Evaluation and optimization of the improved waste activated sludge reduction in linear alkylbenzene sulfonates...

Linear alkylbenzene sulfonates (LAS) coupled with short-time aerobic digestion (STAD) system was proved to achieve efficient waste activated sludge (WAS) reduction. This work focuses on the evaluation and optimization of the operation parameters affecting WAS reduction including LAS dosage, system initial pH and dissolved oxygen (DO) concentration by using response surface methodology (RSM) based on central composite design (CCD). Results showed that all target single factors affected VSS and LAS removal during WAS reduction. The constructed regression model combined with variance analysis found that model predicted value fitted well with experiment result with high values of R² and R²_adj for both VSS and LAS removal (all >0.967). Statistical analysis showed that LAS dosage was the most crucial factor affecting WAS reduction, initial pH and DO concentration were important parameters for VSS and LAS removal, respectively. The interaction between LAS dosage and initial pH also significantly impacts VSS removal (P < 0.05). With LAS dosage 0.10 g/g TSS, initial pH 7.38 and DO concentration 2.48 mg/L, the optimized maximum removal rates of VSS and LAS after aerobically digested for 36 h could reach 41.7% and 98.6% with low error between predict results and experimental data (<1.5%). Thus, RSM based on CCD can be accurately applied for the optimization and prediction of WAS reduction in the LAS coupled STAD system.