RU2109695C1 - Method for consecutive additional purification of usual and industrial sewage after their biological purification against suspended materials, organic impurities, ammonium nitrogen and phosphate phosphorous - Google Patents

Abstract

FIELD: additional purification of usual and industrial sewage after their biological purification against suspended materials, ammonium nitrogen, phosphate phosphorous and organic impurities. SUBSTANCE: biological purification of sewage is followed by its additional purification which takes place with the help of sorbents being used rigorously one after another. To extract suspended materials and organic impurities carbon-containing sorbent is used, to extract ammonium nitrogen cationite being used. For extraction of phosphate phosphorous is used filler, on its surface chemosorption takes place. Sewage being affected by additional purification comprises, mg/l: suspended materials, 2.5-4.5; ammonium nitrogen, 0.15-0.49; phosphate phosphorous, 0.03-0.18. EFFECT: improved efficiency of the method. 2 dwg

Description

 The invention relates to the field of post-treatment of industrial and domestic wastewater to remove suspended solids, organic impurities, determined by BOD or COD, ammonium nitrogen and phosphorus phosphates.

 A known method of removing phosphates from biologically treated wastewater or in the process of biological treatment by coagulation of wastewater with aluminum hydroxide formed in the system when an aluminum sulfate solution is introduced into it [1].

 The achievement of the technical result is hindered by the following: no methods are provided for the post-treatment of wastewater from nitrogen, suspended solids and organic contaminants. The analogue indicates the need for purification of wastewater from phosphates by filtration after x-ray treatment, but the filtering conditions and filter material are not mentioned.

- 8-10 мг/л концентрация фильтрата в очищенной воде - 0,8 мг/л, ХПК - 50 мг/л [2].It is known to remove phosphorus from wastewater by using a flooded biofilter with a charge consisting of a mixture of: Al ₂ O ₃ ; Fe ₂ O ₃ ; CaO; MgO; K ₂ O; SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{3}}$ ; SiO ₂ taken in various ratios, the particle size of the particles is 5-7 mm Mention is made of the effect of Ca ²⁺ on the process of biological phosphation. When treating urban wastewater with a COD of 640-840 mg / l and concentration

- 8-10 mg / l the filtrate concentration in purified water is 0.8 mg / l, COD - 50 mg / l [2].

 The achievement of the technical result is hampered by the lack of information on the removal of nitrogen and suspended solids, the difficulty of preparing the load due to the large number of its components and the need to shift the components of the load in quantities determined by the second decimal place. The quality of purified phosphate water does not meet the requirements of the bodies of the nature protection committee (MPC - 0.6 mg / l).

 A known method of two-stage wastewater treatment on filters with zeolite loading. It is indicated that at the first stage, the grain fineness is 1-5 mm, the filtration speed is 6-10 m / h and the possibility of biofilm formation on the surface of the granular load and the course of nitrification processes. At the second stage, ion-exchange processes predominate. As a result of the application of the method, the quality of the purified water meets the requirements of state environmental protection bodies [3].

 The achievement of the technical result is hindered by the following: there are no data on wastewater treatment from phosphorus.

Closest to the proposed method is the method [4], based on the principle of sorption and characterized by high phosphorus capacity and filtrate performance. Fe (OH) _{3 was} chosen as the sorbent, which was used in the installation in a mixture with sand. With an average water consumption of 60-120 l / day, the degree of phosphorus extraction is reached 95-99%, for nitrogen - 98-99%.

The achievement of the technical result is hindered by the following. No data are given on the reduction of concentrations of organic pollutants and suspended solids. The initial concentrations of phosphorus and ammonium nitrogen are not indicated, which makes it impossible to evaluate the effectiveness of the method. The indicated performance limit is not industrial. The mechanism of nitrogen removal is not clear from the source, the species composition of sand and the ratio of sand to Fe (OH) _{3 are} not indicated, which complicates the analysis and use of this method.

