# Modern Technologies for Waste Management: A Review
## 2 Overview of Technologies
### E-Waste  
Electronic waste, or e-waste, is difficult to process and is one of the fastest-growing wastes with an estimated 120 million metric tons in 2050 [50]. It contains a multiplicity of materials such as aluminum, copper, plastics, printed circuit boards, iron, steel, and hazardous components and compounds [51]. This requires disassembling and possibly further processing (Figure 3). Some parts are easily removable and might be reused right away (i.e., rechargeable batteries, motors, electronic components); others have to be processed. Recent studies show combining milling and chemical treatment methods to  
Figure 2: Simplified AVAC system diagram.  
be effective for retrieving metals (Fe, Cu, Sn, Al, Ni, and Zn) from PCBs [52]. Other than physical separation, like milling, electrostatic and magnetic separation can be used [53]. High stresses and the destruction of bonding in the structure of PCBs during milling makes the extracting process more efficient. A low temperature can improve the process of ball milling even further. A study shows that ball milling at temperatures as low as 154 K reduces different materials to nanoscale powders. Low temperature eliminates unwanted hazardous reactions and emissions. Overall, this method requires more energy compared to chemical and biometallurgical methods, but it allows best recovery and limited waste [54]. Although biometallurgy is not the most energy-efficient, it is the most environmentally friendly route for the extraction and recovery of metals from PCB [53].  
Advances in technology allowed for creating reasonable standards among the devices and reduction of e-waste. Although USB-C itself has been around for almost a decade, not all manufacturers choose to use it. The USB Promoter Group continuously improves USB-C by releasing new standards adapting to power consumption and data-transfer speeds expected by consumers. The latest technical specification, USB4 Version 2.0, has been announced in September 2022. What is more, these standards are backwards compatible, meaning that you can connect two devices using different versions of USB standards and expect it to work (e.g., plug in USB 2.0 pendrive into USB 3.1 port in a computer). The European Union has taken steps to reduce e-waste legislatively. Estimates show chargers pile up to 11,000 tons of e-waste every year. In September 2021, The Commission tabled a document containing 4 proposals:  
* A harmonized charging port for electronic devices: USB-C will be the common port. This will allow consumers to charge their devices with the same USB-C charger, regardless of the device brand.
* Harmonized fast-charging technology will help prevent that different producers unjustifiably limit the charging speed and will help to ensure that the charging speed is the same when using any compatible charger for a device.
* Unbundling the sale of a charger from the sale of the electronic device: consumers will be able to purchase a new electronic device without a new charger. This will limit the number of unwanted chargers purchased or left unused.
* Improved information for consumers: producers will need to provide relevant information about charging performance, including information on the power required by the device and if it supports fast charging. This will make it easier for consumers to see if their existing chargers meet the requirements of their new device or help them to select a compatible charger [55].  
Although modern technologies are useful, some of them are also a source of e-waste. Cryptocurrencies are one of them. For example, Bitcoin requires a computer that performs cryptographic operations billions of times to retrieve a 'block' [56]. The average time of a mining device oscillates between 1.12 and 2.15 years [57]. It is estimated that, at its peak, Bitcoin consumed 204.5 TWh annually between June 2022 and July 2022, which dropped to  
Figure 3: E-waste recovery process flow.  
above 95 TWh as of May 2023. Bitcoin also generates 54.18 kt of electrical waste annually as of 13 May 2023 [58].