Process and installation for the treatment of effluents by oxidation and denitrification in the presence of a heterogeneous catalyst

The invention relates to a process of aqueous phase oxidation of effluents, consisting of subjecting said effluents to oxidation in the presence of at least one catalyst and of at least one oxidising agent, at a temperature of between approximately 20.degree. C. and approximately 350.degree. C., under a total pressure of between approximately 1 and approximately 160 bars, in such manner as to mineralise part of the organic matter and total ammoniated nitrogen contained in said effluents, said oxidation being carried out inside a reactor in which a gaseous phase is set up above the liquid phase consisting of said effluents. characterized in that said catalyst is a heterogeneous catalyst placed inside said reactor above the interface between said gaseous phase and said liquid phase.

The area of the invention is the treatment of industrial or urban effluents 
containing organic matter and nitrogen compounds. 
More generally the invention relates to the treatment of effluents which 
contain organic matter and organic and inorganic compounds of nitrogen, 
such as waste lixiviation products, farm excrements, chemical industry 
effluents (dyes, explosives, anilines, nicotinic acid, polyamides etc.) 
effluents of agro-food industries, treatment plant sludge, output 
effluents from treatment sludge packaging and dehydration etc.. 
The treatment concerned consists of removing from the effluents to be 
treated a substantial part of the undesired compounds they contain so that 
they can be discharged into a natural receiving environment, a treatment 
facility or a collector network. The effluent considered may be water or 
any other fluid liquid. 
The methods conventionally used to treat urban or industrial effluents use 
biological processes intended to reduce their biological oxygen 
requirements (BOR) and their content of nitrogenous nutrients and 
phosphorus. However, certain effluents containing pollutants that are not 
easily biodegradable and have high ammonia contents require the use of 
special processes and/or necessitate the additional use of chemical 
substrates for their treatment. 
One effective treatment adapted to the elimination of chemical oxygen 
requirements (COR) is aqueous phase oxidation which has been described at 
length in the prior art. The objective of this technique is to carry out 
extended oxidation of organic matter that is little biodegradable 
contained in aqueous effluents through the contact of said effluents with 
an oxidising agent. For this purpose the operating conditions of said 
process typically lie between approximately 20 and approximately 
350.degree. C. regarding temperature and between approximately 1 and 
approximately 160 bars in respect of pressure. 
Aqueous phase oxidation processes do not allow substantial elimination of 
ammoniated nitrogen, particularly when the effluents to be treated contain 
high concentrations of ammoniated nitrogen (&gt;200 mg/l). Even oxidation 
under wet conditions (Wet Air Oxidation) which is one of the best 
performing oxidation processes, generally carried out at a temperature of 
between approximately 200.degree. C. and approximately 350.degree. C. and 
a pressure generally lying between approximately 20 and approximately 160 
bars, only achieves limited removal of ammoniated nitrogen with yields of 
5% to 10% whereas organic carbon is destroyed with efficacy in the region 
of almost 80%. Numerous publications have shown that the treatment of 
industrial or urban effluents by wet air oxidation only achieves very 
partial elimination of total Kjeldahl nitrogen of between 5 and 15% and 
that on completion of treatment the latter is essentially in ammoniated 
nitrogen form. 
Physical processes also exist for the removal of ammoniated nitrogen. Air 
or steam stripping, effective for high contents, requires considerable 
investment and is ill-adapted to the treatment of effluents which also 
contain high concentrations of organic matter. Also, it only achieves 
ammonia conversion by concentrating it. With this type of process the 
ammonia is removed by neutralisation with sulphuric acid to form ammonium 
sulphate which has to be stored before being put to further use, which 
constitutes an additional operating charge. With treatment by wet air 
oxidation for example this operation can only be carried out after leaving 
the effluent to settle, cooling to a temperature of less than 80.degree. 
C. and adjusting pH in order to prevent simultaneous release of volatile, 
foul smelling and/or harmful organic compounds during forced aeration at a 
higher temperature. This treatment of ammoniated nitrogen subsequent to 
wet air oxidation leads to much increased investment and operating costs. 
In treatment plants the removal of ammoniated nitrogen may also be made by 
biological nitrification-denitrification treatment. This treatment does 
not easily accept high loads. 
