A method for treating solid residues in a biomass fermentation

Abstract

The application discloses a treatment method of solid residues in biomass fermentation. The treatment method comprises sequentially performing first-stage hydrolysis, second-stage hydrolysis and N-stage hydrolysis on the solid residues, wherein N is an integer greater than or equal to 3; the first-stage hydrolysis is to obtain first-stage hydrolysis solid residues and first-stage hydrolysis filtrate through solid-liquid separation after hydrolyzing the solid residues; the first-stage hydrolysis adopts a first-stage acid solution; the second-stage hydrolysis is to obtain second-stage hydrolysis solid residues and second-stage hydrolysis filtrate through hydrolyzing the first-stage hydrolysis solid residues; the second-stage hydrolysis adopts a second-stage acid solution; the N-stage hydrolysis is to obtain N-stage hydrolysis solid residues and N-stage hydrolysis filtrate through hydrolyzing N-1-stage hydrolysis solid residues; and the N-stage hydrolysis adopts an N-stage acid solution. The application has excellent separation effect, can obtain high-purity lignin, and has high hydrolysis efficiency of cellulose and hemicellulose; the filtrate after hydrolysis can be used for subsequent fermentation, does not involve acid recovery, improves the added value of components, and reduces acid loss.

Description

Technical Field

[0001] This invention relates to the comprehensive utilization of solid residues in biomass fermentation, specifically to a method for treating solid residues in biomass fermentation. Background Technology

[0002] Biomass refers to all living, growing organic matter produced through photosynthesis from the atmosphere, water, and land. Examples include straw (excluding grains and fruits), lignocellulose from trees, byproducts of agricultural and forestry processing, agricultural and forestry waste, and livestock manure and waste from animal husbandry. In recent years, the comprehensive utilization and resource recovery of biomass has attracted widespread attention. This has opened up new avenues for alleviating environmental problems caused by fossil fuels such as oil and coal. Compared to the non-degradability of fossil-based materials, biomass is not only widely available but also has a short cycle time and excellent biodegradability.

[0003] Taking agricultural straw as an example, its main components are cellulose (25%-40%), hemicellulose (20%-35%), lignin (10%-25%), ash (1%-10%), solubles (5%-15%), and others (1%-5%). Cellulose is a linear macromolecule formed by BD-units linked by 1-4-glycosidic bonds; hemicellulose is a general term for non-cellulose polymers in the cell wall, composed of two or more sugar groups, usually with a branched structure; lignin is an aromatic compound with a three-dimensional spatial structure formed by three phenylpropane units linked by ether bonds and carbon-carbon bonds. Cellulose and hemicellulose are generally converted into 5- or 6-carbon sugars through fermentation or hydrolysis, and then into chemical raw materials. Hydrolysis generally consumes large amounts of inorganic acids or alkalis, resulting in high costs and significant environmental harm. Fermentation is relatively simple to operate, environmentally mild, and has low overall production costs. Moreover, the lignin remaining in the fermentation residue has a relatively intact structure, providing a good guarantee for the application of lignin.

[0004] After biomass fermentation, most of the cellulose and hemicellulose are converted into sugars, but the remaining solid residue still contains some cellulose, hemicellulose, a large amount of lignin, and ash. Currently, the fermentation solid residue is only used as fuel, with very low added value. Traditional lignin purification methods involve cooking with alkali at high temperatures to destroy the macromolecular structure of lignin and dissolve it in the alkaline solution (or directly using black liquor from papermaking to precipitate lignin), then adding acid to adjust the pH to 1-3 to precipitate the lignin. This method greatly damages the lignin structure and consumes large amounts of alkali and acid, increasing costs and causing serious environmental pollution and resource waste. Existing dilute acid hydrolysis methods can hydrolyze some cellulose and hemicellulose into sugars, but the sugar conversion rate is low and acid loss is significant. Therefore, finding an efficient process to recover cellulose and hemicellulose from the solid residue, improve acid utilization, and reduce ineffective acid loss (usually using alkali to neutralize acid, which is costly and exacerbates environmental pollution) is crucial for optimizing fermentation processes and improving the utilization rate of effective components in straw.

[0005] Existing technologies have disclosed methods for separating cellulose, hemicellulose, and lignin, but these are mostly for biomass processing and not specifically for the solid residue after biomass fermentation. In fact, directly separating cellulose, hemicellulose, and lignin from biomass is relatively easier. This is mainly because biomass contains relatively high levels of cellulose and hemicellulose and relatively low levels of lignin before fermentation, making separation easier. However, for the solid residue after fermentation, the content of cellulose and hemicellulose decreases significantly, while the proportion of lignin increases dramatically. Furthermore, the remaining, less hydrolyzable cellulose and hemicellulose are tightly bound to lignin, significantly increasing the difficulty of hydrolysis and separation. Therefore, for the solid residue after biomass fermentation, how to process it, efficiently separate lignin, and improve the utilization rate of cellulose and hemicellulose remains an unsolved technical problem. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies, such as the inefficient utilization of solid residues after biomass fermentation and the high cost of existing separation methods for obtaining high-purity lignin. It provides a method for treating solid residues from biomass fermentation. The method of this invention not only effectively separates solid residues after biomass fermentation but also achieves excellent separation results, yielding high-purity lignin. The hydrolysis efficiency of cellulose and hemicellulose is also high. Furthermore, the filtrate after hydrolysis can be used for downstream fermentation without the need for acid recovery, significantly increasing the added value of the components and reducing acid loss.

[0007] The present invention mainly solves the above technical problems through the following technical solutions.

[0008] This invention provides a method for treating solid residues in biomass fermentation, comprising the following steps: sequentially performing a first-stage hydrolysis, a second-stage hydrolysis, ..., and an Nth-stage hydrolysis on the solid residues, where N is an integer ≥3;

[0009] The first-stage hydrolysis involves hydrolyzing the solid residue, followed by solid-liquid separation to obtain a first-stage hydrolyzed solid residue and a first-stage hydrolyzed filtrate; the first-stage hydrolysis is carried out using a first-stage acid solution.

