Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-12-13
2001-12-11
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S610000, C210S611000, C210S630000, C210S757000, C210S758000, C435S262500
Reexamination Certificate
active
06328891
ABSTRACT:
The invention relates to a process for purifying a water in which ammonium perchiorate is dissolved, by means of a biological treatment. The invention applies in particular to the treatment of industrial waste water contaminated with ammonium perchlorate originating from propergols.
Propergols are reliable only for a limited period, beyond which it is necessary to destroy them. This destruction can be carried out by incineration, but this incineration releases toxic fumes and is unsatisfactory. A more advantageous process consists in grinding the propergols under water. Propergols, in particular from rockets or large missiles, generally consist of more than 50% ammonium perchlorate powder. The grinding waters will consequently contain a large amount of dissolved ammonium perchlorate. Now, in order to respect the environment, it is not possible to discard into nature these waters containing both ammonium ions and perchlorate ions, originating from the dissociation of ammonium perchlorate, which are contaminants.
A number of processes for eliminating by treating chlorates and perchlorates dissolved in water have been described.
According to patent FR 2,138,231 corresponding to U.S. Pat. No. 3,755,156, the process consists firstly in mixing spent industrial water with urban waste water and then in carrying out the biological reduction of the chlorates and perchlorates in an anoxic reactor, the biochemical oxygen consumption by the mixture of waters needing to exceed by at least 20 mg/l the amount of oxygen associated in the form of inorganic combinations. This process requires the use of a large amount of urban waste water to obtain the desired value for the biochemical oxygen consumption. The admissible concentration of ammonium perchlorate in the water to be purified is low, of the order of 150 mg/l.
An improvement to this process, described in patent FR 2,277,045 corresponding to U.S. Pat. No. 3,943,055, consists in carrying out the previous process by adding a particular strain of microorganisms known as Vibrio dechloraticans Cuznesove B-1168. The admissible concentration of ammonium perchlorate in the aqueous solution is again low, of the order of 300 mg/l. This process has the same drawbacks as those mentioned above, and, in addition, it is necessary beforehand to obtain and adapt an uncommon strain of microorganisms.
According to another process, described in U.S. Pat. No. 5,302,285, the spent water is treated in an anoxic reactor using a microorganism such as HAP1 and then in an aerobic reactor. The concentration of ammonium perchlorate in the water to be treated is about 7 g/l. As in the preceding process, a specific microorganism must first be cultured. Although the rate of degradation of the perchlorates is improved, this process, like the previous ones, allows removal from the water, primarily, only of the perchlorate ions.
Now, it is not possible to discard into the environment, without the risk of polluting lakes and rivers and also underground water tables and surface waters, waters containing a large amount of nitrogen in ammoniacal form. Aquatic life is in particular affected at and above a concentration of about 2 mg/l of ammonium ions.
There is thus a need for a process for purifying a water containing ammonium perchlorate which is simple and economical and which makes it possible to remove both the perchlorate ions and the ammonium ions, converting the latter ions into molecular nitrogen.
The subject of the invention is consequently a process for the biological purification of a water containing ammonium perchlorate, which consists in treating this water with microorganisms in two successive reactors, characterized in that:
aqueous ammonium perchlorate solution is placed in contact, in a first, aerobic reactor, with an activated sludge containing nitrifying microorganisms, in the presence of at least one source of mineral carbon and nutritional elements for the metabolism of these microorganisms,
and then in that the liquid effluent leaving the first reactor is placed in contact, in a second, anoxic reactor, with an activated sludge containing denitrifying microorganisms and perchlorate-ion-reducing microorganisms, in the presence of at least one source of organic carbon and nutritional elements for the metabolism of these microorganisms.
The process according to the invention is simple to carry out. It does not require the use of complex installations, nor the use of urban waste water, nor that of uncommon microorganisms.
It allows the treatment of aqueous solutions containing very large amounts of ammonium perchlorate, including solutions saturated with an excess of undissolved ammonium perchlorate. The solutions used preferably contain up to 100 g/l thereof.
It allows the degradation both of the ammonium ions into molecular nitrogen and of the perchlorate ions into chloride ions. Specifically, it has been found that, contrary to what might be feared, the perchlorate ions are, under the conditions of the process, non-toxic for the growth of the microorganisms involved in the process for degrading the ammonium ions, and in particular for that of Nitrobacters.
The process is characterized more particularly in that, in the first, aerobic reactor, the operation of placing in contact with the activated sludge is carried out with a content of molecular oxygen, dissolved in the mixture, of greater than 2 mg/l, with a pH of the mixture maintained between 6 and 9 and at a temperature of between 16° C. and 45° C.
The duration of this placing in contact in the aerobic reactor is, in particular, between 15 and 50 days depending on the flow rate chosen and on the ammonium ion concentration of the aqueous solution entering the reactor, as well as on the volume of the reactor, so as to ensure a rate of nitrification of between 1.5 mg and 2 mg of N—NH
4
+
/l/h.
The source(s) of mineral carbon in the reactor are more particularly in an amount such that the mass ratio: mineral carbon atoms
itrogen atoms to be oxidized (C
1
/N
1
), is greater than 1.5.
In the second, anoxic reactor, the operation of placing in contact is more particularly carried out with a content of molecular oxygen, dissolved in the mixture, of less than 0.5 mg/l, at a pH of between 7 and 9 and at a temperature of between 18° C. and 45° C.
The duration of this operation is, in particular, between 15 and 50 days depending on the entry flow rate of the effluent, its concentration of NOx ions and the volume of the anoxic reactor, so as to ensure a rate of denitrification of between 1.5 mg and 2 mg of N—NOx/l/h. The term “NOx ions” means the combination of nitrate and nitrite ions.
The source(s) of organic carbon is(are) present in this anoxic reactor in an amount such that the mass ratio: organic carbon atoms
itrogen atoms to be reduced (C
2
/N
2
), is greater than 1.
By virtue of the process according to the invention, the industrial waste water, in particular propergol washing waters, can be decontaminated and discarded into the environment like other waste waters satisfying the standards in force.
The invention will be understood more clearly in the light of the more detailed description of the process which follows.
In the description and the claims, all the numbers expressing amounts of compounds or of reaction conditions should be interpreted as being preceded by the term “about”. The limits of the ranges are included therein.
The process is generally carried out in the following way. The two reactors, the first aerobic and the second anoxic, are placed in series and are fitted with the necessary devices, in particular for stirring them, for the introduction and removal of the liquids, for the introduction of the various compounds, and for monitoring the pH value and the dissolved oxygen value.
An activated sludge is placed in these two reactors. In the aerobic reactor, the activated sludge should contain microorganisms capable of nitrifying ammonium ions into nitrite and nitrate ions. These microorganisms are common microorganisms, such as those found in urban waste water, for example bacteria b
Gaudre-Longerinas Marie
Tauzia Jean-Michel
Barry Chester T.
Oliff & Berridg,e PLC
SNPE
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