Phosphorus recovery and recycling – closing the loop

Mobility and bio-accessibility of available phosphorus in sewage sludge: Influencing mechanism of hydrothermal pretreatment and incineration

Accurate assessment and enhancement of phosphorus (P) availability are critical for land application of sewage sludge and its thermal-treated products. By simulating different functioning pathways of P in soil, a novel multivariable scheme was developed to evaluate P availability from the perspective of mobility and bio-accessibility, then was applied to investigate the effects of hydrothermal pretreatment (HT), carbonaceous skeleton-assisted HT (CSkel-HT), and incineration on this topic. Sludge contained predominantly slow-release and microbial-available P (>50.0 % of total P). HT and incineration reduced available P through filtrate discharge, organic-P decomposition, and Fe/Al-P volatilization. Surprisingly, CSkel-HT addition promoted soluble Ca/MgHPO4 and thermal-stable Fe/AlPO4 formation under acidic conditions, which not only retained the slow-release and microbial-available P in hydrochar and ash, but also increased the rapid-available and plant-available P contents by 25.0 % and 300.0 %. Our scheme provided more informative insights than traditional single-index methods, and revealed the enhancing mechanism of CSkel-HT on P availability.

Enhanced phosphate recovery in R-MCDI systems: Synergistic effects of modified electrodes and membrane-electrode-current collector assembly

Efficient phosphorus (P) recovery is critical for sustainable wastewater management and resource reuse. This study optimized a reservoir of membrane capacitive deionization (R-MCDI) system by integrating acid-modified activated carbon cloth (ACC) electrodes and a membrane-electrode-current collector assembly (MECA) configuration. Acid modification enhanced the electrode's specific surface area, microporosity, and carboxyl group content, while reducing charge transfer resistance, significantly improving P recovery and selectivity. The ACC-42 electrode achieved optimal performance, achieving a 52% P recovery efficiency and low energy consumption of 8.8 kWh/kg P. The MECA configuration further amplified P recovery by optimizing electric field distribution and maximizing electrode utilization, achieving a fourfold higher recovery rate (0.081 μmol·cm-2·min-1) while reducing energy consumption by 59% compared to alternative setups. Multi-cycle operations validated the system's robustness, with P concentrations reaching 397 mg/L in the electrode chamber and a nearly 15-fold increase in selectivity for P over sulfate. This study highlights the synergistic effects of electrode modification and assembly configuration in enhancing R-MCDI performance, providing a scalable and energy-efficient solution for nutrient recovery in wastewater treatment.

Geospatial analysis of trace metal pollution and ecological risks in river sediments from agrochemical sources in Morocco's Sebou basin

Sediments in agricultural ecosystems serve as critical indicators of environmental pollution, particularly in regions subjected to intensive agricultural practices. This research evaluates the environmental hazards and implications of heavy metal (HM) contamination in river sediments from the Sidi Allal Tazi area within Morocco's Sebou basin. Twenty sediment samples were extracted from strategically designated locations, and the contamination levels were analyzed using a multi-index integration approach, multi-statistical analyses (MSA), and Geographic Information Systems (GIS). The results revealed considerable spatial variability in HM concentrations, with Cd and As displaying the highest contamination levels. Statistical analysis, incorporating Principal Component Analysis (PCA), identified anthropogenic activities as the primary contributors to contamination. Hierarchical Cluster Analysis (HCA) categorized metals based on common pollution pathways, while GIS mapping revealed the spatial distribution of contamination across vulnerable areas. Pollution indicators like the Geo-accumulation Index (Igeo) as well as the Pollution Load Index (PLI). revealed that 75% of sites were categorized under "very high pollution", emphasizing the severity of contamination. Contamination Factor (CF) classified 90% of Cd samples and 100% of As samples as "very high contamination". Risk indices indicated significant ecological threats, with Cd contributing to an RI exceeding 600 in many areas, signifying "very high risk". These findings highlight the urgent need for targeted mitigation strategies and sustainable agricultural practices. The integration of multi-index and GIS methodologies provides a comprehensive framework for assessing and managing sediment contamination, offering critical insights for policymakers and environmental managers.

Intensified Enrichment and Leaching Strategy of Phosphorus in Sewage Sludge via Species-Targeted Conversion

Wet-chemical method for extracting phosphorus (P) from sludge incineration ash suffers from great P loss in the incineration and P-leaching stages due to the multidirectional migration of diversified P species. Existing single-process optimizations are difficult to meet the diverse and often conflicting needs of the two upstream and downstream processes to recover different P species. Herein, we developed a system-oriented strategy, HyperPhosⓅ, to synergistically address multiprocess requirements. It employs a specially designed one-pot pretreatment to create a unique reaction window for the most recoverable Fe/Al-P, achieving the targeted transformation of unstable P species into homogeneous Fe/Al-orthophosphate of 85.6% in proportion. These compounds exhibited remarkable thermal stability during incineration, with volatilization loss of only 60% of conventional technical route (Conv-Tech) even at 1000 °C. Subsequently, these parts of P were completely leached out using H2C2O4 or NaOH through redox reaction and chelating displacement, with the solvent concentration and the codissolution amounts of heavy metals less than half of the mean levels in the literature. Techno-economic analysis showed that HyperPhosⓅ obtained 1.1-2.4 times more P than Conv-Tech, while the unit cost was reduced by up to 49.5%. These findings provide new opportunities to close the P-cycle in a sustainable, economical, and environmentally friendly approach.

