TECHNICAL FIELD

[0001] The present disclosure pertains to the technical field of production of biogas. In particular, the present disclosure relates to a process for production of biogas from lignocellulosic biomass.

BACKGROUND

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Lignocellulose is one of the most abundantly available plant-based material on the earth. This organic matter can be converted into various forms (liquid and gaseous) of green and renewable energy fuels through different biochemical/biological routes. Bio-methane is one of major components of a renewable natural biogas that is derived from the anaerobic digestion of organic or lignocellulosic matter. Biogas production from rapidly degradable carbon sources (food waste, organic waste, poultry litters, distillery spent wash, dairy waste etc.) has been widely studied and large-scale plants at the community levels have been successfully operated. The feed for these plants mainly contains a mixture of different organic feedstock. Lignocellulosic biomass is an alternative carbohydrate-rich source that is abundantly available, relatively cheaper and can be utilized for bio-methane production. The material is, however, recalcitrant and poorly degraded by microbes (anaerobic and aerobic). As such, biogas production from lignocellulosic material has thus far been achieved only at the lab-scale and in a few rare cases, at the pilot-scale. The current processes for producing bio-methane from lignocellulosic substrates are not yet optimized for faster/higher degradation of biomass and to obtain the possible theoretic conversion to biogas.

[0004] There is, therefore, a long standing need in the art of an economical and commercially viable process for an efficient process for production of biogas from a lignocellulosic biomass. The present disclosure fulfils the existing needs, at least in part, and provides an improved process for production of biogas from lignocellulosic biomass.

[0005] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

OBJECTS

[0006] An object of the present disclosure is to provide a process for production of biogas from a lignocellulosic biomass that is economical.

[0007] Another object of the present disclosure is to provide a process for production of biogas from a lignocellulosic biomass that precludes the need of subjecting the lignocellulosic biomass to costly and energy intensive pre-treatment for deconstruction or dissolution of complex lignocellulose or carbohydrates.

[0008] Further object of the present disclosure is to provide a process for production of biogas from a lignocellulosic biomass that minimizes the water and chemical requirement for the process.

[0009] Further object of the present disclosure is to provide a process for production of biogas from a lignocellulosic biomass that generates high quality organic-fertilizer as value- added by-product.

SUMMARY

[0010] The present disclosure pertains to the technical field of production of biogas. In particular, the present disclosure relates to a process for production of biogas from lignocellulosic biomass.

[0011] An aspect of the present disclosure relates to a process for production of a biogas from a lignocellulosic biomass, the process comprising the steps of: (a) taking the lignocellulosic biomass having size ranging from 1 mm to 50 mm; (b) subjecting the biomass to a pre-treatment to obtain a processed biomass, said step of the pre-treatment comprising: (i) treating the biomass with an alkali solution at a temperature ranging from 60°C to 100°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (ii) treating the alkaline treated biomass with an aqueous solution of acid (such as Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3 or Br2) to obtain the processed biomass with a pH ranging from 6.0 to 7.5; (c) subjecting the processed biomass to an impregnation by homogenization to obtain a biomass slurry, said slurry having total solid content ranging from 3% to 7% w/v; and (d) subjecting the biomass slurry to an anaerobic digestion to produce the biogas.

[0012] In an embodiment, the lignocellulosic biomass comprises agricultural residues, wherein the step of subjecting the biomass to the pre-treatment comprises chemopreconditioning including the steps of: (i) treating the biomass with an alkali solution at a temperature ranging from 60°C to 90°C for a time period ranging from 1 hour to 3 hours to obtain an alkaline biomass; and (ii) treating the alkaline biomass with an acid solution (Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2) to obtain the processed biomass with a pH ranging from 6.0 to 7.5.

[0013] In an embodiment, the lignocellulosic biomass comprises lignocellulosic feedstock with low carbohydrate content, wherein the step of subjecting the biomass to the pre-treatment comprises chemo- scouring including the steps of: (i) treating the biomass with hot water at a temperature ranging from 70°C to 90°C for a time period ranging from 10 minutes to 60 minutes; (ii) treating the biomass from step (i) with an alkali solution at a temperature ranging from 70°C to 90°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (iii) treating/neutralizing the treated biomass with an acid solution(Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2) to obtain the processed biomass with a pH ranging from 6.0 to 7.5.

[0014] In an embodiment, the step of subjecting the processed biomass to the impregnation by homogenization comprises: impregnation by homogenization of the processed biomass using a digestate water for a time period ranging from 10 minutes to 60 minutes to obtain the biomass slurry having total solid content ranging from 3% to 7% w/v.

