Daily doses of light in relation to the growth of Scenedesmus obliquus in diluted three‐phase olive mill wastewater

BACKGROUND: The use of olive-oil mill wastewater (OMW) from a three-phase centrifugation process used in the olive-oil industry, has been studied in relation to the production of the microalga Scenedesmus obliquus CCAP 276/3A. The chemical characteristics of OMW indicated nitrogen deficiency. RESULTS:S. obliquus is able to assimilate nutrients present in a culture medium (water-OMW 5%) and grow at its maximum specific growth rate of 0.026 h−1, both under mixotrophic as well as heterotrophic conditions. The different daily doses of light (DDL) used, in the range 0–36 E m−2 d−1, determined light-limited and light-inhibited cultures. The light-inhibited mixotrophic cultures bore characteristics similar to those of the heterotrophic cultures, and became more so when the dose of light received was higher. The low protein yield (258 mg g−1) and high percentage of carbohydrates of the biomass (65.8%) confirmed a nutritional-stress situation associated with nitrogen limitation. CONCLUSION: The similarity between the fatty-acid composition of the heterotrophic and mixotrophic cultures strongly inhibited by light appeared to indicate the cancelling of the photosynthetic behaviour of the cells at high DDL values. The biomass generated can be used for biofuels. The maximum elimination of biological oxygen demand (BOD5) per unit of biomass was achieved in the heterotrophic cultures. Copyright © 2009 Society of Chemical Industry