A system and a continuous hybrid process for high productivity of hydrogen and c2 and c4 fatty acids from acetogenesis of waste

Abstract

The present invention relates to a system and a process for enhanced hydrogen (H₂) and short- chain fatty acid (SCFA) production using both untreated as well as thermally pretreated food waste (TCP-FW) in continuous mode. The process employs non-sacrificial, conductive, and biocompatible electrodes and optimizes the carbon-to-nitrogen (C / N) ratio of TCP-FW for improved H₂ yields. The invention minimizes CO₂ formation while maximizing H₂ and SCFA production. The process is scalable, demonstrated in a 60-L continuous reactor with an L / D ratio of 10, achieving a production rate of 260 L H₂ / day per kg COD with productivity of 10.84 L / h. This method offers a sustainable approach to low-carbon hydrogen production by utilizing municipal biogenic solid waste, reducing greenhouse gas emissions, and generating SCFA as a valuable by-product.

Description

[0001] A SYSTEM AND A CONTINUOUS HYBRID PROCESS FOR HIGH PRODUCTIVITY OF HYDROGEN AND C2 AND C4 FATTY ACIDS FROM ACETOGENESIS OF WASTE

[0002] FIEED OF THE INVENTION

[0003] The present invention relates to a system and a continuous process for high productivity of hydrogen and C2, C4 fatty acids from acidogenesis of waste / food waste. In particular, the present invention relates to using solid waste as substrate for hydrogen production, in both treated and untreated conditions, in batch mode and continuous mode of operation. More particularly, the instant invention relates to continuous hydrogen production using untreated and treated municipal solid waste in continuous mode operation; which was scaled up to 60 L yielding a range of 240 to 260 L of hydrogen per 1 kg COD removed and 0.45 to 0.55 kg of short-chain fatty acids (SCFA); being the highest reported till date. The instant invention relates to renewable energy resources and shall help reduce the dependency on fossil fuel imports and environmental pollution. It shall help attain the 7thsustainable development goal of ‘Affordable and Clean Energy'.

[0004] BACKGROUND OF THE INVENTION AND DESCRIPTION OF PRIOR ART

[0005] Hydrogen production through waste minimizes the waste and produces a renewable and sustainable alternative energy. Using solid waste as raw material to produce hydrogen poses significant energy and environmental challenges. One of the pioneer and emerging techniques for generating hydrogen is through acidogenesis. Within this process, microbes primarily transform organic waste materials into hydrogen through fermentation. As mentioned, acidogenesis relies on organic substrates such as lingo-cellulosic biomass, carbohydrate-rich raw materials like sugar and starch-containing crops, and organic residues from municipal solid waste, food waste, wastewater, and industrial effluents. The waste was mainly used untreated, typically resulting in lower efficiency. This is because untreated food waste contains organic materials, and not all are easily converted into hydrogen gas. Treated food waste can yield higher quantities of hydrogen due to the improved quality of the feedstock and the optimization of hydrogen-producing microorganisms or processes. Treated food waste undergoes preprocessing steps to remove contaminants and optimize the organic content for hydrogen production. This can include mechanical separation, grinding, and removal of non-organic materials. Treated food waste can have higher hydrogen production efficiency compared to untreated waste. The control condition, where food waste was left untreated, acted as the benchmark for evaluating the effects of pre-treatment. These pre-treatment methods positively impacted hydrogen production from the same substrate. Compared to the control condition, all pretreatment conditions significantly influenced the production of acidogenic metabolites (Bhurat et al., Ener. Sour. 45(1): 1017-1029, 2023). In a previous study, soybean straw subjected to acid pre-treatment exhibited the highest hydrogen output at 60.2 mL / g of dry soybean straw, as opposed to 5.46 mL / g for untreated, dry soybean straw, among the various pre-treatment methods examined (Gonzalez et al., BioEner. Research. 16(2): 717-740, 2023). In another investigation, different pre-treatments were assessed for their impact on dark fermentative biohydrogen production from beetroot pulp (Raina et al., Chemo. 294:133712, 2022). They reported the highest hydrogen yield of 115.6 mL / g COD for alkali-treated pulp compared to 90.1 mL / g COD for untreated pulp (Bundhoo et al., Int. Jour. Of Hydro. Ener. 44(32): 17346- 17362, 2019). In another study, a hydrogen yield of 4.2 mol H2 / mol was achieved with the fermentation of beetroot molasses with yeast extract (Badawi et al., Ener. Nex: 100194, 2023). In another study, the dark fermentation of barley straw resulted in an H2 production of 70.1 mL (equivalent to 35.1 L / kg of dry biomass) for untreated raw barley straw, while 45 minutes of ozone treatment significantly increased the H2 yield to 186.8 mL (equivalent to 93.4 L / kg of dry biomass) for the treated barley straw (Bundhoo et al., Inter. Jour, of Hydro. Ener. 44(32): 17346-17362, 2019). However, the present invention seeks to supplant the performance of its predecessors by employing waste as substrate in both treated and untreated conditions for hydrogen production in batch mode and continuous mode of operation, thereby reducing dependence on fossil fuel imports and environmental pollution.

[0006] Reference may be made to US201361893447P, which discloses introducing organic material and microorganisms into a fully blended bioreactor to produce H2, CO2, VFAs, and alcohols. The steps of capturing CO2 in the reactor's upper space, extracting H2 from the upper space, and retrieving a primary liquid output containing microorganisms, VFAs, and alcohols are outlined. Furthermore, a system for generating H2, VFAs, and alcohols from organic material is presented, comprising a fully blended bioreactor designed for dark fermentation, an inlet for providing microorganisms and the organic material to be decomposed, a CO2 capture mechanism in the upper space that employs a solid hydroxide to sequester CO2 gas, and a gas outlet for discharging a gaseous product containing H2 gas. The invention pertains to a procedure involving a mixed bioreactor to facilitate the production of H2, CO2, volatile fatty acids (VFAs), and alcohols in batch mode operation. Furthermore, it encompasses steps such as capturing CO2 in the upper region of the reactor, extracting H2 from the same area, and recovering a principal liquid output comprising microorganisms, VFAs, and alcohols. The present invention operates in a continuous mode operation.

