Effect of hydraulic retention time on performances of gravity-driven membrane (GDM) reactor for seawater pretreatment

This study aims to illustrate the effect of hydraulic retention time (HRT) on reactor performance and biofilm characteristics in the gravity-driven membrane (GDM) reactor pretreating seawater. Three GDM reactors were operated in parallel for similar to 62 days under HRTs of 22 h, 54 h, and 102 h, respectively. The results indicated that the GDM reactors at HRTs of 22 h and 102 h had relatively higher permeate flux and superior permeate quality (especially assimilable organic carbon, AOC) compared to that at HRT of 54 h. Extending HRT benefited to reduce irreversible fouling, but cake layer fouling was maximized at HRT of 54 h. As different HRTs led to significantly dissimilar microbial community structure and cake layer composition, such higher cake layer resistance at HRT of 54 h was attributed to homogenous nature of the biofilm, which contained greater amount of organics and less abundance of Nematoda (dominant predator). Lastly, as increasing similar to 5-time of HRT (from 22 h to 102 h) improved similar to 1.5 of permeate flux, a shorter HRT of 22 h was preferable for the GDM reactor in pretreating seawater with regard to treatment productivity and footprint.

Automated summary

This study examines the impact of hydraulic retention time (HRT) on the performance and biofilm characteristics of a gravity-driven membrane (GDM) reactor used for pretreating seawater. The results show that the GDM reactors with HRTs of 22 h and 102 h had higher permeate flux and better permeate quality (especially AOC) compared to the reactor with an HRT of 54 h. Extending the HRT helped reduce irreversible fouling, but cake layer fouling was highest at an HRT of 54 h. The different HRTs resulted in significant differences in microbial community structure and cake layer composition, with the higher cake layer resistance at an HRT of 54 h attributed to a more homogeneous biofilm with higher organic content and lower abundance of Nematoda (dominant predators). Finally, increasing the HRT by approximately 5 times (from 22 h to 102 h) improved the permeate flux by about 1.5 times, suggesting that a shorter HRT of 22 h is preferable for the GDM reactor in pretreating seawater in terms of treatment productivity and footprint.