Review: Effects of olive mill wastewater application on soil properties and plants growth

Comparative effects of untreated olive mill wastewater (UOMW), treated olive mill wastewater (TOMW) and bioaugmented olive mill wastewater (BOMW) on soil properties, on seeds germination and on plants growth were investigated. The water holding capacity, the salinity, the organic carbon content, humus, total nitrogen, phosphate and potassium increased when the spread amounts of UOMW (50, 100 and 200 m3 ha-1.year-1) or TOMW increased. TOMW increased the total mesophylic number while the number of fungi and nitrifiers decreased. Actinomycetes and spore-forming bacteria were neither sensitive to TOMW nor to UOMW. The total coliforms number increased with higher doses of TOMW and UOMW. Hazard assessments of toxicity were conducted for UOMW, untreated olive mill wastewater organic extract (UOE), TOMW, treated olive mill wastewater organic extract (TOE) and extracts of soils amended with UOMW (SUOMW) and with TOMW (STOMW). Results showed an increase in the germination index when seeds species were cultivated with TOMW. Plants irrigated by TOMW showed an improvement in biomass, spike number, plants growth and a similar or even better dry productivity than plants irrigated with water.