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Agave bagasse (AB) is a lignocellulosic biomass with potential to obtain high value-added products such as lignin, microcrystalline cellulose, and polysaccharides that can be used for biofuel production. A Central Composite Design (CCD) was used to evaluate the effect of temperature, thermal treatment time, ethanol concentration, solid/liquid ratio, size particle, and sodium hydroxide concentration on delignification and lignin recovery from AB. In addition, the influence of delignification on the enzymatic hydrolysis using commercial enzymes was determined. This organosolv process allowed a delignification of 91.49% and 76% of the lignin recovery, at 150 °C, 10 min, 40% (v/v) ethanol, solid/liquid ratio of 1:10 g/mL, particle size of 0.5 mm – 1 mm, and 5.5% (w/v) sodium hydroxide. The maximum specific yield of enzymatic hydrolysis (SYEH), under the best conditions for delignification, was of 844.40 ± 9.70 mg total sugars per g of bagasse pretreated with organosolv (BPO), which was 4.42 times higher than the yield obtained from bagasse without pretreatment (BWP). Additionally, the enzymatic hydrolysate of BPO produced 303.62 ± 10.62 NmLCH4/g BPO. Furthermore, an energy recovery efficiency of 64.13 ± 0.9% was obtained for BPO hydrolysate which is 2.60 times higher than that of BWP hydrolysate (24.88 ± 0.92%). In a biorefinery concept, alkaline organosolv pretreatment of AB was highly efficient for lignin production, and improved the enzymatic hydrolysis of polysaccharides, which allowed a higher energy recovery. [ABSTRACT FROM AUTHOR]

The efficiency of enzymatic saccharification of lignocellulosic biomass is a key step for biofuels production in the biochemical biorefineries. A novel sequential process, hydrothermal pretreatment followed by enzymatic hydrolysis, of agave bagasse was investigated to improve the release of sugars and the methane production. After optimization of the hydrothermal pretreatment by surface response methodology, a hemicellulose removal of 93.6% was obtained at 180 °C/50 min. Hemicellulose removal enhanced cellulose depolymerization during the enzymatic hydrolysis of the pretreated bagasse by 2.3 times as compared to the untreated bagasse. The single-stage batch methane production of the hydrothermal and enzymatic hydrolysates were 0.223 ± 0.02 NL CH 4 / g COD add and 0.305 ± 0.03 NL CH 4 /g COD add respectively, indicating a higher biodegradability of the enzymatic hydrolysate. The combined energy recovered from the hydrothermal and enzymatic hydrolysates was 3.4 times greater than that recovered from untreated agave bagasse hydrolysate. Also, the combined energy recovery was higher than the energy recovery reported in the literature for agave bagasse pretreated with other chemical and hydrothermal pretreatments. Overall, this study enhanced the saccharification efficiency and biodegradability of polysaccharides present in agave bagasse through efficient saccharification of cellulose and hemicellulose. This was reflected in a high value of combined energy recovery efficiency (54.1%) in the form of methane. [Display omitted] • Hydrothermal pretreatment was optimized by surface response methodology. • The pretreatment enhanced cellulose enzymatic saccharification by 2.3 times. • A maximum hemicellulose removal during hydrothermal pretreatment was 93.6%. • Cellulose enzymatic saccharification yield of pretreated bagasse was 81.8%. • Total energy recovery was higher than for other processes. [ABSTRACT FROM AUTHOR]

Abstract: Agave bagasse (AB) is the main solid waste generated by the tequila industry in Mexico, which is an environmental concern due to its considerable volume of production (377,000 Ton in 2016). AB is a lignocellulosic biomass that has been considered as a potential feedstock for different industrial uses in the framework of lignocellulosic biorefinery concept. The lignocellulosic biomass is a complex structure constituted by cellulose, hemicellulose and lignin. Therefore, for a complete waste revalorization, different processing steps would be required. In this work, the scientific advances toward the AB biorefinery composed by three sequential stages: pretreatment, treatment and biofuels production were reviewed. Moreover, the by-products of the process could also be recovered and used for the synthesis of value-added products. This integrative approach of AB in the conceptualized biorefinery generates positive impacts on environment as well as on local and regional economies.Graphical Abstract: [ABSTRACT FROM AUTHOR]

• Four pretreatments were compared in terms of solubilization and methane production. • Dilute acid pretreatment reached the highest solubilization of organic matter. • Hydrolyzates differentiate only in terms of lag phase and the methane production rate. • Most hydrolyzates reached the same biochemical methane potential of 219 mL CH 4 /g COD. Agave bagasse is a lignocellulosic agroindustrial waste suitable for biofuel production. This study aimed to compare biological, enzymatic, chemical, and hydrothermal pretreatments applied to Agave bagasse in terms of solubilization of carbohydrates (CHO) and chemical oxygen demand (COD), as well as the biochemical methane potential (BMP) from hydrolyzates. Most pretreatments behave similarly, with an average yield of 0.16 ± 0.02 g COD /g, only the chemical pretreatment overcame this yield by a factor of 2.6 with a CHO/COD ratio of 0.95. The concentrations of inhibitors – furfural, hydroxymethylfurfural, and phenols – were higher in the chemical hydrolyzates than in the biological and enzymatic hydrolyzates. BMP from most hydrolyzates was the same, on average 219 ± 15 mL/g CODin , hydrolyzates differentiate only in terms of lag phase and the methane production rates. [ABSTRACT FROM AUTHOR]

