No abstract

This study was to experimentally investigate the performance and organic fouling behaviour in a 1-m long RO membrane channel with or without spacer for desalting. It was found that local permeate flux distributed heterogeneously along the long membrane channel without a spacer inserted due to exponential growth of concentration polarization, which also resulted in decreasing salt rejection and increasing organic fouling along the membrane channel in the downstream direction. This heterogeneity could be lessened by inserting a spacer into the channel, which mitigated concentration polarization due to the enhanced turbulence caused by a spacer, especially at the downstream portion of the channel. However, in the upstream of the channel, inserting a spacer exerted an additional vertical resistance which might counteract the effect of concentration polarization mitigation by a spacer and caused a lower permeate flux. This suggests that it is necessary to consider the integral effect of spacer for designing an RO membrane module and an overall RO system in order to prevent extra resistance, reduce concentration polarization and membrane fouling.

This study was to experimentally investigate organic fouling development in a 1-m long RO membrane channel using alginate as a model organic compound. Five parallel local permeate fluxes with a distance interval of 20 cm along the channel were monitored continuously during the organic filtration tests. It was found that organic fouling became more severe towards the outlet of the channel. This might be mainly attributed to the salt concentration polarization formation along the channel. The higher salt concentration downstream increased the interactions involved in organic fouling such as charge-screening and alginate-calcium bridging, which intensively promoted organic fouling formation in the downstream. A higher feed flow was a common option to mitigate fouling at most lab-scale RO research work, but not the case in this long membrane channel. A higher feed flow changed the organic fouling development profile along the channel, but would not eliminate organic fouling.