Aquatic macrophytes tolerance to domestic wastewater and their efficiency in artificial wetlands under greenhouse conditions

Resumo

Aquatic and semi-aquatic plant species of three different water qualities were inventoried, two of the El Tunal river and one of one of its tributaries, considering its content of dissolved oxygen, soluble phosphates, nitrate, ammonia, fecal coliforms, total suspended solids, and measurements of pH and electrical conductivity. A MANOVA/ANOVA demonstrated significant differences among parameters and sites. Twenty-eight species were identified; from them: Schoenoplectus americanus, S. tabernaemontani and Eleocharis densa were selected. All three were grown successfully under greenhouse conditions. Adaptation to local wastewater was evaluated using 5 micro-units: one control with wastewater (WW), another with gravel (G), and three sub-surface flow wetlands, one for each of the three selected plants, in duplicate. For ammonia and phosphate concentration, the systems with gravel removed 96 - 98%, and 99 - 100%, respectively. Fecal coliforms content was reduced about the same in all systems, 98.5 - 98.7%. No significant differences were found in removal of fecal coliforms and ammonia across time or among species. Removal of ions (98% in 48 h) was due mainly to the gravel used as support, for its ionic exchange capacity. Nonetheless, the three selected species are considered as appropriate for wetland construction because they are native, abundant, tolerant to local conditions, easy to propagate and establish, and highly tolerant to wastewater in their place of origin. Its dense growing habit would represent also a refuge for wildlife, another goal for constructing a wetland in the area.