[0010] The second-stage hydrolysis involves hydrolyzing the first-stage hydrolysis solid residue, followed by solid-liquid separation to obtain a second-stage hydrolysis solid residue and a second-stage hydrolysis filtrate; the second-stage hydrolysis is performed using a second-stage acid solution.

[0011] The Nth stage hydrolysis is performed by hydrolyzing the N-1 stage hydrolysis solid residue, followed by solid-liquid separation to obtain the Nth stage hydrolysis solid residue and the Nth stage hydrolysis filtrate; the Nth stage hydrolysis is carried out using an Nth stage acid solution.

[0012] The inventors of this invention discovered that the solid residue obtained through biomass fermentation has a high lignin content, and the remaining cellulose and hemicellulose, which are not easily hydrolyzed, are tightly bound to the lignin, making hydrolysis of cellulose and hemicellulose more difficult and significantly increasing the difficulty of separating them from lignin. However, this invention, by subjecting the solid residue to a specific concentration of acid solution at a certain solid-liquid ratio and hydrolysis temperature for three or more consecutive hydrolysis reactions, can obtain high-purity lignin, and the hydrolysis rate of cellulose and hemicellulose is also at a high level.

[0013] Furthermore, researchers discovered that using the hydrolyzed filtrate as an acid solution to hydrolyze the solid residue three or more times achieved a comparable separation effect to hydrolyzing it the same number of times with a freshly prepared acid solution. This clearly demonstrates that the hydrolyzed filtrate can continue to hydrolyze the fermented solid residue without requiring wastewater treatment, thus maximizing the utilization of the hydrolyzed filtrate. Preferably, the hydrolyzed filtrate is fed into the next stage of hydrolysis via countercurrent flow.

[0014] During the research and development process, the applicant discovered a pattern: within the same system, simply extending the hydrolysis time no longer yields a significant increase in the hydrolysis rate after a certain period. Even after solid-liquid separation of the system following the first-stage hydrolysis, and using the recovered hydrolysis filtrate to further hydrolyze the resulting hydrolyzed residue, the improvement is limited. The inventors discovered that using a countercurrent method with the acid hydrolysis filtrate for multi-stage hydrolysis significantly improves the purity of the lignin and the hydrolysis rates of cellulose and hemicellulose.

[0015] In this invention, the first-stage acid solution is preferably the second-stage hydrolysis filtrate.

[0016] In this invention, the second-stage acid solution is preferably a third-stage hydrolysis filtrate.

[0017] In this invention, the N-1 stage acid solution is preferably the N-stage hydrolysis filtrate. The N-2 stage acid solution is the N-1 stage hydrolysis filtrate, and so on, with each subsequent stage hydrolysis filtrate being countercurrently used as the acid solution for the preceding stage.

[0018] In this invention, the N-stage acid solution is preferably a freshly prepared acid solution, thereby enabling the countercurrent reuse of the hydrolysis filtrate. The freshly prepared acid solution refers to an acid solution that has not undergone a hydrolysis reaction; "freshly prepared" is not a time-related limitation.

[0019] In this invention, when N=4, the treatment method preferably further includes a fourth-stage hydrolysis using a fourth-stage acid solution. After the fourth-stage hydrolysis, solid-liquid separation is performed to obtain a fourth-stage hydrolysis solid residue and a fourth-stage hydrolysis filtrate. The third-stage acid solution is preferably the fourth-stage hydrolysis filtrate, and in this case, the fourth-stage acid solution is a freshly prepared acid solution.

[0020] In this invention, the N-stage hydrolysis solid residue is the lignin obtained through separation.

[0021] The first-stage hydrolysate filtrate is used in the fermentation end where monosaccharides are fermented into lactic acid. The first-stage hydrolysate filtrate contains cellulose and hemicellulose, as well as monosaccharides obtained from the decomposition of cellulose and hemicellulose in the hydrolysis reaction. It is then fed into the fermentation end for hydrolysis and fermentation until the final fermentation product is obtained.

[0022] By using the above-mentioned countercurrent hydrolysis filtrate method, the biomass fermentation solid residue is sequentially hydrolyzed through the first stage hydrolysis, the second stage hydrolysis, ... and the Nth stage hydrolysis to obtain high-purity lignin, and the hydrolysis rates of cellulose and hemicellulose are also at a very high level. At the same time, the hydrolysis filtrate from each stage of hydrolysis is returned to the previous stage of hydrolysis to continue hydrolysis, thereby maximizing the utilization of the hydrolysis filtrate.

[0023] In this invention, the concentration of the first-stage acid solution is preferably less than or equal to the concentration of the second-stage acid solution, and more preferably less than the concentration of the second-stage acid solution, which is the second-stage hydrolysis filtrate.

[0024] In this invention, the concentration of the first-order acid solution is preferably 1 to 30 wt%, more preferably 5 to 15 wt%, for example 8 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, or 20 wt%, where wt% refers to the ratio of the mass of the acid to the total mass of the acid solution.

[0025] In this invention, the acid in the first-order acid solution is preferably one or more of sulfuric acid, phosphoric acid, hydrochloric acid and acetic acid, and more preferably sulfuric acid.

[0026] In this invention, during the first-stage hydrolysis, the mass ratio of the solid residue to the first-stage acid solution can be 1:(1-20), further 1:(1-15), and even further 1:(1-10), for example 1:5, 1:10, 1:13, or 1:18.

[0027] In this invention, the hydrolysis temperature in the first stage of hydrolysis is preferably 80–200°C, more preferably 100–180°C, more preferably 120–160°C, for example 130°C, 140°C or 150°C.

[0028] In this invention, the hydrolysis reaction time in the first stage of hydrolysis can be 1 to 8 hours, further 1 to 6 hours, further 1 to 5 hours, for example 2 hours or 4 hours.

[0029] In this invention, the pressure of the hydrolysis reaction in the first stage of hydrolysis can be 0 to 2 MPa, preferably 0.2 to 1.2 MPa.

[0030] In this invention, the concentration of the second-stage acid solution is preferably less than or equal to the concentration of the third-stage acid solution, and more preferably less than the concentration of the third-stage acid solution, which is the third-stage hydrolysis filtrate.

