Abstract
The objective of the study was to evaluate the performance of three different aquatic macrophytes for treatment of municipal wastewater collected from Taxila in Pakistan. A physical model of a typical treatment plant was constructed and was operated for six experimental runs with each species of macrophyte. Every experimental run consisted of a thirty-day period. Regular monitoring of influent and effluent concentrations were made during each experimental run. Locally available macrophyte species (water hyacinth, duckweed and water lettuce) were selected for testing. To evaluate the treatment performance of each macrophyte, BOD5, COD, and nutrients (nitrogen and phosphorus) were monitored in the effluent from the model at different detention times for each experimental run, after having ensured steady state conditions. The average reduction of effluent value for each parameter, using water hyacinth, was 50.61% for BOD5, 46.38% for COD, 40.34% for nitrogen and 18.76% for phosphorus. For duckweed, the average removal efficiency for the selected parameters was 33.43% for BOD5, 26.37% for COD, 17.59% for nitrogen and 15.25% for phosphorus, and for water lettuce the average removal efficiency was 33.43% for BOD5, 26.37% for COD, 17.59% for nitrogen and 15.25% for phosphorus. The mechanisms of pollutant removal in this system include both aerobic and anaerobic microbiological conversions, sorption, sedimentation, volatilisation and chemical transformations. The rapid growth of the biomass was measured within the first ten days of the detention time. It was also observed that performance of macrophytes is influenced by variations in pH and temperature. A pH of 6-9 and temperature of 15-38 degrees C is most favourable for treatment of wastewater by macrophytes. The option of macrophytes for treatment of municipal sewage under local environmental conditions can be explored by further verifying the removal efficiency under different environmental conditions.