 To achieve a technical result, it is proposed to improve the method of tertiary treatment of domestic and industrial wastewater, which will allow, after biological treatment, tertiary treatment of residual concentrations of polluting components: suspended solids, organic pollutants (estimated by BOD, COD), ammonium nitrogen and phosphate to concentrations not provoking eutrophication of water bodies.

- 0,15-0,49 мг/л;

- 0,003-0,18 мг/л.The technical result is achieved by the fact that the method of sequential treatment of domestic and industrial wastewater after their biological treatment of suspended solids, organic pollutants, ammonium nitrogen and phosphorus phosphates provides for their contact with a developed loading surface from a mixture of sand with adsorbent - Fe (OH) ₃ to extract from wastewater nitrogen and phosphorus. Moreover, the load is differentiated sequentially by the ability to target recovery of these pollutants. A carbon-containing sorbent is used to extract suspended solids and organic impurities, cation exchanger is used to extract ammonium nitrogen, a charge is used to extract phosphorus phosphates, on the surface of which chemisorption occurs, with a suspension of 2.5-4.5 mg / l of suspended solids in the treated wastewater; BOD _p 2.0-2.9 mg / l;

- 0.15-0.49 mg / l;

- 0.003-0.18 mg / l.

Biologically purified water is initially supplied to a carbon-containing feed. Carbon-containing loading with grain sizes of 1.5-2 mm sorb suspended substances and organic contaminants. At the same time, microorganisms develop on the loading grains and, along with physical and chemical sorption, a biosorption process takes place, in which microorganisms use substances that cause organic pollution of biologically treated wastewater in the process of metabolism. In this case, the carbon-containing surface is a catalyst for the enzymatic reactions of microorganisms. Then, the wastewater after purification on a carbon-containing charge is fed to a cation exchange charge. Upon contact of purified water with cation exchange resin, ion-exchange processes take place, intensified by the absence of load calcination due to the extraction of suspended solids at the previous stage and the possibility of using the load in fractions of 0.5-1.5 mm. Further, the wastewater enters the charge, on the surface of which chemical sorption of phosphate ions occurs. In this case, the selection of the sorbent is made on the basis of the conditions for the formation of insoluble phosphates on the surface of the load. Since water-insoluble compounds are formed as a result of the interaction of trisubstituted phosphates with divalent and trivalent cations, it is proposed to use materials containing divalent and trivalent cations, for example, calcium, iron, and aluminum, as sorbents. In this case, the intensification of chemical interaction is carried out as a result of an increase in the specific surface of the sorbent due to the use of a fine-grained charge, the grain size is 0.3-1.0 mm. The use of these fractions is possible as a result of preventing calcination at the 1st and partially 2nd stages of post-treatment. When using the proposed method, the purified wastewater has the following indicators: for suspended solids - 2.5-4.5 mg / l; for BOD _p - 2.0-2.9 mg / l; ammonium nitrogen - 0.15-0.49 mg / l; phosphorus phosphate - 0.003-0.18 mg / l.

 The basis for the selected limits is as follows: exceeding the upper specified limits leads to an irreversible violation of the ecological balance of water bodies, leading to their eutrophication. The reduction in suspended solids, organic pollutants and ammonium nitrogen below the lower limit to the irrational rise in price of the method. The value of phosphorus phosphates below the lower limit is limited by the error of the instruments and the method for determining phosphorus.

The difference between the invention and the prototype is the sequential extraction from wastewater of their biological purification of pollutants: suspended solids and organic pollutants, ammonium nitrogen, phosphorus phosphates using a load differentiated sequentially by the ability to target the specified pollutants. A carbon-containing sorbent is used as a charge for extracting suspended solids and organic impurities, cation exchange resin is used as a charge for extracting ammonium nitrogen, and a charge is used as a charge for extracting phosphorus phosphates on the surface of which chemisorption takes place. As a result of post-treatment, wastewater has the following indicators: for suspended solids - 2.5-4.5 mg / l; for BOD _p - 2.0-2.9 mg / l, for ammonium nitrogen - 0.15-0.49 mg / l; phosphorus phosphate - 0.003-0.18 mg / l.

 Thus, the invention meets the condition of novelty.