[0007] Reference may be made to US 10, 246,724B2, wherein an anaerobic biological process for hydrogen production is disclosed. More specifically, different embodiments of this innovation revolve around a modular energy system and the associated methods for producing hydrogen by utilising organic waste as a raw material. The invention pertains to the hydrogen production from organic wastes and agricultural byproducts and the subsequent use of the hydrogen to generate electricity in modular energy systems comprising a solar collector system in a bioreactor.

[0008] Reference may be made to US7, 709,113B2, entitled “Bio-electrochemically assisted microbial reactor that generates hydrogen gas and methods of generating hydrogen gas” which discloses processes for producing hydrogen using microorganisms in a bio-electrochemically assisted microbial reactor. One method for hydrogen production involves employing a previously described hydrogen production system that includes a reactor. In which anodophilic bacteria are introduced, and an organic material susceptible to oxidation by the anodophilic bacteria's oxidative activity is injected. This mixture is then incubated under conditions conducive to oxidation reactions, leading to the creation of electrons, which are subsequently directed toward the anode. When a power source is activated, the potential difference between the anode and cathode increases, prompting electrons and protons to combine, ultimately yielding hydrogen gas. In one configuration designed for hydrogen production, a reaction chamber is employed, featuring a wall that defines the reactor's interior and the exterior of the reaction chamber. The invention relates to bio-electrochemical assisted systems and processes for producing hydrogen gas in two-chamber MFCs with the anode and cathode separated by a proton exchange membrane (PEM; NAFIONTM 117). The anode electrodes are made of plain carbon cloth, and the cathode electrodes are made of carbon paper containing 0.5 mg-Pt / cm. Instead of sparging the cathode chamber with air, the chamber is sealed and analyzed periodically for hydrogen gas production. The present invention operates continuously with a single reactor chamber system without a membrane using graphite electrodes. Reference may be to US 7473552 B2, wherein a process for producing hydrogen gas and isolating hydrogen-producing microorganisms using replenishing coated substrates” is disclosed. It uses a bioreactor designed to create conditions conducive to the decomposition of organic water-based substances and the production of hydrogen by microorganisms, all while preventing the formation of methane by methanogens. Within this bioreactor, substrates are equipped with a gel-like matrix coating, which is augmented by introducing extra coating material into the inner channels of the substrates. Notably, these substrates allow the coating material to permeate them effectively. This invention relates to a bioreactor for the continuous growth of hydrogen using substrates coated with a gelatinous matrix. The present invention operates in a continuous mode operation with a single reactor chamber in the absence of coating.

[0009] Reference may be made to EP3833769A1, which discloses a process of “Anaerobic digestion with a dynamic recirculation of digestate”. The present invention involves producing hydrogen and volatile fatty acids (VFA) by anaerobic digestion with a dynamic recirculation of digestate in phase-I and phase-II at pH 6 in batch mode operation. The invention relates to the field of anaerobic digestion processes with separate phases in treating organic waste, particularly in recirculating digestate. The present invention operates in a continuous mode in a single system.

[0010] Reference may be made to JP2611835B2, entitled “Anaerobic digestion,” which describes innovation focused on producing VFA (volatile fatty acids) from organic waste, which is achieved by making it soluble through acid fermentation. This process employs Clostridium bifermentans as the predominant bacterial strain, cultivated anaerobically for 2 days at 37°C in PYG culture fluid. Subsequently, methane fermentation is conducted in batch mode, utilizing methane bacteria. The invention improves the efficiency of the anaerobic digestion of organic waste using a novel Clostridium microorganism by bioaugmentation. The present invention operates continuously with acetogenic conditions without applying a bioaugmentation strategy.

[0011] Reference may be made toUS20090107913Al, entitled “Improvement of acidogenic fermentation using an acclimatized microbiome” involves biomasses such as sewage, sewage sludge, chemical waste, food waste processing, agricultural waste, and animal waste for the production of biogas, methane, and biofuels using Class A biosolids, and pathogen-reduced organic liquid fertilizer through the anaerobic digestion process. The invention relates to the anaerobic digestion of biomasses converted into methane and other bioproducts or biofuels, such as biogases, biosolids, safe fertilizers, and bio supplements by the thermophilic process. The present invention operates in a continuous mode with acetogenic conditions.

[0012] Reference may be made to W02005005981A2, entitled “Bio-electrochemical process for producing hydrogen related to the bio-electrochemical process for producing H2 from bio- oxidizable material introduced into a dual chamber reactor provided with an anode and a cathode optionally separated by a cation exchange membrane (CEM) with anodophilic bacteria in aqueous medium. A potential between the anode and cathode of 0.05 and 1.5 volts was employed by maintaining a pH between 3 and 9, collecting H2 gas at the cathode. The invention uses an electrolysis cell comprising an anodic compartment and a cathodic compartment separated by a cation-exchange membrane, a controllable DC power source to be connected to the anode and cathode, an inlet for (dissolved) bio-oxidisable material, a liquid effluent outlet, an outlet for carbon dioxide gas and an outlet for hydrogen gas, optionally with a hydrogen storage facility. The present invention operates in a continuous mode with a single reactor chamber system without a membrane using graphite electrodes.

[0013] Reference may be made to US8093041B1, entitled “Method and apparatus for membranebased, two-stage gas production from solid biomaterials” describes the method and apparatus related to a two-stage membrane -based production of gas, preferably H2 gas from solid biological materials from organic waste materials or the like, comprising anaerobic hydrolysis and fermentation and photo fermentation using microorganisms in various processes at different pH conditions with Hallow fibre membrane. The invention relates to a two-stage membrane-based apparatus and method for gas production from biological materials using fermentative and photosynthetic processes. The present invention operates in a single stage in a continuous mode through an acetogenic process.

[0014] Reference may be made to US9765367, entitled “Method and system for production of hydrogen, methane, volatile fatty acids, and alcohols from organic material” describes a method for producing H2, CH4, VFAs, and alcohols from organic material, including the steps of introducing organic material and microorganisms into a completely mixed bioreactor. The first liquid effluent is into a gravity settler for separating the second liquid effluent into a separation module for separating into a second biomass and a third liquid effluent for production of CH4 and CO2 in CSTR with batch mode operation. The invention relates a downstream gravity settler integrated into the system after the CSTR. The method includes the application of acetone -butanol-ethanol (ABE) fermentation and methanogenesis and integrates a second-stage anaerobic digestion process. The present invention operates with the acetogenic process in a single system with continuous hydrogen production.

