Oxidation and biological reduction reactor, biofiltration method and washing methods used in this reactor

The present invention concerns an oxidation and biological reduction reactor for liquid to be treated by upwards circulation and recirculation including, within a longitudinal vertical enclosure 5 accessible by an admission 9, a lower layer 1 of biomass fixation made of material whose density is lower than that of the liquid and an upper layer of fixation 3 of biomass made of material whose density is higher than that of the liquid, characterized in that the lower layer 1 is separated from the upper layer 3 by a transverse wall 2 preventing the passage of filtration materials between a lower zone located under the wall 2 and an upper zone above the wall 2, an oxidation gas input 8 under the upper layer 3 and above the wall 2, an outlet 10 for the treated liquid is recycled by a pump 12 and an outer pipe 11 on the inlet 9.

BACKGROUND OF THE INVENTION 
The present invention concerns an oxidation and biological reduction 
reactor, a filtration process and washing procedures used in this reactor. 
Such an oxidation and reduction reactor especially applies to the 
elimination of the organic and ammonia nitrogen found in urban and 
industrial waste waters. The oxidation transforms the ammonia nitrogen 
into nitrite and then into nitrate. The reduction transforms the nitric 
nitrogen into nitrogen These reactions are obtained by using bacterial 
cultures and may be carried out according to two methods, one called the 
free culture method, the other called the fixed culture method. 
In the fixed culture of the prior art, the ability of most micro-organisms 
to produce exopolymers enabling their fixation on very different backings 
is used to form a biofilm. The fixed cultures as well as the free cultures 
may be used with aerobic or anaerobic treatments (fine granular medium 
biofilters, biofilters, biodisks, etc.). 
Fixed cultures are used to obtain higher biomass concentrations (and 
sometimes activities) in the reactors, allowing the size of the works to 
be reduced. 
A recommendation has been made to fix the microorganisms on granular 
backings whose effective bead size does not exceed 4 or 5 mm. These 
backings provide a specific developed surface (and thereby an exchange 
surface) that is much greater than that of other methods. By way of 
example, BIOLITE with an effective bead size of 2.7 mm develops an 
exchange surface of 700 m.sup.2 .m.sup.-3. 
Roughly, these granular medium bioreactors may be divided into two main 
categories: 
Those where the matter in suspension initially present in the raw wastes as 
well as the excess sludge produced is retained at the same time as the 
biological purification. The fixed granular filters are also called 
biofilters. 
Those in which the bioreactor only provides biological purification and the 
matter in suspension is separated by works found downstream. In the latter 
case, in order to optimize the micro-organism/substrate exchange surfaces, 
very fine granular materials in movement are used. These are the fluidized 
granular beds, as indicated in U.S. Pat. Nos. 3 846 289 and 4 009 099 
(Ecolotrol denitrification and nitrification). 
In the case of the second category, the fluidized bed reactors have the 
disadvantage of relating the speed of circulation of the fluid to the 
hydraulic characteristics (speed of fluidization, etc.) of the granular 
material chosen as a backing. Moreover, the fluidized beds do not enable 
the reliable and permanent maintenance of two separate zones, one of 
oxidation, the other of reduction in the same bed without the risk of 
mixing the materials and bacteria retained on these materials during 
variations in discharge. 
In the first category, the "fixed granular beds" described above are 
classically made with materials that are more dense than water. In this 
case, we can speak of a "flowing bed". We can speak of a "floating bed" 
when the material is not as dense as water. 
Patent FR 2 604 990 (OTV) describes a device consisting of a flowing bed 
comprising at least two layers of granular materials. Two zones, one 
aerobic and the other anaerobic are found within this bed. There are 
several disadvantages to this process: 
the granulometries of the materials of both zones should be chosen so as to 
avoid the mixture of the grains in the adjacent zones; 
the washing requires very fast water although the reclassification of the 
different layers is not foreseen in case there is a mixture of the zones. 
