Extraction of DMAC from the Pharmaceutical Wastewater by a Multistage Countercurrent Model

A multistage countercurrent solvent extraction model was used for recovering N,N-dimethylacetamide (DMAC) from the pharmaceutical wastewater. The theoretical stages were obtained to be five by graphical method in the light of the fitted phase equilibrium data. And then the five-stage countercurrent extraction experiments were performed in the actual and simulant effluent systems, respectively. It was found that the optimum conditions of the experiments were as follow: pH value of 8, phase ratio (O/A) of 1:1, and addition of 0.05 mass fraction of NaCl solid into wastewater at room temperature. The reliability of the theoretical stages was verified on the basis of the relative errors (<0.0641) calculated by the theoretical and experimental data, as well as the high extraction efficiency obtained by the actual and simulant wastewater systems. The results showed that the content of DMAC in the simulant wastewaters decreased to 0.0074, the actual one dropped to 0.0078, and thus the extraction efficiency of DMAC was 97.53% and 97.40%, respectively.