Treatment of desizing wastewater containing poly(vinyl alcohol) by wet airoxidation

The effectiveness of wet air oxidation (WAO) is studied in a 2-L autoclave for the treatment of desizing wastewater from man-made fiber textile plants . At an oxygen pressure of less than 2 MPa, over 30-min, chemical oxygen de mand (COD) removal was found to increase from 15 to 65% when the temperatur e was raised from 150 to 250 degrees C. The biodegradability of the wastewa ter was also simultaneously increased. Up to 90% of the COD could be remove d within 120 min. A simplified reaction mechanism is proposed which involve s a direct mineralization step in parallel with a step in which an intermed iate is formed prior to mineralization. A kinetic model for COD removal was developed based on this reaction mechanism. The model was tested with expe rimental COD results over the temperature range of the experiments. The dep endence of the specific reaction rate constants was found to follow the Arr henius type of equation. The direct oxidation of poly(vinyl alcohol) (PVA) to carbon dioxide and water is the dominant reaction step. The intermediate s formed are not likely to be the acetic acid but may be short segments of PVA that are easily oxidized.