TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The first module is used to capture carbon dioxide from flue gas flow produced by combustion or another industrial process and then to generate the concentrated carbon dioxide flow. The second module is used to prepare nutritional substrates with optimal content of monomeric and/or oligomeric substances for mixed bacterial populations by starting from a first portion of the biomasses. The third module is used to prepare optimal high alcohol content substrates for mixed bacterial populations by starting from a second portion of the biomasses. The fourth module is used to nutritional and alcoholic substrates, integrated with stimulators, catalysts and nutritional factors, and concentrated carbon dioxide flow by using selected mixed anaerobic bacterial populations to produce methane. The second plant is supplied to the first plant. The second plant is adapted to use air as an oxidant.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Methods: During phase A, carbon dioxide is captured from flue gas flow produced by combustion or other industrial processes to generate the concentrated carbon dioxide flow, the combustion is of the type which uses air as an oxidant. During phase B, optimal biomasses cocktails are formulated with homogeneity, size, total solid content, volatile solid content, general nutritional ratio, and carbohydrate, protein, lipid, macro element, and microelement composition. During the phase B, the biomasses and/or cocktails are subjected to (a) thermal pretreatment through (in)direct heating to carbon dioxide pressurization and to subsequent enzymatic and/or bacterial hydrolysis; (b) to thermal treatment at 36-160 degrees C and at a carbon dioxide pressure of 3-50, preferably 3-12 bar for 5 seconds-1 hour, preferably 5-30 seconds; or (c) enzymatic hydrolysis in carbon dioxide saturated environment including contact with multi-enzymatic complexes containing cellulase, amylase, protease, lipase, and/or with mixed high density hydrolytic and cellulolitic bacterial populations. During phase C, combinations of pretreatment stages included in the phase are carried out as needed from time to time depending on the nature of matrices capable of producing alcoholic substrate containing different types and/or combinations of alcohol, particularly ethanol, methanol, and butanol. During the phase C, when the selected matrices are rich in carbohydrates containing substances with high molecular weight such as hemicellulose, cellulose and lignin, (a) a first pollulant, lignin reduction, and/or removal stage; a second saccharification stage; and a third alcoholic fermentation stage; or preferably a saccharification stage and subsequent alcoholic fermentation stage are carried out; or (b) when the selected matrices are rich in carbohydrates containing oligosaccharides and simple sugars only an alcoholic fermentation stage is carried out. The alcoholic fermentation treatment of matrices rich in carbohydrates containing oligosaccharides and free sugars is carried out to produce high alcohol content substrate through populations of microorganisms, i.e. Saccharomyces sp., Zymomonas sp., or Chalara sp.. The treatment of matrices rich in carbohydrates containing substances with high molecular weight such as hemicellulose, cellulose, and lignin is carried out to produce high cellulose content material which can be readily be saccharified, through contact with ligninolitic multi-enzymatic complexes and/or by inoculating mixed populations of microorganism, i.e. Basidiomycetes, Pseudomonas sp., or Actinomycetes sp.. The saccharification treatment of matrices rich in carbohydrates containing substances with high molecular weight is carried out to produce material rich in oligosaccharides and simple sugars through contact with multi-enzymatic complexes and/or with populations of microorganisms, i.e. Clostridium sp., Pseudomonas sp., or Trichoderma sp.. During phase D; the method comprises distribution of carbon dioxide, nutritional substrate, and alcoholic substrate from phases A, B, and C, respectively as well as further integrating stimulators, catalysts and nutritional factors to acetogenic digester; conversion of carbon dioxide, nutritional, and alcoholic substrates into acetates, acetic acid, and other organic acids through fermentation with selected mixed acetogenic bacterial populations kept at high density in acid environment; separating of substrate particles and microorganisms from effluent of the second stage followed by recirculation within the same stage or at the head of phase B; output of the liquid component to the next stage; output of the gas collected from the second stage to the subsequent stage or recirculation with the same stage; methane conversion of acetates, carbon dioxide, and hydrogen present in the liquid effluent and/or in gaseous effluent coming from the second stage by using selected mixed methanogenic bacterial populations kept at high density; removal of biogas from fifth stage and recirculation within the same stage or output to downstream storage and processing units; separation of substrate particles and microorganisms present in the effluent from the fifth stage; and recirculation within the same stage or at the head of the phase B and output of the liquid component of the second stage or to depuration. The first stage comprises daily supply of the nutritional substrate according to direct relationship with the bacterial population biomass present at the time in second stage. The first stage preferably comprises daily supply of carbon dioxide and alcoholic substrate up to the maximum total load can be used by acetogenic bacterial populations and that can stimulate the desired oxidoreductive reaction in the fermentation reactor, respectively. The acetogenic fermentation is obtained by using mixed high density bacterial populations microorganism, i.e. Clostridium sp., Butyribacterium sp., Ruminococcus sp., Morella sp., or Eubacterium sp.. The fifth stage comprises acetoelastic methanogenesis, and/or hydrogenotropic methanogenesis using bacterial population microorganisms, i.e. Methanosarcina sp., Methanosaeta sp., Methanococcus sp., or Methanobacterium sp.. Preferred Components: The first biomasses portion is made up of highly degradable fresh, ensiled, or semi-finished vegetable and animal matrices. The second biomasses portion is made up of fresh, ensiled, or semi-finished vegetable matrices rich in carbohydrates, particularly sugars, starch, hemicellulose, and cellulose. The high density hydrolytic and cellulolitic bacterial populations is Clostridium sp., Pseudomonas sp., or Bacillus sp.. The ratio is 1:8-1:25, preferably 1:12-1:25. The acetogenic fermentation is obtained using selected mixed bacterial populations of 6-12, preferably 9-12 dry wt.%. Preferred Parameters: The carbon dioxide pressure is adjusted to keep the pH value of cocktails at 3-6, preferably 4-5.5, and at 15-60, preferably 45-55 degrees C. The acetogenic fermentation is obtained at pH 4.5-6.3, preferably 5-6 and 30-80, preferably 30-60 degrees C.