[0015] In an embodiment, the step of subjecting the biomass slurry to the anaerobic digestion comprises: (i) mixing the biomass slurry with a source of nitrogen; and (ii) effecting anaerobic digestion of the slurry from step (i) using residues of anaerobic digestion to produce the biogas.

[0016] In an embodiment, the process comprises: mixing the processed biomass with an organic waste before subjecting said processed biomass to the impregnation by homogenization.

[0017] In an embodiment, the processed biomass is mixed with the organic waste in a weight ratio ranging from 60:40 to 90:10. [0018] In an embodiment, the step of subjecting the biomass slurry to the anaerobic digestion comprises effecting anaerobic co-digestion of the slurry using residues of anaerobic digestion.

[0019] In one embodiment, the process comprises: (a) taking the lignocellulosic biomass comprising agricultural residues, said biomass having size ranging from 1 mm to 50 mm; (b) subjecting the biomass to pre-treatment to obtain the processed biomass, said step of the pretreatment comprising: (i) treating the biomass with an alkali solution at a temperature ranging from 60°C to 90°C for a time period ranging from 1 hour to 3 hours to obtain an alkaline biomass; and (ii) treating the alkaline biomass with an acid solution(Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2)to obtain the processed biomass with a pH ranging from 6.0 to 7.5; (c) subjecting the processed biomass to impregnation by homogenization to obtain a biomass slurry, said impregnation by homogenization being done using a digestate water for a time period ranging from 10 minutes to 60 minutes, and said slurry having total solid content ranging from 3% to 7% w/v; and (d) subjecting the biomass slurry to an anaerobic digestion by: (i) mixing the biomass slurry with a source of nitorgen; and (ii) effecting anaerobic digestion of the slurry from step (i) using anaerobic digestion mud to produce the biogas.

[0020] In another embodiment, the process comprises: (a) taking the lignocellulosic biomass comprising lignocellulosic feedstock with low carbohydrate content, said biomass having size ranging from 1 mm to 50 mm; (b) subjecting the biomass to pre-treatment to obtain the processed biomass, said step of the pre-treatment comprising: (i) treating the biomass with hot water at a temperature ranging from 70°C to 90°C for a time period ranging from 10 minutes to 60 minutes; (ii) treating the biomass from step (i) with an alkali solution at a temperature ranging from 70°C to 90°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (iii) treating the alkaline biomass with an acid solution (Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2)to obtain the processed biomass with a pH ranging from 6.0 to 7.5; (c) subjecting the processed biomass to impregnation by homogenization to obtain a biomass slurry, said impregnation by homogenization being done using a digestate water for a time period ranging from 10 minutes to 60 minutes, and said slurry having total solid content ranging from 3% to 7% w/v; and (d) subjecting the biomass slurry to an anaerobic digestion by: (i) mixing the biomass slurry with a source of nitorgen; and (ii) effecting anaerobic digestion of the slurry from step (i) using anaerobic digestion mud to produce the biogas.

[0021] In an embodiment, the process comprises: (a) taking the lignocellulosic biomass comprising lignocellulosic feedstock with low carbohydrate content, said biomass having size ranging from 1 mm to 50 mm; (b) subjecting the biomass to pre-treatment to obtain the processed biomass, said step of the pre-treatment comprising: (i) treating the biomass with hot water at a temperature ranging from 70°C to 90°C for a time period ranging from 10 minutes to 60 minutes; (ii) treating the biomass from step (i) with an alkali solution at a temperature ranging from 70°C to 90°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (iii) treating the alkaline biomass with an acid solution(Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2)to obtain the processed biomass with a pH ranging from 6.0 to 7.5; (c) subjecting the processed biomass to impregnation by homogenization to obtain a biomass slurry, said impregnation by homogenization being done using a digestate water for a time period ranging from 10 minutes to 60 minutes, and said slurry having total solid content ranging from 3% to 7% w/v; and (d) effecting anaerobic co-digestion of the slurry using anaerobic digestion mud without addition of an external micronutrient thereto to obtain the biogas.

[0022] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0024] FIG. 1 illustrates an exemplary flow-chart showing a process for production of biogas from lignocellulosic biomass in accordance with an embodiment of the present disclosure.

[0025] FIG. 2 illustrates an exemplary flow-chart showing a process for production of biogas from lignocellulosic biomass in accordance with another embodiment of the present disclosure. [0026] FIG. 3 illustrates an exemplary flow-chart showing a process for production of biogas from lignocellulosic biomass in accordance with a further embodiment of the present disclosure.

[0027] FIG. 4A and 4B illustrate the effect of pre-treatment on production of Methane and biogas from garden waste biomass, respectively, in accordance with an embodiment of the present disclosure.

