AWWA WQTC55040

Enhanced coagulation and dissolved air flotation (DAF) reduced spiked arsenic (As) concentrations by 50 to 70 percent during bench and pilot studies. Dual media filtration following DAF further reduced arsenic levels to below the detection limit of 2 pg/L as As. Factors investigated during bench and pilot trials included ferric chloride dose, coagulation pH, flocculation time, DAF hydraulic loading rate, and influent arsenic concentration. The major driver controlling arsenic removal was coagulant dose, with optimum removal occurring at about 8 to 10 mg/L ferric chloride as FeC13. Under conditions evaluated in this work, coagulation pH (6.5 to 7.5), flocculation time (8 to 16 minutes), and DAF hydraulic loading rate (5 to 9 gpmKt2) did not significantly impact arsenic removal efficiency. Increasing ferric chloride dose for arsenic removal increased the total mass of sludge produced and the total mass of arsenic removed from the water. However, the concentration of arsenic in the residuals (mg As per kg sludge) actually decreased. TCLP results of pilot generated sludge were <0.0002 mg/L as As, well below the 5 mg/L arsenic TCLP requirement. Sludge arsenic levels were markedly higher than the Federal 503 land application limit of 41 mg/kg, thereby limiting sludge disposal alternatives. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

01/01/2001

Number of Pages:

20

File Size:

1 file , 1.2 MB