[0015] Based on the prior art, it may be observed that it primarily reports batch mode operation process for H2 production either with anaerobic digestion, anaerobically methane fermentation, microbial electrolysis, microbial fuel cell, anaerobic digestion, modular energy system integrated anaerobic process and bio-electrochemically assisted processes (in dual chamber system with membrane) using waste feedstock such as municipal waste, sewage, agricultural waste / byproducts, glycerol, sewage sludge, chemical waste, food waste and animal waste. Batch processes can be more variable in terms of hydrogen yield and quality because each batch may have different starting conditions, feedstock compositions, and process parameters. Continuous processes, on the other hand, can be more stable and predictable. Scaling up batch processes for large-scale hydrogen production can be challenging. Continuous processes are often more scalable and can be designed to handle larger volumes of feedstock and produce hydrogen consistently. Further, there seems to have been limited exploration of the process optimization and scaling-up aspects in continuous mode systems.

[0016] Accordingly, keeping in view the drawbacks of the hitherto reported prior art, the inventors of the present invention realized that there exists a dire need to provide a system and a process for hydrogen production using both untreated as well as treated municipal solid waste in continuous mode operation; wherein the hybrid process for the generation of hydrogen (H2) and short-chain fatty acids (SCFA) from waste acetogenesis is carried out in a fixed film membrane less single-chambered reactor operated in up-flow mode with self-induced buffering, while capturing CO2 in the reactor's upper space, coated substrates with a gelatinous matrix to prevent methane formation by methanogens, two-stage membrane-based production of gas; and wherein the system has been currently scaled up to 60 L to yield a range of 240 to 260 L of hydrogen per 1 kg COD removal and 0.45 to 0.55 kg of short-chain fatty acids (SCFA) being the highest reported to date.

[0017] OBJCTIVES OF THE INVENTION

[0018] The main objective of the present invention is therefore to provide a system for continuous hybrid production of hydrogen and short-chain fatty acids (C2 and C4) from wastes which obviates the drawbacks of the hitherto reported prior art. Another objective of the present invention is to provide a system that utilizes a fixed-film reactor configuration for efficient processing.

[0019] Still another objective of the present invention is to provide a system that operates in up-flow mode without the need for external circulation.

[0020] Yet another objective of the present invention is to provide a system that features in-situ buffering to regulate the redox environment within a single-stage bioreactor.

[0021] Still another objective of the present invention is to provide a system that operates without the need for membranes, simplifying the design while reducing costs.

[0022] Yet another objective of the present invention is to provide a system that incorporates non- sacrificial, conductive, and biocompatible electrodes for enhanced performance and durability.

[0023] Still another objective of the present invention is to provide a system that integrates acidogenic fermentation with electro-fermentation in a hybrid process within a single reactor.

[0024] Yet another objective of the present invention is to provide a continuous hybrid process for high production of hydrogen and C2, C3 and C4 Fatty acids from acidogenesis of waste / food waste.

[0025] Still another objective of the present invention is to provide a system and a process that employs thermochemically pre-treated food waste (TCP-FW) as a sustainable substrate.

[0026] Yet another objective of the present invention is to provide a process for production of hydrogen and short-chain fatty acids (C2 and C4) from wastes while maintaining a specific C / N ratio of thermo chemical pretreated food waste (TCP-FW) through biological process from the acetogenesis of waste in a 60 L fixed bed membrane-less reactor with self-induced buffering.

[0027] Still another objective of the present invention is to provide a process for H2 production from waste in continuous mode operation for sustained performance.

[0028] SUMMARY OF THE INVENTION The present innovation provides a continuous hybrid process for generating hydrogen (H2) and short-chain fatty acids (SCFA) from waste acetogenesis in a fixed film membrane-less reactor in up-flow mode with self-induced buffering.

[0029] Initially, the experiments were commenced with batch mode operation, utilizing untreated food waste (UT-FW) at an organic load (OL) of 50 g COD / L to produce hydrogen and SCFA.

[0030] Further, to operate in continuous mode, the reactor was fabricated with an inlet port at the bottom and an outlet / sampling port at the top, which was driven by a pump. The continuous reactor performance was evaluated using untreated food waste (UT-FW) at OL levels of 10 g, 30 g, and 50 g COD / L, and the operating conditions were optimized to enhance the hydrogen and SCFA production.

[0031] Subsequently, the reactor was operated continuously, employing thermochemical pretreated food waste (TCP-FW: 1% NaOH at 60 °C for 30 min) at different organic loads of 0.6, 0.9, and 1.08 kg COD / day. Later, urea (NH2CONH2) was introduced as a nitrogen source in the continuous reactor to maintain balanced C / N ratios of 30, 50, and 70.

[0032] Finally, non- sacrificial conductive biocompatible electrodes were incorporated into the continuous mode hybrid reactor without membrane, which was operated with TCP-FW at an OL of 50 g COD / L, and the nutrient source was adjusted using urea to enhance the production of hydrogen and fatty acids.

[0033] In an embodiment, the present invention provides a continuous mode operating system for the production of hydrogen and C2-C4 short chain fatty acids (SCFA) from thermochemical pretreated food waste comprising: a vertical cylindrical reactor having length and diameter ratio of 10:1, inlet port (3), outlet port (7), multiple sample ports (4), inlet feed tank (1), inlet feed pump (2), sampling port (4), gas holding capacity (5), gas collecting bag (6), gas collecting ports (12), effluent tank (8), anode electrode (9), cathode electrode (10), and poly propylene rings (11).

[0034] In another embodiment, the present invention provides a system, wherein the cylindrical reactor’s inlet port (3) is connected to the inlet feed tank (1) through inlet feed pump (2). In still another embodiment, the present invention provides a system, wherein the outlet port (7) is connected to effluent tank (8).

[0035] In yet another embodiment, the present invention provides a system, wherein the gas collecting bag (6) is connected to the reactor through a gas collecting port (12).

[0036] In still another embodiment, the present invention provides a system, wherein non-sacrificial conductive and biocompatible electrodes (9) and (10) are incorporated into the system to facilitate electro-biocatalytic processes. An wherein the anode (9) and cathode (10) are connected using copper wire and a 100-ohm resistor.

