In-situ biostimulation of the hydrolysis of organic matter for optimizing the energy recovery therefrom

Abstract

Some embodiments are directed to a process for the treatment of organic waste which couples in situ biostimulation to produce hydrolytic enzymes and hydrolysis of the refractory organic matter from waste using these enzymes with a view to energy recovery.

Claims

1. A process for the treatment of a first, at least partially organic and at least partially solid, substrate, comprising: A. introduction of an initial volume of said first substrate to be treated into at least one hydrolysis reactor; B. introduction of an initial volume of second substrate into at least one biostimulation reactor; C. biostimulation of the second substrate contained in said biostimulation reactor by indigenous microorganisms and absent inoculated exogenous strains, under aerobic conditions, at a temperature of between 20 C. and 40 C., a pH of between 4 and 7, a moisture level of between 50% and 80% and a residence time of between 1 and 5 days, to ensure at least partial hydrolysis of the organic portion of said substrate and the in situ production of hydrolytic enzymes; D. percolation of a liquid through said volume of second substrate contained in said biostimulation reactor, in order to form a first leachate enriched in hydrolytic enzymes; E. injection of the first leachate enriched in hydrolytic enzymes into at least one hydrolysis reactor containing said first substrate to be treated; and F. hydrolysis of the first substrate at least partially by the first enriched leachate; wherein the succession of the steps C and D define a biostimulation cycle.

2. The process as claimed in claim 1, in which the hydrolytic enzymes are produced by filamentous fungi.

3. The process as claimed in claim 2, in which the filamentous fungi belong to the group consisting of the fungi Trichoderma sp., Aspergillus sp., Pleurotus sp., Penicillium sp., and Fomitopsis sp.

4. The process as claimed in claim 1, wherein the succession of the steps C and D defining a biostimulation cycle is repeated until the initial volume of second substrate in said biostimulation reactor is exhausted.

5. The process as claimed in claim 1, further comprising an additional step G of introduction of a new volume of second substrate into said biostimulation reactor when the initial volume of second substrate is exhausted.

6. The process as claimed in claim 1, wherein the hydrolysis step F is a step of hydrolysis which occurs essentially in the solid phase.

7. The process as claimed in claim 6, in which the step F of hydrolysis occurs in a percolator and comprises: percolation of said first leachate in the hydrolysis reactor through said first substrate to be treated, in order to obtain a second leachate enriched in hydrolytic enzymes and in organic matter; and reinjection of said second leachate into said hydrolysis reactor until the substrate is exhausted.

8. The process as claimed in claim 6, further comprising an additional step H of introduction of a new volume of first substrate into said hydrolysis reactor when the initial volume of first substrate is exhausted.

9. The process as claimed in claim 5, wherein the exhausted substrates, which originate from the biostimulation reactor and/or from the hydrolysis reactor when the hydrolysis step F occurs essentially in the solid phase, are treated by aerobic treatment with a view to obtaining a stabilized compost.

10. The process as claimed in claim 1, wherein the hydrolysis step F is a step of hydrolysis occurring essentially in the liquid phase in a hydrolytic reactor.

11. The process as claimed in claim 6, wherein the products resulting from the hydrolysis step F are exploited by a downstream step of methanogenesis in a methanizer for the production of biogas, at the end of which treated water is obtained.

12. The process as claimed in claim 1, in which the hydrolysis step F is carried out in an anaerobic digestion reactor for the treatment of the first substrate and the production of biogas, at the end of which treated water is obtained.

13. The process as claimed in claim 11, wherein the liquid percolating, during step D, in said biostimulation reactor for extracting the hydrolytic enzymes at least results from the treated water originating from the methanizer or from an anaerobic digester.

14. The process as claimed in claim 11, wherein the treated water originating from the methanizer or from an anaerobic digester are aerated before being recycled to be injected into said biostimulation reactor.

15. The process as claimed in claim 1, wherein the first leachate enriched in hydrolytic enzymes results from a single biostimulation reactor, and supplies a plurality of hydrolysis reactors.

