Abstract
The conventional alkaline pretreatment process for biomass fibre involves a large amount of high-polluted black liquor and washing wastewater discharge. This work aims to develop a zero-discharge process for closed-loop wastewater recovery based on geopolymer pretreatment process. In this study, geopolymer pretreatment achieved highly selective removal of lignin and almost quantitative carbohydrate retention. After acidification and filtration of low-alkali black liquor, high molecular weight lignin removed 66.1 % of chemical oxygen demand (COD), 40.5% of ammonia nitrogen (NH3-N), and 89.1% of total suspended solids (TSS) via hydrogen-bonding interactions and flocculation-net capture. The efficient removal of pollutants from low-alkali black liquor by high molecular weight lignin enables the closed-loop recovery of biorefinery wastewater. The recycled water exhibits low concentrations of pollutants and can be reused for at least 10 times and maintains a stable delignification rate and fibre yield. Compared to conventional alkaline pretreatment, the present process saves 75.5% of water and no washing wastewater is produced. This approach offers a feasible scheme for achieving zero discharge pretreatment of biomass.
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