FI117618B - Procedure for removing ammonium from wastewater - Google Patents

Description

Method for removing ammonium from waste water - Förfarande för avlägs- Nande av ammonium frän avloppsvatten 117618; . ^

The present invention relates to a process for removing ammonium from waste water 5 by chlorination to convert ammonia to nitrogen gas.

It is important to limit the emissions of nitrogen compounds as they have a harmful effect on the environment. Excessive loading of various forms of nitrogen compounds, for example as nitrate nitrogen or ammonium nitrogen, is detrimental to plants, acidifies the soil, causes eutrophication of surface waters, or causes unpleasant ha-10. Excessive nitrogen supply to natural areas can alter the balance of vegetation, promote the evaporation of nitrous oxide, known as greenhouse gas, and pollute groundwater upon absorption into soil. For example, while ammo | industrial waters containing aluminum may be used for specific applications, however | corrosive to metals. 5 15 In the treatment of industrial, agricultural and municipal wastewater, organic and inorganic solids are removed by sedimentation, oxygen-consuming biochemical and chemical substances by an activated sludge process. Usually, even if the waste | since the water is already very clean after these treatments, ammonium nitrogen is still a problem. Ammonium nitrogen is difficult to remove from waste water because of its solubility

* * 20 mouth water is large and is a very stable compound in the form of ammonia. I

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Various processes have been developed to remove ammoniacal nitrogen and ammonia from waste water. Biological nitrogen removal methods are preferred under conditions ... "· Where the nitrogen content of the effluent is relatively low and organic or inorganic material is still present. On the other hand, the elevated nitrogen content of the effluent and the low process temperatures *" * 25 favor chemical nitrogen removal methods.

: e: |: It is known to remove ammoniacal nitrogen from wastewater by various physical and ceramic methods, such as electrodialysis, reverse osmosis, stripping, chlorination and τ * · ion exchange. Each of these processes has advantages and disadvantages. Ion exchange, with many published alternatives and modifications, is the most common method.

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I :. In ion exchangers, the ammonium nitrogen contained in the effluent is adsorbed to the ion-exchange mass, such as the zeolite beds. Adsorption works well and the

*** Lifetime is at least 5-7 years. The total cost of adsorption is good

vin reasonable. However, ion-exchange masses such as zeolite beds must be regenerated! V '117618 2 Regular and regenerative total cost (that is, including investment) is crucial to the competitiveness of a complete NH4 removal process. Several regeneration processes have been developed. The spent ion-exchange mass can be chemically or biologically regenerated. In chemical regeneration, ammonium ions $ 5 are eluted from the ion exchange mass to an alkaline saline solution such as an alkali metal chloride solution, for example sodium chloride solution. The resulting ammonium-containing solution may be subjected to stripping, heat treatment or chemical treatment.

In U.S. Pat. No. 3,929,600, regeneration is accomplished by allowing an alkaline alkali metal-chloride-containing eluent liquid to circulate through a column filled with an ion exchange mass such as zeolite. The liquid eluate containing the ammonium and chloride ions is electrolyzed to decompose the ammonium ion by the oxidizing effect of the chlorine discharged in the electrolysis. The gas mixture produced by electrolysis contains hydrogen, f oxygen, nitrogen, a small amount of chlorine, a negligible amount of nitric oxides, and islamines. This gas mixture is contacted with a control fluid containing an alkali metal hydroxide to absorb chlorine and nitrogen oxides. The alkali metal hydroxide is added to the electrolysed liquid, which is recycled to the column filled with ion-exchange pulp.

From US 6,132,627 a process is known for ammonium-like nitrogen compounds 20 to remove wastewater by adding inorganic chloride to the wastewater up to a concentration "**! Less than the stoichiometric amount relative to the amount required to oxidize the nitrogen compounds ... by electrolysis of waste containing chlorides: * ·: water to form hypochlorite ions, and transferring the wastewater from the electrolysis to a storage tank where nitrogen compounds are oxidized with hypochlorite ions, and chloride ions are regenerated. Partially treated wastewater can be recycled between the storage tank and the h "··, electrolysis tank. Next, the effluent is contacted with a metal peroxide catalyst in a reaction column which is further cleaved by the peroxide catalyst. nitrogen compounds and remove residual hypochlorite ions from the waste water.

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In the two processes discussed above, wastewater containing nitrogen compounds is obtained. 30 under direct electrolysis.