[0028] FIG. 5 illustrates the effect of pre-treatment on biogas yield from rice straw, in accordance with an embodiment of the present disclosure.

[0029] FIG. 6 illustrates results from the studies of biogas production from pre-treated garden waste in 100 L anaerobic digester in accordance with an embodiment of the present disclosure.

[0030] FIG. 7 illustrates results of the studies of CH4 production from pre-treated garden waste in 100 L anaerobic digester in accordance with an embodiment of the present disclosure.

[0031] FIG. 8 illustrates the rate of biogas production from pre-treated garden waste in 100 L anaerobic digester in accordance with an embodiment of the present disclosure.

[0032] FIG. 9A and 9B illustrate results from the study showing production of Methane and biogas from pre-treated rice straw in 100 L anaerobic digester in accordance with an embodiment of the present disclosure..

[0033] FIG. 10 illustrates rate of biogas production in pilot scale CSTR in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0034] The following is a detailed description of embodiments of the present invention. The embodiments are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

[0035] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims. [0036] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability.

[0037] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”

[0038] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0039] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0040] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.”Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.

[0041] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. [0042] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0043] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0044] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.

[0045] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0046] The present disclosure pertains to the technical field of production of biogas. In particular, the present disclosure relates to a process for production of biogas from lignocellulosic biomass.

[0047] An aspect of the present disclosure relates to a process for production of a biogas from a lignocellulosic biomass, the process comprising the steps of: (a) taking the lignocellulosic biomass having size ranging from 1 mm to 50 mm; (b) subjecting the biomass to a pre-treatment to obtain a processed biomass, said step of the pre-treatment comprising: (i) treating the biomass with an alkali solution at a temperature ranging from 60°C to 100°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (ii) treating the alkaline biomass with an acid solution (Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2)to obtain the processed biomass with a pH ranging from 6.0 to 7.5; (c) subjecting the processed biomass to an impregnation by homogenization to obtain a biomass slurry, said slurry having total solid content ranging from 3% to 7% w/v; and (d) subjecting the biomass slurry to an anaerobic digestion to produce the biogas.

[0048] In an embodiment, the lignocellulosic biomass comprises agricultural residues, wherein the step of subjecting the biomass to the pre-treatment comprises chemopreconditioning including the steps of: (i) treating the biomass with an alkali solution at a temperature ranging from 60°C to 90°C for a time period ranging from 1 hour to 3 hours to obtain an alkaline biomass; and (ii) neutralization of alkaline treated biomass to obtain the processed biomass with a pH ranging from 6.0 to 7.5.

[0049] In an embodiment, the lignocellulosic biomass comprises lignocellulosic feedstock with low carbohydrate content, wherein the step of subjecting the biomass to the pre-treatment comprises chemo- scouring including the steps of: (i) treating the biomass with hot water at a temperature ranging from 70°C to 90°C for a time period ranging from 10 minutes to 60 minutes; (ii) treating the biomass from step (i) with an alkali solution at a temperature ranging from 70°C to 90°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (iii) neutralization of alkaline treated biomass to obtain the processed biomass with a pH ranging from 6.0 to 7.5.

[0050] In an embodiment, the step of subjecting the processed biomass to the impregnation by homogenization comprises: homogenizing the processed biomass using a digestate water for a time period ranging from 10 minutes to 60 minutes to obtain the biomass slurry having total solid content ranging from 3% to 7% w/v.

[0051] In an embodiment, the step of subjecting the biomass slurry to the anaerobic digestion comprises: (i) mixing the biomass slurry with a source of nitorgen; and (ii) effecting anaerobic digestion of the slurry from step (i) using anaerobic digestion mud to produce the biogas.

[0052] In an embodiment, the process comprises: mixing the processed biomass with an organic waste before subjecting said processed biomass to the impregnation by homogenization. In an embodiment, the organic waste includes food waste. In an embodiment, the processed biomass is mixed with the organic waste in a weight ratio ranging from 60:40 to 90:10.

[0053] In an embodiment, the step of subjecting the biomass slurry to the anaerobic digestion comprises effecting anaerobic co-digestion of the slurry using anaerobic digestion mud without addition of an external micronutrient thereto.

