Sagar Lonkar

Global warming, steadily increasing energy demand, and limited fossil fuel reserves are growing concerns of modern society. In the past few decades, significant advances in renewable energy research have helped reduce dependence on conventional non-renewable energy sources. Biofuels are sustainable and can replace petroleum-based
fuels. Biofuels can be produced through three different platforms: thermochemical, sugar, and carboxylate. Based on experimental results, this dissertation suggests process improvements in the carboxylate and sugar platform to make biofuels more economically attractive.
The carboxylate platform is a robust and scalable technology that produces fuels and chemicals from biomass. It employs methane-inhibited anaerobic fermentation to produce mainly short-chain fatty acids (SCFA, e.g., acetic, propanoic, butanoic, pentanoic). Medium-chain fatty acids (MCFA, e.g., hexanoic, heptanoic, octanoic acid) are more valuable than SCFAs. By feeding ethanol to the fermentor, MCFA formation is
enhanced through chain elongation. To maximize MCFA production, alcohol
concentrations and temperature were optimized in the mixed-culture fermentation. Chain
elongation occurs at low temperatures (≤40 °C) and does not occur at 55 °C.
Using the sugar platform, enzymes are a major cost contributor in biofuel
production. Conventionally, enzymatic saccharification is performed in batch. To more
efficiently use enzymes, a new continuous countercurrent method is explored. Pseudocontinuous countercurrent saccharification was performed on lime-pretreated corn stoveriii
at enzyme loadings of 1 mg CTec3/g dry biomass and (1 mg CTec3 + 1 mg HTec3)/g
dry biomass and the results were compared with batch. To achieve the same glucan
conversion as compared to batch, countercurrent saccharification reduced enzyme
loading by 1.6 and 1.4 times at 1 mg protein/g biomass and 2 mg protein/g biomass,
respectively.
In rapidly growing developing countries, waste disposal is a major challenge. To
address this challenge, the MixAlco process was investigated as an alternative to create
economic incentives for waste disposal. The MixAlco process is one example of
carboxylate platform. This work focuses on fermenting municipal solid waste in batch
fermentations. Using the Continuum Particle Distribution Model (CPDM), the
performance of continuous countercurrent fermentation was predicted at different
volatile solid loading rates (VSLR) and liquid residence times (LRT)

At pH 4.8 and 50 C, semi-continuous countercurrent saccharification was performed using a-cellulose. Every second day, solids and liquids were transferred countercurrently and liquid samples were taken to determine sugar concentration in each stage. Train 1 (5 mg protein/g biomass, 8 stages) achieved 87.8% glucose conversion and 102 g/L total sugar. Train 2 (2 mg/g, 8 stages) achieved 56.1% glucose conversion and 65 g/L total sugar. Train 3 (2 mg/g, 16 bottles) achieved 73.6% glucose conversion and 67 g/L total sugar. Compared to 5-day batch saccharification, to achieve the same glucose conversion, enzyme requirements were reduced by factors of 16.8, 8, and 20.5 for Trains 1, 2, and 3, respectively. Further improvements can be realized by changing the enzyme addition point and increasing the number of stages.

Using the sugar platform, enzymes are a major cost contributor in biofuel production. Conventionally, enzymatic saccharification is performed in batch. To more efficiently use enzymes, a new continuous countercurrent method is explored. Pseudo-continuous countercurrent saccharification was performed on lime-pretreated corn stover at enzyme loadings of 1 mg CTec3/g dry biomass and (1 mg CTec3 þ 1 mg HTec3)/g dry biomass and the results were compared with batch. To achieve the same glucan conversion as compared to batch, countercurrent saccharification reduced enzyme loading by 1.6 and 1.4 times at 1 mg protein/g biomass and 2 mg protein/g biomass, respectively. In batch saccharification, the effect of hemicellulase addition was investigated. In countercurrent saccharification, as compared to only 1 mg CTec3/g biomass loading, adding 1 mg HTec3/g biomass increased glucose and xylose yields by 6% and 12%, respectively. The effect of product sugars on enzyme inhibition was studied in batch saccharification.

