A bi-phasic solid-state anaerobic digester system for the generation of biogas with methane (bi-ads>90%ch4)

Abstract

The present invention discloses a bi-phasic anaerobic digestion (AD) system [100] designed to produce biohydrogen, biohythane, and high-purity biogas with at least 90% methane content from various organic wastes, including lignocellulosic biomass. This system utilizes a single, closed, horizontal cylindrical reactor with two chambers: acidification chamber I and biomethanation chamber II. It facilitates high-pressure solid-state AD through optimal supplementation of nutrient nanoparticles and bioaugmented inoculum. The system's novel design, featuring a central duct, cones, and perforated plates, ensures efficient mixing and heat and mass transfer. The system can also generate biohythane, containing 15-25% hydrogen and 75-85% methane, by controlling the flow of gases between chambers. Additional features include micro-aeration to enhance hydrolysis, gravity settling chambers for slurry withdrawal, controlled gas passage between chambers to optimize methane production, and a programmable logic controller (PLC) for automated pH, temperature monitoring, and process control.

Description

[0001] A BI-PHASIC SOLID-STATE ANAEROBIC DIGESTER SYSTEM FOR THE GENERATION OF BIOGAS WITH METHANE (Bi-ADS >90%CIl4)

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a bi-phasic anaerobic digester system [(Bi-ADS >90% CH4)] in a single horizontal closed cylindrical vessel having two chambers (Chamber I and Chamber II). Particularly, the present invention relates to an operational process strategy for the generation of biogas with more than 90 % methane from organic wastes. More particularly, the present invention relates to the generation of biohydrogen with 80 to 85 % purity (by operating acidification chamber I only) and biohythane which is a mixture of 15 to 25% H2 and 75 to 85 % CH4.

[0004] BACKGROUND OF THE INVENTION

[0005] This invention relates to an advanced method for the bi-phasic AD of various organic wastes for the generation of biohydrogen, biohythane and biogas with > 90 % CH4. After the advent of indigenous high-rate AD systems, the limitations such as low volatile solids loading and degradation rate, longer residence times, methane content in the range of 58 - 62 % in biogas present in the conventional as well as the existing high-rate anaerobic digesters have been addressed. However, even the high-rate AD systems still suffer from the generation of biogas with low methane content. Therefore, the present invention is related to the development of a bi-phasic anaerobic digester system by incorporating novel operational strategies so that the methane in biogas can be improved from 58 - 62 % to above 90 %. Integrating the novel operational strategies not only enhances the methane content in biogas, biohydrogen and biohythane production but also improves the volatile solids degradation rate, lowers residence time and increases the product yield and improves the process efficiency.

[0006] References may be made to Patent US4985149, which describes the anaerobic digestion method. This patent describes the pretreatment of sewage sludge or an agricultural or fish waste material in the form of a wet mill followed by the biomethanation of the pretreated waste. The wet mill pretreatment is applied primarily as a shear force on solids which are suspended in water so as to refine them. The wet mill pretreatment includes rotating cylinder mill, a vibrating ball mill, a centrifugal ball mill, a medium stirring mill, a colloid mill etc. The pretreatment is suitable for wastes like high solids sludge, agriculture wastes where the wastes are extensively crushed into fine particles that can be easily utilized as a substrate by anaerobic bacteria. References may be made to PCT Publication No. W02007 / 075762 A2, which describes the anaerobic phased solids (APS) digester for biogas production from organic solid wastes. Further, it also provided a device for the practice of the methods of the invention. This invention is an APS -digester system which is space-efficient, high-rate solids digestion system. The APS digester system comprises of one or more hydrolysis reactors, a buffer tank and biogasification reactor. The existing single phase AD systems in which the organic substrate and the microorganisms are housed together for ease of operation and economic benefits, but these systems generate biogas with 30 - 35 % carbon dioxide. The high carbon dioxide content of the biogas is attributable to the slow growth of methanogenic microorganisms and their inhibition by high concentrations of volatile fatty acids (VFA) as intermediates. Therefore, the high carbon dioxide in biogas and VFA in the slurry as intermediate is the main reason for low methane in biogas and instability of the digester. Therefore, the single stage system is bifurcated into two phase system by separating the hydrolysis part of the process in a separate reactor to enhance the conversion efficiency. The organic substrate is fed to the hydrolytic reactor, where the VFAs are formed in the slurry and the product gas rich in H2 and CO2 is generated. The product gas that is produced in the biogasification reactor of the system is processed or scrubbed to separate the methane component. The effluent from the hydrolytic reactor is transferred to the biogasification reactor for biogas generation which is a mixture of CH4 and CO2. The buffer tank is used to mix the effluent from hydrolysis tank and the biogasification reactor for recirculation.

[0007] References may be made to Patent US6342378 Bl, which describes the anaerobic-phased solids digester system (APS -digester) for biogasification of solid waste (straw) at different pretreatment temperatures (60 °C, 90 °C, 110 °C) at a solid loading rate of 50 g / L. To address the limitations of single stage reactors and one among them is to reduce the inhibition of the microorganisms by the VFAs, the two-phase digester has been introduced. The process comprises incubating a first mixture have a solid organic component and an aqueous liquid component under anaerobic conditions, in a hydrolysis digester having an upper portion and lower portion and containing a hydrolysis means. After a period of incubation, a portion of the liquid is transferred to the methanogenic reactor. The apparatus also consists of a methane collection port. The pH in the hydrolysis reactor is maintained between 4.5 and 6.5 while the pH in biogasification reactor is maintained between 6.5 and 7.5. The hydrolysis reactor is operated in batch or semi-batch mode to ease the handling of solid materials while the biogasification reactor is operated continuously to maintain active bacterial culture in the system for the production of biogas at a relatively constant level. References may be made to US Patent Application No. 20020079266 Al, which describes the integrated anaerobic digester system. This invention provided a system for converting cellulose-containing feedstock into useful materials. The system comprises of a slurry feeder, pressurizable anaerobic digester with a means for agitation, ports for feed and discharge. The digester is preferably operated at pressures between 10 to 265 psi, more preferably between 10 and 100 psi. The pressure inside the reactor system is created by an external pressurizer using external compressed gas source. The system also comprises of gas scrubbers, heaters, preheating mechanism for slurry, slurry tanks, water storage tanks, supernatant tanks, sludge storage tanks, dryers, scum storage tanks, CO2 tanks. The digester in this system is fed with high solids up to 90 % wt. more preferably about 1 - 40 % wt. solids. The integrated system has a facility to recirculate the scum, separate the CO2 or ammonia gas from the discharge gas line.