[0054] In one embodiment, the process comprises: (a) taking the lignocellulosic biomass comprising agricultural residues, said biomass having size ranging from 1 mm to 50 mm; (b) subjecting the biomass to pre-treatment to obtain the processed biomass, said step of the pretreatment comprising: (i) treating the biomass with an alkali solution at a temperature ranging from 60°C to 90°C for a time period ranging from 1 hour to 3 hours to obtain an alkaline biomass; and (ii) neutralization of alkaline treated biomass to obtain the processed biomass with a pH ranging from 6.0 to 7.5; (c) subjecting the processed biomass to impregnation by homogenization to obtain a biomass slurry, said impregnation by homogenization being done using a digestate water for a time period ranging from 10 minutes to 60 minutes, and said slurry having total solid content ranging from 3% to 7% w/v; and (d) subjecting the biomass slurry to an anaerobic digestion by: (i) mixing the biomass slurry with a source of nitorgen; and (ii) effecting anaerobic digestion of the slurry from step (i) using anaerobic digestion mud to produce the biogas.

[0055] FIG. 1 illustrates an exemplary flow-chart illustrating the process in accordance with an embodiment of the present disclosure. As can be seen from FIG. 1, the lignocellulosic biomass (100) primarily including agricultural residues is taken, said biomass having size ranging from 1 mm to 50 mm, preferably, ranging from 3 mm to 30 mm, more preferably, ranging from 5 mm to 10 mm. Any conventional method for reducing the size of lignocellulosic biomass such as shredding may be used to obtain the lignocellulosic biomass of desired particle size.

[0056] The lignocellulosic biomass is then subjected to a pre-treatment (110) to obtain the processed biomass (120). The pre-treatment step aids in breaking down the lignocellulosic biomass and greatly enhances the yield of biogas. During the series of experiments, it could be noted that for the lignocellulosic biomass primarily including agricultural residues, chemo- preconditioning pre-treatment is advantageous. The step of pretreatment (110) includes: treating the biomass with an alkali solution (112) at a temperature ranging from 60°C to 90°C for a time period ranging from 1 hour to 3 hours to obtain an alkaline biomass; and then neutralization (114) of alkaline treated biomass to obtain the processed biomass (120) with a pH ranging from 6.0 to 7.5. Although any alkali solution may be used in the step of pre-treatment of the biomass, in accordance with an embodiment of the present disclosure, an aqueous solution of sodium hydroxide (NaOH) of appropriate strength is used for treating the biomass. In an embodiment, an aqueous solution of sodium hydroxide (NaOH) with strength of 0.1% to 1.0% w/v is used for treating the biomass. The treatment of the biomass with alkali solution may be effected at a temperature ranging from 60°C to 90°C, preferably, from 60°C to 80°C, more preferably, from 60°C to 70°C and most preferably, from 60°C to 65 °C. The treatment of the biomass with alkali solution may be effected for a time period ranging from 1 hour to 3 hours. The alkaline biomass so obtained is then neutralization of alkaline treated biomass to obtain the processed biomass (120) with a pH ranging from 6.0 to 7.5. Although any acid such as Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2 and the likes of any desired strength may be used, in an embodiment, acid solution with strength of 0.5% to 3.5% w/v is used for treating the alkaline biomass. The treatment of the alkaline biomass with acid solution may be effected at a temperature ranging from 60°C to 90°C, preferably, from 60°C to 80°C, more preferably, from 60°C to 70°C and most preferably, from 60°C to 65°C. The treatment of the alkaline biomass with acid solution may be effected for a time period ranging from 1 hour to 3 hours. Any conventional apparatus, such as a continuous or a batch reactor, as known to or appreciated by a skilled person may be used for effecting the pre-treatment of the lignocellulosic biomass. Particularly, it could be noted during the series of experiments, albeit surprisingly, that when the biomass is treated with an alkali solution at an elevated temperature, followed by neutralization of biomass, it affords dramatic improvement in efficiency of the process as compared to treatment of biomass with alkali solution alone or treatment of biomass with acid alone. Without wishing to be bound by the theory, it is believed that treatment of the alkaline biomass with acid solution may aid in promoting the direct electron transfer between acidogenic/acetogenic bacteria and methanogenic bacteria, which is essential for maintaining the microbial synergy in the anaerobic digester and consequently, may improve the efficiency of the process.

[0057] The processed biomass so obtained from the pre-treatment step is then subjected to impregnation by homogenization (130) to obtain a biomass slurry (140). Any conventional milling apparatus, suitable to effect impregnation by homogenization of the biomass may be used in the process of the present disclosure. Any conventional solvent, preferably, an aqueous solution may be used to effect impregnation by homogenization of the biomass. In accordance with an embodiment of the present disclosure, the biomass is homogenized using digestate water (150), which may have been obtained from the step of anaerobic digestion of the biomass. This may confer two-fold advantages, in that it affords recycling of the water, and use of the digestate water may further aid in anaerobic digestion of the biomass slurry. In an embodiment, the impregnation by homogenization is done using a digestate water (150) for a time period ranging from 10 minutes to 60 minutes. In an embodiment, the slurry has a total solid content ranging from 3% to 7% w/v of the slurry. Although several embodiments of the present disclosure are described, wherein alkaline biomass is neutralized with acid solution as part of the pre-treatment step, a skilled artisan would immediately realize that one can also use the aqueous solution of acid for impregnation by homogenization precluding the step of treatment of alkaline biomass with acid solution as part of the pre-treatment, and such variations all fall within the ambit of the presently claimed invention.

