Non-plastic biological film support element for biological wastewater treatment plant

Abstract

The invention relates to a biological film support element for a biological wastewater treatment plant, this support element being made of a lignocellulosic plant compound having asperities and / or grooves, or of a part of such a compound, this compound or part of a compound having been previously washed, dried and treated in order to be waterproofed and to have sufficient density to be kept in suspension and in motion in the water.The invention further relates to a process for treating a lignocellulosic plant compound having asperities and / or grooves, or a part of such a compound, to obtain a support element as defined above, the process comprising the following steps: - a washing step, - a drying step, - a heat treatment step, and - a waterproofing step, with at least one waterproofing compound, the heat treatment step being able to be carried out before the waterproofing step or concurrently with it.

Description

Title of the invention: Non-plastic biological film support element for biological wastewater treatment plant Technical field of the invention

[0001] The invention relates to the field of biological treatment installations for wastewater, of municipal and industrial origin.

[0002] More specifically, the invention relates to biological film support elements for such installations, the biomass present on these support elements making it possible to reduce the pollution of the water passing through them. The invention also relates to a treatment method making it possible to obtain such support elements. Technical prior art

[0003] The biological film support elements (hereinafter "support elements") used in such installations are usually in the form of plastic elements ranging in size from a few millimeters to a few centimeters. These elements have high specific surfaces, a large part of which delimit cavities or reliefs in which the biomass can develop while being protected, in particular against friction between the elements. Such support elements are notably marketed under the name AnoxKaldnes® K5 media. These support elements advantageously have a density slightly less than 1, allowing them to be carried along by the movements of the water in the reactor. During the implementation of such water treatment installations, these support elements are thus kept in suspension and in movement within the reactor containing them.

[0004] Wastewater treatment installations incorporating such mobile support elements make it possible to increase the quantity of biomass per unit of volume without increasing the size of the reactors, and thus advantageously make it possible to treat, at a constant volume, larger quantities of wastewater and / or pollution than activated sludge installations.

[0005] The plastic materials used to manufacture the support elements in question allow them to be given numerous dimensions and shapes. They are also inexpensive and therefore allow for the production of these support elements at low cost.

[0006] The use of such plastic support elements also has the following advantages: - rapid growth of bacteria on support elements, even at low temperatures; - a high tolerance of the biofilm of the support elements to variations in load of pollution to be treated, and toxic substances, which helps protect the biofilm created - pollution control efficiencies higher than prior art activated sludge processes; - an adjustable filling rate of the support elements in the reactor, depending on the pollution load to be treated in the reactor; - a more stable decontamination process, given that the biofilm is reliably fixed on the support elements.

[0007] However, in an era of growing environmental concern, the use of such plastic support elements is increasingly criticized. Various incidents have occurred following which these support elements have ended up in the natural environment (cargo grounding, leaks from wastewater treatment plants) leading to the pollution of beaches and aquatic environments. These plastic support elements also have the disadvantage of degrading over time by releasing very small particles (microplastics) which are now recognized as potentially toxic to humans and animals, particularly marine animals.

[0008] Thus, there is a need to replace these support elements made of plastic material with support elements made of other materials that are more respectful of man and nature, it being understood that these support elements must: - be made of a material allowing the development of biomass; - present a structured surface for hanging it in a durable manner over time; - have a density adequate to be set in motion in a treatment reactor, such density having to be mainly constant over time; - be resistant over time, particularly with regard to the abrasion generated by the friction of other support elements, the movement of the water to be treated and possibly the air bubbles used to oxygenate the biomass and keep the support elements suspended and moving in a treatment reactor.

[0009] In this context, prior art is known of biological wastewater treatment processes using support elements made of non-plastic materials, essentially ceramic, the majority of these processes however using these support elements in a fixed bed.

[0010] Ceramic support elements are advantageously colonized thanks to their protected surfaces and allow efficient treatment of carbon and nitrogen. However, the manufacture of these ceramic support elements consumes a lot of energy and is very complicated to carry out in series. It is possible to produce them by additive manufacturing techniques, thanks to a 3D printer, but this type of process remains very expensive and relatively complicated to implement.

[0011] Furthermore, such support elements made of non-plastic materials do not always have physical characteristics that allow the corresponding support elements to be used for economically advantageous periods in wastewater treatment installations. Thus, they may prove to be insufficiently resistant to compression, fracture and aging.