[0008] References may be made to US Patent Application No. US 2021 / 0079340 Al, which describes the development of microbial consortium for enhancing the methane production from feedstock. In particular, this invention relates to the development of a novel enviro -tolerant methane-producing microbial consortium and a method for the production of biogas having high methane. The microbial consortium developed in this invention produces stable biogas without any seasonal variation impact. The microbial consortium is thermophilic, microaerophilic and salinity tolerant in nature and comprises of acetoclastic methanogens, hydrogenotrophic methanogens, methanotrophic methanogens and electroactive bacteria. The acetoclastic methanogens comprised of Desulfovibrio sp. (IOC-2), Brevibacterium sp. (IOC- 5), Methanothermobacter sp. (IOC-12), Methanolobus sp. (IOC-6), Thermotoga sp. (IOC-8). The hydrogenotrophic methanogens consists of Methanosarcina sp. (IOC-1), Clostridium sp. (IOC-3), Methanobacterium sp. (IOC-4) and Lactobacillus sp. (IOC- 11). The methanotrophic archaea comprised of Methanosaeta sp. (IOC-7), Moorella sp. (IOC- 10), and Lactobacillus sp. (IOC-11). The electroactive bacterium comprised of Clostridium sp. (IOC-3), Methanosaeta sp. (IOC-7), Pyrococcus sp. (IOC-7) and Shewanella sp. (MTCC 25020). The listed species were used to develop the microbial consortium that were provided with buffering agents, growth stimulating nutrients, electron donors, and their combinations. The developed microbial consortium is effective at a temperature range of 5 - 65 °C, pH of 4 - 10 and salinity of 0 - 5 %. Using the microbial consortium, the biogas having 80 - 90 mole % of CH4 and less than 10 mole % of CO2 can be produced. References may be made to US Patent 4722741, which describes the production of high methane content [more than 90 %] product gas by two phase anaerobic digestion. Production of product gas by lowering the CO2 content under pressurized conditions to achieve higher conversion efficiency rates and high methane. The CO2 produced during the anaerobic digestion process may be physically and chemically separated and removed thereby reducing the overall CO2 content in the product gas. The system consists of two reactors namely acetogenic reactor and methanogenic reactor. The acetogenic reactor results in the generation of high CO2 containing gas while the methanogenic reactors produce high methane containing gas. There is an air stripping unit in between the two reactors which is used to strip the high CO2 content gas generated from the acetogenic reactor and the outlet from the stripping unit is passed through the methanogenic reactor.

[0009] References may be made to Patent US4735724, which describes the solids concentrating anaerobic digestion process and apparatus. This innovation is providing a process and an apparatus for AD of feedstocks containing biodegradable solids wherein the passive concentration of solids in the range of 1 to about 100 % from feed and microorganisms occurs in an upper portion of the digester. This invention also helps in reducing or eliminating the supplemental nutrient requirements and eliminate scum formation by recycling a small portion of the digester contents withdrawn from the middle to bottom of the digester to the surface of the reactor contents without disturbing the solids concentration gradient established in the reactor. Liquids and non-biodegradable components tend to accumulate in the middle and bottom of the digester, and digester effluent is withdrawn from the middle to the bottom of the reactor. Due to this, the upper solids have longer retention time while the middle compartment solids have shorter retention time. This process and apparatus help in achieving 90 % bioconversion efficiency and approximately 20 to 25 % more methane in the product gas compared to the conventional stirred tank reactors.

[0010] References may be made to PCT Publication No. W02008 / 094282 Al, which describes the system for the production of methane from CO2 in a bioreactor containing methanogenic archaea to catalyze the chemical reaction where 1 mole of CO2 reacts with 4 moles of H2 to produce 1 mole of methane and 2 moles of H2O. The microbial species used in the culture are Methanococcus maripaludis and Methanosarcina barkeri. This invention reveals that 4: 1 mixture of H2 and CO2 gases can be provided at a total flow rate of 0.1 L gas per L culture per min to > 1.0 L / (L.min) resulting in more than 95 % of the CO2 converted to methane and the rest of the CO2 is converted in the input being converted to cellular biomass. The gas was passed over a palladium catalyst in the bioreactor. References may be made to Patent US 9416373 B2, describes the biogas production from organic wastes using metallic nanoparticles in the bioreactor. The inventors of this patent found that the addition of iron oxide (FC3O4) nanoparticles in the bioreactor increased biogas generation from organic wastes. Addition of colloidal solution of the surface modified iron oxide nanoparticles with a size in the range of 3 nm to 100 nm in the bioreactor for increased biogas generation. The concentration of iron oxide nanoparticles in the solvent phase is between 0.6 and 0.9 mg / mL.

[0011] References may be made to Patent AU2014200009 B2, which describes the anaerobic gas lift reactor for treatment of organic waste. This invention presents an embodiment namely Anaerobic Gas lift Reactor comprising of three compartments namely bottom, middle and top. This reactor is developed substantially to overcome one or more disadvantages present in the conventional anaerobic reactors. The reactor is provided with downer to ensure downward movement of the liquid based on differential pressure in the compartments. The reactor is provided with three phase separation mechanism for the separation of solids, liquids and a gaseous separation zone. The reactor is provided with feeding arrangement, digestate withdrawal ports, biogas collection as well as biogas (pressurized gas from pressure tank) and slurry recirculation (from ports of the compartment or drain ports) periodically in the digester to ensure efficient mixing. The reactor can be extensively used to treat the biodegradable wastes containing low solids and C / N ratio.

[0012] The above state-of-the-art literature through patents disclosed that high pressure AD, biphasic AD, application of nanoparticles, solid-state AD and mixed microbial consortia are some of the operational strategies that are known to enhance the efficiency, product and the process yield. However, the main limitations in the above state-of-the-art literature (US4985149) is the use of single stage reactor suitable for selective organic wastes for the generation of biogas with < 90 %. W02007 / 075762 A2 although disclosed a two-stage AD system but the CH4 is obtained by scrubbing the CO2 externally. In addition, the product gas (mixture of CO2 and H2) from hydrolytic chamber is not utilized efficiently. US20020079266 A 1 describes a reactor that is operated under high pressure ranging between 10 and 265 preferably between 10 and 100 psi (0.68 to 6.8 bar) but the pressure inside the reactor is created through an external pressurizer. US4722741 describes a two-stage AD system for the generation of 90 % CH4 but the main drawback is that the CO2 is scrubbed using chemicals and the CO2 from acetogenic chamber is stripped and then passed to methanogenic reactor. US473524 and AU20142000009 B2 describes a single stage reactor system where the product gas is biogas with less than 90 % CH4. The main drawback in the patent US 9416373 B2 is the use of single metallic nanoparticles of iron oxide (FC3O4) passed over palladium catalyst which may not be economical in the practical application.

[0013] The present invention offers a major advantage i.e., the production of biogas with 90 % methane, biohydrogen and biohythane as main products from various organic wastes in a biphasic AD system which is one of the major limitations in the above cited state-of-the-art. Further, the present invention is operated under auto-generative high pressure up to 14 bar instead of using external pressurizers; supplemented with numerous micro (composite nanoparticles) and macro nutrients (granular activated carbon and sodium acetate). Specially developed bioaugmented acidogenic mixed microbial consortia and bioaugmented methanogenic mixed microbial consortia are used to produce the product gases. The product gases i.e., mixture of CO2 and H2 are efficiently utilized either as a product or is directly utilized for CH4 generation in the bi-phasic system. The reactor design ensures the movement of slurry towards upward flow regime and the auto-generative gas (H2 & CO2) pressure in the reactor facilitates the movement of slurry towards top and the baffles in chamber I ensures the retainment of maximum solids below the baffle and allows the acidified liquid rich in VFAs to flow towards the gravity settling chamber I. Micro aeration facility in chamber I, pH sensor, chemical dosing tank, PLC controlled system are some of the added advantages in the present invention.

