Evaluation of Impacts to the Oxygen Transfer Efficiency in High Strength Industrial Wastewater Systems - A Case Study

The characteristics of wastewater from a polyethylene (PET) manufacturing plant were found to impact the oxygen transfer for aeration in an MBR system, and this effect was correlated with the load and concentration of ethylene glycol in the influent. OTE values of 70-80% were observed during production cycles that discharged lower quantities of ethylene glycol (EG). During production cycles that involved the discharge of elevated ethylene glycol (EG) to the wastewater treatment process, OTE values of 35-40% were observed. The mechanism by which the change in wastewater characteristics impacts OTE remains unknown. As the levels of soluble COD and EG in the mixed liquor were found to be constant, the direct impact of EG on OTE by increase in viscosity and surfactant levels was not apparent. As MLSS was kept constant at 11-12 g/L, the drop in OTE was not correlated with a rise in MLSS levels, which would normally cause an increase in viscosity. Another possible cause of OTE loss, increased gas flow rate (higher gas liquid ratio) was also rejected, due to the low gas flow rates over which the equipment was operated.These results demonstrate that in wastewater treatment facilities with variation in influent wastewater composition and load, the oxygen transfer efficiency of aeration systems under field conditions can be impacted by factors other than MLSS, surfactant levels, and gas flow rates. One possible explanation is that spikes in F/M could lead to changes in the MLSS properties, either the microbial species distribution or membrane surface properties, which lead to a rise in viscosity independent of MLSS concentration and a drop in OTE.