Impact of Hot Water and Alkaline Pre-treatments in Cellulosic Ethanol Production from Banana Pseudostem

Abstract

For every 1 tonne of bananas produced, 3 tonnes of pseudostem waste is also created. The aim of this research is to improve the pre-treatment methods used in converting this renewable resource to bioethanol. The microwave-assisted liquid hot water and alkaline with sodium hydroxide were performed on banana pseudostem followed by saccharification and fermentation to ethanol. The liquid hot water pre-treatment was performed over a range of severities (1.88–4.84). The alkaline pre-treatment was carried out to evaluate the effect of NaOH loading (0.09–0.3 g NaOH g−1 dry banana pseudostem) and severity factor (3.65–4.84). The severity factor of 4.84 from the liquid hot water pre-treatment and run 1 (Log Ro 3.65, 0.09 g NaOH g−1 dry banana pseudostem) from the alkaline pre-treatment reached the highest enzymatic hydrolysis yields for each pre-treatment conditions and were chosen to be submitted to fermentation. Subsequently, simultaneous saccharification and fermentation (SSF) at 25 °C for 120 h, using samples from alkaline (Log Ro 3.65, 0.09 g NaOH g−1 dry banana pseudostem) and liquid hot water (Log Ro 4.84) pre-treatments, resulted in 92 wt% and 95 wt% of the theoretical ethanol yield respectively, comparing to 60 wt% from the untreated biomass. The liquid hot water is considered a more suitable pre-treatment, as it is more economical and is an environmentally friendly alternative compared to the alkaline pre-treatment. The latter can lead to pollution as the sodium discharge in the process effluent is difficult to recycle and so may limit its application on a commercial scale.