CS263862B1 - A method of treating waste water containing polyphosphate and emulsified petroleum compounds - Google Patents

Abstract

The process concerns the purification of non-acidic or alkaline wastewater containing polyphosphates and emulsified petroleum substances by coagulation with iron or aluminum salts. If the molar volume of Fe(Al):P is lower than 3.0, calcium salts are added to the clarified water in such an amount that the molar ratio between Ca:P is in the range of 1.5 to 9.0, preferably 3 to 4. The addition of calcium sulfate is preferred, which, due to its limited solubility in water, does not significantly increase the salinity of the purified water. After mixing, a coagulant is added to the wastewater and, after pH adjustment, the precipitated sludge is separated by sedimentation or, if necessary, by heating.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wastewater treatment comprising polyphosphates and emulsified petroleum products.

When clarifying waste waters with iron or aluminum salts, coagulation is adversely affected in the presence of some anions. Sorbed anions on the surface of the formed hydroxides increase the negative charge of the coagulation sludge, thereby reducing the efficiency of the process of removing emulsified petroleum substances or fats (usually having a negative charge). Phosphates are often present in industrial waste water (part of degraded alkaline illase and rinse water from alkaline degreasing). Phosphates reduce the charge of the formed hydroxide and promote the formation of a fine dispersion of hydroxides. These colloids do not settle and conventional hydroseparation processes (flotation, sedimentation) are ineffective. Especially katena polyphosphates negatively affect the clarification process.

In the treatment of polyphosphate catenous waste water, considerable excess iron or aluminum salts must be used for coagulation. Another method is the separation of waste waters with a high content of polyphosphate catenate and their separate treatment.

The essence of the proposed treatment is the addition of calcium salts to the waste water prior to coagulation with iron or aluminum salts. Catenapolyphosphates have a negative effect on the coagulation process if the Fe (Al): P molar ratio is less than 3.0, when colloidal precipitates are formed which are very difficult to separate. Of the category of polyphosphorates, the most important factor in the coagulation process is phosphate (pyrophosphates). The negative effect can be substantially reduced if calcium salts, preferably calcium sulfate, are added to the neutral or alkaline wastewater in an amount such that the molar ratio

The Ca: P was in the range of 1.5 to 9.0, preferably 3 to 4.

Katena polyphosphates are precipitated in the form of insoluble calcium salts when the p1 Ι of the wastewater is higher than 7.0. The clarifying efficiency of these calcium salts is very low. Calcium sulphate, due to its limited solubility in water, can also be added in considerable excess, without the enrichment of wastewater by electrolytes and the formation of volumetric sludge.

The process for the purification of polyphosphate caten waste water is further described in two exemplary embodiments.

Example 1

The weakly alkaline effluent contained 41.7 mg of katena polyphosphates. . I ' ¹ (as P). The concentration of the emulsified petroleum substances stabilized with the non-ionic surfactant was 430 mg. I ^-1 . After addition of 200 milligrams. 1 ^_1 crystalline aluminum sulphate (molar ratio Al: P = 0.45) lhodinové sedimentation, the residual concentration of 415 mg of oil products. 1 ^_1 . If before the addition of crystalline aluminum sulphate, 500 mg of calcium chloride was added to the waste water. ¹¹ (Ca: P molar ratio is 3.3), the residual content after coagulation was 25 mg. I ^-1 .

Example 2

To a waste water of the same composition as Example 1, calcium sulfate was added in an amount such that the Ca: P molar ratio was 4.0. After mixing and adding 200 mg. I ^{-1 of} crystalline aluminum sulfate, pH adjustment and 1 hour sedimentation, the residual oil content in the purified water was 21 mg. I ¹ .

Claims (1)

Process for the purification of neutral or alkaline waste waters containing catena polyphosphates and emulsified petroleum substances by coagulation with iron or aluminum salts, characterized in that if the molar ratio of Fe (Al): OF THE INVENTION: P is less than 3.0, calcium chloride is added to the treated waste water in an amount such that the Ca: P molar ratio is in the range of 1.5 'to 9.0, preferably 3 to 4.