High susceptibility of aerobic microbiota in membrane bioreactor (MBR) sludge towards olive oil as revealed by high-throughput sequencing of 16S rRNA genes

•High-throughput DNA sequencing of oil-contaminated MBR sludge communities.•Aerobic microorganisms in MBRs are highly susceptible to oil contamination.•Oxygen supply is critical in maintaining MBR stability during oil degradation.

Advanced microbiological characterization was conducted to evaluate the dynamics of microbial communities in a membrane bioreactor (MBR) during periodic amendments of olive oil. An MBR undergoing stable treatment of a model domestic wastewater for 10 days was subjected to the staged dosages of olive oil at 200, 400, 600 and 800 mg L−1 during days 11-17, 18-25, 26-33 and 34-36. High-throughput Illumina sequencing of 16S rRNA genes was applied to detect any changes in microbial communities at the different stages. The total organic carbon, chemical oxygen demand and fatty acid analyses revealed no significant changes in reactor performances up to the 30th day. Total nitrogen and ammonia concentrations only slightly increased during this period. Despite the stable treatment observed, principal coordinate analysis of the Illumina sequence data revealed that the microbial community structure has already shifted even in the early stages of the olive oil amendment (day 11). The Chao1, Shannon and Simpson reciprocal indices showed a decrease in the richness and evenness of microbial communities. High-resolution phylogenetic analysis revealed the major presence of an aerobic betaproteobacterial Comamonas serinivorans in the sludge together with a wide variety of anaerobic microorganisms. This suggests the high susceptibility of MBR to factors that affect the oxygen supply to the system. Hence, when the olive oil supply was increased to 600 mg L−1, the other aerobic degraders declined and were excluded from the dominant species. A highly effective aeration system is crucial for the maintenance of MBR performances during episodes of olive oil contamination.

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