A modified aeration process for promoting nutrient removal using water hyacinth to treat sewage

In an attempt to upgrade some conventional aeration processes, a laboratory-scale system for promoting nitrogen and phosphorus removal was set up and studied through a series of experiments, in which water hyacinth was planted on the surface of the mixed liquor in aeration tanks. The main purpose of this study was to evaluate the effects of aeration, organic load (chemical oxygen demand) and residence time on the nutrient removal efficiency of a wafer hyacinth based system for the purification of raw and settled sewage wastewaters. The experiments indicated that the aeration with airflow intensity of 41 min(-1) can provide enough oxygen supply but no significant disturbance of water hyacinth growth. The water hyacinth grew better in a moderate organic strength of chemical oxygen demand (COD) = 18-80 mg l(-1). In this study, it was observed that chlorosis of water hyacinth occurred under conditions of nutrient deficiency, and possibility that it was caused by iron (Fe) deficiency was analyzed. The increase of solids retention time (SRT) from 5 to 20 days was of benefit for organic and nutrient removals. The system demonstrated a high performance of nitrogen and phosphorus removals up to 86 % and 80 % respectively from the raw sewage, which are far better than that in floating aquatic macrophyte-based treatment systems (FAMS) and wetland systems. Dissimilation via nitrification and denitrification was considered as a major pathway of N removal, and assimilation via plant uptake was thought to be responsible for more than half of the P removal in the designed system.