16. The process as claimed in claim 1, in which the hydrolytic enzymes are produced by filamentous fungi, wherein the second substrate is a sample of the first substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages and particular features of the present invention will emerge from the following description, given by way of nonlimiting example and made in reference to the appended figures:

(2) FIG. 1A represents a schematic diagram of a biostimulation reactor 3 during step C of biostimulation of a substrate 2 in order to extract hydrolytic enzymes 31 therefrom;

(3) FIG. 1B represents a schematic diagram of the biostimulation reactor 3 of FIG. 1A during step D of percolation of a liquid through the substrate of FIG. 1A;

(4) FIG. 1C represents a schematic diagram of the biostimulation reactor 3 of FIGS. 1A and 1B for the aerobic treatment of the exhausted substrate in order to obtain a stabilized compost;

(5) FIG. 2A represents a schematic diagram of a percolator 40 for the hydrolysis of a substrate to be treated according to a first embodiment of the process according to the invention;

(6) FIG. 2B represents a schematic diagram of the percolator 40 of FIG. 2A associated with a methanizer 7 for exploiting, by methanogenesis, the products resulting from the hydrolysis of the substrate to be treated originating from the percolator of FIG. 2A;

(7) FIG. 2C represents a schematic diagram of the percolator 40 of FIGS. 2A and 2B for the aerobic treatment of the exhausted substrate in order to obtain a stabilized compost;

(8) FIG. 3 represents a schematic diagram of a hydrolytic reactor 41 for carrying out the hydrolysis of a substrate to be treated according to a second embodiment of the process according to the invention;

(9) FIG. 4 represents a schematic diagram of an anaerobic digestion reactor 42 for carrying out the hydrolysis of a substrate to be treated according to a third embodiment of the process according to the invention;

(10) FIG. 5 represents a schematic diagram of the entirety of the procedure.

DETAILED DESCRIPTION

(11) Identical elements represented in FIGS. 1 to 5 are identified by identical numerical references.

(12) In FIGS. 1A to 1C a biostimulation reactor 3 is represented, in which the biostimulation cycle of a substrate 2 occurs (second substrate which is not the substrate to be treated 1, but which may be identical to or different from this substrate 1).

(13) FIG. 1A illustrates the step C of biostimulation in aerobic medium of a substrate 2 for producing hydrolytic enzymes 31, according to the following operation conditions: temperature: between 20 C. and 40 C., pH: between 4 and 7, moisture level: between 50% and 80%, and residence time (in the biostimulation reactor): between 1 and 5 days.

(14) Outside these operating ranges, the biostimulation of the substrate is possible but it does not have very good performance.

(15) FIG. 1B illustrates step D of percolation of a liquid 8 through the substrate 2 of FIG. 1A in order to extract the hydrolytic enzymes 31 produced during step C in the form of a first leachate 5. The liquid 8 used for this enzyme extraction may be freshwater or a treated water (effluent) obtained from recycling leachates by anaerobic digestion, as illustrated in FIG. 5. This treated water may moreover be advantageously aerated before being re-used.

(16) The substrate 2 may be used for 3 to 5 biostimulation cycles.

(17) Once exhausted, it is withdrawn from the biostimulation reactor 3 and may advantageously be treated by aerobic treatment in order to obtain a stabilized compost 9, as illustrated in FIG. 1C.

(18) In FIGS. 2A to 2C, a percolator 40 is represented in which the hydrolysis of a substrate 1 to be treated occurs according to a first embodiment of the process according to the invention.

(19) FIG. 2A illustrates the hydrolysis F as is, of the substrate 1 to be treated according to a first embodiment of the process according to the invention, which occurs in the solid phase, as follows: the first leachate 5 loaded with hydrolytic enzymes is injected into a percolator 40 containing the substrate to be treated, this first leachate 5 percolates through the substrate to be treated 1 to hydrolyze the organic matter of this substrate 1: at the outlet of the percolator 40 a second leachate 6 is then obtained, loaded with hydrolytic enzymes and with organic matter, which is recirculated into the percolator 40 until the hydrolyzable organic matter of the substrate 1 has in large part been hydrolyzed (substrate 1 exhausted).

(20) Once this hydrolysis step has finished, this second leachate loaded with hydrolytic enzymes and with hydrolyzed organic matter is conveyed into a methanizer 7 for the production of methane, as illustrated in FIG. 2B. The treated water 8 at the outlet of the methanizer 7 is partially recycled upstream of the process according to the invention by being reinjected into the biostimulation reactor 3 (cf. FIG. 5 representing the procedure in its entirety).

(21) Once exhausted, the substrate 1 is withdrawn from the percolator 40 and may advantageously be treated by aerobic treatment in order to obtain a stabilized compost 9, as illustrated in FIG. 2C.

(22) A hydrolytic reactor 41 is represented in FIG. 3, in which the liquid-phase hydrolysis F of a substrate 1 to be treated occurs according to a second embodiment of the process according to the invention: the first leachate 5 loaded with hydrolytic enzymes originating from the biostimulation reactor 3 is injected into a hydrolytic reactor 41 upstream of a methanizer 7 in order to improve its performance in the context of a two-step treatment by anaerobic processes, such as, for example, the Biomet process; at the same time, the waste 1 to be treated is injected into this hydrolytic reactor 41.

