“Optimization of Electrostatic Separation of Plastics from Beach Litter”

Accumulation of waste on coastlines is a common problem in the Mediterranean Sea with significant environmental and economic consequences. These accumulations, mostly consisting of natural materials (i.e., Posidonia oceanica) and anthropogenic debris (e.g., plastics, wood, metals), are classified as urban waste (Legislative Decree 152/2006) and are not serviced by waste management consortia, leading to disposal primarily in authorized landfills. Although it is clear that maintaining the natural material is essential for preserving the coastal ecosystem, local authorities frequently face pressure to remove these deposits to improve beach aesthetics. Moreover, biomass accumulations are notably rich in anthropogenic materials. The collection and treatment of beach litter is crucial in safeguarding marine-coastal environments and recovering Secondary Raw Materials (SRM). Electrostatic separators represent a promising technology for recovering valuable fractions from mixed granular waste. The key principle lies in exploiting the different electrical properties of materials to separate them into high-purity streams. This article presents the first results of an experimental study aimed at electrostatic separation of natural inorganic fractions (i.e., sand) from plastic anthropogenic wastes. In particular, we focused on separating several mixtures of sand (particle size ≈ 1 mm) and polyamide (PA) plastic (particle size ≈ 1.4 mm). The primary goal was to evaluate the separation efficiency based on specific operating parameters (e.g., angles of electrodes and electrode voltage) of a 10 kg/h laboratory pilot plant. In each test, the fraction recovered after separation was analyzed to determine both the separation efficiency (the percentage of correctly separated material) and the final purity (the percentage of sand or plastic free from contaminants) by sIRoPAD (automatic Near Infrared measuring system for all kinds of non-black plastic flakes, granules and pellets). Operating parameters were adjusted for each test to identify the combination that maximized efficiency and purity. Preliminary trials identified a set of optimized conditions yielding the best separation performance. Under these conditions, a separation efficiency of about 96% and a final product purity of 90% were achieved. These results highlight the critical importance of fine-tuning both the electrostatic parameters (voltage, electrode positions) and the mechanical parameters (drum speed, vibration, deflectors) to effectively separate similarly sized particles of different materials. The findings demonstrate that properly optimized electrostatic separation can provide an efficient method for recovering valuable fractions from granular mixtures composed of different materials with similar dimensions. This approach is particularly promising for recycling and reusing plastic fractions, but it could also be extended to other material combinations with analogous particle size ratios. Future efforts will involve testing on an industrial scale, exploring additional plastic types, and assessing sustainability impacts, with the ultimate goal of integrating this technology into broader waste management systems.