[0058] The slurry (140) so obtained can then be subjected to an anaerobic digestion (160) as known in the state-of-art. In an embodiment, the biomass slurry (140) is mixed with a source of nitrogen (which may act as micronutrient), and the mixture is then fed to a digester for effecting anaerobic digestion of the mixture (slurry) using anaerobic digestion mud to produce the biogas. The digester may be a mesophillic-anaerobic digester, preferably, a continuously stirred tank reactor (CSTR) containing biomass- specific (adapted) anaerobic digestion mud for biogas production. The step of anaerobic digestion is not detailed herein for being very well known to the skilled persons. The solid remnants from the digester (after the anaerobic digestion of the biomass) can advantageously be used as organic fertilizer, while the liquid residues (digestate water) may be recycled and reused in the process for example, for the purpose of wet-milling. The biogas produced in accordance with embodiments of the present disclosure typically comprises: CH4 (48-50 % mol.), H2 (8-10 % mol.), CO2 (35-38 % mol.) and traces of N2 (1-5 % mol.) gases. The biogas so produced may be stored or directly used for the applications well known in the art. Alternatively, the biogas may be upgraded to bio-methane (90-95 % mol.) through conventional biogas purification process.

[0059] In another embodiment, the process comprises: (a) taking the lignocellulosic biomass comprising lignocellulosic feedstock with low carbohydrate content, said biomass having size ranging from 1 mm to 50 mm; (b) subjecting the biomass to pre-treatment to obtain the processed biomass, said step of the pre-treatment comprising: (i) treating the biomass with hot water at a temperature ranging from 70°C to 90°C for a time period ranging from 10 minutes to 60 minutes; (ii) treating the biomass from step (i) with an alkali solution at a temperature ranging from 70°C to 90°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (iii) neutralization of alkaline treated biomass to obtain the processed biomass with a pH ranging from 6.0 to 7.5; (c) subjecting the processed biomass to impregnation by homogenization to obtain a biomass slurry, said impregnation by homogenization being done using a digestate water for a time period ranging from 10 minutes to 60 minutes, and said slurry having total solid content ranging from 3% to 7% w/v; and (d) subjecting the biomass slurry to an anaerobic digestion by: (i) mixing the biomass slurry with a source of nitorgen; and (ii) effecting anaerobic digestion of the slurry from step (i) using anaerobic digestion mud to produce the biogas.

[0060] FIG. 2 illustrates an exemplary flow-chart illustrating the process in accordance with an embodiment of the present disclosure. As can be seen from FIG. 2, the lignocellulosic biomass (200) primarily including low carbohydrate content containing lignocellulosic feedstock is taken. Particle size of the biomass ranges from 1 mm to 50 mm, preferably, ranging from 3 mm to 30 mm, more preferably, ranging from 5 mm to 10 mm. The lignocellulosic biomass is then subjected to a pre-treatment (210) to obtain the processed biomass (220). During the series of experiments, it could be noted that for the lignocellulosic biomass primarily including lignocellulosic feedstock with low carbohydrate content, chemoscouring pre-treatment is advantageous. The step of pre-treatment (210) includes: (i) treating the biomass (200) with hot water (shown as 212) at a temperature ranging from 70°C to 90°C for a time period ranging from 10 minutes to 60 minutes; (ii) treating the biomass from step (i) with an alkali solution (shown as 214) at a temperature ranging from 70°C to 90°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (iii) neutralization of alkaline treated biomass (shown as 216) to obtain the processed biomass (220) with a pH ranging from 6.0 to 7.5. In an embodiment, an aqueous solution of sodium hydroxide (NaOH) of appropriate strength is used for treating the biomass. In an embodiment, an aqueous solution of sodium hydroxide (NaOH) with strength of 0.1% to 1.0% w/v is used for treating the biomass. The treatment of the biomass with alkali solution may be effected at a temperature ranging from 70°C to 90°C, preferably, from 75°C to 90°C, more preferably, from 80°C to 90°C and most preferably, from 80°C to 85°C. In an embodiment, acid solution (Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2)with strength of 0.5% to 3.5% w/v is used for treating the alkaline biomass. The treatment of the alkaline biomass with acid solution may be effected at a temperature ranging from 70°C to 90°C, preferably, from 75°C to 90°C, more preferably, from 80°C to 70°C and most preferably, from 80°C to 85°C. The treatment of the alkaline biomass with acid solution may be effected for a time period ranging from 10 minutes to 2 hours. The processed biomass so obtained from the pre-treatment step is then subjected to impregnation by homogenization (230) to obtain a biomass slurry (240). In an embodiment, the biomass is wet milled using digestate water (250), which may have been obtained from the step of anaerobic digestion of the biomass. In an embodiment, the impregnation by homogenization is done using a digestate water (250) for a time period ranging from 10 minutes to 60 minutes. In an embodiment, the slurry has a total solid content ranging from 3% to 7% w/v of the slurry. The slurry (240) so obtained can then be subjected to an anaerobic digestion (260) as known in the state-of-art. In an embodiment, the biomass slurry (240) is mixed with a source of nitrogen (which may act as micronutrient), and the mixture is then fed to a digester for effecting anaerobic digestion of the mixture (slurry) using anaerobic digestion mud to produce the biogas.

