Abstract
Thirty-two strains isolated from olive oil production plants were screened for their tolerance to the polyphenols and their ability to grow in olive oil mill wastewaters (OMW). An Ascomycete isolate that grew best on OMW was selected for further study to evaluate its effect on removal of organic pollutants, phenolic compounds and OMW toxicity. This strain was identified by DSMZ as Aspergillus niger van Tieghem. The growth of Aspergillus niger van Tieghem on stored OMW decreased pH and led to the reduction of phenolic compounds with a resultant discoloration of OMW and significant reduction of chemical oxygen demand (COD), in proportion to the dilution of OMW. The reduction of the COD, phenolics and color exceeded 50%. Tannase, the enzyme detected in the growth medium of Aspergillus niger van Tieghem was produced during primary metabolic growth. The maximal enzyme activity attaining 0.68 EU/ml was achieved in 3rd days of cultivation. The phytotoxicity of the stored OMW was reduced to about 40% after 4 days’ incubation with Aspergillus niger van Tieghem.
Highlights
Over 750 million olive trees are cultivated worldwide, 95% of which are in the Mediterranean region
Thirty-two strains isolated from olive oil production plants were screened for their tolerance to the polyphenols and their ability to grow in olive oil mill wastewaters (OMW)
Two different fungal strains were used in the OMW treatment experiments: a strain isolated from olive oil production plants using the agar plate technique and classified by DSMZ (Braunschweig, Germany) as Aspergillus niger van Tieghem (DSM 24787) and Phanerochaete chrysosporium Burdsall M1 (DSM 13583) [10] isolated from OMW
Summary
Over 750 million olive trees are cultivated worldwide, 95% of which are in the Mediterranean region. Olive mill wastewaters (OMW) are dark liquid effluents, which pose a critical problem for olive oil producing countries. They have a very high organic load, chemical oxygen demand (COD) generally varying from 50 to 200 g/l. These values are 200 to 400 times higher than municipal water [2]. Because of its special characteristics, OMW treatment and valorization are serious problems for Mediterranean countries producing annually around 30 million·m3 of OMW [4]. Because toxicity has been directly linked to the phenolic fraction, higher fungi such as Yarrowia lipolytica [7] and Paecilomyces farinosus [8] have
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