Solid state co-fermentation as pretreatment of lignocellulosic palm empty fruit bunch for organic acid recovery and fiber property improvement

• Intense acid in a prolong contact to biomass can be controlled in ALBR operation.
• Pig manure, fermentation time and flush interval improved hydrolysis–acidogenesis.
• Multiple regression with 3D response surfaces showed relationship of the parameters.
• Organic acids produced helped remove hemicellulose 56.9% and leach K off 83.5  ±  4.0%.
• Heating value of the EFB fiber increased after fermentation pretreatment.

Batch co-fermentation of lignocellulosic fiber from oil palm empty fruit bunch (EFB), and pig manure (PM) was carried out in anaerobic leach bed reactors under intermittent flushing mode to improve organic acid production and fiber fuel property. Higher PM addition (%PM), long fermentation time (FT), and long leachate flushing interval (FI) showed positive impacts on hydrolysis yield and acidification yield leading to a higher total volatile fatty acid production. Their relationships were described using multivariate models through three-dimensional response surface plots. Volatile solids release from the EFB fiber after 60-day treatment improved by 6.9 times when %PM and FI increased from 0% and 12 h to 50% and 48 h, respectively. Mild acids produced were able to remove as high as 56.9% of hemicellulose and leach 83.5  ±  4.0% of potassium (K) off the fiber. This also resulted in the increased heating value and lowered K content that could minimize slag formation when used in combustion. Addition of PM also supplemented plant nutrients to the EFB digestate. This study demonstrated that co-fermentation could be one of the pretreatment methods to recover valuable products from EFB and help ease its subsequent transformations.

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