Impact of olive mill wastewater (OMW) on the soil hydraulic and solute transport properties

Abstract

The Mediterranean area concentrates the world’s largest production area of olive oil. The olive oil industry represents, in this basin, one of the leading sectors of the agri-food economy. Olive mill water (OMW) is the principal waste effluent produced by the olive oil industry. Due to its high pollution load, this aqueous by-product cannot be directly disposed of in domestic wastewater treatment plants (especially those with a biological treatment unit). Untreated OMW is currently used for agronomic purposes in several countries, mainly because it is rich in valuable plant nutrients. However, OMW is characterized by toxic phenols, high organic matter, high salinity, suspended solids and several other components that may have possible negative effects on chemical and physical soil properties, as well as soil biological activities. In the present research, we focused on the effects of OMW application on transport and hydraulic soil properties. Three distinct soils from a pedological point of view were selected and a series of laboratory steady-state miscible flow tests were conducted under saturated conditions, on both OMW-treated and -untreated soil columns. Tests were conducted on disturbed and undisturbed soil columns. The approach proposed by Kachanoski, based on soil impedance (Z) measurements via the time domain reflectometry (TDR) technique, was used to monitor the leaching experiments. The breakthrough curves (BTCs) exhibited different shapes that allowed the repercussions of OMW applications on soil transport behaviour to be distinguished. Several additional tests conducted on OMW-treated and -untreated soil cores to determine water retention curves (SWRCs) and saturated hydraulic conductivity Ks allowed us to infer the probable mechanisms involved in soil hydrological behaviour changes under OMW treatments. The results show that when OMW leaches into the soil immediately after its disposal there is little effect on the evaluated hydraulic and hydrodispersive properties. By contrast, we demonstrated that a short incubation period (i.e. a short contact time between OMW and soil) of 10 days is enough to exert a great influence on all the values determined (e.g. soil pore velocity v and Ks reduced by up to one order of magnitude). These effects were especially evident in undisturbed soil samples. Graphic Abstract

Development and Application of an IoT-Based System for Soil Water Status Monitoring in a Soil Profile

“…Figure 10a,b illustrate the θ(h) and K(θ) relationship at the reference depth z 4 ; K values were determined via the IPM method using Equation (4). The empirical retention model by van Genuchten [56] and van Genuchten integrated with the Mualem [57] expression were used to predict, respectively, the experimental θ(h) and K(θ) functions.…”

“…The soil unsaturated zone (or the vadose zone) is the connection zone between the atmosphere and the groundwater and, from a hydrological point of view, plays a fundamental role in the partition of precipitation between surface water, soil water and groundwater [1][2][3][4]. The amount of water that enters the soil is stored in the vadose zone and, from here, can be subjected to several hydrological processes that cause water to move within the soil profile.…”

Comparing actual transpiration fluxes as measured at leaf-scale and calculated by a physically based agro-hydrological model

“…In this paper, a novel fast soil hydraulic characterisation method called the TDR-2Dmod method, was used, which integrates time domain reflectometry (TDR) measurements and 2D transient modelling of the water content dynamics in the wetted bulb developing in the soil under a point-source (Coppola et al, 2022). TDR is a consolidated geophysical method for measuring soil water content and electrical conductivity in the same observation volume (Coppola et al, 2016;Dragonetti et al, 2018Dragonetti et al, , 2022Schaap et al, 2003), which has recently been applied also to monitor immiscible contaminants in natural (Comegna et al, 2013(Comegna et al, , 2017(Comegna et al, , 2022a and artificial (Belviso et al, 2022;Comegna et al, 2022b) porous media. In practice, the method consists of irrigating the soil with a dripper (the point source) and monitoring the water content dynamics in the wetted bulb in soil under the dripper by one or more TDR probes (Figure 2).…”

Impact of Zeolite from Coal Fly Ash on Soil Hydrophysical Properties and Plant Growth

“…The RETC software package [53] was employed to determine van Genuchten's model parameters via a nonlinear least squares optimization approach [54]. In the RETC procedure, θ r is assumed to be zero.…”