Biological treatment of olive mill wastewater by non-conventional yeasts
Introduction
The olive oil consumed in the world is mainly produced in the Mediterranean basin countries. With an estimated olive oil production of 40 thousand tones per year, Portugal is one of the 10 major producers.
Pressing (traditional system) and continuous (three- or two-phase) are the most important extraction processes, applied for olive oil production. Three- and two-phase extraction technologies differ in the water supplies. Large amounts of water are required to an extraction process with a three-phase decanter and large amount of a liquid by-product is generated. This effluent is known as olive mill wastewater (OMW) and it is a stable emulsion composed of water, olive pulp and oil (Lanciotti et al., 2005). The OMW constituents, quality and quantity, depend on many factors, such as, type of olives and its maturity, climacteric conditions, region of origin, cultivation methods and specially the technology used for oil extraction (Roig et al., 2005). The organic fraction of OMW includes sugar, tannins, polyphenols, polyalcohols, pectins and lipids, which results in high values of chemical oxygen demand (COD) (Papanikolaou et al., 2008), with values up to 220 g L−1.
The phytotoxicity of the olive mill wastewaters can be attributed to the phenolic compounds (Lanciotti et al., 2005). In fact, the olive pulp is very rich in phenolic compounds but only 2% of the total phenolic content of the olive fruit remains in the oil phase, while the remaining amount is lost in the OMW (approximately 53%) and in the pomace (approximately 45%) (Rodis et al., 2002). Due to their instability, OMW phenols tend to polymerize during storage into condensed high-molecular-weight polymers that are difficult to degrade (Crognale et al., 2006). Thereby, uncontrolled OMW disposal can create several risks to the environment and it is urgent to develop a suitable treatment. Due to the seasonality of olive oil production the OMW treatment process should be flexible enough to operate in a non-continuous mode. Moreover, the olive mills are small enterprises, scattered around the olive production areas, making individual on-site treatment options unaffordable (Paraskeva and Diamadopoulos, 2006).
Several methods have been proposed, which include, mainly, physical–chemical treatments. The most common method applied has been the storage of OMW in lagoons, followed by evaporation during summer season (Azbar et al., 2004). This method is not satisfactory since it only reduces the volume of waste, without treating the pollutants, and a black foul-smelling sludge, difficult to remove, is produced. The anaerobic biological degradation of OMW can lead to methane production even if large periods of biomass adaptation have been reported as a disadvantage of the process. Biological treatment by aerobic microorganisms (fungi and yeasts) has also been proposed (Eusébio et al., 2002).
Instead of disposal solutions an approach of using this waste as a resource to be valorized is of greater interest. Some lipolytic yeast species can grow well in OMW media, consume the organic material and, at the same time, produce biomass and other valuable products (Scioli and Vollaro, 1997, D’Annibale et al., 2006), like enzymes and organic acids. The extraction and purification of biologically active compounds (namely biophenols) turns OMW into a source of natural antioxidants. These compounds are object of growing interest in pharmaceutical and food industries since reactive oxygen species are involved in the onset of several human diseases and in the oxidative degradation of food (De Marco et al., 2007).
The aim of the present investigation was the valorization of different OMW by producing high-value compounds from OMW while degrading this waste. Thus, the objective of this study was the OMW aerobic treatment with lipase and/or biomass production, with process conditions optimization and strains selection.
Section snippets
Microrganisms and OMW used
Strains of Candida rugosa (PYCC 3238 and CBS 2275), Candida cylindracea CBS 7869 and Yarrowia lipolytica (CBS 2073, W29 ATCC 20460 and IMUFRJ 50682) were maintained in YPD Agar at 4 °C. Cells were pre-grown in YPD medium (10 g L−1 yeast extract, 20 g L−1 peptone and 20 g L−1 glucose) and then harvested (12225 g, 5 min) from the pre-culture and re-suspended in the OMW-based media.
The OMW samples were collected from different three phases’ olive oil mills, from the north of Portugal, and were stored at −20
Comparison of different strains degrading different OMW
Experiments with Y. lipolytica W29 and C. rugosa PYCC 3238, in OMW were performed using 1000 mL Erlenmeyer baffled flasks, with 400 mL of OMW-based media. The OMW used were OMW1 and OMW2. Both strains were able to grow on both OMW, without dilution (Fig. 1), increasing about 1.7 log the cell number. Cell mass production was higher for OMW1 than for OMW2, for both strains, probably due to the higher content of sugars and lower content of phenolic compounds in this medium (Table 1). Both strains
Conclusions
The results of this study confirmed the potential application of the non-conventional lipolytic yeasts for OMW valorization, by its use as culture medium for biomass and enzymes production. The ability of all strains used, to produce lipase from undiluted OMW was shown. Moreover, C. cylindracea was the best strain concerning the lipase production and also for the COD reduction.
The OMW samples did not inhibit the yeasts cell growth, comparably to YPD medium. Catechol was found to be the most
Acknowledgements
The authors acknowledge the financial support provided by “Fundação para a Ciência e Tecnologia” (Project PTDC/AMB/69379/2006; Grant SFRH/BD/27915/2006).
References (21)
- et al.
Effect of different carbon sources on lipase production by Candida rugosa
Enzyme Microb. Technol.
(2000) - et al.
Olive-mill wastewaters: a promising substrate for microbial lipase production
Bioresour. Technol.
(2006) - et al.
Characterization and fractionation of phenolic compounds
Food Chem.
(2007) - et al.
Use of Yarrowia lipolytica strains for the treatment of olive mill wastewater
Bioresour. Technol.
(2005) - et al.
Citric acid production by Yarrowia lipolytica cultivated on olive-mill wastewater-based media
Bioresour. Technol.
(2008) - et al.
The use of Yarrowia lipolytica to reduce pollution in olive mill wastewaters
Water Res.
(1997) - et al.
Surface properties of Yarrowia lipolytica and their relevance to γ-decalactone formation from methyl ricinoleate
Biotechnol. Lett.
(2005) - APHA, AWWA, WPCF, 1989. Standard Methods for the Examination of Water and Wastewater, 17th ed. Washington,...
- et al.
A review of waste management options in olive oil production
Crit. Rev. Environ. Sci. Technol.
(2004)
Cited by (95)
Studies on the activated sludge process crucial parameters controlling olive mill wastewater treatment
2022, Science of the Total EnvironmentInfluence of olive mill waste phenolic compounds levels on carotenoid production by Rhodotorula spp.
2022, Process BiochemistryVersatility of filamentous fungi in novel processes
2022, Current Developments in Biotechnology and Bioengineering: Filamentous Fungi BiorefineryRecovery and valorization of agri-food wastes and by-products using the non-conventional yeast Yarrowia lipolytica
2021, Trends in Food Science and TechnologyMicroalgal-bacterial consortia for biomass production and wastewater treatment
2021, Handbook of Algal Biofuels: Aspects of Cultivation, Conversion, and Biorefinery