Operational and biochemical aspects of co-digestion (co-AD) from sugarcane vinasse, filter cake, and deacetylation liquor.

This work performed co-AD from the vinasse and filter cake (from 1G ethanol production) and deacetylation liquor (from the pretreatment of sugarcane straw for 2G ethanol production) in a semi-Continuous Stirred Tank Reactor (s-CSTR) aiming to provide optimum operational parameters for continuous CH4 production. Using filter cake as co-substrate may allow the reactor to operate throughout the year, as it is available in the sugarcane off-season, unlike vinasse. A comparison was made from the microbial community of the seed sludge and the reactor sludge when CH4 production stabilized. Lactate, butyrate, and propionate fermentation routes were denoted at the start-up of the s-CSTR, characterizing the acidogenic phase: the oxidation-reduction potential (ORP) values ranged from -800 to -100 mV. Once the methanogenesis was initiated, alkalizing addition was no longer needed as its demand by the microorganisms was supplied by the alkali characteristics of the deacetylation liquor. The gradual increase of the applied organic load rates (OLR) allowed stabilization of the methanogenesis from 3.20 gVS L-1 day-1: the highest CH4 yield (230 mLNCH4 g-1VS) and average organic matter removal efficiency (83% ± 13) was achieved at ORL of 4.16 gVS L-1 day-1. The microbial community changed along with the reactor operation, presenting different metabolic routes mainly due to the used lignocellulosic substrates. Bacteria from the syntrophic acetate oxidation (SAO) process coupled to hydrogenotrophic methanogenesis were predominant (~ 90% Methanoculleus) during the CH4 production stability. The overall results are useful as preliminary drivers in terms of visualizing the co-AD process in a sugarcane biorefinery integrated to scale. KEY POINTS: • Integration of 1G2G sugarcane ethanol biorefinery from co-digestion of its residues. • Biogas production from vinasse, filter cake, and deacetylation liquor in a semi-CSTR. • Lignocellulosic substrates affected the biochemical routes and microbial community. • Biomol confirmed the establishment of the thermophilic community from mesophilic sludge.

Anaerobic co-digestion of residues in 1G2G sugarcane biorefineries for enhanced electricity and biomethane production.

The energy potential of residue-derived biogas via electricity and biomethane production was assessed in an integrated 1G2G sugarcane biorefinery concept. The mono-digestion of 1G-vinasse (1G-VN) was compared with different co-digestion systems, namely, 1G-VN + filter cake (FC) + deacetylation liquor (DL) in the season and FC + DL in the off-season. Gross energy output values and the resulting sugarcane use efficiency were also assessed in different biorefinery schemes. Electricity production from 1G to VN (5.0 MW) could be increased by over 400% through its co-digestion with FC and DL (22.3 MW). Alternatively, biomethane could fully supply the diesel-powered fleet (1.8 × 106 Nm3 month-1) of a sugarcane plant processing 10 million tons of sugarcane per harvest, and the surplus biogas could flexibly provide 36 MW of extra electricity. Biomethane could enhance the energy output of 1G2G sugarcane biorefineries by 15%. However, 2G processes still require marked improvements to maximize energy production from sugarcane.