Devices using floating beds have been recommended: 
For example, patent FR 2 330 652 (Preussag) proposes the use of floating 
materials such as expanded polystyrene to create a biological 
denitrification reactor. However, this process can not be used to carry 
out the biological nitrification reaction since it only comprises one zone 
adapted to one reduction reaction (denitrification). This arrangement 
requires a large chamber at the upper part for the accumulation of 
washings in order to enable washing with a downward flow. 
Several patents describe the devices using two layers of different 
materials in the reactor: 
Patent FR 2 278 378 (Erpac) recommends the successive crossing of one 
floating bed layer and then two flowing bed layers in order to carry out 
the filtration. However, this does not enable a biological reactor to be 
envisaged since there is no injection of air. It has the disadvantage that 
it includes several means of support and retention or compaction of the 
materials. In addition, the washing conditions for the different beds are 
not favourable. 
Patent GB 2 021 428 (Ishigaki Kiko) comprises a floating bed layer and an 
upper flowing bed layer separated by an intermediate wall. As in the 
previous patent, it does not enable a biological reactor for an oxidation 
reaction and a reduction reaction to be considered since there is no air 
injection for the process part and there is no introduction of washing 
air. In fact, the lower layer is designed for the filtration and the upper 
layer for the physico-chemical adsorption is not designed for washing. 
Patent FR 2 632 947 (OTV) uses a bed consisting of layers serving as a 
biological reactor. It considers using these layers for the nitrification 
or denitrification. However, if both nitrification and denitrification 
reactions are to be combined within the same reactor, the characteristics 
of the materials from both layers may not be chosen independently. The 
characteristics of these two layers are related by the constraints 
resulting from the washing conditions. In fact, the washing is carried out 
with expansion since it is necessary to maintain the classification of the 
different layers 
Moreover, the oxidation gas circulates in the direction of the compression 
of the bed leading to a blockage of the circulation of the gas. This is 
the main problem that this patent wants to solve by choosing a density of 
material for the lower layer so that the layer is "agitated" (the patent 
indicates "fluidised"). The material, such as expanded floating slate or 
light polypropylene, which has such a density, is not available at a cost 
that is economically reasonable on an industrial scale. 
This compression of the bed is therefore not favourable for the part of the 
bed forming the three-phase aerobic reactor In addition, this patent 
foresees the intermittent injection of the air (the patent indicates "by 
pulsation") to limit this disadvantage. In fact, there is a risk of air 
embolism and the preferential passage of the water or gas when the 
progressive fouling of the bed increases the loss of water circulation 
load 
The disadvantage of the prior art process is that it does not allow 
effective and economic nitrification and denitrification reactions (or 
more generally oxidation and reduction) in the same reactor. 
SUMMARY OF THE INVENTION 
The first object of the invention is to provide an oxidation and reduction 
reactor that is simple and economical to make, not requiring any 
reclassification operation of the materials used after washing and 
enabling a maximum choice of materials as regards granulometry and 
density. 
This object is reached due to the fact that the oxidation and biological 
reduction reactor of liquid requiring treatment by upward circulation and 
recirculation includes, within a longitudinal vertical enclosure 
accessible by an inlet of liquid for treatment and an outlet of treated 
liquid respectively located at the lower and upper end of the enclosure, a 
lower layer for the fixation of the biomass made of material whose density 
is lower than that of the liquid and an upper layer for the fixation of 
the biomass made of material whose density is higher than that of the 
liquid, the lower layer is separated from the upper layer by a transverse 
wall only allowing the passage of the liquid between a first and second 
zones as defined, within the enclosure, the lower layer is located under 
the wall the upper layer above the wall, an admission of fluid or 
oxidation gas (for example air) is provided under the upper layer and 
above the wall, the outgoing treated liquid is recycled by a pump and an 
outer pipe on the inlet. 
According to another characteristic of the invention, micro-organisms 
provide the oxidation forming the biomass fixed on the upper layer and 
bacteria provide the reduction forming the biomass fixed on the lower 
layer. 
According to another characteristic, the microorganisms providing the 
oxidation are preferably nitrosomonas and the bacteria of nitrobacteria 
genus. 
