Nature-based solutions as an economical option for the removal of micropollutants in artificial wastewater: the case of a laboratory constructed wetland planted with Phragmites australis

Discharge of micropollutants laced untreated or partially treated wastewater into the environment is one of the significant contributors to water quality decline. This study adopted the method of hydrological balance proposed by Kadlec and Wallace for the construction of a combination of Horizontal Subsurface Flow Constructed Wetlands and Vertical Subsurface Flow Constructed Wetlands planted with Phragmites australis to investigate micropollutants load removal as well as the treatment efficiency of lab constructed wetlands. Artificial wastewater with Pb, Cd and Cr concentrations of 0.368 mg/l, 0.377 mg/l, and 0.362 mg/l respectively, was prepared using 99.99% Pb(NO₃)2 crystals, 1000mgl/l Cd(NO3)2 and Cr(NO₃)3 standard solutions to serve as influent wastewater for the wetlands. A test run of the setup was done with an influent flow rate of 0.8 L per hour for optimisation purposes after which effluent samples after treatment in the wetlands were analysed every other day using a HACH LT 200 heating block for digestion, HACH LCK 306, LCK 313 and LCK 308 cuvettes reagents and a HACH DR 3900 spectrophotometer for the determination of concentrations of Pb, Cr, and Cd. Pre and post treatment of Pb, Cr and Cd concentrations, pollution loads, and the overall treatment efficiency were tested for significance using T-test and one way ANOVA. There were significant reductions of 0.268 mg/l, 0.356 mg/l and 0.347 mg/l between the pre-treatment concentrations and post-treatment concentrations of Pb, Cd and Cr respectively. Micropollutant removal efficiency was in the order of Cd (95.85%) > Cr (94.43%) > Pb (72.80%) respectively. This study will contribute to ongoing research on nature-based solutions for the removal of micropollutants from wastewater at a relatively lower cost.