RU2237619C1 - Waste water dephosphatization method - Google Patents

Abstract

FIELD: waste water treatment.

SUBSTANCE: treatment of phosphorus-containing waste water, which can be applied on water-treatment plants, in particular on sewage treatment plants, is conducted with the aid of aluminum chloride solution obtained as ethylbenzene production waste, which is characterized by aluminum chloride concentration 1.5-8,2 g/L, that of free hydrochloric acid 1.1-48.0 g/L, and pH 0.9-2.9. This solution is preliminarily treated with alkali solution adjusting pH to 3.8-4.3 and then is added water in amount 1.0-3.2 L/m³ (on conversion to Al³⁺ 1.6-5.0 mg/L). treatment of effluents and sedimentation are effected at pH 6.5-7.4.

EFFECT: enabled production of good-quality clarified water, reused production waste, and simplified and stabilized sedimentation process and subsequent biological purification process.

Description

The invention relates to reagent treatment of domestic and industrial wastewater, namely to the treatment of effluents from phosphates, and can be used at treatment and water treatment plants, in particular at biological treatment facilities (BF).

Phosphorus is one of the biogenic elements that are of particular importance in the biological cycle both in water bodies and in the activated sludge of biological treatment plants. With a lack of phosphorus compounds in water, the growth and development of aquatic flora and fauna is inhibited, however, their excess also leads to negative consequences, causing the development of ectrophication processes and the deterioration of water quality. Therefore, in the technology of biological treatment of domestic and industrial wastewater at BF there is an urgent need to reduce the concentration of phosphates in treated effluents to the standards provided by sanitary standards.

Phosphorus compounds in natural and waste waters are represented as orthophosphates, polyphosphates and organic phosphorus compounds, with orthophosphates being the predominant form.

Phosphoric acid (medium strength), being a tribasic, is able to form three types of salts, for example:

Acid salts:

- NaH ₂ PO ₄ primary sodium phosphate;

- Na ₂ HPO ₄ secondary sodium phosphate;

Medium Salt:

- Na ₃ PO ₄ tertiary sodium phosphate.

All primary phosphates are highly soluble in water, only a very few of the secondary and tertiary are soluble, in particular sodium salts (B.N. Nekrasov. Fundamentals of General Chemistry, Vol. 1, ed. 3rd ed. And add., M. : Chemistry, 1973, p.440).

In waters, phosphorus compounds, both mineral and organic, can be present in dissolved, colloidal, and suspended states. The transition from one form to another is relatively easy.

Wastewater treatment is carried out at wastewater treatment plants with or without the use of chemicals. The treatment of water with coagulants makes it possible to convert mineral impurities into an insoluble form. Such reagents include salts of calcium, iron and aluminum.

A method of wastewater treatment, characterized by improved characteristics of the separation of solid particles, reduced biological oxygen demand (BPC) in treated wastewater and increased removal of nitrogen and phosphate, is described in US Pat. RU 2148033, 7 C 02 F 3/30. From Pat. RU 2145942, 7 C 02 F 1/52, 1/54, publ. 02/27/2000, No. 6, it is known that wastewater is treated using lime and a hydrolyzable salt of iron or aluminum at optimal pH values. A method of wastewater treatment, including mixing wastewater with aluminum sulfate (12-20 mg / l) at a given pH value (6.5-7.6), is set forth in US Pat. RU 2145575, 7 C 02 F 1/52, publ. 02/20/2000, No. 5.

For the purification of large-tonnage industrial effluents using chemical reagents, a high consumption of scarce and expensive coagulants is characteristic, the production of which is associated not only with significant material costs, but also with environmental problems. At the treatment plants, there is an urgent need for the construction of reagent farms and their equipping with special technological equipment, which leads to the high cost of cleaning due to the large material and energy costs.

