RU2790709C1 - Method of cleaning the filtrate in smw landfills - Google Patents

Abstract

FIELD: environmental protection.

SUBSTANCE: invention relates to water treatment and can be used to clean the filtrate from solid municipal waste (SMW) landfills from dispersed, emulsified and dissolved organic and inorganic substances. The method for treating industrial wastewater and filtrate from SMW landfills includes two stages of reagent treatment with a coagulant and a flocculant, flotation treatment, ozonation, aeration, ion-exchange treatment, mechanical treatment and a three-stage reverse osmosis. The method includes two stages of reagent treatment with coagulant and flocculant, flotation purification, ozonation, aeration, ion-exchange purification, mechanical purification and three-stage reverse osmosis separation. At the first stage of reverse osmosis separation, high-pressure membrane apparatuses are used and the concentrate is recirculated. At the second and third stages of reverse osmosis, the permeate is refined.

EFFECT: high degree of purification of the filtrate from SMW landfills and reduction in the volume of the utilized concentrate.

2 cl, 1 ex, 1 tbl

Description

The invention relates to the field of environmental protection, namely, to water treatment and can be used to clean the filtrate from solid municipal waste (MSW) landfills from dispersed, emulsified and dissolved organic and inorganic substances.

A known method of purification of drainage waters of solid waste landfills (RF patent 2589139, publ. 10.07.2016), including the stage of two-stage electrochemical treatment with the release of active chlorine and hydroxyl radicals at the anode, two-stage filtration, including settling and ultrafiltration, as well as two-stage reverse osmosis permeate separation and water treatment with ion exchange resins. The known method makes it possible to purify the drainage water of MSW landfills to the required MPC, however, it is characterized by high energy costs, as well as obtaining a large volume of the resulting concentrate.

There is a known method for treating waste, drainage and oversludge waters of industrial facilities and facilities for the disposal of production and consumption waste (RF patent 2740993, publ. 22.01.2021). Contaminated industrial water is sequentially subjected to primary purification from mechanical impurities, electroflotation purification, ultrafiltration, reverse osmosis desalination of the first stage, reverse osmosis desalination of the second stage by permeate and final purification from ammonium ions. At the same time, the primary purification of contaminated water from mechanical impurities is carried out using a hydrocyclone, after which it is subjected to coagulation in a tubular coagulator. After ultrafiltration, the water is subjected to two-stage ozonation in labyrinth columns. The concentrate obtained at the first stage of reverse osmosis desalination is subjected to reverse osmosis desalination of the second stage by concentrate, and the permeate obtained at this second stage is returned to the first stage of reverse osmosis desalination. The final purification of water from ammonium ions is carried out using a backfill filter with zeolite. The known method does not provide for maximum wastewater treatment prior to the stage of reverse osmosis desalination, therefore, initially a larger volume of concentrate is formed.

The objective of the present invention is to develop a method for cleaning the leachate from MSW landfills to obtain a high quality of water treatment and reduce the volume of the utilized concentrate.

To solve the problem, a method is proposed for cleaning the filtrate of MSW landfills, including the first stage of reagent treatment with a coagulant and flocculant, flotation treatment, ozonation, aeration, followed by the second stage of reagent treatment with coagulant and flocculant, ion-exchange treatment, mechanical treatment and three-stage reverse osmosis separation, while at the first reverse osmosis stages use high-pressure membrane apparatuses and recirculate the concentrate; the second and third stages of reverse osmosis perform post-treatment by permeate.

The method may include dosing the permeate with alkali and then disinfecting it.

The technical result of the claimed invention is to achieve a high degree of purification of the filtrate from MSW landfills and reduce the volume of the concentrate to be disposed of.

Reagent processing of the filtrate is carried out in two technological stages. Firstly, dosing of coagulant and flocculant is carried out to intensify the process of enlargement of suspended fine particles before the flotation plant. The use of a coagulant contributes to a decrease in the degree of oxidation of the treated water masses, a decrease in the content of suspended particles in them, and an improvement in the main technological processing processes that occur in treatment facilities and clarifiers. The flocculant provides adhesion of unstable aggressive particles and thereby intensifies the process of flake formation. After the reagent treatment, flotation treatment of the source waters is carried out. At the inlet of the flotation plant, pH is automatically controlled and corrected (acid or alkali). The suspended colloidal substances are then settled in the flotation plant using thin-layer modules. The flotation unit removes more than 70% of all suspended solids, reduces BOD and COD by more than 60%.