If the effluent has sufficiently high COR content it is possible to carry 
out simultaneous removal of organic matter and of organic and inorganic 
nitrogen compounds by incineration. This technique leads to the formation 
however of a large quantity of NOx nitrogen oxides (x=1 and 2), by 
oxidation of a substantial part of the nitrogenous load. In order to 
comply with NOx release standards therefore, it is necessary to treat 
incineration fumes, in particular by catalytic reduction of NOx by NH3, a 
technique which is expensive to set in operation. 
It is also possible to reinforce the efficacy of wet air oxidation for the 
removal of ammoniated nitrogen through the use of heterogeneous catalysts 
in contact with the effluent to be treated, made up for example of 
titanium dioxide, a rare earth oxide and a precious metal oxide such as 
described in European Patent EP-A431 932, or in American Patent U.S. Pat. 
No. 3,988,259. However, such catalysts have the disadvantage of showing 
substantial loss of activity with time due to the fact that they are 
immersed during use. A further disadvantage of catalytic wet air oxidation 
arises from the fact that the heterogeneous catalyst may be affected by 
the precipitation in its structure of calcium carbonates and sulphates and 
of metals present in traces in the effluents such as mercury, cadmium, 
lead, zinc etc. which are known poisons for numerous catalysts by acting 
to form combinations or alloys in particular with precious metals. All 
these disadvantages mean that the process of wet air oxidation is not 
currently used to treat effluents. 
It will also be noted that as no catalysts are used for processes such as 
wet air oxidation for example, this leads to gaseous ammonia being carried 
by treatment gases which causes the formation of ammonium salt deposits 
such as ammonium sulphate, ammonium acetate etc. These deposits may lead 
to fouling of essential parts such as conduits and valves. 
The purpose of this invention is to provide a process for the oxidation of 
effluents in aqueous phase which will remedy the disadvantages of the 
current state of the art. More precisely, the purpose of the present 
invention is to provide a process for treating industrial or urban 
effluents containing organic matter and organic and inorganic nitrogen 
compounds which achieves substantial removal of total ammoniated nitrogen 
and simultaneously achieves a substantial decrease in the COR of said 
effluents and in the release of harmful or foul smelling gases. 
A further objective of the invention is to provide a process and 
installation which allows disadvantage-free use of heterogeneous catalysts 
for wet air oxidation processes. 
Yet another objective of this invention is to describe a process which will 
substantially increase the life of such heterogeneous catalysts. 
A further objective of the invention is to improve the efficacy of aqueous 
phase oxidation processes and to reduce the costs incurred for their 
implementation. 
These objectives and others which will be described later are achieved with 
this invention which relates to a process of aqueous phase oxidation of 
effluents, which consists of subjecting said effluents to oxidation in the 
presence of at least one catalyst and of at least one oxidising agent at a 
temperature of between approximately 20.degree. C. and approximately 
350.degree. C. under a total pressure lying between approximately 1 and 
approximately 160 bars, in such manner as to mineralise part of the 
organic matter and total ammoniated nitrogen contained in said effluents, 
said oxidation being carried out inside a reactor in which a gaseous phase 
is set up above the liquid phase consisting of the effluents 
characterized in that said catalyst is a heterogeneous catalyst placed 
inside said reactor, above the interface between said gaseous phase and 
said liquid phase. 
With said process it is possible to remove total ammoniated nitrogen by 
oxidation in N.sub.2 molecular nitrogen without forming NOx nitrogen 
oxides(x=1 or 2). 
The catalyst used in this way is also able to achieve simultaneous removal 
of the carbon monoxide CO usually formed during wet air oxidation through 
oxidation into carbon dioxide, and the removal of volatile organic 
compounds by oxidation into carbon dioxide and water. 
It was found, in surprising manner, that such positioning of the catalysts 
inside the reactor allowed the removal with great efficacy of both 
ammoniated nitrogen and CO which in turn allowed release of the residual 
gas into the atmosphere with no complex subsequent treatment. In 
unexpected manner, the transfer of ammoniated nitrogen to the gaseous 
phase of the reactor, as far as the catalysts in view of oxidation, is 
sufficiently efficient to avoid having to proceed with pH adjustment to 
higher levels as is the case with forced aeration. 
