Growth of water hyacinths in treated sewage effluent

Two thousand plants of the water hyacinth,Eichornia crassipes Solms., were introduced on April 11, 1971, into a series of five ponds, each 5000 sq. ft. in area and 2.6 ft. deep. Treated waste water effluent from the Ames sewage treatment plant filled the ponds and was added to pond 1 at 127 gallons per minute. By growth and vegetative reproduction, these plants increased to more than 500,000, and all five ponds were covered completely by July 26. On that date, the extrapolated estimate of total wet weight was 287 U.S. tons/ acre (645 metric tons/hectare; 64500g/m²). The estimate of oven dry weight was 13.2 U.S. tons/acre (29.7 metric tons/hectare; 2970g/m²). Ammonia and nitrate disappeared rapidly from the pond water, and phosphate concentrations were lowered appreciably. Evapotranspiration and seepage accounted for water losses of more than 0.5 inches per day. The potential economic values of this plant and its possible use in tertiary treatment to reduce N and P components in waste waters are discussed briefly.