Characterization of Effluent Water Quality from Hydroponic Cultivation System

Hydroponics, a soilless cultivation system, has received attention because of its application in industry and being thought as the option to support the increased world population by increasing crop yields with less water. A highly concentrated nutrient solution is used in the system; this solution is discharged after use because the composition becomes imbalanced, and hazardous substances and pathogens may accumulate. Water quality surveys were conducted to identify the characteristics of the hydroponic effluent, which has not been previously documented. Twenty-one effluents were collected from 16 facilities in Kochi, Japan. The concentrations of nutrients varied significantly: i.e. 9.8–526 mg N/L of nitrate, and 3.0–131 mg P/L of phosphorus. Statistical analysis revealed five properties that explained the variation in the effluents. Mass balances of nutrients were evaluated in a facility raising eggplant. The efficiencies of the nutrient investment in hydroponics seemed higher than those in soil cultivation systems: 34–41 moles (478–572 mg N) of nitrogen and 1.1–5.9 moles (35–184 mg P) of phosphorus were discharged during the cultivation of 1 tonne of eggplant.