Nitrogen and Phosphorus Removal Capacity of Water Lettuce, Water Hyacinth and Hydrilla in Domestic Wastewater of Sri Lankan Households

Domestic wastewater is one of the major issues for eutrophication due to its high nutrient content. To address it, the wetland wastewater treatment system can be applied as a low-cost and onsite treatment method. The current study focused on the households of Sri Lanka. Nitrate and Phosphate removal capacity of the three macrophytes; Water Lettuce, Water Hyacinth, and Hydrilla were observed on the laboratory scale in rainy and non-rainy seasons. In the non-rainy season, 1: 1 dilution is needed for raw domestic wastewater to enter the wetland system because macrophytes tend to die off without dilution due to high nutrient concentration. Water Lettuce > Water Hyacinth> Hydrilla effectively removes the Nitrate concentration in 90%, 78%, and 52% respectively, and Phosphate concentration in 85%, 72%, and 68% respectively within a 9-day retention period. In the rainy season, 1: 1 dilution was used and macrophytes took a 3-day retention period to get nutrient removal until reaching permissible levels. Water Lettuce> Water Hyacinth > Hydrilla removed the Nitrate concentration at 88%, 80%, and 64% respectively, and Phosphate concentration at 91%, 80%, and 70% respectively. Water Lettuce is the most effective nutrient removal macrophyte within these three macrophytes which can treat domestic wastewater up to the permissible level within a 9-day retention period in the non-rainy season and a 3-day retention period in the rainy season.