To improve the efficiency of phosphorus (P) release from marine sediments and contribute to P loop closure, this study proposed a novel strategy combining bio-inoculation with polyphosphate-accumulating organisms (PAOs) and chemical enhancement via chelating agents. Based on prior findings, two-stage experiments were conducted. In Stage 1, anaerobic batch tests assessed the effect of different chelating agents for P release. While citrate showed no promoting effect, the addition of ethylenediaminetetraacetic acid (EDTA) significantly enhanced total P release, reaching 48.5 % within 15 days. In Stage 2, PAO-acclimated sediments were introduced into the system, followed by alternating anaerobic-aerobic fed-batch operation for 7 days, and subsequent EDTA addition with anaerobic incubation for another 6 days. This combined approach achieved a total P release efficiency 83.4 %, with final soluble P concentrations reaching 145.9 mg/L. During this process, PAOs were rapidly enriched, with their relative abundance increasing from 12.9 % to 65.0 %. Metagenomic analysis revealed that EDTA promoted environmental filtering, selectively enriching PAOs (Candidatus Accumulibacter) and thereby reinforcing their specific contributions to P functional genes. The resulting P-rich supernatant was then subjected to precipitation. PHREEQC simulations guided the prediction of optimal precipitation conditions, and laboratory experiments confirmed that most soluble P, especially Fe-bound forms, could be efficiently recovered, with maximum precipitation efficiencies of 98.8 %.

Calcium oxalate (CaOx) crystallization under laminar flow conditions, relevant for kidney stone formation, was studied in a microfluidic device simulating the geometry of kidney collecting ducts. In a typical microfluidic experiment, two reactive solutions with designated concentrations of calcium (Ca) and oxalate (Ox) ions were brought into contact in a microfluidic channel to create a laminar co-current flow of the two streams. As the streams flow co-currently in the channel, diffusion takes place between the two streams across the channel width, resulting in reactive crystallization leading to CaOx nucleation and growth of CaOx crystals along the mixing front. We studied the growth of these crystals in artificial urine as a function of the fluid flow rate in the channel, the molar ratio of Ca : Ox in the medium and the presence of an organic protein, osteopontin (OPN), known to inhibit the growth of CaOx crystals. Three different flow velocities at a fixed molar ratio of Ca : Ox = 7.5 and four molar ratios of Ca : Ox at a fixed mean flow velocity of 0.035 m s−1 were tested. Lastly, three additive OPN concentrations were evaluated: 2.4 × 10−8 mol m−3, 6 × 10−8 mol m−3 and 8.4 × 10−8 mol m−3. The mean flow velocity did not alter the crystal growth of CaOx in the studied range, whereas altering the molar ratio of Ca : Ox had a high impact on the growth rate. In addition, the type of pseudopolymorph which nucleated appears to depend strongly on the molar ratio. At a low Ca : Ox ratio, both calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) nucleated simultaneously and the growth of the two pseudopolymorphic forms of CaOx crystals was observed. The lowest applied OPN concentration decreased the growth rate of COD, while higher concentrations of OPN slowed down the nucleation kinetics to a point that it completely inhibited the formation of any CaOx crystal in artificial urine within the investigated timeframe. COD was seen under all the conditions investigated, whilst COM was seen in experiments for Ca : Ox molar ratio values between 5 and 6. Our results were rationalized using finite element simulations supported by solution chemistry modelling.

The consumption of niobium-based compounds has risen due to the broadening of the range of applications. Recent technological and industrial developments have increased the Nb demand, particularly in aviation, construction, electronics, communication, energy as well as the automotive, metallurgical and steel industries. In this regard, recovery of Nb from secondary sources is necessary to produce new compounds with high economic value. In this context, we used the Fe-Nb alloy fines, out of the commercial specifications, as a secondary source of niobium to produce an alkaline liquor to recover niobium compounds at relatively low temperatures and atmospheric pressure. Potassium niobate was obtained from the cooling crystallization of potassium alkaline liquor and was used as a precursor for producing niobic acid. The XRD and chemical analysis indicated that potassium niobate was formed in different crystalline phases – KNbO3 and K4Nb6O17 – with microscopy images showing isolated plate-like crystals. The chemical composition of the solid was 42.3 % of Nb, 24.7 % of K, 23.3 % of O and 9.7 % of other impurities. An amorphous niobic acid with residual potassium sulphate was obtained through precipitation from a potassium niobate solution with H2SO4 0.5 mol/L. The chemical composition of niobic acid was 54.7 % of Nb, 11.7 % of K, 30.3 % of O and 2.4 % of S. The niobic acid was calcined at 900 °C for 5 h to produce niobium oxide. The XRD indicated the presence of a potassium niobate phase 61.2 % of Nb, 12.1 % of K, 32.6 % of O and 1.9 % of S. The presence of impurities in the solids is expected, due to its presence in the starting material. No impurity removal protocol was implemented.