[0031] In this invention, the concentration of the secondary acid solution is preferably 1-30 wt%, more preferably 5-15 wt%, for example 8 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, or 20 wt%, where wt% refers to the ratio of the mass of the acid to the total mass of the acid solution.

[0032] In this invention, the acid in the secondary acid solution is preferably one or more of sulfuric acid, phosphoric acid, hydrochloric acid and acetic acid, and more preferably sulfuric acid.

[0033] In this invention, during the second stage of hydrolysis, the mass ratio of the first stage hydrolysis solid residue to the second stage acid solution can be 1:(1-20), further 1:(1-15), and even further 1:(1-10), for example 1:5, 1:10, 1:13, or 1:18.

[0034] In this invention, the hydrolysis temperature in the second stage of hydrolysis is preferably 80-200°C, more preferably 100-180°C, more preferably 120-160°C, for example 130°C, 140°C or 150°C.

[0035] In this invention, the hydrolysis reaction time in the second stage of hydrolysis can be 1-8 hours, more specifically 1-6 hours, more specifically 1-5 hours, for example 2 hours or 4 hours.

[0036] In this invention, the pressure of the hydrolysis reaction in the second stage of hydrolysis can be 0 to 2 MPa, preferably 0.2 to 1.2 MPa.

[0037] In this invention, the concentration of the N-1 level acid solution is preferably less than or equal to the concentration of the N level acid solution, and more preferably less than the concentration of the N level acid solution.

[0038] In this invention, the concentration of the N-level acid solution is preferably 1-30 wt%, more preferably 5-15 wt%, for example 8 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, or 20 wt%, where wt% refers to the ratio of the mass of the acid to the total mass of the acid solution.

[0039] In this invention, the acid in the N-level acid solution is preferably one or more of sulfuric acid, phosphoric acid, hydrochloric acid and acetic acid, and more preferably sulfuric acid.

[0040] In this invention, in the Nth stage hydrolysis, the mass ratio of the N-1 stage hydrolysis solid residue to the Nth stage acid solution can be 1:(1-20), further 1:(1-15), even further 1:(1-10), for example 1:5, 1:10, 1:13 or 1:18.

[0041] In this invention, the hydrolysis temperature in the Nth stage hydrolysis is preferably 80-200°C, more preferably 100-180°C, more preferably 120-160°C, for example 130°C, 140°C or 150°C.

[0042] In this invention, the hydrolysis reaction time in the Nth stage hydrolysis can be 1-8 hours, further 1-6 hours, further 1-5 hours, for example 2 hours or 4 hours.

[0043] In this invention, the pressure of the hydrolysis reaction in the Nth stage hydrolysis can be 0 to 2 MPa, preferably 0.2 to 1.2 MPa.

[0044] In this invention, the first-stage hydrolysis, the second-stage hydrolysis, ... and the Nth-stage hydrolysis are carried out in a pressure-resistant metal reactor or a pressure-resistant glass reactor.

[0045] In this invention, the solvent in the first-level acid solution, the second-level acid solution, ... and the Nth-level acid solution is generally water.

[0046] In this invention, the solid-liquid separation can be conventional in the art, such as using filtration to separate hydrolyzed solid residue and hydrolyzed filtrate. The main component of the hydrolyzed solid residue is lignin, and the main components of the hydrolyzed filtrate include cellulose and its hydrolysis products, and hemicellulose and its hydrolysis products.

[0047] In this invention, the main components of the hydrolysis filtrate in each stage of hydrolysis are glucose, xylose, arabinose, pigment, protein, metal ions, acid and water, wherein the acid refers to the acid in the stage 1 acid solution, the stage 2 acid solution or the stage 3 acid solution.

[0048] In this invention, the main component of the hydrolysis solid residue in each stage of hydrolysis is lignin, but it also includes small amounts of cellulose, hemicellulose, acid, sugar and water.

[0049] In this invention, step (3) preferably also includes washing the N-stage hydrolysis solid residue.

[0050] The washing solvent is generally water. The washing methods include, but are not limited to, rinsing and / or soaking. To improve utilization, the washing liquid after washing is preferably combined with the first-stage hydrolysis filtrate. Since water is used as the washing solvent, the washing liquid can dissolve residual sugar compounds, thus allowing it to be used for further fermentation, improving bioavailability. At the same time, the washing liquid contains virtually no lignin or only a small amount of residue that does not affect further fermentation.

[0051] Preferably, the washing is performed three times.

[0052] Preferably, the washing involves washing the insoluble matter until the pH value is 6.5 to 7.5.

[0053] The washing process includes a drying operation to remove residual moisture. The drying method can be freeze drying, atmospheric pressure drying, vacuum drying, or spray drying.

[0054] In this invention, the N-stage hydrolysis filtrate and the washing liquid generated during washing can be mixed evenly to form a dilute acid aqueous solution containing sugar, which can then be recycled to the fermentation end for reuse.

[0055] In this invention, the biomass is derived from agricultural and forestry waste, and may include one or more of straw, rice husks, cork, hardwood, branches, and livestock manure, preferably straw. The straw includes, for example, one or more of corn stalks, wheat stalks, rice straw, rapeseed stalks, barley stalks, oat stalks, and sorghum stalks.

[0056] In this invention, the fermentation can be conventional in the art, especially the fermentation of lactic acid produced using strains that ferment lactic acid, generally including the following steps: pretreating and / or detoxifying the biomass, and then fermenting it using strains that ferment lactic acid. The strain that ferments lactic acid is preferably *Pediococcus lactis*.

[0057] The pretreatment is a routine operation, in which the biomass is washed and dried, then mechanically crushed to reduce its size, and then pretreated. The pretreatment may include dilute acid method, sulfur dioxide method, ammonia fiber expansion explosion method, or steam expansion explosion method, preferably the dilute acid method. More preferably, the pretreatment involves soaking the biomass in a dilute sulfuric acid solution and maintaining it at 180–200°C for 1–10 minutes.

