INTEGRATED WET AIR OXIDATION AND BIOLOGICAL TREATMENT OF POLYETHYLENEGLYCOL-CONTAINING WASTEWATERS

The treatment of a model wastewater containing polyethylene glycol (PE G) of molecular weight 10 000 in an integrated wet air oxidation-aerob ic oxidation process was investigated. Partial wet air oxidation under mild operating conditions was capable of converting the original poly mer to lower molecular weight compounds, such as oligomers and short-c hain organic acids. The effect of molecular weight on the aerobic biod egradability of polyethylene glycol was assessed by performing shake f lasks experiments with various polyethylene glycols in a molecular wei ght range from 200-35 000 and it was found that biodegradability gener ally decreased with increasing molecular weight. Aqueous solutions of PEG 10 000 were subjected to continuous wet air oxidation at a tempera ture of 423 K and a residence time of 30 min and the oxidised effluent s were then subjected to subsequent continuous aerobic oxidation at re sidence times varying between 0.5 and 4 days. Simultaneously, continuo us aerobic oxidation experiments on solutions of PEG 10 000 were perfo rmed and used to compare the efficiency of the integrated treatment pr ocess with that of the direct biological treatment. Partial pretreatme nt by wet air oxidation under mild operating conditions resulted in ef fluents whose biodegradation rates were significantly higher than thos e of the original, unoxidised wastewater, as assessed by total organic carbon (TOC) removal rates. The original wastewater was practically n on-biodegradable at a 0.5-day residence time with direct biological tr eatment, while an 80% TOC removal was achieved when biological treatme nt was coupled with a preceding wet air oxidation step. Conversely, wi th a 4-day residence time for the direct biological treatment the orig inal wastewater was only partially degradable with 60-70% TOC removal recorded; with the integrated treatment process at a 4-day residence t ime in the bioreactor the overall TOC removal was greater than 90%.