Max Ehleben

The growing accumulation of plastics in marine environments and their fragmentation into microplastics have increased the demand for durable and sustainable materials for aquaculture applications. Oyster shell waste is particularly attractive because it is an abundant by-product of shellfish aquaculture and consists predominantly of biogenic calcium carbonate (CaCO₃), a mineral naturally associated with oyster habitats. This study investigates the feasibility of incorporating oyster shell powder into polyamide 6 (PA6) to produce 3D-printable composites for potential oyster spat collector applications. PA6 composites containing 10, 20, and 30 wt% oyster shell powder were compounded, extruded into filaments, and processed via fused deposition modeling (FDM). The materials were characterized with respect to processability, thermal and mechanical properties, moisture uptake, filler composition, and CaCO₃ dissolution behaviour. All formulations showed good processability and were successfully printed into mechanically stable specimens. Increasing filler content increased stiffness but reduced ductility, while melting and crystallization temperatures remained largely stable but influenced enthalpy properties at higher filler loadings. Immersion experiments revealed partial dissolution of the mineral phase, indicating partial CaCO₃ dissolution without visible degradation of the PA6 matrix. Overall, the results demonstrate the feasibility of highly filled PA6/oyster shell composites for additive manufacturing and provide a foundation for future studies addressing seawater exposure, oyster larval settlement and field-scale validation.

Reliable polymer identification is a prerequisite for high-quality recycling of post-consumer fishing nets and ropes. Differential Scanning Calorimetry (DSC) provides precise thermal characterization but requires stationary laboratory infrastructure and is not applicable at coastal collection points or small-scale recycling operations. This study describes and validates Melting Box 1.0 (MB 1.0), a low-cost, field-deployable device for qualitative screening of softening and melting ranges in small polymer samples. MB 1.0 repurposes a commercial vaporizer’s existing temperature-controlled heating and display functionality into a purpose-built screening tool, rather than introducing a new analytical measurement principle. Representative materials from Vietnamese fishing net recycling projects—polyethylene (PE), polypropylene (PP), polyamide (PA), and PE/PP blends—were assessed with a standardized three-tier visual scale (0 = no change; * = softening; x = melting) across five replicate measurements per sample. Agreement with the Kofler hot bench is good (mean bias for T_melt,start: +2.9 °C; SD = 9.1 °C; n = 7), and a systematic offset of +20.6 °C (range +14.1 to +27.6 °C) was observed for PE relative to DSC first-heating peak-end temperatures. The correct material ranking (PE < PP < PA) is preserved, and all four polymer groups are reliably distinguished. At an estimated cost of 150–200 EUR—one to three orders of magnitude below the Kofler hot bench, portable NIR, or DSC—MB 1.0 is intended as a field-deployable screening complement to, not a replacement for, laboratory-grade analytics in resource-constrained recycling contexts.

Extended producer responsibility (EPR) is intended to link producer design decisions to end-of-life costs, but collective EPR schemes typically weaken this link by routing funding through producer responsibility organisations. We develop a multi-level framework of consumer-integrated environmental protection (CIEP) and argue that individual producer responsibility (IPR), where producers bear product-specific end-of-life liability, can function as a governance mechanism that reconnects design, consumer behaviour and waste governance. This paper is a qualitative multiple-case research study—not a systematic review—which draws on three funded research projects: (i) small and medium-sized enterprise (SME) tools for design-for-recyclability, (ii) an artificial intelligence (AI) application for household waste sorting, and (iii) closed-loop recycling of fishing gear in Vietnam. Within the first project (ToCoReRaM), a PRISMA-based systematic review of web-accessible circular economy tools finds that only 2 of 23 tools are SME-accessible through standard web searches. The AI-based waste-sorting application achieves approximately 75% classification accuracy under real-world conditions. The fishing gear study demonstrates technical and economic viability of closed-loop recycling, and a survey of more than 1500 Vietnamese fishers finds 95.8% willingness to return used gear given appropriate incentives. Together, the cases show that effective circular governance requires four complementary elements: IPR-based producer accountability, SME-accessible design tools, digital consumer guidance at the point of disposal, and context-sensitive governance capacity. These findings inform policy pathways for Sustainable Development Goal (SDG) 12 and SDG 14.