Corn stover was pretreated with submerged lime plus shock, a mechanical treatment that subjects biomass to a detonation wave. In a series of bottles, pretreated corn stover was countercurrently sac-charified with enzyme loadings of CTec3 (1 mg protein/g dry biomass), CTec3 (1 mg protein/g dry biomass) þ HTec3 (1 mg protein/g dry biomass), and CTec3 (2 mg protein/g dry biomass) þ HTec3 (2 mg protein/g dry biomass). To reach a given glucan conversion at low enzyme loadings, countercurrent saccharification reduced enzyme loadings by 1.9 times compared with batch saccharification but was not helpful at high enzyme loadings. To preserve the sugars during saccharification, volatile anti-microbials (chloroform and essential oils from thyme and oregano) prevent the growth of contaminating microorganisms. A simple packed column is proposed to perform commercial-scale countercurrent saccharification.

In rapidly growing developing countries, waste disposal is a major challenge. Current waste disposal methods (e.g., landfills and sewage treatment) incur costs and often are not employed; thus, wastes accumulate in the environment. To address this challenge, it is advantageous to create economic incentives to collect and process wastes. One approach is the MixAlco process, which uses methane-inhibited anaerobic fermentation to convert waste biomass into carboxylate salts, which are chemically converted to industrial chemicals and fuels. In this paper, humanure (raw human feces and urine) is explored as a possible nutrient source for fermentation. This work focuses on fermenting municipal solid waste (energy source) and humanure (nutrient source) in batch fermentations. Using the Continuum Particle Distribution Model (CPDM), the performance of continuous countercurrent fermentation was predicted at different volatile solid loading rates (VSLR) and liquid residence times (LRT). For a four-stage countercurrent fermentation system at VSLR = 4 g/(L day), LRT = 30 days, and solids concentration = 100 g/L liquid, the model predicts carboxylic acid concentration of 68 g/L and conversion of 78.5 %.

To feed a growing population, alternative sources of animal feed (e.g., lignocellulose) are needed to replace grains (e.g., corn). Oxidative lime
pretreatment (OLP) increases lignocellulose digestibility by removing lignin and hemicellulose acetyl content. Adding a mechanical pretreatment (e.g., ball milling) further improves digestibility. This study
determines the effectiveness of OLP and ball milling to enhance the ruminant digestibility of lignocellulose. For forage sorghum, the 48-h in vitro TDN were 40, 64, and 84 g nutrients digested/100 g organic matter (OM) for raw, short-term OLP, and short-term OLP + ball milling, respectively. In terms of compositional changes, OLP increases NDF and decreases non-fiber carbohydrate (NFC) and crude protein (CP), all of
which would normally be associated with a decrease in digestibility. However, because OLP and ball milling beneficially change composition (lignin removal) and structural features (reduced crystallinity), digestibility actually increases. Although ball milling increases digestibility according to standard laboratory assays, it reduces particle size possibly allowing fne particles to escape from the rumen before they are digested, thus limiting its practical application. Nonetheless, this study indicates that mechanical pretreatment greatly increases digestibility, and therefore it is desirable to identify an effective mechanical treatment that retains fiber integrity

Medium-chain fatty acids (MCFA, e.g., caproic, heptanoic, caprylic acid) are more valuable than short-chain fatty acids (SCFA, e.g., acetic, propionic, butyric, valeric acid). SCFAs are major products in methane-inhibited mixed-culture anaerobic fermentation. By feeding ethanol to the fermentor, MCFA formation is enhanced through chain elongation. Microorganisms such as Clostridium kluyveri elongate short-chain acids by combining them with alcohol. Very low ethanol concentration reduces chain elongation rates, whereas very high ethanol concentrations inhibit microorganisms. To maximize MCFA production, different ethanol concentrations were investigated in the mixed-culture fermentation of office paper and chicken manure. At 10 g/L ethanol concentration , 10 g/L MCFA was formed. High ethanol concentrations (above 40 g/L) inhibit microorganisms resulting in no chain elongation. For chain elongation, propanol was found to be more inhibitory than ethanol. The data suggest that MCFA production will increase by continuously extracting MCFA and maintaining 5-10 g/L ethanol concentration by periodic addition.