[0012] Finally, they do not necessarily have a density compatible with optimal movement within a treatment reactor. In particular, the support elements made of non-plastic materials used until now, once loaded into a treatment reactor and impregnated with water, do not have an adequate density allowing them to be correctly kept in suspension and in movement.

[0013] The main objective of the invention is therefore to propose support elements for biomass not made of plastic material capable of hosting a biofilm and capable of being implemented sustainably in wastewater treatment installations. Thus, one objective of the invention is to propose an ecological alternative to the plastic support elements of the prior art conventionally used in this type of installation.

[0014] Another objective of the invention is to propose such biomass support elements which can be kept in suspension and in movement optimally in a treatment reactor.

[0015] Another objective of the invention is to provide such support elements which are easy to manufacture, and inexpensively.

[0016] Another objective of the invention is to propose such support elements whose carbon footprint during manufacture is significantly lower than that of the plastic elements used in the prior art. Summary of the invention

[0017] These objectives are achieved in whole or in part thanks to the invention which relates to a biological film support element for a biological wastewater treatment installation, characterized in that it is made up of a lignocellulosic plant compound having asperities and / or grooves, or of a part of such a compound, this compound or this part of compound having been previously washed, dried and treated in order to be waterproofed and to have a density suitable for being kept in suspension and in movement in a reactor.

[0018] Indeed, after numerous tests, the inventors were able to validate that these compounds or parts of lignocellulosic plant compounds having asperities and / or grooves, washed, dried and waterproofed, could accommodate, thanks to their surfaces protected from friction with other compounds of the same type, a biological film in a durable manner, and could be used in treatment installations biological wastewater treatment using biological film support elements, replacing the plastic support elements of the prior art. Such lignocellulosic plant compounds according to the invention have a protected surface area of ​​between 400 m2 / m3 and 1500 m2 / m3.

[0019] The use of non-plastic support elements according to the invention therefore makes it possible to reduce the environmental impact of the wastewater treatment installations using them.

[0020] According to the invention, these compounds and / or parts of compounds are washed, dried and waterproofed to make them suitable for constituting biomass support elements in wastewater treatment installations which are effective in reducing the pollution of these waters in a satisfactory and sustainable manner over time.

[0021] This treatment makes it possible to eliminate most of the hemicellulose initially present on the surface of these compounds and / or parts of compounds and to coat them with a waterproofing compound. Their density is thus modified to allow them to be suspended and moved in a biological treatment reactor for the water to be treated, by aeration or mechanical agitation, by optimizing the amount of energy required to do this. In practice, this treatment makes it possible to bring the density of these compounds or parts of compounds to a value slightly lower than that of water. The biomass support elements must not float on the surface of the water in the reactor and must not be too heavy so as not to require too much energy to be suspended and moved.

[0022] These non-plastic support elements of natural origin can be set in motion in a reactor in the presence of water to be treated alone, or in the presence of a mixture of water to be treated and sludge.

[0023] According to one embodiment, the compound or part of the compound is a kernel or part of a fruit kernel, preferably of the fruit of a plant chosen from the group consisting of walnut trees, almond trees, peach trees, olive trees and cherry trees.

[0024] For the purposes of the present invention, the term "walnut" means trees of the genus Juglans, and in particular the species Juglans regia, which corresponds to the common walnut. However, other species of the genus Juglans may be used, the fruits of which have characteristics similar to the fruits of the species Juglans regia, for example the species Juglans nigra.

[0025] According to the usual meaning, the term "kernel" here refers to the hard central element of the fruit. In botany, such a kernel includes the endocarp and the seed protected by it.

[0026] For the purposes of the present invention, the term kernel part is preferably understood to mean kernel valve. The term valve is used in botany to designate the two parts of the shell constituting the kernel of certain fruits. Thus, nuts consist of a shell formed of two valves and containing a seed called a kernel.

[0027] These natural elements being food waste, the invention allows their recycling.

[0028] These cores and / or part of cores have a large protected surface which allows the optimal development of a bacterial biofilm capable of breaking down the pollutants in the water to be treated. Their irregular surface, having asperities and / or grooves, allows the biofilm formed to develop while being protected.

[0029] Such cores and / or parts of cores also have a hardness which makes it possible to limit their attrition in the reactors.

[0030] Also, these nuclei and / or parts of nuclei are inert with respect to the environment and do not release toxic compounds.

[0031] The waterproofing of these cores and / or part of cores also makes it possible to prevent their consumption by the biomass.

