MXPA99001766A - Method of treating ammonia-comprising waste water - Google Patents

Abstract

The invention relates to a method of treating ammonia-comprising waste water in which the bicarbonate ion is the counter ion of the ammonium ion present in the waste water. According to the invention half the ammonium is converted into nitrite, yielding an ammonia- and nitrite-containing solution, and in the second step the nitrite is used as oxidant for the ammonia. In the method according to the invention the conversion of half the ammonia into nitrite occurs automatically, providing a method which requires fewer controls. Also, the method according to the invention requires no external additive.

Description

METHOD OF TREATMENT OF WASTEWATER COMPRISING AMMONIA Description of the invention The present invention is concerned with a method of treating waste water or wastewater comprising ammonia, wherein, in a first stage, wastewater comprising ammonia is subjected to to a nitrification treatment by using a nitrifying microorganism and by adding oxygen, to produce a solution comprising an ammonia oxidation product and in a subsequent step the ammonia oxidation product, together with the ammonia, is converted to nitrogen, through the influence of a denitrifying microorganism. Such a method is known from the specification of U.S. Patent No. 5,078,884. The nitrate formed by the oxidation of cniac is used as an oxidant to convert, under substantially anaerobic conditions and with the help of a microorganism, the ammonia still to be degraded, which acts as an electron donor. During this process nitrogen is formed that is discharged into the atmosphere. The disadvantage of this method is that there is no reliable degradation of ammonia, as can be seen (in the right half of) Figure 2 of said publication. This means that undesirable discharges may occur to surface water. To prevent this, all kinds of investments would be required, such as control and measurement equipment. Finally, this method involves the addition of bleach (see reaction equation 5 of that publication), which must also be controlled. The objective of the present invention is to improve the method according to the preamble and in particular to provide a more reliable method, effective in cost, which does not require additives and partly because it is simpler from a technological control point of view . Surprisingly, this objective can be obtained by a method which is characterized in that by using waste water containing bicarbonate, which is substantially devoid of bicarbonate by air supply and in the first stage, maintaining the pH at a value less than or equal to a 7.2 to control the aeration, part of the ammonia present in the waste water is converted to nitrite, to produce a solution containing nitrite and in the second stage the denitrifying microorganism uses the nitrite thus formed as an oxidant for the remaining ammonia. In this way, a method that offers considerable advantages is provided, one of which is that it is of a substantially more self-regulating nature. In addition, the use of additives is avoided. A method is known from the prior art, comprising a nitrification step in which the ammonia is converted to nitrite. In a denitrification stage, the nitrite is converted to nitrogen, while a source of organic carbon is added as a substrate for a denitrification organism. Methanol is used as an organic carbon source. When the methanol is degraded, the acid, formed during the nitrification step, is consumed, to provide the pH control of the denitrification process. The disadvantage of this non-continuous method is that additive is required and much control is required, such as time control and control of substrate feeding. The total conversion of ammonia is not, under all conditions, satisfactory and is limited to at most 90% and for this reason a subsequent treatment is often required. A first favorable embodiment of the method is characterized in that, in the first stage, the waste water containing ammonia is fed to a nitrification reactor, in an amount such that the nitrification reactor operates without sludge retention, the temperature of a solution subjected to nitrification is maintained at a temperature between 25 and 60 ° C and the pH at a value of between 6 and 7.2 In this way favorable conditions are provided for the conversion of ammonia to nitrite, not to nitrate. In the second stage, the temperature of the solution in the denitrification reactor which is subjected to the denitrification treatment is preferably maintained at a temperature between 25 and 60 ° C and the pH at a value between 6 and 9.

