WET AIR OXIDATION OF POLYETHYLENE GLYCOLS - MECHANISMS, INTERMEDIATESAND IMPLICATIONS FOR INTEGRATED CHEMICAL-BIOLOGICAL WASTE-WATER TREATMENT

The wet air oxidation of aqueous solutions of polyethylene glycol, a s ynthetic polymer used in a wide range of applications, has been invest igated at temperatures from 383 to 513 K and oxygen partial pressures From 2 to 3 MPa. Molecular weights From 62 (ethylene glycol) to 35,000 were studied with respect to their behaviour under wet oxidation cond itions in terms of the intermediate compounds produced and the reactio n mechanisms. It was found that the autocatalytic mechanism of thermoc hemical autoxidation was capable of converting macromolecules to lower molecular weight end-products, such as oligomers and carboxylic acids , at very short reaction times and mild operating conditions. The oxid ation of the lower molecular weight products was also studied to aid t he mechanistic interpretation. Total oxidation of these compounds to c arbon dioxide proved to be difficult since compounds such as ethylene glycol and acetic acid are very resistant to chemical oxidation even u nder more severe conditions. Assessments of the aerobic biodegradabili ty of polyethylene glycols, before and after wet air oxidation, were p erformed by measuring BOD5/COD ratios and the results are compared to those reported in the literature. The drawbacks of using BOD/COD ratio s as an index of aerobic biodegradability are discussed and implicatio ns for integrated chemical-biological treatment are given. Copyright ( C) 1996 Elsevier Science Ltd