Removal of polyacrylonitrile oligomers from acrylic fiber wastewater using two-stage flotation

It is a very interesting work to sufficiently treat the industrial wastewaters containing the suspended solids (SS) which are difficultly removed and biodegraded. The SS of acrylic fiber wastewater were polyacrylonitrile (PAN) oligomers from FTIR analysis and they were one of the most bio-refractory contaminants. For effectively removing PAN oligomers and then greatly decreasing chemical oxygen demand (COD) from the wastewater, a two-stage flotation was developed using cetyl trimethyl ammonium bromide (CTAB) as a collector. In the first stage, a high volume ratio 8.3 ± 0.4 was obtained and the PAN oligomers in the foamate were easily precipitated. In the second stage, the recovery percentage of CTAB reached 66.8 ± 3.3% by using the residual solution of the first stage as the feeding solution of the second stage. At last, 82.1 ± 4.1% of CTAB could be reused by recovering CTAB from the supernatant solution after the free setting of the first stage and the foamate of the second stage. Furthermore, the total removal efficiencies of SS and COD reached 98.2 ± 4.9% and 81.0 ± 4.1%, respectively, under the suitable conditions of two-stage flotation. This work was aimed at removing PAN oligomers cost-effectively from the wastewater and supplying a new method for removing other refractory SS of industrial wastewaters.