Kinetic growth and biochemical composition variability of Chlorella pyrenoidosa in olive oil washing wastewater cultures enriched with urban wastewater

Abstract

Olive mills generates wastewaters (OMWs) characterized by high organic and inorganic load, which includes sugars, phenolic compounds, polyalcohols, pectins, lipids, Na, K, Ca ..., but deficient in nitrogen and phosphorus. Urban wastewater treatment plants with primary (natural sedimentation) and secondary (biological removal) treatments are unable to remove the total nitrogen and phosphorus from these wastewaters, which can be therefore considered as a sustainable source of both nutrients. The enrichment of OMW with urban wastewater from secondary treatment (UW) can provide optimal nutrient concentrations to produce an algal biomass with high added value. Chlorella pyrenoidosa is a green unicellular alga that can eliminate nutrients and produce biomass with high lipids content. Experiments have been carried out in photobioreactors of 0.5 L useful capacity. Different enriched dilutions of olive oil washing wastewater (OOWW) with ultrapure water (%OOWWenriched = 5–100% v/v) were prepared as culture media. Common operating conditions were pH 8, aeration level 1 v/v/min, initial illumination intensity 126.2 μE/(m2 s) under 12 h light/12 h dark cycles and temperature of 25 °C. Results obtained showed that the highest values of maximum specific growth rate and volumetric biomass productivity were μm = 0.0203 h−1 and Pb = 1.73 × 10-3 g/(L h), respectively. Maximum percentages of chlorophylls (0.96 %) and carotenoids (0.24 %) were obtained in the final biomass of the culture formed by 30 % (v/v) of OOWWenriched. The highest proteins (43.7 %) and lipids (51.5 %) contents were obtained in the biomass from the culture medium with 100 % (v/v) of OOWWenriched, which is suitable for biofuel production. Final treated water could be discharged into water public channels, used in irrigation or as drinking water if other operation units such as ultrafiltration and reverse osmosis are added to the bioprocess.