Comparisons of Organic Acid and Inorganic Acid Pretreatment for Production of Reducing Sugar and Ethanol Production from Coffee Shell

Abstract

Growing consumption of coffee beverages leads to a vast amount of coffee waste production, and there are few official reports on proper waste management. Via a biorefining process, coffee waste, as a type of lignocellulose, has the potential to be converted to value-added biochemicals and biofuels. In a biorefining process of lignocellulose, pretreatment process is an important step for modification of the structure of lignocellulose to be more vulnerable to enzymatic saccharification. In this study, the effects of pretreatments by using organic acids (oxalic acid, citric acid, and acetic acid) and inorganic acid (sulfuric acid and hydrochloric acid) of coffee shell on reducing sugar and ethanol production were comparatively evaluated. Reducing sugars obtained from citric acid-pretreated were 27.16 mg, which were higher than untreated samples by 1.62-fold times. The cellulose content of citric acid-pretreated sample was enriched to 38.25%, while the cellulose content in untreated sample was 13.10%, suggesting the removal of hemicellulose caused by acid pretreatment. Citric acid pretreatment improves ethanol production by 5.1-fold times when compared to untreated sample. Altogether, organic acid is demonstrated to be an effective chemical for coffee waste pretreatment with lower toxicity and cost, compared to inorganic acid.