(292a) Anaerobic Fermentation Of Sugarcane Bagasse To Carboxylic Acids

Serious issues that post an urgent call for a sustainable energy sources other than the currently used are: the inevitable exhaustion of fossil fuels due to their not renewable nature, the economic crisis in the chemical industry given by the almost total dependence on exhaustible sources of energy and critically adverse climate changes due to the increase of green house gasses in the atmosphere.

The synthesis of ethanol via biomass is possible through different routes, for example, fermentation using microorganisms that have and have not been genetically modified to produce first and second generation biofuels. This work considers biofuels production through the MixAlco^® process, which makes use of agricultural, industrial, and municipal waste to produce biofuels and other commodity chemicals through a combination of a biological and chemical steps. This process does not use genetic engineering and does not compromise food security, nor shifts the traditional agricultural activity. In addition, this route has proved to be more feasible economically, technically and environmentally than other routes.

MixAlco^® fermentation is "a process that is characterized by its Mixed-Acid fermentation which employs a mixed culture of acid forming bacteria (not a mono culture) and it is not sterile which lowers capital and operating costs".

This study was focused on kinetic characterization over the production of Equivalent Acetic Acid (EAA) per gram of Volatile Solid (VS) at varying Volatile Solid Loading Rates (VSLR, define as the rate at which the reactive biomass is added to the system) and Liquid Residence Times (LRT, define as the time how long the liquid remains in the system). These fermentations were made at thermophilic conditions and using MixAlco^® technology with three native inocula. In this work, incoula were obtained from two types of environments: marine (i) and brackish (ii and iii). Thus, one of the inocula was taken from marine environment, and the other two were taken from brackish environment. Pretreated sugarcane bagasse and chicken manure mixture was used as substrate.

In the first part, batch experiments were made (during 28 d) at different concentration of substrate (20, 40, 70 and 100 g/L), obtaining EAA production curves against time. These experiments were made using inocula without microbial adaptation to any carbon source (sugars). Next, data were adjusted to an empirical expression that represents the velocity of reaction for these specific systems with each inocula. Through Continuum Particle Distribution Model (CPDM), a simulation of four (4) Continuous Stirred Tank Reactors (CSTR) in countercurrent was made, predicting the final concentration of EAA (g/L) and conversion (VS digested/g VS fed) for a set of VSLR (g L^-1d^-1) and LRT (d). The values used for VSLR were 4, 6, 8, 10, 12 (g L^-1d^-1), and for LRT were 10, 15, 20, 25, 30 d. Thus, the maximum EAA predicted for marine inoculum (i) was 10.75 g/L at VSLR = 6 g L^-1d^-1 and LRT = 30 d with a conversion of 0.125 g VS digested/g VS fed. The maximum conversion predicted was 0.234 g VS digested/g VS fed with an EAA production of 4.85 g/L at VSLR = 4 g L^-1d^-1 and LRT = 10 d. The maximum EAA predicted for brackish inoculum (ii) was 11.6 g/L at VSLR = 10 g L^-1d^-1 and LRT = 30 d with a conversion of 0.10 g VS digested/g VS fed. The maximum conversion predicted was 0.27 g VS digested/g VS fed with an EAA production of 4.56 g/L at VSLR = 4 g L^-1d^-1 and LRT = 10 d. The maximum EAA predicted for brackish inoculum (iii) was 14.52 g/L at VSLR = 10 g L^-1d^-1 and LRT = 30 d with a conversion of 0.08 VS digested/g VS fed. The maximum conversion predicted was 0.22 g VS digested/g VS fed with an EAA production of 5.93 g/L at VSLR = 4 g L^-1d^-1 and LRT = 10 d. 

In the second part, batch experiments were made (during 28 d) at the same substrate concentration (20, 40, 70 and 100 g/L), but using the liquid remain from the previous batch. This liquid is expected to contain adapted microbial community to carbon sources (cellulose and hemicellulose). In the same way, EAA production curves against time were obtained and CPDM predictions were made at the conditions mentioned above. Thus, the maximum EAA predicted for marine inoculum (i) was 26 g/L at VSLR = 12 g L^-1d^-1 and LRT = 30 d with a conversion of 0.19 g VS digested/g VS fed. The maximum conversion predicted was 0.327 g VS digested/g VS fed with an EAA production of 8 g/L at VSLR = 4 g L^-1d^-1 and LRT = 15 d. The maximum EAA predicted for brackish inoculum (ii) was 25.7 g/L at VSLR = 12 g L^-1d^-1 and LRT = 30 d with a conversion of 0.19 g VS digested/g VS fed. The maximum conversion predicted was 0.309 g VS digested/g VS fed with an EAA production of 4.94 g/L at VSLR = 4 g L^-1d^-1 and LRT = 10 d. The maximum EAA predicted for brackish inoculum (iii) was 24.1 g/L at VSLR = 12 g L^-1d^-1 and LRT = 30 d with a conversion of 0.19 g VS digested/g VS fed. The maximum conversion predicted was 0.304 VS digested/g VS fed with an EAA production of 7.02 g/L at VSLR = 4 g L^-1d^-1 and LRT = 15 d.

In the third part, countercurrent experiments using each inoculum were made, obtaining the difference between theoretical and experimental results (EEA and conversion). Finally, comparison from reported results in literature was made, showing that EEA produced for each inoculum is feasible for MixAlco^® process.