Optimization of cost-effective enzymatic saccharification using low-cost protic ionic liquid as pretreatment agent in Agave bagasse.

This work studied the optimization of enzymatic saccharification of Agave tequilana bagasse (ATB) pretreated with the low-cost protic ionic liquid (PIL) ethanolamine acetate ([EOA][OAc]) using the highly available and cost-effective mixture of the enzymatic cocktails Celluclast 1.5L-Viscozyme L. Response surface methodology (RSM) was employed to maximize the sugars concentration and yield. The RSM optimization conditions of the enzymatic saccharification of pretreated ATB that achieved the maximum reducing sugars (RS) concentration were: 11.50 % w/v solids loading, 4.26 pH with 0.76 and 1.86 mg protein/mL buffer of Viscozyme L and Celluclast 1.5L, respectively. Similarly, the conditions that maximize the sugar yield (SY) were solids loading of 5.62 % w/v, and 4.51 pH as well as 1.07 and 2.03 mg protein/mL buffer of Viscozyme L and Celluclast 1.5L, respectively. Saccharification performance of the first-generation and low-cost enzyme mixture Celluclast 1.5L-Viscozyme L was compared with that reached by a second-generation and higher-cost CTec2, where Celluclast 1.5L-Viscozyme L achieved 60.86 ± 2.66 % y 79.25 ± 3.34 % of the sugars released by CTec2 at the same hydrolysis time (12 h) for the sugar concentration and yield models, respectively. These results are encouraging since they positively contribute to cost reduction and availability issues, which are key parameters to consider when thinking about scaling-up the process.

Enhancing biohydrogen production from Agave tequilana bagasse: Detoxified vs. Undetoxified acid hydrolysates.

The aim of this work was to compare the biohydrogen production potential of undetoxified and detoxified acid hydrolysates from A. tequilana bagasse. Detoxification was carried out with activated carbon at different concentrations and pH values. Results indicated that pH was not a significant variable, while the lowest evaluated concentration of activated carbon (1% p/v) significantly promoted the highest removal of acetic acid (89%) with minimal losses of fermentable sugars. Regarding dark fermentation experiments, central composite designs were used to optimize COD and pH variables for both substrates, undetoxified and detoxified hydrolysates (activated carbon 1% p/v and pH 0.6). At optimal conditions, the detoxified hydrolysate produced 33% more biohydrogen than the undetoxified one. Hydrogen molar yields were 1.71 and 1.23 mol H2/molsugar, respectively. This improvement was correlated to changes in metabolic byproducts, since the detoxified hydrolysate produced only acetic and butyric acids, while lactic acid was detected in the undetoxified hydrolysate.

Mild reaction conditions induce high sugar yields during the pretreatment of Agave tequilana bagasse with 1-ethyl-3-methylimidazolium acetate.

Sequential 2k factorial and central composite designs were used to optimize Agave tequilana bagasse (ATB) pretreatment by using 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]). Reaction time, temperature and solids loading were the studied factors while sugar yield was the response variable. Results indicated that optimal conditions (119 °C, 142 min) using high solids loading (30%) were achieved at lower temperatures and reaction times than those previously reported in the literature. It was also revealed that solid recovery after pretreatment with [Emim][OAc] is a key factor. The increase in enzymatic digestibility of pretreated ATB was correlated to a decrease in crystallinity and lower lignin content as observed using microscopy techniques and weaken chemical bonds by Fourier transform infrared spectroscopy. Yields of glucose and xylose in the hydrolysate were 41.3, and 13.0 kg per 100 kg of untreated ATB, which are equivalent to glucan and xylan conversions of 75.9% and 82.9%, respectively.

Agave tequilana bagasse for methane production in batch and sequencing batch reactors: Acid catalyst effect, batch optimization and stability of the semi-continuous process.

