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

Abstract

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 m3/ha was studied for two 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 m3/ha OMW was significantly higher compared to the soil that received water. However, a dose of 200 m3/ha did not affect soil microflora. Consequently, using OMW by direct spreading can be recommended at doses of 50 and 100 m3/ha. Doses higher than those studied, which are considered excessive and not recommended, could have undesirable repercussions. HIGHLIGHTS Soil microflora is responsible for biodegradation of OMW polyphenols.; Spreading OMW to 100 m3/ha on alkaline soil stimulated the activity of soil microflora.; Application of OMW to 100 m3/ha could be recommended as a soil biofertilizer.; For 200 m3/ha of OMW, particular attention must be paid to polyphenols and to electrical conductivity.; This study has removed all fears and ambiguities about the spreading of OMW on the soil.;

Keywords

• microbial activity
• olive mill wastewater
• organic matter
• polyphenols
• soil
• spreading