Treatment of wet corn-milling wastewater with filamentous fungi was investigated as a means of obtaining fungal biomass as an additional byproduct. Competitive bacterial growth is a common problem during this nonaseptic treatment process. Selective disinfection with ozone was evaluated for eliminating bacterial populations during fungal cultivation. Three laboratory-scale continuous flow aerated reactors were operated under nonaseptic conditions at 38 degrees C, hydraulic retention time of 8 h and pH of 4. The bacterial population was reduced by one log with respect to the control when ozone was dosed at a concentration above 47 +/- 2 mg/L. An ozone dosage of about 57 mg/L was found to be most effective in improving both fungal biomass production and soluble chemical oxygen demand (SCOD) removal (up to 90%). Fungal biomass concentration increased from c. 1.45 g/L (control) to c. 1.75 g/L at a 57-mg/L ozone dosage. Higher and lower dosages of ozone resulted in poorer fungal growth and lower SCOD removal. (c) 2008 Elsevier Ltd. All rights reserved.