Description

Technical field

[0001] The invention is directed towards a systenn which allows the removal of micropollutants from wastewater.

Background art

[0002] One of the current state of the art technologies for removing micropollutants is a conventional activated carbon column or a conventional filter, often called Rapid Gravity Filter (RFG) with activated carbon or with a layer of activated carbon included into the system. These filters or columns are normally equipped with a backwash (treated water with an air-scour). The columns can be either operated in up-flow or down- flow mode while filters, with the exception of pressure filters, are operated in down-flow mode. A disadvantage of this kind of water treatment is the costs associated with replacing or regenerating the activated carbon particles.

[0003] Ozone treatment or UV treatment, with or without addition of other oxidising agents such as peroxide derivatives are also known in the art of treatment of water and wastewater. These treatments are often followed by sand filtration. A disadvantage of such wastewater treatment is the costs associated with generating the ozone or the UV light. Furthermore, the design of such system should be safely conceived, leading also to different costs which can be relatively high. The chemicals included in the system, must also be safely stored.

[0004] Prior art patent document published WO 2012/160526 A2 relates to microorganism-comprising particles and to the use of the same for the removal of contaminants from water or soil, for reducing nitrate overload in water, for purifying food industry wastewater or for purifying pharmaceutical wastewater. The bioreactor system of said prior art document comprises particles that may be cultured in a separate area, namely in divided internal chambers separated by a perforated separator of said bioreactor system. The particles are freeze-dried bacteria and are thus fed by nutrients useful for bacterial growth and prosperity. Freeze- dried bacteria are used for conferring long life span to the system. Although possibly efficient, such a system needs to be settled with the freeze-dried bacteria necessary for treating a type of wastewater. For example, this disclosure describes a list of specific bacteria to use in case of treatment of petroleum wastewater, of municipal wastewater, of food industry wastewater, of pharmaceutical wastewater and/or of de- nitrification of wastewater. The drawback of this disclosure is that the bioreactor system needs to be adapted adequately as a function of the wastewater to be treated.

[0005] Prior art patent document published CN 102557274 (A) describes a method for treating wastewater by microbial directional produced enzyme. A microorganism is thus trained to produce an enzyme useful for the removal of contaminant and is then added to the wastewater treatment aeration tank in a controlled dosage. The disadvantage of this method is that the enzyme is trained separately to the treatment system.

Summary of invention

Technical Problem

[0006] The invention has as an objective to solve all the above mentioned drawbacks of the wastewater treatment system known in the art. In particular, the systems known in the art do not train the bacteria in the system as such which can generate difficulties regarding the storage and/or the transfer of those bacteria into the system as such. Furthermore, the systems in the art are not really practical because they demand preliminary studies of which type of bacteria should be used in order to digest all or most of the micropollutants comprised into the wastewater to be treated. Technical solution

[0007] The first object of the invention is directed to a device adapted for wastewater treatment, said wastewater comprising at least one sort of micropollutant, said device comprising a column and a backwashing system in fluid connection with said column through an inlet. Said column comprises said inlet and an outlet, said inlet being upstream to said outlet. Said column further comprises a zone comprising bacteriologically activated carbon being downstream to said inlet and being divided in subzone A, subzone B and subzone C; subzone A being upstream to subzone B and subzone B being upstream to subzone C. Said column also comprises a backwashing space, said backwashing space being downstream to said zone comprising bacteriologically activated carbon. Said device is remarkable in that the bacteriologically activated carbon of subzone A comprises starving micro-organisms, the bacteriologically activated carbon of subzone B comprises micro-organisms fed through a first feeding system, the bacteriologically activated carbon of subzone C comprises micro-organisms fed through a second feeding system.

[0008] According to a preferred embodiment, that said backwashing system is configured to mix said subzones A, B and C together.

[0009] According to a preferred embodiment, said starving micro-organisms of subzone A are able to degrade said at least one sort of micropollutant and/or said micro-organisms fed through said first feeding system are able to degrade said at least one sort of micropollutant.

[0010] According to a preferred embodiment, said first feeding system is adapted to feed said micro-organisms with ethanol, sugar derivatives, preferentially molasses, and/or nutrients, preferentially Lysogeny broth.

[001 1] According to a preferred embodiment, said second feeding system is adapted to feed said micro-organisms with structural analogs of components comprised into said wastewater.

[0012] According to a preferred embodiment, said micro-organisms are bacteria.

