Water hyacinth growth in anaerobic digester effluents

Growth characteristics and N assimilation of water hyacinth (Eichhornia crassipes [Mart] solms) were evaluated for diluted and undiluted effluents from anaerobic digesters containing ¹⁵N-labeled water hyacinth as feedstock. The diluted effluents were an excellent growth media for plants and resulted in high dry weight gains. The highest gain in plant dry weight (18 gm⁻² day⁻¹) was noted for the diluted effluent having an initial NH₄N concentration of 65 mg liter⁻¹ and an electrical conductivity (EC) of 1·6 dSm⁻¹. Plant death was observed in four of the six undiluted effluents. Ammonium loss from the effluents was described with first-order kinetic rate constants which ranged from 0·175 to 0·593 day⁻¹. Plant assimilation of ¹⁵NH₄N ranged from 36 to 66% in diluted effluents and from 2 to 77% in undiluted effluents. Plant survival was not dependent entirely on NH₄N concentrations or EC of the effluents.