In this way favorable conditions are provided for the conversion of nitrite and ammonia to nitrogen. According to a second embodiment of the method according to the invention, the first stage and the second stage are carried out simultaneously in a bioreactor, in which bioreactor the nitrifying and denitrifying microorganisms are present in a solid phase, the microorganism nitrifying is substantially present in the external, aerobic part of the solid phase and the denitrifying microorganism is substantially present in the internal anaerobic part of the solid phase and oxygen is fed, depending on the concentration of ammonia in the bioreactor, in an amount which limits the first stage. The advantage of this method is that only one reactor is required. The somewhat rough carrier preferably comprises a biofilm, ie a layer comprising the nitrifying and denitrifying microorganisms and the first step is carried out in the aerobic, external part of the biofilm. Due to the limitation of oxygen, this aerobic, external part of the biofilm is unable to convert more than 50% of the supplied ammonia and the ammonia, together with the nitrite formed in the aerobic, external part of the biofilm, will be converted , in the aerobic part, internal, of the biofilm to nitrogen. The solid phase may consist of a spontaneously formed aggregate.

Preferably as the solid phase a chosen phase of a particle carrier carrying the biopelic and an immobile carrier carrying the biopeiic acid is used. If the carrier consists of particles, the carrier size is preferably 0.1 to 1 mm. In this way, a high density of biomass is provided and the size of the bioreactor can be maintained at a limit. In a typical case, the ammonia load of the biofilm surface is greater than 2-3 g N / m2-day. Some roughness of the carrier surface is advantageous. In the second stage, the temperature of a solution subjected to the denitrification-nitrification reaction in the reactor is preferably maintained at a value between 5 and 60 ° C and the pH at a value between 6 and 9. This creates conditions favorable for the conversion of ammonia to nitrogen. The invention will be further explained by means of the detailed specification referred to the example of the method according to the invention, the parameters of which are given in the attached figure. The method according to the present invention comprises a nitrification reaction and a denitrification reaction. As can be seen from the overall reaction equation I shown in the formula sheet and as will be explained later herein, no addition of means adjusting the pK is necessary. Nitrification according to reaction equation II produces two equivalents of protons per equivalent of converted ammonia. In the waste water that can be treated appropriately by the application of the invention, HCO3- is the counter ion of the ammonia ion. Examples of such waste water include percolation water from waste deposits and the effluent from aerobic purifications. The air supply necessary for the oxidation of the ammonia during the nitrification reaction also ensures that the CO2 is removed according to reaction equation III. Thus, the nitrification reaction has a net yield of one acid equivalent per equivalent of converted ammonia. The denitrification reaction according to ca i. The reaction equation IV requires an acid equivalent per equivalent of converted ammonia. This means that by using the C02-depleted effluent from the denitrification reactor, no pH adjustment is required. When separating the C02, the solution submitted to nitrification is devoid of HCO3-, to diminish the capacity to buffer the pH of the solution. This means that its pH can vary, in particular that it can fall due to the formation of the acid in this stage. The pK of HCO3 *, ie the pH at which the HCO3- regulates the pH optimally, is 6.37. The pH drop inhibits the nitrification process and the ammonia is only partially converted but, according to the understanding provided by the present invention, to the desired extent (ie, up to 50%). As a result, an appropriate amount of ammonia is available for the subsequent denitrification process that uses acid and thus benefits from the low pH value. Without being limited by any theory, it is assumed that the good quality of control is obtained due to the fact that the nitrifying organism only perceives the NH3 V1-N02 and not NH4"and NO2". When the pH drops, the concentration of NH3 (substrate) decreases and the concentration of HN02, which inhibits the nitrification reaction, increases.