To intensify the oxidative process of organic compounds and other impurities, the source water after flotation purification is subjected to ozonation.

After that, the filtrate of MSW landfills is subjected to aeration in aeration tanks for their biological post-treatment with activated sludge and the oxidation of organic substances, as well as some metals and their transition to an undissolved form. After that, the water is re-treated with a flocculant and a coagulant - to coarsen the impurities remaining in the filtrate, in particular iron, manganese, etc.

Further, the filtrate of MSW landfills is exposed to an anion exchange and cation exchange resin, which helps to get rid of nitrates, nitrites, phosphates, ammonium cations, aluminum, zinc, lead, lithium, sodium, etc.

After ion-exchange purification, the filtrate enters the mechanical post-treatment, during which turbidity and other suspensions are removed from the water, which were enlarged at the stage of the second reagent treatment.

The technologies described above for the treatment of leachate from MSW landfills are known, but individually they do not provide a high degree of purification. Due to the given sequence of purification steps and their combination in the claimed method, the last purification step - a three-stage reverse osmosis separation - receives the most purified and demineralized water, which predetermines the formation of a smaller concentrate. Thus, the initial reagent treatment carried out before flotation treatment, due to which suspended particles are enlarged, contributes to the maximum purification of water. After that, the waters are ozonized, intensifying the process of oxidation of substances, which then continues in the aerotanks. The claimed method provides for repeated reagent treatment to coarsen the remaining impurities, which are then deposited on mechanical filters. Sorption by anion-exchange and cation-exchange resins contributes to the effective removal of certain impurities from the filtrate of MSW landfills, in particular acid residues. Thus, the claimed method includes operations aimed at purifying polluted waters from various impurities. The combination and sequence of these operations makes it possible to supply the final purification stage - reverse osmosis separation - with the most purified, clarified and demineralized water, which, together with the cascade use of a three-stage reverse osmosis and the return of the concentrate to the system (recirculation of the concentrate) at the first stage, leads to a significant decrease in the volume of the concentrate - 5-15% in the remainder and obtaining high-quality purified water - with acceptable levels of discharge into the environment.

At the stage of reverse osmosis separation of the MSW landfill filtrate, the following is carried out. At the first stage, under the influence of high water pressure (45-85 atmospheres), passing through a number of membrane devices, they are separated into permeate and concentrate, while the permeate passes sequentially through a number of membrane devices, the concentrate after subsequent membrane devices recirculates - returns to the first membrane device. Thus there is a constant return of the concentrate in the system, which allows a significant reduction in the percentage of concentrate at the exit. At the second and third stages of reverse osmosis, the permeate is additionally purified. The concentrate obtained at these stages is discharged into a storage tank.

After the reverse osmosis separation step, the resulting permeate can be dosed with alkali to adjust its pH and hydrogen peroxide to disinfect it.

Example.

The source water - the filtrate of the MSW landfill in the amount of 10,000 liters, is treated with solutions of a flocculant (high molecular weight polymer) and a coagulant, for example, ferric chloride (FeCl ₃ ), using dosing units for reagents. After the reagent treatment, the filtrate is cleaned by flotation, after which the clarified waters are ozonated and fed into aeration tanks, where they are subjected to biological treatment with activated sludge, after which they are re-treated with a flocculant and coagulant, which is calcium chloride (CaCl ₂ ). After that, water is fed to the sorption of cation-exchange and anion-exchange resins, for example, R-COOH or R-HSO ₃ and R-OH or R-Cl, resulting in a decrease in the content of sodium, calcium, and some acidic residues. Further, the waters are purified by mechanical filters to reduce turbidity, color, remove iron, manganese, mechanical particles of various nature. Gravel is used as a filtering load and a filtering load: a mixture of hydroanthracite and quartz sand in a ratio of 50/50. A flow of 9.7-10.7 m ³ /hour (total mixture of the initial filtrate and concentrate of the second and third stages of reverse osmosis) is fed to the block of fine filter bags with a filtration rating of 5 microns, which prevents the smallest suspensions from entering the channels of reverse osmosis membrane elements and further on the dosing unit of the inhibitor of precipitation on the surface of the membranes, coupled with a static mixer of the inhibitor.