Impact of phosphorus on the functional properties of extracellular polymeric substances recovered from sludge

Extracellular Polymeric Substances (EPS) are ubiquitous in biological wastewater treatment (WWT) technologies like activated sludge systems, biofilm reactors, and granular sludge systems. EPS recovery from sludge potentially offers a high-value material for the industry. It can be utilized as a coating in slow-release fertilizers, as a bio-stimulant, as a binding agent in building materials, for the production of flame retarding materials, and more. P recovered within the extracted EPS is an intrinsic part of the recovered material that potentially influences its properties and industrial applications. P is present in EPS in different speciation (e.g., P esters, poly-P, ortho-P, etc.). Such P species are already intensively used in the chemical industry to enhance thermal stability, viscoelasticity, emulsification, water-holding capacity, and many other properties of some natural and petroleum-derived polymers. The translation of this knowledge to EPS is missing which prevents the full utilization of phosphorus in EPS. This knowledge could allow us to engineer EPS via phosphorus for specific target properties and applications. In this review, we discuss how P could affect EPS properties based on experiences from other industries and reflect on how these P species could be influenced during the EPS extraction process or in the WWTPs.

Comparative evaluation of phosphorus recovery from sewage sludge thermal products via magnesium ammonium phosphate and hydroxyapatite methods

Shortage of phosphorus resource has become a global concern. Due to the high phosphorus content in sewage sludge, phosphorus recovery can be realized from thermal products of sewage sludge. Phosphorus recovery performance of smoldering ash (SA), incineration ash (IA) and pyrolysis char (PC) was investigated. The precipitate rate of phosphorus in acid and alkali leaching solutions is over 94 % by magnesium ammonium phosphate (MAP) and hydroxyapatite (HAP) methods. For MAP method, the recovered P contents in the precipitations of SA, IA and PC are 23.25 ± 0.35, 31.71 ± 0.79 and 23.76 ± 0.24 mg/g, respectively. For HAP recovery, the phosphorus contents per unit mass of precipitated products are lower than that by MAP, ranging from 13.67 ± 0.10 to 22.89 ± 0.34 mg/g. The purity of the recovered products was evaluated based on the contents of major elements and heavy metals in recovered products. Most of major elements and heavy metals can coprecipitate with phosphorus in the recovery products by acid leaching-MAP method. Due to the low impurity content in the alkali leaching solution and insolubility of most heavy metals in it, the products recovered by alkali leaching-HAP shows higher purity than that by acid leaching-MAP method. The phosphorus recovery performance, reagent consumption and purity of recovered products of the two methods were compared. Acid leaching-MAP recovery is optimal for IA due to its highest P recovery and purity, with lower reagent consumption compared to alkali leaching-HAP. For SA and PC, alkali leaching-HAP recovery is preferable due to its higher P recovery purity and market price of hydroxyapatite products.

Wastewater biorefineries: exploring biological phosphorus removal and integrated recovery solutions

The emphasis on phosphorus removal and recovery from wastewater treatment plants has intensified in recent years due to the urgent need to reduce dependency on nonrenewable phosphorus reserves. Enhanced biological phosphorus removal (EBPR), driven by a diverse community of polyphosphate-accumulating organisms with distinct metabolic capabilities, offers several advantages over chemical precipitation methods. These benefits include reduced chemical use, lower sludge volumes, decreased reliance on costly chemical precipitants, and improved phosphorus recovery quality. Recent advancements in recovery technologies now enable efficient phosphorus extraction from digester supernatant, dewatered digested sewage sludge, and sewage sludge ash, each yielding different recovery efficiencies. Despite these advances, a comprehensive assessment of the phosphorus recovery potential from these target streams in conjunction with EBPR remains crucial and has yet to be fully explored.

Phosphate-enabled mechanochemical PFAS destruction for fluoride reuse

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are persistent, bioaccumulative and anthropogenic pollutants that have attracted the attention of the public and private sectors because of their adverse impact on human health1. Although various technologies have been deployed to degrade PFASs with a focus on non-polymeric functionalized compounds (perfluorooctanoic acid and perfluorooctanesulfonic acid)2-4, a general PFAS destruction method coupled with fluorine recovery for upcycling is highly desirable. Here we disclose a protocol that converts multiple classes of PFAS, including the fluoroplastics polytetrafluoroethylene and polyvinylidene fluoride, into high-value fluorochemicals. To achieve this, PFASs were reacted with potassium phosphate salts under solvent-free mechanochemical conditions, a mineralization process enabling fluorine recovery as KF and K2PO3F for fluorination chemistry. The phosphate salts can be recovered for reuse, implying no detrimental impact on the phosphorus cycle. Therefore, PFASs are not only destructible but can now contribute to a sustainable circular fluorine economy.

