Advanced Treatment of Facultative Lagoon Effluent: Microfiltration and Nanofiltration for Water Reuse

Abstract

This study assessed the effectiveness of microfiltration (MF) as pretreatment combined with nanofiltration (NF) for tertiary treatment of secondary wastewater effluent (SWE) from a facultative lagoon system. The SWE was found to have turbidity levels which require pretreatment, and microfiltration was chosen in this study for its ability to remove particles to 1 micro, its low-cost and ease to obtain system components. Three commercially available NF membranes (NF90, NF245, and NF270) were evaluated using a bench-scale system operated in recycle mode, in which a fixed batch volume of SWE obtained from Tuba City, Arizona, was continuously recirculated through each membrane module. The NF90 membrane demonstrated the highest rejection of organic and inorganic compounds and consistently maintained a 96% reduction in total dissolved solids throughout 7 days of operation. In contrast, the NF245 and NF270 membranes showed decreasing performance over time due to fouling. All membranes successfully removed more than 95% of contaminants of emerging concern. Characterization of the membranes indicated changes in hydrophobicity and surface charge for NF245 and NF270 after SWE filtering, while the properties of the NF90 membrane surface remained relatively unchanged. The treated effluents from NF245 and NF270 met Arizona's Class A+ reclaimed water standards for non-potable reuse. This study illustrates the potential of MF-NF treatment to upgrade facultative lagoon effluents to satisfy water reuse standards and to offer a sustainable solution for small communities experiencing water scarcity.