ES2622003B1 - Improved procedure for the removal of nitrates from ground and surface waters and equipment for performing said procedure - Google Patents

Abstract

The invention provides a method and a device for removing nitrates from ground and surface waters based on a denitrification by biological filtration, including a chemical conditioning stage of the water to be treated; a biofiltration stage and a biofilter wash stage, where, in the biofiltration stage, the water to be treated is passed to the reactor containing the biofilter following a horizontal flow, the water entering the reactor at one end and leaving the water treated by the opposite end and the washing step is carried out without adding treated water, with the water originally to be treated, the excess biomass accumulated in the biofilter support material being removed along with the water.

Description

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PROCEDURE

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ELIMINATION OF NITRATES OF

UNDERGROUND AND SURFACE WATERS AND EQUIPMENT FOR THE PERFORMANCE OF THIS PROCEDURE

The present invention relates to an improved process for the removal of nitrates from ground and surface waters, as well as to an equipment for carrying out said procedure, said procedure based on a process of denitrification by biological filtration, in which those responsible for the reduction of nitrate compounds to be eliminated are microorganisms that, in most cases, exist naturally in the waters themselves to be treated.

Nitrates commonly found in ground and surface waters constitute a risk to human health and an environmental problem. Frequently, these pollutants appear in waters at levels that exceed the maximum allowed for human consumption, for use as irrigation water or for their discharge into the environment. Similarly, nitrates are responsible for various diseases in humans, being involved in the

methemoglobinemia and the generation of nitrosamines, as well as the appearance of various types of gastric cancers, among others, according to scientific evidence. On the other hand, some plants and vegetables adsorb some of these nitrates, which then pass into the food chain, with the risk that this entails.

The decrease in the concentration of nitrates (NO3 ") in water can be done through different technologies based on two clearly differentiated principles, the biological and the physical-chemical.

Within the processes for nitrate elimination based on physicochemical principles, there are, for example, ion exchange, electrodialysis and reverse osmosis. Recently, the electrolytic reduction system is also applicable.

In an ion exchange process, the necessary resins (composed of a high concentration of polar, acidic or basic groups, incorporated into a matrix

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of a synthetic polymer (styrenic resins, acrylic resins, etc.) act by taking ions of the solutions (usually water) and yielding equivalent amounts of other ions, in this case the exchange occurs between nitrate ions from feedwater and chloride ions Resin supported. This type of process has the disadvantage that the resins must be regenerated with NaCl, resulting in a hazardous waste composed of high concentrations of nitrates and chlorides, and replaced every so often.

Electrodialysis is based on the separation of anions and cations by membranes and an electric current. It usually requires a pre-treatment, has a high maintenance and generates waste with high concentrations of nitrates.

Reverse osmosis is a high pressure separation process, where there is an inlet of water to be treated and two outlets of water, one of treated water and another of water with high concentration of contaminants separated by the membrane. This treatment only manages to recover a value of approximately 60% of the water entering the plant, that is, the other 40% of water is not recovered, it is a residue that integrates high concentrations of the separated nitrates, requires a pretreatment and It has high maintenance costs, especially energy, as well as generates a large volume of waste.

Finally, electrolyte reduction operates by reducing nitrates in a cathode mostly to N2 and minority to ammonium. Being an electrolytic process, intensive use of electrical and chemical products is required, which considerably increases the cost of production.

On the other hand, the biological processes are based on the well-known process of denitrification, a metabolic process that uses nitrate as the terminal electron acceptor under anoxic conditions (absence of oxygen) mainly, performed exclusively by certain microorganisms, among which Alcaligenes, Paracoccus, Pseudomonas, Thiobacillus, Rhizobium, Thiosphaera, among others, and that, in most cases, exist naturally in the waters to be treated.

The process of reducing nitrates to nitrogen gas occurs in successive stages, catalyzed by different enzyme systems, appearing as intermediate nitrites, nitric oxide and nitrous oxide.

N03- -► N02- -> NO -> N2O N2

5 Denitrification requires an organic or inorganic oxidizable substrate that acts as a source of energy, so denitrification can be carried out by both heterotrophic and autotrophic bacteria. In heterotrophic denitrification, using an organic substrate as a source of carbon and energy, the most widespread and on which the present invention is based, said organic substrate, such as methanol, ethanol, acetic acid, glucose, etc., acts as a source of energy (electron donor) and carbon source.

The biggest problem of biological denitrification is the potential contamination of water treated with: bacteria, residual carbon source (heterotrophic denitrification) and the possibility of nitrite formation, which makes post-treatment necessary.

