RU2161594C2 - Method of removing stable forms of iron - Google Patents

Abstract

FIELD: water supply system, more particularly purification of natural water containing dissolved organo-iron compounds, and water preparation system for water supply purposes. SUBSTANCE: original water is aerated and directed into bioreactor ins ascending current at rate of 3-4 mm/s. Destruction of complex organoiron compounds occurs due to metabolysis of iron-oxidizing microorganisms during self-spontanesous discharge of excessive amount of biomass. Density of microorganisms is not in excess of 10-15% in total volume of working zone of bioreactor. After biological purification, water is directed for filtration. EFFECT: simplified technology of water preparation which eliminates necessity of regeneration of bioreactor, biomass does not develop therein, secondary contamination of purified water is thus avoided due to biocorrosion and decontamination with chlorine. 2 dwg, 1 ex

Description

 The invention relates to the field of water supply, in particular to the purification of natural waters containing dissolved organometallic compounds, and can be used in water treatment systems for water supply.

A known method of water purification from iron, carried out using a slow filter (USSR patent N 1771470, MKI ⁵ C 02 F 1/64, 01 D 24/46, 1992), which consists in aeration of the source water, settling in the filter housing and filtering through blocks with a granular load, on the surface of which a biofilm is formed with iron-oxidizing microorganisms, which ensure the destruction of dissolved organometallic compounds.

The disadvantages of this method are the low efficiency of the filter, due to the following:
- low filtration rates (up to 0.1 - 0.2 m / h), which determines the large overall dimensions of the installation with a water treatment system capacity of more than 1-2 thousand m ³ / day;
- the possibility of use only for groundwater purification with an iron (II) content of up to 10 mg / l in them, including in the presence of organo-iron compounds up to 2 mg / l.

 A known method of purifying water from iron, which consists in preliminary aerating the water and filtering it through a granular load of a biological filter in which iron bacteria develop (A. Dequin, D. Siben, Deferrisation bioloqique appliquee a la preparation de leau potable. Lean. Lindustrie, les nuisances 1988, N 117, s. 29-30).

The disadvantage of this method is the low efficiency of groundwater treatment, due to the following:
- the possibility of unregulated removal of biomass until the "biological maturation" of the biofilter;
- the possibility of "slip" of dissolved organometallic compounds after the regeneration of the granular load;
- the possibility of secondary pollution of water when organics get into the water distribution system - into the water distribution network and the development of iron bacteria in it, which also causes biocorrosion;
- the possibility of the formation of toxic organochlorine compounds when using chlorine as a disinfectant;
In addition, with a high concentration of iron in the source water, the cleaning technology is much more complicated, since additional measures are required to reduce the period of “biological maturation” of the load, for example, processing it in a nutrient medium after each filter cycle.

 A known method of biological deferrization of groundwater, which consists in aeration and two-stage filtration of the treated water through a biofilter with gravel loading, on which iron bacteria and a clarification filter with a sand loading develop as filtering. Moreover, the filters are self-washed and granite crushed stone with a grain size of 10 ... 30 mm with a layer height of 1500 ... 2000 mm is used as a biofilter loading, and quartz sand with a grain size of 0.7 is used to load the clarification filter. . . 1.5 mm with a layer height of 800 ... 1000 mm (Development and research of new self-washing filters for deferrization of groundwater: Research report (final report) / Ukrainian Institute of Aquatic Economy "UNIIVH"; Head N. Safonov 33-4; N GR 01827023535; Inv. N 0285. 0068458.-Exactly, 1985, pp. 37-46).

 A disadvantage of the known technical solution is the low cleaning efficiency at a high concentration of organometallic compounds in the source water and at pH <6.8, as well as with a "breakthrough" of dissolved organics after regeneration of the filter load of the biofilter and clarification filter until they "biological ripen", which leads to to the ingress of organic compounds into the distribution network and the development of iron bacteria in it, to secondary pollution of water, and during chlorination, to the formation of toxic organochlorine compounds.

 A known method of removing highly concentrated stable forms of iron from groundwater by aeration, liming, settling in a thin-layer sump and filtering (G.I. Nikoladze. Improving the quality of groundwater. -M.: Stroyizdat, 1987, p. 96, Fig. 2.14d). Removal of iron is achieved after the complete oxidation of iron (II) and the destruction of complex organometallic compounds at a pH of at least 7.1. The process of separation of iron compounds in a thin-layer sump is cyclical in nature and the effect of iron removal depends mainly on the flow rate in thin-layer modules, the initial concentration of iron and the dose of alkaline reagent. For agglomeration of flakes of iron hydroxide, which sit in the sump, the capacity of the vortex-type flocculation chamber, combined with the sump, should be such that the treated water stays for at least 15 minutes.