Another object of the invention is to provide the retention of the matter 
in suspension (MiS) at the same time as the biological purification. 
This object is reached by the fact that the granulometry of the material 
whose density is lower than that of the liquid is chosen to be greater 
than that of the material whose density is greater than that of the liquid 
so that the flowing bed provides a filtration effect. 
According to another characteristic of the invention, the granular material 
of the flowing bed for example, consists of sand, anthracite, pumice 
stone, expanded clay. The effective size is preferably between 1 and 5 mm 
and the material forming the floating bed for example consists of expanded 
polystyrene, polypropylene, polyurethane foam and its effective size is 
preferably between 1 and 5 mm, the size of the latter being greater than 
that of the former. 
Another object is to allow part of the gas derived from the purification to 
be trapped. 
This object is reached since the wall is made of impervious material and 
pintles are planned at regular intervals in the wall. 
According to another characteristic, the pintles consist of an upper 
cylindrical cover, forming a fringe around the periphery, connected to a 
central tube passing through the wall and entering the compartment in the 
enclosure located under the wall by an opening communicating with the bed 
of floating material by a second cylindrical cover forming a fringe. 
According to another characteristic, a blow-off or air admission opening is 
planned under the wall between the lower level of the wall and the level 
of the opening communicating with the pintles. 
According to another characteristic, the reactor comprises a vent at the 
top of the enclosure, a water outlet valve at the top of the enclosure and 
a water flush valve at the bottom of the enclosure. 
According to another characteristic, the reactor comprises a washing air 
supply pipe and a washings supply pipe entering the enclosure 
approximately at the level of the transverse wall. 
Another object of the invention is to propose different washing procedures 
that may be used on the reactor. 
This object is reached by the fact that the reactor washing process 
includes the following steps: 
opening of the vent, opening of the sludge evacuation valve located below 
the enclosure to evacuate the sludge from the floating bed; 
introduction of the washings by a washings pipe; 
then closing of the enclosure valve to evacuate the sludge from the flowing 
bed towards the top. 
Another object of the invention is to propose another washing process. 
This object is reached since the washing process includes the following 
steps. 
washing of the flowing bed with circulation of the matter in suspension 
towards the lower zone leading to an accumulation of the matter in 
suspension in the floating bed; 
washing of the floating bed; 
According to another characteristic, the floating bed is washed by 
supplying the pump with untreated water, inverting the direction of 
circulation in the pipe by known means and by opening the lower evacuation 
valve to flush the sludge and provoke fluidization. 
According to a characteristic of the invention, the floating bed is washed 
by rapid flushing provoking the fluidization and unwatering of this bed. 
Finally, a final object of the invention is to provide a washing method 
including the following steps: 
circulation of the water in the enclosure by the pump from the bottom to 
the top in the outer pipe to wash the floating bed by accumulation of the 
matter in suspension in the flowing bed; 
stop the pump; 
supply untreated water by the input pipe of the untreated water for 
treatment; 
washing air supply by the washing air feed pipe; 
open the overflow air and water evacuation valve; 
close the washing air admission; 
air bleed the enclosure by opening the blow-off valve.

The reactor in FIG. 1 includes an enclosure 5 containing a floating bed 1 
consisting of material whose density is lower than that of water, retained 
by a wall 2. A flowing bed 3 is assembled on this wall 2 consisting of 
materials that are more dense than water. The density of the granular 
material of the flowing bed 3 is higher than that of water and, for 
example, may consist of sand, anthracite, pumice stone, expanded clay, 
etc. Its effective size may be between 0.5 and 10 mm, preferably between 1 
and 5 mm. The density of the granular material forming the floating bed 1 
is lower than that of water and may, for example, consist of expanded 
polystyrene, polypropylene, polyurethane foam, etc. Its effective size may 
be between 0.5 and 10 mm, preferably between 1 and 5 mm. The 
characteristics of granulometry and density of both materials are 
independent of each other provided that one is floating and the other 
flowing. In an advantageous manner, the floating material may be chosen 
with a granulometry that is higher than that of the flowing material so 
that the flowing bed carried out a filtration operation by retention of 
the matter in suspension at the same time as oxidation. The choice of 
granulometry and the density of each of the two materials may therefore be 
carried out in an optimum manner, in order to obtain the biomass backing 
effect that should be nitrogen-reducing in the floating bed and 
nitrogen-fixing in the flowing bed and also in order to obtain a 
filtration effect in the flowing bed. The nitrogen-fixing biomass is 
chosen so as to oxidize the ammonia nitrogen into nitrite and then into 
nitrate according to the following reaction in which the degrees of 
oxidation are indicated in Roman numerals. 
