Study on the influence of different factors on the direct treatment of high turbidity water by microfiltration processes

Abstract

Currently, traditional high turbidity water treatment technologies (coagulation–sedimentation–filtration) face issues such as non-compliant effluent quality, sediment compaction, and poor sludge discharge. Meanwhile, membrane filtration technology suffers from severe membrane fouling in high turbidity water treatment. Therefore, the development of green and low-carbon high turbidity water treatment technologies is urgently needed. This study employs microfiltration to directly filter high turbidity water, investigating turbidity, filtration methods, and transmembrane pressure difference to elucidate the mechanisms of mitigating membrane fouling in high turbidity water treatment. The results indicate that both excessively high and low influent turbidity are detrimental to high turbidity water treatment. Low turbidity fails to effectively protect the membrane, exacerbating membrane fouling, while high turbidity leads to excessive cake layer thickness, reducing membrane flux. Therefore, the optimal treatment turbidity must be determined based on the specifications of the experimental setup. In this study, the optimal treatment turbidity is 900 NTU. Under constant pressure conditions, cross-flow filtration effectively controls the thickness of the filter cake layer, mitigates membrane fouling, and maintains a high membrane flux. When the influent turbidity is 900 NTU, the membrane flux recovery rate and filtration flux are 80.14% and 0.9077 m h⁻¹, respectively, with irreversible membrane fouling being only 0.97 × 10¹⁰ m⁻¹. At a constant influent turbidity, higher transmembrane pressure difference increases the filtration flux but exacerbates membrane fouling. When the pressure increases from 6.67 kPa to 33.33 kPa, irreversible membrane fouling increases by 27.97%, while the filtration flux increases by 116.91%. At a pressure of 13.33 kPa, although the filtration flux is 56.83% of that at 33.33 kPa, the irreversible membrane fouling is only 62.25%. Therefore, this study identifies 13.33 kPa as the optimal transmembrane pressure difference. The Hermia model revealed that transmembrane pressure difference was the primary factor aggravating membrane fouling. Finally, through dosing FeCl₃ as a coagulant for cake layer regulation, the cake layer structure formed at 15 mg per L dosage showed optimal pollutant interception and removal efficiency: humic acid (HA) removal efficiency reached 75.86% in actual water sources with 79.06% flux recovery rate; simulated feed water achieved 77.44% HA removal with 84.31% flux recovery rate. This study aims to provide reference for microfiltration processes in direct treatment of high-turbidity water.