 The disadvantage of this method is the low cleaning efficiency at a high concentration of organometallic compounds and at a pH below 7.0, since only with aeration, liming and thin-layer sedimentation, a sufficiently complete destruction of stable, difficultly oxidized forms of organic iron compounds can not occur. A stable biologically active medium is not created in a thin-layer sump, and on the surface of the filtering load, a biologically active layer formed from iron bacteria does not practically participate in the destruction of organometallic complex compounds, since it is constantly washed out during daily filter regeneration. In this regard, it remains possible for organometallic compounds to enter the distribution network, where in the presence of organic matter iron bacteria may develop, contributing to corrosion of the metal elements of the network and secondary pollution of insufficiently purified water, deterioration of its organoleptic properties often in the range significantly exceeding the regulated ones, but not during chlorination of water formation of toxic organochlorine compounds is excluded.

 Closest to the claimed technical solution according to the technical nature and the achieved technical effect is the method (Semenov V.I., Nikitina L.S., Skroba V.A. Groundwater purification from organo-iron compounds for water supply of facilities located in the North // New studies on networks and structures of water supply systems, L., 1985, p. 152-157), including preliminary aeration of the treated water, decomposition - the destruction of organometallic complexes and oxidation of ferrous iron by microorganisms grown on surfaces of crushed stone loading with a size of 10-30 mm, with turbulization of the flow of treated water in the pores of crushed stone loading and subsequent filtering on quick sand filters.

 The disadvantage of this method is its low efficiency, due to the complexity of its implementation, in particular due to the rapid colmatization - biological fouling of the crushed stone load and, therefore, the need for its frequent regeneration, the complexity of hydraulic washing of such a load when solidly fixed biological formations accumulate on its surface. In addition, due to the impossibility of ensuring uniform flow in the pores of crushed stone loading during the inter-regeneration period, in the low-flow zones there is an accumulation of excess biomass in the form of dying microorganisms of their metabolic products, in which the occurrence of rotting processes can occur, which significantly reduces the efficiency of water purification at a high concentration in it organometallic compounds, since there remains the danger of filtering out rotting products containing organic matter, especially if with respect to turbulization of the flow in the pores of crushed stone loading. It is especially necessary to note that the thickness of the biofilm formed by microorganisms should not exceed 200 microns, since the penetration of oxygen to a great depth is difficult. Therefore, the main drawback of the entire pellet load is the formation of anaerobic zones, in which, when biomass accumulates during the inter-regeneration period, the iron bacteria do not provide for the destruction of complex organic compounds and a significant part of them remains in the dissolved state, enters the filter and is contained in the filtrate. In this regard, it remains possible for organic compounds to enter the distribution network, where in the presence of these compounds iron bacteria can develop, contributing to corrosion of the metal elements of the network and secondary pollution of insufficiently purified water, deterioration of its organoleptic properties often in the range significantly exceeding regulated ones, and when chlorinating water formation of toxic organochlorine compounds is not ruled out.

 The objective of the invention is to ensure the destruction of stable forms of organometallic compounds in a biologically active medium, formed due to the development of specific microorganisms attached to the nozzle, providing the optimal hydraulic regime for their life during spontaneous discharge of excess biomass. This will simplify the water treatment technology by eliminating the need for bioreactor regeneration, since excess biomass is spontaneously dumped, eliminating the possibility of biomass decay in the bioreactor, eliminating organic matter from entering the distribution network and developing iron bacteria in it, and, therefore, eliminating secondary pollution of purified water due to biocorrosion and during chlorine disinfection, the formation of toxic organochlorine compounds; this eliminates the alkalization operation at a pH above 6.2 - 6.5, which simplifies the technology of purification of groundwater containing stable forms of iron.

 The specified problem is solved as follows.

