Enzyme-assisted dewatering of oil sands tailings: Significance of water chemistry and biological activity

Abstract

Remediation of oil sands tailings is a crucial environmental aspect of the Canadian oil sands industry. Because of the poor released water quality and slow consolidation of tailings, engineered non-natural strategies to improve the consolidation of tailings are warranted. Here, we investigated enzymatic treatment (using cellulase, protease, and lysozyme) to accelerate the dewatering of fluid fine tailings (FFT). Our findings illustrated that lysozyme (0.5% and 1%) significantly improved FFT dewatering by increasing the water recovery (WR) up to 20% compared with the other enzymes (up to 12%) or the control (2%). Moreover, lysozyme treatment resulted in the highest increase in ionic strength (0.038 to 0.1 mol L−1), decrease in diffuse double layer (DDL) thickness (1.54 × 10−7 to 9.40 × 10−8 cm), and increase in zeta potential (−34.7 to −14.8 mV). Increased methane production was observed for cellulase (0.5% and 1%), lysozyme (0.5% and 1%), and protease (0.5%). The enhanced dewatering could be linked to the ebullition of methane gas resulting from the methanogenic activity, which created pathways for the trapped water release. In addition, the dissolution of carbonate minerals during the release of methane gas increased ionic strength and decreased the DDL of the FFT. Lysozyme 1% treatment was also the most effective in reducing naphthenic acid fractions (1934.6 to 243 ng mL−1); however, the released water had high toxicity toward Vibrio fischeri and had a slight decrease in microbial populations. This study provides a fundamental insight into enzymatic treatment for oil sand tailings.