Combined biological treatments of olive mill wastewater using fungi and microalgae

Olive mill wastewaters (OMWs), which are mainly composed of phenolic compounds, present an important environmental issue. This effluent was treated using fungal laccases from Tetraselmis sp. and Chlorella sp. and two green microalgae. In the first step in the removal of phenolic compounds, enzymatic pretreatment of diluted OMWs (30% v/v) with the fungal laccases led to a 57.79 ± 2.21% decrease in phenol concentration and a 54.79 ± 3.44% decrease in the dark coloration of the diluted OMWs. This preatreated wastewater was suitable for microalgae culture under mixotrophy. The growth and biochemical composition of the two microalgae strains were determined and compared to those obtained from a control culture under autotrophy. Under mixotrophy, the growth of Chlorella sp. and Tetraselmis sp. reduced dramatically. Moroever, their photosynthetic pigment productivities (0.0071 ± 0.08 mg/104 cells/mL/day for Chlorella sp. and 0.011 ± 0.002 mg/104 cells/ mL/day for Tetraselmis sp.) were decreased when compared to those attained under autotrophy. In terms of starch and lipid production, the highest final contents of starch and lipids were obtained under autotrophy: 13.38 ± 2.17% and 4.2 ± 0.35% for Chlorella sp. and 15.66 ± 0.92% and 5.22 ± 0.79% for Tetraselmis sp., respectively. The mixotrophic cultivation mode of Chlorella sp. reinforces protein synthesis. These results highlight the opportunity to achieve high-value biomass production by the mixotrophic cultivation of microalgae using pretreated OMWs as a low-cost raw material.