Abstract
Land application of olive mill wastewater (OMW) is considered a promising low-cost practice for olive-oil producing countries. The objectives of this work were to investigate: (i) OMW treatment potential of a land treatment system (LTS), planted with a E. camaldulensis species, regarding N, P, C, and phenols; (ii) the effects of OMW on chemical properties of soil and soil solution characteristics; and (iii) the performance of E. camaldulensis in terms of biomass production and N and P recovery. E. camaldulensis received OMW for two growing seasons at rates based on maximum organic loading. These rates were almost equivalent to the reference evapotranspiration of the area. Soil solution and soil samples were collected from three different depths (15, 30 and 60 cm) at specified time intervals. -Also, samples of plant tissues were collected at the end of application periods. OMW land application resulted in significant reduction in inorganic and organic constituents of OMW. At 15 cm of soil profile, the average removal of COD, TKN, NH4+-N, TP, In-P, and total phenols approached 93%, 86%, 70%, 86%, 82%, and 85%, respectively, while an increase in soil depth (30 and 60 cm) did not improve significantly treatment efficiency. Furthermore, OMW increased soil organic matter (SOM), total kjeldahl nitrogen (TKN), and available P, particularly in the upper soil layer. In contrast, low inorganic N content was observed in the soil throughout the study period caused probably by increased competition among soil microorganisms induced by the organic substrate supply and high C/N ratio. Also, electrical conductivity (EC) and SAR increased by OMW addition, but at levels that may do not pose severe risk for soil texture. Enhancement of soil fertility due to OMW application sustained eucalyptus trees and provided remarkable biomass yield. In conclusion, land application of OMW has a great potential for organic matter and phenol assimilation and can be effectively used for OMW detoxification.
Highlights
Olive mill wastewater (OMW) is the liquid by-product generated mainly in three-phase olive mills during olive oil production
Decreasing trends were observed for total phenols concentration from 2600 mg/L to mg/L, in accordance with previous study [4], attributable to microbiota activity present in OMW [30,31]
Our finding indicates the great potential of OMW in terms of the organic matter assimilation and increase of soil organic matter (SOM) content in the soil, an effect with great importance for the olive-oil producing countries in most of which soils suffer from low organic matter content and gradual degradation as a result of the favorable environmental conditions and thee applied agronomic practices
Summary
Olive mill wastewater (OMW) is the liquid by-product generated mainly in three-phase (olive oil-OMW-pomace) olive mills during olive oil production. In areas that have not yet adopted the newer two-phase extraction technique (olive oil-liquid pomace) the most common adopted practices to manage OMW remain the storage in evaporation ponds [2] and the direct application onto land [3]. Earlier study demonstrate the high potential of soil in terms of the assimilation and removal of both inorganic and organic OMW constituents at application rates up to 1000 mm/year [6]. This is efficiency due to presence of decomposable organic compounds in OMW that stimulate soil microorganisms and their activities [7,8] inducing decomposition and mineralization processes. Given the high organic loading in OMW and the presence of vegetation the optimization of OMW application rates and treatment potential—still remains a challenge
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