[0014] OBJECTIVE OF THE INVENTION

[0015] The main objective of the present invention is to provide a bi-phasic anaerobic digester system

[0100] , [(Bi- ADS >90% CH4)].

[0016] Another object of the present invention is to provide a process to produce biogas with more than 90 % methane from various organic wastes in a bi-phasic anaerobic digester (AD) system. Yet another object of the present invention is to provide a process for the generation of biohydrogen with 80 to 85 % purity from acidification chamber I.

[0017] Yet another object of the present invention is to provide a process for the generation of biohythane which is a mixture of 15 to 25% H2 and 75 to 85% CH4 in which mixture of CO2 and H2 is withdrawn from chamber I, while the CO2 and CH4 are withdrawn from chamber II for the production of biohythane.

[0018] Yet another object of the present invention is to provide a process for the generation of biogas with more than 90 % CH4 from high solids (solid-state AD) organic waste and the improvement of CH4 in biogas by lowering the CO2; improving the volatile solids reduction rate by operating it under auto-generative high pressure, and the production of maximum product gas yield by the supplementation of additives at optimum dosages and the usage of bioaugmented microbial consortia (culture I and culture II) in a bi-phasic AD system comprising of two chambers.

[0019] Yet another object of the present invention is to provide solid-state AD of organic wastes including agriculture waste at a total solid’s consistency between 20 and 40 %.

[0020] Yet another object of the present invention is to provide a process for the generation of output gas stream I from the chamber I which is passed to chamber II at a controlled flow rate of 0.1 L / min to enhance the conversion of CO2 to CH4 (biogas or biohythane production). Controlled introduction of H2 and CO2 (4: 1 ratio) from chamber I to chamber II for the conversion of CO2 to CH4 to eliminate external purification / separation steps.

[0021] Yet another object of the present invention is to provide a process with variation in hydraulic residence time (HRT) of chamber I (5 - 8 days) as well as the chamber II (22 - 30 days) depending on the type of substrate and co-substrate used for digestion and elimination of rapid acidification phenomena that usually happens in a single reactor with feedstocks like food waste.

[0022] Yet another object of the present invention is to provide a process in which micro -aeration facility through an air sparger in chamber I of the reactor is provided to enhance rapid acidification phenomena of organic wastes.

[0023] Yet another object of the present invention is to provide a central duct extended towards the bottom with a cone ensures the movement of slurry towards upward flow regime and the perforated plate facilitates the overflow of digested low-density materials in chamber II (gravity settling tank II) to the digestate collection tank while retaining the solids below the perforated plate.

[0024] Yet another object of the present invention is to provide higher volatile solids destruction in the bi-phasic AD system in addition to the production of VFAs, H2 and CO2 as intermediate products and biogas with 90 % CH4 and the digestate as the final product.

[0025] Yet another object of the present invention is to provide culture II abundant in hydrogenotrophic methanogens which is developed by using H2 and CO2 as feed and enriched in suitable media solution. The developed culture II is supplemented with sodium acetate at a dosage of 3.6 g / L which not only acts as a buffer agent but also as precursor feed to the methanogens.

[0026] Yet another object of the present invention is to provide the supplementation of additives i.e., the composite nanoparticles at an optimum dosage of 150 mg / L including the macro nutrient granular activated carbon at a dosage of 1 g / L. The composite nanoparticles comprised of FcsCL. C0CI2, NiCb, and MoOs were synthesized through chemical co-precipitation method. Yet another object of the present invention is the generation of biogas from chamber II containing more than 90 % CH4 and its partial recirculation to chamber II using a gas sparging mechanism to ensure effective mixing and mass transfer.

[0027] Yet another object of the present invention is the recirculation of final digestate from the chamber II to the buffer tank for enhanced buffering and utilization of unconsumed additive material.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Fig. 1 represents bi-phasic anaerobic digester system

[0100] for the generation of biohydrogen, biohythane and biogas with atleast 90% methane.

[0030] Fig. 2 represents experimental set up for the production of biohythane.

[0031] SUMMARY OF THE INVENTION

[0032] The present invention provides a bi-phasic solid-state anaerobic digester system

[0100] (Bi- ADS >90%CH4) comprising: i. a crusher / grinder

[0001] ; ii. a feed tank [2]; iii. closed horizontal cylindrical vessel called reactor [3] comprising acidification chamber I and biomethanation chamber II; wherein the chamber I and chamber II are further provided with gravity settling chambers I [7] and II

[0011] respectively; iv. a central duct with inverted cone [5] and baffles [6] in chamber I; v. a central duct passing through the perforated plate

[0010] with two inverted cones [8] and [9] in chamber II; vi. a buffer tank

[0012] vii. an intermediate gas storage tank

[0015] ; viii. an air compressor

[0014] ; ix. a gas compressor

[0016] ; x. a H2S scrubber

[0017] ; xi. a H2O trap

[0018] ; xii. a biogas receiver

[0019] ; xiii. an air sparger

[0024] and gas sparger

[0025] ; xiv. sample collection ports [28 and 30]; xv. H2 and CCh / biogas transfer lines

[0016] through gas sparger

[0025] ; xvi. feeding pumps / lines [4 and 13]; xvii. main drain ports [27 and 29] ; xviii. digestate collection tank

[0020] ; xix. programmable logic controller

[0026] .

[0033] In an embodiment of the present invention provides that the programmable logic controller

[0026] further comprising an automatic pH sensors

[0021] a thermocouple

[0022] ; a chemical dozing tank

[0031] ; pressure gauges

[0023] and gas flow controllers

[0031] .

[0034] In another embodiment of the present invention provides that the acidification chamber I and biomethanation chamber II in the reactor is controlled through a programmable logic controller

[0026] ,

[0035] In yet another embodiment discloses an acidification chamber I is suitable for the generation of biohydrogen with 80 to 85 % purity and biomethanation chamber II is suitable for the generation of biogas with at least 90% methane from organic wastes. Biohythane can also be produced from the reactor having 15 - 25 % H2 and 75 - 85 % CH4.

[0036] In yet other embodiment discloses the reactor is operated in batch mode at high auto-generative pressure in the range of 25 to 30 bar while in semi continuous and continuous mode of operation the maximum auto-generative pressure is up to 14 bar in both the chambers

[0037] In other embodiment of the present invention discloses a culture I and culture II further comprising a bioaugmented acidogenic mixed microbial consortia and a bioaugmented methanogenic mixed microbial consortia respectively.

