Colloidal fouling and scaling in reverse osmosis (RO) process
Date of Issue2017-05-16
School of Civil and Environmental Engineering
Singapore Membrane Technology Centre
Water is crucial and essential for life. Despite having majority of the earth surface covered by water, accessing safe water source is an increasing challenge faced by human population. Hence, recycling used water and converting non-potable water to potable are the options being adopted in alleviating the issue. Membrane technology plays an important and reliable role in water treatment. Apart from being energy intensive in most of the water treatment operation, membrane fouling affecting it performance is the biggest issue that the industry faces. Colloidal fouling and scaling are common types of membrane fouling. Trans-membrane pressure, flux and rejection rate are the common methods used to monitor membrane fouling. However, by the time these parameters indicate an event, fouling might have already become very severe. Electrical Impedance Spectroscopy (EIS) is used in this project in monitoring fouling pattern in experiments with colloidal silica, calcium sulfate (CaSO4) scalant and mixture of both. Results show that colloidal fouling exacerbates the effect of cake enhancement concentration polarisation (CECP), reduce the permeate quality. Conductance of the diffusion polarisation layer (GDP) indicates the presence of CECP effect. Scalant formation on membrane surface provides an extra non-porous layer on membrane surface for filtration, hence increases permeate quality. Conductance of the diffusion polarisation layer (GDP) derived from the EIS measurement and scanning electron microscopy (SEM) suggest that surface crystallisation is the main mechanism for scalant formation on the membrane surface in this study. The study which involves both colloidal silica and scalant showing that colloidal silica is the dominant foulant as compared to scalant and this could be observed from the GDP plot as well.
Final Year Project (FYP)
Nanyang Technological University