Treatment of volatile organic compounds from a typical waste printed circuit board dismantling workshop by a pilot-scale biotrickling filter

From present to future: A review of e-waste recycling processes

The global acceleration of electronic waste (e-waste) generation has created significant environmental, economic, and social challenges. Emerging technologies and shorter product lifespans are expected to intensify this growth. Despite the potential for material recovery, only a small fraction of e-waste is formally recycled, with a significant loss of critical resources such as rare earth elements and increased environmental degradation. Although prior studies address specific economic or environmental dimensions of e-waste management, detailed evaluations of recycling technologies from all three sustainability pillars are limited. This paper uses a structured sustainability framework to review five major recycling processes, including physical disassembly, pyrolysis, hydrometallurgy, biometallurgical treatment, and supercritical fluid technology. Social implications include occupational health and safety risks, public health impacts, and socioeconomic disruptions associated with transitions from an informal to a formal system. The results show physical disassembly and hydrometallurgical methods are widely used, however, they create considerable health risks and require better environmental impact data. Biometallurgical approaches have lower environmental toxicity but are constrained by limited scalability and process efficiency. Pyrolysis provides partial energy recovery but generates concerns over pollutant emissions and worker safety. Supercritical fluid technologies have high technical promise, however, their economic and operational viability are underdeveloped. The paper proposes a roadmap for advancing e-waste recycling systems by identifying data gaps and technology-specific opportunities for sustainable scale-up.

Study on Gaseous Chlorobenzene Treatment by a Bio-Trickling Filter: Degradation Mechanism and Microbial Community

Large-flow waste gas generated from the pharmaceutical and chemical industry usually contains low concentrations of VOCs (volatile organic compounds), and it is also the key factor that presents challenges in terms of disposal. To date, due to the limitations of mass transfer rate and microbial degradation ability, the degradation performance of VOCs using the biological method has not been ideal. Therefore, in this study, the sludge from a chlorobenzene-containing wastewater treatment plant was inoculated into our experimental bio-trickling filter (BTF) to explore the feasibility of domestication and degradation of gaseous chlorobenzene by highly active microorganisms. The kinetics of its mass transfer reaction and microbial community dynamics were also discussed. Moreover, the main process parameters of BTF for chlorobenzene degradation were optimized. The results showed that the degradation effect of chlorobenzene reached more than 85% at an inlet concentration of chlorobenzene 700 mg·m−3, oxygen concentration of 10%, and an empty bed retention time (EBRT) of 80 s. The mass transfer kinetic analysis indicated that the process of chlorobenzene degradation in the BTF occurred between the zero-stage reaction and the first-stage reaction. This BTF contributed significantly to the biodegradability of chlorobenzene, overcoming the limitation of gas-to-liquid/solid mass transfer of chlorobenzene. The analysis of the species diversity showed that Thermomonas, Petrimona, Comana, and Ottowia were typical organic-matter-degrading bacteria that degraded chlorobenzene efficiently with xylene present.

Performance and microbial community evolution of toluene degradation using a fungi-based bio-trickling filter

Fungi have their unique advantages in capturing and degrading hydrophobic VOCs. To study the performance of fungi-based bio-trickling filters (BTFs) with respect to the degradation of toluene, and the succession process of the fungal colony under different operating conditions, a three-layer BTF packed by dominant Fusarium oxysporum immobilized with ceramic particles were set up. The fungal BTF started quickly within 7 days and restarted less than 7 days after starvation; its average RE was higher than 92.5% when the toluene inlet loading rate (ILR) ranging from 7.0 to 100.9 g m^-3 h^-1 at steady state. Moreover, the maximum elimination capacity (EC) of 98.1 g m^-3 h^-1 was obtained at a toluene ILR of 100.3 g m^-3 h^-1. The microorganism analysis of time and space revealed that the dominant fungi Fusarium were replaced by Paramicrosporidium saccamoebae after a certain evolutionary period. The intermediate layer had more microbes and a more complex community than the other two layers, and was more suitable for the survival of the varieties of microbes.

Removal of benzene, toluene, xylene and styrene by biotrickling filters and identification of their interactions

Biotrickling filters (BTFs) are becoming very potential means to purify waste gases containing multiple VOC components, but the removal of the waste gases by BTF has been a major challenge due to the extremely complicated interactions among the components. Four biotrickling filters packed with polyurethane foam were employed to identify the interactions among four aromatic compounds (benzene, toluene, xylene and styrene). The elimination capacities obtained at 90% of removal efficiency for individual toluene, styrene and xylene were 297.02, 225.27 and 180.75 g/m3h, respectively. No obvious removal for benzene was observed at the inlet loading rates ranging from 20 to 450 g/m3h. The total elimination capacities for binary gases significantly decreased in all biotrickling filters. However, the removal of benzene was enhanced in the presence of other gases. The removal capacities of ternary and quaternary gases were further largely lowered. High-throughput sequencing results revealed that microbial communities changed greatly with the composition of gases, from which we found that: all samples were dominated either by the genus Achromobacter or the Burkholderia. Different gaseous combination enriched or inhibited some microbial species. Group I includes samples of BTFs treating single and binary gases and was dominated by the genus Achromobacter, with little Burkholderia inside. Group II includes the rest of the samples taken from BTFs domesticated with ternary and quaternary gases, and was dominated by the genus Burkholderia, with little Achromobacter detected. These genera were highly associated with the biodegradation of benzene series in BTFs.