 The proof of compliance of the invention with the condition of inventive step may be as follows. The proposed method consists of three stages, united by a single method for the extraction of pollutants - using processes that occur on developed surfaces, namely, with the use of sorbents that work in strict sequence. Moreover, at each stage of post-treatment, a load adapted to the selective extraction of pollutants (which is connected with the indicated sequence of stages) and having a different fractional composition is used. The fractional composition and type of loading are determined by the presence of the indicated pollutants in the wastewater entering each stage of post-treatment. So, the first stage receives wastewater with a high content of suspended solids and organic pollutants. To increase the time between washings of the load and taking into account the effective retention of suspended solids in the first stage, load fractions of 1.5-2 mm in size are used. Organic contaminants are recovered both during their adsorption on the loading surface and as a result of biosorption. To increase the extraction of organic contaminants as a result of biosorption, carbon-containing sorbents with a large number of micropores are used that contribute to the development of biosorption. The possibility of biosorption is due to the presence of an organic substrate (organic contaminants) and nutrients in biological wastewater.

Wastewater with suspended solids content not exceeding 2.5-4.5 mg / L as a result of purification in the first stage arrives at the second stage, therefore, the possibility of load calculation in the second stage is reduced and it becomes possible to use finer charge fractions relative to the first stage 0 5-1.5 mm. In addition, at the first stage, there is a decrease in the content of organic pollutants in dissolved form, which eliminates the occurrence of biosorption at the second stage of post-treatment, makes it possible to most effectively use the ion-exchange qualities of exchange sorption realized on cation exchange resin, and to extract ammonium nitrogen. In the third stage, wastewater is supplied with permissible low concentrations of suspended solids and organic pollutants in dissolved form that do not lead to load calcification, which do not lead to the development of biosorption, and with a high content of phosphate ions. Wastewater sent for purification from phosphates has a pH value of 6-8. Phosphates in this case are presented in the form of a phosphate ion H ₂ PO $\genfrac{}{}{0ex}{}{\text{-}}{\text{4}}$ . In the interaction of phosphate ions with sorbents, along with physical sorption, chemisorption is possible, proceeding by the ion-exchange mechanism:
Al-H ₂ O] ⁺ + H ₂ PO $\genfrac{}{}{0ex}{}{\text{-}}{\text{4}}$ _ → Al-H ₂ PO ₄ ] + H ₂ O
or
Al-OH] + H ₂ PO $\genfrac{}{}{0ex}{}{\text{-}}{\text{4}}$ _ → Al-H ₂ PO ₄ ] + OH ^-
The effect of removing phosphate ions from wastewater is higher during chemisorption. Since in this case, the desorption process does not significantly affect alkali metal orthophosphates, monosubstituted and disubstituted alkaline earth metal phosphates are quite soluble in water, and trisubstituted phosphates of divalent and trivalent cations are very difficult to dissolve in water. Therefore, it is proposed to use natural and synthetic materials as sorbents, the main components of which are divalent and trivalent cations, for example, Ca, Fe, Al. For almost complete extraction of phosphate ions with the achievement of residual concentrations of up to 0.003-0.18 mg / l on phosphorus, an additional mechanism of chemisorption during loading is used for sorption. Moreover, due to the treatment of water at the first stage, favorable conditions are created (exclusion of calcination) to increase the specific surface of the sorbent due to the use of fine fractions of 0.3-1.0 mm. In this case, the selection of the sorbent is made on the basis of the conditions for ensuring the process of chemisorption. And all taken together allows you to improve the method of purification of domestic and industrial wastewater after biological treatment from residual concentrations of polluting components: suspended solids, organic pollutants (estimated by BOD _p , COD) of ammonium nitrogen and phosphorus phosphates to concentrations that do not provoke eutrophication of water bodies.

 Thus, the invention meets the condition of inventive step.

