Abstract
Phenolic compounds in olive mill wastewater (OMW) are considered an environmental threat due to their antimicrobial properties. Because of the metabolic versatility of microalgae, a biotic removal of these compounds seems a suitable approach. To investigate the biotic removal of phenolic compounds, the three microalgae species Chlorella vulgaris, Acutodesmus obliquus and Monoraphidium braunii were cultivated in flasks under constant light (50 µmol/m2s) and dark (1 g/L glucose) conditions in presence of different concentrations of OMW. Addition of 1% (v/v) OMW to the culture medium was shown to be non-inhibitory or even growth enhancing, and phenolic compounds were removed by 7–21% by all tested species. Cultivations with 6% (v/v) OMW resulted in a few exceptional experiments in fast growth (C. vulgaris under light, M. braunii under dark conditions) and removal of phenolic compounds (M. braunii, dark). Higher percentages (12 and 25%, v/v) of OMW were inhibitory. Under dark conditions microalgae first consumed glucose and removed phenolic compounds in a diauxic process. Removal of phenolic compounds was favoured under light conditions. Results of this study reveal the opportunities and the challenges of a microalgae-based removal of phenolic compounds and valorization of toxic OMW.Graphic abstract
Highlights
The production of olive oil generates worldwide around 30 billion L of wastewater originating from washing of fruits and equipment
In the following the growth of the microalgae C. vulgaris, A. obliquus and M. braunii in olive mill wastewater (OMW) as well as their ability to remove phenolic compounds from the supernatant under light and dark conditions will be discussed
Microalgal growth, removal of phenolic compounds and glucose consumption for the three strains are displayed in Fig. 1 for the cultivation under dark and Fig. 2 for the cultivation under light conditions
Summary
The production of olive oil generates worldwide around 30 billion L of wastewater originating from washing of fruits and equipment. Olive mill wastewater (OMW) possesses high biological oxygen demand (BOD5) and chemical oxygen demand (COD) values between 35–132 g/L and 30–320 g/L, respectively [1,2,3], as well as increased values of phosphorous (0.63%, w/w), nitrogen (0.88%, w/w) [4] and phenolic compounds [5, 6]. The latter originate from olive oil, as they are formed by olive trees and enriched in the fruits. The increased production of olive oil results in increased formation of phenol-containing OMW [10], which is mostly released into the environment [11]
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