Pilot-scale treatment of waste-water from carbon production by a combined physical-chemical process

BACKGROUND: Due to its strong colour, high concentrations of fluorides and chemical oxygen demand (CODCr) and large amount of suspended solids (SS), the waste-water from carbon production (WCP) seriously affects the stability of the circulating system of Guizhou Branch, Aluminium Corporation of China. In this paper, the performance of a pilot-scale (24 m(3) d(-1)) combined treatment plant, consisting of chemical precipitation, coagulation, and Fenton oxidation, for the treatment of WCP was investigated. RESULTS: Lime precipitation and hydrated ferrous sulphate (HFS) coagulation, with polyacrylamide (PAM) as a coagulation aid, proved to be effective in the removal of colour (>70%), suspended solids (SS) (>90%) and fluoride (>80%) from the WCP. Subsequent Fenton oxidation combined with coagulation as a final treatment efficiently removed SS, F-, CODCr, dissolved organic carbon (DOC) and colour. The average total removal efficiencies of these parameters in the pilot-scale combined technology were as follows: SS = 98.8%, F- = 95.7%, CODCr = 94.8%, DOC = 91.8% and colour = 98.3%, giving an average effluent quality: colour 24 (multiple), CODCr 168 mg L-1, DOC 80 mg L-1, F- 38 mg L-1 and SS 44 mg L-1, consistent with the reusable water limits for the process. CONCLUSIONS: The current experimental results and the economic evaluation suggest that the combined process could be advantageous and feasible for the treatment of WCP. (C) 2009 Society of Chemical Industry