This study explores fractional and simultaneous precipitation methods to recover metals from a synthetic solution containing the major components from lithium-ion battery recycling leachates: Co, Ni, Mn, Li, and H₂SO₄. Thermodynamic simulations analyzed the behavior of the metal-bearing solutions during hydroxide precipitation to guide process design. The fractional precipitation process was divided into three steps: pH-adjustment (D1), Co and Ni recovery (D2), and Mn recovery (D3). D2 achieved 89.7% Ni and 76.8% Co recovery; alongside Mn and Li were also removed (15% and 25% respectively). D3 showed mainly Mn recovery (68%) along with 18.7% Co and 7.3% Ni. Simultaneous precipitation resulted in over 99.7% recovery of Co, Ni, and Mn, with a small amount of Li (15%) being recovered from the solution. Na removal from the solution was observed across all experiments. X-ray diffraction analysis revealed that the phases formed were distinct from the predictions. Regardless of the presence of NH₄OH as a chelating agent in solution, a mixed nickel-cobalt-manganese oxide could be obtained after calcination. This approach offers a potentially less laborious method for recovering metals in products relevant to cathode precursors in a single step from recycling leachate.

Volatile fatty acids (VFAs) are platform chemicals with a higher value with wide applications. The feasibility of producing high-purity VFAs from source-separated wastewater using mixed-culture fermentation and membrane techniques was investigated. Batch studies were conducted for VFA production from blackwater and food waste under acidic and alkaline conditions. The VFA production from blackwater was higher at initial pH 9 with yield of up to 0.82 ± 0.03 gCOD/gCOD_fed due to higher buffer capacity, homogeneity, and biodegradability. The highest VFA yield from food waste was 0.36 ± 0.02 gCOD/gCOD_fed at initial pH 5. VFAs from the blackwater were dominated by acetic acid (up to 93 %), regardless of pH VFAs from the food waste were dominated by butyric acid (up to 76 %) and propionic acid (up to 52 %) at pH 5 and 9, respectively. Both the substrate types and pH influenced the microbial communities of the fermentation reactors. Bacteroides (up to 40 %) and Atopostipes (up to 51 %) were dominant genii for blackwater at initial pH 5 and 9, while Clostridium_sensu_stricto clusters (up to 58 %) and Romboutsia (up to 37 %) dominated food waste fermentation microbial communities at pH 5 and 9, respectively. VFAs were separated and purified with nanofiltration (NF) and reverse osmosis (RO). NF produced high-purity, but low-concentration permeate (900 −1500 mgCOD/L) at 50 % permeate recovery (with up to 42 % of acetic acid permeating the NF membrane). A higher concentration of pure VFAs (3x higher) was achieved with a subsequent step of RO. The study highlights the feasibility of the recovery of functional chemicals from waste.

This study explores the dual challenge of enhancing the properties of protein-based foams produced from agricultural by-products through the incorporation of red mud waste from alumina production. Foams were manufactured using an extrusion process, employing gluten and zein proteins, with raw red mud and its oxalic acid leachates serving as additives. A factorial design was utilized to assess the significance of various parameters on the mechanical properties of materials. The results indicate that red mud-based additives do not improve foam mechanical stability in terms of stiffness (as measured by Young's modulus) and thus do not function effectively to form short crosslinking bridges. However, the results show red mud serves mainly as a plasticizer and reducing/oxidizing agent, while also potentially enhancing the formation of long crosslinking bridges. This is evidenced by a significant increase in foam strain when red mud powder is extruded with gluten, reaching 190% strain at break and densities between 500 and 1500 kg/m³. Consequently, red mud shows potential to be repurposed as an additive in protein-based foams, suitable for applications requiring elastic deformation while keeping a stable porous structure manufactured via continuous extrusion.

