Simultaneous cellulose nanocrystals extraction and organic halides removal from paper mill excess sludge via alkali-oxygen cooking and ultrasonication

Abstract

Pulp mill excess sludge (PMES) is an industrial biomass waste containing high moisture, many organic compounds, and highly concentrated adsorbed organic halides (AOX). The safe disposal and recycling of PMES using an environmentally friendly and sustainable treatment represents a major challenge. In this study, alkali-oxygen cooking was used to recover cellulose nanocrystals (CNC) from PMES while removing AOX in a one-pot process. Single-parameter experiments showed that more than 95% of AOX was effectively removed, meeting sewage emission standards, and greater than 70% of cellulose was recovered as CNC. A response surface experimental design was then applied to determine the optimal reaction conditions. A temperature of 200 °C, alkali dosage of 35 wt%, and reaction time of 5 h resulted in an AOX removal rate of 96.57% and CNC recovery rate of 73.78%. The results of this study not only demonstrate an environmentally friendly, sustainable strategy for the treatment and recycling of PMES into CNC, And the alkali-oxygen cooking process can be applied other cellulose-rich industrial wastes to recover value-added products.