[0058] The detoxification process generally refers to the simultaneous or prior inoculation of *Pediococcus lactis* into the pretreated biomass with detoxifying molds (such as *Cladosporium spp.*, *Paecilomyces wani*, etc.) to remove inhibitors affecting fermentation, such as organic acids like formic acid, acetic acid, furfural, and hydroxymethylfurfural produced during pretreatment. Pretreatment and detoxification facilitate subsequent fermentation.

[0059] In this invention, the fermentation conditions are preferably as follows: fermentation temperature 35-50℃, and / or pH 4.5-6.5, fermentation time 50-100 hours, and / or the mass fraction of biomass in the fermentation broth is 10-45%, and / or the cellulase content is 1-30 mg protein / g biomass (dry basis), and / or the inoculum amount of the bacterial strain during fermentation is 5%-15% (v / v).

[0060] In this invention, the fermentation can refer to the steps in CN112941117A, which involves simultaneous saccharification and fermentation of lignocellulose materials after solid-state biodegradation to remove inhibitors. More specifically, for example, the fermentation method for corn stalks after pretreatment and final biodegradation to remove inhibitors disclosed in Example 2.

[0061] In a specific embodiment of the present invention, the fermentation includes the following steps: Corn stalks in solid granular form with a solid content of 30% (w / w) after dry dilute acid pretreatment and detoxification by *Penicillium wani* are placed in a fermenter containing a certain amount of water. Cellulase at a protein content of 5 mg / g corn stalk (dry basis) is added, and pre-saccharification is carried out at 48°C and 200 rpm for 6.5 h. After pre-saccharification, *Pediococcus lactis* seed culture is inoculated into the fermenter at a rate of 5% (v / v), and nutrient solution is added simultaneously. During fermentation, calcium carbonate is used as a neutralizing agent to adjust and maintain the pH of the fermentation broth at 5.4. Fermentation is carried out at 42°C and 200 rpm for 96 h. Then, the fermentation broth and solid residue are separated to obtain the solid residue from the biomass fermentation. The nutrient solution may include 10 g / L peptone, 10 g / L yeast extract, 2 g / L diammonium hydrogen citrate, and 0.25 g / L manganese sulfate monohydrate. After fermentation, the fermentable monosaccharides in corn stalks can be converted into lactic acid. The lactic acid fermentation liquid is then filtered to separate it from the biomass solid residue.

[0062] In this invention, the term "solid residue" can be interpreted in the conventional sense in the art, generally referring to the solid residue separated after biomass fermentation.

[0063] In this invention, the solid residue generally includes lignin, cellulose, and hemicellulose.

[0064] The lignin content is preferably 30-80 wt%, more preferably 40-70 wt%, for example 50 wt%, 52.14 wt%, 55 wt%, or 60 wt%, where wt% is the percentage of the total mass of the solid residue.

[0065] The cellulose content is preferably below 30 wt%, more preferably 1-20 wt%, even more preferably 10-20 wt%, for example 15 wt%, 16.45 wt%, 17 wt%, or 18 wt%, where wt% is the percentage of the total mass of the solid residue.

[0066] The content of hemicellulose is preferably below 20 wt%, more preferably 1 to 10 wt%, even more preferably 1 to 5 wt%, for example 2 wt%, 2.82 wt%, 3 wt%, or 4 wt%, where wt% is the percentage of the total mass of the solid residue.

[0067] In this invention, the solid residue may also include other components, which are generally understood to be substances obtained from biomass fermentation other than lignin, cellulose and hemicellulose.

[0068] The content of the other components may include 10-30 wt%, for example, 20-30 wt%.

[0069] The other components may include one or more of lactic acid, inorganic salts, metal ions, pigments, proteins, monosaccharides, and oligosaccharides. The oligosaccharides mentioned herein are defined in the conventional understanding of the art, generally referring to polymers composed of 2 to 10 glycosidic bonds.

[0070] In one specific embodiment of the present invention, the solid residue is composed of 15-20 wt% cellulose, 1-5 wt% hemicellulose, 50-70 wt% lignin, and other components, wherein the other components are in the balance. These other components may include one or more of lactic acid, protein, and inorganic salts.

[0071] In one specific embodiment of the present invention, the solid residue is composed of 16.45 wt% cellulose, 2.82 wt% hemicellulose, 52.14 wt% lignin, and 28.59 wt% other components. The other components may include one or more of lactic acid, protein, and inorganic salts.

[0072] In this invention, the fineness of the solid residue is preferably 50-200 mesh, more preferably 50-150 mesh, for example 100-150 mesh. The fineness of the solid residue affects the effectiveness of the hydrolysis reaction. In this invention, a fineness within this range, combined with other hydrolysis conditions, can achieve better separation efficiency while maintaining lower preparation costs.

[0073] In this invention, the fermentation product after biomass fermentation can be conventional in the art, such as lactic acid or ethanol.

[0074] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0075] The reagents and raw materials used in this invention are all commercially available.

[0076] The positive and progressive effects of this invention are as follows:

[0077] (1) The processing method of the present invention achieves the hydrolysis of solid residues in biomass using only acid solution by performing more than three hydrolysis reactions on the solid residues in biomass fermentation, obtaining hydrolyzed solid residue and hydrolyzed filtrate. The hydrolyzed solid residue is high-purity lignin, while the hydrolyzed filtrate mainly contains monosaccharides (hydrolyzed products of cellulose and hemicellulose), acids (acids in the acid solution), and small amounts of cellulose and hemicellulose. These can be input into the process of fermenting monosaccharides into lactic acid to play an important role. Monosaccharides are directly used as fermentation raw materials to convert into products such as lactic acid, while acids play a catalytic role in biomass fermentation, promoting biomass decomposition and greatly reducing the amount of acid used in fermentation. This effectively avoids the cost disadvantages of traditional processes in the recovery of chemical reagents and eliminates the dependence on the combined action of multiple chemical reagents in component separation processes.

[0078] (2) The processing method described in this invention requires a low temperature, has a simple operation process, and a high sugar conversion rate, which can save production costs, reduce energy consumption, and increase the added value of biomass solid residue.