Closest to the technical solution to the proposed invention, the method described in US Pat. RU 2151172, 7 C 12 F 3/10, publ. 06/20/2000. Number 17. The essence of this technical solution is to remove suspended, colloidal and dissolved organic and mineral impurities by coagulation at the stage of precipitation with aluminum hydroxide.

A common feature of the present invention is the use for agglomeration of particles at the stage of deposition of a hydrolyzable aluminum salt. This method has the above disadvantages.

Closest to the claimed method of purifying water from phosphates (prototype) is the method for extracting phosphate from wastewater (CB), described in (V.A. Proskuryakov, L.I. Schmidt. Wastewater treatment in the chemical industry. Chemistry Publishing House, Leningradskoye Department, 1977, p.138). The essence of this technical solution is the precipitation of phosphates by aluminum sulfate in an alkaline environment. The cleaning efficiency is 90-95%.

In addition to the above disadvantages, in this case there is a secondary pollution of clarified water with salts and ions, because a characteristic feature of technical reagents is the high content of ballast in them and a small amount of the main substance (active principle).

The objective of the invention is:

- expanding the range of highly effective, affordable and inexpensive reagents for the extraction of phosphates from wastewater while maintaining a high degree of water purification;

- prevention of secondary pollution of treated effluents with salts and ions contained in the used reagent solutions;

- reducing the cost of cleaning by reducing material and energy costs;

- simplification and increasing the stability of the process;

- qualified use of production waste.

The elimination of these shortcomings in the method of purification of wastewater from phosphates, including the treatment of water with a hydrolyzed aluminum salt, and the achievement of a technical result is possible due to the fact that an aluminum chloride solution is used as a hydrolyzed aluminum salt - a waste product from ethylbenzene production, which is characterized by the following indicators, g / dm ³ : aluminum chloride 1.5-8.2, free hydrochloric acid 1.1-48.0, pH 0.9-2.9, and before use, it is treated with a solution of alkali, bringing the pH to 3.8-4, 3, the reagent is administered water in an amount of 1.0-3.2 dm ³ / m ³ (based on A1 ⁺³ 1,6-5,0 mg / dm ^3), and the pH of the treated water varies within 6.5-7.4 .

A comparative analysis of the prototype and the present invention shows that a common feature is the use of hydrolyzable aluminum salts as precipitators of phosphates.

The difference of the proposed method from the prototype lies in the fact that as an aluminum-containing reagent for the precipitation of phosphates, ethylbenzene production waste is used - an aluminum chloride solution, which is treated with alkali before adding to the purified water to a pH of 3.8-4.3, the dose of the reagent is 1.0- 3.2 dm ³ / m ³ (in terms of Al ⁺³ 1.6-5.0 mg / dm ³ ), and the pH of the treated water varies between 6.5-7.4.

A distinctive feature of this reagent is that it was obtained under industrial conditions from the production of ethylbenzene using anhydrous aluminum chloride as a catalyst and represents waste water. Before discharging into factory-wide sewage facilities, these effluents are treated with alkali to comply with sanitary standards in terms of pH. Practice has shown that there are high material costs for alkalizing waste and its further neutralization.

It is proposed to alkalize the aluminum chloride solution to a pH of 3.8-4.3, which makes it possible to obtain a solution of aluminum hydroxychlorides of the general formula Al (OH) _n Cl _m , where n = 1-5, m = 6-n. The alkali consumption is significantly reduced.

The proposed method is tested in laboratory conditions. The alkali-treated solution of aluminum chloride is added to a mixture of household and chemically contaminated phosphorus-containing effluents entering the primary settling tanks of biological treatment plants (BWF) in an amount of 1.0-3.2 dm ³ / m ³ (in terms of Al ⁺³ 1.6-5-5, 0 mg / dm ³ ).

For comparison, phosphorus-containing water is treated with a solution of aluminum sulfate, the amount of added reagent in terms of A1 ⁺³ is 2.0 mg / dm ³ (24.7 mg / dm ³ for Al ₂ (SO ₄ ) ³ × 18 N ₂ O).

