Mesh coated with microbially induced nanoscale vaterite for oil-in-water emulsion separation

Abstract

Microbial-induced calcium carbonate precipitation (MICP), with its hydrophilic rough microstructures and as an environmentally friendly material modification method, has shown great potential for oil-water separation. However, its efficiency in separating oil-in-water emulsions remains challenging. This study advances the MICP method by producing microbially induced nanoscale calcium carbonate on a mesh using calcium acetate instead of traditional calcium chloride, successfully achieving efficient separation of oil-in-water emulsions. The stainless-steel mesh (SSM) after calcium acetate-MICP treatment obtained nano-elliptical flake-like vaterite (vaterite-SSM) and demonstrated superior superhydrophilicity and underwater superoleophobicity compared to the mesh coated with micro-cubic structured calcite (calcite-SSM) treated by calcium chloride-MICP. Notably, vaterite-SSM achieved a flux of up to 309 L·m−2·h−1 and an oil rejection rate of over 98.7 % in gravity-driven separation of oil-in-water emulsions, demonstrating significant reusability after 6 cycles. Conversely, calcite-SSM was ineffective in emulsion separation due to coating instability and large particle spacing. Additionally, vaterite-SSM effectively separated various oil-water mixtures, maintaining high performance across 30 separation cycles. This study underscores the important use of calcium acetate in MICP to obtain nano-elliptical flake-like vaterite for efficient oil-water emulsion separation, advancing the promise of MICP as an effective and sustainable method for environmental applications.