[0061] In another embodiment, the process comprises: (a) taking the lignocellulosic biomass comprising lignocellulosic feedstock with low carbohydrate content, said biomass having size ranging from 1 mm to 50 mm; (b) subjecting the biomass to pre-treatment to obtain the processed biomass, said step of the pre-treatment comprising: (i) treating the biomass with hot water at a temperature ranging from 70°C to 90°C for a time period ranging from 10 minutes to 60 minutes; (ii) treating the biomass from step (i) with an alkali solution at a temperature ranging from 70°C to 90°C for a time period ranging from 30 minutes to 3 hours to obtain an alkaline biomass; and (iii) neutralization of alkaline treated biomass to obtain the processed biomass with a pH ranging from 6.0 to 7.5; (c) subjecting the processed biomass to impregnation by homogenization to obtain a biomass slurry, said impregnation by homogenization being done using a digestate water for a time period ranging from 10 minutes to 60 minutes, and said slurry having total solid content ranging from 3% to 7% w/v; and (d) effecting anaerobic co-digestion of the slurry using anaerobic digestion mud without addition of an external micronutrient thereto to obtain the biogas.

[0062] FIG. 3 illustrates an exemplary flow-chart illustrating the process in accordance with an embodiment of the present disclosure. As can be seen from FIG. 3, lignocellulosic biomass (300) primarily including lignocellulosic feedstock with low carbohydrate content such as garden waste biomass is taken. Particle size of the biomass ranges from 1 mm to 50 mm, preferably, ranging from 3 mm to 30 mm, more preferably, ranging from 5 mm to 10 mm. The lignocellulosic biomass is then subjected to a pre-treatment (such as chemoscouring, as detailed above) to obtain the processed biomass (320). The processed biomass so obtained from the pre-treatment step is then mixed with an organic waste (320b) such as food waste to obtain a mixed biomass (325). In an embodiment, the processed biomass is mixed with the organic waste in a weight ratio ranging from 60:40 to 90:10. The mixed biomass (325) is then subjected to impregnation by homogenization (330), using any conventional milling apparatus, to obtain a biomass slurry (340). In an embodiment, the biomass is wet milled using digestate water (350) for a time period ranging from 10 minutes to 60 minutes. In an embodiment, the slurry has a total solid content ranging from 3% to 7% w/v of the slurry. The slurry (340) so obtained can then be fed to a digester, preferably, without addition of an external micronutrient thereto, for co-digestion (i.e. anaerobic digestion, 360) with the help of anaerobic digestion mud to produce the biogas.

[0063] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

EXAMPLES

[0064] Lignocellulosicbiomass

[0065] Lignocellulosic biomass (rice straw and mixed biomass) were procured from local market. Each of the lignocellulosic biomass was subjected to size reduction to -lOmrn using a shredder and the same were analyzed for its composition (provided below in Table 1 below) by following the standard NREL_LAP procedures. The composition analysis revealed that the total carbohydrate content of the raw Garden Waste (GW) was ~29 % wt. which was ~1.8 fold lesser than the carbohydrate content of rice straw (Note: only this portion can be converted into biogas during anaerobic digestion).

