FERTILIZING EFFECT OF MICROBIALLY TREATED OLIVE MILL WASTE-WATER ON TRIFOLIUM PLANTS

Olive mill wastewater (OMW) with added N and Mg was used as a medium i n a shake-flask, repeated-batch fermentation process with a passively immobilized, acid-producing, strain of Aspergillus niger. The latter w as able to reduce the phenolic content of the waste material to 59% of its initial amount and to lower the pH of the medium. Rock phosphate, added to the OMW medium was solubilized to a maximum amount of 0.5 g/ l during the fourth batch cycle with a corresponding productivity of 1 0.6 mg P/l.h. Five types of OMW +/- RP, microbially treated or not, we re tested in a soil-Trifolium system for their fertilizing ability. Th e beneficial effect of microbially treated OMW was more evident during the first crop cycle. The best plant growth response and P uptake wer e found in mycorrhizal plants grown in soil amended with fungal treate d OMW+RP. (C) 1998 Elsevier Science Ltd. All rights reserved.