PURIFICATION OF REFINERY WASTEWATER BY DIFFERENT PERENNIAL GRASSES GROWING IN A FLOATING BED

Four species of perennial grasses [Geophila herbacea O Kumtze (GHK), Lolium perenn CV. Caddieshack (LCC), Lolium perenne Topone (LPT) and Lolium perenne L. (LPL)] were used to remove nutrients and pollutants from refinery wastewater, of which the average concentration of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (CODMn), total petroleum hydrocarbons (TPH) were 15.6 mg L-1, 0.6 mg L-1, 142.8 mg L-1 and 1720 mg L-1, respectively. These perennial grasses had performed extremely well in removing the nutrients and pollutants and were capable of removing up to 60% of TN and 56% of TP from the refinery wastewater during 35 days treatment period, to which plant uptake contributed only 5%-10% and 10%-20%. The removal rates of CODMn and TPH were fluctuating within 52% to 67% and 40% to 55%, respectively. The nutritional value of these perennial grasses as animal feeds such as crude protein, crude fat, crude fiber, crude ash and nitrogen-free extraction after growing in refinery wastewater for 35 days were analyzed and the results suggested that these indicators were superior to national animal feed thresholds, with its nitrites and several heavy metals including zinc (Zn), arsenic (As), cadmium (Cd), and lead (Pb) concentration far below the thresholds. We concluded that perennial grass floating-bed system was effective for purifying refinery wastewater during its growing season and harvested perennial grass had great value as animal feeds.