[0037] In yet another embodiment, the present invention provides a system, wherein the anode electrode (9) and cathode electrode (10) are selected from graphite, stainless steel, activated carbon cloth, either alone or in combination thereof.

[0038] In a further embodiment, the present invention provides a process for the production of hydrogen and C2-C4 short chain fatty acids (SCFA) from thermochemical pre-treated food waste via the developed continuous operating system, wherein the steps comprising:

[0039] (a) homogenizing the food waste to form a uniform mixture;

[0040] (b) pre-treating the homogenized food waste as obtained in step (a) with 1% base at a temperature of 60 to 80 degree C for 30 minutes to obtain a mixture;

[0041] (c) allowing the mixture obtained in step (b) to settle and separating the solid waste at the bottom, while retaining the supernatant in the inlet tank (1) as the feedstock;

[0042] (d) inoculating the pre-heated mixed microbial culture for the growth of Hydrogen producing bacteria added to the reactor from the top inlet (13) followed by addition of polypropylene rings (12)

[0043] (e) transferring the feedstock obtained in step (c) into the reactor of step (d) from the inlet tank (1) containing microbial inoculum under anaerobic conditions using an inlet feed pump (2) with a flow rate ranging from 0.84 L / h to 1.5 L / h with various organic loads selected from 30, 50, and 70 g COD / L and nitrogen sources;

[0044] (f) moving the injected feed in an up-flow direction in the reactor, to facilitate acidogenesis to produce hydrogen and C2-C4 short chain fatty acids (SCFA); (g) collecting the hydrogen gas in a gas collecting bag (6), and C2-C4 short-chain fatty acids (SCFA) in the effluent tank (8).

[0045] In still another embodiment, the present invention provides a process, wherein the base used in step (b) is selected from hydroxides of alkali and alkaline earth metals and the nitrogen source in step (e) is selected from urea, NaNCh, and KNO2.

[0046] In yet another embodiment, the present invention provides a process, wherein pre-heated microbial culture in step (d) is selected from culture dominated by Staphylicoccus sciuri / Mammalicoccus sciuri MTCC13609, Bacillus subtilis MTCC13610, Bacillus velezensis MTCC13611.

[0047] In still another embodiment, the present invention provides a process for the production of Hydrogen gas and C2-C4 short-chain fatty acids (SCFA) as claimed in claim 6 wherein the flow rate in step (v) is 1.25 L / h.

[0048] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0049] Figure 1 illustrates the operation of an up-flow continuous mode reactor. It was filled with polypropylene rings to facilitate biofilm formation and accommodated graphite electrodes serving as the anode and cathode in a single chamber connected to a 100 Q resistance. A pump was employed to supply the feed to the system to operate in continuous mode, while an outlet tank was utilized to collect the acidogenic effluent.

[0050] DETAILS OF BIOLOGICAL RESOURCES USED IN THE INVENTION

[0051] Details of all the biological resources [BR] used in the invention are provided herein below, in order to comply with section 10(4) of the Indian Patents Act, 1970 and section 6 of the Biological Diversity Act, 2002.

[0052] Drainage Sludge was collected from Hyderabad Municipal Drainage System, Nacharam and the sludge was filtered through the mesh to remove coarse particles then heated at 100°C for 2 hours to enhance the hydrogen producing bacteria followed by using in reactor system for Hydrogen production. The microbial culture was analyzed and isolated three major bacterial species viz., Staphylicoccus sciuri / Mammalicoccus sciuri MTCC13609, Bacillus subtilis MTCC13610, Bacillus velezensis MTCC13611 which were deposited on 10thMay 2024 at CSIR-Institute of Microbial Technology, Sector 39A Rd, 39A, Sector 39, Chandigarh, 160036 an IDA recognized under the Budapest Treaty.

[0053] DETAILED DESCRIPTION OF THE INVENTION

[0054] The present invention relates to a system and a process for continuous and high production of hydrogen and C2, C3 and C4 Fatty acids from acidogenesis of waste / food waste. The reaction is carried out in a 60 L fixed film reactor. The invention reports batch mode operation, utilizing untreated food waste (UT-FW) at an organic load (OL) of 50 g COD / L to produce hydrogen and fatty acids. Further, continuous mode operation using untreated food waste (UT-FW) at OL levels of 10 g, 30 g, and 50 g COD / L, was operated for hydrogen and fatty acid production. Subsequently, the reactor was operated continuously, employing chemically pre-treated food waste (CPT-FW) at different OL rates of 0.6, 0.9, and 1.08 kg COD. In an aspect, the present invention provides a continuous process for higher productivity of Hydrogen and Fatty acids (C2, C3 and C4) from acidogenesis of waste and more particularly food waste. The invention reports the scale-up in 60 L fixed film reactor and the process with optimized conditions achieving a 260 L H2 / d from one kg COD with a high productivity rate (10.84 L / h). In another aspect, the present invention provides a system that uses electrodes especially the Graphite Electrode to enhanced Hydrogen production in optimized conditions with continuous mode operation.

[0055] In still another aspect, the present invention provides a system that can reduce the dependency on fossil fuel imports and Environmental Pollution.

[0056] In yet another aspect, the present invention provides a process for continuous and high production of hydrogen and C2, C3 and C4 Fatty acids from acidogenesis of waste which minimizes the formation of CO2 while giving valuable by-products in the form of fatty acids. The process is not only more sustainable but also environmentally friendly method for hydrogen production. It reduces the greenhouse gas emissions by using municipal solid waste a substrate. The nutrient source is adjusted to improve the production of hydrogen and fatty acids.

[0057] In another aspect, the present invention provides a continuous mode operating system for the production of Hydrogen gas and C2-C4 short-chain fatty acids (SCFA) from thermochemical pre-treated food waste comprising a vertical cylindrical reactor having length and diameter in the ratio of 10:1, inlet port (3), outlet port (7), multiple sample ports (4), inlet feed tank (1), inlet feed pump (2), sampling port (4), gas holding capacity (5), gas collecting bag (6), gas collecting ports (12), effluent tank (8), anode electrode (9), cathode electrode (10), and poly propylene rings (11).

