Stratification in Laboratory Simulations of Water Hyacinth Ponds

Abstract

The technical and economical feasibility of using water hyacinth ponds for the treatment of wastewater is well established. However, various purification mechanisms operative in a pond have not been understood fully. In the present work, an attempt has been made to study stratification in four laboratory scale models of different depths operated continuously over a period of 4 months. It was concluded from this study that stratification did not occur in ponds. An attempt also was made to study the possible reasons for it. First, dense water hyacinth canopy stops radiation in excess of 90%. This prevents the growth of algae and subsequent increase in dissolved oxygen. Second, based on temperature profiles, thermal and density stratification also were found to be absent. Third, the secondary circulation in the ponds, induced because of influent and effluent being at different levels, also assists in checking the stratification. All these effects make a water hyacinth pond unstratified, which helps in uniform treatment throughout the depth and maintenance of designed hydraulic detention time.