Land spreading of olive mill wastewater (OMW): biodegradation of organic matter and polyphenols in soil and effect on the activity of the total soil microflora

Agricultural spreading of olive mill wastewater (OMW) can represent a promising alternative solution, provided that the operation is controlled and the doses applied are respected. However, a reserve toward OMW spreading remains, for fears of possible microbiological negative incidences on the soil. To contribute to assessing this area, we have tried to study their microbiological impact and the fate of OMW polyphenols in soil in a greenhouse. In comparison with untreated soil with OMW (control), the application of 50, 100, and 200 m(3)/ha was studied for 2 months. The results obtained revealed that phenolic extracts from raw OMW showed five major peaks by HPLC at 280 nm, which were present only in trace amounts after 2 weeks of treatment at neutral pH. The phenols and organic matter (OM) from OMW were biodegraded or reorganized, and the bacterial population of soil treated with 50 and 100 m(3)/ha OMW was significantly higher compared to the soil that received water. However, a dose of 200 m(3)/ha did not affect soil microflora. Consequently, using OMW by direct spreading can be recommended at doses of 50 and 100 m(3)/ha. Doses higher than those studied, which are considered excessive and not recommended, could have undesirable repercussions.