An AM2 model modification is proposed by including the parameter identification and a robust feedback control synthesis. The contribution is shown by experimental proof-of-concept. The AM2 model is modified with the aim of including the CODs changes in the effluent near the steady state with the inlet CODt concentration changes at a fixed flow rate. The parameter identification is experimentally implemented on-line and computationally performed via the Levenberg–Marquardt algorithm. To this end, an experimental set-up was carried out each from a two-stage biomethane production process stage as an instrumented and automated bioreactor. Afterward, robust feedback control is implemented for each stage. For the first stage, the VFA productivity maximum is defined as the control goal whereas the biomethane maximum flow is the aim on the second stage. The feedback control is robust against kinetics and parametric uncertainties such that the biogas production reaches biomethane maximum production. In this sense, the contribution shows the biomethane production can be optimized through enzymatic agave bagasse hydrolysate. • Biogas yielding via enzymatic hydrolysate of agave bagasse needs model modification. • A modified model renders an accurate structure for kinetics parameter identification. • A robust feedback control allows us to enhance the biomethane production. • An experimental benchmark shows the concept of enhancing biomethane production. [ABSTRACT FROM AUTHOR]

• Plants of 500 tons/d of Agave bagasse to produce methane and power were simulated. • Biological, enzymatic, dilute acid, and steam explosion pretreatments were considered. • The capital expenses (CAPEX) and operative expenses (OPEX) were analyzed. • Pretreatment and anaerobic digestion parameters were based on experimental data. • The energy produced was two times the energy consumed in all the scenarios. Agave bagasse is an agricultural residue that has the potential to be used as feedstock biorefineries. However, its complex structure requires a pretreatment step to facilitate the accessibility to carbohydrates for its subsequent conversion. In this study, the capital and operative expenses (CAPEX and OPEX) were simulated for industrial plants processing 500 ton/d of Agave bagasse using different pretreatment platforms for methane production and power generation on experimental data. The scenarios consisted of i) biological, ii) enzymatic, iii) dilute acid, and iv) steam explosion pretreatments and a case-based scenario without pretreatment. All these scenarios included milling, pretreatment, anaerobic digestion, and cogeneration stages. The results showed that those pretreatments carried out under soft conditions (biological and enzymatic) decreased between 2.1 and 2.8 times CAPEX compared to the highest value obtained in the diluted acid and case-based scenarios. The steam explosion, a pretreatment carried out under severe conditions, was less effective reducing CAPEX by only 1.2 times compared to the highest value. Furthermore, compared to the case-base scenario, only the biological pretreatment reduced the OPEX by a factor of 2, whereas the other pretreatments resulted in OPEX that were 2.0 to 3.5 times higher. Among the utilities (cooling water, steam generation, and energy) the steam generation contributed 47% to 76% of the total OPEX. The energy produced (kW⋅h/yr) was approximately twice the energy consumed for all scenarios. A sensitivity analysis demonstrated the robustness of the platforms since fluctuations in the prices of feedstock and raw materials did not impact the total production cost of methane, except for biological and enzymatic pretreatments. For all platforms, the solid loading was the process parameter with the highest impact on the production cost of methane. Overall, the study showed that biological and enzymatic pretreatments had the best economic performance. However, low substrate conversion and the high cost of enzymes and equipment, respectively, remained the main challenges to address in future research. [ABSTRACT FROM AUTHOR]

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 CH 4 /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. [ABSTRACT FROM AUTHOR]

• Cellulase 50XL is comparable to Celluclast 1.5 L and it is locally-available and less expensive. • Volumetric methane production rate (VMPR) was 2.3 times higher in the UASB than in the CSTR. • Low solid retention time in CSTR was detrimental to VMPR. • Organic loading rates and hydraulic retention times framed the microbial community structure. • Hydrogenotrophic methanogens were dominant in UASB and acetoclastic methanogens in CSTR. Methane production from an enzymatic agave bagasse hydrolysate was evaluated in a continuous stirred tank reactor (CSTR) and in an upflow anaerobic sludge blanket reactor (UASB). The effect of different organic loading rates (OLRs) and hydraulic retention times (HRTs) on volumetric methane production rate (VMPR) was tested. To hydrolyze the bagasse, Cellulase 50XL, a food-grade enzyme, allowed a saccharification yield of lignocellulosic biomass similar to Celluclast 1.5L, which is used to treat lignocellulosic substrates. The UASB reactor operated at larger OLR (e.g., 20 g CODs/L-d) and shorter HRT (e.g., 30 h) than the CSTR (e.g., OLR of 7.3 g CODs/L-d and HRT of 66 h). The UASB achieved a VMPR of 4.5 ± 0.1 L CH 4 /L-d and COD removal of 94% while the CSTR had a VMPR of 1.92 ± 0.03 L CH 4 /L-d and COD removal of 88%. The better performance of the UASB than the CSTR can be explained by the high solid retention time (SRT) and the microbial community composition, which was less diverse than the CSTR's community. Hydrogenotrophic methanogens were abundant in the UASB while acetoclastic methanogens dominated in the CSTR. The high VMPR obtained by the UASB reactor and the use of Cellulase 50XL can be advantageous features for future industrial application. [ABSTRACT FROM AUTHOR]