The position of the heterogeneous catalyst above the interface between the 
gaseous and liquid phases in the oxidation reactor also avoids the use of 
costly catalysts able to resist against the corrosive conditions of the 
liquid phase, and also avoids any risk of particle fouling of the catalyst 
and any risk of loss of activity of the catalysts by dissolution of its 
active phase or by reaction with contaminants present in the liquid phase. 
According to a variant of interest of this invention, the process is set in 
operation at a temperature of between approximately 200.degree. C. and 
350.degree. C. under a total pressure of between approximately 20 and 
approximately 160 bars. It therefore constitutes a process of wet air 
oxidation. 
Preferably, said heterogeneous catalyst is a metal belonging to the group 
made up of vanadium, niobium, chromium, molybdenum, tungsten, manganese, 
iron, cobalt, nickel, copper, cerium, platinum, rhodium, palladium, 
ruthenium and iridium and the mixtures and compounds of one or more of 
these. 
The catalyst may advantageously be placed on a mineral support made up for 
example of an oxide such as alumina, silica, zeolites, titanium dioxide, 
zirconium etc. 
The catalyst may be prepared by any other means known to men of the art, in 
particular by impregnation of a porous support with a solution of one or 
more compounds of metals producing metals or metallic oxides by heat 
activation, or by a mixture of an oxide support and one or more metal 
compounds then given form by extrusion, pelleting, granulation, 
compressing etc. 
The catalyst of the invention may be in the form of beads, drops, 
cylindrical or polylobate extrudates, rings, ceramic or metallic 
honeycombs, or any other form appropriate for setting up a fixed catalyst 
bed placed in the wet air oxidation reactor above the interface between 
the gaseous and liquid phases. Preferably, metallic honeycombs are used as 
they have the combined advantages of being cheap, easy to use, easy to 
lock into position inside the reactor and easy to move inside the reactor. 
As specified above, oxidation in aqueous phase is carried out in a reactor 
operating continuously or intermittently at a temperature of between 
approximately 20.degree. C. and approximately 350.degree. C. under a total 
pressure lying between approximately 1 bar and 160 bars. To perform said 
oxidation at least one oxidising agent is used chosen from among air, 
oxygen enriched air, oxygen, ozone, hydrogen peroxide, peracids, gaseous 
chlorine, chlorine dioxide, sodium hypochlorite, potassium permanganate or 
any other oxidising agent known to men of the art. 
If the oxidising agent used is placed in the treatment reactor in liquid or 
solution form, as for example hydrogen peroxide, sodium hypochlorite, 
potassium permanganate etc . . . the invention preferably comprises a gas 
flow into the reactor made up of at least one agent chosen from among air, 
oxygen enriched air, oxygen, ozone, water steam or nitrogen gas. 
Catalytic oxidation is carried out at a temperature of between 
approximately 200.degree. C. and approximately 350.degree. C., preferably 
between 250.degree. C. and 300.degree. C. When setting in operation a 
process of wet air oxidation, positioning of the catalyst inside the 
reactor, owing to the temperature prevailing inside said wet air oxidation 
reactor (between 200.degree. C. and 350.degree. C.) proves to be highly 
effective in carrying out oxidation reactions of NH.sub.3 into N.sub.2 and 
N.sub.2 O, of CO into CO.sub.2 and of volatile organic compounds into 
CO.sub.2 and H.sub.2 O without the need to heat the gases as in the case 
of treating said gases in an additional reactor located outside the wet 
air oxidation reactor. Also, since the different oxidation reactions 
catalysed in this way are highly exothermic, the heat emitted by said 
reactions is for the most part transmitted by radiation, conduction and 
convection to the entire reactor which improves its thermal output and in 
particular enables treatment of more diluted effluents containing less COR 
without the need to supply additional calories to balance the overall 
thermal output of the oxidation process according to a variant of interest 
of this invention, this catalytic oxidation temperature may be higher than 
the oxidation temperature in aqueous phase. It will then be possible not 
to bring the entire inside of the reactor up to catalytic oxidation 
temperature but only the area in which this catalytic oxidation takes 
place, which means that lower pressures can be used for oxidation in 
aqueous phase. To set in operation said variant of the invention, specific 
heating means are used to heat the catalytic oxidation area, which are 
placed at the same level as the area of the reactor in which the 
heterogeneous catalyst is positioned. These means may in particular be 
made up of a heating collar placed on the outside surface of the reactor. 