[0032] Preferably, the kernels used are peach kernels, and the kernel parts used are peach half-kernels. These kernels and half-kernels have the advantage of having a particularly wrinkled surface and, consequently, a high specific surface area, suitable for accommodating a significant quantity of biomass.

[0033] According to one variant, the kernel part is a nutshell.

[0034] According to another variant, the kernel is an almond fruit kernel.

[0035] Almond fruit kernels have the advantage of being particularly hard and therefore particularly resistant to friction, which is an advantage in the context of the invention.

[0036] According to yet another variant, the core part is a piece of olive or cherry core.

[0037] In order for such an olive or cherry stone to be suitable for receiving and protecting a biofilm during the treatment process, it is preferable that it be broken into pieces.

[0038] Within the scope of the present invention, it is understood that any fruit kernel or part of a fruit kernel having characteristics similar to these previously presented fruit kernels can be used in the invention. For example, apricot kernels could also be used, which are preferably used in pieces, such as for pieces of olive or cherry kernels.

[0039] The invention also relates to a method for treating a lignocellulosic plant compound having asperities and / or grooves, or a part of such a compound, to obtain a support element as defined above, characterized in that it comprises the following steps: - a washing step, - a drying step, - a heat treatment step, and - a waterproofing step with at least one waterproofing compound, the heat treatment step can be implemented before the waterproofing step or concomitantly with it.

[0040] Such a treatment method according to the invention is simple to implement, and does not require particularly specific equipment. It also has the advantage of possible modulation at the level of the order of the heat treatment and waterproofing steps. In addition, the initial washing and drying steps make it possible to improve the quality of the heat treatment and waterproofing.

[0041] Preferably, the heat treatment step is carried out at a temperature between 100°C and 350°C, preferably between 150°C and 280°C, for a duration between 10 minutes and 24 hours, preferably between 30 minutes and 120 minutes.

[0042] Preferably, the at least one waterproofing compound comprises a natural drying oil.

[0043] Since such an oil is natural, it also has a positive impact on the environment.

[0044] The natural drying oil may in particular be chosen from tung oil and linseed oil.

[0045] According to one variant, the at least one waterproofing compound comprises natural drying oil and organic and / or inorganic additives.

[0046] Such additives may, for example, have the role of making the support element even more resistant and hydrophobic, by impregnating most of the fibers of the plant support element. These additives may also serve to increase the waterproofing duration of the support element. In this case, additives are used which have a lower biodegradability than that of the waterproofing compound.

[0047] Examples of such additives are ground glass powder, alginate, kaolin, pine resin, chitosan, or natural salt.

[0048] Advantageously, the waterproofing step comprises:

[0049] - a first sub-step of placing the support element under vacuum at a pressure between 0.3 bar and 1.5 bar, preferably between 0.6 bar and 1 bar, for a duration between 10 min and 120 min, preferably between 15 min and 60 min, and

[0050] - a second sub-step of bringing the support element into contact with the at least a waterproofing compound at a pressure of between 1.7 bar and 20 bar, preferably between 2 bar and 10 bar, for a duration of between 10 min and 20 hours, preferably between 30 min and 12 hours, and at a temperature of between 20°C and 200°C, preferably between 40°C and 120°C.

[0051] Finally, also advantageously, the waterproofing step is followed by a final dehydration step, at a temperature between 20°C and 200°C, preferably between 50°C and 100°C, for a duration between 0.5 days and 20 days, preferably between 1 day and 10 days. Brief description of the figures

[0052] An embodiment of the invention is described below with reference to the drawings in which,

[0053] [Fig-1]: [Fig.l] shows two views of a half peach pit, before and after complete treatment by the method according to the invention;

[0054] [Fig.2]: [Fig.2] schematically illustrates the representative experimental reactor presenting reactors conventionally used in biological wastewater treatment installations using support elements kept in suspension and in movement, such as those of [Fig.l];

[0055] [Fig.3]: [Fig.3] represents a diagram illustrating the daily load of CODs (in Kg O2 / m3.J) (soluble chemical oxygen demand representative of the carbon contents) to be treated and eliminated in the reactor represented by [Fig.2], as a function of time (in days);

[0056] [Fig.4]: [Fig.4] shows two views taken with a binocular magnifying glass of a support element showing the external and internal faces of the latter after having spent 22 days in the reactor described according to [Fig.2].

[0057] Description of an embodiment of the invention

[0058] According to one embodiment of the invention, the non-plastic support elements made of lignocellulosic plant compound having asperities and / or grooves used in a stirred reactor, and treated according to the treatment method of the invention, comprise half peach pits.

