Effect of Macrophyte Pruning on Microorganisms Adhered to the Support Medium and the Organic Load in Artificial Wetlands

Abstract

This research evaluated the effect of macrophyte pruning on microorganisms adhered to the support medium and the removal of BOD5 in three experimental subsurface flow artificial wetlands (FFSCW) with species of Phragmites australis (FFSCW-Carrizo), Pontederia sagittata (FFSCW-Tule) and gravel as a control (FFSCW-Grava), being nine units (with replicas). The FFSCW 1.2 m wide, 2.5 m long and 0.5 m deep were fed with 200 L/d domestic wastewater. The variables studied to the support medium were adhered microorganisms, porosity, density, diameter and humidity to estimate the retention time and hydraulic conductivity. In the species, the productivity variables were measured after pruning and the removal and the degradation kinetic coefficient k for the BOD5 were estimated. The experiment was a one-factor (treatment) design with three levels (FFSCW-Tule, FFSCW-Carrizo and FFSCW-Grava); being evaluated during three months, after the year of operation. Treatments were evaluated by ANOVA (parametric) and the Kruskal-Wallis rank test (non-parametric) between groups before and after pruning (p < 0.05). The gravel presented on average (N = 12) 22.92 ± 1.47 % humidity, 2.32 ± 0.15 cm in diameter, particle density 2.71 ± 0.10 gr/cm3 and porosity of 36.52 ± 3.36 %, the TRH was 3.1 days in all the treatments. The best treatment was FFSCW-Tule, before pruning the biomass of microorganisms presented median values (N = 12) of 42931.6 mg/kg (Q1 = 40259.7; Q3 = 54478.4) and after pruning of 33444.6 mg/kg (Q1 = 31210.9; Q3 = 36581.8), the vegetable biomass removed in pruning was 40.85 ± 2.58 kg, removing 95.44 % of BOD5 with k = 1.004 days-1 (27.6 °C), which allows complying with NOM-001-Semarnat-1996.