Olive mill waste as a substrate for nitrogen fixation

Olive mill wastewaters (OMWW) because of their low content in nitrogenous organic components and reachness in carbon sources offer a highly favourable environment for the growth of free-living dinitrogen fixing microorganisms. This property is manifested both in natural environments and in axenic cultures. Repetitive addition of OMWW to soil under aerobic conditions leads progressively to its enrichment with dinitrogen fixers, the activity of which is beneficial to soil fertility. The microbial consortium that develops in soil is dominated mostly by members of Azotobacter. A very efficient N-2-fixing and slime producing strain of Azotobacter vinelandii (strain A) was isolated from such an enriched soil sample. The isolate is deposited in the culture collection of our laboratory and its biochemical and molecular characteristics ate investigated. The strain proved to be effective in bio-remediation processes of OMWW both in a laboratory-scale fermenter unit and a field pilot plant of ca 5 m(3) capacity. The inhibitory growth-limiting components of the principal OMWW constituents and their impact on the duration of the lag period of N-2-fixing activity recovery is examined. The design of a multi-stream two stage process is described which provides a stable N-2-fixing system suitable for the bio-transformation of OMWW into an agro-biological product and/or for the production of extracellular polysaccharide 'slime' in high yields. (C) 1997 Elsevier Science Limited.