Oxygen Transfer of Fine-Bubble Aeration in Activated Sludge Treating Saline Industrial Wastewater

Abstract

Aeration is usually the most energy-intensive part of the activated sludge process, accounting for 50% to 80% of the total requirement. To achieve high efficiency, designers and opera-tors of WWTPs must, therefore, consider all influencing factors, including salinity. With increasing salinity, oxygen transfer increases compared to tap water (TW), due to the inhibition of bubble coa-lescence. Previous saline water (SW) experiments showed that by using small slits in the diffuser membrane design, oxygen transfer and aeration efficiency increase further. In this study, we present a modified approach for considering the salt effect on oxygen transfer and assess the transferability of SW results to saline-activated sludge (sAS) conditions. Therefore, we operated a pilot-activated sludge plant over 269 days with a saline industrial wastewater influent. The oxygen transfer of disc-diffusers with two different membrane designs was measured continuously via the off-gas method. The salt concentration (cSalt) measured via ion analysis ranged between 4.9 and 11 g/L. Despite a high cSalt fluctuation, COD elimination was >90% all the time. Our results confirm previous SW re-sults. Oxygen transfer in sAS is up to three times higher compared to non-saline conditions. Aeration efficiency shows that despite a higher pressure drop, diffusers with smaller slits are to be rec-ommended in order to improve aeration in sAS.