# IoT-Based Solid Waste Management Solutions: A Survey
## 1 Introduction
The IoT paradigm [4] has a main role as a key facilitator of the integration of various application solutions and communication technologies, such as identification and tracking [5; 6], sensor networks, wired and wireless actuators [7], improved communication protocols, and distributed intelligence for objects. According to the Internet Business Solutions Group (IBSG), a milestone of IoT emergence occurred when the Earth's population was exceeded by the number of objects connected to the Internet, which happened in 2008-2009. IBSG predicts that by 2020, about 50 billion devices will be connected to the Internet [8; 9; 10; 11]. IoT can include a large number of applications designed to assist in many sectors, such as industry, transportation, markets, education, agriculture, healthcare, environment, and smart cities (Figure 1) [12; 13; 14; 15]. The European Union has defined smart cities (SC) as a system where people interact and use energy, materials, services, and waste to stimulate economic development and improve the quality of life. These interaction flows are considered intelligent because they make strategic use of infrastructures, services, information, and communication in planning urban management, a way to meet the social and economic needs of society. Despite being a relatively recent concept, the smart city topic has already become synonymous with sustainable development within global discussions on sustainability [16]. Currently, cities in emerging countries are investing heavily in smart products and services to sustain economic growth and, at the same time, developed countries need to upgrade existing urban infrastructures to remain competitive. Among the evolutions that have been taking place to classify an intelligent city, a vast range of applications can be listed, such as waste management based on an IoT approach [17; 18; 19; 20; 21]. The IoT concept predicts a world in which physical, digital, and virtual objects are interconnected in a network supporting higher order applications. The intelligence of objects comes from the automated data processing of an existing state or the environmental state in which it is immersed. These data are then transmitted to a processing node where they are analyzed, and an appropriate performance profile is determined, considering data acquired from various objects. This actuation profile is then transmitted back to the smart object [22]. The waste management system is included in this context because it has a large number of containers with an inconsistent level of filling that can last from days to weeks, with the possibility of seasonal changes, as well as different emptying requirements, such as distances and type of waste. However, biomedical, chemical, and electronic residues have specific collection points, usually with uniform production and long filling periods. There is considerable difficulty in identifying the filling level of the dumps because of the differences in the waste packaging process, such as the variety and the irregularity of the discarded materials, which in a certain way generate unnecessary costs to the municipal collection system [23; 24]. Recognizing the vast scope that IoT offers for waste management in urban environments, it is the focus of this study. This survey analyzes the state-of-the-art based on intelligent waste management through IoT. Thus, the main contributions of this paper are the following:  
* An in-depth review of state-of-the-art on solid waste management;
* Presentation of architecture models for solid waste management identified in the literature based on IoT requirements;
* Comparison of the most promising solutions and identification of open research issues able to suggest further research works on the topic. The remainder of this paper is organized as follows. Section 2 overviews the types and methods of solid waste disposal and Section 3 provides an insight regarding solid waste management. Section 4 addresses available IoT architecture reference models for waste management systems.