization of waste activated sludge (WAS) are analyzed. The feasibility of utilization of this waste as a feedstock for producing sorbent for cleaning effluents from the refinery is examined. A technological scheme for producing, applying, and utilizing WAS-based sorbent is proposed.The Saratov Refinery (SarNPZ) refines six million tons of crude oil per year and produces Euro-2-class gasoline, kerosene, residual fuel oil, diesel oil, asphalt, sulfur, vacuum gas oil, etc.The Saratov Refinery has wastewater-cleaning plants and faces problems of utilization of waste activated sludge (WAS). The latter is a large-tonnage waste, which is difficult to utilize because of high content of oil products, heavy metals, and other toxic matters. At the same time, activated sludge has high resource and energy potentials because it contains 37-52% proteins, 20-35% amino acids, fats, carbohydrates, vitamin B, etc. The annual growth of biomass of waste activated sludge comprises several thousand tons. On an average, 3.2-3.5 m 3 of WAS is produced per 1000 m 3 of cleaned effluents. Waste activated sludge has been stored for the past 39 years on nine sludge dumpsites without being utilized (Fig. 1), which does not conform to present ecological requirements. That is why works on finding a solution to the problem of utilization of WAS are topical and are of great practical importance.The purpose of this work was to develop a technology for producing a sorbent from the WAS of the Saratov Refinery and to appraise the feasibility of its use for cleaning wastewaters (WW) from the oil products (OP).Polluted WW of the enterprise with an OP concentration of about 100 mg/liter of WW flow into the oil trap for cleaning from mechanical impurities and oil products. The throughput of the plant is 2600 m 3 /h. The efficiency of wastewater cleaning from OP does not exceed 75%. Thereafter, the oil-containing WW with a concentration of 25 mg/liter are sent for biological cleaning in aeration tanks of the stages I and II, where the effluents are continuously mixed with cultures of the activated sludge (1 m 2 of activated sludge contains 2·10 14 bacteria) with injection of oxygen. If the sludge concentration in the aeration tank exceeds 200 mg/liter, it is transferred to secondary precipitation tanks, where the sludge precipitates. The final stage of wastewater cleaning is filtration on ten quartz filters and treatment with ultraviolet radiation. The cleaned water (about two million cubic meters per year) is saturated with oxygen and discharged through sewer into the river Volga. After biological cleaning, the WAS is sent for sludge concentration and next for aerobic stabilization and is pumped out to sludge dumpsites.On an average, 3.2-3.5 m 3 of WAS with a moisture content of ~97% is produced per 1000 m 3 of cleaned effluents. It is difficult to utilize the WAS because of diversity of biomass composition and high moisture content.

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