Stability and performance of mesophilic anaerobic fixed-film reactors during organic overloading.

The stability of downflow stationary fixed-film (DSFF) reactors was evaluated under extreme organic shock loads. Reactors could handle five- to sevenfold increases in organic loading and recover to normal performance in a relatively short period of time (usually 24-72 h) during treatment of well-buffered sucrose and acetic acid wastewater at 27 and 35 degrees C. Overloading was characterized by elevated volatile-acid concentrations, decreased reactor pH, and excess biofilm sloughing. Reactors could not cope with extreme organic shocks during treatment of poorly buffered sucrose wastewater. The pH of the mixed liquor was observed to be a more important factor than the volatile-acid concentration in determining whether DSFF reactors would recover in a reasonable period of time.