2. Materials and methods
2.1. Characteristics of soils and olive wastes
Two types of agricultural soils, named S1 and S2 in the following, were selected among the most common in the Medi- terranean area. Their main physical and chemical properties are summarized in Table 1. The grain size analysis of the soils was performed on the fine earth obtained by sifting through a 2 mm mesh.
The texture is sandy loam for both soils. According to the FAO system of soil Classification (ISSS-ISRIC-FAO, 1994) the soil S1 is classified as Luvisols-Phaeozems, and the S2 as Phaeozems- Cambisols. Although S1 and S2 belong to the same texture class, the different percentages of gravel and sand affect their hydraulic properties such as porosity and hydraulic conductivity. In partic- ular, the soil S2 allows much more drainage than the soil S1, due to the high percentage of gravel that makes its behaviour more similar to that of a gravel soil (40% of gravel).
The OMW used in this study came from a continuous centrifu- gation system, and its main chemical and physical characteristics are reported in Table 2.
It was used either as received or after a fourfold dilution with freshwater (see Section 2.3). Olive waste compost was obtained by mixing exhausted olive pomace (91% w/w) with straw (2%) and poultry manure (7%), and its composition is reported in Table 3.
2.2 Experimental setup พร้อมแปล2แบบ
2.2. Experimental setup
The test was carried out by using thirty cylindrical fiberglass lysimeters (Fig. 1) with height of 120 cm and diameter of 105 cm.
They were equipped in the bottom with a system for leachate drainage, connected to a central hole, and a layer of 15 cm thickness of expanded clay. The clay layer was bounded at both ends with geotextile sheets to allow the drainage and to prevent leakage of solid matrix from the drainage hole. Each lysimeters was filled up to 1 m height with one type of soil, previously sifted through a 1.5 cm mesh. Soil was saturated from the bottom to the top with fresh- water to remove the air entrapped in the pores and to facilitate natural arrangement. The excess water was then allowed to drain until the soil reached the field capacity, and olive waste amend- ments were finally applied.
Five different treatments, referred to as T1-T5 in the following, were conducted in triplicate for each soil. Each lysimeters received a total volume of 27.5 L of water, either wastewater or freshwater, as described below:
T1 27.5 L of OMW catalytically digested with manganese oxide (MnO2) following the procedure described in Brunetti et al. (2007);
T2 exhausted olive pomace compost equivalent to 120 kg ha 1 of nitrogen, added with 27.5 L of freshwater;
T3 diluted OMW, obtained by adding 6.8 L of OMW to 20.7 L of freshwater, and corresponding to 80 m3 ha 1;
T4 27.5 L of OMW used as received, corresponding to
320 m3 ha 1;
T5 27.5 L of freshwater (control).
The amount of OMW added in treatments T3 and T4 was established following the Italian law about the spreading of OMW on soils for agronomical use (Law No. 574, 1996). The maximum amount allowed is 80 m3 ha 1. A fourfold amount was applied in treatment T4 to assess the impact on groundwater of an inten- tionally excessive amount of OMW.