Abstract
Olive mill wastewater (OMW), which is generated during olive oil production, has detrimental effects on the environment due to its high organic load and phenolic compounds content. OMW is difficult to biodegrade, but represents a valuable resource of nutrients for microbial growth. In this study, yeast strains were screened for their growth on phenolic compounds usually found in OMW and responsible for antimicrobial effects. Candida tropicalis ATCC 750 demonstrated an extraordinary capacity to grow in phenolics and was chosen for further experiments with OMW-based medium. The effects of nitrogen supplementation, the pH, and the stirring rate on cellular growth, OMW-components consumption, and added-value compounds production were studied in batch cultures in Erlenmeyer flasks and in a bioreactor. Candida tropicalis was able to reduce 68% of the organic load (chemical oxygen demand) and 39% of the total phenols of OMW in optimized conditions in bioreactor experiments, producing lipase (203 U·L−1) and protease (1105 U·L−1). Moreover, intracellular lipids were accumulated, most significantly under nitrogen-limited conditions, which is common in this type of wastewater. The high potential of C. tropicalis to detoxify OMW and produce added-value compounds from it makes this process an alternative approach to other conventional processes of OMW treatment.
Highlights
The olive oil production industry is an important and traditional agro-industry in Mediterranean countries, accounting for 97% of the world’s production of olive oil [1]
Candida tropicalis ATCC 750, Candida utilis CBS 621, Candida rugosa PYCC 3238, Candida cylindracea CBS 7869, Yarrowia lipolytica IMUFRJ 50682, Yarrowia lipolytica CBS 2073, Yarrowia lipolytica NYCC 1026, Yarrowia lipolytica CBS 2075, Yarrowia lipolytica W29, and Pichia pastoris CBS 2612 were maintained on Yeast Peptone Dextrose (YPD) agar medium (20 g·L−1 glucose, 20 g·L−1 peptone, 10 g·L−1 yeast extract, and 20 g·L−1 agar) at 4 ◦ C for a maximum of two weeks
Culture samples were collected from Erlenmeyer flasks and bioreactor for quantification of the cellular concentration, reducing sugars, total phenols, chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN), lipase activity, protease activity, and microbial lipids and their composition of long chain fatty acids (LCFA)
Summary
The olive oil production industry is an important and traditional agro-industry in Mediterranean countries, accounting for 97% of the world’s production of olive oil [1]. Three systems are used worldwide to extract olive oil, namely, the traditional press system, the three-phase centrifugation system, and the twophase centrifugation system. The dark color and phytotoxic and antimicrobial effects of OMW have been attributed to the phenolic compounds that are found in various concentrations in the wastewater [1,5]. The recovery of phenolic compounds can provide an economic opportunity (in food, cosmetic, detergent, and pharmaceutical industries), and reduce the environmental charge of the wastewater. It is hardly applicable at the industrial level due to its operating costs [3,6]
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