Table 1: Compositions of Lignocellulosic biomass

[0066] EXAMPLE 1: Biochemical Methane Potential (BMP) tests [0067] BMP tests were performed to evaluate the potential methane/biogas volume that can be generated from each substrate. All the BMP tests were performed in 500 mL Scott bottles with a rubber cork and gas removal provision. Each test comprised of two elements: a) anaerobic digestion mud and b) sample. The anaerobic digestion mud was taken from the running pilot-plant in HPGRDC. The anaerobic digestion mud was fed an amount of sample on a VS ratio basis (PS) (2:1), gas yield was then measured continuously in real time by water displacement system. The gas was measured and converted to units of ml/gram VS substrate at Standard conditions for Temperature and Pressure (STP). Triplicates were carried out for these experiments including a blank, which indicated the productivity of the anaerobic digestion mud, in order to obtain the production of the sole substrate, and a control with substrate to verify the activity of the mud. The results provided by the BMP assays were obtained from the triplicate average for each bottle and were expressed as the net volume of methane per g of VS added (mlCH4/gVSadded).The BMP were finished when a daily production of less than 1% of the whole production occurred as it is indicated in the following equation, where “n” represents the day of the experiment.

(Gross production (ml)n — Gross production (ml)n — 1)

Production — X 100

(Gross production (ml)n

[0068] FIG. 4A and 4B illustrate the effect of pre-treatment on production of Methane and biogas from garden waste biomass, respectively. FIG. 5 illustrates the effect of pretreatment on biogas yield from rice straw. As can be seen from FIG. 4A, 4B and FIG. 5, the advantageous pre-treatment of the biomass affords several-fold increase in the production of biogas and methane.

EXAMPLE 2

[0069] Pre-treatment of the lignocellulosic biomass

[0070] The same shredded biomass prepared above was directly used for pre- conditioning/pre-treatment studies. All the pre-conditioning experiments were carried out in a blender at 5- 10kg scale. The developed chemo -preconditioning method was optimized (chemical concentrations, treatment temperatures & residence times were optimized) for each feedstock.

[0071] Pre-treatment method for Garden waste/mixed biomass: The size reduced biomass (5-10 mm) was first treated with hot-water (80 - 85 °C) to remove the attached soil and water soluble phenolics/extractives etc., and then subjected to the NaOH(0.5 % w/v) treatment at 70°C for 60 minutes, during which the pH of solids increased to 11. Post NaOH treatment, the treated solids were treated with any of the acid (Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2)to adjust the pH to neutral. The wash water generated during the pre-conditioning process was recycled after separation of soil (by static settling).

[0072] Pre-treatment method for Rice straw biomass: The size reduced biomass (15- 20 mm) was directly subjected to the NaOH (1.5 % w/v) treatment at 60°C for 3 hours during which the pH of solids increased to 13. Post alkali treatment, the treated solids was neutralized with diluted acid (Formic acid, acetic acid, HC1, H2SO4, H3PO4, HNO3, HF, HI, Boric acid, Perchloric acid, other Lewis acids made up of H ⁺ , K ⁺ , Mg ²⁺ , Fe ³⁺ , BF3, CO2, SO3, RMgX, AICI3, Br2)to adjust the pH close to neutral. Composition of each of the pre-treated biomass is provided in Table 2 below.

Table 2: Composition of pre-treated biomass

[0073] Impregnation by homogenization of the processed biomass

[0074] Feed for mono-digestion: The pre-treated biomass was then (wet) milled using crusher with diluent (water or recycled digestate liquid stream) to generate feed slurry with solids consistency of about 5.5 % w/v. During wet-milling, the particle size in the feed slurry was reduced by 3-4 fold than that of initial size of biomass. External nitrogen supplements (Urea) were also added during the slurry preparation in order to maintain the optimum C/N value (20 - 25) in the anaerobic digester.

[0075] Feed for co-digestion: The pre-treated biomass was then (wet) milled using crusher with diluent (water or recycled digestate liquid stream) to generate feed slurry with solids consistency of about 5.5 % w/v. During wet-milling, the particle size in the feed slurry was reduced by 3-4 fold than that of initial size of biomass. For co-digestion, the nitrogen and other micro-nutrients were supplied in the form of organic waste/food waste. The minced food waste/organic waste was mixed with the biomass feed in optimum proportion of 80 (biomass): 20 (food waste) in order to maintain the optimum C/N value (20 - 25) in the anaerobic digester.

