Removal of contaminants of emerging concern by Wolffia arrhiza and Lemna minor depending on the process conditions, pollutants concentration, and matrix type

Abstract

Research was carried out on the removal of a group of six contaminants of emerging concern: bisphenol A, N,N-diethyl-m-toluamide, diethylstilbestrol, triclosan, estrone and estradiol from the water matrix during contact with small floating macrophytes Wolffia arrhiza and Lemna minor. The optimal conditions for the process, such as pH, light exposure per day, and plant mass, were determined using the design of experiments chemometric approach based on central composite design. Experiments conducted under the designated optimal conditions showed that after 7 days, the removal efficiency equals 88-98% in the case of W. arrhiza and 87-97% in the case of L. minor, while after 14 days of the experiment, these values are 93-99.6% and 89-98%, respectively. The primary mechanism responsible for removing CECs is the plant uptake, with the mean uptake rate constant equal to 0.299 day^-1 and 0.277 day^-1 for W. arrhiza and L. minor, respectively. Experiments conducted using municipal wastewater as a sample matrix showed that the treatment efficiency remains high (the average values 84% and 75%; in the case of raw wastewater, 93% and 89%, and in the case of treated wastewater, for W. arrhiza and L. minor, respectively). Landfill leachate significantly reduces plants' ability to remove pollutants (the average removal efficiency equals 59% and 56%, for W. arrhiza and L. minor, respectively).

Keywords: Bisphenol A; DEET; Hormones; Landfill leachates; Phytoremediation; Removal mechanisms; Wastewater.

Figure 1

The Pareto charts for TRC, DES, and E2 (x₁ = pH; x₂ = light exposure per day (h); x₃ = amount of plant (g)).

Figure 2

Effects of pH and light exposure time on CECs removal efficiency (mass of the plant 2 g).

Figure 3

CECs removal efficiency observed during experiments with W. arrhiza and L. minor; first research cycle: C₀ = 100 µg/L, second research cycle: C₀ = 500 µg/L.

Figure 4

The concentration of CECs in W. arrhiza and L. minor tissues after 7-days cultivation in culture medium enriched with DEET, TRI, BPA, DES, E1, E2 (100 µg per 1 g of the plant).

Figure 5

The removal efficiency of CECs registered after 1, 3, 5 and 7 days of contact of raw municipal wastewater, treated municipal wastewater and landfill leachates with W. arrhiza (a), L. minor (b).