[0058] In still another aspect, the present invention provides a continuous hybrid process to produce H2 and SCFA by acetogenesis of waste in a fixed film reactor as described above, wherein the steps comprising: i. Food waste was collected, ground, and homogenized to form a uniform mixture. ii. The homogenized mixture was pre-treated with 1% base at a temperature of 60-80°C for 30 minutes to enhance the release of soluble sugars. iii. After pre-treatment, the mixture was allowed to settle, separating the solid waste at the bottom. The supernatant was taken as the feedstock and stored in the inlet tank (1). iv. Introduction of Inoculated pre-heated mixed microbial culture into the reactor from the top inlet (13) followed by polypropylene rings (12) v. The feedstock with various organic loads and nitrogen sources was transferred into the reactor under anaerobic conditions from the inlet tank (1) using an Inlet feed pump (2) with a flow rate range of 0.84 L / h-1.5 L / h. vi. The injected feed was moved in an up-flow direction in the reactor, which facilitates the process of acidogenesis to produce Hydrogen gas and C2-C4 short-chain fatty acids (SCFA) vii. The produced hydrogen gas was collected in a Gas collecting bag (6), and C2-C4 shortchain fatty acids (SCFA) were collected in the effluent tank (8) viii. The maximum H2 production was obtained in a range of 240 to 260 L / d with the hybrid process compared to conventional processes (H2: 194 L / d) shown in Fig 11. Moreover, the SCFA production was in the range of 0.45 to 0.55 kg / d (Acetic acid: 0.342 kg, and Butyric acid: 0.158 kg) with hybrid process compared to conventional processes (SCFA: 0.34 to 0.45 kg / d).

[0059] The instant invention focuses on producing H2 and SCFA (C2 and C4) from untreated food waste (UT-FW) via acetogenesis. To measure the efficacy of a batch mode system, the parameters were optimized to increase the products during the acetogenesis process. The process was then moved to optimize in continuous mode operation to improve the H2 and SCFA production.

[0060] A lab-scale reactor was designed with an effective volume of 60 L (Length, 180 cm; diameter, 18 cm; L / D ratio 10) and a working volume of 40 L. The reactor was fabricated with an acrylic material and provided with an inlet port at the bottom and an outlet / sampling port at the top. It was also connected to a U-shaped tube to prevent any gas escape. Before starting the experiment, the reactor was inoculated with pretreated microbial culture (dominated by Staphylicoccus sciuri / Mammalicoccus sciuri MTCC13609, Bacillus subtilis MTCC13610, Bacillus velezensis MTCC13611) at 10% v / v and filled with polypropylene rings to support the growth of the film.

[0061] Furthermore, the reactor was continuously operated with untreated food waste [UT-FW] and then with thermochemical pretreated food waste (TCP-FW) with 1% NaOH at 60 °C for 30 min at various flow rates with a pump at different OL to improve H2 and SCFA production. The reactor was inoculated with PT culture and filled with polypropylene rings to support the growth of the film. The initial pH of the reactor was adjusted to 6.5-6.8.

[0062] Initially, the reactor was operated continuously with UT-FW at different OLs of 10, 30, and 50 g COD / L. After obtaining steady performance with UT-FW, the reactor was shifted to TCP- FW at various OLs of 0.6 kg / d (0.84 L / h), 0.9 kg / d (1.25 L / h), and 1.08 kg / d (1.5 L / h) with constant COD of 30 g / L.

[0063] Subsequently, to enhance the H2 and SCFA production, the continuous mode reactor was operated with any one of urea (NH2CONH2), NaNO2 and KNO2 but not limited to as listed used as a nitrogen source to achieve a balanced C / N ratio. Low nitrates were observed with all OLs of UT-FW and TCP-FW without adding any nitrogen source. Therefore, the reactor was then operated with C / N ratios 30, 50, and 70 by adding a nitrogen source.

[0064] Later, further improvement of the H2 and SCFA production by applying an electro-biocatalytic process with non- sacrificial conductive and biocompatible electrodes (graphite) in a continuous mode in the single reactor system without a membrane was carried out. After evaluating the maximum H2 production and COD removal efficiency (65%) of various organic loads (OLs) during continuous operation, further augment the production of H2 and SCFA. Finally, the reactor was operated with TCP-FW (OL of 50 g COD / L) with adjustment of nutrient source in closed circuit mode (100 ohms resistance).

[0065] Finally, the continuous H2 productivity was observed in the range of 240 to 260 L and 0.45 to 0.55 kg SCFA (Acetic acid: 0.342 kg, and Butyric acid: 0.158 kg) compared to conventional process (H2: 194 L) per kg COD removed using TCP-FW at OL of 50 g COD / L with C / N ratio of 50 using urea as nitrogen source was obtained in the hybrid process by integrating acidogenic and electro-fermentation in a single reactor without using membrane and graphite as electrodes with self-induced buffering. The system operates with regulated buffering conditions. The process of the acetogenic microenvironment was controlled and regulated by induced air.

[0066] EXAMPLES

[0067] The following examples are given by way of illustration only and therefore should not be construed to limit the scope of the present invention in any manner.

[0068] Example 1 - Batch mode operation with UT-FW This invention focused initially on the batch mode operation to produce H2 with untreated food waste through acetogenesis. With OL of 50 g COD / L, maximum H2 production of 145 - 155 L per kg COD accounting for an H2 composition of 61% along with 39% CO2 co-generation was obtained. SCFA production of 25 - 25.77 g / L of SCFA composed of acetic (HAc: 15.2 ± 1.98 g / L), propionic (HPr: 4.89 ± 1.26 g / L) and butyric (HBu: 5.67 ± 0.96 g / L) acids was obtained at the end of cycle. The acidification potential was used to quantify the effectiveness of a batch mode system in converting the substrate into H2 and SCFA.

