Enhanced phenol removal by floating fungal populations in a high concentration phenol-fed membrane bioreactor

Sludge bulking and washing-out phenomena may inhibit the efficiency and stability of treatment performances when activated sludge processes are used to treat phenol contamination at high concentration levels. In this study, a membrane bioreactor (MBR), as a modified activated sludge process, was applied to enhance the removal of high-loading phenol contamination by capturing non-flocculating degradatative populations in a bioreactor. The specific objectives were (i) to evaluate the validity of use of MBRs in enhancing the removal of highly-loaded (∼1000 mg/L) phenol contamination, and (ii) to characterize the community structure and phenol degradation rate of non-flocculating populations that could tolerate phenol-mediated stresses. When fed with phenol at a non-toxic level (∼100 mg/L), phenol was efficiently removed with maintaining stable and steady MBR performance. No shift in cellular and population morphologies was observed. When fed with phenol at a toxic level (∼1000 mg/L), however, a microbial community shift was observed. Milky floating populations appeared in the bioreactor after an acclimation period of 3 days. Interestingly, the appearance of the non-flocculating populations resulted in an enhanced removal of phenol in the high phenol fed MBR. Small subunit rDNA analysis showed that most of the non-flocculating populations were fungal members. The specific phenol degradation rate for the floating fungal populations was approximately five times greater than that for settling microbes in the high phenol fed reactor. These findings suggest that the efficient containment of degradation-active floating populations by the MBR process led to an enhanced removal of phenol in the high phenol fed bioreactor.