The catalytic oxidation area may also be heated using the Joule effect. 
Heating the catalytic oxidation area to a temperature that is higher than 
that of the liquid effluent also has the advantage of avoiding any 
condensation of said effluent. 
According to a variant of the process, said oxidation in aqueous phase may 
be carried out in the presence of a homogeneous catalyst intended to 
increase the efficacy of COR reduction. According to said variant, 
oxidation is therefore carried out in the presence of two catalysts, a 
heterogeneous catalyst placed above the interface between the gaseous 
phase and the liquid phase, and a homogeneous catalyst. 
Preferably, said catalyst is a metal belonging to the group made up of 
manganese, iron, cobalt, nickel, copper, zinc and the mixtures and 
compounds of one or more of these. In particularly advantageous manner, a 
soluble compound of copper is used (such as copper sulphate) or of zinc or 
their mixture, the mass ratio of catalyst metal/chemical oxygen 
requirements (COR) of the effluent before treatment lying preferably 
between approximately 5/10.sub.-4 and 3.10.sub.-1. 
It will also be noted that another catalyst may be used placed at the exit 
of the reactor, for example for additional treatment of the carbon oxide 
and of volatile organic compounds. 
For continuous operation reactors, it may prove to be advantageous to 
recycle at least part of said gaseous phase in said aqueous phase 
oxidation reactor, in such manner as to ensure sufficient contact time to 
obtain substantial removal of NH.sub.3, CO and volatile organic compounds 
usage a heterogeneous catalyst placed inside said reactor. 
According to a further variant of the process, the effluent treated 
comprises a solid phase, and the process comprises a stage consisting of 
recycling at least part of the solid phase present in the oxidation 
reactor. This stage provides sufficient contact time to ensure oxidation 
of the organic part of this solid phase. 
Also according to a variant of interest of this invention, the process 
comprises a stage consisting of adjusting the pH of said effluents to a 
value of 7 to 12. It was observed that said adjustment increased the 
efficacy of catalytic oxidation of ammonia without increasing the 
formation of nitrogen oxides. 
The invention relates to any reactor for aqueous phase oxidation of a 
liquid effluent by an oxidising agent, characterised in that it comprises 
means of holding a heterogeneous catalyst above the surface of said liquid 
effluent. 
Also preferably, said reactor includes means adjusting the position of said 
holding means, in such manner as to be able to adjust the height between 
the catalyst and the surface of the liquid effluent inside the reactor. 
This height may vary in relation to the type of effluent to be treated, 
particularly in relation to whether or not stirring means are provided 
within the reactor. 
According to a variant the reactor comprises a devesiculator between the 
liquid phase and the catalyst.

EXAMPLE 1 (NOT REPRESENTATIVE OF THE INVENTION) 
In a first series of tests wet air oxidation is examined of a liquid 
effluent having the following characteristics: 
COR: 34.6 g/l 
N-NH4 content: 1.89 g/l 
pH: 5.41 
This effluent is placed in an autoclave reactor in the presence of an 
oxygen/COR stoichiometry of 1.5, at a temperature of 235.degree. C. and 
under a total pressure of 46 bars with a reaction time of 10 min. For 
comparison with a test without heterogeneous catalyst, catalysts 
containing precious metals are placed inside the autoclave on an alumina 
support in cylindrical drop form (2.8 mm.times.3.5 mm) comprising 
respectively 0.5% ruthenium (615 mg of type 146 catalyst produced by 
Johnson Matthey), 0.5% platinum (610 mg of type 73 catalyst produced by 
Johnson Matthey) and 5% palladium (110 mg of type 49 catalyst produced by 
Johnson Matthey). 
The following COR and N-NH4 values were noted at the end of the test. 
______________________________________ 
Without catalyst 
0.5% Ru 0.5% Pt 5% Pd 
______________________________________ 
COR (g/l) 31.9 31.0 28.0 30.3 
COR red. (%) 7.8 10.4 19.0 12.4 
N--NH4 (g/l) 2.28 2.10 1.67 2.33 
N--NH4 red (%) -17.3 -11.3 -11.3 -23.6 
______________________________________ 
It is observed that the presence of Ru and Pd based catalysts does not 
significantly alter reductions of COR and ammoniated nitrogen. On the 
other hand, the Pt based catalyst leads to a COR reduction of 19% and 
removal by oxidation of 11% of ammoniated nitrogen. However, after a 
reaction time of 10 min, all the catalysts used lost most of their 
precious metal content through suspension in the solution further to shock 
and friction due to stirring of the effluent in the reactor required for 
reaction purposes. Although it shows some efficacy in removing ammonia, 
the platinum based heterogeneous catalyst placed in the liquid effluent to 
be treated does not show sufficient long-lasting properties for industrial 
use. 