[0076] Anaerobic digestion of biomass slurry

[0077] Mesophilic (anaerobic) mono-digestion process: Anaerobic mono-digestion of slurry obtained above was carried out in CSTR (with bottom driven impeller) capacity of 100 L digester with working volume of 80 L in a semi-batch mode. The anaerobic digestion was conducted under mesophilic (~37 °C) conditions using adapted mixed microbial consortia. About 5 L of biomass feed slurry with total solids of 300 - 400 g was added into the anaerobic digester. The charging of feed to the digester was done for every 48 h. Before charging the feed (5 L) into the digester, ~5 L of digestate was removed from the digester. The volume of biogas generated during anaerobic digestion was continuously measured using biogas flow meter while the composition of biogas was analyzed by Residual Gas Analyzer (RGA) for each batch of feeding. The digestate slurry was subjected to solid-liquid separation and the liquid stream (contains residual mud) was recycled back while the solid stream (organic fertilizer) was tested for its nutritional composition (NPK, other microelements and humus).

[0078] FIG. 6 illustrates results from the studies of biogas production from pre-treated garden waste in 100 L anaerobic digester (from batches 1 through 14). FIG. 7 illustrates results of the studies of CH4 production from pre-treated garden waste in 100 L anaerobic digester (from batches 1 through 14). FIG. 8 illustrates the rate of biogas production from pre-treated garden waste in 100 L anaerobic digester. FIG. 9A and 9B illustrate results from the study showing production of Methane and biogas from pre-treated rice straw in 100 L anaerobic digester.

[0079] Mesophilic (anaerobic) co-digestion process

[0080] Anaerobic co-digestion of slurry with food waste was carried out in CSTR (with bottom driven impeller) capacity of 100 L digester with working volume of 80 L in a semibatch mode. The anaerobic digestion was conducted under mesophilic (~37 °C) conditions using adapted mixed microbial consortia. About 5 L of biomass feed slurry with total solids (biomass + food waste) of 300 - 400 g was added into the anaerobic digester. The charging of feed to the digester was done for every 48 h. Before charging the feed (5 L) into the digester, ~5 L of digestate was removed from the digester. The volume of biogas generated during anaerobic digestion was continuously measured biogas flow meter while the composition of biogas was analyzed by Residual Gas Analyzer (RGA) for each batch of feeding. The digestate slurry was subjected to solid-liquid separation and the liquid stream (contains residual mud) was recycled back while the solid stream (organic fertilizer) was tested for its nutritional composition (NPK, other microelements and humus). Table 3 below provides results from the co-digestion of garden waste (GW) with food waste (FW).

Table 3: Co-digestion of garden waste (GW) with food waste (FW).

[0081] EXAMPLE 3: Evaluation of biogas production at pilot-scale

Q [0082] Based on the results obtained at 100 L scale, the process was scaled-up to -4 m CSTR. The feeding rate in the pilot CSTR was kept similar as 100 L CSTR, i.e. for every 48 h. For each batch 5.5 kg of pre-treated biomass, as obtained in Example 2, was charged into the digester. About 8 batches were performed (5.5 kg X 8 no. = 44 kg biomass) and obtained almost similar biogas yields as observed in 100 L CSTR. Total biogas production was ~2.4 Q m per batch and the rate of biogas production was found to be -47.9 L/h (as shown in FIG. 10). Based on the gas yields obtained at pilot-scale; -59 kg of CH4 could be produced from 1 Ton of Garden waste biomass while for Rice straw the CH4 yield (107 kg) was almost 2-fold higher which might be due the presence of higher utilizable carbohydrates. Based on the theoretical methane potential of these feedstock (provided in Table 5 below), the methane conversion efficiencies for garden waste and rice straw were found be 88 % and 93 %, respectively (provided in Table 4 below). The biogas produced from pre-treated garden waste and rice straw showed -48 % mol. of CFLpresence (provided in Table 5 below). Further, the composition analysis of solid-fertilizer generated during anaerobic digestion of garden waste and rice straw showed almost similar nutritional quality (provided in Table 7 below). Table 4: Biogas/CEU yields from rice straw and mixed biomass at pilot-scale

Table 5: Theoretical biogas/CEG yields from rice straw and mixed biomass Table 6: Composition of biogas produced from mixed biomass (garden waste) and rice straw

Table 7: Composition of organic fertilizer produced during conversion of rice straw and mixed biomass

*A, feedstock was mixed garden waste biomass

*B, feedstock was Rice straw

ADVANTAGES [0083] The present disclosure provides a process for production of biogas from a lignocellulosic biomass that is economical.

[0084] The present disclosure provides a process for production of biogas from a lignocellulosic biomass that precludes the need of subjecting the lignocellulosic biomass to costly and energy intensive pre-treatment for deconstruction or dissolution of complex lignocellulose or carbohydrates.

[0085] The present disclosure provides a process for production of biogas from a lignocellulosic biomass that minimizes the water and chemical requirement for the process.

[0086] The present disclosure provides a process a process for production of biogas from a lignocellulosic biomass that generates high quality organic-fertilizer as value-added by- product.