The development of biofuels as an alternative fuel source highlights the MixAlco process as one method to convert organic waste into alcohol fuels. The pretreatment and fermentation of waste is integral to the process and represents a principal cost consideration due to the large structure needed to encapsulate the fermenting materials. This research developed papercrete as a potential construction material to reduce the cost of a structure. Papercrete is a mixture of paper, cement, and sand. The strengths, thermal conductivity, and other physical properties were compared with those of conventional building materials. This research identified acceptable property ranges necessary for using a structural papercrete facility and recorded compressive and tensile strengths that were too weak to build an economical structure. The identification of a hybrid papercrete-concrete structure produced results and economics within acceptable ranges. The papercrete-concrete alternative was tested on the same basis as the papercrete for structural and economic analysis, which provided acceptable results. The results indicate that a papercrete-concrete structure is a viable alternative structurally and economically within a range of sizes for the structure.

The MixAlco process uses an anaerobic, mixed-culture fermentation to convert lignocellulosic biomass to carboxylate salts. The fermentation broth must be clarified so that only carboxylate salts, water, and minimal impurities remain. Carboxylate salts are concentrated by evaporation and thermally decomposed into ketones. The ketones can then be chemically converted to a wide variety of chemicals and fuels. The presence of excess lime in the thermal decomposition step reduced product yield. Mixtures of calcium carboxylate salts were thermally decomposed at 450 degrees C. Low lime-to-salt ratios (g Ca(OH)2/g salt) of 0.00134 and less had a negligible effect on ketone yield. In contrast, salts with higher lime-to-salt ratios of 0.00461, 0.0190, and 0.272 showed 3.5, 4.6, and 9.4% loss in ketone yield, respectively. These losses were caused primarily by increases in tars and heavy oils; however, a three-fold increase in hydrocarbon production occurred as well. To predict ketone product distribution, a random-pairing and a Gibbs free energy minimization model were applied to thermal decompositions of mixed calcium and sodium carboxylate salts. Random pairing appears to better predict ketone product composition. For sodium and calcium acetate, two types of mixed sodium carboxylate salts, and two types of mixed calcium carboxylate salts, activation energy (EA) was determined using three isoconversional methods. For each salt type, EA varied significantly with conversion. The average EA for sodium and calcium acetate was 226.65 and 556.75 kJ/mol, respectively. The average EA for the two mixed sodium carboxylate salts were 195.61, and 218.18 kJ/mol. The average EA for the two mixed calcium carboxylate salts were 232.78, and 176.55 kJ/mol. In addition, three functions of conversion were employed to see which one best modeled the experimental data. The Sestak-Berggren model was the best overall. Possible reactor designs and configurations that address the challenges associated with the continuous thermal decomposition of carboxylate salts are also presented and discussed. Methods of fermentation broth clarification were tested. Flocculation showed little improvement in broth purity. Coagulation yielded broth of 93.23% purity. Filtration using pore sizes from 1 micrometer to 240 Daltons increased broth purity (90.79 to 98.33%) with decreasing pore size.

The rising price of oil is hurting consumers all over the world. There is growing interest in producing biofuels from non-food crops, such as sugarcane trash. Lignocellulosic biomass (e.g., sugarcane trash) is an abundant, inexpensive, and renewable resource. The patented MixAlco process is a cost-effective solution, which does not require sterility or the addition of expensive enzymes to convert lignocellulosic biomass to transportation fuels and valuable chemicals. In this study, the MixAlco process was used to convert sugarcane trash to carboxylic acids under thermophilic conditions. Lime-treated sugarcane trash (80%) and chicken manure (20%) was used as the feedstock in rotary 1-L fermentors. Ammonium bicarbonate buffer was used to mitigate the effects of product (carboxylic acid) inhibition. Marine inoculum was used because of the high adaptability of the mixed culture of microorganisms present. Iodoform solution was added to inhibit methanogenesis. Preliminary batch studies over a 20-day period produced 19.7 g/L of carboxylic acids. Sugarcane trash had the highest average yield (0.31 g total acid/g VS fed) and highest average conversion (0.70 g VS digested/g VS fed) among the three substrates compared. Countercurrent fermentations were performed at various volatile solid loading rates (VSLR) and liquid residence times (LRT). The highest acid productivity of 1.40 g/(L�d) was at a total acid concentration of 29.9 g/L. The highest conversion and yield were 0.64 g VS digested/g VS fed and 0.36 g total acid/g VS fed, respectively. The continuum particle distribution model (CPDM) was used to predict acid concentration at various VSLR and LRT. The average error in between the predicted and experimental acid concentration and conversion were 4.62% and 1.42%, respectively. The effectiveness of several pretreatment methods was evaluated using the CPDM method. The best-performing method was short-term, no-wash, oxidative lime pretreatment with ball milling. At an industrial-scale solids loading of 300 g VS/L liquid, the CPDM ?map? predicts a total acid concentration of 64.0 g/L at LRT of 30 days, VSLR of 7 g/(L�d), and conversion of 57%. Also high conversion of 76% and high acid concentration of 52 g/L are achieved at a VSLR of 4 g/(L�d) and LRT of 30 days.

