Adaptation and population dynamics of Azotobacter vinelandii during aerobic biological treatment of olive-mill wastewater

Abstract

Olive-mill wastewater (OMW) has a high organic and polyphenol content and is resistant to biodegradation. Its disposal leads to a major environmental pollution problem in the Mediterranean basin. The detoxification of OMW following inoculation with Azotobacter vinelandii (strain A) was performed for two successive 5-day-period cycles in an aerobic, biowheel-type reactor, under non-sterile conditions. The phytotoxicity of the processed product was reduced by over 90% at the end of both cycles. To exclusively monitor the A. vinelandii population in the reactor a most probable number-PCR approach was employed and applied daily to serial dilutions of total DNA extracted from reactor samples. PCR sensitivity was independent of the presence of OMW or non-target DNA. The A. vinelandii population dynamics were successfully monitored, showing an initial adaptation period, followed by a sharp population maximum on the fourth day of both cycles (1.6x10(8) and 9.6x10(7) cells ml(-1) respectively), after a major phytotoxicity decline. N(2) fixation rates were estimated using the acetylene reduction assay and reached a peak during the first 1-2 days of each cycle (36 and 29 nmol C(2)H(2) ml(-1) h(-1) respectively). The data are consistent with an initial physiological adaptation phase, where the presence of phenolic compounds limits A. vinelandii growth but stimulates N(2) fixation, followed by a rapid growth phase as phytotoxicity declines.

An overview on olive mill wastes and their valorisation methods

“…The use of OMW as substrate for Azotobacter vinelandii growth and application of the treated effluent to cultivated Table 1 Main chemical characteristics of olive mill wastewater (OMW) given by several authors soils as fertiliser was recently proposed by Ehaliotis et al (1999) and Piperidou et al (2000). Although all of these methods are very interesting from a scientific point of view, they are not usually used at the industrial scale.…”

Effect of organic loading rate on the performance of an up-flow anaerobic sludge blanket reactor treating olive mill effluent

“…3) [8,18,19]. OME typically harbors macromolecules, including polysaccharides, lipids and proteins, as well as a number of monocyclic and polymeric aromatic molecules generally referred to as phenolic compounds [20,21]. Phenolic compounds are recalcitrant to biodegradation and are partially responsible for the toxicity of OME.…”

Polyphenols dynamics and phytotoxicity in a soil amended by olive mill wastewaters

“…To solve the problems associated with OMW, different elimination methods based on physicochemical and biological treatments have been proposed (Levi-Menzi et al, 1992;Ehaliotis et al, 1999;Paredes et al, 2000;Marques, 2001;Kissi et al, 2001;Casa et al, 2003). However, the most frequently used methods nowadays are the direct application to agricultural soils and storage in evaporation ponds (Fiestas and Borja, 1992;Martinez Nieto and Garrido, 1994).…”