Wastewater treatment by Lemna minor and Azolla filiculoides in tropical semi-arid regions of Ethiopia

In this study, wastewater blended from textile, distillery, and domestic sources at a corresponding volumetric ratio of 3:1:18, was treated using Lemna minor and Azolla filiculoides for 28 days in a batch system installed in a shade house. Analysis of variance between the two macrophytes showed no statistical differences in removals of all tested parameters (p < 0.05) except for the biochemical oxygen demand where removal was higher in the L. minor. Electrical conductivity, pH, total dissolved solids, the studied heavy metals, and sulfate met the agricultural reuse and discharge limits. The removal of chemical oxygen demand by A. filiculoides (96%) was slightly higher than the L. minor (92%), but the biochemical oxygen demand removal by L. minor (92%) was significantly higher than A. filiculoides (90%). Despite the high removals of chemical and biochemical oxygen demands, total phosphorus and total nitrogen attained, the concentrations were found exceeding the discharge and agricultural reuse limits. Finally, while the number of total coliform in both macrophyte populated chambers were too numerous to count, the number of colonies of fecal coliform were 400 in the L. minor and 267 in the A. filiculoides treatments. In conclusion, the higher removals of all the studied parameters in the macrophyte populated chambers compared with the control might be attributed to the contributions of the macrophytes.