Oily Wastewater Biodegradation By Membrane Bioreactor With Rhamnolipid

Membrane bioreactor (MBR) is becoming widespread in wastewater treatment, but the hydrophobic of oil in the waste often causes membrane fouling seriously, and becomes the bottleneck of membrane bioreactor application. As one kind of biosurfactants, rhamnolipid has some good features, such as non-toxic, easily biodegradable, surface activity and so on. It can reduce the interfacial tension, promote emulsion, and cause cells contact with large droplets easily. After solubilization, organic molecules can dissolve in the micelles formed by biosurfactant, and then disperse in the aqueous phase in which bacteria are taken in oil droplets easily. Water treatments with rhamnolipid not only promote oil degradation, but also can reduce membrane fouling.The performance of membrane bioreactor (MBR) with rhamnolipid for oily wastewater treatment was investigated in lab-scale. The experimental study mainly focused on the effect of rhamnolip additon on sludge particle size, hydrophobicity, sludge activity and bacteria flora. Membrane fouling and the degradation of oil wastewater was aslo analyzed in detail. Result showed that the particle size of the sludge in aeration tank after operated 30 days in the presence of rhamnolipid increased from 53.059μm to 116.73μm, and the contact angle also increased from 43°to 57°by analyzing the aerobic dehydrogenase activity. The result of the deformation gradient gel electrophoresis (DGGE) suggested that the addition of rhamnolipid did not affect the microbial activity and biological flora of activated sludge. When hydraulic retention time (HRT) was 24h and intermittent ratio was 2:8, the remove rate of COD without rhamnolipid for oily wastewater was between 60% and 80%, while the removal rate of COD with rhamnolipid treated oily wastewater was about 95%. The change of membrene flux and the image of scanning electron microscope (SEM) showed that rhamnolipid in MBR could mitigate membrane fouling effectively eapecially in low concentration oily wastewater treatment. The membrane flux was about 5 times larger than that without rhamnolipid.