Enhancement of the Plant-Accessible Phosphate Fraction in Sewage Sludge Ashes by Na+ or K+ Addition Prior to Combustion

With the aim of transforming sewage sludge into a P-fertiliser material in a single combustion step, the chemical processes underlying sewage sludge combustion were analysed using powder X-ray diffraction (P-XRD), infrared spectroscopy (IR), thermogravimetric (TGA) as well as elemental analyses (EA). In addition to the combustion of sewage sludge on its own ("mono-combustion"), additions of different additives prior to the combustion step were also carried out. Based on the very positive effects of the additives sodium and potassium carbonate on the obtained ashes concerning their phosphate solubilities in neutral ammonium citrate (NAC) solution, sewage sludge combustions after additions of Na2CO3 or K2CO3 were investigated in detail. We found that these additions altered the main phosphate-containing product found in the ashes from whitlockite (Ca9(Mg,Fe)(PO3OH)(PO4)6), a hardly plant-accessible species, to other phosphate containing compounds such as buchwaldite (CaNaPO4), which is known for a long time as a very good P-source for plants. Consecutive greenhouse experiments with maize (Zea mays L.) as test plant confirmed the results of the chemical analyses and demonstrated that Na- or K-ashes obtained from a "co-combustion" of sewage sludge mixed with alkali carbonates exhibit relative P-fertilising efficiencies of up to ~80 % in comparison to commercial superphosphate, making these materials promising surrogate phosphate mineral sources for agricultural production.

One-Step Esterification of Phosphoric, Phosphonic and Phosphinic Acids with Organosilicates: Phosphorus Chemical Recycling of Sewage Waste

Global concerns regarding the depletion and strategic importance of phosphorus resources have increased demand for the recovery and recycling. However, waste-derived phosphorus compounds, primarily as chemically inert phosphoric acid or its salts, present a challenge to their direct conversion into high-value chemicals. We aimed to develop an innovative technology that utilizes the large quantities of sewage waste, bypasses the use of white phosphorus, and enables esterification of phosphoric acid to produce widely applicable phosphate triesters. Tetraalkyl orthosilicates emerged as highly effective reagents for the direct triple esterification of 85 % phosphoric acid, as well as the esterification of organophosphinic and phosphonic acids. Furthermore, we achieved esterification of recovered phosphoric acid with tetraalkyl orthosilicate, thus pioneering a recycling pathway from sewage waste to valuable phosphorus chemicals. Experimental and theoretical investigations revealed a novel mechanism, wherein tetraalkyl orthosilicates facilitate multimolecular aggregation to achieve alkyl transfer from tetraalkylorthosilicate to phosphoric acid via multiple proton shuttling.

Heterogeneous Interface Engineering of 2D Black Phosphorus-Based Materials for Enhanced Photocatalytic Performance

Photocatalysis has garnered significant attention as a sustainable approach for energy conversion and environmental management. 2D black phosphorus (BP) has emerged as a highly promising semiconductor photocatalyst owing to its distinctive properties. However, inherent issues such as rapid recombination of photogenerated electrons and holes severely impede the photocatalytic efficacy of single BP. The construction/stacking mode of BP with other nanomaterials decreases the recombination rate of carriers and extend its functionalities. Herein, from the perspective of atomic interface and electronic interface, the enhancement mechanism of photocatalytic performance by heterogeneous interface engineering is discussed. Based on the intrinsic properties of BP and corresponding photocatalytic principles, the effects of diverse interface characteristics (point, linear, and planar interface) and charge transfer mechanisms (type I, type II, Z-scheme, and S-scheme heterojunctions) on photocatalysis are summarized systematically. The modulation of heterogeneous interfaces and rational regulation of charge transfer mechanisms can enhance charge migration between interfaces and even maximize redox capability. Furthermore, research progress of heterogeneous interface engineering based on BP is summarized and their prospects are looked ahead. It is anticipated that a novel concept would be presented for constructing superior BP-based photocatalysts and designing other 2D photocatalytic materials.

Glycogen-accumulating organisms promote phosphate recovery from wastewater by pilot-scale biofilm sequencing batch reactor: Performance and mechanism

A high phosphate (P) recovery concentration was achieved in pilot-scale biofilm sequencing batch reactor (BSBR) with a low carbon source (C) cost. Especially, a high-abundance glycogen-accumulating organisms (GAOs) (13.93-31.72%) was detected that was accompanied by a high P recovery concentration of BSBR. High-abundance GAOs obtain additional C through various C compensation pathways (split tricarboxylic acid cycle (TCA cycle), glyoxylate shunt and gluconeogenesis), thus reducing the need to compete with polyphosphate-accumulating organisms (PAOs) for C and weakening the adverse effects on P recovery by PAO cells. Under the action of N-acyl homoserine lactones (AHLs)-mediated quorum sensing (QS), GAOs promoted the secretion of a large amount of extracellular polymeric substances (EPS), which helped to realize the P recovery of EPS-dominated biofilms (68.02%-96.89%). This study provides a low-carbon technology for the recovery of high concentration P from municipal wastewater, and improves the ecological theory of P recovery in collaboration with GAOs and PAOs.