Abandoned, lost or otherwise discarded fishing gear (ALDFG) is a global challenge that negatively affects marine ecosystems and fishers’ livelihoods. Survey results from 1864 capture fishers in Vietnam show that the total mass of ALDFG is 82,720 kg/year, with an average loss rate of 0.24% of the total plastic used. The average ALDFG mass from gillnet fisheries is 26.0 ± 1.2 kg/vessel/year, trap fisheries 16.1 ± 2.6 kg/vessel/year, hook and line fisheries 13.8 ± 1.4 kg/vessel/year, trawl fisheries 8.8 ± 1.1 kg/vessel/year, stick-held falling net fisheries 5.1 ± 2.1 kg/vessel/year, and purse seine fisheries 4.2 ± 1.4 kg/vessel/year. Polyethylene (PE) accounts for 47.4%, polyamide (PA) 29.5% and polypropylene (PP) 17.2% of the total ALDFG mass. Results from the selected partial proportional odds model show that fishers’ concern about ALDFG increases with education, fishing experience, vessel length, and stronger awareness of environmental and economic impacts, whereas age, days at sea, perceived navigation hazards, and perceived impacts on fish stocks are negatively associated with concern; perceived tourism impacts show a statistically significant threshold-varying effect across concern levels. These findings provide a scientific basis for developing sustainable fishing-gear management policies, aiming to reduce marine plastic pollution in Vietnam. These findings provide evidence for conservation-oriented fishing-gear management in Vietnam by identifying the gear types and fisher perceptions most relevant to reducing ghost fishing, marine plastic leakage, and risks to marine biodiversity and coastal ecosystems.

The collective architecture of Extended Producer Responsibility (EPR) assigns financial obligations to Producer Responsibility Organisations, severing the link between individual producer design decisions and end-of-life costs — eliminating the upstream design incentive that constitutes EPR's theoretical rationale for environmental management. This paper argues that Individual Producer Responsibility (IPR) — wherein end-of-life liability is assigned directly and proportionally to the originating producer — represents the regulatory precondition for a structurally coherent system of Consumer-Integrated Environmental Protection (CIEP): a four-level applied environmental management architecture (Design–Regulation–Behaviour–System) in which IPR activates recyclable product design, consumer disposal guidance, and transnational waste governance simultaneously. Three applied research projects provide convergent evidence. ToCoReRaM (Level 1) demonstrates through PRISMA-compliant systematic review and 14 SME interviews that only 2 of 23 circular economy tools are discoverably accessible in standard search behaviour, establishing that IPR creates design obligations without compliance pathways unless SME-operable tools are mandated. WERTIS-KI (Level 3) deploys AI-based image recognition achieving approximately 75% classification accuracy to bridge the attitude–behaviour gap in household waste sorting, generating product-level missorting data that IPR eco-modulation requires. REVFIN (Level 4) demonstrates closed-loop fishing gear recovery feasibility in Vietnam, introduces 'end of recyclability' as a temporally bounded material property requiring incorporation into environmental governance design, and models replicable governance transfer. Effective waste and marine litter management requires simultaneous deployment of IPR-based accountability, SME-operable tools, digital consumer guidance, and context-sensitive governance capacity — mutually reinforcing instruments constituting a minimum viable environmental management architecture directly addressing SDG 12 (responsible consumption and waste) and SDG 14 (life below water).

Plastic waste in coastal waters has become a major environmental concern and a visible sign of ocean pollution. A significant share of the floating waste material originates from used and lost fishing gear. By establishing suitable recycling processing chains, used fishing gear can become a valuable resource for the manufacturing of products, fostering its extraction from the water and boosting local economies. Post-use fishing gear, however, is a very challenging input material for processing into recylcates. Understanding its degradation mechanisms is crucial for designing a recycling process that will yield high value materials. There are particular obstacles connected with each recycling step, starting with the collection of very heterogeneously aged and deteriorated fishing gear. Consecutively, shredding of the waste material requires the development of specific technological solutions. Marine dirt adds additional obstacles. Further processing steps that need to be adapted include extrusion, pelletizing injection molding and marketing of the products from recycled material in competition with ones using raw materials. This study presents a waste-to-value process chain design that addresses the specific challenges of recycling fishing gear collected from coastal waters. Data has been collected to identify and quantify sources of plastic waste from fishing activities, and solutions have been developed in local higher education through a joint German-Vietnamese effort.