| The production of liquid biofuels and biochemicals from renewable,low-cost and accessible no-food lignocellulosic biomass is one of the core areas in future economic and social developments,and manufacturing technological advancements,in terms of many vital demands such as mitigation of climate change,substitutions of fossil and food resources,and the outlet of crop straw.However,the lignocellulosic biorefinery demonstration has experienced a significant stagnation in the last decade owing to the technical barriers including large-scale wastewater discharge,high energy comsupiton,low conversion efficiency with the economics hurdels.Overcoming these technical barriers is a prerequisite for the further revival of this highly prosming technology into commercial-scale practice,and then truly serves to address a series of serious challenges caused by climate change and sustainable development faced by human society.Corn dry milling provides a mature process for the establish of dry biorefinery technology.The easily hydrolysable and inhibitors free lignocellulosic biomass was obtained by dry acid pretreatment and biodetoxification with zero wastewater emission and low energy consumption in the dry biorefinery processing.The dry biorefinery maximizes the potentials of subsequent simultaneous saccharification and co-fermentation(SSCF)for cellulosic ethanol.Both the fermentation efficiency,wastewater discharge and energy consumption in the current dry biorefining are very close to that of corn dry milling processing,indicaing that the dry biorefinery has the initial potential for industrial application.There are still many technical barriers affecting the process efficiency and economics in the current dry biorefinery,and the further technical upgrades are required,which are as follows:(1)The present biodetoxificaion Amorphotheca resinae ZN1 has the poor environmental adaptability,the biodetoxification must conducted at 30℃ and neutral pH;(2)The biodetoxificaion must conducted on solid state,resulting in large fermentation volume,high oxygen demand,poor mixing uniformity,and wide local temperatures and pH fluctuations,making it difficult to match the actual industrial production of bioconversion process in the form of liquid feedstock;(3)The mineral acid catalyst,sulfuric acid,used in dry acid pretreatment would be neutralized to solid calcium precipitates as the potential sulfur oxide source in downstream lignin combustion;(4)The carbon footprint of dry biorefinery processing has not been established.In this thesis,a series of technological innovations have been made to the current dry biorefinery processing.A new concept of starch-like biorefinery technology was prosed and verified by overcoming the above-mentioned technical barriers.In the first part of this thesis,a strain with potential for biodetoxification was isolated and identified as Paecilomyces variotii FN89.P.variotii FN89 is well tolerance to a wide temperaure range of 28-42℃ and low pH.P.variotii FN89 can ultimately and rapidly degrade various kinds of lignocellulose-derived inhibitors including acetic acid,furfural,5-hydroxymethyfurfural(HMF),vanillin,syringaldehyde,and 4-HBA with minimal loss of fermentable suagrs.P.variotii FN89 has significant advantages over the present biodetoxification strain A.resinae ZN1 in various biodetoxification scenarios.The globle transcriptome analysis showed that the sugars metabolism of P.variotii FN89 is decreased in the presence of inhibitors,indicating the potential of using inhibitors as the preferred carbon source rather than fermentabler sugars.The modification of sugars metabolism and intracellular ATP generation modes,as well as the enhancement of macromolecular DNA repair and mitochondrial protein chaperone function at low pH contribute to cellular resistance to acidic environment.In the second part of this thesis,lignocellulose feedstock was successfully transormed into starch-like carbohydrates,similar to dry milled corn meal in morphology,fermentable sugar content,enzymatic hydrolysis yield,element contents,and ethanol fermentablility by biodegradable acid catalyzed pretreatment and low pH biodetoxification.The oxalic acid catalyst was effective on disrupting the lignocellulose structure and also biodegradable at low pH value.The biodetoxification fungus P.variotii FN89 was capable of degrading the furan/phenolic aldehydes and oxalic acid simultaneously and ultimately,while the fermentable sugars loss of lower than 6%.The obtained starch-like carbohydrates from wheat straw and corn stover were similar to dry milled corn meal in terms of morphological properties,fermentable sugar contents,enzymatic hydrolysis yield,elemental contents,and free of inhibitors and acid catalyst.The bioconversion of starch-like wheat straw and corn stover produced 78.5 and 75.3 g/L of ethanol(9.9%and 9.5%,v/v)with