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

Abstract

Sunflower residues are considered a prominent renewable source for biogas production during anaerobic digestion (AD). However; the recalcitrant structure of this lignocellulosic substrate requires a pretreatment step for efficient biomass transformation and increased bioenergy output. The aim of the present study was to assess the effect of alkaline pretreatment of various parts of the sunflower residues (e.g., heads and stalks) on their methane yield. Experimental data showed that pretreatment at mild conditions (55 °C; 24 h; 4 g NaOH 100 g−1 total solids) caused an increase in the biochemical methane potential (BMP) of both heads and stalks of the sunflower residues as determined in batch tests. The highest methane production (268.35 ± 0.11 mL CH4 g−1 volatile solids) was achieved from the pretreated sunflower head residues. Thereafter; the effect of alkaline pretreatment of sunflower head residues was assessed in continuous mode; using continuous stirred-tank reactors (CSTRs) under two operational phases. During the first phase; the CSTRs were fed with the liquid fraction produced from the pretreatment of sunflower heads. During the second phase; the CSTRs were fed with the whole slurry resulting from the pretreatment of sunflower heads (i.e., both liquid and solid fractions). In both operating phases; it was observed that the alkaline pretreatment of the sunflower head residues had a negligible (phase I) or even a negative effect on biogas production; which was contradictory to the results of the BMP tests. It seems that; during alkaline pretreatment; this part of the sunflower residues (heads) may release inhibitory compounds; which induce a negative effect on biogas production in the long term (e.g., during continuously run digesters such as CSTR) but not in the short-term (e.g., batch tests) where the effect of the inoculum may not permit the inhibition to be established.

Kinetics of Diauxic Biogas Production from Energy Crops: Sunflower (Helianthus annus) and Napier Grass (Pennisetum purpureum) with Animal Manure

“…However, the VS content of the energy crops, SF and NG were higher than the livestock manure, CD, indicating that the energy crops used in the experiment contain more digestible organic materials than CD and are essentially prospective organics for bioenergy production. The high TS and VS values of the energy crops (SF and NG) in this study are similar to that reported by Feng et al [17] and Zhurka et al [9] for Sunflower and Haryanto et al [18] for Napier grass.…”

“…In the anaerobic digestion of Sunflower biomass for biogas production, several pretreatment methods have been evaluated to increase biogas yield because of the lignocellulosic nature of the biomass. However, some of the pretreatment methods such as alkaline pretreatment showed a negative effect on biogas production [8,9]. In another pretreatment approach, Sunflower stalks were exposed to commercial-scale pretreatment by hot-water maceration and steam explosion technology to enhance biogas production.…”

Comparative Assessment of Biogas Production Potential of the Most Abundant Agro-residues in Turkey

“…On the other hand, the biomethane potential range is quite wide for wheat straw (150-250 mL/gVSinfluent) [34,35] and our results are in line with the previous studies carried out in Turkey and Germany [23,28]. In another study, the biomethane yield for sunflower head was determined as 211 mL CH4/gVinfluent which was higher than the result obtained from this study [26]. However, this result needs to be interpreted with caution because the authors dried the sunflower heads at 40 °C and milled them finely before digestion.…”

“…Anaerobic digestion is a sequential process in which diverse microbial communities including hydrolytic, acidogenic, and acetogenic bacteria and methanogenic archaea interact mutually [9]. The lignocellulosic structures of agro-residues limit the hydrolysis rates which then affect the methane yields [9,25,26]. Thus, appropriate inoculum should be used during the start-up period which includes necessary microbial communities having an ability to degrade lignocellulosic feedstock.…”

Performance of a Full-Scale Biogas Plant Operation in Greece and Its Impact on the Circular Economy

“…The CH 4 production rate recorded was 2972 ± 121 m 3 day −1 , which was 12.2% lower than the one targeted (3195 m 3 day −1 , see Table 2). This was anticipated, since the CH 4 production in the biochemical methane potential (BMP) tests was the maximum possible in ideal experimental conditions as compared to the continuous operation digesters [19]. The electrical energy produced was correlated with the COD introduced in the digester (Figure 4b).…”