Potential for Waste Reduction in Activated Sludge Systems: Evaluation of the Initial Conditions of a Rapid Test with Rhamnolipid Biosurfactant

Adding chemicals that alter the microbial metabolism and reduce cell growth, without affecting organic matter removal, is an alternative technology to reduce sludge production. This study was intended to determine the best initial conditions to conduct a rapid test (4 h), which evaluates the potential of chemicals to reduce microbial growth and chemical oxygen demand removal. A commercial biosurfactant was used as model product and a central composite design (face centered) was performed using substrate/inoculum ratio and rhamnolipid/inoculum ratio as independent variables, and cellular yield coefficient, substrate consumption rate, and specific oxygen uptake rate for exogenous respiration as response variables. Lower values of substrate/inoculum ratio permitted larger reductions of cellular yield coefficient with lower rhamnolipid concentrations. The best condition was 1.06 g chemical oxygen demand/g total suspended solids and 25 mg rhamnolipid/L or 25 mg rhamnolipid/g total suspended solids, which achieved a reduction of 50-75% in cellular yield coefficient.