The experiments simulate the process of sedimentation of wastewater in the sedimentation tanks of BFW and they are carried out as follows. Wastewater is mixed and poured into graduated cylinders, then a calculated aliquot of this or that reagent is added. All samples are thoroughly and uniformly mixed for 1-3 minutes and settled for 2 hours at 18-22 ° C. During sedimentation, the kinetics of sedimentation of the precipitate formed is monitored, and after 2 hours the clarified water is decanted from the latter and analyzed .

Experimental data show that when the above-mentioned reagents are added to the purified water, intense flocculation, agglomeration of small particles, and precipitation of the resulting hydrolysis products with pollutants adsorbed on their surface (phosphates, incl.) Are observed.

The efficiency of the separation of phosphates from the treated with aluminum chloride (2.0 mg / dm ³ in Al ⁺³ ) water is at least 90 wt.%. When using aluminochloride in an amount of 2.0 mg / dm ³ (according to A1 ⁺³ ), the pH value changes within the sanitary standards and is 6.9-7.4. An increase in the concentration of this reagent in wastewater to 5 mg / dm ³ (for Al ⁺³ ) does not require adjustment of their pH value, which ranges from 6.5-7.2. A positive point when using an aluminum chloride solution as a reagent is a more stable water purification process. The achieved degree of purification of effluents from phosphates using waste products seems to be quite acceptable, because their residual concentration in clarified water is necessary and sufficient for the normal further conduct of the biological treatment of the above wastewater. Successful biochemical wastewater treatment, as well as effective denitrification and dephosphatization, are due to the fact that in the water treated with the proposed reagent, the ratio of the concentration of BOD to the concentration of nitrogen and phosphorus compounds meets the requirements of sanitary standards.

The depth of water purification from phosphates by aluminum sulfate (2.0 mg / dm ³ in Al ⁺³ ) is at least 97 wt.%. However, when using aluminum sulfate, a significant drawback is a twofold increase in the concentration of sulfate ions and the total salt content in clarified water, a decrease in the pH of clarified water to 4.4-6.4, the possibility of an overdose of the reagent and destabilization of the water treatment process. The addition of aluminum sulfate to the clarified water in an amount of more than 2.0 mg / dm ³ (for Al ⁺³ ) without adjusting the pH value is also not possible, because The pH of the water drops to 4.3-5.7. The latter, in addition, is not optimal for the precipitation of phosphates.

The proposed method of wastewater treatment from phosphates allows:

- expand the range of reagents for the extraction of phosphates and get a high cleaning effect;

- eliminate the need for complex, time-consuming and expensive processing (for example, centrifugation and heating) of industrial waste before use;

- reduce material costs for the treatment of industrial waste and purified water;

- eliminate the disadvantages characteristic of reagents traditionally used in water treatment processes, namely: to reduce the influence of the reagents used on the parameters of the sanitary norms of the treated water; eliminate the need for additional processing (adjusting the pH value) of the treated water both at the stage of precipitation of phosphates and at the stage of biological treatment; reduce the secondary pollution of the treated water with the ingredients contained in the reagents used;

- to simplify and increase the stability of the process of precipitation of phosphates and then the process of biological treatment of this water;

- Dispose of waste products, a valuable component of which is used in the same enterprise.

Claims (1)

A method of treating wastewater from phosphates, including treating water with a hydrolyzed aluminum salt, characterized in that an aluminum chloride reagent is an aluminum chloride solution — an ethylbenzene production waste, which is characterized by the following parameters, g / dm ³ : aluminum chloride 1.5–8.2; free hydrochloric acid 1.1-48.0; the pH is 0.9-2.9, and before use it is treated with an alkali solution, bringing the pH to 3.8-4.3, and then added to water in an amount of 1.0-3.2 dm ³ / m ³ ( in terms of A1 ⁺³ - 1.6-5.0 mg / dm ³ ), the pH of the purified water in this case varies between 6.5-7.4.