15 The processes of denitrification by biological filtration essentially include a stage of chemical conditioning of the water where they are added to the water to treat a source of carbon and phosphorus, essential nutrients for the development of microorganisms; a biofiltration stage where the water containing nitrates is passed through a biofilter consisting of a support where the 20 denitrifying microorganisms are fixed and their growth and development is favored. This biofilter is usually found in a closed reactor to favor the absence of oxygen, where the flow of the incoming water is usually ascending, that is, the water flows from the bottom up through the filter bed to facilitate the removal of nitrogen gas into the atmosphere. The contaminating substances adhere to the biomass biofilm formed on the support and are subsequently digested by the microorganisms. Subsequently, the biomass produced must be removed from the effluent through a biofilter wash stage, which must be carried out periodically, usually every day. This washing step can be done by pumping water or water and air by means of corresponding

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reactor pumps. Thus, in this known procedure, it is necessary to adapt the biofilters by using clean water that is introduced into the reactor by pumping.

For example, in document ES2208108 a process of this type is described, where it is necessary to use a first reactor to which the water to be treated is pumped from the bottom of the reactor causing an upward flow through a biofilter disposed in the reactor, and a second wash tank where the water that rises and leaves the reactor is partly recirculated to the wash tank downstream for biofilter washing.

The present invention solves the disadvantages of the known processes of the prior art of denitrification technique by biological filtration eliminating the need to provide water for washing the biofilters and improving their support to favor the adhesion and growth of the denitrifying microorganisms .

To this end, in one aspect, the invention provides an improved process for removing nitrates from ground and surface waters based on said process in a biological filtration denitrification process as described above, that is, including a chemical water conditioning stage. where they are added to the water to treat a source of carbon and phosphorus; a biofiltration stage where the water containing nitrates is passed through a biofilter consisting of a support where the denitrifying microorganisms are fixed, the biofilter being in a closed reactor, and a biofilter washing stage, where, in the biofiltration stage, the water to be treated is passed to the reactor containing the biofilter following a horizontal flow, the water entering the reactor at one of its ends and the treated water leaving the opposite end and the washing step is carried out within the same reactor with the water originally to be treated, by driving the water, or a mixture of water and air, at high speed or by an agitator arranged at the bottom of the reactor and subsequently emptying the water from the reactor by gravity, removing excess accumulated biomass along with the water in the support material.

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This form of washing avoids the need to provide treated water, also guaranteeing sufficient agitation of the biofilter support material and the release of excess biomass attached to it, which is subsequently removed along with the water from the reactor.

A general scheme of the process of the invention is shown in Figure 1.

In one embodiment of the process of the invention, the support material used for fixing the microorganisms is an aluminosilicate with a SIO2 content greater than 50%, AI2O3 greater than 10% and Fe2Ü3 greater than 5%. This preferred support material, which has a density of less than 540 kg / m3, which is suspended or fluidized inside the reactor, with an average particle size between 4 and 20 mm and with a porosity greater than 40% and a high specific surface, greater than 1,500 m2 / m3, facilitates both the fixation of the microorganisms due to their porosity, size and high specific surface, as the stage of washing the biofilter, since its density allows to increase the contact with the volume of water of the reactor and thereby facilitate the washing of the biofilter by stirring.

Once the nitrates have been eliminated, depending on the destination or use, the treated water can be:

• Water for human consumption according to Royal Decree 140/2003, of February 7, which establishes the sanitary criteria for the quality of water for human consumption.

• Water for urban uses (irrigation of urban green areas), agricultural (crop irrigation), industrial (cooling towers), recreational (golf course irrigation) or environmental (aquifer recharge) according to ROYAL DECREE 1620/2007, of December 7, which establishes the legal regime for the reuse of purified water.

• Its use in the aquaculture sector.

• Discharge to the sewer or the environment.

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For the above uses of treated water, the process of the invention includes an additional post-treatment step by any of the following processes or by a combination thereof, in order to obtain a high quality water, minimizing the environmental impact. and at a low production cost:

• Water aeration

• Sand filtration

• Activated carbon filtration

• Ultra-Filtration (UF)

• Disinfection by chlorine, hypochlorite, chlorine dioxide, ozone, hydrogen peroxide, ultraviolet (UV) light, ...

In a second aspect, the invention provides equipment for carrying out the process described above, said equipment including means for feeding the water to be treated, means for dosing the source of carbon and phosphorus for the water to be treated, a denitrification reactor which it includes a supported biofilter and outlet means for the treated water and the wash water, where the equipment also includes a stirring system located at the bottom of the reactor that drives and agitates the biofilter support and the feeding means of the water to be treated they reach the reactor at their bottom or top and the outlet means for the wash water leave the reactor at the same level as the inlet means.

