# Metal Recovery from Wastes: A Review of Recent Advances in the Use of Bioelectrochemical Systems
## 1 Introduction  
The rapid development and expansion of technology have made electronic devices indispensable in our daily lives [1]. This increase in the demand for electronic devices, coupled with the shift towards clean energy and decarbonization, has elevated the importance of metals in this technological era. The accelerated pace of technological advancements and the frequent replacement of existing technologies are causing electronic products to become obsolete prematurely, generating a significant amount of electrical and electronic waste (EEW) [1, 2]. In fact, EEW is one of the fastest-growing waste streams across the world. Unfortunately, this problem will be worsened in the near future due to three main aspects: (1) The increase in the global population, (2) the extensive range of applications for electricaland electronic devices, and (3) the modern lifestyle (driven by the need for fast information and communication access). These three aspects will increase the demand for electrical and electronic devices in the near future and, consequently, the EEW generation [3]. In 2019, the global generation of EEW surpassed 53 million metric tons, with projections suggesting this figure could exceed 74 million metric tons by 2030 [4]. EEW encompasses a wide range of electrical and electronic equipment, including large and small household appliances, electronic tools, medical devices, monitoring and testing equipment, and telecommunication devices [5; 6; 7]. The EEW is classified as hazardous due to its high content of metals such as lead, cadmium, nickel, chromium, and copper, which pose substantial environmental risks. Additionally, EEW contains substances like brominated flame retardants, persistent organic pollutants, and polychlorinated biphenyls, which could cause environmental and health problems [8; 9]. Although metals are naturally present in the environment, anthropogenic activities are the primary source of metal contamination due to the substantial volume of minerals processed as well as the metal wastes generated daily [10]. Metal pollution has become a significant environmental issue, polluting water and soil. Heavy metals--characterized by their high atomic weight, e.g., Pb, Hg, As, Cr, Ni, Tl, Co, Cu, and Zn--are not biodegradable and tend to bioaccumulate in plants and animals, affecting ecosystems and causing environmental problems. They also pose serious health risks in humans, including cancer, neurological damage, kidney damage, respiratory and cardiac issues, and may contribute to diseases like Alzheimer's [1; 11; 10]. Beyond metal pollution, there is a critical need for a reliable supply of metals to manufacture new generations of electrical and electronic devices. Consequently, the metal extracting and processing industry faces new challenges in achieving the required metal production within the environmental and economic frames [2; 7]. Despite increasing mineral extraction rates to meet today's high consumption demands, the depletion of high-quality ore deposits is leading to a decline in the quality of extracted materials, making it more challenging and costly to obtain the necessary metals. This situation forces metal extracting and processing companies to rely on lower-quality ores as raw materials for production [12; 13]. Therefore, it is essential to consider alternative metal resources such as low-grade ores, aqueous reserves, slag, but also EEW [7; 14]. In particular, EEW represents a significant secondary metal reserve within the industry [1; 13]. These wastes are rich sources of valuable metals, including rare earth elements, precious metals like gold, and base metals such as iron and copper [8]. As a result, the utilization of EEW as a metal source has increased in recent decades and is now recognized as a viable secondary source for obtaining these crucial materials for the technological industry [2; 15].