[0038] In yet another embodiment provides a process for bi-phasic anaerobic digestion of organic wastes using reactor as claimed in claim 1, wherein the process comprising the steps of: i. crushing / grinding the feed in the crusher / grinder [1] and followed by diluting with water to obtain a dense slurry with 20 to 40 % solids; ii. feeding the dense slurry as obtained in step (i) from the feed tank [2] to chamber I; iii. inoculating the chamber I with culture I having relative abundance of hydrolytic bacteria and acidogens while maintaining the pH between 6 and 6.5 to obtain an output gas stream I containing 80 - 85 % H2; 15 - 20 % CO2 on volume basis and acidified slurry; iv. allowing microaeration in the acidified slurry as obtained in step (iii) in chamber I to obtain acidified volatile fatty acids (VFAs) rich slurry followed by transferring the acidified VFA rich slurry having 40 - 50 g / L of VFA containing 20 to 30 % solids from gravity settling chamber I [7] to buffer tank

[0012] through valve mechanism; v. supplementing the acidified VFA rich slurry as obtained in step (iv) in the buffer tank with sodium acetate at a dosage ranging between 2.6 to 3.6 g / L and chemicals from chemical dozing rank

[0031] to ensure the increase in pH to 7.0 along with partial recycling of digestate that is collected into the digestate tank

[0020] from gravity settling chamber II

[0011] to obtain neutralized slurry; (the acidified slurry rich in VFAs will be at a pH less than 4.5 and this slurry is adjusted to a pH 7.0 using an alkali solution is called the neutralized slurry). vi. pumping the feed slurry as obtained in step (v) from the buffer tank

[0012] to chamber II through pumping mechanism; vii. inoculating the chamber II with the culture II having higher relative abundance of acetoclastic and hydrogenotrophic methanogens; viii. supplementing the culture II in chamber II with composite nanoparticles;

[0039] (ix) partially passing the output gas stream I generated from chamber I to chamber II in 4: 1 ratio at a controlled flow rate ranging between of 0.1 to 0.25 L / min for the conversion of CO2 in the gas to CH4 by the utilization of H2 by hydrogenotrophic bacteria / methanogens inside chamber II and for the conversion of CO2 that is generated inside chamber II to CH4 by the utilization of H2 that is passed from chamber I to chamber II;

[0040] (x) maintaining the auto-generative pressure in the range between 1 to 14 bar in both the chambers I and II to obtain biogas with CH4 and the digestate as the final product.

[0041] (xi) alternatively, utilizing the H2 and CO2 from chamber I and CO2 and CH4 from chamber II to produce biohythane with a composition of 15 - 25 % H2 and 75 - 85 % CH4.

[0042] In another embodiment provides the composite nanoparticles are selected from group comprising Iron nanoparticles (FesCU), Cobalt nanoparticles (C0CI2), Molybdate nanoparticles (MoOs), nickel nanoparticles (NiCh) and Zinc Oxide nanoparticles (ZnO).

[0043] In yet another embodiment of the present invention discloses the residence time required for the substrate to be converted to VFAs, H2 and CO2 in chamber I is between 5 - 8 days. The yet other embodiment discloses the residence time required for the conversion of biodegradable material in chamber II to biogas is between 22 and 30 days depending on the type of substrate and co-substrate digested.

[0044] The yet another embodiment discloses the chamber I and II is maintained at a temperature in the range of 30 to 40°C for mesophilic digestion and at a temperature in the range of 50 to 60°C for thermophilic digestion. DETAILS OF THE BIOLOGICAL MATERIAL USED

[0045] Source and origin of the biological material used in the present invention are also follows The bioaugmented acidogenic mixed microbial consortia used in the present invention was developed using food waste as a substrate and the seed inoculum was sourced from an existing single stage anaerobic digester (AU20142000009 B2) operated with food waste in CSIR-Indian Institute of Chemical Technology (IICT), Uppal road, Tarnaka, Hyderabad 500007, Telangana State. The consortia was subjected to heat shock, acid and alkali pretreatment to enhance the abundance of hydrolytic and acidogenic microorganisms at a pH ranging between 4.5 and 5.5. The developed inoculum was used in the acidogenic chamber I of the present invention for the maximization of volatile fatty acids (VFA) in the slurry and generation of output gas stream I (mixture of H2 and CO2). This inoculum is referred to as “Culture I” from here on.

[0046] The bioaugmented methanogenic mixed microbial consortia used in the present invention was developed using the seed inoculum sourced from an existing anaerobic digester in CSIR- Indian Institute of Chemical Technology (IICT), Uppal road, Tarnaka, Hyderabad 500007, Telangana State. Food waste was acclimatized and a mixture of H2 and CO2 was passed in the ratio of 4: 1 to enhance the relative abundance of acetoclastic and hydrogenotrophic methanogens at a pH of 7.0. The developed inoculum was used in the methanogenic chamber II for the generation of output gas stream II (biogas containing 90 % methane or biohythane). This inoculum is referred to as “Culture II” from here on.

[0047] DETAILED DESCRIPTION OF THE INVENTION

[0048] Present invention provides a bi-phasic anaerobic digester system suitable for the generation of biogas with more than 90 % CH4 as the main product biohydrogen with 80 to 85 % purity (by operating acidification chamber I only) and biohythane which is a mixture of 15 to 25% H2 and 75 to 85% CH4 (by operating acidification chamber I and biomethanation chamber II and collecting the H2 & CO2 from chamber I and CH4 & CO2 from chamber II from organic wastes). The present invention relates to a bi-phasic anaerobic digester system

[0100] in a single horizontal closed cylindrical vessel comprising of two chambers: i. Acidification chamber I; ii. Biomethanation chamber II.

[0049] The reactor [3] for bi-phasic anaerobic digestion of various organic wastes as shown in comprising of:

[0050] • a cru sher / grinder ( 1 ) ;

[0051] • a feed tank (2); • closed horizontal cylindrical vessel called reactor (3) comprises of chamber I and chamber II; the chamber I and chamber II are provided with sub-chambers called gravity settling chambers I (7) and II (11) respectively;

[0052] • a central duct with inverted cone (5) and baffles (6) in chamber I;

[0053] • a central duct passing through the perforated plate (10) with two inverted cones (8 & 9) in chamber II;

[0054] • air sparger (24) and gas sparger (25);

[0055] • a buffer tank (12); intermediate gas storage tank (15);

[0056] • H2S scrubber (17); H2O trap (18) and Biogas receiver (19);

[0057] • Gravity settling tanks (7 & 11);

[0058] • pH sensors (21); thermocouple (22); Pressure gauges (23); chemical dozing tank (31);

[0059] • sample collection ports (28, and 30);

[0060] • H2 and CCh / biogas transfer lines (16) through gas sparger (25);

[0061] • feeding pumps / lines (4 & 13); air compressor (14); gas compressor (16);

[0062] • main drain ports (27 & 29) for discharge of solids; digestate collection tank (20);

[0063] • programmable logic controller (PLC) (26).