EXAMPLE 2 
In a second series of tests wet air oxidation of sludge from a treatment 
plant with the following characteristics was examined: 
matter in suspension: 40.7 g/l 
volatile matter: 60.7% 
COR: 48.7 g/l 
N-NH4 content: 0.938 g/l 
pH: 6.3 
This sludge is placed in a wet air oxidation reactor according to the 
present invention as shown in FIG. 4. 
The reactor is supplied with effluent to be treated by injection pipe 1. 
This reactor is fitted with heating means able to bring the effluent to a 
temperature lying between approximately 100.degree. C. and 350.degree. C. 
Pressurising means are provided to bring the effluents to be treated in 
the reactor under a pressure of between approximately 5 bars and 
approximately 160 bar. 
In conventional manner, the reactor is fitted with two pipes 2 and 3: 
an outlet pipe 3 to discharge a water saturated gaseous phase, 
an outlet pipe 2 to discharge an essentially liquid phase chiefly 
containing residual soluble organic matter and an essentially mineral 
solid phase in suspension. 
The injection of oxygen 6 is made by a sludge recirculation loop 7 from 
base 8 of reactor 1 towards its upper part. This layout is advantageous 
but not compulsory. It is also possible to inject oxygen into another part 
of the reactor. A heat exchanger 9 is provided to recover and return the 
calories from treated effluents with a view for further use, for example, 
to preheat the effluent to be treated. 
In accordance with the essential characteristic of the invention, a 
heterogeneous catalyst is placed in a basket container 4 above interface 
10 between the liquid phase and the gas phase present in the reactor in 
such manner as to leave between said interface 10 and said catalyst a 
security volume which will prevent or at least minimise contact of said 
effluent with said catalyst. This security volume is obtained by 
maintaining sufficient partial pressure above the liquid while maintaining 
the latter at a given level. Means 11 made up of notches on the inner wall 
of the reactor are provided to change the position of said basket 
container. 
Under the present example, the sludge is placed in this reactor under an 
oxygen/COR stoichiometry of 1.5, at a temperature of 235.degree. C. and 
under a total pressure of 38 bars. For comparison with tests without a 
heterogeneous catalyst, a heterogeneous catalyst in accordance with the 
present invention is placed in the autoclave. The catalyst used is a 
catalyst containing 0.5% platinum on an alumina support in the form of 
cylindrical drops (2.8 mm.times.3.5 mm, type 73 catalyst produced by 
Johnson Matthey) contained in a grid basket container placed horizontally 
approximately 30 cm above the liquid-gas interface at rest (no stirring). 
Certain tests are carried out by adding to the sludge to be treated a 
homogenous catalyst (copper sulphate with a copper content of 500 mg/l), a 
catalyst intended to accelerate COR reduction. 
The results given in FIG. 1 show that the homogeneous copper catalyst used 
alone (with no platinum based heterogeneous catalyst) only accelerates the 
conversion kinetics of organic nitrogen (amino acids, peptides, proteins . 
. . ) into ammoniated nitrogen but does not contribute to removing 
ammoniated nitrogen by oxidation compared with a test without copper. On 
the contrary, the 3 tests carried out in the presence of the platinum 
catalyst show substantial reduction of ammoniated nitrogen of up to 86% 
after a reaction time of 1 hour. 
It is observed from the results given in FIG. 2 that the presence of the 
platinum catalyst does not in any way affect COR reduction during the wet 
air oxidation reaction. Unlike the prior art, and in particular the 
disclosures of EP patent 431 932, according to which the presence of a 
heterogeneous catalyst, for example containing platinum, in contact with 
the effluent increases the removal rate of COR and ammoniated nitrogen, 
the use of the heterogeneous catalysts of the invention leads to extended 
nitrogen removal without affecting COR decline in any way. 
