Investigating the performance of duckweed in municipal wastewater treatment :

Abstract

This research report suggests the use of duckweed pond systems for the treatment of municipal wastewater. In the current study, an aquatic plant duckweed that is locally available in quiescent waters, ponds and lakes with high nutrient contents were used as an alternative cost effective biological tool for the treatment of municipal wastewater to remove concentrations of organic matter, nutrients and pathogens. Duckweed fronds were introduced into the experimental setup that was carried out at Busitema University premises; where a known mass of duckweed fronds was introduced in the basin. Wastewater quality parameters were tested basing on the varying intervals in the retention period. The experiments were conducted under outdoor environmental conditions for a retention period of 21 days. Efficiencies of duckweed for the treatment of municipal wastewater were assessed by measuring some of the physico-chemical parameters and faecal coliforms in the treated wastewater. The observations showed reduction levels of COD (82.60- 83.28%), Nitrate Nitrogen (63.79 – 67.74%), Ammonia Nitrogen (86.22-87.20%), Total Nitrogen (70.11-73.48%), dissolved phosphorus (82.11-85.83%), total phosphorus (73.54-75.88%), faecal coliforms (95.50- 99.70%) for duckweed ponds and COD (82.30- 84.84%), nitrate-nitrogen (65.69-68.28%), ammonia nitrogen (64.24-67.02%), total nitrogen (63.59-69.42%), dissolved phosphorus (43.5850.12%), total phosphorus (54.09-58.66%), faecal coliforms (99.63- 99.73%) for ponds without duckweed. Compared with the National standards for discharge of effluents to the environment, all parameters of the duckweed effluents were within the standard limit values except the value for the faecal coliforms which was outside the range. The results showed that duckweed can be successfully used for treatment of municipal wastewater. An experiment about how the amount of duckweed used affects the nutrient uptake was also conducted. A total of 4 density loads: M1 (25%), M2 (55%), M3 (80%), M4 (100%) of inoculation masses were used. Changes in wastewater and duckweed mass characteristics were recorded for a period of 21 days. The nutrient load in the wastewater reduced significantly in all the three replications of the 4 experimental setups where the experiment of the 25% duckweed mass showed the maximum nutrient removal from the wastewater.