[0064] Present invention further relates to a process for the generation of biogas with more than 90% methane from organic wastes. The bi-phasic anaerobic digestion process to be carried out in the reactor, where the biodegradable organic waste can be converted to biogas containing more than 90 % CH4 from various organic feedstocks incorporating the novel process strategies. The invention is also suitable for the generation of biohydrogen as a product having 80 - 85 % purity from acidification chamber I, while it is also suitable for the generation of biohythane having 15 - 25 % H2 and 75 - 85 % CH4 (withdrawal of mixture of CO2 and H2 from chamber I, while the CO2 and CH4 from chamber II for the production of biohythane) incorporating novel operational strategies as follows. i. Two stage anaerobic digestion i.e., acidification followed by biomethanation at an auto-generative high pressure (up to 14 bar) ii. Solid-state AD i.e., influent total solids between 20 to 40 % iii. Usage of culture I with relative abundance of hydrolytic bacteria and acidogens iv. Usage of culture II with relative abundance of acetoclastic and hydrogenotrophic organisms v. Supplementation of micro (Iron oxide, Nickel, Cobalt, Molybdenum and composite) and macronutrients (Granular activated carbon, biochar) and in the form of nanoparticles

[0065] The novelty of the present invention lies in the integration of all these novel strategies under optimized conditions altogether in a single bi-phasic anaerobic digester system without the need of any external purification step.

[0066] The bi-phasic anaerobic digestion process to be carried out in the reactor, where the biodegradable organic waste can be converted to biogas containing more than 90 % CH4 from various organic feedstocks such as food waste, animal wastes, agriculture wastes, and organic fraction of municipal solid waste incorporating the novel process strategies.

[0067] The feed slurry (2) with 20 - 40 % solids with single substrate or along with a co-substrate is pumped to the chamber I from the feed tank (2) through inlet feed line that passes through the central duct extending towards the cone (5) at the bottom, where in the presence of cone ensures the movement of slurry towards upwards flow regime and the auto-generative gas (H2 & CO2) pressure in the reactor facilitates the movement of slurry towards top and the baffles in chamber I ensures the retainment of maximum solids below the baffle and allows the acidified liquid rich in VFAs to flow towards the gravity settling chamber I.

[0068] The chamber I is inoculated with culture I for the generation of VFAs, H2 and CO2 and the reactor is maintained under auto-generative pressure, wherein the produced gas (output gas stream I) that is passed to chamber II at a flow rate of 0.1 L / min through gas purging line (25). The hydraulic residence time (HRT) of chamber I is maintained between 5 and 8 days depending on the type of substrate used and the pH of slurry in chamber I of the reactor is determined using pH sensors and the pH is adjusted between 6 and 6.5 using required chemical (acid / alkali) addition from the chemical dozing tank (31); where in the provision of the microaeration facility through an air sparger in chamber I of the reactor enhances the rapid acidification phenomena of organic wastes.

[0069] The pH sensor is used to measure the pH value of the slurry.

[0070] The provision of a chemical dozing tank is for the supply of the source acid or base so as to maintain pH of the slurry at about the predetermined value.

[0071] The thermocouple meant for the measurement of temperature and a heating mechanism which is controlled using a PLC so as to maintain a predetermined temperature (mesophilic / thermophilic ) .

[0072] The gas flow controllers for the controlled passage of product gas from chamber I to chamber II. The effluent i.e., VFA rich liquid from chamber I is allowed to flow into gravity settling tank

[0073] I (7) through gravitational flow effect, where in the effluent is withdrawn into the buffer tank. The chamber II is fed with the slurry consisting of 20 - 30 % solids from the buffer tank through pumping mechanism via a feed inlet line (13), where in the effluent in the buffer tank is supplemented with sodium acetate at a dosage of 3.6 g / L which creates effective buffering capacity by increasing the pH and acts as a chemical catalyst to accelerate the activity of the methanogens in chamber II.

[0074] The feed slurry from buffer tank (12) with 20 - 30 % solids is pumped to chamber II through inlet feed line that passes through the central duct extending towards the cone (8 & 9) at the bottom of the reactor, where in the presence of cone ensures the movement of slurry towards upward flow regime and the auto-generative gas (CH4 & CO2) pressure in the reactor facilitates the movement of slurry towards the perforated plate (10) at the top, where in the perforated plate allows the digested low density liquid towards the top while the solids are retained below the plate, where in the low density liquid flows in to the gravity settling tank II (11) under gravitational effect and the product gas generated in the reactor contains 90 % and above methane collected in biogas holder (19).

[0075] The chamber II is inoculated with culture II prepared by the supplementation of the required micro and macro nutrients in the form of nanoparticles and additives i.e., the composite nanoparticles at an optimum dosage of 150 mg / L including the macro nutrient granular activated carbon at a dosage of 1 g / L where in the composite nanoparticles comprised of FcsCL, C0CI2, NiCh, and MoOs were synthesized through chemical co -precipitation method.

[0076] The output gas stream I from chamber I is passed to chamber II at a controlled flow rate of 0.1 L / min to ensure the conversion of the CO2 produced in chamber II and the CO2 present in the output gas stream I from chamber I to CH4 by utilizing the hydrogen partial pressure, where in the output gas stream II is partially recirculated in to the reactor to facilitate effective mixing for efficient heat and mass transfer.

[0077] The chamber II is operated at mesophilic temperature and / or thermophilic temperature under auto-generative high pressure up to 14 bar, where in the digestate from the gravity settling tank

[0078] II in chamber II is collected in the digestate collection tank which is partially sent to the buffer tank to ensure buffering.

[0079] The addition of additives in the chamber II results in the promotion of direct interspecies electron transfer (DIET) which enhances the syntropy between the acetoclastic methanogens and hydrogenotrophic methanogens for enhanced biogas production from acids rich substrate. The residence time of chamber II is between 22 and 30 days depending on the type of substrate and co-substrate digested, where in the addition of additive materials to chamber II results in the increase in relative abundance of the methanogenic bacterial species in the bioaugmented inoculum.

[0080] The bi-phasic AD system can be operated in batch mode at high auto -generative pressure (up to 25 to 30 bar), while in semi-continuous and continuous modes of operation, chamber I and chamber II should be operated at pressure up to 14 bar.

[0081] The operational process strategy involves the auto -generative high pressure (up to 14 bar) biphasic (acidogenic followed by methanogenic) solid-state AD of organic wastes at high solids (20 to 40 % total solids) by the supplementation of additive materials (nanoparticles of micro and macronutrients) and the use of culture I and culture II (acetoclastic and hydrogenotrophic methanogens) to achieve the following:

[0082] 1. Recovery of biogas with 90 % methane, biohydrogen and biohythane as products;

[0083] 2. Improved methane / biogas yield between 30 and 40 % compared to other high-rate digesters;

[0084] 3. Improved volatile solids degradation efficiency;

[0085] 4. Intake of high solids influent with 20 to 40% solids;

[0086] 5. Reduction in the residence time for solids degradation;

[0087] 6. Maintenance of digester stability by balancing the syntrophic microorganisms (acetoclastic and hydrogenotrophic methanogens);

[0088] 7. Increase in the relative abundance of microorganisms (hydrolytic, acetoclastic, hydrogenotrophic and methanotrophic microorganisms).

