# Waste-to-Energy Process to Recover Dangerous Pollutants in an Environmental Protected Area
## 2 Materials and Methods
### Description of Arganda Lagoon: Hydrocarbon Waste Disposal  
The lagoon is located in the natural area of Boca Alta in the \"Parque Regional del Sureste\", in the municipality of Arganda del Rey (Madrid Region). The approximate surface area of the lagoon is 12,750 m\({}^{2}\), with a shape similar to an irregular rectangle of 120 \(\times\) 90 m. It consists of an estimated accumulation of 50,000 m\({}^{3}\) of oily petroleum sulfonate, which is the main component, known as \"acid tar\" (Figure 2). The soil is contaminated with total petroleum hydrocarbons and heavy metals--mainly Pb and Zn, but to a lesser extent, Ba, Hg, Ni, and Va. The existing pollution in the lagoon leads to damage to plants and microorganisms, which originate due to the toxic, carcinogenic, and mutagenic potential of the hydrocarbons [34]. In order to use all the material extracted from the lagoon and after its subsequent treatment, it has been decided to distribute it in nine cement industries in Spain. This distribution has been made throughout the entire extraction process, from 2015 to 2018, in a proportional manner and according to the consumption of each of the industries, as well as the geographical location and the availability of the waste at any time. This distribution is compared with the alternative of direct incineration of hazardous waste. The main residues have been treated: layers A, B, and C have already been extracted, and the extraction work of the non-pumpable layer (D) started at the beginning of 2020 (Figure 3). Figure 1: Initial situation of the waste pond at Arganda del Rey, Madrid. The geological location of the waste is in the alluvial plain of the Vega Baja of the Jarama River and is shaped by alluvial terraces. Its geological lithology presents alternations of conglomerates, gravels, sands, silts, and clays. Near the area where the lagoon is located, there are two large aquifers. The ancient mining activity that carried out excavations below the phreatic level led to the origin of this artificial lagoon. The content of the contaminating material is due to the discharge of petroleum sulfonate from the waste oil regeneration activity [35]. These effluents are pumpable material that is extracted and managed through energy recovery. The lagoon effluents have been stratified in different phases, generating various layers:  
Figure 3: Current situation at Arganda Lagoon. Figure 2: Arganda Lagoon and location of the cement plants considered in this study. * Layer A: the most superficial oily phase, with a low density and a thickness of less than 0.10 m, formed by hydrocarbon compounds, therefore presenting a dark brown color. * Layer B: composed of water from stationary rains, which are contaminated by being in direct contact with A and C layers. * Layer C: with an approximate volume of 45,143 m\({}^{3}\) and composed by oily petroleum sulphate, it is very viscous and has a black color. It is the most voluminous, so it is catalogued as the main nucleus of the lagoon. It does not have a constant thickness but varies according to the topography of the lagoon (5-7 m). Density, fluency, and viscosity vary with depth, so the deeper it is, the more viscous it is. This layer is considered in the present study. * Layer D: has an approximate volume of 4238 m\({}^{3}\). This layer is the densest and deepest, occupying the bottom of the lagoon and part of the slopes. Black in color, it is composed of heavy hydrocarbons and cannot be pumped at room temperature. It has a very high viscosity but is fluid. Its thickness is variable, with an average of 0.5 m. This material comes from the thermal de-asphalting carried out for the recovery of oils. Also, in the deepest part of this layer, there are salts and sandy salts that provide additional waterproofing and with severe impact, because they contain heavy hydrocarbons, Polycyclic aromatic hydrocarbons (PAHs), and metals, followed by sands and gravel.