Role of Scirpus lacustris in bacterial and nutrient removal from wastewater

Experimental microcosms using macrophytes were set up to determine the role of the plants and their rhizosphere in the removal of nutrients and fecal indicators from rural wastewater. Scirpus lacustris was grown in hydroponic culture and in siliceous gravel to compare them with the efficiency of gravel beds without macrophytes. Design parameters for the different experiments were as follows (surface loads in g/m(2)/d): 1.1-6.4 BOD, 0.8-1.6 VSS, 0.3-3.5 TN, 0.1-0.3 TP; hydraulic load 4-7 cm/d; and retention time 4-8 d. Organic carbon removal was not significantly correlated to the presence of S. lacustris. The removal of phosphorus and nitrogen was enhanced in the presence of plants, even with extremely low C:N ratios. The presence of S. lacusutris was responsible for 30% of TN and 20% of TP removal in summer. Probably due to changes in plant activity, removal efficiencies for these nutrients increased 10% from spring to summer. Concerning pathogen removal, efficiencies of gravel beds with macrophytes were significantly higher than those from the other treatments, reaching up to 99.999%. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.