THE USE OF EICHHORNIA-CRASSIPES TO CLEANSE OIL-REFINERY WASTE-WATER IN CHINA

Water hyacinth (Eichhornia crassipes) can grow in oil-refinery wastewater after the water has undergone an initital treatment of oil-separation, flotation and aeration. When the wastewater COD is below 131 mg/l, E. crassipes does not suffer long-term toxic effects. By numerical value analysis, the optimum COD under which E. crassipes can be used to oxidize oil-refinery wastewater is between 65 and 131 mg/l and the highest possible COD is 262 mg/l. Eichhornia crassipes, grown in two 3750-m2 oil-refinery wastewater oxidation ponds, improved the quality and transparency of outlet water. After 2 to 4 days retention in oxidation ponds, turbidity decreased by 32%, phenol oil decreased by 18%, COD decreased by 8-13%, nitrogen decreased by 6-18%, phosphorus decreased by 12-24%, and several heavy metals decreased by 3-54% more than the unvegetated control. Eichhornia crassipes removed various pollutants through the absorption and uptake of toxic organic matter and heavy metals. In addition, its oxygenated root zone helps to bring about flotation and flocculation of oil residue, increased aerobic degradation, and a large microbial population to stimulate decomposition.