The use of bioproducts that change the cellular metabolism and reduce microbial growth without affecting the organic matter removal is very promising for reducing the amount of sludge in wastewater treatment systems. In this study, two bioproducts were evaluated and compared with a well-known chemical (2,4-DiNitroPhenol – DNP) in activated sludge treating petroleum refinery wastewater. In batch experiments, 10 mg/L of DNP, 0.8 mg/L of a bioproduct based on Folic Acid (FA) and 10 mg/L of a bioproduct based on Stress Proteins (SP) led to 30.6%, 43.2% and 29.8% lower disposal of total solids, respectively. Operating on a continuous regimen, the addition of 10 mg/L of the bioproduct based on SP led to 45.7% lower disposal for 50 days. In all cases, no loss of efficiency in the Chemical Oxygen Demand (COD) removal was observed.