[0079] (3) The treatment method effectively improves the purity of lignin in the residue while hydrolyzing the cellulose and hemicellulose of the solid residue in biomass fermentation, providing a new approach for the extraction and purification of lignin. Moreover, the lignin has a low degree of dissociation, which greatly preserves the three-dimensional spatial structure of lignin and helps to improve the performance of lignin in the material application process. Attached Figure Description

[0080] Figure 1 This is a flowchart of the solid residue treatment process in Embodiment 1 of the present invention. Detailed Implementation

[0081] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0082] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials used are commercially available; the physical properties of each raw material or the performance parameters of the product are measured using conventional methods in the art.

[0083] (1) Test methods for solid residue composition in biomass fermentation

[0084] In this invention, the determination of cellulose and hemicellulose content employs high-performance liquid chromatography (HPLC), using Phenomenex Rezex™ RPM-Momosaccharide Pb+2 or Biorad Aminex HPX-87P columns and their equivalents. Cellulose and hemicellulose primarily decompose into glucose, xylose, and arabinose under acidic conditions. Using the same testing method and standard sugar calibration, the relative content of each sugar can be directly calculated via HPLC, thereby determining the cellulose and hemicellulose content.

[0085] The hydrolysis rates of cellulose and hemicellulose were calculated using measured content assays.

[0086] (2) The method for determining the lignin content in this invention is ultraviolet spectrophotometry and gravimetric method.

[0087] Weigh 300.0 mg of fermentation residue or hydrolyzed residue into a pressure-resistant test tube, then add 3.00 mL of 72% sulfuric acid solution and mix thoroughly. Place the pressure-resistant tube in a 30°C water bath shaker (150 r / min) and react for 60 min. After that, remove the pressure-resistant tube from the water bath shaker and add 84.00 mL of deionized water. Tighten the cap and invert the pressure-resistant tube several times to mix the sample thoroughly. Place the pressure-resistant tube and the pre-prepared sugar recovery standard solution in a high-temperature autoclave and react at 121°C for 1 h. After hydrolysis is complete and the mixture cools to room temperature, filter the solution through a constant-weight glass frit crucible. Collect the filtrate in an Erlenmeyer flask and rinse the pressure-resistant test tube with at least 100 mL of deionized water to remove any remaining acid-insoluble residue, ensuring that all residue is retained in the glass frit crucible. The collected filtrate was used to determine the content of cellulose and hemicellulose, as well as the content of acid-soluble lignin. The filter residue in the glass core crucible was used to determine the content of acid-insoluble lignin. The acid-soluble lignin and acid-insoluble lignin were added together to obtain the lignin content.

[0088] In the following examples, the solid residue was obtained by the following fermentation method: Pretreated corn stalks in solid granular form with a solid content of 30% (w / w) were placed in a fermenter, and 5 mg cellulase / g stalk (dry weight) was added. Pre-saccharification was carried out at 48°C and 200 rpm for 6.5 h. After pre-saccharification, *Pediococcus lactis* seed culture was inoculated into the fermenter at an inoculation rate of 5% (v / v), along with nutrient solution (10 g / L peptone, 10 g / L yeast extract, 2 g / L diammonium citrate, and 0.25 g / L manganese sulfate monohydrate). During fermentation, calcium carbonate was used as a neutralizing agent to maintain the pH of the fermentation broth at 5.4. Fermentation was carried out at 42°C and 200 rpm for 96 h. The fermentation broth and solid residue were then separated to obtain the solid residue from the biomass fermentation.

[0089] The composition of the solid residues treated in Examples 1 to 17 was determined to be as follows: cellulose 16.45 wt%, hemicellulose 2.82 wt%, lignin 52.14 wt%, and other components 28.59 wt%, including lactic acid, protein, and inorganic salts.

[0090] The solid residue used in biomass fermentation in Examples 1 to 17 below is as follows: the dried solid residue after biomass fermentation is crushed by a pulverizer to obtain powdered residue with a particle size of 100-150 mesh.

[0091] Before proceeding with the following embodiments, a countercurrent treatment system for the hydrolysate is first established: the system comprises a first-stage hydrolysis tank, a second-stage hydrolysis tank, and a third-stage hydrolysis tank connected in series.

[0092] Simultaneously, 20g of fermented solid residue was added to each of the three hydrolysis tanks, along with a freshly prepared acid solution to initiate the hydrolysis reaction. After each hydrolysis reaction was completed, 20g of fermented solid residue was added to the first-stage hydrolysis tank, and a freshly prepared acid solution of a specific concentration was added to the third-stage hydrolysis tank, until the following process was achieved: Figure 1 As shown:

[0093] In the first-stage hydrolysis tank, the second-stage hydrolysis filtrate produced in the second-stage hydrolysis tank is used to hydrolyze the solid residue after biomass fermentation, producing first-stage hydrolysis solid residue and first-stage hydrolysis filtrate. The first-stage hydrolysis solid residue enters the second-stage hydrolysis tank, while the first-stage hydrolysis filtrate is used in subsequent fermentation stages.

[0094] In the second-stage hydrolysis tank, the third-stage hydrolysis filtrate produced in the third-stage hydrolysis tank is used to hydrolyze the first-stage hydrolysis solids to produce second-stage hydrolysis solids and second-stage hydrolysis filtrate. As mentioned above, the second-stage hydrolysis filtrate enters the first-stage hydrolysis tank for reuse, while the second-stage hydrolysis solids enter the third-stage hydrolysis tank to continue the hydrolysis reaction.

[0095] In the third-stage hydrolysis tank, a freshly prepared acid solution is used to hydrolyze the second-stage hydrolysis solid residue, producing a third-stage hydrolysis solid residue and a third-stage hydrolysis filtrate. As mentioned earlier, the third-stage hydrolysis filtrate enters the second-stage hydrolysis tank for reuse, and the third-stage hydrolysis solid residue is washed and dried to obtain the high-purity lignin.

[0096] Each stage of hydrolysis tank is a pressure-resistant device; in the following embodiment, a pressure-resistant stainless steel container is used.

[0097] Example 1

[0098] (1) Acid hydrolysis: The countercurrent treatment system was established using the above method. When it was established, the acid solution was a 12wt% sulfuric acid aqueous solution. The solid-liquid ratio in each hydrolysis tank was 1:5 (w / w). The hydrolysis reaction temperature in each hydrolysis tank was 140℃. The hydrolysis reaction was carried out in each hydrolysis tank under stirring. The hydrolysis reaction time in each hydrolysis tank was 4h.