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One disadvantage of the method of US 3,929,600 is that the adjustment and optimization of the ammonium decomposition process in the electrolytic cell is difficult to achieve. This is due to the fact that the flow rate through the electrolytic cell is dependent on the flow rate of the regeneration fluid through the zeolite bed. Also, pH and residence time are difficult to adjust by direct electrolysis. Zeolite Regeneration • '' '% 117618 3

During the passage, there is a large variation in the ammonium content of the liquid flowing out of the filter bed, and in direct electrolysis it is difficult to adjust the amount of hypochlorite produced to the amount required to decompose the ammonium. Zeolite beds can be used to prevent undue additional salt loading in the sewage system's sewage | 5 need to rinse with water after regeneration with saline.

The used flushing water must be taken into the regeneration cycle. Direct electrolysis of such low salt water is problematic.

One object of the present invention is to provide a method that avoids the above disadvantages.

According to the invention there is provided a process for removing ammonium from an aqueous ammonium solution obtained by regenerating an ammonium-charged ion-exchange mass with an eluent liquid containing a chloride-containing salt, comprising the step of feeding said ammonium-containing solution to the reactor.

aqueous solution or condensate containing ammonia, obtained from By stripping said aqueous ammonium containing solution and removing ammonia from the stripping gas by condensation, and a separate aqueous solution of alkali metal hypochlorite * to convert ammonia / ammonia to nitrogen gas and to produce a substantially ammonium-free effluent, the process being characterized by

* *. ···. Thus, in a first embodiment of the invention, the process comprises the step of feeding to said reactor said aqueous ammonium-containing solution and said separate aqueous solution of an alkali metal hypochlorite to convert ammonium to nitrogen gas.

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In another embodiment of the invention, the process comprises the step of: | 25 is fed an ammonia containing condensate obtained by stripping said aqueous ammonium solution and removing ammonia by stripping. gas by condensation, and said separate aqueous solution of alkali metal hypochlorite. to convert ammonia to nitrogen gas. At least some of the liquid from the stripping may be returned to the regeneration of ammonium-charged ion exchange * * ·: 30 as eluent.

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An aqueous solution of alkali metal hypochlorite can be prepared on-site with alkaline • · · ·· *! by direct electrolysis of an aqueous metal chloride solution. In that case, part of the reactor effluent stream may be returned to the electrolysis as an aqueous alkali metal chloride solution. ! *. 117618?

According to the present invention, it is also possible to take an aqueous solution of an alkali metal hypochlorite from a storage tank. In that case, part of the reactor effluent is returned as eluent liquid to regenerate the ammonium-charged ion exchange mass. 5 $ 5 Preferred ion-exchange mass includes zeolite. The zeolite may be a commercially available zeolite comprising American, Greek, Cuban 4 or Australian clinoptilolite, saponite, phillipsite or synthetic zeolite.

The chloride-containing salt is preferably sodium chloride, the alkali metal hypochlorite is preferably sodium hypochlorite and the alkali metal chloride is preferably sodium chloride. ? The eluent liquid may contain 20-75 g NaCl / l, preferably 50-60 g NaCl / l, or equivalent amounts of the second alkali metal chloride. .¾

Said aqueous ammonium solution may contain from 0.2 to 4 g of ammoniacal nitrogen per liter r, preferably 0.4-2 g ammonium nitrogen / l.

The following advantages are achieved by the process of the present invention.

The flow rate through the electrolysis device is independent of the flow rate of the regeneration fluid through the ion exchange mass and is based on the fact that the control and optimization of the conditions of the ammonia decomposition process are easily accomplished. Due to optimum process conditions and easier process control, less unwanted by-products are formed which are most likely to be removed from the · · 20 regeneration fluid before it can be reused in the ion-exchange pulp regeneration.

• * • * · * · 4h *: * In a separate reactor of the present invention, pH and residence time are easy, | adjust. pH and dwell time are both important variables in optimizing process conditions.

