Ultrafiltration as tertiary treatment for municipal wastewater reuse

Water reuse is an enduring topic that benefits the society and future generations of mankind. Ultrafiltration (UF) is one of the most cost-effective treatment technologies for improving water quality. In this study, a semiindustrial UF pilot plant with periodical classic backwash (CB) and air backwash (AB) was operated automatically to evaluate its feasibility and sustainability for municipal wastewater reuse and find out the optimized filtration condition. This study carried out 15 filtration conditions to investigate the impacts of flux (J in L center dot h-1 center dot m- 2), filtration cycle time (t in min), and air backwash frequency (BW) on membrane hydraulic filtration performance and membrane fouling management. Through comparative analysis of all conditions in water quality, permeability variation, irreversible fouling management, and water recovery rates, the sustainable conditions J80t40BW1/3 (flux of 80 L center dot h- 1 center dot m- 2, filtration cycle time of 40 min, 1 AB followed with 3 CBs), J60t60BW1/4 (flux of 60 L center dot h- 1 center dot m- 2, filtration cycle time of 60 min, 1 AB followed with 4 CBs), and J60t60BW1/ 3 (flux of 60 L center dot h- 1 center dot m- 2, filtration cycle time of 60 min, 1 AB followed with 3 CBs), stood out from the others with higher overall performances. Additionally, air backwash showed excellent reversibility on membrane fouling control, which was around 1.25-2 times that of CB in average. After all, long term operation on condition J60t60BW1/3 in winter and in summer confirmed that the UF system could provide sustainable and adaptable filtration performance regardless of the temperature and feed water quality. The UF permeate quality is good enough to be reused in non-potable applications as it met reuse guidelines of the World Health Organization, reuse standards of France and the most recent EU regulation for agricultural irrigation. This work confirms the great interest of UF as tertiary treatment for water reuse and gives operational indications for future industrialscale production of reclaimed water.