Integrated process for olive oil mill wastewater treatment and its revalorization through the generation of high added value algal biomass

Abstract

The two-phase continuous centrifugation process for olive oil extraction generates high amounts of olive oil mill wastewater (OMW), characterized by containing large concentrations of numerous contaminant compounds for the environment. An integral process based on physico-chemical (flocculation, photolysis and microfiltration) and microalgal growth stages was proposed for its treatment. Chemical oxygen demand (COD) removal percentages were 57.5%, 88.8% and 20.5% for flocculation, photolysis and microfiltration, respectively. The global removal percentages of organic load in the primary treatment were 96.2% for COD, 80.3% for total organic carbon (TOC) and 96.6% for total phenolic compounds (TPCs). In secondary treatment, different experiments using the microalgae Chlorella pyrenoidosa were performed on a laboratory scale in stirred batch tank reactors. The OMW concentrations in each culture medium were: 5%, 10%, 25%, 50%, 75% and 100% (v/v). The common experimental conditions were: pH = 7, temperature = 25 °C, agitation speed = 200 rpm, aeration rate = 0.5 (v/v) and illumination intensity = 359 μE m^-2 s^-1. The highest maximum specific growth rate (0.07 h^-1) and volumetric biomass production (1.25 mg/(L h)) values were achieved in the culture with 50% of OMW (v/v). The final biomass obtained had a high percentage of carbohydrates, whose content ranged from 30.3% to 89.2% and the highest lipid content (34.2%) was determined in the culture with 25% of OMW (v/v). The final treated water is suitable for its use in irrigation, discharge to receiving waters or for being reused in the same process.

Keywords: Biomass growth; Chlorella pyrenoidosa; Flocculation; Olive oil mill wastewater; Photolysis; Treatment.