Preparation of a spherical biochar colloidal probe and its application in deciphering the mechanism of biochar mitigating membrane fouling

To better unravel biochar's interface behavior and mitigation mechanism on membrane fouling, spherical bio-char colloidal probes were prepared by adhering microspheres to the free end of the probe cantilever. The prepared colloidal probes were used to measure the interaction forces between the membrane and foulant/ biochar and between the foulant and foulant/biochar by atomic force microscopy (AFM). The study investigated the differences in physicochemical properties of biochars and their mitigating effects on membrane fouling caused by bovine serum albumin (BSA). Results indicated that dosing biochar strengthened the electrostatic repulsion between BSA and membranes, thereby, mitigating the adhesion or deposition of BSA on the membrane surface. Additionally, spherical biochar (SBC) and hydrochar (HC) exhibited better membrane fouling mitigation than conventional biochar (CBC) due to better physicochemical properties, adsorption capacity, and a more porous fouling layer structure composed of microparticles. Importantly, the stronger adhesion force of SBC-PVDF (0.90 mN/m) than BSA-PVDF (0.50 mN/m) alleviated membrane fouling in the initial stage of the filtration, and the adhesion force of SBC-BSA (0.049 mN/m) alleviated membrane fouling in the later stage, resulting in higher water flux. The interaction force between mature SBC and BSA was comparable to that between BSA and BSA (0.14 mN/m) and stronger than that between original SBC and BSA (0.049 mN/m), implying further membrane fouling mitigation.