Optimization of operating conditions for the acidification metabolites production with waste sludge using response surface methodology (RSM)

The acidification liquid of waste activated sludge (WAS) could be used as the additional carbon source of biological nutrient removal. Recently, the optimization of operating conditions for the acidification metabolites has attracted much attention. In this study, a three-factor Box-Behnken design (BBD) was applied to determine the relative importance of the various factors and the optimum operating during acidification using response surface method (RSM). The importance of the individual variables on the production of soluble chemical oxygen demand (SCOD) was suspended solids (SS) > shaking rate > initial oxidation-reduction potential (ORP). The increase on SS content led to a decrease on the acidification degree. Low SS could promote mass exchange and microbial activity. The maximum SCOD yield (9288.5 mg/L) was predicted under the optimum condition at 8.0 g/L SS, 144.0 mV initial ORP, and 60.0 r/min shaking rate. Also, the releasing of soluble protein and carbohydrate was calculated as responses. The individual effect of shaking rate and initial ORP had significant effect on soluble protein and carbohydrate releasing, respectively. This study would provide valuable information for increasing the efficiency of acidification.