Treatment of olive mill wastewater through employing sequencing batch reactor: performance and microbial diversity assessment

This work describes the performance of a sequencing batch reactor (SBR) and the involvement of a novel reconstituted
bacterial consortium in olive mill wastewater (OMW) treatment. The organic loading rate applied to the SBR was serially
increased in terms of initial COD from 10 to 75 g L−1 to allow gradual acclimatization of activated sludge to high concentrations
of toxic compounds in OMW. After the acclimatization period, up to 60% of the total COD content were effectively
biodegraded from OMW at 75 g L−1 COD within 30 day hydraulic retention time. The diversity and community composition
of cultivable bacteria participating in the aerobic process of treating OMW were further assessed. A total of 91 bacterial
strains were isolated from the reactor and analyzed by amplification of the 16S-23S rRNA internal transcribed spacer (ITS)
region and by 16S rRNA gene sequencing. The most abundant phylum was Firmicutes (57.1%) followed by Proteobacteria
(35.2%) and Actinobacteria (7.7%). The use of the Biolog® Phenotype Microarray system to evaluate the ability of isolated
strains to utilize OMW phenolic compounds is reported in this work for the first time. Interestingly, results showed that
all species tested were able to utilize phenolics as sole carbon and energy sources. The removals of COD and phenolics
from undiluted OMW by the reconstituted bacterial consortium were almost similar to those obtained by the acclimatized
activated sludge, which suggest that cultivable bacteria play the major role in OMW biodegradation. Phytotoxicity assays
using tomato seeds showed a significant improvement of seed germination values for treated OMW. Our overall results suggest
that the novel developed bacterial consortium could be considered as a good prospect for phenolics-rich wastewaters
bioremediation applications.