Abstract: Wastewater from an industrialized turtle-breeding farm,treated with a single application of nitric acid to adjust the ratio of NO₃^--N and NH₄⁺-N and initial pH,was tested as medium for hydroponics of cos lettuce（Lactuca sativa var.romana）.Results show that after two weeks of operation under 22—28 ℃,SS and COD（Cr） in the wastewater with pH ranging between 6—9 was reduced to less than 20 mg·L^-1 and 100 mg·L^-1,respectively,meeting Grade 1 criteria of the "Integrated Standard for Wastewater Discharge"（GB 8978—1996）;and NH₄⁺-N and TP was lowered down to 22.1—30.3 （mg·）L^-1 and 0.64—0.69 mg·L^-1,respectively,approaching or meeting Grade 2 criteria of the standard（GB 8978—1996）.Moreover, the cos lettuce grew quite well in the wastewater with a growth rate of 19.9%—25.1% in biomass.

Key words: wastewater, purification, turtle-breeding, hydroponics, cos lettuce