(23) The products obtained at the outlet of the reactor 41 are exploited downstream in the methanizer 7 by the production of biogas and the treated water 8 at the outlet of the methanizer 7 is partially recycled upstream of the process according to the invention by being reinjected into the biostimulation reactor 3, as illustrated in FIG. 5 which represents the procedure in its entirety.

(24) An anaerobic digestion reactor 42 is represented in FIG. 4, in which the hydrolysis F of a substrate 1 to be treated occurs according to a third embodiment of the process according to the invention: the first leachate 5 loaded with hydrolytic enzymes originating from the biostimulation reactor 3 is injected into an anaerobic digestion reactor 42 in order to improve the performance of the process of the invention (by producing biogas especially); the steps of hydrolysis and of methanogenesis are carried out here in the same reactor 42 and correspond to anaerobic digestion; in the same way as for the first and second embodiments of the process according to the invention, the treated water 8 at the outlet of the reactor 42 is partially recycled upstream of the process according to the invention by being reinjected into the biostimulation reactor 3, as illustrated in FIG. 5 which represents the procedure in its entirety.

(25) The following examples illustrate the invention without however limiting the scope thereof.

EXAMPLES

(26) Various types of waste are hydrolyzed in an anaerobic digestion reactor 42 such as that illustrated in FIG. 4.

(27) In the first example, this hydrolysis is carried out according to a conventional process, that is to say without addition of enzymes, whereas in the second example, commercial enzymes are added, produced by fermentation in liquid medium.

(28) In the third example, the waste is hydrolyzed in accordance with the process according to the invention, by injecting, into the anaerobic digestion reactor 42, hydrolytic enzymes 31 originating from a biostimulation reactor associated with the anaerobic digestion reactor 42. These enzymes are produced in situ in the biostimulation reactor 3, in which the cycle of biostimulation of a substrate of household or agricultural waste (identical to or different from the waste to be treated) occurs according to the following operating conditions: residence time: 5 days moisture: 60% pH: 5 temperature: 30 C.

(29) At the end of the biostimulation step C, a liquid (for example fresh water) is percolated (step D) through the substrate in order to form a leachate enriched in hydrolytic enzymes, which is injected into the anaerobic reactor 42.

(30) Products

(31) commercial enzymes, produced by fermentation in liquid medium, for example those sold by DSM under the trade name MethaPlus. household waste substrate, agricultural waste substrate, these two types of waste being rich in lignocellulose, refractory organic matter which is not degraded in anaerobic conditions.
Tests

(32) In the three examples described below, the hydrolysis performance of the waste to be treated is evaluated by measuring the gain in methane production (denoted by the acronym BMP, for biomethane potential).

(33) The BMP analysis is carried out according to the recommendations described by Angelidaki et al.sup.8. (2009).

(34) Test Results

(35) Table 1 below collates the BMP measurements obtained for the three examples tested. These measurements are presented in table 1 in the form of an index relative to the conventional process, which is assigned an index of 100.

(36) TABLE-US-00001 TABLE 1 BMP measurements Example 2 Example 3 Process Process Example 1 employing according Conventional commercial to the process enzymes invention Household 100 137 (gain 108 (gain waste of 37%/ of 8%/ conventional conventional process) process) Agricultural 100 120 (gain 111 (gain waste of 20%/ of 11%/ conventional conventional process) process)

(37) In order to carry out these measurements, the same volumes of enzymatic mixtures were added for the three examples. However, the compositions of these mixtures are not identical. Table 2 below presents the composition of the mixtures used in the processes of hydrolysis and of methanogenesis of examples 2 and 3. This composition is indicated in table 2 in enzymatic units/ml for 3 main enzymes: total cellulase or FPase, carboxymethylcellulase or CMCase, and -glucosidase.

(38) TABLE-US-00002 TABLE 2 Composition of the mixture Composition of the leachate of commercial enzymes originating from the used in example 2 biostimulation reactor 3, (in enzymatic used in example 3 (in units/ml) enzymatic units/ml) - - FPase CMCase glucosidase FPase CMCase glucosidase 4 23 133 2 9 10

(39) The results from table 1 certainly show that the BMP gain is greater, compared to the conventional process, if commercial enzymes are used (37/8=4.6 times greater for household waste, and 20/11=1.8 times greater for agricultural waste). However, in terms of enzymatic units, the differences are much greater between the mixture of commercial enzymes of example 2 and the leachate of example 3 according to the invention: they vary between 2 and 13.3 times more commercial enzymes.

(40) This means that, for a comparable yield, it will be necessary to add more commercial enzymes than enzymes produced by biostimulation. It should be noted that the latter are produced under operating conditions which require fewer operational costs. The enzymatic mixtures from biostimulation may indeed contain additional enzymes which enable more effective hydrolysis.

REFERENCE LIST

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