[0089] The chamber I and chamber II are provided with unique hydrodynamic mechanism by the provision of inverted cones. Chambers I and II are both provided with feed inlet ports, gas outlet ports, sample collection ports, gas inlet port, drain ports. Chamber I of the bi-phasic AD system is provided with a central duct extending towards the bottom with an inverted cone, while the chamber II is provided with a similar central duct extending towards the bottom with two inverted cones. In addition to this, chamber I is provided with baffles while the chamber II is provided with the perforated plate above the cones. The purpose of the inverted cones is to ensure expansion of the slurry and then create an upward flow regime. The perforated plate / sheet in chamber II and the baffles in chamber I are meant for the retainment of maximum solids in the reactor so that the lighter / thin liquid is allowed to flow to the gravity settling chambers. The biogas generated from chamber II is partially recirculated to chamber II periodically to ensure uniform mixing and the digestate that is withdrawn from gravity settling chamber II is partially recycled to the chamber II through buffer tank. The chamber I and chamber II in the reactor are provided with pH sensors and pH adjustment through chemical (acid / alkali) addition from chemical dosing tank, temperature measurement (thermocouple) and control using heating mechanism, gas flow controllers and pressure recording arrangement (pressure guage) through a programmable logic controller (PLC). The reactor is provided with four outlets / drain valves to withdraw the high solids accumulated in the bottom of each chamber and sub-chambers. The drain valve of the gravity settling chamber I is connected to the buffer tank to collect the acidified slurry for subsequent feeding to chamber II. The biphasic AD system can be operated in batch, semi-continuous and continuous mode. The hydraulic residence time of the chamber I is between 5 and 8 days while that of chamber II is between 22 - 30 days depending on the type of feedstock. Feedstocks such as food waste, cattle manure, press mud, bagasse, rice husk, and rice straw have been anaerobically digested in the present embodiment to achieve the desired results. The lignocellulosic biomass such as rice straw, rice husk, press mud, bagasse requires a longer residence time of 8 days in chamber I and 22 to 30 days in chamber II while the other biodegradable wastes like food waste, animal manures, organic fraction of municipal solid wastes requires less than 5 days for acidification in chamber I and 22 - 30 days for biomethanation in chamber II for the production of biogas. The temperature in both the chambers can be maintained either between 30 to 40°C for mesophilic digestion or 50 to 60°C for thermophilic digestion, alternatively either of the chambers could be mesophilic or thermophilic.

[0090] The product gas i.e., biogas generated from chamber II contains CH4 more than 90 %, CO2 in the range of 7 and 8 %, H2S in the range of 0.01 to 0.03 % and H2O in the range of 0.5 to 1 %. The H2O and H2S removal are ensured through moisture trap and a scrubber respectively.

[0091] The enhancement of CH4 in biogas from a general 60 - 62 % to more than 90 % in this biphasic AD system is due to the unique design features leading to hydrodynamic behavior of slurry, auto-generative high pressure, low moisture in substrate (solid state AD), bioaugmented inoculum and the supplementation of additive materials (nutrients in the form of composite nanoparticles).

[0092] The final digestate from chamber II after completion of the residence time is collected in the digestate collection tank for its use as a fertilizer as well as a buffering agent in the buffer tank. Utilization of digestate from chamber II in the buffer tank not only reduces the intake of fresh water for dilution, and increases the pH of the acidified slurry but also ensures the utilization of unconsumed additive materials back in the reactor.

[0093] Supplementation of additive materials in the form of nanoparticles accelerates the digestion process and increases the metabolic activity of methanogens through direct interspecies electron transfer (DIET) mechanism. The interspecies transfer of electrons allows the concurrent oxidation of organic matter and reduction of CO2 to CH4 efficiently under thermodynamically favourable conditions. DIET is the principal link for syntrophic methanogenesis to occur. It means the intervention of bacteria and the methanogens to break through the thermodynamic limitations to promote the microbial population growth. The influence of direct (inherent characteristics of substrate) and indirect (intermediates such as VFAs, ammonia nitrogen (NH3-N)) inhibitors is more effective in the absence of conductive materials. Addition of conductive materials such granular activated carbon minimizes the impact of inhibitors and induces stimulatory effects between the acidogens, acetogens and methanogens for enhanced syntrophic metabolism via electronic conduction.

[0094] The chamber I for acidification and chamber II for biomethanation are compartments in the closed horizontal cylindrical embodiment constructed with suitable material (stainless steel, MS with epoxy coating or any other suitable non-corrosive material) with a suitable capacity depending on the input feed flow rate of the biodegradable organic material. The feed tank, buffer tank, digestate collection tank are the three embodiments that are closed containers with an open / close lid provision. The biogas from chamber II can be collected and stored in a storage tank / biogas holder or it can directly be pipelined to the utility.

[0095] EXAMPLES

[0096] Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

[0097] PHASE I EXPERIMENTS

[0098] Example 1

[0099] Anaerobic digestion of food waste in a simple bi-phasic AD system

[0100] Experiments were conducted in a bi-phasic AD system consisting of chamber I and chamber II in a single horizontal cylindrical reactor with food waste as feedstock at a solids consistency of 15 %. The chamber I and the chamber II were fed with food waste slurry consisting of 15 % and 10 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 5 and 25 days respectively. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The volatile solids destruction in the chamber I is 40 % while that of chamber II is 70 %. The maximum VFAs in the chamber I is between 30 - 35 g / L. The product gas yield from chamber I is 0.4 m3 / kg VSreduced while the biogas yield from chamber II is 0.55 m3 / kg VSreduced with CH4 of 62 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi- ADS operated with food waste is shown in Table.1.

[0101] Table. 1 Performance evaluation of Bi- ADS with food waste

[0102] Example 2

[0103] Auto-generative high pressure solid-state anaerobic digestion of food waste in a bi-phasic system

[0104] The chamber I and the chamber II were fed with food waste slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 5 and 25 days respectively. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The volatile solids destruction in the chamber I is 40 % while that of chamber II is 80 %. The maximum VFAs in the chamber I is between 38 - 45 g / L. The product gas yield from chamber I is 0.5 m3 / kg VSreduced while the biogas yield from chamber II is 0.7 m3 / kg VSreduced with CH4 of 80 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi-ADS operated with food waste is shown in Table.2. Table. 2 Performance evaluation of Bi-ADS with food waste under auto-generative high pressure Example 3

[0105] Auto-generative high pressure solid-state anaerobic digestion of food waste in a biphasic system supplemented with additive materials

[0106] The chamber I and the chamber II were fed with food waste slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 5 and 25 days respectively. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber

[0107] II. The chamber II was supplemented with composite nanoparticles and other macronutrient (granular activated carbon. The volatile solids destruction in the chamber I is 55 % while that of chamber II is 85 %. The maximum VFAs in the chamber I is between 38 - 40 g / L. The product gas yield from chamber I is 0.45 m3 / kg VSreduced while the biogas yield from chamber II is 0.65 m3 / kg VSreduced with CH4 of 84 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi- ADS operated with food waste is shown in Table.3.