It is therefore possible for example in the case of a residual water 
treatment plant, by using wet air oxidation treatment, to remove total 
ammoniated nitrogen from sludge and to produce an effluent made up chiefly 
of volatile fatty acids, alcohols and ketones, said effluent forming a 
very efficient carbonated source to remove the nitrogen contained in the 
effluent entering the plant by biological denitrification. 
EXAMPLE 3 
In a third series of tests, wet air oxidation of sludge from a treatment 
plant is examined, the sludge having the following characteristics: 
matter in suspension: 40.7 g/l 
volatile matter: 60.7% 
COR: 48.7g/l 
N-NNH4 content: 0.938 g/l 
pH: 6.3 
This sludge is placed in the reactor described in FIG. 4 in the presence of 
an oxygen/COR stoichiometry of 1.5, at a temperature of 235.degree. C. and 
under a total pressure of 38 bars, with a reaction time of 15 min. For 
comparison with tests with no heterogeneous catalyst, the same load of 
catalyst containing 0.5% platinum as used for the second series of tests 
is placed in the autoclave in a grid basket container positioned either 
horizontally approximately 30 cm above the liquid-gas interface at rest 
(test H3) or vertically approximately 80 cm above the liquid-gas interface 
at rest (test V8). Certain tests are carried out by adding to the sludge 
to be treated a homogeneous catalyst (copper sulphate, with a copper 
content of 500 mg/l)) a catalyst intended to accelerate COR decrease. 
Optionally the initial pH of the sludge (6.3) is adjusted to a value of 10 
by adding a soda solution. 
The results in Table 1 show that the increase of the initial pH of the 
sludge increases the catalytic oxidation efficacy of ammonia and that 
there is no significant formation of NOx nitrogen oxides, which would 
become soluble in the effluent treated in the form of NO.sub.2 - nitrite 
and NO.sub.s -nitrate ions. 
TABLE I 
______________________________________ 
Contact 
Initial Final time N--NH4 N--NO2 N--NO3 
Catalysts pH pH (min) (mg/l) (mg/l) (mg/l) 
______________________________________ 
-- 6.3 7.660 0 1407 12 n.d. 
Pt (H3) 6.3 4.560 15 189 15 0.2 
Pt (H3) 6.3 5.860 15 126 25 0.7 
Cu 6.3 6.515 15 1361 4.5 n.d. 
Cu,Pt (V8) 6.3 6.115 15 867 9 0.4 
Cu,Pt (V8) 10.0 6.815 15 696 8 0.3 
______________________________________ 
n.d.: not determined 
EXAMPLE 4 
In a fourth series of tests wet air oxidation of an effluent derived from a 
thermal sludge packaging process is examined which has the following 
characteristics: 
COR: 9.4 g/l 
N-NH4 content: 1.52 g/l 
pH: 7.85 
This effluent is placed in an autoclave reactor in the presence of an 
oxygen/CIR stoichiometry of 1.5, at a temperature of 235.degree. C. under 
a total pressure of 35 bars with a reaction time of 15 min/ For comparison 
with a test with no heterogeneous catalyst, the same load of catalyst 
containing 0.5% platinum already used for the second and third series of 
tests, is placed in the autoclave vertically approximately 80 cm above the 
liquid-gas interface at rest. 
TABLE 2 
______________________________________ 
Contact 
Initial Final time N--NH4 N--NO2 N--NO3 
Catalysts pH pH (min) (mg/l) (mg/l) (mg/l) 
______________________________________ 
-- 7.85 7.85 0 1521 323 
Cu,Pt (H3) 7.85 6.7 15 720 117 
Cu,Pt (H3) 10.0 7.6 15 600 116 
______________________________________ 
The results given in Table 2 confirm that the increase of the initial pH of 
the effluent from 7.85 to 10.0 increases the efficacy of the catalytic 
oxidation of ammonia and that there is no significant increase in the 
total oxidised forms of nitrogen, NO.sub.2- nitrite and NO.sub.3- nitrate 
in the effluent treated. 
