Biovalorization of Olive Mill Waste Water for the Production of Single Cell Protein from Saccharomyces cerevisiae, Candida utilis and Pleurotus ostreatus

Aims: The aim of this work was to investigate and optimize the potential of olive mill waste water (OMWW) to be utilized as a substrate for the production of single cell protein (SCP).

Study Design: The study was divided in two phases, a preparatory phase for the removal of olive polyphenols and/or condensation of OMWW, and a bioprocessing-fermentation phase.

Place and Duration of Study: The study was conducted at the TEI of Thessaly from January 2013 to August 2015.

Methodology: OMWW was used as a fermentation substrate for production of SCP after dephenolization by microfiltration, condensation via reverse osmosis, and addition of minerals/nitrogen sources. Saccharomyces cerevisiae (S. cerevisiae), Candida utilis (C. utilis) and Pleurotus ostreatus (P. ostreatus) were grown in this substrate under controlled process conditions in shake flasks and a 15 lt bioreactor. Biomass, sugars, phenol concentration of OMWW and the protein content of the harvested biomass were evaluated.

Results: Dephenolization of OMWW is essential for sufficient growth of both yeasts, while P. ostreatus grows better in the untreated substrate, as it can degrade the polyphenols while the dephenolization step reduced also the sugar content of OMWW. Optimum process conditions for S. cerevisiae included a pH 7, 350 rpm agitation rate, addition of (NH4)2SO4 to a 3/1 condensed medium, while C. utilis grew best at pH 5, 250 rpm, after addition of NH4NO3 in a 3/1 condensed medium. Maximum biomass concentration was 13.5 g/l and 14.6 g/l, respectively. 14.8 g/l of P. ostreatus biomass were obtained at pH 5, 150 rpm after addition of NH4NO3. This mold had the highest yield but lowest productivity due to slow growth.

Conclusion: P. ostreatus is a good producer of SCP in OMWW and reduces its organic load, but it has lower protein content. C. utilis had the highest SCP productivity, and the two yeasts had the highest protein concentration but require dephenolization of OMWW.