Treatment train for tailings pond water using Opuntia ficus-indica as coagulant

In this study, the mucilage of Opuntia ficus-indica, a type of cactus was used as a bio-coagulant to treat tailings pond water (TPW) from the oil sands process industry. The performance of Opuntia ficus-indica was compared with conventional coagulants such as alum and ferric chloride for the removal of turbidity and dissolved organic carbon (DOC). Albeit at a higher dose of 900 mg/L, compared to that of alum (190 mg/L) and ferric chloride (104 mg/L), Opuntia ficus-indica could remove 98% of the turbidity of tailings pond water. The DOC removal was low for all coagulants and ranged from 15 to 28%, but acidification of TPW effluent improved DOC removal significantly. FTIR analysis showed the presence of oxidized napthenic acids and carboxylic groups on the surface of the TPW solids and flocs. The settling velocity of the flocs was 6.28 cm/min, 4.54 cm/min, and 3.01 cm/min generated by Opuntia ficus-indica, alum, and ferric chloride, respectively. Of several heavy metals present in TPW, Opuntia ficus-indica showed higher arsenic removal (64%) compared to alum and ferric chloride, while alum and ferric chloride showed significantly higher phosphorous removal compared to Opuntia ficus-indica. Activated carbon was used as the final treatment step for removal of residual organics; Opuntia ficus-indica treated TPW showed about 1.8 times greater adsorption capacity for activated carbon than that treated with alum.