According to the present invention, it is possible to simulate a hypochlorite tank between an electrolysis reactor and an ammonium decomposition reactor. Such a container serves as both a hydrogen removal vessel and a buffer tank which, at any given moment, provides a · **. • · · * to get the right amount of hypochlorite needed separately. in an ammonium decomposition reactor for optimal process conditions. The Hypoclo ** · · * "30 Capacity Tank also allows the use of a smaller electrolysis device and

* ··· * optimal process conditions for electrolysis. I

5, 117618

The present invention will now be described in more detail with reference to the accompanying figure, in which Figure 1 is a flow chart illustrating one preferred embodiment of the present invention.

applications. I

Ammonium is removed from the wastewater by feeding the wastewater through the zeolite bed 1 where the ammonium is adsorbed onto the granular zeolite. The ammonium-charged zeolite bed 1 must be regenerated regularly. The ammonium-charged zeolite bed 1 is regenerated by feeding sodium chloride regeneration solution 2 through the zeolite bed. The pH of the regeneration solution 2 is about 9 and the concentration of sodium chloride is about 20-75 g per liter.

The eluate solution 3 from the zeolite bed contains ammonium and its sodium chloride content is reduced. Said ammonium-containing eluate 3 contains about 0.2-4 g of ammoniacal nitrogen per liter. The eluate 3 is then fed to the refractive point chlorination reactor 4. The sodium hypochlorite solution 5 produced in the electrolysis cell 6 provided with the buffer tank is also fed to the reactor 4. In the reactor 4, the sodium hypochlorite reacts with ammonia to form nitrogen gas 7 and sodium chloride. The substantially ammonium-free sodium chloride solution 8 leaving reactor 4f can be fed to storage tank 9, of which part 10 is recycled as regeneration solution to zeolite bed 1. The second part 11 can be recycled to electrolytic cell 6. Add ΐ

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of sodium chloride. The invention will now be illustrated by the following examples • · '·γ, * ··

Example 1 An autoclave of 2.0 L volume equipped with a magnetic stirrer was charged with 1000 ppm of ammonium ions (NH4 +), 2.2 g of sodium hydroxide (NaOH). ) and 1800 g of water The autoclave was pressurized to atmospheric pressure The reactor was heated to 25 ° C ** · * 25 and sodium chlorite (NaCl 10; 7 wt%) was charged to the reactor at 1.2 g / min over a 4 hour period. ppm.

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Example 2 f ··· • · *: In the same manner, 1100 ppm NH4 + ions, 144 g NaCl and s, .. were added to the reactor. 1800 g of water. For a period of 1.25 hours, NaCIO (7 wt.% 30%) was charged to the reactor at 4.5 g / min, as was NaOH (5 wt.%) * At 1.25 g / min. The amount of NH4 + dropped to 4 ppm. * • · -ίδ • · · "Γ ··

Claims (9)

A process for removing ammonium from an ammonium-containing aqueous solution obtained by regenerating an ammonium-charged ion exchange mass with an elution liquid containing a chloride-containing site, comprising a step of feeding said ammonium-containing aqueous solution or an ammonium-containing aqueous ammonium solution. obtained by stripping said ammonium-containing aqueous solution and removing ammonia from the stripping gas by condensation, and a separate aqueous solution of alkali metal hypochlorite in a reactor for transferring ammonium / ammonia to nitrogen gas and producing a hydrogen | The ammonium-free effluent is characterized by the fact that at least part of the effluent from the reactor is recycled as elution liquid for the regeneration of the ammonium-charged ion exchange mass. $ Process according to claim 1, characterized in that the aqueous metal hypochlorite solution is produced in situ by direct electrolysis of an aqueous solution of alkali metal chloride. Process according to claim 2, characterized in that part of the effluent from the reactor is fed back to the electrolysis as the aqueous solution of alkali metal chloride. 4. A process according to claim 1, characterized in that the aqueous solution of alkali metal hypochlorite is taken from a storage container. ····· • * · Λί '. ***. 20 5. A process according to claim 1, characterized in that at least part of the liquid from the stripping is returned as an eluent liquid for the regeneration of the ammonium charged ion exchange mass. * · ..Li * 6. A process as claimed in claims 1-5, characterized in that the ion-exchange mass contains zeolite. 25 Process according to one of claims 1-6, characterized in that the chloride-containing salt is sodium chloride, the alkali metal hypochlorite is sodium hypochlorite, and the alkali metal chloride is sodium chloride. · ** • · ♦ • ® ·. ···. The process according to claim 7, characterized by the elution liquid containing * 1 * 20-75 g NaCl / l, preferably 50-60 g NaCl / l. * ·· ·· **. ** ·. 30 A method according to any one of claims 1-8, characterized in that | said ammonium-containing aqueous solution contains 0.2-4 g of ammonium nitrogen / l, preferably 0.4-2 g of ammonium nitrogen / l.