Ecological Risk Evaluation and Removal of Emerging Pollutants in Urban Wastewater by a Hollow Fiber Forward Osmosis Membrane

Abstract

Forward osmosis (FO) is a promising technology for the treatment of urban wastewater. FO can produce high-quality effluents and preconcentrate urban wastewater for subsequent anaerobic treatment. This membrane technology makes it possible to eliminate the pollutants present in urban wastewater, which can cause adverse effects in the ecosystem even at low concentrations. In this study, a 0.6 m² hollow fiber aquaporin forward osmosis membrane was used for the treatment of urban wastewater from the Valladolid wastewater treatment plant (WWTP). A total of 51 Contaminants of Emerging Concern (CECs) were investigated, of which 18 were found in the target urban wastewater. They were quantified, and their ecotoxicological risk impact was evaluated. Different salts with different concentrations were tested as draw solutions to evaluate the membrane performances when working with pretreated urban wastewater. NaCl was found to be the most appropriate salt since it leads to higher permeate fluxes and lower reverse saline fluxes. The membrane can eliminate or significantly reduce the pollutants present in the studied urban wastewater, producing water without ecotoxicological risk or essentially free of pollutants. In all cases, good recovery was achieved, which increased with molecular weight, although chemical and electrostatic interactions also played a role.

Keywords: Contaminants of Emerging Concern (CECs); ecological risk quotient; forward osmosis (FO); organic matter concentration; urban wastewater.

Figure 1

Experimental setup of concentrating urban wastewater by FO membrane.

Figure 2

$J_w/J_{w,0}$ in time with different pretreatments of urban wastewater. A, centrifuged at 10,000 rpm and filtered by a filter with 0.7 μm pores; B, centrifuged at 10,000 rpm; C, urban wastewater without any pretreatment.

Figure 3

Scenario C. (A) Lumen plugging after use. (B) Membrane after opening and physical cleaning.

Figure 4

Water flux for the different types of draw solutions used over time. The curve is just a visual guide.

Figure 5

Average water flux versus a correlation between the Van’t Hoff factor and the diffusion coefficient of the different solutes. Here, NaAc stands for sodium acetate (CH₃COONa).

Figure 6

Average reverse salt flux versus each type of draw solution.

Figure 7

Water flux over time for each NaCl concentration (0.5 M, 1.0 M, 1.5 M, and 2.0 M). (Solid lines are just a visual guide to analyze trends).

Figure 8

Average water flux (left side) and average reverse salt flux (right side) versus NaCl concentration.

Figure 9

Total Organic Carbon (TOC) recovery in aquaporin forward osmosis membrane. FS corresponds to the %TOC after the experiment; FS wash corresponds to the %TOC after the membrane washes according to the order FS 1 wash, 2 wash, and 3 wash.

Figure 10

Recovery of contaminants grouped according to their charge at pH = 7.

Figure 11

Recovery in the FS of the different CECs after the FO processes against the molecular weight and log D.