The Future of Phosphoric Acid Production -Why We Have to Leave Trodden Paths

This paper examines the need for innovation in phosphorus fertilizer production. An important area requiring action is the use of sulfuric acid in the wet chemical process (WCP), which is the dominant process in phosphate fertilizer production. About 50 % of the sulfuric acid produced worldwide is used for fertilizers, and ~95 % of the world's fertilizers are based on sulfuric acid. The latter is almost exclusively a by-product of gas and oil production, so the production of conventional P fertilizer is largely dependent on the availability of oil and gas. In addition to rendering P fertilizer production independent of fossil raw materials, energy consumption, CO2 emissions, phosphogypsum production and water consumption should also be considered. With the example of the PARFORCE process and the Improved Hard Process (IHP), new non-sulfuric acid-based alternatives are discussed with respect to overcoming the drawbacks of the classical WCP by being completely independent of fossil sources, working with renewable energies as the sole energy source, and the option of using seawater instead of fresh water. These new processes adhere to the principles of climate neutrality, zero waste production, low CO2 footprint, water conservation, renewable energy use, and energy and resource efficiency. This demonstrates what sustainable innovation can look like from a production perspective. The discussion will focus on whether current incentives are sufficient to realize the sustainability innovations discussed.

Phosphorus bioavailability and recycling potential in various organic Waste: Assessment by enzymatic hydrolysis and 31P NMR

Phosphorus(P) recycling from waste streams is crucial to mitigate the P depletion crisis. P forms and contents in organic waste are critical for determining the recycling method and efficiency. We constructed an approach to characterize P forms in seven organic waste by combining chemical sequential extraction, enzymatic hydrolysis, and nuclear magnetic resonance(NMR). Livestock manure and straw exhibited a higher active P(H2O-P&NaHCO3-P)(70.54%-84.40% and 65.78%-85.26% of total P) than sewage sludge(18.22%) and food waste(43.90%). Enzymatic hydrolysis revealed over 10% P in the so-called active P of corn(11.30%) and rice straw(13.32%) was phytate-like P, which is not bioavailable. These findings indicate the chemical sequential extraction inaccurately gauges bioavailable-P and underscores the need to convert phytate into plant-available P in recycling processes(biogas, composting), especially for crop straws and chicken manure. This work introduces a novel methodological framework for assessing P potential bioavailability in organic waste, providing fundamental knowledge for the P recycling process optimization.

Effects of additives on shifting phosphorus to solid phase during Solid-Liquid separation of digestate in full-scale biogas plant

Phosphorus (P) is critical for plant growth, but global reserves are exhausting within 250-300 years, therefore enhancing phosphate recycling is crucial for the future. Biogas digestate, rich with nutrients is a promising resource for nutrient recovery. Conventional solid-liquid separation shifts approximately 35 % of the total P in the digestate to the solid phase. Separation trials with additive treatment using a screw press with a 0.75 mm sieve were performed at University of Hohenheim's full-scale biogas plant. After 22 h, 67.41 % (kieserite treatment) and 52.35 % (strawflour treatment) of total P shifted to the solid phase. Treatment with kieserite enhanced P shift into the solid phase by forming non-labile fractions through a chemical bond between P and Mg2+ ions. Kieserite treatment for 22 h effectively increases the share of total P in the separated solid phase, it also ensures a sustainable nutrient supply and mitigates the risk of nutrient runoff.

Effect of thermochemical treatment of sewage sludge on its phosphorus leaching efficiency: Insights into leaching behavior and mechanism

Thermochemical conversion, including hydrothermal processing, pyrolysis and incineration, has become a promising technology for sewage sludge (SS) treatment and disposal. Furthermore, acid leaching is considered as an effective method to recover phosphorus (P) from SS and its thermochemical treatment products. This study has investigated the potential of P reclamation from SS and its thermochemical derivatives, including hydrochar (HC), biochar (BC), and SS incinerated ash (SA). Comparative analyses of physicochemical properties of these derivatives revealed a decrease in hydroxyl and aromatic groups and an increase in aliphatic and oxygen-containing functional groups in HC and BC. Leaching experiments using 1 M sulfuric acid (H2SO4) and 1 M oxalic acid (C2H2O4) suggested that H2SO4 slightly outperformed C2H2O4 in terms of P leaching efficiency. HC achieved 79.1 % optimal leaching efficiency in 60 min using H2SO4, while BC, SS, and SA required 360 min to achieve comparable efficiency. SS and BC reached optimal leaching efficiency at 74.1 % and 76.2 % in H2SO4, while SA achieved 80.9 % in C2H2O4. Importantly, HC and SA are more favorable for P extraction using acid leaching, whereas BC tends to be a potential P carrier. Time-dependent kinetics revealed a two-stage leaching process, i.e., fast and slow reaction stages. Shrinking core model indicates product layer diffusion as the primary rate-limiting step in both stages. Overall, these fundamental insights play an important role in practical P recovery through acid leaching of SS derived residues after thermochemical treatment.

