Application of optimized alkaline pretreatment for enhancing the anaerobic digestion of different sunflower stalks varieties

Abstract

The use of lignocellulosic residues such as sunflower stalks (SS) for the production of bioenergy such as methane is a promising alternative to fossil fuels. However, their recalcitrant structure justifies the use of pretreatment to enhance the accessibility of holocelluloses and their further conversion into methane. First, different conditions of alkaline pretreatment (i.e. duration and NaOH concentration (g/100 g TS) at a fixed temperature of 55 degrees C) were tested to enhance the methane potential of the stalks of the Serin sunflower (193 mL of methane per gram of volatile solids (VS)). The greatest improvement to the methane potential (262 mL CH4 g(-1) VS) was observed at 55 degrees C, 24 h, 4 g NaOH/100 g TS. Fourier Transform Infrared spectra highlighted an accumulation of lignin in the digestate and the degradation of holocelluloses during the anaerobic process, both for pretreated and untreated SS. In a second stage, this optimum condition for alkaline pretreatment (55 degrees C, 24 h, 4 g NaOH/100 g TS) was applied to the stalks of three other varieties of sunflower. Alkaline pretreatment was effective in the delignification of the stalks of the different sunflower varieties, with lignin reduction varying from 23.3% to 36.3% VS. This reduction of lignin was concomitant with the enhancement of methane potential as compared to that of raw SS, with an increase ranging from 29% to 44% for the different SS.

Biogas Production from Sunflower Head and Stalk Residues: Effect of Alkaline Pretreatment

“…In the case of the present study, the residues were collected approximately 2-3 weeks after harvesting. Finally, it is noteworthy that Monlau et al [6] achieved higher methane potential from sunflower stalks (259 ± 6 mL CH 4 g −1 raw VS) as compared to this study (Table 4), after pretreatment at 55 • C with 4% NaOH for 24 h. In another study, Monlau et al [10] found a methane potential of 262 mL CH 4 g −1 raw vs. from sunflower stalks using identical alkaline pretreatment. The BMP of the untreated sunflower stalks was also higher than this study (193 mL CH 4 g −1 raw vs. > 128 mL CH 4 g −1 raw VS).…”

“…These compounds might have an inhibitory or even toxic effect on anaerobic microorganisms and therefore, should be always taken into consideration. Monlau et al [6,10] applied various chemical pretreatments on sunflower straw studying their influence on lignin removal and evaluating the biochemical methane potential (BMP). They reported that alkaline pretreatment at 55 • C, for 24 h with 4 g NaOH 100 g −1 total solids, was the most suitable for enhancing the anaerobic digestion process and methane potential.…”

The impact of Ni, Co and Mo supplementation on methane yield from anaerobic mono-digestion of maize silage

“…Furthermore, it must also be taken into account that, in an agricultural biogas digester fed with renewable biomass, along with proper supplementation of macro-and micronutrients (trace metals), optimization of process variables, such as pretreatment techniques applied to the biomass, temperature, pH and mixture ratios (if the biogas plant is operated in co-digestion mode), is also of paramount importance. [35][36][37][38][39] …”

A physicochemical method for increasing methane production from rice straw: Extrusion combined with alkali pretreatment

“…8-1:19) and ALRs (1-152%) [14][15][16][17][18][19]. In general, pretreatment increases methane production (from 0% to 174.2%) from LB compared with untreated samples [13,[20][21][22][23][24][25]. Biomass size reduction always occurs prior to NaOH pretreatment and affects the pretreatment.…”