[0069] Further, the process was optimized in continuous mode operation. Table 1: Batch mode operation with UT-FW

[0070] Example 2 - Continuous mode operation with UT-FW

[0071] With optimized batch mode operation, the invention focused on continuous mode operation using untreated food waste (UT-FW) as a substrate at OL of 10 g COD / L for 40 days. This mode of operation leads towards higher bio-Fh production with respect to the fermentation time with cumulative H2 production (CBHP) of 2 to 2.06 L by the end of the experiment representing 51% of the total biogas. The invention later focused on operation at OL of 30 g COD / L. The total biogas production of the reactor gradually increased with fermentation time. The maximum biogas production reached 80 L / day by the end of the day, with an H2 yield of 32 L / day and an H2 content of 40% in the total biogas. Initially, total biogas was observed very low (40 L / day) with 12 L and 16 L of H2 yield on the 3rdand 6thday, then slowly increased to 80 L / day with the enhanced volume of H2 production on the 15thday of acidogenic operation. Finally, the bioreactor was fed with an influent COD concentration of 50 g / L of UT-FW as substrate. The COD concentration of 14 g / L was observed on the 9thday, with a very low removal efficiency. Maximum biogas production reached 60 L / day with an H2 yield of 24 L / day and an H2 content of 40% in the total biogas. Among all of these OLs, it was found that 30 g COD / L of OL was more suitable for enhancing maximum production compared to OLs with 10 and 50 g COD / L with UT-FW. Hence, the invention significantly increased the bio-H2 production with optimized COD load in a continuous mode of operation. Then, the process was optimized in continuous mode operation.

[0072] Table 2: Continuous mode operation with UT-FW

[0073] Example 3 - Continuous mode operation with TCP-FW

[0074] With the above (example-2) optimized condition of continuous mode operation, the invention further focused on using chemical-treated food waste (TCP-FW) as a substrate in the continuous mode operation. This invention with the TCP-FW process started at OL of 30 g COD / L leading towards higher bio-Fh production with respect to the fermentation time compared to UT-FW. The maximum biogas production reached 100 L / day with an Ph yield of 40-45 L / day and an H2 content of 45% in the total biogas. Then, the process was optimized at various OLs in continuous mode operation. Table 3: Optimized conditions with UT-FW results of continuous mode operation

[0075] Example 4 - Continuous mode operation with TCP-FW at various OLs

[0076] Based on example-3 with TCP-FW, this invention was focused on various flow rates (0.84 L / h (OL: 0.6 kg / d), 1.25 L / h (OL: 0.9 kg / d), and 1.5 L / h (OL: 1.08 kg / d)) using TCP-FW with constant COD of 30 g / L in continuous mode operation. The maximum H2 production reached 75.6 L / d at a flow rate of 1.5 L / h (OL: 1.08 kg / d) followed by 73.5 L / d at 1.25 L / h (OL: 0.9 kg / d), and 45 L / d at 0.84 L / h (OL: 0.6 kg / d) shown in Fig 2. However, the maximum H2 production observed was almost equal with a flow rate of 1.25 L / h (73.5 L) compared with a flow rate of 1.5 L / h (75.6 L) by the end of the day. Moreover, the maximum SCFA was also observed at 205 g / d with OL of 1.08 kg / d (1.5 L / h) followed by 140 g / d with OL of 0.9 kg / d (0.25 L / h), and 96 g / d with OL of 0.6 kg / d (0.84 L / h). COD removal efficiency was also observed with a flow rate of 1.25 L / h (OL: 0.9 kg / d). Finally, we concluded the continuous mode reactor's best flow rate was 1.25 L / h with TCP-FW as substrate. Later on, the process was optimized at various C / N ratios.

[0077] Table 4: Optimized conditions with TCP-FW results of continuous mode operation

[0078] Example 5 - Continuous mode operation with TCP-FW at C / N ratio

[0079] Based on example-4 with OL of TCP-FW, this invention was focused on the C / N ratio of substrate was adjusted with the addition of urea as a nitrogen source. The reactor was operated with varying C / N ratios of 30, 50, and 70 with different OLs in continuous mode operation. The maximum H2 production reached 208 L / d with a C / N ratio of 70 followed by 194 L / d H2 with a C / N ratio of 50, and 122.4 L / d H2 with a C / N ratio of 30. However, the maximum H2 production observed was almost equal with C / N ratios of 50 (H2: 194 L) and 70 (H2: 208 L) compared with the C / N ratio of 30 (H2: 122.4 L) by the end of the day shown in Fig 6. Moreover, the maximum SCFA was also observed at 444 g / d with a C / N ratio of 50 followed by 324 g / d with a C / N ratio of 70, and 247 g / d with a C / N ratio of 30. According to the maximum production of hydrogen with a C / N ratio, the reactor was further operated with graphite electrodes to enhance the production of hydrogen and fatty acids. Finally, the process was optimized by introducing electrode assembly in continuous mode operation.

[0080] Table 5: Continuous mode operation with TCP-FW at C / N ratio

[0081] Example 6 - Continuous mode operation with TCP-FW Using Electrodes

[0082] Finally, the continuous mode reactor was operated with non-sacrificial, conductive, and biocompatible (graphite) electrodes with the best conditions based on example-5 with a C / N ratio of TCP-FW. This invention was focused on the electro-biocatalytic process using graphite electrodes in continuous mode operation in up-flow mode without circulation. The reactor was operated at OL of 50 g COD / L of TCP-FW with C / N ratios of 50. The maximum H2 production was obtained in a range of 240 to 260 L / d with the hybrid process compared to conventional

[0083] 5 processes (H2: 194 L / d) shown in Fig 11. Moreover, the SCFA production was in the range of 0.45 to 0.55 kg / d (Acetic acid: 0.342 kg, and Butyric acid: 0.158 kg) with hybrid process compared to conventional processes (SCFA: 0.34 to 0.45 kg / d).

[0084] Table 6: Results of continuous mode operation with electrogenesis process

[0085] 10

[0086] Results of H2 and SCFA production using the claimed system and process

[0087] Table 7 illustrates the total biogas production observed at different flow rates (0.84, 1.25, and 1.5 L / h) using CPT-FW at a concentration of 30 g COD / L compared with UT-FW as a substrate in a continuous mode reactor. The system was operated continuously for 66 days under three 15 different flow rates (0.84 L / h, 1.25 L / h, and 1.5 L / h). During the initial days at a flow rate of

[0088] 0.84 L / h, TBG production was recorded at 60 L / day with UT-FW. Under the same flow rate of 0.84 L / h, TCP-FW resulted in a total biogas output of 180 L / day. When the flow rate was increased to 1.25 L / h and 1.5 L / h, the total biogas production was observed to be 120 L / day and 150 L / day, respectively.