Selectively self-recyclable, highly transparent and fire-safe polycarbonate plastic enabled by thermally responsive phosphonium-phosphate

Both the circular economy and fire-safety of polymer plastics have become a global consensus. Herein, an integrated strategy for selectively self-recyclable, highly-transparent and fire-safe polycarbonate plastic is proposed by thermally responsive phosphonium-phosphate (DP). During its service life, DP, as a flame-retardant with good compatibility, enables polycarbonate plastic with high transparency in visible light, excellent self-extinguishing and high fire-safety. After consumption, DP, as a catalyst, triggers the selective self-recycling of DP-containing polycarbonate in mixed plastics and even in same-kind polycarbonate plastics without an external catalyst. Importantly, the oxygen-consuming mechanism at high temperature in fire accidents (>350 °C) and the double hydrogen bond catalysis mechanism at a lower temperature (180 °C) of DP are key to the life cycle management of polycarbonate from use-stage to post-consumption. This work inspires a new solution to plastic pollution by designing sustainable plastics that satisfy both service-stage and end-of-life criteria, striving towards a zero-waste circular economy.

31P Nuclear Magnetic Resonance Spectroscopy for Monitoring Organic Reactions and Organic Compounds

31P NMR spectroscopy is a consolidated tool for the characterization of organophosphorus compounds and, more recently, for reaction monitoring. The evolution of organic synthesis, mainly due to the combination of elaborated building blocks with enabling technologies, generated great challenges to understand and to optimize the synthetic methodologies. In this sense, 31P NMR experiments also became a routine technique for reaction monitoring, accessing products and side products yields, chiral recognition, kinetic data, intermediates, as well as basic organic parameters, such as acid-base and hydrogen-bonding. This review deals with these aspects demonstrating the essential role of the 31P NMR spectroscopy. The recent publications (the last ten years) will be explored, discussing the experiments of 31P NMR and the strategies accomplished to detect and/or quantify distinct organophosphorus molecules, approaching reaction mechanism, stability, stereochemistry, and the utility as a probe.

Spatial and temporal dynamics of sewage sludge phosphorus recovery potential in the cities of Yangtze River Zone in China: Implications for regional recycling policies

Sewage sludge phosphorus (P) recovery presents opportunities to sustainably recycle P from cities to agriculture and alleviate global P scarcity. However, limited research explores sustainable recovery targets considering spatial-temporal variations in sludge generation and implications based on city-level local P demand. This study analyzed sludge production form 2009-2021 across 130 cities in China's Yangtze River Zone, which increased by almost 35 % from 2009 to 2021. Per capita gross domestic product (GDP), influent chemical oxygen demand (COD), and per capita drainage infrastructure were identified as the main significant influencing factors. City-level analysis revealed pronounced spatial-temporal disparities, with yearly sludge generation spanning five orders of magnitude (62-5.4 × 105 t/a). An indicator, "Potential of P recovery to local P demand", was defined, indicating the average city-level P recycle contribution increased from 5.3 % to 18.9 % from 2009-2021. A novel frame paradigm classified cities into six types based on the local P supply-demand characteristics, prioritizing sludge P recovery and implementing strategic management. City-specific dynamics and possibilities of broader "city clusters" to match supply and demand should be considered for policy implement. Recovering P from livestock manure and kitchen waste alongside sludge can further strengthen urban P cycles. This study provides novel city-scale analysis and strategic considerations for regional sludge P recycling policies in China and beyond.

Food industry side streams: an unexploited source for biotechnological phosphorus upcycling

The phosphorus shortage is an unavoidable challenge that requires strategies to replace phosphorus sourced from ores. Food industry by-products are an unscoped resource for sustainable phosphorus recovery. Recent advances include biotechnological phosphorus upcycling from phytate-rich plant residues to polyphosphate as a food additive. The valorization of by-products such as deoiled seeds or brans additionally provides low-phosphorus feed and thereby minimizes the environmental burden. Phytate reduction in a cereal-rich diet by adding enzyme formulation is a further strategy that limits its antinutritive effect. However, sustainable P-management depends on phytases that have been customized and enhanced for thermostability and specific activity. The circular phosphorus economy is driven by emerging value chains and maturing phosphorus recovery technologies for market entry.

