Biological treatment of landfill le

Biological treatment of landfill leachate usually results in low nutrient removals because of high chemical oxygen demand (COD), high
ammonium-N content and the presence of toxic compounds such as heavy metals. Landfill leachate with high COD content was pre-treated
by coagulation-flocculation with lime followed by air stripping of ammonia at pH ¼ 12. Nutrient removal from pre-treated leachate was
carried out using a lab-scale sequencing batch reactor (SBR). Three different operations consisting of different numbers of steps were tested
and their performances were compared. These operations were the three-step anaerobic (An)/anoxic (Ax)/oxic (Ox); the four-step
(An/Ox/Ax/Ox), and the five-step (An/Ax/Ox/Ax/Ox) operations with total residence time of seven hours each. Experiments were carried out
using three consecutive operations with a total cycle time of 21 h at a constant sludge age of 10 days. The lowest effluent nutrient levels were
realized by using the five-step operation which resulted in effluent COD, NH4-N and PO4-P contents of 1,400, 107 and 65 mg l21,
respectively, at the end of 21 h. Addition of domestic wastewater (1/1, v/v) and powdered activated carbon (PAC, 1 g l21) to the pre-treated
leachate improved nutrient removals in the five-step SBR operation, resulting in 75% COD, 44% NH4-N and 44% PO4-P removals after 21
hours of operatio