 In the known method of purification of groundwater from stable forms of iron, including aeration of the source water and the destruction of organometallic complex compounds due to the metabolism of iron-oxidizing microorganisms with subsequent filtration, the destruction of organometallic complex compounds is carried out in a biologically active medium formed by the development of specific microorganisms attached to the nozzle, providing optimal hydraulic mode - uniform flow of treated water in the working area of the bior ctor during spontaneous discharge of excess biomass, and the destruction of organometallic complex compounds due to the metabolism of iron-oxidizing microorganisms is carried out in a bioreactor with a brush nozzle in an upward flow at a speed of no higher than 3-4 mm / s with a density of microorganisms in the total volume of the working zone of not more than 10-15% .

Distinctive features of the prototype of the features of the claimed technical solution are:
- the destruction of organometallic complex compounds is carried out in a biologically active medium, which is formed due to the development of specific microorganisms attached to a nozzle, which ensures an optimal hydraulic regime - a uniform flow of treated water in the working zone of the bioreactor during spontaneous discharge of excess biomass;
- the destruction of organometallic complex compounds is carried out in a bioreactor with a brush nozzle in an upward flow at a speed of no higher than 3-4 mm / s;
- the destruction of organometallic complex compounds is carried out at a density of microorganisms in the total volume of the working zone of not more than 10-15%.

 The destruction of organometallic complex compounds is carried out in a biologically active medium, which is formed due to the development of specific microorganisms attached to the nozzle, which provides an optimal hydraulic regime - a uniform flow of treated water in the working area of the bioreactor with spontaneous discharge of excess biomass, while ensuring a uniform supply of nutrient substrate - treated water containing organometallic compounds to the colonies of microorganisms attached to the nozzle, it allows one to actively oxidize - mineralizovyvat dissolved zhelezoorganicheskie stable complexes agglomerating flakes saline and extracted from the solution and precipitation of iron forms them into a bioreactor. At the same time, water enters the filter, in which iron is almost completely absent in complex oxidizable organic forms, which helps to prevent organics from entering the spreading network and the development of iron bacteria in it, which contribute to biocorrosion and secondary pollution of water, and the formation of toxic organochlorine compounds during chlorination is eliminated.

 The destruction of organometallic complex compounds is carried out in an upward flow at a speed of no higher than 3-4 mm / s, which ensures more complete precipitation of the iron compounds extracted from the solution in the bioreactor, including due to the settling effect in the suspended layer, and ensures a decrease in the concentration of iron in water entering the filter, prevents the "removal" of an excessive amount of waste products of iron bacteria and, therefore, significantly improves the operating conditions of the filter and at optimal sizes of bioreact ora eliminates the possibility of slip resistant forms of dissolved iron in the water distribution system.

 The destruction of organometallic complex compounds is carried out in a bioreactor equipped with a nozzle having a developed surface, with a density of microorganisms in the total volume of the working zone of the bioreactor of not more than 10-15%, which provides optimal conditions for the fixation of microorganisms, their uniform distribution and the mode of their "nutrition", since higher density, more intensive death of bacteria is possible due to lack of "nutrition" and removal of decay products to the filter.

 Thus, a causal relationship is ensured between the set of distinctive features of the claimed invention and the achieved technical result - providing increased efficiency in the purification of groundwater containing stable forms of organometallic complex compounds due to the destruction of these compounds in a biologically active medium using the metabolism of iron-oxidizing microorganisms.

 An example of industrial applicability of the invention.

 Figure 1 presents a diagram illustrating the sequence of operations of the proposed method (arrows indicate the direction of the treated water); in FIG. Figure 2 shows the dependence of the effect of biological oxidation of organometallic compounds on the upward velocity in the bioreactor.

 The source water containing stable forms of organometallic compounds is supplied from wells to an aeration device 1, for example, to a vacuum ejection apparatus, from which oxygen-saturated water is fed into the receiving pocket 2 of the bioreactor 3, from where it enters the zone above the sedimentator 4 - the pyramidal part of the bioreactor 3 forms an upward flow passing through the working area 5 of the bioreactor 3, in which a nozzle with a developed surface, for example a brush made of a synthetic thread, in particular of a polyester thermal thermofixed (345 TEKS according to GOST 24662-81). When passing the treated water containing organometallic compounds and other dissolved iron salts, certain types of microorganisms - iron bacteria, capable of using dissolved organics in the course of their metabolism, providing mineralization of these compounds, develop on the brush nozzle in the working area 5 when passing treated water containing organometallic compounds and other dissolved iron salts. Iron-bound natural waters, in which iron compounds are represented by organic forms, represent the specific habitat of microorganisms. Its specificity lies in the fact that in the course of their activity, the destruction of organic compounds occurs not only by direct destruction by the iron bacteria, which are autotrophs, but also by the release of hydrogen peroxide, the concentration of which can reach 10-20 mg / l. The release of hydrogen peroxide, for example in Leptothrix, leads to inhibition of bacterial growth, especially with an increase in the concentration of organic substances, up to the lysis of cells.

