Bioderived ionic liquid-based pretreatment enhances methane production from Agave tequilana bagasse

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.

Pretreatment of agave bagasse with ruminal fluid to improve methane recovery

Agave bagasse, a lignocellulosic waste that results from the milling and juice extraction of Agave tequilana var azul pineapples, is a suitable substrate for the production of methane through anaerobic digestion. However, it is necessary to apply a pretreatment to convert the bagasse into energy. In this context, this paper proposes using ruminal microorganisms to hydrolyze agave bagasse. This study evaluated the effect of the initial agave bagasse to ruminal fluid (S0/X0) ratio (0.33, 0.5, 1, and 2) on the hydrolysis efficiency. Subsequently, the supernatant was used for methane production. The hydrolysis efficiency increased as the S0/X0 ratio decreased. A hydrolysis efficiency of 60 % was achieved using an S0/X0 ratio of 0.33. The S0/X0 ratio of 0.33 optimally improved the specific methane production and energy recovery (155 ± 2 mL CH4/g TS and 6.1 ± 0.1 kJ/g TS) compared to raw biomass. The most abundant hydrolytic bacteria were Prevotella, Ruminococcus and Fibrobacter, and Engyodontium was the most abundant proteolytic fungus.

Prokaryotic population dynamics and interactions in an AnSBBR using tequila vinasses as substrate in co-digestion with acid hydrolysates of Agave tequilana var. azul bagasse for hydrogen production

AIMS

The purpose of this study was to characterize the prokaryotic community and putative microbial interactions between H₂ -producing bacteria (HPB) and non-HPB using two anaerobic sequencing batch biofilm reactors (AnSBBRs) fed with tequila vinasses in co-digestion with acid hydrolysates of Agave tequilana var. azul bagasse (ATAB).

METHODS AND RESULTS

Two AnSBBRs were operated for H₂ production to correlate changes in physicochemical and biological variables by principal component analysis (PCA). Results indicated that H₂ yield was supported by Ethanoligenens harbinense and Clostridium tyrobutyricum through the PFOR pathway. However, only E. harbinense was able to compete for sugars against non-HPB. Competitive exclusion associated with competition for sugars, depletion of essential trace elements, bacteriocin production and resistance to inhibitory compounds could be carried out by non-HPB, increasing their relative abundances during the dark fermentation (DF) process.

CONCLUSIONS

The global scenario obtained by PCA correlated the decrease in H₂ production with the lactate:acetate molar ratio in the influent. At the beginning of co-digestion, this ratio had the minimum value considered for a net gain of ATP. This fact could cause the reduction of the relative abundance of C. tyrobutyricum.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study that demonstrated the feasibility of H₂ production by Clostridiales from acid hydrolysates of ATAB in co-digestion with tequila vinasses.