Combinatorial application of ammonium carbonate and sulphuric acid pretreatment to achieve enhanced sugar yield from pine needle biomass for potential biofuel–ethanol production

Lignocellulosic biomass (LB) despite its huge potential as a renewable bioenergy resource faces bottlenecks due to its recalcitrance and lack of appropriate pretreatment approaches. The current study evaluates the combinatorial application of alkali and acid pretreatment of pine needle biomass (PNB), for achieving high sugar release upon enzymatic saccharification. Pine needle accumulation poses a big threat to the forest soil fertility and overall ecosystem and environment. However, pine needle waste can be valorized after appropriate pretreatment and enzymatic saccharification for production of renewable energy, i.e. biofuel–ethanol. In combinatorial pretreatment strategy, first PNB was subjected to ammonium carbonate pretreatment, and parameters like ammonium carbonate concentration, incubation time and pretreatment temperature were optimized using design of experiment (DoE) approach. The relative influence of parameters on efficacy of pretreatment was established individually and in interactive terms. Based on DoE, sugar yield of 7.56 mg/g of PNB was obtained. Furthermore, DoE-based pretreated PNB was subjected to sulphuric acid pretreatment, followed by enzymatic saccharification. The sugar released during various steps was pooled (8.19 g/100 g), concentrated and subjected to ethanol fermentation with dual yeast cultures using Saccharomyces cerevisiae and Pichia stipitis. An ethanol yield of 8.8%, v/v (6.94% w/v), was obtained. This represents the process efficiency of 19.34% for bioethanol production from PNB.