In the foregoing, the dosing means of the source of carbon and phosphorus, the feeding means of the water to be treated and the outlet means of the washing water are not particularly limited, being able to treat, for example, conduits controlled by corresponding valves, provided that the condition of the provision cited above is met.

In an embodiment of the equipment according to the invention, the support for the supported biofilter is as described above, an aluminosilicate with a SIO2 content greater than 50%, AI2O3 greater than 10% and Fe2Ü3 greater than 5%, further preferred with a density of less than 540 kg / m3, suspended or fluidized inside the reactor, with an average particle size between 4 and 20 mm and

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with a porosity greater than 40% and a high specific surface area, greater than 1,500 m2 / m3.

From the above description of the invention, with reference to both the process and the equipment for carrying it out, the following advantages can be derived in comparison with the known solutions of the prior art:

• Produces high quality water, according to the quality criteria of the WHO (World Health Organization).

• It has a low cost of production, since the need for complementary washing devices to the reactor is eliminated and it is not necessary to provide water for washing to the process;

• The reactor of the system is of horizontal flow, imitating the flow of water in a river, which facilitates both the feeding of the water to be treated and the output of the treated water, without the need for superfluous pumping systems;

• The washing cycle is carried out without waste of treated water.

• The effluent from the washing of the reactors can be evacuated to the sewer system without prior treatment, since its quality is sufficient, without the need for other treatment.

• It is respectful with the environment.

• Offers water production rates above 98%.

• It is not necessary to regularly replace the support medium for the fixation of the microorganisms of the reactors, since they have a useful life of more than 30 years.

The main applications of the method and of the device according to the invention are:

• Treatment of groundwater and surface water for human consumption.

• Treatment of purified water for urban uses (irrigation of urban green areas), agricultural uses (crop irrigation), industrial uses (cooling towers, aquaculture), recreational uses (golf course irrigation), environmental uses (aquifer recharge ).

• Treatment of water from the concentrate of reverse osmosis systems (membranes) for discharge into the sewer system or the environment.

Claims (1)

5 10 fifteen twenty 25 30 Improved procedure for the elimination of nitrates from ground and surface waters, said procedure being based on a process of denitrification by biological filtration that includes a stage of chemical conditioning of the water where a source of carbon and phosphorus is added to the water; a biofiltration stage where the water containing nitrates is passed through a biofilter consisting of a support where the denitrifying microorganisms are fixed, the biofilter being in a closed reactor, and a biofilter washing stage, characterized in that in the biofiltration stage, The water to be treated is passed to the reactor containing the biofilter following a horizontal flow, the water entering the reactor at one of its ends and the treated water leaving the opposite end and the washing step is carried out within the same reactor, without add treated water, with the water originally to be treated, driving and stirring this water, if necessary together with air, at high speed or by means of a stirrer arranged at the bottom of the reactor and subsequently emptying the water from the reactor by gravity, withdrawing along with water excess biomass accumulated in the biofilter support material. Improved procedure for the removal of nitrates from water underground and surface according to claim 1, characterized in that the biofilter support is of an aluminosilicate with a SIO2 content greater than 50%, AI2O3 greater than 10% and Fe2Ü3 greater than 5%, has a density less than 540 kg / m3, an average particle size between 4 and 20 mm, a porosity greater than 40% and a high specific surface area, greater than 1,500 m2 / m3. Improved procedure for the removal of nitrates from water underground and surface according to claim 1 or 2, characterized in that the support is suspended or fluidized within the reactor. Equipment for carrying out the method of claim 1, said equipment including means for feeding the water to be treated, means for dosing the source of carbon and phosphorus to the water to be treated, a denitrification reactor that includes a supported biofilter and means for outlet for the treated water and the wash water, characterized in that the equipment also includes an agitator means located at the bottom of the reactor that drives the water and air into the reactor and the means of feeding the water to be treated reach the reactor by its lower or upper part and the outlet means for the wash water leave the reactor at the same level as said inlet means of the water to be treated. Equipment for carrying out the process according to claim 4, characterized in that the biofilter support is of an aluminosilicate with a SIO2 content greater than 50%, AI2O3 greater than 10% and Fe2Ü3 greater than 5%, has a density less than 540 kg / m3, an average particle size between 4 and 20 mm, a porosity greater than 40% and a high specific surface area, greater than 1,500 m2 / m3.