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.
Highlights
Lignocellulosic substrates are considered important feedstocks for the production of second-generation biofuels (e.g., H2, CH4 )
The recalcitrant structure of lignocellulosic substrates consisting of holocelluloses that are embedded in the lignin network, requires the application of pretreatment, to increase the accessibility of holocelluloses to bacteria during anaerobic digestion [3]
20.8% in comparison to heads, which is in agreement with the higher volatile solid (VS) content of stalks (87.7% of total solids; TS for heads and 79.9% of TS for stalks)
Summary
Lignocellulosic substrates are considered important feedstocks for the production of second-generation biofuels (e.g., H2 , CH4 ). Agricultural residues comprise a renewable resource which does not compete with plant cultivation for food, since they consist of the nonedible parts of the plants (leaves, stalks), which are usually burned on the fields creating environmental issues related with biomass incineration in the open air [1]. This is the case with sunflower residues (stalks, leaves, heads) which are produced in large quantities and left in the fields after seed harvesting. The recalcitrant structure of lignocellulosic substrates consisting of holocelluloses (cellulose, hemicelluloses) that are embedded in the lignin network, requires the application of pretreatment, to increase the accessibility of holocelluloses to bacteria during anaerobic digestion [3]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
