Treatment of swine effluent mixed with domestic wastewater and vegetation development in monoculture and polyculture horizontal subsurface flow wetlands

The aim of this study was to evaluate horizontal subsurface flow (HSSF) treatment wetlands (TW) for the treatment of swine effluents mixed with domestic wastewater, as well as to compare the efficiency of systems with monocultures and polycultures. Three species of plants were used in both monoculture and polyculture experimental systems: a) Heliconia latispatha, b) Typha latifolia, c) Cyperus alternifolius, d) Heliconia latispatha + Typha latifolia, e) Heliconia latispatha + Cyperus alternifolius and f) control (without plant). Each cell operated with a hydraulic loading rate of 5.4 cm/d. The measured variables included environmental parameters (temperature, relative humidity, light intensity, evapotranspiration, pH and dissolved oxygen –DO–), vegetative growth (plant height, width and leaf length, stem thickness, leaf number and biomass production) and pollutant measurements (chemical oxygen demand –COD–, total coliforms –TC–, total suspended solids –TSS–, volatile suspended solids –VSS–, total nitrogen –TN– and total phosphorus –TP–). The results indicated that there were significant differences (p ≤ 0.001) between the systems. In general, those systems with vegetation removed more TP (from 44.3% to 63.4%) and TN (from 68.1% to 74.9%) than the system without vegetation (32.9% for TP and 55.6% for TN). In addition, the experimental configuration as mono or polyculture was a determinant factor in the efficiency of the systems; the polyculture system with H. latispatha + T. latifolia was the most efficient in the removal pollutants such as COD (68.9 ± 10.6%), TSS (55.6 ± 0.5%), VSS (57.8 ± 0.6%), TC (69.5 ± 6.1%) and TN (74.9 ± 1.4). With regard to the evaluated species, H. latispatha showed the highest relative growth in both monoculture and polyculture systems with this high nutrient-concentration wastewater. These results demonstrate the HSSF TWs planted with monocultures and polycultures of plants in tropical climates represent an option to reduce the pollutant load of wastewater resulting from the mixing of domestic wastewater and pig farming wastewater.