Characterization of the microbial communities in jet-loop (JACTO) reactors during aerobic olive oil wastewater treatment

The olive oil industry is one of the most typical and economically important Portuguese agro-industries, 29,900 tons of olive oil having been produced in 2002/2003. This industry generates large amounts of olive oil wastewaters (OOWW), which are difficult to degrade and thus cause a negative environmental impact. Jet-loop reactors (JACTO) developed and scaled-up by our group have been successfully used for biological treatment of winery and OOWW. This study aimed to determine the interactions of reactor hydrodynamics with microflora profiles during bio-treatment of OOWW. Bio-treatment was performed using a 20-dm³ JACTO bioreactor achieving a chemical oxygen demand (COD) and phenolic compounds removal rate of 70% at a hydraulic retention time of 12 days. Bio-treatment was scaled-up to 200-dm³ JACTO bioreactor, reaching 87% COD removal and 80% phenolic compounds removal. Microflora present on OOWW were identified on samples taken before, during, and at the end of bio-treatment. Identification of isolates was carried out at genus and/or species level. Samples from the bio-treatments did not show any fungi; most of the isolates belonged to the Bacillus genus (with predominance of Bacillus megaterium, Bacillus sphaericus, and Brevibacillus brevis). The good COD and phenolic compounds removal rate indicates that the microbial community selected during the treatment is well adapted to the stress conditions imposed by this special type of bioreactor.