Agave tequilana bagasse is the main solid waste of the tequila manufacturing and represents an environmental issue as well as a potential feedstock for biofuel production due to its lignocellulosic composition and abundance. In this contribution, this feedstock was subjected to pretreatments with HCl and H2SO4 for sugar recovery and methane was produced from the hydrolysates in batch and sequencing batch reactors (AnSBR). Sugar recovery was optimized by using central composite designs at different levels of temperature, acid concentration and hydrolysis time. Results showed that at optimal conditions, the HCl pretreatment induced higher sugar recoveries than the H2SO4 one, 0.39 vs. 0.26 g total sugars/g bagasse. Furthermore, the H2SO4 hydrolysate contained higher concentrations of potential inhibitory compounds (furans and acetic acid). Subsequent anaerobic batch assays demonstrated that the HCl hydrolysate is a more suitable substrate for methane production; a four-fold increase was found. A second optimization by using HCl as acid catalyst and methane production as the response variable demonstrated that softer hydrolysis conditions are required to optimize methane production as compared to sugar recovery (1.8% HCl, 119 °C and 103min vs. 1.9% HCl, 130 °C and 133min). This softer conditions were used to feed an AnSBR for 110 days and evaluate its stability at three different cycle times (5, 3 and 2 days). Results showed stable reactor performances at cycle times of 5 and 3 days, obtaining the highest methane yield and production at 3 days, 0.28 NL CH4/g-COD and 1.04 NL CH4/d respectively. Operation at shorter cycle times is not advised due to microbial imbalance.

Nutrient composition of culture media induces different patterns of CO2 fixation from biogas and biomass production by the microalga Scenedesmus obliquus U169.

Microalgae are considered as a promising biotechnological strategy to capture CO2 from biogas, producing biomass with valuable energetic compounds. This study has evaluated the biotechnological potential to fix CO2 from biogas and biomass production by Scenedesmus obliquus cultured in four different formulations of culture media, C30, Bristol, Bold 3N, and C30+M, as well as the effect of methane (CH4) of biogas during CO2 fixation and biomass production. The results obtained showed that different nutrient composition and concentration of culture media, mainly micronutrient and vitamin concentrations, induced different patterns of CO2 fixation from biogas and biomass production in S. obliquus. The highest CO2 fixation (23.03 ± 0.24%) and biomass production (4.63 ± 0.31 g L-1) were attained in the microalgae growing in C30+M medium, accumulating mainly proteins. Moreover, these results demonstrated that the CH4 of biogas did not affect CO2 fixation from biogas and biomass production by S. obliquus. Overall, these results demonstrated that a culture medium with a balanced nutrient supply is crucial to increasing the biotechnological potential of microalgae to fix CO2 from biogas.

CO2 Removal from Biogas by Cyanobacterium Leptolyngbya sp. CChF1 Isolated from the Lake Chapala, Mexico: Optimization of the Temperature and Light Intensity.

In the present study, the capacity of the cyanobacterium Leptolyngbya sp. CChF1 to remove CO2 from real and synthetic biogas was evaluated. The identification of the cyanobacterium, isolated from the lake Chapala, was carried out by means of morphological and molecular analyses, while its potential for CO2 removal from biogas streams was evaluated by kinetic experiments and optimized by a central composite design coupled to a response surface methodology. Results demonstrated that Leptolyngbya sp. CChF1 is able to remove CO2 and grow indistinctly in real or synthetic biogas streams, showing tolerance to high concentrations of CO2 and CH4, 25 and 75%, respectively. The characterization of the biomass composition at the end of the kinetic assays revealed that the main accumulated by-products under both biogas streams were lipids, followed by proteins and carbohydrates. Regarding the optimization experiments, light intensity and temperature were the studied variables, while synthetic biogas was the carbon source. Results showed that light intensity was significant for CO2 capture efficiency (p = 0.0290), while temperature was significant for biomass production (p = 0.0024). The predicted CO2 capture efficiency under optimal conditions (27.1 °C and 920 lx) was 93.48%. Overall, the results of the present study suggest that Leptolyngbya sp. CChF1 is a suitable candidate for biogas upgrading.

Methane production from acid hydrolysates of Agave tequilana bagasse: evaluation of hydrolysis conditions and methane yield.

Evaluation of diluted acid hydrolysis for sugar extraction from cooked and uncooked Agave tequilana bagasse and feasibility of using the hydrolysates as substrate for methane production, with and without nutrient addition, in anaerobic sequencing batch reactors (AnSBR) were studied. Results showed that the hydrolysis over the cooked bagasse was more effective for sugar extraction at the studied conditions. Total sugars concentration in the cooked and uncooked bagasse hydrolysates were 27.9 g/L and 18.7 g/L, respectively. However, 5-hydroxymethylfurfural was detected in the cooked bagasse hydrolysate, and therefore, the uncooked bagasse hydrolysate was selected as substrate for methane production. Interestingly, results showed that the AnSBR operated without nutrient addition obtained a constant methane production (0.26 L CH4/g COD), whereas the AnSBR operated with nutrient addition presented a gradual methane suppression. Molecular analyses suggested that methane suppression in the experiment with nutrient addition was due to a negative effect over the archaeal/bacterial ratio.