Example A stirred batch reactor (2.4 liters) is put into operation with retention of lodes and is fed with ammonia rich waste water (41 mM, pH '=' 8.0). During the day, 80% of the reactor volume is replenished. The temperature was maintained at 33 ° C and the dissolved oxygen concentration was 20%. Under these conditions the biomass concentration was 140 mg dry weight per liter. The pH of the reactor effluent was about 6.7. N.B .: The pH was not adjusted by the addition of a substrate compound such as methanol, 40-50% of the ammonia in the waste water were converted. 1.2 ml / minute of the effluent was fed to a fluidized bed reactor (2 liters capacity). The pH in the fluidized bed reactor was stable and was about 7.9. The Kjeldahl nitrogen was converted into the fluidized bed reactor at a rate of 0.6 Kg N / m3-day. The total elimination of nitrogen was 83%. The relevant parameters are given in the figure. This percentage can be increased by returning a portion of the effluent from the fluidized bed reactor to the batch reactor. Due to the stable pH in the fluidized bed reactor the return amount is not very critical and can be adjusted to a permanent value. Too high a return results in an increased degradation of the ammonia in the batch reactor. This causes the acid consumption to fall into the fluidized bed reactor, as a result of which the degradation of the ammonia decreases again. Although the method according to the invention has a substantially more self-regulating nature and automatically results in an overall degradation of the ammonia of at least about 80%, the pH of the content of the nitrification reactor can optionally be adjusted by means of the feed of the effluent from the denitrification reactor. Thus, no external additive is added. According to "another embodiment of the method of the invention, the waste water is fed to a denitrification stage.During denitrification, a portion of the ammonia from the waste stream and a portion of the reactor are used. The nitrite is fed to the nitrification reactor, where the nitrite is fed to the denitrification reactor, and in case the effluent from the denitrification stage is discharged, the effluent can first be subjected to a stage of nitrification in order to avoid the discharge of nitrite The appropriate microorganisms can be obtained without great difficulty from the iodine of the existing water treatment plants in which the ammonia is degraded, in the manner described in the literature. the crop for denitrification can be obtained from the Centraai Bureau vocr Schimmecultures, Baarn, The Netherlands, registered under the number 949. 87

Claims (6)

1. Rei indications 1. A waste water treatment method is comprised of ammonia, wherein, in a first step, a waste water comprising ammonia is subjected to a nitrification treatment by the use of a nitrifying microorganism and by the addition of oxygen, to produce ur-a solution comprising an oxidation product of ammonia and er-a second stage, the ammonia oxidation product, together with ammonia, is converted to nitrogen by means of the influence of a denitrifying microorganism, characterized in that waste water containing bicarbonate is used, which is substantially devoid of bicarbonate feed air and in the first stage the pH is maintained at a value of less than or equal to 7.2 when controlling aeration, part of the ammonia present in the water of waste is converted to nitrite, to produce a solution containing nitrite and in the second stage, the microorganism of denit The use of the nitrite thus formed as an oxidant for the remaining ammonia is used.
2. 2. A method according to claim 1, characterized in that in the first stage the waste water containing ammonia is fed to a nitrification reactor, in an amount such that the nitrification reactor operates without sludge retention, the The temperature of a solution subjected to nitrification is maintained at a value between 25 and 60 ° C and the pH at a value between 6 and 7.2.
3. 3. A method according to claim 1 or 2, characterized in that in the second step, the temperature of the solution in the denitrification reactor, which is subjected to the denitrification treatment, is preferably maintained at a value of between 25 and 60 ° C and the pH at a value between 6 and 9.
4. 4. A method according to claim 1, characterized in that the first stage and the second stage are carried out simultaneously in a bioreactor, in which bioreactor microorganisms nitrifying and denitrifying are present in a solid phase, the nitrifying microorganism is substantially present in the aerobic, external part of the solid phase and the denitrifying microorganism is substantially present in the anaerobic, internal part of the solid phase and oxygen is fed, depending on the concentration of ammonia in the reactor, in an amount that limits the first stage.
5. 5. A method according to claim 4, characterized in that a chosen phase of a particulate carrier carrying the biofilm and an immobile carrier carrying the biofilm is used as the solid phase. biofilm
6. 6. A method according to claim 1 or 2, characterized in that the temperature of a solution in the reactor, which is subjected to a denitrification-nitrification treatment, is maintained at a value of between 5 and 60 ° C and the a value between 6 and 9.