Ozone pretreatment for effective biodegradation of monoethylene glycol

Monoethylene glycol (MEG) undergoes various stages during metabolic degradation pathways from acetaldehydes to acetic acid before converting to carbon dioxide and water in a degradation process. Sequential degradation of MEG through biological route obsesses higher retention time. Ozone is considered as an effective oxidant for MEG degradation but involves higher operating cost. When used as pretreatment chemical, ozone is effective in improving the COD: BOD ratio, hence coupling chemical and biological process exhibit a viable option. An attempt was made to enhance the biodegradation by ozone pretreatment. MEG degradation was investigated by ozone pretreatment followed by a continuous bench scale reactor based on activated sludge bio-process. The influence of process variables such as pH, ozone concentration, and hydraulic retention time was studied during the pretreatment studies. The results indicate that pH plays an important role in effective treatment by ozone and would require around pH 10.5. An optimum concentration of 50 mg/L of ozone is required to improve the downstream biodegradation process. Improvement in biodegradation was measured by BOD: COD ratio and formation of intermediates. The intermediates were identified as acetaldehyde and acetic acid. The rate of MEG biodegradation was reduced to 4 hrs compared to reported values of 10 hrs after ozone pretreatment. The reaction time was found 2 hrs during ozone pretreatment. The overall COD reduction was achieved 93% after the biological process.