Red mud is a hazardous waste of the alumina refining process, with 1–1.5 tons generated per ton of alumina produced. This study presents a first-of-its-kind understanding of a biomass-based pathway for recovering iron from red mud. Simultaneous red mud reduction and biomass gasification (SRG) is proposed as a viable pathway to produce zero-valent iron. This metallic iron can potentially be recovered by weak magnetic separation and integrated into the iron-making industry. The steps of the red mud-biomass phenomena were investigated through thermogravimetric analysis followed by XRD characterization. Complete reduction from Fe³⁺ to Fe⁰ was achieved at temperatures near 900 °C and verified by XRD, XPS, and FTIR. Bench-scale SGR experiments were also performed to survey the compositions of gaseous and tar products. Bench-scale SRG experiments confirmed increased syngas (CO and H₂) production and demonstrated the tar-cracking catalytic activity of red mud.

To evaluate the feasibility of enriching polyphosphate-accumulating organisms (PAOs) within marine sediment for achieving phosphorus (P) recovery, two sediment-inoculated sequencing batch reactors (SBRs), fed with propionic acid (R1) and glucose (R2), were operated for 119 days. For comparison, two sewage sludge-inoculated reactors (R3 and R4) were also set up. The sediments/sludge fed with 200 mg/L chemical oxygen demand (COD) equivalent propionic acid exhibited satisfactory P release/uptake performance after 56 days of culture. The maximum P release and uptake rates for R1 were 3 mg P/g VSS•h−1 and 2.5 mg P/g VSS•h−1, respectively, while for R3 they were 2.6 mg P/g VSS•h−1 and 5.8 mg P/g VSS•h−1, respectively. Meanwhile, the PAO family (Rhodocyclaceae) in R1 increased from almost 0 % initially to 16.0 % after 42 days. However, the glucose-fed SBRs did not exhibit enhanced biological phosphorus removal (EBPR) performance throughout the operation. As the COD feeding concentration increased to 400 mg/L, the reactors showed EBPR deterioration. Total P in R1 and R3 significantly decreased from 423.7 mg to 307.2 mg and from 368.0 mg to 94.9 mg, respectively. Key intracellular polymer responses indicated that introduction of excessively high COD significantly reduced poly-P content and the anaerobic synthesis of polyhydroxyalkanoate. Microbial analysis suggested that the breakdown of EBPR performance could be attributed to glycogen-accumulating organisms outcompeting PAOs under high carbon feeding conditions. Additionally, PHREEQC simulations confirmed that P-rich supernatant from the anaerobic phase could theoretically be recovered as struvite, with a recovery efficiency of up to 94 %.

The aim of this study was recovery of phosphorus (P) from marine sediment, and our results revealed the influence of P release from the sediment stimulated with different types and concentrations of carbon sources. During the 15-day anaerobic operation, the sediments stimulated with 1 g/L propionic acid and glucose exhibited more prominent effects compared to other trials, with 5.98 mg/L and 6.44 mg/L of P released, respectively, with a total solid content of 4 %. Notably, the excessive addition of carbon sources was shown to can partially inhibit P release. As microbial activity intensified, P was utilized for microbial synthesis, resulting in a decreased P in the supernatant. For example, in glucose-fed systems with concentrations of 5 g/L and 10 g/L, the P concentration decreased from 5 mg/L on Day 3 to approximately 3 mg/L on Day 15. The sequencing results indicated distinct evolutions within different carbon source-fed systems over the 15-day operations. Feeding high concentrations of glucose resulted in rapid enrichment of fermentative bacteria under anaerobic conditions, while sulfate-reducing bacteria promoted P release in volatile fatty acids-fed systems. Metabolic analysis revealed that carbon sources not only influence gene expression in different systems, but also impact the metabolic pathways involved in nutrient cycling, which can be interrelated. For example, a significant positive correlation was observed between the abundance of P and sulfur cycling functional genes (phoD, cysD).

Crystallization abounds in nature and industrial practice. A plethora of indispensable products ranging from agrochemicals and pharmaceuticals to battery materials are produced in crystalline form in industrial practice. Yet, our control over the crystallization process across scales, from molecular to macroscopic, is far from complete. This bottleneck not only hinders our ability to engineer the properties of crystalline products essential for maintaining our quality of life but also hampers progress toward a sustainable circular economy in resource recovery. In recent years, approaches leveraging light fields have emerged as promising alternatives to manipulate crystallization. In this review article, we classify laser-induced crystallization approaches where light-material interactions are utilized to influence crystallization phenomena according to proposed underlying mechanisms and experimental setups. We discuss nonphotochemical laser-induced nucleation, high-intensity laser-induced nucleation, laser trapping-induced crystallization, and indirect methods in detail. Throughout the review, we highlight connections among these separately evolving subfields to encourage the interdisciplinary exchange of ideas.