Enhanced phosphorus removal from anoxic water using oxygen-carrying iron-rich biochar: Combined roles of adsorption and keystone taxa

Anthropogenic enrichment of phosphorus (P) in water environment can cause eutrophication, harmful algal blooms, and water quality deterioration. Adsorbents are often used for the removal and recovery of P from water, however, P is highly susceptible to re-release in anoxic benthic environments. As a response, this study prepared oxygen-carrying iron-rich biochar (O-Fe-BC) as an effective oxygen micro-nanobubble carrier (Q = 8.7024 cm³/g STP at 1.5 MPa) and P adsorbent (qm = 16.7097 mg P/g, q0.1 = 3.1974 mg P/g). Over the 90-day experimental period with O-Fe-BC, dissolved oxygen (DO) levels in the overlying water could maintain at ∼4 mg/L (peaking at ∼9.5 mg/L), and total phosphorus (TP) and soluble reactive phosphorus (SRP) levels decreased by over 96 %. The higher inorganic phosphorus content in the surface sediment-biochar mixture, along with the lower labile P and Fe concentration in the sediment pore water in the O-Fe-BC group compared to other groups, suggested the enhanced P immobilization. Further mechanism exploration revealed the combined roles of adsorption and microbial response, in which O-Fe-BC achieved efficient phosphate adsorption primarily through inner-sphere complexation via ligand exchange and keystone taxa (particularly Candidatus Electronema) played a crucial role in driving water chemistry divergence. Specially, these cable bacteria could provide large pools of Fe oxides in the surface sediment, binding with P to prevent its release, as supported by significant correlations between Ca. Electronema abundance and oxidation-reduction potential (ORP), TP, SRP, and sediment Fe-P variations. Additionally, a pot experiment with mung bean seedlings showed that the recovered O-Fe-BC significantly promoted the seed germination and growth, indicating its potential as a novel material for removing and recovering P from eutrophic waters. Taken together, our work provided a promising strategy for sustainable anoxia and P pollution mitigation, and also highlighted the indispensable roles of inner-sphere adsorption in P recovery and microbial keystone taxa in P cycling regulation.

A polychloride-enabled synthesis of [NEt3Me][PCl6] serving as a potential PCl3-storage and PCl5-reagent

Reaction of the ionic liquid [NEt3Me][Cl3] with white phosphorus (P4) gives, quantitatively, hexachlorophosphate [NEt3Me][PCl6]. This compound shows similar reactivity as PCl5, as confirmed for the reaction with phenol, carboxylic acids and ammonium chloride. At elevated temperature, [NEt3Me][PCl6] releases PCl3 and can therefore be used as a potential PCl3-storage material.

Screening of metal-modified biochars for practical phosphorus recovery

The utilization of metal-modified biochars (MBCs) for practical phosphorus recovery has attracted significant research interest recently. However, the optimal choice of metals and modification methods for MBCs remains unclear. This study addresses this gap by comparing the phosphate adsorption capabilities of various MBCs using real municipal wastewater. The results show that zinc-modified biochar exhibits superior phosphate adsorption compared to biochars modified with calcium, magnesium, aluminum, and iron. Specifically, zinc-modified biochar prepared through metal-mediated biomass pyrolysis with alkaline soaking (ZnBC-OH) demonstrates the highest adsorption capacity, achieving 36.6 mg P/g in wastewater with a phosphate concentration of 5 mg P/L. This performance surpasses that of previously reported non-lanthanide modified biochars and is comparable to lanthanide-modified biochars. Mechanistic investigations reveal that the exceptional performance of ZnBC-OH is due to the presence of highly dispersed ZnO sites, which facilitate the formation of Zn3(PO4)2·4H2O precipitation, effectively retaining phosphate. Furthermore, a techno-economic analysis indicates that using ZnBC-OH in a fixed-bed column system can reduce phosphate levels from 6 mg L-1 to below 0.5 mg L-1 at a cost of 1.834 USD per ton of secondary treated wastewater, underscoring its promising application potential.

Optimizing phosphorus precipitation from acidic sewage sludge ash leachate: Use of Mg-rich mining by-products for enhanced nutrient recovery

Phosphorus recovery from Sewage Sludge Ashes (SSA) by wet chemical extraction followed by selective precipitation has gained great attention in recent years, attempting to reduce the anthropic pressure on natural reserves. This study investigates the selective precipitation process at lab- and small pilot-scales by means of two conventional and one innovative precipitating agents, the latter derived from a low-grade magnesium oxide mining by-product (LG-MgO named PC8), assessing the role of the most relevant operating parameters. Lab-scale experiments were performed on leachates obtained from bottom and fly ashes, in which several operating conditions were tested, differing in the type of precipitating agent, target pH and nutrient molar ratio. Based on experimental results, small pilot-scale experiments were conducted with Ca(OH)2 and PC8 at pH 7. Effective phosphorus precipitation was obtained at lab-scale at pH equal to 4 for high Al/P molar ratio, while SSA leachate with low Al/P molar ratio promoted improved phosphorus precipitation (>90%) only at pH higher than 8 with PC8. Small pilot-scale findings confirmed the effectiveness of PC8 in increasing simultaneously the pH and the nutrient content of the solid precipitate. The comprehensive assessment of the samples denoted compliance with the European Regulation (EU 2019/1009), which allows the formulation of different fertilizers with agronomic relevance. This is the first time that experiments from small pilot-scale tests in the field of phosphorus recovery from SSA were investigated using an innovative precipitant providing key information for the process scale-up.

