An effective way in application of coagulants for more accurate fouling control via transparent exopolymer particles (TEP) determination

Membrane fouling caused by organics in feedwater is a bottleneck factor limiting the development of membrane technology, which is often alleviated by addition of coagulants. However, the effect mechanism of coagulant components on organic foulants are lack of in-depth analysis. In this study, sodium alginate is selected as the surrogate of organic foulants to study the influence mechanism of typical coagulants Al³⁺ and Fe³⁺ on fouling control, especially the impact on the morphological characteristics of foulants at the micro level and the related fouling mitigation mechanism. The results show that the addition of different concentrations of coagulants will deeply affect the process of polysaccharide aggregation to form transparent exopolymer particles (TEP). Combination of filtration tests and analysis of fouling mechanism reveal that the small and amorphous TEP developed at low concentration of coagulant is intercepted by the membrane and forms a dense fouling layer resulting in the decreasing of membrane flux, while larger granular TEP developed from alginate accumulates on the membrane surface to form a porous fouling layer which in turn acts as a pre-filtering layer mitigating fouling. This study indicates that the addition of coagulants significantly changes the microscopic properties of foulants and thus the fouling problems. With the qualitative and quantitative analysis of TEP formed by foulant, the theoretical basis and data support are provided for the addition of coagulation to construct an effective pre-filtering layer for membrane fouling control. This work therefore, provides an effective way in application of coagulants for more accurate fouling control.