[0059] The use of peach pits is particularly interesting in view of the initial composition of these elements. Indeed, the peach pit comprises a significant lignin content, i.e. more than 30% of its total composition. The presence of lignin in the cell wall of the pit gives it rigidity, impermeability and resistance to microbial attacks and oxidative stress. Lignin constitutes a polymorphic network of heteropolymers of phenyl-propane units resulting from the oxidative polymerization of p-coumaryl, coniferyl and sinapyl alcohols. It is generally considered to be the "glue" which binds the different components of the lignocellulosic matrix of the plant cell wall, which matrix is ​​composed of lignin, hemicellulose and cellulose, and is insoluble in water.Due to its proximity and association with cellulose microfibrils, lignin is often identified as a major obstacle to the enzymatic hydrolysis of lignocellulosic biomass. Thus, the rigid structure of the peach kernel shell allows good bacterial attachment, for the development of a biofilm.

[0060] The treatment carried out on these peach pits according to the invention also allows, to reduce the mass, and therefore the density, of these shells, and to make them hydrophobic, for optimal fluidization in the moving bed reactor in which they will be loaded. This treatment also improves their resistance to various frictions and shocks (due for example to air bubbles, other nuclei, or even the walls of the reactor), as well as to water and biological attacks. Process for processing peach kernel halves

[0061] According to the embodiment described herein, peach kernel halves were treated according to the treatment method of the invention.

[0062] Peach pits from the food industry were therefore recovered and washed. The two valves of these pits were mechanically separated and the seed removed. These half-pits were then dried in the open air, or in a dryer at a temperature between 30°C and 100°C.

[0063] These washed and dried half-cores then underwent a heat treatment step, at a temperature between 150°C and 280°C, in order to eliminate the hemicellulose present in the shells.

[0064] These hemicellulose-free half-cores then underwent a waterproofing step, which consisted firstly of placing the half-cores in an enclosure, inside which a pressure of between 600 and 1000 mbar prevailed, for a period of between 15 min and 60 min, in the absence of any waterproofing compound. Then, a natural drying oil was added to the enclosure, corresponding to China oil or linseed oil, as well as an inorganic additive in powder form, corresponding to glass flour. This additive impregnates most of the fibers of the peach half-cores, from their core to their external surface, to make them more resistant and hydrophobic. The pressure in the enclosure was then increased between 2 bars and 10 bars, for a period of between 30 minutes and 12 hours, and at a temperature of between 40°C and 120°C.

[0065] The peach half-stones thus waterproofed were then dehydrated by drying in the open air, at a temperature between 50°C and 100°C, for a period of between 1 and 10 days. In all cases, the temperature used for this final drying is lower than the temperature range allowing the heat treatment of the half-stones, so as not to alter the impregnation of the waterproofing compound in the shells.

[0066] Support element obtained using the treatment method

[0067] [Fig.l] illustrates two views of a half peach pit.

[0068] In the left part of [Fig.l], the half peach kernel, which has already been washed and dried but has not yet been heat-treated or waterproofed, corresponds to a half peach kernel resulting from the normal consumption of such a fruit. It is colored brown, matte, and its surface is porous, slightly rough.

[0069] On the right-hand side of [Fig.l], we see that the half-kernel which has undergone the heat treatment and waterproofing steps according to the invention has a different appearance from the untreated half-kernel. It is in fact gray / black in color, slightly shiny, and its surface is less porous than the untreated half-kernel. The peach half-kernel thus treated is therefore more hydrophobic than the untreated half-kernel.

[0070] The two views of this figure also show very well the irregular surface of such cores, with hollows and grooves, capable of allowing the formation of a biofilm and protecting it.

[0071] Installation containing a layer of support elements

[0072] [Fig. 2] illustrates an example of a biological wastewater treatment plant 1 including an experimental reactor 10 of 8 liters, provided with an inlet pipe 11 for water to be treated in the lower part of the reactor, and an outlet pipe 12 for treated water in the upper part of the reactor. This reactor 10 accommodates support elements 14 obtained according to the method of the invention, these support elements 14 being made from peach half-stones as described above. Finally, the plant also comprises air injection ramps 15, provided in the lower part of the reactor 10, intended for suspending and moving the support elements and for aerating the biological reactor.

[0073] Results of the use of the support elements according to the invention in a moving bed reactor

[0074] The peach kernel halves treated according to the invention were loaded into the reactor described in [Fig. 2], and the reactor was then supplied with water to be treated. The support elements were kept in motion and in suspension by a continuous injection of air.

