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

Abstract

This work performed co-AD from the vinasse and filter cake (from 1G ethanol production) and deacetylation liquor (from the pre-treatment of sugarcane straw for 2G ethanol production) in a semi-Continuous Stirred Tank Reactor (s-CSTR) aiming to provide optimum operational parameters for continuous CH 4 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 CH 4 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 microrganisms was supplied by the alkali-characteriscs 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 CH 4 yield (230 NmLCH 4 gSV -1 ) 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 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 (~ 2% Methanoculleus) during the CH 4 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.

Fe3O4nanoparticles to optimize the co-digestion of vinasse, filter cake, and deacetylation liquor: operational aspects and microbiological routes

“…At the beginning of the operation, the ORP varied between -350 and -550 mV, and this variation is a characteristic of acidogenesis and reactor start-up (Volpi et al, 2021b). However, this variation in a start-up was much smaller than reported in Volpi et al (2021b) (−800 and -300 mV) indicating greater stability of the operation.…”

“…The Shannon index obtained from sample A1 was close to 5.0, while that from sample A2 was less than 3.75. As discussed in Volpi et al, 2021b, when the value of the Shannon index is greater than 5.0, it indicates greater microbial diversity in anaerobic digesters (de Souza Moraes et al, 2019). Thus, it can be seen that the A2 sample has a much lower microbial diversity than the A1, since these microorganisms are in stabilized metabolic routes for CH 4 production, indicating that this microbial community is even more specific.…”

“…At the beginning of the operation, the ORP varied between -350 and -550 mV, and this variation is a characteristic of acidogenesis and reactor start-up (Volpi et al, 2021b). However, this variation in a start-up was much smaller than reported in Volpi et al (2021b) (−800 and -300 mV) indicating greater stability of the operation. After approximately 40 days (Figure 5a), it is observed that the ORP remains practically constant until the end of the operation, varying between -480 and -400 mV, although the literature shows that the ORPs characteristic of the acidogenic and methanogenic phase is between -330 and -428 mV (Golkowska and Greger, 2013).…”

“…The s-CSTR operation was followed according to previous work by our research group (Volpi et al, 2021b). 5L-Duran flask with 4L-working volume kept under agitation at 150 rpm by using an orbital shaking table Marconi MA 140.…”

“…For this reason, it was decided to choose a lower concentration of NPs, to cause a less environmental impact on AD. With this, it is possible to observe differences in the operation of the continuous reactor with the addition of NP compared to the same reactor operation, but without the addition of NP (Volpi et al, 2021b).…”