Under normal conditions, hydrogen peroxide is decomposed by disproportionation, while the reaction proceeds as follows:
H ₂ O ₂ + H ₂ O ₂ = 2H ₂ O + O ₂ ,
where one peroxide molecule acts as an electron donor, the second as an acceptor.

Hydrogen peroxide, which occurs as an intermediate or final oxidation product, is released from the cells and accumulates in the structures surrounding them. To detoxify hydrogen peroxide, microorganisms synthesize a specific enzyme - catalase, which significantly intensifies the process of decomposition of peroxide:
2H ₂ O ₂ ---> (catalase) ---> 2H ₂ O + O ₂ .

At the same time, ferrous iron ions are also able to significantly accelerate the decomposition of hydrogen peroxide. In a neutral or slightly alkaline environment, the oxidation of Fe ²⁺ to Fe ³⁺ occurs as a result of direct interaction with hydrogen peroxide as follows:
2Fe ²⁺ + H ₂ O ₂ ---> 2Fe ³⁺ + H ₂ O + O ₂ .

 This process takes place in capsules, covers, mucous secretions, on the surface of the cell wall, in which all components of the reaction are concentrated: reduced iron compounds and hydrogen peroxide, in addition, hydrogen peroxide can be released from the cell into the medium, and iron oxides can accumulate as in cellular exopolymers, and in the medium in the form of an amorphous structureless precipitate.

Iron ions catalytically accelerate the decomposition of hydrogen peroxide, although in the presence of catalase this reaction proceeds 10 ⁹ times faster. This explains the very active growth of such microorganisms in waters rich in ferrous iron compounds, since under the conditions of low nutrient value of groundwater, the costs of catalase synthesis may not be covered by the energy extracted by microorganisms from organic substances dissolved in natural water. At the same time, the presence of ferrous iron compounds in water, which are oxidized by hydrogen peroxide, allows microorganisms not to synthesize the catalase necessary for detoxification of hydrogen peroxide. As a result of this, microorganisms can exist due to the minimum amount of nutrients found in natural water.

 If the organic part of the molecule of the complex organic compound of iron is destroyed, the microorganisms must not selectively accumulate any metal, and the iron ion should also be indifferent in the acid or oxide form. However, in conditions of low nutritional value of water, i.e. when the microbial activity of a cell cannot be fully provided by organic substances found in natural water, the presence of ferrous iron compounds in water becomes very important, since under these conditions ferrous iron compounds replace catalase. In addition, the release of hydrogen peroxide by microorganisms contributes to a more efficient destruction of organic compounds.

 Thus, biological deferrization according to the proposed cleaning scheme ensures the destruction of organic compounds dissolved in water, both due to the direct use by microorganisms of these compounds as a nutrient substrate, and due to the destruction of organic compounds as a result of contact with the metabolic product (hydrogen peroxide) data microorganisms.

 The density of microorganisms in the working area 5 of the bioreactor 3 is determined by the bearing capacity of the type of nozzle used, in particular its specific surface. With a variable concentration of organic forms of iron in the treated water, the effect of self-regulation of the density of microorganisms is observed and bacteria that do not receive “food” die off and are discharged from the nozzle, accumulating in sediment collector 4 or are reversed and re-activated when the organic content in the water increases. With an increase in the specific surface area of the nozzle in the bioreactor 3 and, consequently, an increase in the density of microorganisms more than 10-15% in the total volume of the working zone 5 of the bioreactor 3, microflora is unstable, and the "non-mineralized" organics and decay products of dying microorganisms from the working zone 5 are not excluded bioreactor 3 to the filter 7. In this regard, the active surface of the nozzle should provide the optimal density of microorganisms in the working area 5 of the bioreactor 3 not more than 10-15% of the total volume of this zone.

