A pilot-scale forward osmosis membrane system for concentrating low-strength municipal wastewater: performance and implications

Abstract

Recovery of nutrients and energy from municipal wastewater has attracted much attention in recent years; however, its efficiency is significantly limited by the low-strength properties of municipal wastewater. Herein, we report a pilot-scale forward osmosis (FO) system using a spiral-wound membrane module to concentrate real municipal wastewater. Under active layer facing feed solution mode, the critical concentration factor (CCF) of this FO system was determined to be 8 with 0.5 M NaCl as draw solution. During long-term operation at a concentration factor of 5, (99.8 ± 0.6)% of chemical oxygen demand and (99.7 ± 0.5)% of total phosphorus rejection rates could be achieved at a flux of 6 L/(m2 h) on average. In comparison, only (48.1 ± 10.5)% and (67.8 ± 7.3)% rejection of ammonium and total nitrogen were observed. Cake enhanced concentration polarization is a major contributor to the decrease of water fluxes. The fouling also led to the occurrence of a cake reduced concentration polarization effect, improving ammonium rejection rate with the increase of operation time in each cycle. This work demonstrates the applicability of using FO process for wastewater concentrating and also limitations in ammonium recovery that need further improvement in future.

Forward osmosis with an algal draw solution to concentrate municipal wastewater and recover resources

“…Concentrating the FS reduces the footprint and improves the resource recovery of the downstream treatment processes such as anaerobic digestion (Chen et al, ; Linares et al, ; Xie, Nghiem, Price, & Elimelech, ). A pilot‐scale FO trial has proven that FO is feasible to concentrate low‐strength municipal wastewater in full‐scale applications (Wang, Zheng, Tang, Wang, & Wu, ). Furthermore, thin‐film composite (TFC) FO membranes achieve initial water flux of 18 L m −2 hr −1 or higher (Kwan et al, ; Lutchmiah, Verliefde, Roest, Rietveld, & Cornelissen, ; Yip, Tiraferri, Phillip, Schiffman, & Elimelech, ).…”

Influences of mechanical pretreatment on the non-biological treatment of municipal wastewater by forward osmosis

“…Wang et al [15] achieved an average water flux rate of 6 L·m -2 ·h -1 with diluted wastewater and used 0.5 M NaCl as the model draw solution when using a cellulose triacetate membrane (CTA) from HTI. Similar values were also obtained by Holloway et al [37], who reported water fluxes of 13 10.1 L·m -2 ·h -1 for concentrated anaerobic digests using CTA membranes from HTI.…”

“…Wang et al [15] recently published a study using real diluted municipal wastewater with solute rejections of ammonium and total nitrogen (TNt) of 68% and 48%, respectively, and rejections of chemical oxygen demand (COD) and total phosphorus (TPt) of more than 99%.…”

“…[18] Most of these studies focused on using synthetic wastewater as feed for FO processes [19][20][21][22], and only a few studies have been performed using real diluted raw municipal wastewater. [15,23] Furthermore, Xie et al [16] reviewed different membrane-based processes for nutrient recovery and used FO as the sole technology for treating urine, synthetic wastewater and activated sludge.…”

“…An alternative could be forward osmosis (FO) because FO has recently been shown to achieve solute rejections as high as RO. [15,16] FO is driven by an osmotic pressure gradient across a selectively permeable membrane, which allows water molecules to migrate from a feed solution (FS) with a low osmotic pressure, such as wastewater, to a draw solution with a high osmotic pressure, such as seawater. Because the FO process is operated in the absence of applied hydraulic pressure, this process has an intrinsically lower fouling propensity and requires less energy than RO.…”