The Nonsteady-State-Biofilm Process for Advanced Organics Removal

Efficient and economic removal of organics to very low concentrations is best achieved by biofilm processes, in which bacteria are attached to fixed media and remove organic compounds from the wastewater flowing over them. A laboratory-scale reactor was used to evaluate the ability of a biofilm to remove low levels of organic substrate from water during extended operation. Nonsteady-state operation, in which low concentrations of organic substrate were treated by a biofilm previously grown on a relatively high concentration feed, demonstrated that a slowly decaying biofilm achieved high efficiency removal for at least 1 year without reactivation. A kinetic model to describe the transient growth and decay of the biofilm was developed, and it predicted the growth and steady-state phases of the biofilm when input parameters were determined independently. The slow loss rate of the biofilm prolonged the usefulness of the nonsteady-state-biofilm process and was explained by adaptation to oligotrophic conditions and production of supplemental organic material during nitrification activity.