# Prediction of Total Petroleum Hydrocarbons and Heavy Metals in Acid Tars Using Machine Learning
## 1 Introduction  
The diversity of the operations and increasing growth of the petroleum industry has resulted in huge amounts of various waste materials that need proper disposal and/or valorization [1, 2]. Among the existing types of petroleum waste, this paper studied the acid tars from a refinery storage lagoon in Romania. Acid tars are residual materials that resultfrom refining and petrochemical technologies applied at the beginning of the oil industry development and which, by now, are abandoned [3; 4; 5]. Once formed, acid tars were stored in large-scale pits the size of a football field, called lagoons, which thus became permanent and potential pollution sources for the air, soil, subsoil, and water [6; 7; 8]. In addition to countries such as the USA, Russia, United Kingdom, Netherlands, Belgium, Germany, Latvia, Slovenia, Slovakia, China, Zimbabwe, and Ukraine, which store acid tar in the open air in spent pits, storage ponds, lagoons, or near landfills, there is also Romania [7; 8; 9]. On the problem of ATLAS, scientific reports can be found in the literature, for example, in the USA, Germany, Belgium, Russia, UK, Slovenia, France, Latvia and Ukraine while the extent of the problem has not been limited to these countries [4; 5; 7; 8]. The reason for conducting the research developed and described in this article is the historical existence of acid tar lagoons in five refineries in Prahova County, four being in the immediate vicinity of Ploiesti city, refineries put into operation at the beginning of the 20 th century [9; 10; 11]. At present, although the quantity of acid tars generated has been greatly reduced due to the development of efficient catalytic processes in the refining industry, an effective treatment method is needed for existing acid tars lagoons [6]. The composition of the acid tars stored in the lagoons varies with the period of production, the product treated with sulfuric acid, and the age of the tars [12; 13; 14; 15]. Acid tars have a variable composition between sites and even within one lagoon [15]. The need to study, characterize, and stabilize/dispose of the acid tars from these huge storage lagoons is determined by the fact that they have an extreme acidity (pH 1-2), high concentrations of hydrocarbons and heavy metals, with significant mobility and easily leachable, dangerous for the storage site and its neighboring residential area [7; 8; 15]. The low pH is an important chemical factor that influences the increase in the mobility of metals and their interaction with natural minerals [16]. [PERSON] [3], [PERSON] et al. [12], [PERSON] [17], and especially [PERSON] et al. [5; 13] and other [18; 19] reviewed various methods for the processing of acid tars into useful products but concluded that none of the approaches are satisfactory and thus, it is necessary to apply an effective remediation method of acid tars lagoons [20; 21; 22; 23; 24]. Evaluation and choosing a technology for the remediation of acid tar lagoons is a complex activity that requires the consideration of numerous factors: the type and properties of the emerging contaminants, their quantity, the dynamics of the pollutants, the hydrogeological characteristics of the soil, the climatic factors [8; 9; 15]. Finally, the economic aspects, namely the costs of remediation, also matter. This work is associated with complex research that refers to a composition and process for the physical and chemical stabilization, in situ, of acid tars and of soil contaminated with acid tar from one selected lagoon through neutralizing, stabilization, and encapsulation procedure [25; 26]. Acid tar samples from the studied lagoon were sampled, and the following steps were taken:  
* Acid tar and leachate analysis from the stabilized tars is done by determining the following indicators: pH, TPH, and metals content, as well as As. * Identification, testing, and determination of the optimal recipes for stabilizing the acid tar in the lagoon.