[0099] Subsequently, 20g of biomass fermentation solid residue was continuously added to the first-stage hydrolysis tank until the first-stage hydrolysis tank could be used to hydrolyze the biomass fermentation solid residue with the second-stage hydrolysis filtrate to obtain first-stage hydrolyzed solid residue and first-stage hydrolysis filtrate; the first-stage hydrolyzed solid residue was hydrolyzed with the third-stage hydrolysis filtrate in the second-stage hydrolysis tank; and the second-stage hydrolyzed solid residue was hydrolyzed with a freshly prepared 12wt% sulfuric acid aqueous solution in the third-stage hydrolysis tank. After the hydrolysis reaction in the first-stage hydrolysis tank was completed, the oil bath was turned off, 100mL of water was added to lower the system temperature, and the liquid was filtered to obtain third-stage hydrolyzed solid residue.

[0100] (2) Washing: The solid residue from the third-stage hydrolysis was washed with deionized water and then filtered. The filtrate was collected and mixed with the filtrate from the first-stage hydrolysis to obtain a mixed hydrolysate and crude lignin. The hydrolysis efficiencies of cellulose and hemicellulose in the mixed hydrolysate were characterized as 90.32% and 98.98%, respectively.

[0101] (3) Recovery: The mixed hydrolysate obtained in step (2) is recovered to the fermentation end for reuse, providing a direct sugar source for fermentation.

[0102] (4) Drying: The crude lignin from step (2) was placed in a freeze dryer to remove moisture and obtain crude lignin with a mass of 11.27 g and a purity of 88.73%.

[0103] Example 2

[0104] In this embodiment, the solid-liquid ratio in each stage of the hydrolysis tank is 1:10 (w / w), and the rest is the same as in Example 1, using the reverse flow of the hydrolysis filtrate to carry out the hydrolysis reaction.

[0105] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 90.51% and 87.73%, respectively. The mass of the freeze-dried crude lignin was 11.58 g, and the purity of the lignin was characterized as 89.81%.

[0106] Example 3

[0107] In this embodiment, the solid-liquid ratio in each hydrolysis tank is 1:13 (w / w), and the rest is the same as in Example 1, using the reverse flow of the hydrolysis filtrate for the hydrolysis reaction.

[0108] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 93.15% and 99.32%, respectively. The mass of the freeze-dried crude lignin was 10.73 g, and the purity of the lignin was characterized as 91.23%.

[0109] Example 4

[0110] In this embodiment, the solid-liquid ratio in each hydrolysis tank is 1:18 (w / w), and the rest is the same as in Example 1, using the reverse flow of the hydrolysis filtrate for the hydrolysis reaction.

[0111] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 99.23% and 99.93%, respectively. The mass of the freeze-dried crude lignin was 11.32 g, and the purity of the lignin was characterized as 88.05%.

[0112] Example 5

[0113] In this embodiment, the oil bath temperature in each stage of the hydrolysis tank is 150°C, and the rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate for the hydrolysis reaction.

[0114] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 97.15% and 72.32%, respectively. The mass of the freeze-dried crude lignin was 11.22 g, and the purity of the lignin was characterized as 88.52%.

[0115] Example 6

[0116] In this embodiment, the oil bath temperature in each stage of the hydrolysis tank is 160°C, and the rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate for the hydrolysis reaction.

[0117] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 45.37% and 87.13%, respectively. The mass of the freeze-dried crude lignin was 13.17 g, and the purity of the lignin was characterized as 73.93%.

[0118] Example 7

[0119] In this embodiment, the oil bath temperature in each hydrolysis tank is 130°C and the hydrolysis reaction time in each hydrolysis tank is 2 hours. The rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate for the hydrolysis reaction.

[0120] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 67.54% and 89.89%, respectively. The mass of the freeze-dried crude lignin was 12.97 g, and the purity of the lignin was characterized as 74.35%.

[0121] Example 8

[0122] In this embodiment, the oil bath temperature in each hydrolysis tank is 120°C and the hydrolysis reaction time in each hydrolysis tank is 6 hours. The rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate for the hydrolysis reaction.

[0123] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 87.32% and 87.17%, respectively. The mass of the freeze-dried crude lignin was 11.87 g, and the purity of the lignin was characterized as 79.87%.

[0124] Example 9

[0125] In this embodiment, the oil bath temperature in each hydrolysis tank is 120°C and the hydrolysis reaction time in each hydrolysis tank is 8 hours. The rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate for the hydrolysis reaction.

[0126] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 76.39% and 89.17%, respectively. The mass of the freeze-dried crude lignin was 12.14 g, and the purity of the lignin was characterized as 78.15%.

[0127] Example 10

[0128] In this embodiment, the concentration of the prepared sulfuric acid aqueous solution is 4 wt%, the temperature of the oil bath in each hydrolysis tank is 150°C, and the rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate to carry out the hydrolysis reaction.

[0129] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 83.12% and 85.72%, respectively. The mass of the freeze-dried crude lignin was 12.15 g, and the purity of the lignin was characterized as 75.35%.

[0130] Example 11

[0131] In this embodiment, the concentration of the prepared sulfuric acid aqueous solution is 8 wt%, the temperature of the oil bath in each hydrolysis tank is 180°C, and the rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate to carry out the hydrolysis reaction.

[0132] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 87.97% and 63.15%, respectively. The mass of the freeze-dried crude lignin was 11.94 g, and the purity of the lignin was characterized as 80.23%.

[0133] Example 12

[0134] In this embodiment, the concentration of the prepared sulfuric acid aqueous solution is 10 wt%, and the rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate for the hydrolysis reaction.

[0135] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 89.86% and 67.13%, respectively. The mass of the freeze-dried crude lignin was 11.53 g, and the purity of the lignin was characterized as 88.88%.

