Abstract
This paper builds upon a research project funded by the Italian Ministry of Environment, and aims to recover stranded driftwood residues (SDRs), in order to transform a potential pollution and safety issue into valuable bio-resources. In particular, one of the experiments consisted of bioethanol production from lignocellulosic residues. The SDRs were gathered from the Italian coast (Abruzzo Region, Italy) after an intense storm. The biomass recalcitrance, due to its lignocellulosic structure, was reduced by a steam explosion (SE) pretreatment process. Four different pretreatment severity factors (R0) were tested (LogR0 3.65, 4.05, 4.24 and 4.64) in order to evaluate the pretreated material’s accessibility to enzymatic attack and the holocellulose (cellulose plus hemicellulose) recovery. A first enzymatic hydrolysis was performed on the pretreated materials by employing a solid/liquid (S/L) ratio of 1% (w/w) and an enzyme dosage of 30% (w enzyme/w cellulose), in order to estimate the maximum enzymatically accessible cellulose content. Since the primary goal of pretreatment and hydrolysis is to convert as much cellulose as possible into monomeric glucose and recover all the holocellulose, the two pretreated materials showing these features were selected for bioethanol production process. The pretreated materials underwent a semi-simultaneous saccharification and fermentation (SSSF). The SSSF process was performed into two lab-scale bioreactors (5 L) with an S/L ratio of 15% and an enzyme dosage of 15% for five days. The efficiency of the whole bioethanol production process was assessed as ethanol overall yields (g ethanol/100 g raw material). The best overall yield was achieved by sample BS04 (8.98 g ethanol/100 g raw material).
Highlights
The accumulation of stranded driftwood residues (SDRs) is an issue that has been afflicting the Italian coastal zone for a long time and it has been amplified in recent years because of increased flooding [1]
The best overall yield was achieved by sample BS04 (8.98 g ethanol/100 g raw material (RM)) after undergoing steam explosion (SE) pretreatment at LogR0 4.64, enzymatic hydrolysis (0.15 g enzyme/g cellulose) with a
SDRs at a high LogR0 and so giving up the hemicellulose recovery and employment. This aspect could be related to the origin of SDRs, which could have produced a collapse of the whole lignocellulosic matrix, causing difficulties in ethanol production
Summary
The accumulation of stranded driftwood residues (SDRs) is an issue that has been afflicting the Italian coastal zone for a long time and it has been amplified in recent years because of increased flooding [1]. SDRs deposited along the coast are unsightly and unwelcoming to tourists or beachgoers, resulting in losses for seaside tourism [3]. The first approach is characterized by high management cost, which is estimated to be around 120 €/ton (mean of the values provided by municipalities), and environmental issues, such as the occupation of valuable land space and air-water-soil pollution due to discharging wood degradation products into the atmosphere, earth and groundwater. Second-generation bioethanol is produced starting from lignocellulosic biomass after an appropriate pretreatment method, saccharification by cellulosic enzyme and yeast fermentation. Three different process configurations can be employed for the production of bioethanol from pretreated biomass, such as separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF) and semi-simultaneous saccharification and fermentation (SSSF). The results are presented in terms of ethanol yield, and expressed as grams of produced ethanol on 100 grams of raw material (RM)
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