Life cycle assessment of fermentative xylitol production from wheat bran: A comparative evaluation of sulphuric acid and chemical-free wet air oxidation-based pretreatment

Abstract

Xylitol, a sugar alcohol is a low-calorie sweetener has wide applications in food and pharmaceutical industry and hence considered as a high value premium product. The conventional methods for fermentative xylitol production uses chemicals (acid/alkali) which generates inhibitors affecting fermentation and downstream purification of xylitol. In the present study, wet air oxidation was evaluated as a chemical-free pretreatment option of wheat bran for xylose release which is subsequently fermented to xylitol. Life cycle assessment was used as a tool to compare wet air oxidation with conventional methods like dilute acid pretreatment for valorization of wheat bran, a model agro-industrial remnant. A comparative evaluation of wet air oxidation and dilute acid pretreatment was investigated for fermentative production of xylitol (1 g/L as functional unit) with the aim of identifying the process involved with the lowest environmental impact, while also demonstrating the higher xylose recovery of 13.52 g/L coupled with FO based concentration unit. The inputs and outputs of the process involving energy use, chemicals employed, and emissions produced were evaluated with respect to food and environment perspective. Environmental impacts of wet air oxidation and dilute acid pretreatment with fermentative xylitol production of 6.134 and 1.42 g/L, respectively showed emission results of 1.476 and 5.288 kg CO2 equivalent, respectively. Though, primary energy demand of wet air oxidation was almost found to be equivalent to dilute acid, due to energy penalty for reactor mixing was higher in wet air oxidation. However, energy demand of wet air oxidation-based pretreatment was found to be energy efficient by 30% as compared to dilute acid. Coupling biogas reduces energy demand by 3.5%. The reduction in impacts relevant to food safety namely, marine aquatic and freshwater ecotoxicity potential were found by 74.29% and 84.97% substantially lower in wet air oxidation as compared to dilute acid based xylitol production. The effect of sulphate, as input form of sulphuric acid in dilute acid showed an impact of 3.83 folds higher on human toxicity potential as compared to wet air oxidation pretreatment process.