Membrane modification with semiconductor diode laser to reduce membrane biofouling for external MBR system and modelling study

Abstract

Membrane biofouling is one of the major problem for membrane-based wastewater treatment. In this study, we used laser technology to modify ultrafiltration polyethersulfone (UP150) membrane in order to decrease membrane biofouling. Semiconductor laser diodes with different wavelengths of 405, 520, and 658 nm and different power density of 1.5, 2.0, 2.5 mW were used to improve membrane structure against biofouling. The pure water permeability (Lp), contact angle, porosity, and the average pore size were determined for pristine and modified membranes. Lp value of the pristine UP150 membrane (721.18 L/(m2 h bar)) was higher than modified membrane (22.08 L/(m2 h bar)). The contact angle values were presented that hydrophilicity was decreased from 75.1° to 61.2° for 2 h at 2.5 mW laser irradiation. Membrane porosity increased from 63.2 to 67.7%; however, the average pore size decreased from 88 to 23 nm after laser modification. The impact of laser wavelength and irradiation time on the rejection of protein (bovine serum albumin, BSA) and the fractions of soluble microbial products (as protein and carbohydrate) was systematically investigated. A maximum rejection of 32.17% and 41.86% was obtained for carbohydrate and protein when activated sludge was filtrated through modified membrane. Moreover, 100% BSA rejection was obtained by the modified membrane when BSA solution was filtrated. The modified membranes were extensively characterized by AFM, FTIR, SEM, and mechanical strength test analyses to observe morphological changes of the membrane before and after modification. The results showed that laser irradiation was changed the membrane morphology. Our results presented that laser-modified membranes with red wavelength changed the pore size, porosity, hydrophilicity of the pristine membrane. Also, membrane surface melting was revealed with a study called “Thermal Analysis on Membrane Surface Modelled 3D” using Solidworks CAD/CAM software. The results obtained from Solidworks thermal analysis was presented with 98.7% ratio of successful approach.