RU1798323C - Method for purification sewage against phosphates - Google Patents

Description

purification rates remain virtually unchanged; therefore, for economic reasons, the lower limit of the Ca +: P ratio is limited to 2.7.

The precipitation of phosphates by the claimed method produces a bladder having a sludge rate under the indicated conditions (35-50 ° C, GPAA) up to 1.5 m / h (0.42 mm / s), which is approximately 20 times higher than the sludge rate sludge in the known method (1) with a degree of purification of a solution of 1-1.5 mg / DM residual phosphorus.

With a large initial phosphate concentration of 7.5 g / dm3, the volume of compacted sludge is negligible and amounts to 21-23%. According to (1), the same sludge volume is assigned to a significantly lower initial phosphate concentration - 1.35 g / dm.

Mineralized effluents, which often contain a large excess of soda ash (e.g., polycarbonate effluents), can be used to purify CB from phosphates. In the absence of carbonate ions in the effluent, a solution of soda ash is added to the solution to be purified in accordance with the stoichiometry of equation (2) -CO327P 1.

After purification from phosphates, the sodium chloride content in the effluent increases according to equation (2). Moreover, it is possible to utilize said salt waste, for example, in the production of chlorine and caustic. To purify phosphate solutions, a sodium chloride solution (crude brine) containing calcium chloride as an impurity can be used directly as a calcium-containing reagent.

Thus, in the presence of carbonate ions, phosphate ions react with calcium ions, forming a new compound that can significantly accelerate the sludge process, due to the structure of the precipitate, which intensifies and simplifies the purification process as a whole.

Example 1.1l of wastewater having a composition (g / dm3): NaaPCM - 7.5; No. 2CO3 -13; NaOH - 12.5; NaCI - 1.7 is heated to 40 ° C and treated with a solution of calcium chloride at the rate of 4.86 g / dm3 of Ca2 +, which corresponds to a molar ratio of Ca to P equal to 2.7. It is stirred for 10 minutes, after which 10 mg / dm of hydrolyzed polyacrylamide (GPAA) is added and sedimented. The sludge settling rate is 1.45 m / h or 0.4 mm / s, the transparency of the clarified solution is 100%; impurity content in clarified wastewater: + phosphorus - 1 mg / dm3, 8 g / dm3, NaOH 11.6 g / dm3. Volume

compacted sludge - 21%. No waste water filtration is required.

Examples 2-6. In the conditions of example 1, the solutions are purified at different

molar ratio Ca / P. The results are shown in table. 1.

L e m s 7-11. Under the conditions of Example 1, solutions were purified at various temperatures. Examples are given in table. 2.

Examples 12-13. Under the conditions of Example 1, solutions were purified with a dosage of flocculant - hydrolyzed polyacrylamide before the sedimentation stage and without flocculation of 5 lt. The results are shown in table. 3.

EXAMPLE 14.1 L of a solution containing 7.5 g / dm3 of MazP04, 1 g / dm3 of NaOH, 1.7 g / dm3 of NaCl (NaACO3 absent) is heated to 40 ° C, a solution of soda ash is added, the dose of which corresponds to control stoichiometry (2) —CO3 / P - 1 is treated with a solution of calcium chloride, the dose of which corresponds to a molar ratio of Ca + / P of 2.7. Mix

5-10 min, add 10 mg / dm3 GPAA and assert. The phosphorus content in the solution after sludge is 1 mg / dm, the transparency is 100%, the sludge sedimentation rate is 1.65 m / h (0.46 mm / s), the sludge volume is 20%.

Example 15. 200 ml of a solution having a composition (g / dm3): No. zrol - 7; 5, Ma2COz - 13; NaOH - 1; NaC113.1 is heated to 40 ° C and 1 L of saturated brine containing 300 g / dm3 NaCl and 4.1 g / dm3 is added.

5 CaCl2 (1 g / dm3 Ca j, which corresponds to a molar ratio of Ca / P of 2.7. Stir for 10 minutes, after which 3 mg / dm of HPAA are added and stand.

The phosphorus content in the sediment

0 solution - 1 mg / dm, solution transparency 99%, sludge sedimentation rate 3.6 m / h (1 mm / s). The slurry volume is 9%. The sodium chloride solution is sent to chlorine production.

5

Example 16.1 L of a solution containing (g / dm3): NasPO4-7.5; NaOH-12.5, NaCf-1.7, NaACO3 - absent, heated to 40 ° C and worked out with a solution of chloride

0 calcium at the rate of 3.35 g / dm3 Ca2, which corresponds to a molar ratio of Ca and P equal to 1.87. in the presence of a returous sludge, a previously formed calcium hydroxylapatite precipitate, which was added to the zone

5 reactions in an amount of 50% to the freshly formed hydroxylapatite precipitate. The mixture was stirred for 90 minutes and settled. The sludge settling rate is 0.19 m / h (0.05 mm / s), the transparency of the clarified part of the solution is 80%, the residual phosphorus content in the filtered solution is 15 mg / dm3, and the volume of sludge is 40%.

The results of the experiments show that the optimal conditions for conducting the process of purifying wastewater and technological solutions from phosphates is the ratio of reagents Ca2 + / P 2.3-2.7 (Table 1), maintaining the temperature within 35-50 ° C ( Table 2), the addition of flocculant - hydroisolated polyacrylamide before the sludge stage (Table 3), the presence of soda ash in the cleaning process (Example 1).

The upper and lower limits of the limitation of the molar ratio Ca2 + / P (2.3 - 2.7) are due to the achievement of deep purification from phosphorus, a high sedimentation rate with a minimum amount of sludge. In addition, the conduct of the process with a Ca / P ratio of more than 2.7 is impractical due to the increased consumption of the precipitating reagent (see Table 1).

The data given in Table 2 show that, when the temperature rises above 50 ° С, the previously precipitated phosphorus begins to pass back into solution. At temperatures below 35 ° C, the reaction rate and sludge settling rate are negligible. The optimum temperature range is 35-50 ° C.

As can be seen from Table 3, with the use of flocculant, the sludge settling rate significantly increases and its volume decreases. The dose of HPAA depends on the initial phosphate content in the effluent, the amount of sludge generated and is determined experimentally in each case.

The research results show that in the absence of soda ash, the process of the formation of hydroxylap

tita even at elevated temperature (40 ° C) and v a large dosage of reture sludge (50% of the formed) has unsatisfactory technical indicators (example 16),

Thus, the proposed technical solution, in comparison with the known one, allows, along with a deep purification from phosphate, to intensify the process due to a significant increase in the sludge removal rate, and a decrease in its volume. Ensuring the transparency of the clarified solution 99-100% eliminates the additional step of filtering the clarified solution. The consumption of reagent-precipitator is reduced, and the possibility of disposal of treated effluents appears. All this makes the process technological and cost-effective.

Claims (2)

1. The method of purification of wastewater from phosphates by treatment with a calcium-containing reagent in an alkaline medium followed by separation of sludge, characterized in that, in order to intensify and simplify the purification process while ensuring a high degree of purification of wastewater from phosphates, as a calcium-containing reagent a solution of calcium chloride is used, and purification is carried out at a molar ratio of Ca2 + / P equal to 2.3-2.7 and a temperature of 35-50 ° C in the presence of soda ash followed by the introduction of hydrolyzed polyacrylamide. 2. A method according to claim 1, characterized in that a crude brine of sodium chloride is used as the calcium chloride solution. Table 1 -2-1Са / Р 2,7, GPAA dose 10 mg / dm 3 table 2 Table 3