MICROSAND BALLASTED FLOCCULATION AND CLARIFICATION: EFFECTS ON REMOVAL OF TSS, OIL & GREASE, AND METALS FROM A STEEL MILL WASTE STREAM

A seventeen-day pilot operation demonstrated the feasibility of microsand ballasted flocculation and clarification for removal of TSS, oil & grease, and multiple regulated metals from steel plant wastewater. The process was insensitive to varying influent conditions tested including normal and simulated “worst case” conditions.Overflow rates of 25 and 75 gpm/ft2, equivalent to 25,000 gpm process and 150,000 gpm combined process/stormwater flows, were tested. Average removal efficiencies of 96% for TSS and 92% for oil & grease were achieved. Effluent copper concentrations below 6.1 μg/l and nickel concentrations below 20 μg/l were also achieved. Various process pH's and sulfide dosages were evaluated for compliant metals removal. For influent copper and nickel concentrations below 140 μg/l, a pH of 10.5 and 3 mg/l (as S) sulfide addition proved optimal.