[0136] Example 13

[0137] In this embodiment, the concentration of the prepared sulfuric acid aqueous solution is 20 wt%, the temperature of the oil bath in each hydrolysis tank is 130°C, and the rest is the same as in Example 2, using the reverse flow of the hydrolysis filtrate to carry out the hydrolysis reaction.

[0138] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 96.71% and 66.43%, respectively. The mass of the freeze-dried crude lignin was 10.97 g, and the purity of the lignin was characterized as 89.93%.

[0139] Example 14

[0140] In this embodiment, the concentration of the acid solution prepared is the same as in Example 2, and acid is added to the first-stage hydrolysis tank and the second-stage hydrolysis tank so that the concentration of the sulfuric acid aqueous solution in the hydrolysis filtrate is consistent with the concentration of the sulfuric acid aqueous solution prepared.

[0141] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 93.52% and 89.32%, respectively. The mass of the freeze-dried crude lignin was 10.88 g, and the purity of the lignin was characterized as 92.85%.

[0142] Example 15

[0143] This embodiment only includes a first-stage hydrolysis tank and a second-stage hydrolysis tank. The first-stage hydrolysis tank uses the second-stage hydrolysis filtrate generated in the second-stage hydrolysis tank for hydrolysis, and the second-stage hydrolysis tank uses a freshly prepared acid solution for hydrolysis. The other parameters and steps are the same as in embodiment 2.

[0144] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 78.25% and 68.06%, respectively. The mass of the freeze-dried crude lignin was 12.22 g, and the purity of the lignin was characterized as 83.91%.

[0145] Example 16

[0146] The acid solution used in this embodiment is hydrochloric acid. The solid-liquid ratio in each hydrolysis tank is 1:10 (w / w). The rest is the same as in Example 1, where the hydrolysis filtrate is flowed in the opposite direction to carry out the hydrolysis reaction.

[0147] The hydrolysis efficiencies of cellulose and hemicellulose in the washed mixed hydrolysis filtrate were 89.73% and 87.19%, respectively. The mass of the freeze-dried crude lignin was 10.32 g, and the purity of the lignin was characterized as 87.85%.

[0148] Example 17

[0149] A freshly prepared acid solution was used for a single hydrolysis to obtain hydrolyzed solid residue and hydrolyzed filtrate. The purity of the lignin in the first-stage hydrolyzed solid residue was tested by washing it. At the same time, the washing liquid was mixed with the hydrolyzed filtrate to test the hydrolysis rate of cellulose and hemicellulose. The test results are shown in Table 1 below. The parameters of the hydrolysis reaction are the same as in Example 2.

[0150] In Table 1, the solid-liquid ratio, acid type, hydrolysis temperature, and hydrolysis time in Examples 1 to 17 refer to the parameters in each stage of the hydrolysis reaction in each example, and the acid concentration refers to the concentration of the acid solution prepared in each example.

[0151] Table 1

[0152]

[0153] Based on the experimental results obtained above, it can be seen that by using the specific acid solution of the present invention to perform a hydrolysis reaction at a specific temperature and solid-liquid ratio for a certain period of time to treat the solid residue in biomass fermentation, and by performing three consecutive hydrolysis reactions on the same batch of solid residue, lignin with a purity of more than 70% was obtained, while the hydrolysis rates of cellulose and hemicellulose were also at a high level.

[0154] Furthermore, this invention cleverly reverses the flow of the hydrolysis filtrate while the solid residue to be hydrolyzed flows forward. The hydrolysis filtrate from the subsequent stage is used to hydrolyze the solid residue from the previous stage, which not only fully utilizes the acid solution but also yields lignin with higher purity and higher hydrolysis rates of cellulose and hemicellulose. The final hydrolysis filtrate is reused for subsequent fermentation, eliminating the need for acid recovery. In this embodiment, the high-purity lignin obtained has increased sulfonable groups when used as a water-reducing agent, resulting in better water-reducing effects. It also achieves higher hydrolysis rates of cellulose and hemicellulose, leading to higher content of pentose and hexose sugars available for subsequent fermentation and a significantly increased yield of lactic acid products.

[0155] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for treating solid residues from biomass fermentation, characterized in that, It includes the following steps: The solid residue is subjected to stage 1 hydrolysis, stage 2 hydrolysis, ... and stage N hydrolysis in sequence, where N is an integer ≥ 3; The first-stage hydrolysis involves hydrolyzing the solid residue, followed by solid-liquid separation to obtain a first-stage hydrolyzed solid residue and a first-stage hydrolyzed filtrate; the first-stage hydrolysis is carried out using a first-stage acid solution. The second-stage hydrolysis involves hydrolyzing the first-stage hydrolysis solid residue, followed by solid-liquid separation to obtain a second-stage hydrolysis solid residue and a second-stage hydrolysis filtrate; the second-stage hydrolysis is performed using a second-stage acid solution. The Nth stage hydrolysis involves hydrolyzing the N-1th stage hydrolysis solid residue, followed by solid-liquid separation to obtain the Nth stage hydrolysis solid residue and the Nth stage hydrolysis filtrate; the Nth stage hydrolysis is carried out using an Nth stage acid solution. In the first stage of hydrolysis, the second stage of hydrolysis, and the Nth stage of hydrolysis, the hydrolysis reaction temperature is 80–200°C, and the hydrolysis reaction time is 1–8 hours. The types of acids in the first-stage acid solution, the second-stage acid solution, and the Nth-stage acid solution are each independently selected from one or more of sulfuric acid and hydrochloric acid; the concentrations of the first-stage acid solution, the second-stage acid solution, and the Nth-stage acid solution are each independently 1–30 wt%. The solid residue is obtained after biomass fermentation, and the biomass includes one or more of straw, rice husks, cork, hardwood, and branches; the solid residue includes lignin, cellulose, and hemicellulose, the lignin content is 30-80 wt%, the cellulose content is less than 30 wt%, and the hemicellulose content is less than 20 wt%, where wt% is the percentage of the total mass of the solid residue.