[0108] Table. 3 Performance evaluation of Bi-ADS with food waste under auto-generative high pressure by the supplementation of additive materials

[0109] Example 4

[0110] Auto-generative high pressure solid-state anaerobic digestion of food waste in a bi-phasic system supplemented with additive materials and inoculated with bioaugmented inoculum

[0111] The chamber I and the chamber II were fed with food waste slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 5 and 25 days respectively. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The chamber II was inoculated with bioaugmented inoculum as well as supplemented with composite nanoparticles and macronutrients (granular activated carbon). The volatile solids destruction in the chamber I is 55 % while that of chamber II is 85 %. The maximum VFAs in the chamber I is between 38 - 40 g / L. The product gas yield from chamber I is 0.45 m3 / kg VSreduced while the biogas yield from chamber II is 0.65 m3 / kg VSreduced with CH4 of 84 % in biogas. The product gas from chamber I to chamber II was transfer at a flowrate of 0.1 L / min. The performance parameters of Bi-ADS operated with food waste is shown in Table.4.

[0112] Table. 4 Performance evaluation of Bi-ADS with food waste under auto-generative high pressure by the supplementation of additive materials and bioaugmented inoculum

[0113] PHASE EXPERIMENTS

[0114] Example 1

[0115] Auto-generative high pressure solid-state anaerobic digestion of food waste and rice husk in a bi-phasic system

[0116] The chamber I and the chamber II were fed with food waste and rice husk slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 8 and 27 days respectively. The ratio of food waste and rice husk was 80:20. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The volatile solids destruction in the chamber I is 49 % while that of chamber II is 82 %. The maximum VFAs in the chamber I is between 38 - 45 g / L. The product gas yield from chamber I is 0.5 m3 / kg VSreduced while the biogas yield from chamber II is 0.7 m3 / kg VSreduced with CH4 of 82 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi- ADS operated with food waste and rice husk is shown in Table.5. Table. 5 Performance evaluation of Bi-ADS with food waste and rice husk under auto- generative high pressure

[0117] Example 2

[0118] Auto-generative high pressure solid-state anaerobic digestion of food waste and rice husk in a bi-phasic system supplemented with additive materials The chamber I and the chamber II were fed with food waste slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 8 and 27 days respectively. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The chamber II was supplemented with composite nanoparticles and other macronutrient (granular activated carbon. The volatile solids destruction in the chamber I is 55 % while that of chamber II is 85 %. The maximum VFAs in the chamber I is between 35 - 40 g / L. The product gas yield from chamber I is 0.45 m3 / kg VSreduced while the biogas yield from chamber II is 0.65 m3 / kg VSreduced with CH4 of 86 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi- ADS operated with food waste and rice husk is shown in Table.6. Table. 6 Performance evaluation of Bi-ADS with food waste and rice husk under auto- generative high pressure by the supplementation of additive materials

[0119] Example 3 Auto-generative high pressure solid-state anaerobic digestion of food waste and rice husk in a bi-phasic system supplemented with additive materials and inoculated with bioaugmented inoculum

[0120] The chamber I and the chamber II were fed with food waste slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 8 and 27 days respectively. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The chamber II was inoculated with bioaugmented inoculum as well as supplemented with composite nanoparticles and macronutrients (granular activated carbon). The volatile solids destruction in the chamber I is 54 % while that of chamber II is 88 %. The maximum VFAs in the chamber I is between 40 - 48 g / L. The product gas yield from chamber I is 0.55 m3 / kg VSreduced while the biogas yield from chamber II is 0.69 m3 / kg VSreduced with CH4 of 90 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi-ADS operated with food waste and rice husk is shown in Table.7. Table. 7 Performance evaluation of Bi-ADS with food waste and rice husk under auto- generative high pressure by the supplementation of additive materials using bioaugmented inoculum

[0121] PHASE III EXPERIMENTS Example 1 Auto-generative high pressure solid-state anaerobic digestion of food waste and press mud in a bi-phasic system

[0122] The chamber I and the chamber II were fed with food waste and press mud slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 5 and 25 days respectively. The ratio of food waste and rice husk was 70:30. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The volatile solids destruction in the chamber I is 50 % while that of chamber II is 75 %. The maximum VFAs in the chamber I is between 45 - 50 g / L. The product gas yield from chamber I is 0.6 m3 / kg VSreduced while the biogas yield from chamber II is 0.7 m3 / kg VSreduced with CH4 of 83 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi-ADS operated with food waste and press mud is shown in Table.8. Table. 8 Performance evaluation of Bi-ADS with food waste and press mud under auto-generative high pressure

[0123] Example 2

[0124] Auto-generative high pressure solid-state anaerobic digestion of food waste and press mud in a bi-phasic system supplemented with additive materials

[0125] The chamber I and the chamber II were fed with food waste and press mud slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 5 and 25 days respectively. The ratio of food waste and rice husk was 70:30. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The volatile solids destruction in the chamber I is 50 % while that of chamber II is 88 %. The maximum VFAs in the chamber I is between 48 - 52 g / L. The product gas yield from chamber I is 0.55 m3 / kg VSreduced while the biogas yield from chamber II is 0.7 m3 / kg VSreduced with CH4 of 83 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi-ADS operated with food waste and press mud is shown in Table.9.

[0126] Table. 9 Performance evaluation of Bi-ADS with food waste and press mud under auto- generative high pressure by the supplementation of additive materials

[0127] Example 3

[0128] Auto-generative high pressure solid-state anaerobic digestion of food waste and press mud in a bi-phasic system supplemented with additive materials and inoculated with bioaugmented inoculum

[0129] The chamber I and the chamber II were fed with food waste slurry consisting of 35 % and 25 % solids at a feed flow rate of 7 and 2 L / day at a hydraulic residence time (HRT) of 5 and 25 days respectively. The pH in the chamber I was maintained at 6.5 while it was 7.0 in chamber II. The chamber II was inoculated with bioaugmented inoculum as well as supplemented with composite nanoparticles and macronutrients (granular activated carbon). The volatile solids destruction in the chamber I is 60 % while that of chamber II is 85 %. The maximum VFAs in the chamber I is between 40 - 50 g / L. The product gas yield from chamber I is 0.55 m3 / kg VSreduced while the biogas yield from chamber II is 0.7 m3 / kg VSreduced with CH4 of 84 % in biogas. The product gas from chamber I to chamber II was transferred at a flowrate of 0.1 L / min. The performance parameters of Bi-ADS operated with food waste and press mud is shown in Table.10.

[0130] Table. 10 Performance evaluation of Bi-ADS with food waste and press mud under auto- generative high pressure by the supplementation of additive materials using bioaugmented inoculum

[0131] Phase IV

[0132] Experimental study for the production of biohythane

[0133] This experiment is conducted to produce biohythane from the present invention bi-phasic AD system. The product gas stream rich in H2 and CO2 from chamber I (acidification chamber) and the product gas stream rich in CH4 and CO2 from chamber II (methanation chamber) produced from various organic wastes is passed through a caustic scrubber for the removal of CO2, so as to obtain a product gas rich in H2 and CH4 which is known as biohythane as shown in Figure. A. The product gas stream from chamber I is a mixture of 80 - 85 % H2 and 15 - 20 % CO2 whereas the product gas stream from chamber II is a mixture of 90 % CH4 and 10 % CO2. Both the gas streams are allowed to pass through the caustic scrubber having 0.5 M solution made of CaO, CaOH, NaOH, NaHCCh etc. The product gas that is obtained after caustic scrubbing is the gas rich in H2 and CH4. The composition of product gas is 15 - 25 % H2 and 75 - 85 % CH4 which is known as Biohythane. In this experimental study, about 99 % of the CO2 is absorbed in the caustic solution and the spent caustic solution is withdrawn into a tank which is again recycled back to the scrubber after suitable dilution. ADVANTAGES OF THE INVENTION

[0134] • The main advantage of the present invention is the generation of biogas with more than 90 % CH4 from high solids (solid-state AD) organic waste and the improvement of volatile solids reduction rate.