 The formation of the upward flow due to the supply of treated water from the bottom of the bioreactor 3 provides the effect of sedimentation "in the suspended layer", since the flow passes from the bottom up to the working area 5, where the flakes of iron compounds formed as a result of oxidation and mineralization, as well as the decay products of microorganisms form a counter flow. This contributes to the coagulation and effective deposition of inorganic iron compounds released from the solution. In addition, in the working zone 5 of the bioreactor 3, the upward flow of the treated liquid is provided with microorganisms that are fixed on the surface (threads) of the nozzle, which causes the activation of the mineralization of dissolved organic iron compounds, their isolation from the solution, and precipitation. The resulting flakes of iron having a negative hydraulic particle size are deposited and accumulate in the sediment accumulation zone 4 of the bioreactor 3. In this case, it is important to ensure the most complete precipitation of the iron compounds extracted from the solution in the bioreactor 3, avoiding their "removal" to the filter 7, which is ensured by the optimal speed upward flow in the working area 5 of the bioreactor 3, which, as shown by experimental studies (Fig. 2), should not exceed 3 ... 4 mm / s At a higher upstream speed, the effect of water purification in the bioreactor 3 from organometallic compounds is significantly reduced due to the discrepancy between this speed and hydraulic fineness, the resulting flakes and organic residues - metabolic products of iron bacteria, and also due to the deterioration of the contact conditions of the treated water with fixed microorganisms, since increasing the speed of the upward flow of the fiber nozzles take a position close to vertical, and the total contact area of the fixed m organisms with the flow of treated water is reduced. At a speed of less than 3 mm / s, the effect of water purification from organic iron compounds does not significantly increase, but the overall dimensions of the bioreactor 3 increase, and at the upward flow rate of the liquid being cleaned in the working zone 5 of the bioreactor 3 less than 1 mm / s, the nozzle fibers also occupy the position close to vertical, due to which the “nutrition” conditions of microorganisms worsen and the effect of water purification from organometallic complex compounds decreases. In addition, the effect of purification from stable organic forms of iron in the bioreactor 3 depends on the duration of contact of the treated water with the biologically active medium in the working zone 5. In this regard, the height of the working zone 5 of the bioreactor 3 should correspond to the rate of the process of biological oxidation of these iron forms due to metabolism microorganisms attached to the nozzle in the working area of the bioreactor, which ensures the most complete oxidation of dissolved iron and a sufficiently high cleaning effect. In particular, at an ascending flow rate of 3-4 mm / s and at a height of 0.8 m of the working area 5 and a contact time of 3.5-4.5 min, the effect of purification from organic iron compounds is 55-60% (Fig. 2) and with a height of 1.6 m of the working area 5 and a contact time of up to 9 min, the cleaning effect increases to 90-95%. The necessary contact time of the treated water with the biologically active medium depends to a large extent on the properties of the organometallic compounds dissolved in the water and should be determined according to technological modeling. As the biological mass accumulates on the nozzle fibers, it spontaneously discharges, this sediment moves downward and accumulates in accumulation zone 4, from where it is periodically discharged by pipe 6 to the sediment treatment facilities.

 Further, the water treated in the bioreactor 3, in which a sufficiently complete destruction of the stable forms of iron is ensured — the mineralization of organometallic compounds, enters a filter device, for example, an quick filter 7, and after filtration through a granular filter load 8 is completely freed from iron, including residual amount of organometallic complexes. The purified water is collected in the drainage system 9 of the quick filter 7 and is discharged to the disinfection unit 10 and, after, for example, chlorination, is supplied to the distribution network to the consumer. Due to the fact that in the bioreactor 3 and in the filter 7, the water is completely purified from organometallic compounds in the distribution network, there are no conditions for the development of iron bacteria, which excludes the possibility of biocorrosion and, consequently, secondary water pollution. In addition, chlorination does not produce toxic organochlorine compounds, which ensures a favorable environmental situation in the water supply system.

Claims (1)

 The method of purification of groundwater from stable forms of iron, including aeration of the source water and the destruction of organo-iron complex compounds due to the metabolism of iron-oxidizing microorganisms, followed by filtration, characterized in that the destruction of organo-iron complex compounds is carried out in the bioreactor working zone in an upward stream of treated water at a speed of no higher than 3 - 4 mm / s due to the metabolism of iron-oxidizing microorganisms, fixed on a brush nozzle, with spontaneous discharge and redun- dant biomass, the density of microorganisms in the total bioreactor working area is not more than 10 - 15%.

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