2. The method for treating solid residues in biomass fermentation as described in claim 1, characterized in that, The first-stage acid solution is the second-stage hydrolysis filtrate; And / or, the second-stage acid solution is a third-stage hydrolysis filtrate; And / or, the N-1 stage acid solution is the N-stage hydrolysis filtrate; And / or, the N-level acid solution is a freshly prepared acid solution; And / or, the concentration of the first-order acid solution is ≤ the concentration of the second-order acid solution; And / or, the concentration of the second-level acid solution is ≤ the concentration of the third-level acid solution; And / or, the concentration of the N-1 grade acid solution is ≤ the concentration of the N grade acid solution.

3. The method for treating solid residues in biomass fermentation as described in claim 2, characterized in that, The concentration of the first-stage acid solution is less than the concentration of the second-stage acid solution; And / or, the concentration of the second-level acid solution is less than the concentration of the third-level acid solution; And / or, the concentration of the N-1 grade acid solution is less than the concentration of the N grade acid solution.

4. The method for treating solid residues in biomass fermentation as described in claim 2, characterized in that, The concentration of the first-order acid solution is 5–15 wt%; And / or, in the first stage of hydrolysis, the mass ratio of the solid residue to the first stage acid solution is 1:(1-20); And / or, in the first stage of hydrolysis, the temperature of the hydrolysis reaction is 100–180°C; And / or, in the first stage of hydrolysis, the hydrolysis reaction time is 1 to 6 hours.

5. The method for treating solid residues in biomass fermentation as described in claim 4, characterized in that, In the first stage of hydrolysis, the mass ratio of the solid residue to the first stage acid solution is 1:(1-15); And / or, in the first stage of hydrolysis, the hydrolysis reaction temperature is 120–160°C.

6. The method for treating solid residues in biomass fermentation as described in claim 4, characterized in that, In the first stage of hydrolysis, the mass ratio of the solid residue to the first stage acid solution is 1:(1~10); And / or, in the first stage of hydrolysis, the hydrolysis reaction time is 1 to 5 hours.

7. The method for treating solid residues in biomass fermentation as described in claim 2, characterized in that, The concentration of the grade 2 acid solution is 5–15 wt%; And / or, in the second stage of hydrolysis, the mass ratio of the first stage hydrolysis solid residue to the second stage acid solution is 1:(1-20); And / or, in the second stage of hydrolysis, the hydrolysis reaction temperature is 100–180°C; And / or, in the second stage of hydrolysis, the hydrolysis reaction time is 1 to 6 hours.

8. The method for treating solid residues in biomass fermentation as described in claim 7, characterized in that, In the second stage of hydrolysis, the mass ratio of the first stage hydrolysis solid residue to the second stage acid solution is 1:(1-15); And / or, in the second stage of hydrolysis, the hydrolysis reaction temperature is 120–160°C.

9. The method for treating solid residues in biomass fermentation as described in claim 7, characterized in that, In the second stage of hydrolysis, the mass ratio of the first stage hydrolysis solid residue to the second stage acid solution is 1:(1-10); And / or, in the second stage of hydrolysis, the hydrolysis reaction time is 1 to 5 hours.

10. The method for treating solid residues in biomass fermentation as described in claim 2, characterized in that, The concentration of the N-grade acid solution is 5–15 wt%; And / or, in the Nth stage hydrolysis, the mass ratio of the N-1 stage hydrolysis solid residue to the Nth stage acid solution is 1:(1~20); And / or, in the Nth stage of hydrolysis, the temperature of the hydrolysis reaction is 100–180°C; And / or, in the Nth stage of hydrolysis, the hydrolysis reaction time is 1 to 6 hours.

11. The method for treating solid residues in biomass fermentation as described in claim 10, characterized in that, In the Nth stage of hydrolysis, the mass ratio of the N-1 stage hydrolysis solid residue to the Nth stage acid solution is 1:(1-15); And / or, in the Nth stage of hydrolysis, the hydrolysis reaction temperature is 120–160°C.

12. The method for treating solid residues in biomass fermentation as described in claim 10, characterized in that, In the Nth stage of hydrolysis, the mass ratio of the N-1 stage hydrolysis solid residue to the Nth stage acid solution is 1:(1~10); And / or, in the Nth stage of hydrolysis, the hydrolysis reaction time is 1 to 5 hours.

13. The method for treating solid residues from biomass fermentation as described in any one of claims 1 to 12, characterized in that, Step (3) also includes washing the N-stage hydrolysis solid residue.

14. The method for treating solid residues in biomass fermentation as described in claim 13, characterized in that, The solvent used for washing is water; And / or, the washing is to wash the N-stage hydrolyzed solid residue until the pH value is 6.5 to 7.5; And / or, the washing process may be followed by drying.

15. The method for treating solid residues from biomass fermentation as described in any one of claims 1 to 12, characterized in that, The straw includes one or more of the following: corn straw, wheat straw, rice straw, rapeseed stalks, barley straw, oat straw, and sorghum straw.

16. The method for treating solid residues from biomass fermentation as described in any one of claims 1 to 12, characterized in that, The fineness of the solid residue is 50-200 mesh; And / or, the fermentation includes the following steps: pretreating and / or detoxifying the biomass, and then fermenting it using a strain that ferments lactic acid.

17. The method for treating solid residues in biomass fermentation as described in claim 16, characterized in that, The fineness of the solid residue is 50-150 mesh; And / or, the strain that ferments lactic acid is Pediococcus lactis; And / or, the fermentation conditions are: fermentation temperature 35-50℃, and / or pH 4.5-6.5, fermentation time 50-100 hours, and / or, the mass fraction of biomass in the fermentation broth is 10-45%, and / or, the cellulase content is 1-30 mg protein / g biomass, and / or, the inoculum size of the bacterial strain during fermentation is 5%-15%.

18. The method for treating solid residues in biomass fermentation as described in claim 16, characterized in that, The fineness of the solid residue is 100-150 mesh.

19. The method for treating solid residues in biomass fermentation as described in claim 1, characterized in that, The lignin content is 40–70 wt%; And / or, the cellulose content is 1-20 wt%; And / or, the content of the hemicellulose is 1 to 10 wt%.

20. The method for treating solid residues in biomass fermentation as described in claim 1, characterized in that, The cellulose content is 10-20 wt%; And / or, the content of the hemicellulose is 1 to 5 wt%.

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