[0135] • The invention is also suitable for the generation of biohydrogen as a product having 80 - 85 % purity from acidification chamber I.

[0136] • The invention is also suitable for the generation of biohythane having 15 - 25 % H2 and 75 - 85 % CH4.

[0137] • Another advantage of the process invention is the separation of acidogenic and the methanogenic phases of AD process which facilitates proper maintenance of the process operating conditions.

[0138] • The application of the process in the simple closed horizontal cylindrical vessel / reactor designed as a bi-phasic AD system that can be scaled up to any capacity.

[0139] • Another advantage of the present invention is the maximization of VFAs and biohydrogen production in chamber I inoculated with culture I rich in hydrolytic bacteria and acidogens.

[0140] • Another advantage of the present invention is the conversion of CO2 to CH4 in the presence of H2 in chamber II inoculated with culture II rich in acetoclastic and hydrogenotrophic methanogens.

Claims

WE CLAIM1. A bi-phasic solid-state anaerobic digester system [100] (Bi- ADS >90%CH4) comprising:

1. a crusher / grinder [1]; ii. a feed tank [2] ; iii. closed horizontal cylindrical vessel called reactor [3] comprising acidification chamber I and biomethanation chamber II; wherein the chamber I and chamber II are further provided with gravity settling chambers I [7] and II [11] respectively; iv. a central duct with inverted cone [5] and baffles [6] in chamber I; v. a central duct passing through the perforated plate [10] with two inverted cones [8] and [9] in chamber II; vi. a buffer tank [12] vii. an intermediate gas storage tank [15]; viii. an air compressor [14]; ix. a gas compressor [16]; x. a H2S scrubber [17]; xi. a H2O trap [18]; xii. a biogas receiver [19]; xiii. an air sparger [24] and gas sparger [25]; xiv. sample collection ports [28 and 30];XV.H2 and CCh / biogas transfer lines [16] through gas sparger [25]; xvi. feeding pumps / lines [4 and 13]; xvii. main drain ports [27 and 29] ; xviii. digestate collection tank [20] ; xix. programmable logic controller [26].

2. The bi-phasic anaerobic digester system [100] as claimed in claim 1, wherein the programmable logic controller [26] further comprising an automatic pH sensors [21] a thermocouple [22]; a chemical dozing tank [31]; pressure gauges [23] and gas flow controllers [31].

3. The bi-phasic anaerobic digester system [100] as claimed in claim 1, wherein the acidification chamber I and biomethanation chamber II in the reactor is controlled through a programmable logic controller [26].

4. The bi-phasic anaerobic digester system [100] as claimed in claim 1, wherein the acidification chamber generates biohydrogen with 80 to 85 % purity and biomethanation chamber II generates biogas with atleast 90% methane from organic wastes.

5. The bi-phasic anaerobic digester system [100] as claimed in claim 1, wherein the reactor is operated in batch mode at high auto-generative pressure in the range of 25 to 30 bar. while in semi continuous and continuous mode of operation the maximum auto -generative pressure is up to 14 bar in both the chambers.

6. The bi-phasic anaerobic digester system [100] as claimed in claim 1, for use in the generation of biohydrogen with 80 to 85 % purity and biohythane with a composition of 15 to 25 % H2and 75 to 85 % CH4.

7. A process for bi-phasic anaerobic digestion of organic wastes using reactor as claimed in claim 1, wherein the process comprising the steps of: i. crushing / grinding the feed in the crusher / grinder [1] and followed by diluting with water to obtain a dense slurry with 20 to 40 % solids; ii. feeding the dense slurry as obtained in step (i) from the feed tank [2] to chamber I; iii. inoculating the chamber I with culture I is having hydrolytic bacteria and acidogens maintaining the pH between 6 and 6.5 to obtain an output gas stream I containing 80 - 85 % H2; 15 - 20 % CO2on volume basis and acidified slurry; iv. allowing microaeration in the acidified slurry as obtained in step (iii) in chamber I to obtain acidified volatile fatty acids (VFAs) slurry followed by transferring the acidified VFA slurry having 40 - 50 g / L of VFA containing 20 to 30 % solids from gravity settling chamberI [7] to buffer tank [12] through valve mechanism; v. supplementing the acidified VFA slurry as obtained in step (iv) in the buffer tank [12] with sodium acetate at a dosage ranging between 2.6 to 3.6 g / L and chemicals from chemical dozing tank [31] to increase pH to 7.0 along with partial recycling of digestate that is collected into the digestate tank [20] from gravity settling chamber II [11] to obtain neutralized slurry at a pH of 7.0; vi. pumping the neutralized slurry as obtained in step (v) from the buffer tank [12] to chamberII through pumping mechanism; vii. inoculating the chamber II with the culture II is having acetoclastic and hydrogenotrophic methanogens;viii. supplementing the culture II in chamber II with composite nanoparticles; ix. partially passing the output gas stream I generated from chamber I to chamber II in 4: 1 ratio at a controlled flow rate ranging between 0.1 to 0.25 L / min for the conversion of CO2 in the gas to CH4 by the utilization of H2 by hydrogenotrophic bacteria / methanogens inside chamber II and for the conversion of CO2 that is generated inside chamber II to CH4 by the utilization of H2 that is passed from chamber I to chamber II;(x) maintaining the auto-generative pressure in the range of 1 to 14 bar in both the chambers I and II to obtain biogas with atleast 90 % CH4 and the digestate as the final product.(xi) alternatively, utilizing the H2 and CO2 from chamber I and CO2 and CH4 from chamber II to produce biohythane with a composition of 15 - 25 % H2 and 75 - 85 % CH4.

8. The process as claimed in claim 7, wherein culture I and culture II further comprising a bioaugmented acidogenic mixed microbial consortia and a bioaugmented methanogenic mixed microbial consortia respectively.

9. The process as claimed in claim 7, wherein the composite nanoparticles are selected from group comprising Iron nanoparticles (FesC ), Cobalt nanoparticles (C0CI2), Molybdate nanoparticles (MoOs) and nickel nanoparticles (NiCh).

10. The process as claimed in claim 7, wherein the residence time required for the substrate to be converted to VFAs, H2 and CO2 in chamber I is between 5 - 8 days.

11. The process as claimed in claim 7, wherein the residence time required for the conversion of biodegradable material in chamber II to biogas is between 22 and 30 days depending on the type of substrate and co-substrate digested.

12. The process as claimed in claim 7, wherein the chamber I and II are selected from mesophilic and thermophilic digestion, wherein the temperature is maintained in the range of 30 to 40°C for mesophilic digestion and in the range of 50 to 60°C for thermophilic digestion.

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