With increasing energy demand, decreasing oil supply, and continuously accumulating waste in landfills, the interest in converting lignocellulosic biomass to liquid fuels has grown. The MixAlco™ process requires no exogenous enzymes, no sterility, can be adapted to any biodegradable feedstock, and converts lignocellulosic biomass into valuable chemicals and transportation fuels. This work focuses on the effects different feedstocks and inocula have on mixed-acid/hydrogen fermentations. When volatile solids (VS) are digested, mixed-acid fermentations produce hydrogen gas as a secondary byproduct. Hydrogen is only produced when there is an excess of NADH within the cell and when the energy selectivity (gamma) of the system has not been met. Continuous fermentations of paper produced 16.7 g carboxylic acid/L and 15.7 mL H2/g VS digested. Continuous fermentations of pretreated bagasse produced 17.1 g carboxylic acid/L and 41.1 mL H2/g VS digested. Both fermentations produced a fraction of the theoretical amount of hydrogen. The paper fermentation had a hydrogen percent yield of 6.9 percent, whereas the bagasse fermentation had a hydrogen percent yield of 22.6 percent. Hydrogen production was capped at this level because gamma had been met for these systems. The Bioscreening Project, a joint project between three departments, sought to improve the MixAlco™ process by finding natural cultures containing high biomass converters and high acid producers. A total of 505 inoculum samples were collected from 19 sites and screened using paper and yeast extract fermentations. The best converters were analyzed with Continuum Particle Distribution Modeling (CPDM). Nine inocula were run in paper and yeast extract countercurrent fermentations in which the overall performance varied less than 13 percent. Comparisons between six countercurrent train cultures showed an average culture similarity of 0.40 (Yue-Clayton similarity). With the dissimilar microbial cultures and the very similar fermentation performance, the performance of the MixAlco™ process depends on fermentation conditions, not on the microorganisms. Batch fermentations of office paper wastes, pineapple residue, Aloe vera rinds, wood molasses, sugar molasses, extracted algae, non-extracted algae, crude glycerol, obtained from the biodiesel process, and pretreated water hyacinths produced sufficient carboxylic acids and had sufficiently high conversions to be viable substrates for the MixAlco™ process.

Naturally occurring microbial communities from high-salt and/or high-temperature environments were collected from sites across the United States and Puerto Rico and screened for their efficacy in the MixAlco biofuel production platform. The MixAlco process, based on the carboxylate platform, is a sustainable and economically viable platform for converting lignocellulosic biomass to biofuels. Using a mixed culture of anaerobic organisms, lignocellulosic biomass is fermented into carboxylic acids, which are neutralized to their corresponding carboxylate salts. These salts can then be converted into a wide variety of chemical products and fuels (alcohols, gasoline, diesel, jet fuel). The central hypothesis is that microbial communities from relatively extreme environments, having evolved to withstand selection pressures similar to the conditions in the carboxylate platform, will exhibit high rates of biomass conversion. A total of 559 soil communities was screened as inocula in established laboratory-scale fermentations. We used pyrotag sequencing of 16S rRNA genes to characterize the bacterial components of the best-performing microbial communities. The best performing communities converted up to 3 times more biomass to acids than a standard marine community inoculum. The community analyses have allowed us to determine the extent to which the same functional types are favored during fermentation, at both laboratory and demonstration plant scales. In all cases, we observed a shift from the more diverse sediment community to post-fermentation communities with relatively low diversity dominated by organisms in the phylum Firmicutes, specifically Bacilli and Clostridia classes. Despite the fact that the inoculum sources were both geographically and ecologically diverse, all of the post-fermentation communities were more similar to each other in community structure than to the corresponding original inoculum community. In addition, studies of the sediments used as inocula revealed that environmental parameters, such as pH and water content, were significantly correlated with bacterial community composition. The wealth of data provided by current sequencing technologies allowed us to question whether communities with high process performances tend to achieve that performance with similar community structures.