Example 1. The post-treatment process is schematically represented in FIG. 1. Wastewater that has undergone biological treatment (not shown in the diagram), composition: t = 20 ^o C; BOD ₅ = 10 mg / l; suspended solids - 15 mg / l; ammonium nitrogen - 10 mg / l; phosphorus - 2 mg / l, fed to limestone-shell rock (I), grain size - 1.5 mm, filtering speed - 1 m / h. As a result of the contact of wastewater with the loading, a biofilm is formed on the surface of the grains. When creating favorable conditions (aeration), aerobic microorganisms in the process of metabolism extract organic substances contained in the wastewater supplied to the aftertreatment, and causing organic pollution, estimated by BOD. Suspended matter is retained in the loading layer. The established decrease in the concentration of suspended solids from 15 mg / L to 4 mg / L and the extraction of organic pollutants according to BOD ₅ from 10 mg O ₂ / L to 1.8 mg O ₂ / L in wastewater purified on limestone-shell rock (BOD _n = 2.2 mg O ₂ / L). Wastewater treated after purification on limestone-shell rock was then fed to a clinoptilolite (2) charge with a grain size of 0.7 mm. The filtration rate for the extraction of ammonium ions is 1 m / h. The highest sorption of NH cations $\genfrac{}{}{0ex}{}{\text{+}}{\text{4}}$ observed at pH = 7.0. The post-treatment efficiency was 95%, which corresponded to a concentration of ammonium nitrogen at the output of 0.45 mg / L. at the final stage of post-treatment, the wastewater was fed to the load — limestone-shell rock (3) with a grain size of 0.7 mm and a filtration rate of 1 m / h, on the surface of which chemisorption occurred with the formation of sparingly soluble compounds, presumably octocalcium phosphate - Ca ₄ (PO ₄ ) ₃ H • 3H ₂ O with pK = 146.9. The maximum extraction of phosphate ions was observed at pH 7-7.5. In the purified water, the concentration of phosphorus was 0.1 mg / L.

- 5 мг/л,

- 3 мг/л, подают на загрузку, представляющую собой углеродсодержащие отходы (УСО) электродного производства (графитированный кокс) (1). Диаметр зерен УСО - 1,5 мм. Скорость фильтрования - 2 м/ч. При этом одновременно с подачей сточной воды осуществляли аэрацию. На зернах загрузки и межпоровом пространстве образовалась биопленка, причем ферментативное разложение органических загрязнений катализируется углеродом, входящим в состав УСО, таким образом осуществляется процесс биосорбции органических загрязнений в сточной воде, поступающей на доочистку 15 мг O₂/л (по БПК₅), а доочищенной на УСО сточной воде концентрация органических загрязнений составляла 2,8 мг O₂/л. Взвешенные вещества задерживаются в межпоровом пространстве и при концентрации взвешенных веществ в сточной воде, направляемой на доочистку, - 20 мг/л, в доочищенной воде концентрация взвешенных веществ составляет 4,0 мг/л, затем доочищенную на УСО сточную воду подавали на следующую загрузку - клиноптилолит (2) с размерами зерен 1 мм, скорость фильтрования 2 м/ч, в результате ионообменных процессов из сточной воды извлекались ионы аммония при значении сточной воды - pH 7, извлечение ионов аммония составило 92% и при исходной концентрации азота аммонийного в сточной воде 5 мг/л в фильтрате концентрация азота аммонийного составила 0,4 мг/л. Полученный фильтрат после доочистки сточной воды на клиноптилолите фильтровали через гидроксид алюминия (3) с размерами зерен 0,5 мм, скорость фильтрования 2 м/ч, pH воды - 7,2. Гидроксид алюминия является загрузкой, на поверхности которой протекает процесс хемосорбции, в результате чего из сточной воды извлекаются фосфат-ионы, а на загрузке образуются труднорастворимые соединения AlPO₄, 2H₂O (варисцит) pK = 30,5. Предполагается также формирование других фосфатов, например Al₆(PO₄)₄(OH)₆ • 5H₂O, и концентрация фосфора в фильтрате относительно исходной снижается на 99,0% и при концентрации фосфора в сточной воде, фильтруемой через гидроксид алюминия, - 5 мг/л, в фильтрате концентрация фосфора составила 0,05 мг/л.Example 2. The post-treatment process is schematically shown in FIG. 2. Biologically treated wastewater (not shown in the diagram), of the following composition: suspended solids - 20 mg / l; BOD ₅ - 15 mg / l;