[0089] 20 Table 7

[0090] Table 8 illustrates the total biogas composition observed at different flow rates (0.84, 1.25, and 1.5 L / h) using CPT-FW at a concentration of 30 g COD / L compared with UT-FW as a substrate in a continuous mode reactor. The biogas composition was observed at various flow rates using TCP-FW: 0.84 L / h (H2: 48%, CO2: 49%, CH4: 2%), 1.25 L / h (H2: 51%, CO2: 45%, CH4: 1%), and 1.5 L / h (H2: 50%, CO2: 47%, CH4: 3%). The maximum percentage of H2achieved was 51% at a flow rate of 1.25 L / h, followed by 50% at 1.5 L / h and 48% at 0.84 L / h. In contrast, using UT-FW, the H2percentage observed was 39% at a flow rate of 0.84 L / h.

[0091] Table 8

[0092] Table 9 illustrates the COD variation at different flow rates (0.84, 1.25, and 1.5 L / h) using CPT-FW at a concentration of 30 g COD / L compared with UT-FW as a substrate in a continuous mode reactor. The COD removal was observed at flow rates of 0.84, 1.25, and 1.5 L / h with constant OL (30 g / L) of TCP-FW. The maximum COD removal of 22 g / L (73%) was observed at a flow rate of 1.25 L / h, followed by 18 g / L (60%) at a flow rate of 0.84 L / h, 18 g / L (60%) at a flow rate of 1.5 L / h with TCP-FW, and 16 g / L (53%) at a flow rate of 0.84 L / h with UT-FW. Table 9

[0093] Table 10 illustrates the VFA production observed at different flow rates (0.84, 1.25, and 1.5 L / h) using CPT-FW at a concentration of 30 g COD / L compared with UT-FW as a substrate in a continuous mode reactor. The highest VFA production of 6.65 g / L was observed at a flow rate of 1.25 L / h, which was 2.25 times higher than the UT-FW (2.87 g / L at 0.84 L / h), 1.86 times higher than at 1.5 L / h, and 1.35 times higher than at 0.84 L / h. Therefore, at flow rates of 0.84, 1.25, and 1.5 L / h, VFA concentrations were 3.36 g / L, 6.65 g / L, and 5.56 g / L respectively, representing increases of approximately 2.25, 1.86, and 1.35 times compared to the UT-FW.

[0094] Table 10

[0095] Table 11 illustrates the total biogas production from various organic loadings (OL) of CPT- FW at different C / N ratios, which were adjusted using urea as a nutrient source and without urea. The maximum TBG production of 300 L / day was recorded at an OL of 50 g COD / L, 5 followed by 240 L / day at 30 g COD / L, and 220 L / day at 70 g COD / L. A comparative analysis revealed a substantial increase in hydrogen production from 240 L / day to 300 L / day as the OL increased from 30 g COD / L to 50 g COD / L.

[0096] Table 11

[0097] 10

[0098] Table 12 illustrates biogas composition from various OL of CPT-FW at different C / N ratios, which were adjusted using urea as a nutrient source and without urea. Biogas composition analysis revealed that at an OL of 50 g COD / L, bioFL constituted 51%, CO243%, and CH42%. Similarly, at 30 g COD / L, bioFL accounted for 51%, CO243%, and CH4 3%. At the higher OL 15 of 70 g COD / L, the biogas composition shifted slightly to 48% bioFL, 49% CO2, and 2% CH4.

[0099] BioFh production was consistently highest at an OL of 50 g COD / L across the conditions tested. The biogas production increased progressively during the fermentation period, reaching a maximum yield of 300 L / day, with a bioFL content of 51% and CO2 contributing 43% of the total gas. Initially, bioFh production was lower (39%) without nitrogen supplementation, but 20 after optimizing the nitrogen source in TCP-FW, bioFL production increased to 51% at 50 g

[0100] COD / L.

[0101] Table 12

[0102] Table 13 illustrates the VFA Production from various OL of CPT-FW at different C / N ratios, 25 which were adjusted using urea as a nutrient source and without urea. The highest VFA concentration was observed at an OL of 50 g COD / L (426 g / d), followed by 70 g COD / L (312 g / d) and 30 g COD / L (246 g / d) with nitrogen supplementation. In contrast, operating at 30 g COD / L without a nitrogen source resulted in a significantly lower VFA concentration of 89 g / d. The enhanced VFA production at OLs of 50 and 70 g COD / L can be attributed to an enriched acidogenic microbial population and increased substrate availability.

[0103] 5 Table 13

[0104] Table 14 illustrates the variation of nitrate, phosphates, and sulphates from various OL of CPT- FW at different C / N ratios, which were adjusted using urea as a nutrient source and without urea. During the first 17 days, the nitrate concentrations decreased slightly, reaching 400 mg / L at OL 30 g / L and 350 mg / L at OL 50 g / L. This decrease likely indicates that the complex 10 polysaccharides in TCP-FW were processed slowly and inefficiently by the microbial community. With the addition of urea as a nitrogen source, the outlet nitrate concentrations decreased to 150 mg / L, 249 mg / L, and 287 mg / L at OLs of 30, 50, and 70 g / L, respectively.

[0105] Table 14

[0106] 15 Table 15 illustrates the variation of inlet and outlet COD from various OL of CPT-FW at different C / N ratios, which were adjusted using urea as a nutrient source and without urea. The highest COD removal of 32 g / L (64%) occurred at an OL of 50 g COD / L, followed by removals of 36 g / L (51%) at 70 g COD / L, 26 g / L (86%) at 30 g COD / L with nitrogen supplementation, and 18 g / L (60%) at 30 g COD / L without nitrogen adjustment (control). At an influent COD 20 concentration of 30 g COD / L, the effluent COD dropped to 4 g / L, resulting in an approximately 86% removal efficiency. At 50 g COD / L, the effluent COD was reduced to 18 g / L, achieving about 64% removal. However, at 70 g COD / L, the effluent COD increased to 34 g / L, corresponding to a 51.3% removal efficiency.

[0107] 25 Table 15

[0108] Table 16 illustrates the total biogas production observed without and with graphite electrodes in the continuous mode operation system. The biogas production in systems with and without electrodes. In the control system, biogas production reached 420 L / d due to the absence of 5 external electron transfer led to suboptimal metabolic efficiency, limiting bioFL production and reducing the effective utilization of organic substrates. In contrast, the introduction of electrodes into the electro-acidogenesis system increased biogas and bioFL production to 480 L / d and 260 L / d respectively, with the H2 fraction rising to 52%. This improvement can be attributed to the role of electrodes in maintaining redox balance, particularly favouring 10 hydrogen-evolving reactions.