The initial filtrate of the MSW landfill prepared in this way - maximally purified and desalinated - enters the first stage of a three-stage reverse osmosis plant, where it is partially demineralized (almost all ions are retained by 96.5-99%). A high-pressure plunger pump supplies water to the first-stage membrane units in the amount of five units, each with five high-pressure membrane elements, providing the necessary pressure.

First, water enters the first membrane apparatus, where, using the pump of the first apparatus with a capacity of 13-17 m ³ /h, they are repeatedly circulated along the circuit. The specified circulation speed prevents the formation of a helium layer on the membrane surface of contaminants that can block the separating ability of the membrane elements. As a result of exposure to excess pressure and tangential flow of liquid above the surface of the membrane sheet, the source water is separated into partially demineralized water - permeate and water with a high salt content - concentrate. A similar process takes place on the second membrane apparatus - the separation of the initial liquid into permeate and concentrate. After each membrane apparatus, the concentrate is returned for further treatment to the first membrane apparatus, which contributes to its maximum desalination and subsequent utilization of the smallest volume of concentrate. The permeate from the first stage enters the second reverse osmosis stage, which includes a high-pressure pump with one membrane unit with five reverse osmosis medium-pressure membrane elements. When passing through the membrane apparatus, the incoming water is divided into demineralized water - permeate (of the second stage) and water with a high salt content - concentrate, which is returned to the original storage tank. Further, the permeate after the second stage enters the third stage. When passing through the membrane apparatus of the third stage, the incoming water is divided into demineralized water - the permeate of the third stage and water with a high salt content - the concentrate, which is returned to the original storage tank. Water is supplied to the membrane apparatus of the third stage by a high-pressure pump, providing the necessary pressure. There are five reverse osmosis medium-pressure membrane elements in the body of the membrane apparatus.

At the outlet of the reverse osmosis unit, an alkali dosing unit can be provided to adjust the pH of the outgoing permeate and a hydrogen peroxide dosing unit to disinfect the permeate.

The table shows the treatment efficiency indicators by stages, confirming the high quality of source water treatment. So, when comparing the values of the quality indicators of the filtrate and permeate, according to the data of the table, by the claimed method, we obtain purified water with a content of only about 1.3% of impurities, which indicates a high quality of purification. Thus, the indicators of BOD and COD decreased by more than 99.8%, the total indicators of dry residue become less by 97%, the indicators of total organic carbon and ammonium nitrogen decreased by more than 99%, the chemical indicators of chloride anions and sulfate anions decreased by 67 and 99% respectively, the iron and calcium levels decreased by 99%, silicon was almost completely removed (by 99.9%), the oil products decreased by more than 99.8%, and the color of the water from dark brown became characteristic transparent. The composition of the resulting permeate complies with the standards for discharge onto the terrain and into surface water bodies. The amount of permeate obtained at the outlet of the plant is 9350 liters - 93.5% of the initial value, which indicates the receipt of a reduced volume of concentrate - in the amount of 6.5% of the initial volume of wastewater.

Thus, the claimed method, due to the maximum purification and desalination of source waters at the stages preceding the reverse osmosis separation, as well as through the use of a three-stage reverse osmosis separation with concentrate recirculation at the first stage, makes it possible to reduce the volume of the resulting concentrate and effectively clean the filtrate of MSW landfills to discharge standards for landforms and surface waters.

Claims (2)

1. A method for cleaning the filtrate of MSW landfills, including the first stage of reagent treatment with a coagulant and flocculant, flotation treatment, ozonation, aeration, followed by a second stage of reagent treatment with a coagulant and flocculant, ion-exchange treatment, mechanical treatment and three-stage reverse osmosis separation, while the first stage uses membrane high-pressure apparatuses and carry out recirculation of the concentrate, at the second and third stages of reverse osmosis, they perform post-treatment by permeate. 2. The method according to p. 1, characterized in that after reverse osmosis separation, the permeate is dosed with alkali and disinfected.

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