- 5 mg / l

- 3 mg / l, fed to the load, which is a carbon-containing waste (USO) of electrode production (graphite coke) (1). The diameter of the grains of USO is 1.5 mm. Filtering speed - 2 m / h. At the same time, aeration was carried out simultaneously with the supply of wastewater. A biofilm was formed on the loading grains and the inter-pore space, and the enzymatic decomposition of organic pollutants is catalyzed by carbon, which is part of the USO, thus the process of biosorption of organic pollutants in the wastewater entering the purification of 15 mg O ₂ / l (according to BOD ₅ ) is carried out, and the purified the concentration of organic pollutants in ODS wastewater was 2.8 mg O ₂ / L. Suspended matter is retained in the inter-pore space and at a concentration of suspended solids in the wastewater sent to the aftertreatment is 20 mg / l, the concentration of suspended solids in the treated water is 4.0 mg / l, then the wastewater treated with ODS is fed to the next charge clinoptilolite (2) with a grain size of 1 mm, a filtration rate of 2 m / h; as a result of ion-exchange processes, ammonium ions were extracted from the wastewater at a wastewater value of pH 7, the extraction of ammonium ions was 92% and at the initial nitrogen concentration of ammonia Niine in the waste water 5 mg / l in the filtrate of ammonium nitrogen concentration was 0.4 mg / l. The filtrate obtained after purification of wastewater on clinoptilolite was filtered through aluminum hydroxide (3) with a grain size of 0.5 mm, a filtration rate of 2 m / h, and a water pH of 7.2. Aluminum hydroxide is a charge, on the surface of which a chemisorption process takes place, as a result of which phosphate ions are extracted, and sparingly soluble AlPO ₄ , 2H ₂ O compounds (variscite) pK = 30.5 are formed on the charge. It is also assumed that other phosphates are formed, for example, Al ₆ (PO ₄ ) ₄ (OH) ₆ • 5H ₂ O, and the phosphorus concentration in the filtrate decreases by 99.0% relative to the initial one, and when the phosphorus concentration in wastewater filtered through aluminum hydroxide is 5 mg / l; in the filtrate, the phosphorus concentration was 0.05 mg / l.

 The following can serve as evidence of the conformity of the invention to the requirement of industrial applicability. The considered method is intended for the purification of industrial and domestic wastewater from suspended solids, ammonium nitrogen, phosphorus and organic pollutants. The possibility of carrying out the invention is reflected in the information section of the application, confirming the possibility of implementing the method. The proposed method, when it is implemented, ensures the achievement of a technical result, which consists in improving the method of tertiary treatment of domestic and industrial wastewater, allowing, taking into account the composition of the wastewater after biological treatment, to carry out their tertiary treatment from residual concentrations of suspended solids, organic contaminants (estimated by BOD, COD), nitrogen ammonium and phosphorus phosphates to concentrations that do not provoke eutrophication of water bodies.

 Thus, the invention meets the condition of industrial applicability.

Claims (1)

The method of sequential treatment of domestic and industrial wastewater after biological treatment of suspended solids, organic pollutants, ammonium nitrogen and phosphorus phosphates, comprising contacting the drains with a developed loading surface from a mixture of sand with an adsorbent Fe (OH) ₃ to extract nitrogen and phosphorus from the purified water , characterized in that the load is differentiated sequentially by the ability to target the extraction of pollutants: for the extraction of suspended solids and organic pollutants use carbon-containing sorbent, for the extraction of ammonium nitrogen - cation exchanger, for the extraction of phosphorus phosphates - loading, on the surface of which chemisorption is carried out, with the achievement of the content of suspended substances in the pre-treated waste water of 2.5 - 4.5 mg / l, BOD _p - 2.0 - 2.9 mg O ₂ / L,

0.15 - 0.49 mg / l,

0.003 - 0.18 mg / l.

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