[0075] COD measurements in mgO2 / L were carried out on the wastewater to be treated and on the treated water in order to calculate in kg O2 / m3.D the daily COD load to be treated in the reactor and the daily COD load eliminated by the treatment.

[0076] The reactor volume was filled to 25% by support elements and the movement and suspension of these elements was carried out with continuous aeration. The CODs of the water entering the reactor and of the water leaving the reactor were measured for 101 days.

[0077] [Fig.3] illustrates the daily COD load entering the reactor (triangles), as well as the daily COD load removed from the reactor (circles), in kg O2 / m 3.J, as a function of time, in days.

[0078] In this experiment, it was thus possible to measure that the soluble COD load (indicator of carbon pollution) eliminated from the reactor on day 30 was 0.95 kg O2 / m3.J. At the end of the tests, on day 91, the maximum COD load eliminated was 2 kg O2 / m3.J.

[0079] These results demonstrate that the use of peach pit halves as biofilm support elements in a moving bed reactor effectively removes organic pollution from wastewater. This result suggests that the surface of the support elements made from peach pit halves used in this experiment was quickly colonized by biomass. A macroscopic observation of the treated peach pit halves was carried out on day 22. It was thus observed that the treated peach pit halves exhibited significant bacterial colonization on their external face (left part of [Fig.4]), as well as on their hollow internal face (right part of [Fig.4]). This colonization allowed the formation of a homogeneous heterotrophic biofilm on the majority of the half-pit. It is the natural structure of the peach pit that allowed this optimal bacterial attachment.The bacteria were able to grow mainly on the protected areas of the half-core, to protect themselves from the shear forces in the reactor.

Claims

Claims

1. Biological film support element for a biological wastewater treatment plant, characterized in that it is made of a lignocellulosic plant compound having asperities and / or grooves, or of a part of such a compound, said compound or said part of compound having been previously washed, dried and treated in order to be waterproofed and to have a density which allows it to be suspended and moved in the reactor.

2. Support element according to claim 1, characterized in that said compound or said part of compound is a kernel or part of a fruit kernel, preferably of fruit of a plant chosen from the group consisting of walnut trees, almond trees, peach trees, olive trees and cherry trees.

3. A support element according to claim 2, characterized in that said core is a peach core and said core portion is a half peach core.

4. Support element according to claim 2, characterized in that said core part is a valve of a walnut shell.

5. Support element according to claim 2, characterized in that said core is an almond fruit core.

6. Support element according to claim 2, characterized in that said core portion is a piece of olive or cherry core.

7. Process for treating a lignocellulosic plant compound having asperities and / or grooves, or a part of such a compound, to obtain a support element according to any one of claims 1 to 6, characterized in that it comprises the following steps: - a washing step, - a drying step, - a heat treatment step, and - a waterproofing step, with at least one waterproofing compound, said heat treatment step being able to be carried out before said waterproofing step or concomitantly therewith.

8. Treatment method according to claim 7, characterized in that said heat treatment step is carried out at a temperature between 100°C and 350°C, preferably between 150°C and 280°C, for a period of between 10 minutes and 24 hours, preferably between 30 minutes and 120 minutes.

9. Method according to claim 7 or 8, characterized in that said at least one waterproofing compound comprises a natural drying oil.

10. Method according to claim 9 characterized in that said natural drying oil is chosen from tung oil and linseed oil.

11. Method according to claim 9 or 10, characterized in that said at least one waterproofing compound comprises said natural drying oil and organic and / or inorganic additives.

12. Treatment method according to any one of claims 7 to 11, characterized in that said waterproofing step comprises: - a first sub-step of placing said support element under vacuum at a pressure of between 0.3 bar and 1.5 bar, preferably between 0.6 bar and 1 bar, for a duration of between 10 min and 120 min, preferably between 15 min and 60 min, and - a second sub-step of bringing said support element into contact with said at least one waterproofing compound at a pressure of between 1.7 bar and 20 bar, preferably between 2 bar and 10 bar, for a duration of between 10 min and 20 hours, preferably between 30 min and 12 hours, and at a temperature of between 20 °C and 200 °C, preferably between 40 °C and 120 °C.

13. Method according to any one of claims 7 to 12, characterized in that said waterproofing step is followed by a final dehydration step, at a temperature between 20°C and 200°C, preferably between 50°C and 100°C, for a duration between 0.5 days and 20 days, preferably between 1 day and 10 days.

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