With the inevitable depletion of the petroleum supply and increasing energy demands in the world, interest has been growing in bioconversion of lignocellulosic biomass (e.g., sugarcane bagasse). Lignocellulosic biomass is an abundant, inexpensive, and renewable resource. Most of current conversion technologies require expensive enzymes and sterility. In contrast, the patented MixAlco process requires no enzymes or sterility, making it attractive to convert lignocellulosic biomass to transportation fuels and valuable chemicals. This study focuses on pretreatment and thermophilic fermentation in the MixAlco process. Ammonium bicarbonate (NH4HCO3) was discovered to be a better pH buffer than previously widely used calcium carbonate (CaCO3) in anaerobic fermentations under thermophilic conditions (55°C). The desired pH should be controlled within 6.5 to 7.5. Over 85% acetate content in the product was found in paper fermentations and bagasse fermentations. Hot-lime-water-treated bagasse countercurrent fermentations buffered by ammonium bicarbonate achieved 50–60% higher total product concentrations than those using calcium carbonate. It was nearly double in paper batch fermentations if the pH was controlled around 7.0. Ammonium bicarbonate is a “weak” methane inhibitor, so a strong methane inhibitor (e.g., iodoform) is still required in ammonium bicarbonate buffered fermentations. Residual calcium salts did not show significant effects on ammonium bicarbonate buffered fermentations. Lake inocula from the Great Salt Lake, Utah, proved to be feasible in ammonium bicarbonate buffered fermentations. Under mesophilic conditions (40°C), the inoculum from the Great Salt Lake increased the total product concentration about 30%, compared to the marine inoculum. No significant fermentation performance difference, however, was found under thermophilic conditions. The Continuum Particle Distribution Model (CPDM) is a powerful tool to predict product concentrations and conversions for long-term countercurrent fermentations, based on batch fermentation data. The experimental acid concentrations and conversions agree well with the CPDM predictions (average absolute error < 15%). Aqueous ammonia treatment proved feasible for bagasse. Air-lime-treated bagasse had the highest acid concentration among the three treated bagasse. Air-lime treatment coupled with ammonium bicarbonate buffered fermentations is preferred for a “crop-tofuel” process. Aqueous ammonia treatment combined with ammonium bicarbonate buffered fermentations is a viable modification of the MixAlco process, if “ammonia recycle” is deployed.

In this work, 80% lime-treated rice straw and 20% lime-treated chicken manure were used as substrates in rotary fermentors. Countercurrent fermentation was performed at various volatile solid loading rates (VSLR) and liquid residence times (LRT). The highest acid productivity of 1.69 g/(L·d) was at a total acid concentration of 32.4 g/L. The highest conversion and yield were 0.692 g VS digested/g VS fed and 0.29 g total acids/g VS fed, respectively. The continuum particle distribution model (CPDM) was used to predict product concentrations at various VSLR and LRT. CPDM predicted the experimental total acid concentration and conversion at an average error of 6.41% and 6.55%, respectively. A fixed-bed fermentation system was designed to perform pretreatment and fermentation in the same unit. High product concentrations (~48 g/L) as well as high conversions (0.741 g VS digested/g VS fed, F4, Train B) were obtained from the same fermentor. CPDM was extended to predict product concentrations in the fixed-bed fermentation system. The model gave a good estimate of the product concentrations and retention time. After biomass fermentation, the residue can be combusted to generate heat. For pretreatment purposes, the use of ash can replace lime. A study was performed using ash as a potential pretreatment agent. Ash from raw poplar wood was effective in pretreating poplar wood; however, ash from bagasse fermentation residues was not useful in pretreating bagasse. Previous modeling studies indicate that a conversion of 95% could be achieved with bagasse using countercurrent fermentation. Because lignin constitutes 13% of the dry weight of bagasse, this means lignin would have to be digested to obtain a conversion of 95%. Experiments on the fermentation of enzymatically liberated lignin from both poplar wood and bagasse do not show that solubilized lignin was fermented to organic acids by using a mixed culture of marine microorganisms. Two buffer systems (ammonium bicarbonate and calcium carbonate) were used to compare product concentrations of carboxylic acid fermentations using office paper and chicken manure. It has been demonstrated that the total product concentration using ammonium bicarbonate is almost double the product concentration using calcium carbonate.

