In the face of rising energy demands for high-salinity wastewater treatment, the abundant salt content presents a novel opportunity for salinity gradient energy harvesting, which can drive metal recovery processes. A “waste-controls-waste” strategy was developed by exploiting the salinity gradient to drive chromium reduction, achieving synergistic energy recovery and heavy metal removal. Based on this, an asymmetric nanochannel was designed to couple high-salinity and Cr-containing wastewater, enabling a green, self-powered treatment process. A cation-selective heterogeneous membrane was fabricated via a facile vacuum filtration method, wherein one-dimensional aramid nanofibers (ANFs) were intercalated between two-dimensional graphene oxide (GO) sheets to form an ordered lamellar structure. The structure was subsequently assembled onto an anodized aluminum oxide (AAO) substrate. The ANF-GO/AAO membrane, with a “line-plane” hybrid architecture, exhibited high cation selectivity and pronounced ion rectification due to its bipolar charge configuration. By mixing high-salinity wastewater and Cr-laden wastewater through the ANF-GO/AAO membrane, substantially high-power density of up to 39.22 W m⁻² was achieved, along with an energy conversion efficiency of 25.60% under extreme salinity gradients. Nernst-Planck simulations revealed that ion selectivity and energy conversion in the heterogeneous membranes are dictated by their asymmetric architecture and the negatively charged selective layer. The harvested electrical energy directly drove the electrochemical reduction of Cr (VI), achieving a removal amount of 18.77 mol cm⁻² under acidic conditions. A “waste-controls-waste” strategy harnesses salinity gradients to drive Cr(VI) reduction, achieving simultaneous energy recovery and heavy metal removal. An asymmetric nanochannel couples high-salinity and Cr-laden wastewater, enabling a green, self-powered treatment system.

Recycling-oriented alloy design is a crucial part of material sustainability, as it reduces the need for raw material extraction and minimises environmental impact. This requires that scraps be reused or repurposed effectively, even when the scraps are co-mingled and have higher costs for further sorting and separation. In this work, we explore an alloy design concept by creating a compositionally flexible domain that can recycle multiple alloy grades and yet maintain relatively consistent properties across chemical variations. This is demonstrated through the Fe-Cr-Ni-Mn system to identify compositionally flexible austenitic stainless steels (CF-ASS) and accommodate the recycling of mixed austenitic stainless steel scraps. Alloys within the nominal composition spaces exhibit relatively consistent mechanical properties and corrosion resistance despite significant variations in different alloy compositions. We illustrate how we can utilise the compositionally flexible austenitic stainless steels to recycle mixed 200 and 300-series stainless steel and ferronickel scraps, demonstrating its practical viability. While this demonstration focuses on the stainless steel system, the underlying principles can be extended to other systems related to mixed scrap recycling.

Pipe materials appear to play an important role in the development of biofilms in drinking water distribution systems. However, there is controversy as to whether pipe materials shape the composition and diversity of bacterial communities in biofilms. To investigate the long-term effects of pipe materials on biofilms, triplicate samples of mature biofilms on unplasticized polyvinyl chloride (PVC-U), grey cast iron and asbestos cement (pipe age > 40 years) were obtained from three areas of an unchlorinated drinking water distribution system in the Netherlands. Illumina sequencing was performed and 773 OTUs (730 OTUs-814 OTUs) were detected within the biofilms on the three pipe materials, all of which were dominated by Proteobacteria (36.2%-46.1%). Both the alpha and beta diversity results showed that the bacterial communities of the biofilms formed on different pipe materials were highly similar. The neutral community model revealed that the assembly of the biofilm communities was governed by environmental selection rather than neutral processes. Among the 142 shared OTUs between the water and biofilm samples, there were 25 enriched OTUs (e.g., OTU7, assigned as Nitrospira spp.), which accounted for 62.6% of the total sequences, while 16 OTUs were disadvantaged (e.g., OTU14 and OTU40, assigned as Hyphomicrobiaceae), accounting for 2.2% of the sequences. Based on the findings, we propose and discuss a harmonisation process by which biofilms with significant differences due to the pipe material harmonize over time resulting in biofilms with similar bacterial communities. Our findings provide valuable insights into long-term biofilm development, bridging an essential gap in our current understanding of the influence of pipe materials on biofilm communities. These findings also highlight the importance of long-term studies and point to a potentially masked harmonizing process during biofilm development over years/decades.