[0013] According to a preferred embodiment, the length of subzone B is shorter than the length of subzone A and that the length of subzone C is larger than the length of subzone B. [0014] According to a preferred embodiment, said column further comprises one safety zone being downstream to said backwashing space and upstream to said outlet and/or in that said column further comprises one packing system being downstream to said inlet and upstream to said zone comprising bacteriologically activated carbon.

[0015] The second object of the invention is directed to a method for wastewater treatment, said wastewater comprising at least one sort of micropollutant, said method comprising the step of passing said wastewater in a device, said method being characterized in that said device is in accordance with any the first object of the invention.

[0016] According to a preferred embodiment, said method further comprises the step of backwashing the column of said device, said step of backwashing being configured to mix said subzones A, B and C together.

[0017] According to a preferred embodiment, said method comprises the step of treating said wastewater in a membrane bioreactor and/or through an activated sludge process prior to said step of passing said wastewater in said device.

[0018] According to a preferred embodiment, said wastewater has, prior to said step of passing said wastewater in said device, a chemical oxygen demand comprised between 5 ppm and 50 ppm, preferentially comprised between 10 ppm and 20 ppm.

[0019] According to a preferred embodiment, said at least one sort of micropollutant is a xenobiotic, in particular diclofenac, carbamazepine, lidocaine, metoprolol, atenolol, sulfadimidine, derivatives thereof, and/or any combinations thereof.

[0020] According to a preferred embodiment, said method further comprises the step of feeding the micro-organisms with ethanol, sugar derivatives, preferentially molasses, and/or nutrients, preferentially Lysogeny broth, through the first feeding system of said device.

[0021] According to a preferred embodiment, said method further comprises the step of feeding the micro-organisms with structural analogs of components comprised into said wastewater. [0022] According to a preferred embodiment, the concentration of said structural analogs of components comprised into said wastewater is comprised between 0% and 1000% of the concentration of the components comprised into said wastewater, preferentially between 50% and 300%.

Advantages of the invention

[0023] The invention is particularly interesting in that the claimed device allows the continuous variation of the environment of the micro-organism which causes starvation, recovery and learning to the micro-organism. In the starvation mode (without external substrates), the micro-organisms are very efficient in degrading complex molecules, i.e. micropollutants comprised into the wastewater. In the recovery mode, the micro-organisms get enough food and/or nutrient for cell synthesis and in the learning mode, the micro-organisms adapt themselves to the micropollutants which are targeted. As all these three modes are achieved in a whole single system by the design of the device of the present invention, this provides efficacy and simplicity of wastewater treatment, leading furthermore to a cost reduction.

Brief description of the drawings

[0024] Figure 1 : Schematic representation of the wastewater treatment system/device according to the present invention.

Description of an embodiment

[0025] The wastewater comprises micropollutants that need to be removed in order to produce treated effluents. Those micropollutants are qualified in terms of COD (chemical oxygen demand) and may also contain various components, such as xenobiotics. Typical xenobiotics targeted by the system of the present invention are diclofenac, carbamazepine, lidocaine, metoprolol, atenolol, sulfadimidine, and/or derivatives thereof.

[0026] The wastewater with a COD of about 500 ppm, or of about 1000 ppm, is first treated in a conventional membrane bioreactor (MBR) and/or through a conventional activated sludge process (CAS). The resulting effluent ends up with a COD comprised between 5 ppm and 50 ppm, preferentially between 10 ppm and 20 ppm. Besides COD, the concentration of micropollutants is at the scale of the nanogram per litre.

[0027] The effluent is then treated in the system 2 of the present invention and that will be further detailed below.

[0028] The device of the present invention consists in a column 2 as depicted in figure 1.

[0029] The column 2 comprises an inlet 4 and an outlet 6 and is equipped with a backwashing system (not shown). The backwashing system is in fluid connection with the column 2 through the inlet 4. In the direction of the flow (the direction of the arrows on figure 1 ), three subzones are delimited. Subzone A, which is positioned in the upstream part of the column 2, followed by subzone B and subzone C. Those three subzones are therefore positioned in the upstream part of the column 2. The downstream part of the column 2 is used as a backwashing space 10 (when the backwash system is functioning) and a safety margin 12.

[0030] The safety zone 12, also called safety margin, is a zone in which all the components of the column 2 can stay safely within the column even when they are mixed up through the backwashing process. The safety margin is delimited by a dashed line on figure 1.

[0031] It is to be understood that the safety margin 12 is located downstream of the column 2 and may be more or less large, depending on the power of the backwashing system. It will therefore be apparent for the skilled in the art to determine the length of said safety zone in function of the backwashing system.

[0032] The column may be further equipped with a packing system 18, in accordance with the packing system known in the art.