The carboxylate biofuels platform (CBP) involves the conversion of cellulosic biomass into carboxylate salts by a mixed microbial community. Chemical engineering approaches to convert these salts to a variety of fuels (diesel, gasoline, jet fuel) are well established. However, prior to initiation of this project, little was known about the influence of inoculum source on platform performance. The studies in this dissertation test the hypothesis that microbial communities from particular environments in nature (e.g. saline and/or thermal sediments) are pre-adapted to similar industrial process conditions and, therefore, exhibit superior performances. We screened an extensive collection of sediment samples from extreme environments across a wide geographic range to identify and characterize microbial communities with superior performances in the CBP. I sought to identify aspects of soil chemistry associated with superior CBP fermentation performance. We showed that CBP productivity was influenced by both fermentation conditions and inocula, thus is clearly reasonable to expect both can be optimized to target desired outcomes. Also, we learned that fermentation performance is not as simple as finding one soil parameter that leads to increases in all performance parameters. Rather, there are complex multivariate relationships that are likely indicative of trade-offs associated within the microbial communities. An analysis of targeted locus pyrosequence data for communities with superior performances in the fermentations provides clear associations between particular bacterial taxa and particular performance parameters. Further, I compared microbial community compositions across three different process screen technologies employed in research to understand and optimize CBP fermentations. Finally, we assembled and characterized an isolate library generated from a systematic culture approach. Based on partial 16S rRNA gene sequencing, I estimated operational taxonomic units (OTUs), and inferred a phylogeny of the OTUs. This isolate library will serve as a tool for future studies of assembled communities and bacterial adaptations useful within the CBP fermentations. Taken together the tools and results developed in this dissertation provide for refined hypotheses for optimizing inoculum identification, community composition, and process conditions for this important second generation biofuel platform.

The objective of this research was to develop novel and applicable methodologies to solve systematically problems along a roadmap of constructing a globally optimum biorefinery design. The roadmap consists of the following problems: (1) synthesis of conceptual biorefinery pathways from given feedstocks and products, (2) screening of the synthesized pathways to identify the most economic pathways, (3) development of a flexible biorefinery configuration, and (4) techno-economic analysis of a detailed biorefinery design. In the synthesis problem, a systems-based "forward-backward" approach was developed. It involves forward synthesis of biomass to possible intermediates and reverse synthesis starting with desired products and identifying necessary species and pathways leading to them. Then, two activities are performed to generate complete biorefinery pathways: matching (if one of the species synthesized in the forward step is also generated by the reverse step) or interception (a task is determined to take a forward-generated species with a reverse-generated species by identifying a known process or by using reaction pathway synthesis to link to two species.) In the screening problem, the Bellman's Principle of Optimality was applied to decompose the optimization problem into sub-problems in which an optimal policy of available technologies was determined for every conversion step. Subsequently, either a linear programming formulation or dynamic programming algorithm was used to determine the optimal pathways. In the configuration design problem, a new class of design problems with flexibility was proposed to build the most profitable plants that operate only when economic efficiency is favored. A new formulation approach with proposed constraints called disjunctive operation mode was also developed to solve the design problems. In the techno-economic analysis for a detailed design of biorefinery, the process producing hydrocarbon fuels from lignocellulose via the carboxylate platform was studied. This analysis employed many state-of-the-art chemical engineering fundamentals and used extensive sources of published data and advanced computing resources to yield reliable conclusions to the analysis. Case studies of alcohol-producing pathways from lignocellulosic biomass were discussed to demonstrate the merits of the proposed approaches in the former three problems. The process was extended to produce hydrocarbon fuels in the last problem.

Using mixed-culture fermentation, the carboxylate platform produces carboxylic acids, which are chemically converted into chemicals and fuels. To optimize the mixed-acid fermentation, different bioreactor configurations and operating modes were investigated. Intermittent air exposure did not affect fermentation performance and bacterial profiles, but reduced the high-molecular-weight carboxylic acids. The microbial flora contained strict and facultative microbes, suggesting the presence of a facultative anaerobic community existing in a biofilm. Compared to countercurrent trains, propagated fixed-bed fermentations have similar selectivity and acid distribution, but lower yield, conversion, productivity, and acid concentration. One- to six-stage countercurrent fermentations were operated with similar conditions. Fewer stages increased conversion, whereas more stages increased acid concentration and selectivity. One to four stages achieved similar yield, and four to six stages achieved similar maximum acid concentration. Maximum conversion was achieved with a single stage. Recycling residual biomass retained microorganisms and nutrients and increased yield and productivity. Relative to lower biomass reflux, higher reflux increased conversion, decreased selectivity, and did not affect yield. The recommended carbon-nitrogen ratio is ~24 g carbon/g nitrogen. In four-stage fermentations, recycle to the second fermentor and in parallel to the first three fermentors was optimal. Fermentations with excess or insufficient nitrogen had higher selectivity, but decreased yield and conversion. The glucose-utilization assay is a rapid and repeatable method for determining the amount of microbial activity in a sample. This method determined ~25% efficiency of a new cell separation method. In continuous fermentation, compared to no cell recycle, recycling cellular biomass increased selectivity and yield, but decreased conversion. Compared to lower cell reflux, higher reflux increased productivity, yield, and conversion, but decreased selectivity. Compared to residual biomass recycle, cell recycle had increased selectivity and yield, but decreased conversion. A new method to screen and rank inoculum sources from natural environments was successfully developed and tested.