Interactions between Struvite and Humic Acid and Consequences on Fertilizer Efficiency in a Nonacidic Soil

The effect of humic acid extracted from peat (AHt) on improving the struvite (STR) fertilizing efficiency is explored. To this end, a soil incubation study is correlated to plant assays comparing STR, STR-AHt, and superphosphate (SSP). Characterization techniques confirm the incorporation of the AHt into the STR. The P-pool distribution of STR and SSP is similar in the soil incubation, with STR-AHt presenting a higher labile P at 90 days passing from 10 to 15% P from SSP and STR to 25% P with STR-AHt. However, when applied to barley and tomato, STR yields more shoot P content, aboveground biomass, and residual P in soil than SSP. STR-AHt does not improve the STR results. The poor correlation observed between soil incubation and plant trials highlights the role of the rhizosphere in testing the fertilizer efficiency of STR. Mechanistic assays indicate the key role of rhizosphere pH. Finally, molecular modeling reveals a higher stabilization of STR with AHt, which could reduce P release decreasing the fertilizing potential of STR-AHt, as observed in the pot trials.

Efficient phosphorus recovery from waste activated sludge: Pretreatment with natural deep eutectic solvent and recovery as vivianite

Recycling phosphorus from waste activated sludge (WAS) is an effective method to address the nonrenewable nature of phosphorus and mitigate environmental pollution. To overcome the challenge of low phosphorus recovery from WAS due to insufficient disintegration, a method using a citric acid-based natural deep eutectic solvent (CA-NADES) assisted with low-temperature pretreatment was proposed to efficiently release and recover phosphorus. The results of 31P nuclear magnetic resonance (NMR) confirmed that low-temperature pretreatment promoted the conversion of organic phosphorus (OP) to inorganic phosphorus (IP) and enhanced the effect of CA-NADES. Changes in the three-dimensional excitation-emission matrix (3D-EEM) and flow cytometry (FCM) indicated that the method of CA-NADES with low-temperature thermal simultaneously release IP and OP by disintegrating sludge flocs, dissolving extracellular polymeric substances (EPS) structure, and cracking cells. When 5 % (v/v) of CA-NADES was added and thermally treated at 60 °C for 30 min, 43 % of total phosphorus (TP) was released from the sludge. The concentrations of proteins and polysaccharides reached 826 and 331 mg/L, respectively, which were 6.30 and 14.43 times higher than those of raw sludge. The dewatering and settling of the sludge were also improved. Metals were either enriched in the solid phase or released into the liquid phase in small quantities (most efficiencies of less than 10 %) for subsequent clean recovery. The released phosphorus was successfully recovered as vivianite with a rate of 90 %. This study develops an efficient, green, and sustainable method for phosphorus recovery from sludge using NADES and provides new insights into the high-value conversion of sludge.

Reagent-free phosphorus precipitation from a denitrified swine effluent in a batch electrochemical system

There is high interest in the recovery of phosphorus (P) from wastewater through crystallization processes. However, the addition of chemical reagents (e.g., sodium hydroxide) to raise the pH may result in high treatment costs and increased concentrations of undesired metal ions (e.g., sodium). As an alternative, in this research we considered electrochemical mediated precipitation at low current densities (0.4-1.2 A m-2) without using chemical reagents. For that purpose, a two-chamber electrochemical system was operated in batch for treating denitrified swine effluent (48 mg P L-1). By applying current at 1.2 A m-2, and targeting pH 11.5, a maximum P removal rate of 33.4 mmol P (L·d-1) was obtained while the P removal efficiency was above 90 %. New solids that formed mostly remained suspended in the catholyte. Before discharge, the catholyte effluent was recirculated to the anodic compartment to neutralize the pH, achieving a final pH of 6.4 ± 0.1. Chlorine (Cl2) production in the anodic compartment was favored by a small anode surface and a high initial pH of the catholyte. Although the production of chlorine achieved was limited (the highest concentration was 8.6 ± 0.1 mg Cl2 L-1) these findings represent a new opportunity for the recovery and onsite use of this side-product. Electrochemical impedance spectroscopy tests confirmed that the deposition of solids inside the cathodic compartment during the experimental period was limited. Membrane analysis revealed significant scaling of carbonate compounds. The electrochemical treatment described above was shown as a promising alternative to sodium hydroxide and sulfuric acid dosage for pH adjustment when crystallizing phosphate salts.