##STR1## 
This reaction takes place in two steps by autograph micro-organisms: 
oxidation of NH.sub.4.sup.+ (degree of oxidation minus 3) into 
NO.sub.2.sup.- (degree of oxidation plus 3): this is essentially the work 
of the nitrosomonas; 
oxidation of NO.sub.2.sup.- into NO.sub.3.sup.- (degree of oxidation plus 
5): the bacteria responsible for this second reaction mainly belong to the 
genus nitrobacteria. 
The overall simplified reaction for the nitrification may be written as: 
##STR2## 
The biomass of denitrification produces a reduction represented by the 
following reaction in which the degrees of oxidation are indicated in 
Roman numerals. 
##STR3## 
During this reaction, certain bacteria reduce the nitric nitrogen (degree 
of oxidation plus 5) to a lower state of oxidation. 
Preferably, heterotrophic bacteria are used whose activity is greater than 
that of autotroph bacteria so as to carry out the following simplified 
overall reaction: 
##STR4## 
The wall 2 is equipped with pintles 6 that, as represented in FIG. 2, 
include a central tube 60 opening on the upper part of the rudder pintle 
located above the wall 2 by a cover 62 with a fringe 61 around the 
periphery. This central tube has an opening 600 at the lower part located 
below the wall 2 at a distance A from the wall 2 providing the trapping of 
the nitrogen gas between the wall 2 and the level A. The periphery of tube 
60 is surrounded by a fringe 63 and a lower cover 64 which avoids the 
migration of the floating material towards the nitrification zone. A 
blow-off valve 50 connected to a fringe 51 located inside the reactor is 
provided in the wall 5 of the enclosure between the level of the wall 2 
and the level of the opening 600 to allow for the evacuation of the gas 
accumulated during the filtration process or washing process. During 
washing, the pintles 6 allow for the separate or simultaneous circulation 
and distribution of air or water through the wall 2. The reactor is 
equipped with an untreated water admission pipe 9 and a treated water 
outlet pipe 10. A pipe 11 equipped with a pump 12 and the means to reverse 
the direction of circulation in the pipes 11, among other things, enables 
the recirculation of the treated liquid from the top towards the bottom of 
the enclosure 5 in order to recycle it for denitrification. An untreated 
water inlet 120 on the pump 12 allows it to send the washings towards the 
top of the enclosure. The top of the device includes a pipe 15 equipped 
with a valve 150 enabling the evacuation of the washing air or the 
aeration of the enclosure. The reactor is equipped with a pipe 8 providing 
the air from the process associated inside the enclosure with a 
distributor enabling the distribution of the air and to distribute it to 
the bottom of the flowing bed layer 3. In addition, a washing inlet 7 
provided near the wall 2, above or below it, may be associated with a 
distributor and enable the distribution of the water to provide the 
washing of the floating bed layer 1. Finally, a washing air inlet 70 is 
provided below the wall 2. Two washing sludge outlets 13, 14 are 
respectively available at the top and bottom of the device and are 
operated by the respective valves 130, 140. 
The water to be treated by the reactor is introduced by the pipe 9 and 
circulates upwards in turn through both beds, first the floating bed 1 and 
then the flowing bed 3. 
As seen above, the nitrification reaction requires oxygen which will be 
distributed at the bottom of the flowing bed 3 (the top bed) by the 
distributor 8. This flowing bed forms a three-phase reactor providing the 
co-current circulation of two fluids (water and oxidation gas). The fluids 
circulate in the direction of the decompression of the bed (therefore 
there is not any compaction during the increase in the loss of load during 
the cycle), avoiding the difficulties of gas circulation (risk of air 
embolism and preferential passage of water or gas) described in the prior 
art. 