[0033] The column is filled with bacteriologically activated carbon 8, which is then spread all over the three subzones, subsequently in the upstream part of the column 2.

[0034] When the backwash system is in functioning mode, in accordance with the normal means known by the skilled person in the art, the bacteriologically activated carbon 8 residing in the upstream part of the column is spread over the totality of the column 2, more particularly in the zone including the bacteriologically activated carbon 8 before backwashing and in the backwashing space 10. It is nevertheless that some of the particles would be thrown beyond the backwashing space 10, ending up therefore in the safety zone 12. During this backwashing process, all the particles of bacteriologically activated carbon 8 are mixed in a random fashion.

[0035] Therefore, it is apparent for the skilled person in the art that a particle of bacteriologically activated carbon 8 which was positioned in subzone A before the start of the backwashing process will have equal chances (relative to the size of the subzone) to end up in either subzone A, subzone B or subzone C after the end of the backwashing process. Similar conclusions have to be made for a particle located in subzone B before the start of the backwashing process, which will have equal chances to end up in one of the three zones after the end of said process, and for a particle located in subzone C before the start of the backwashing process, which will also have equal chance to end up randomly in one of the three subzones after the end of said process.

[0036] When the effluent with COD comprised between 10 ppm and 20 pmm is injected in the column 2 through the inlet 4, the effluent first reaches the subzone A. Then, a certain number of micro-organisms, in particular bacteria, start to degrade the micropollutants which are comprised in the MBR effluent. The micro-organisms are in fact adsorbed by the bacteriologically activated carbon 8.

[0037] Upon backwashing of the column, as the bacteriologically activated carbon 8 is spread all over the three subzones as explained above. Therefore, some of the bacteria also end up in the subzones B and C of the column.

[0038] In subzone B, the bacteria are fed, through the first feeding system 14 of the column 2, with food readily available for the bacteria, for example sugar derivatives, such as molasses, and/or ethanol, and/or nutrient, such as Lysogeny broth. This subzone is in fact the subzone where the bacteria on the bacteriologically activated carbon 8 will recover and grow. [0039] In subzone C, the bacteria will be trained by being fed, through the second feeding system 16 of the column, with components almost similar to the micropollutants to be degraded. Those components almost similar to the micropollutants to be degraded are called structural analogs. Those structural analogs are tailored to govern bacteria activity towards the degradation of micropollutants. This will trigger a certain exo-enzyme profile which leads to an enhanced micropollutant removal. Upon backwashing, as some bacteria on the bacteriologically activated carbon 8 will end up in subzone A, the entering MBR effluent will be in close contact with a biofilm which is trained to digest the micropollutants contained in said effluent. For example, if the micropollutant in question is diclofenac, benzoic acid may be the component which is given to the bacteria located in subzone C of the column. The amount of structural analogs which is given to the micro-organisms is either zero (in this case, the bacteria are sufficiently efficient to work without any training) or ten times the amount of components comprised into the wastewater. The amount of structural analogs is preferably comprised between 50% and 300% of the concentration of the components comprised into the wastewater.

[0040] In order to improve the efficacy of the device of the present invention, the length of subzone B is shorter than the length of subzone A and the length of subzone C is larger than the length of subzone B. Indeed subzone B is the subzone where the micro-organisms grow by being fed with food which is readily degradable. In this subzone, the micro-organisms are less exposed to the micropollutants of the wastewater. Feeding on readily degradable substrates is subjected to high growth kinetics. Therefore, subzone B is shorter than subzone A, i.e. subzone B has less residence time. Similarly, in order to train the micro-organisms to purify the water by degrading the micropollutant, subzone C must be longer than subzone B since slowly degradable compounds are applied.

[0041] Once the wastewater has passed all through the column 2, the purified wastewater exits through the outlet 6.

[0042] The wastewater treatment system of the present invention allows the bacteria (i) to degrade the micropollutants comprised into the wastewater, (ii) to train and/or adapt (in subzone C) and (iii) to recover from starvation and grow (in subzone B). The column 2 of the present invention allows the variation of the environment of the micro-organisms which causes starvation (in subzone A, the bacteria have only the effluent with a COD comprised between 5 ppm and 30 ppm, preferentially between 10 ppm and 20 ppm to be fed), recovery and grow (in subzone B, the bacteria get sugar derivatives, nutrients and/or ethanol) and learning and/or adapting (in subzone A, the bacteria get trained by being fed with tailored substrates triggering exo-enzymes capable to cleave micropollutants comprised in the wastewater).