Impact of chromium and copper on fixed-film biological systems

A laboratory investigation was performed to study the recovery of a biological tower (fixed-film biological wastewater treatment unit) after dosing the influent with copper or chromium. The pilot-scale biotower (1.83 m high) was shocked with copper at three different influent concentrations (3, 56, and 47 mg/L). A continuous 3 mg/L dose had no significant impact on soluble 5-day biochemical oxygen demand removal performance. After slug doses of 56 or 57 mg/L for 10 h, the biotower established a new steady-state condition, in terms of soluble 5-day biochemical oxygen demand in the effluent, within 14 h. Recoveries from shock loads of chromium were slower: Recovery from doses of 9 mg/L of chromium occurred after 12 h, but recovery from doses of 38 and 96 mg/L required approximately 250 h. The metals concentrations in both biofilm and effluent were described by a power function with a concentration equal to a constant multiplied by time to a power. Uptake of chromium was determined to be nearly independent of dose, at the doses tested.