This nitrification reaction produces nitrates. A fraction of the treated 
flow containing nitrates is recycled by the pump 2 and the pipe towards 
the reactor entry. 
During biofiltration, the air is introduced by the pipe 8, the treated 
waters are evacuated by the pipe 10 and the mixture is recycled towards 
the bottom by the pump 12 and the pipe 11 as shown in FIG. 3. 
The biofiltration process is regularly interrupted to carry out the washing 
operations of the reactor beds. This washing may be carried out according 
to three variants. 
The first washing variant shown in FIGS. 4 and 5 is carried out by 
introducing the washings by the pipe 7 between the two layers. The washing 
sludge exits by the pipe 14 if the floating bed 1 is washed and by the 
pipe 13 when the flowing bed 3 is washed. In order to increase the 
effectiveness of washing, it is also possible to use air which is 
introduced separately or simultaneously with water. The air may be 
introduced between the floating bed and flowing bed layers, as shown in 
FIG. 5, by the pipe 70. 
A second washing variant by accumulation in the floating bed is shown in 
FIGS. 6 to 8 using the external circulation by the pump 12 in the pipe 11. 
The flowing bed 3 is first washed by sending the washing air in the pipe 
70 and by circulating the water from the top to the bottom in the pipe 11 
by the pump 12. The vent valve 15 is opened. The matter in suspension 
derived from the flowing bed 3 is then recycled towards the floating bed 
1, stopped by the latter and accumulates. Following this first step, the 
floating bed is loaded with the matter in suspension from both beds and it 
is washed according to one of the following options. 
As shown in FIG. 7, the first option consists of using the pipe 120 to 
supply the pump 12 with untreated water to send the water towards the top 
of the enclosure and open the lower evacuation valve 140 towards the pipe 
14 in order to provide the fluidization of the floating bed. This 
fluidization is maintained until all of the matter in suspension is 
eliminated. 
As shown in FIG. 8, a second option consists of opening the upper valve 150 
of the vent 15 and the lower valve 140, using the water located below the 
flowing bed 3, to carry out fluidization combined with the unwatering of 
the floating bed 1 according to the process described in French patent 2 
611 529. 
A third washing process with accumulation in the flowing bed, represented 
in FIGS. 9 and 10, consists of opening the valve 150 and then, as shown in 
FIG. 9, starting the pump 12 in the direction of circulation going from 
the bottom to the top in the pipe 11 in order to carry out, by the 
circulation of the water from the enclosure, the washing of the floating 
bed layer 1 by accumulating the matter in suspension in the flowing bed 3. 
The second stage in the washing procedure consists of opening the valve 130 
of the pipe 13, sending the air through the pipe 70 and washing the layer 
3 with the untreated water introduced by the pipe 9 while the pump 12 is 
stopped. The untreated water prefiltered by the floating bed 1 cleans the 
flowing bed 3 and is evacuated by the pipe 13. The arrival of the washing 
air is then stopped by closing the pipe 70 and the air is blown off by the 
blow-off valve 50. The procedure ends by a rinsing stage consisting of 
introducing untreated water by the pipe 9 in the layer 1 and then resuming 
the treatment after rinsing 
In addition to the advantage of enabling the use of several washing 
methods, due to the separation wall 2, the described reactor allows for 
the use of materials whose granulometry and density are easier to choose. 
In addition, since the air distribution pipe 8 is in contact with the 
wall, it will be subject to less constraints than in devices using prior 
art procedures in which these pipes were subject to the stress of fouling 
filtration layers that act directly. This reactor also enables the 
creation of a type of washing without the consumption of clean water 
stored outside. 
Finally, the air blow-off 50 under the floor avoids the conservation of an 
air cushion after washing the upper layer 3 which would result in the 
development of a nitrification process in the denitrification zone. 
Any modification accessible to the professional is also part of the spirit 
of the invention.