[0109] Table 16

[0110] Table 17 illustrates the variation in biogas composition observed without and with graphite 15 electrodes in the continuous mode operation system. In the control system, biogas composition of 47% CO2 and 51% H2. The shift in biogas composition from 46% H2 in the control system to 52% H2 in the electro-acidogenesis system underscores the significant impact of the electrochemical intervention, with CO2 and CH4 concentrations remaining lower than in the control system.

[0111] 20 Table 17

[0112] Table 18 demonstrates the production of VFA, observed both without and with graphite electrodes in the continuous fermentation process. In the electro-acidogenesis system, the VFA concentration reached 18.5 g / L, compared to 14.82 g / L in the control system. The introduction 25 of electrodes resulted in a significant 20% increase in total VFA concentration during continuous operation. Specifically, in the electro-acidogenesis system, HAc emerged as the dominant VFA, reaching 11.4 g / L, followed by HBu at 5.27 g / L and HPr at 1.9 g / L. In contrast, the control system exhibited lower concentrations of HAc (7.55 g / L), HBu (3.84 g / L), and HPr (2.28 g / L).

[0113] Table 18 Table 19 depicts the variation in inlet COD and outlet COD, both observed with and without graphite electrodes in the continuous mode system. Additionally, variations in COD removal are evident throughout the fermentation process. The impact of electro-acidogenesis on COD removal was evaluated by comparing systems with and without electrodes. In the control system, a maximum COD reduction of 68% (34 g / L) was achieved by the 12th day, with an initial COD removal of 56%. However, the electro-acidogenesis system outperformed the control, achieving a higher COD reduction of 80% (40 g / L) on the 20th, 28th, and 33rd days. The enhanced performance of the electro-acidogenesis system can be attributed to improved electron transfer. Consequently, the electro-acidogenesis system achieved an 80% COD reduction, significantly exceeding the 68% observed in the control system.

[0114] Table 19

[0115] ADVANTAGES OF THE INVENTION • Continuous mode operation for sustained performance.

[0116] • Utilizes a fixed-film reactor configuration for efficient processing.

[0117] • Employs thermochemically pretreated food waste (TCP-FW) as a sustainable substrate.

[0118] • Operates in up-flow mode without the need for external circulation.

[0119] • Features in-situ buffering to regulate the redox environment within a single-stage bioreactor. • Operates without the need for membranes, simplifying the design and reducing costs.

[0120] • Incorporates non- sacrificial, conductive, and biocompatible electrodes for enhanced performance and durability.

[0121] • Integrates acidogenic fermentation with electro-fermentation in a hybrid process within a single reactor.

Claims

WE CLAIM:

1. A continuous mode operating system for the production of hydrogen and C2-C4 short chain fatty acids (SCFA) from thermochemical pre-treated food waste comprising: a vertical cylindrical reactor having length and diameter ratio of 10:1, inlet port (3), outlet port (7), multiple sample ports (4), inlet feed tank (1), inlet feed pump (2), sampling port (4), gas holding capacity (5), gas collecting bag (6), gas collecting ports (12), effluent tank (8), anode electrode (9), cathode electrode (10), and poly propylene rings (11).

2. The system as claimed in claim 1, wherein the cylindrical reactor’s inlet port (3) is connected to the inlet feed tank (1) through inlet feed pump (2).

3. The system as claimed in claim 1, wherein the outlet port (7) is connected to effluent tank (8).

4. The system as claimed in claim 1, wherein the gas collecting bag (6) is connected to the reactor through a gas collecting port (12).

5. The system as claimed in claim 1, wherein non-sacrificial conductive and biocompatible electrodes (9) and (10) are incorporated into the system to facilitate electro -biocatalytic processes. An wherein the anode (9) and cathode (10) are connected using copper wire and a 100-ohm resistor.

6. The system as claimed in claim 1, wherein the anode electrode (9) and cathode electrode (10) are selected from graphite, stainless steel, activated carbon cloth, either alone or in combination thereof.

7. A process for the production of hydrogen and C2-C4 short chain fatty acids (SCFA) from thermochemical pre-treated food waste via the continuous operating system as claimed in claim 1, wherein the steps comprising:(a) homogenizing the food waste to form a uniform mixture;(b) pre-treating the homogenized food waste as obtained in step (a) with 1% base at a temperature of 60 to 80 degree C for 30 minutes to obtain a mixture;(c) allowing the mixture obtained in step (b) to settle and separating the solid waste at the bottom, while retaining the supernatant in the inlet tank (1) as the feedstock;(d) inoculating the pre-heated mixed microbial culture for the growth of Hydrogen producing bacteria added to the reactor from the top inlet (13) followed by addition of polypropylene rings (12)(e) transferring the feedstock obtained in step (c) into the reactor of step (d) from the inlet tank (1) containing microbial inoculum under anaerobic conditions using an inlet feed pump (2) with a flow rate ranging from 0.84 L / h to 1.5 L / h with various organic loads selected from 30, 50, and 70 g COD / L and nitrogen sources;(f) moving the injected feed in an up-flow direction in the reactor, to facilitate acidogenesis to produce hydrogen and C2-C4 short chain fatty acids (SCFA);(g) collecting the hydrogen gas in a gas collecting bag (6), and C2-C4 short-chain fatty acids (SCFA) in the effluent tank (8).

8. The process as claimed in claim 7, wherein the base used in step (b) is selected from hydroxides of alkali and alkaline earth metals and the nitrogen source in step (e) is selected from urea, NaNCh, and KNO2.

9. The process as claimed in claim 7, wherein pre-heated microbial culture in step (d) is selected from culture dominated by Staphylicoccus sciuri / Mammalicoccus sciuri MTCC13609, Bacillus subtilis MTCC13610, Bacillus velezensis MTCC13611.

10. The process for the production of Hydrogen gas and C2-C4 short-chain fatty acids (SCFA) as claimed in claim 6 wherein the flow rate in step (v) is 1.25 L / h.

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