the yield of 0.47 and 0.45 g ethanol/g cellulose/xylose,respectively,compared with 78.7 g/L(10.0%,v/v)from corn meal and the yield of 0.48 g ethanol/g starch.Mass balances suggest that the ethanol yield,wastewater generation,and elemental recycling of the starch-like carbohydrates from lignocellulose were essentially the same as those of corn meal.Therefore,the lignocellulose feedstock after oxalic acid pretreatment and low pH biodetoxification is defined as starch-like biomass;the biorefinery processing including the subsequent high solids loading SSCF is defined as starch-like dry biorefinery.In the third part of this thesis,the valorization of the solid waste generated in starch-like biorefinery was investigated.The essential form of solid waste was the ash from the lignin residue combustion.The characterizations of SEM/EDX,XRD and FTIR showed that the ash contains a significant amount of calcium carbonate,which has the potential to be recycled as a neutralizer in the biorefinery process,thereby reducing the emission of solid waste and CO2·Using the combustion as the neutralizer for preteated wheat straw,the final lactic acid titer reached 94.6 ± 2.5 g/L,similar to calcium carbonate as the neutralizer.Using the combustion as lactic acid fermentation neutralizer,the final lactic acid titer reached 78.3 ± 3.5 g/L,which is 17.6%higher than calcium carbonate as neutralizer.The overall materials balance showed that at least 867.0 tons of calcium carbonate and 1232.1 tons of calcium hydroxide per year can be saved by recovering the combustion ash in a biorefinery plant with the processing capacity of 300,000 tons of dry wheat straw per year.In the fourth part of this thesis,the current dry biorefinery chain was reframed to efficiently convert corn fiber to cellulosic ethanol.High hemicellulose content of corn fiber lignocellulose is a unique property of this material.Most of the xylose molecules present in the hemicellulose backbone are acetylated and a large amount of free acetic acid is released when the hemicellulose is hydrolyzed,which severely inhibits the growth of ethanol-producing strain.This study reframed the regular biorefinery chain by conducting enzymatic hydrolysis before biodetoxification to completely release acetic acid from hemicellulose in corn fiber.Then the biodetoxification was followed immediately to degrade acetic acid,furfural and HMF with the minimum loss of glucose and xylose.The improved ethanol production(70.2 g/L,0.43 g/g)was obtained by the reframed chain of corn fiber biorefining.In the fifth part of this thesis,the direct acid hydrolysis of lignocellulose for cellulosic ethanol production was re-examined after a novel biodetoxification approach was introduced to de-bottleneck the inhibitor barrier in order to avoid using high-cost cellulase.The cocktail of sulfuric acid,phosphoric acid and oxalic acid hydrolyzed corn stover to the 51.1 g/L of glucose(0.50 g/g cellulose)and 18.1 g/L of xylose(0.22 g/g xylan).The furfural,5-hydroxymethylfurfural and acetic acid in the corn stover hydrolysate were completely removed by Paecilomyces variotii FN89,leading to the successful ethanol fermentation of 24.2 g/L,corresponding to 72.6 kg per metric ton of dry corn stover.The techno-economic evaluations suggest that the cost reduction of replacing cellulase enzyme with cheap acid catalysts compensated the partial ethanol loss of sugar conversion to inhibitors(21.5-89.1%).The energy consumption per ton of ethanol produced by acid hydrolysis is also significantly higher than that of enzymatic hydrolysis process.The re-examination of acid hydrolysis process reveals that the technical and economic performance of acid hydrolysis process is still far below that of the enzymatic hydrolysis process even after the inhibitor barrier was solved.In the sixth part of this thesis,the mass balances of different cellulosic L-lactic acid production technologies on dry biorefinery platforms are calculated based on rigorous Aspen Plus software,and the corresponding life cycle analysis(LCA)is conducted.The results showed that the CO2 emission per kg of L-lactic acid ranged from 0.279 to 0.815 kg.The CO2 emission can be further reduced to 0.267 kg per kg of L-lactic acid when the oxalic acid generated from glucose oxidation is selected as biodegradable pretreatment catalyst.In summary,the starch-like biorefining technologies proposed in this thesis further upgraded the current dry biorefinery processing.The starch-like biorefining technologies overcome the key technological barriers such as the application limitations of the current biodetoxificaion,sulfuric acid catalyst residue,solid waste disposal,etc.,providing an effective biodetoxification strain and process engineering for the industrialization of lignocellulosic biorefinery technology. |
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