EXAMPLE 5 
FIG. 3 shows the effect of the final pH of the treated effluents on the 
percentage of removal of ammoniated nitrogen in the different tests made 
in the presence of an oxygen/COR stoichiometry of 1.5, at a temperature of 
235.degree. C. for 15 minutes under a total pressure of 38 bars in the 
presence of a homogeneous catalyst (copper sulphate with a copper content 
of 500 mg/I) and a catalyst load containing 0.5% platinum contained in a 
grid basket container placed either horizontally approximately 30 cm above 
the liquid-gas interface at rest (test H3) or vertically approximately 80 
cm above the liquid gas interface at rest (V8). Optionally the initial pH 
of the effluent is adjusted to a value of 10 by adding a soda solution. 
These results confirm that the removal of ammoniated nitrogen is helped by 
an increase in the effluent's pH; 
EXAMPLE 6 
In this test wet air oxidation of an effluent is examined which contains 
the following compounds: 
Urea (NH.sub.2 CONH.sub.2 : 0.026 mol/l) 
Hexamethylenetetramine or HTM (C.sub.6 H.sub.12 N.sub.4): 0.036 mol/l) 
COR: 7.6 g/l 
This effluent is placed in a reactor in the presence of an oxygen/COR 
stoichiometry of 1.5 at a temperature of 285.degree. C. under a total 
pressure of 86 bars with a reaction time of 10 min. For comparison with a 
test with no heterogeneous catalyst, a precious metal based catalyst is 
placed in the autoclave on an alumina support in cylindrical honeycomb 
shape comprising 0.5% platinum. 
TABLE 3 
______________________________________ 
Treatment with 
Treatment with 
Initial solution no catalyst catalyst 
______________________________________ 
COR g/l 7.6 0.4 0.03 
N--NO3 g/l -- 0.008 0.075 
N--NO2 g/l -- 0 0.04 
N--NH4 g/l -- 2.76 0.045 
pH 7.5 9 6 
______________________________________ 
The results obtained (see Table 3) show that in the presence of a catalyst, 
the percentage of ammonia removal reaches 98% and that there is no 
significant increase in the total oxidised forms of nitrogen, NO.sub.2- 
nitrite and NO.sub.3- nitrate, in the treated effluent. 
EXAMPLE 7 
In this test, wet air oxidation of an effluent is tested which contains the 
following compounds: 
Urea (NH.sub.2 CONH.sub.2): 0.0335 mol/l 
Amino-4-benzenesulfonamide (C.sub.6 H.sub.8 N.sub.2 O.sub.2 S): 0.0697 
mol/l 
COR: 11.4 g/l 
pH: 6.8 
This effluent is placed in an autoclave reactor in the presence of an 
oxygen/COR stoichiometry of 1.5, at a temperature of 285.degree. C. under 
a total pressure of 86 bars with a reaction time of 10 min. For comparison 
with a test with no heterogeneous catalyst, a catalyst containing precious 
metals is placed in the autoclave on an alumina support in cylindrical 
honeycomb form comprising 0.5% platinum. 
TABLE 4 
______________________________________ 
Treatment with 
Treatment with 
Initial solution no catalyst catalyst 
______________________________________ 
COR g/l 11.4 0.5 0.24 
N--NO3 g/l -- 0.002 0.010 
N--NO2 g/l -- 0 0.010 
N--NH4 g/l -- 1.8 0.34 
pH 6.8 8.3 2.1 
______________________________________ 
The results obtained (Table 4) show that the presence of the catalyst 
allows ammonia to be removed with a yield of 81% and that there is no 
significant increase in the total oxidised forms of nitrogen, NO.sub.2- 
nitrite and NO.sub.3- nitrate, in the treated effluent. 
All the results given above clearly show the numerous advantages related to 
the use of an effluent treatment according to the process of the 
invention, in a reactor within which said effluents are subjected to wet 
air oxidation, in the presence of a heterogeneous catalyst and optionally 
of a homogeneous catalyst and of at least one oxidising gas such as air or 
oxygen at a temperature of between approximately 20.degree. C. and 
approximately 350.degree. C. under a total pressure of between 
approximately 1 bar and approximately 160 bars. This is in no way a 
restrictive description of the invention in respect of the type of 
effluent, the formulation and conditions of use of the catalysts, nor of 
the conditions of use of the process representing the invention. Finally 
it will be noted that the process described in the present patent 
application is compatible with the process of wet air oxidation with 
internal recycling of solid residues described in French patent 
application n.degree. 9403503 filed on Mar. 21, 1994 by the applicant.