Phosphorous speciation in EPS extracted from Aerobic Granular Sludge

Wastewater treatment technologies opened the door for recovery of extracellular polymeric substances (EPS), presenting novel opportunities for use across diverse industrial sectors. Earlier studies showed that a significant amount of phosphorus (P) is recovered within extracted EPS. P recovered within the extracted EPS is an intrinsic part of the recovered material that potentially influences its properties. Understanding the P speciation in extracted EPS lays the foundation for leveraging the incorporated P in EPS to manipulate its properties and industrial applications. This study evaluated P speciation in EPS extracted from aerobic granular sludge (AGS). A fractionation lab protocol was established to consistently distinguish P species in extracted EPS liquid phase and polymer chains. 31P nuclear magnetic resonance (NMR) spectroscopy was used as a complementary technique to provide additional information on P speciation and track changes in P species during the EPS extraction process. Findings showed the dominance of organic phosphorus and orthophosphates within EPS, besides other minor fractions. On average, 25% orthophosphates in the polymer liquid phase, 52% organic phosphorus (equal ratio of mono and diesters) covalently bound to the polymer chains, 16% non-apatite inorganic phosphorus (NAIP) precipitates mainly FeP and AlP, and 7% pyrophosphates (6% in the liquid phase and 1% attached to the polymer chains) were identified. Polyphosphates were detected in initial AGS but hydrolyzed to orthophosphates, pyrophosphates, and possibly organic P (forming new esters) during the EPS extraction process. The knowledge created in this study is a step towards the goal of EPS engineering, manipulating P chemistry along the extraction process and enriching certain P species in EPS based on target properties and industrial applications.

Phosphorus recovery via struvite crystallization in batch and fluidized-bed reactors: Roles of microplastics and dissolved organic matter

Struvite crystallization, a promising technology for nutrient recovery from wastewater, is facing considerable challenges due to the presence of emerging contaminants such as microplastics (MPs) ubiquitously found in wastewater. Here, we investigate the roles of MPs and humic acid (HA) in struvite crystallization in batch and fluidized-bed reactors (FBRs) using synthetic and real wastewater with a Mg:N:P molar ratio of 1:3:(1-1.3) at an initial pH of 11. Batch reactor (BR) experiment results show that MPs expedited the nucleation and growth rates of struvite (e.g., the rate of crystal growth in the presence of 30 mg L-1 of polyethylene terephthalate (PET) was 1.43 times higher than that in the blank system), while HA hindered the formation of struvite. X-ray diffraction and the Rietveld refinement analysis revealed that the presence of MPs and HA can result in significant changes in phase compositions of the reclaimed precipitates, with over 80 % purity of struvite found in the precipitates from suspensions in the presence of 30 mg L-1 of MPs. Further characterizations demonstrated that MPs act as seeds of struvite nucleation, spurring the formation of well-defined struvite, while HA favors the formation of newberyite rather than struvite in both reactors. These findings highlight the need for a more comprehensive understanding of the interactions between emerging contaminants and struvite crystallization processes to optimize nutrient recovery strategies for mitigating their adverse impact on the quality and yield of struvite-based fertilizers. ENVIRONMENTAL IMPLICATION: The presence of microplastics in wastewater poses a significant challenge to struvite crystallization for nutrient recovery, as it accelerates nucleation and growth rates of struvite crystals. This can lead to changes in the phase compositions of the reclaimed precipitates, with implications for the quality and yield of struvite-based fertilizers. Additionally, the presence of humic acid hinders the formation of struvite, favoring the formation of other minerals like newberyite. Understanding the interactions between emerging contaminants and struvite crystallization processes is crucial for optimizing nutrient recovery strategies and mitigating the environmental impact of these contaminants on water quality and struvite-based fertilizers.

Metal-doped biochar for selective recovery and reuse of phosphate from water: Modification design, removal mechanism, and reutilization strategy

Phosphorus (P) plays a crucial role in plant growth, which can provide nutrients for plants. Nonetheless, excessive phosphate can cause eutrophication of water, deterioration of aquatic environment, and even harm for human health. Therefore, adopting feasible adsorption technology to remove phosphate from water is necessary. Biochar (BC) has received wide attention for its low cost and environment-friendly properties. However, undeveloped pore structure and limited surface groups of primary BC result in poor uptake performance. Consequently, this work introduced the synthesis of pristine BC, parameters influencing phosphate removal, and corresponding mechanisms. Moreover, multifarious metal-doped BCs were summarized with related design principles. Meanwhile, mechanisms of selective phosphate adsorption by metal-doped BC were investigated deeply, and the recovery of phosphate from water, and the utilization of phosphate-loaded adsorbents in soil were critically presented. Finally, challenges and prospects for widespread applications of selective phosphate adsorption were proposed in the future.

Advancing sustainable wastewater management: A comprehensive review of nutrient recovery products and their applications

Wastewater serves as a vital resource for sustainable fertilizer production, particularly in the recovery of nitrogen (N) and phosphorus (P). This comprehensive study explores the recovery chain, from technology to final product reuse. Biomass growth is the most cost-effective method, valorizing up to 95 % of nutrients, although facing safety concerns. Various techniques enable the recovery of 100 % P and up to 99 % N, but challenges arise during the final product crystallization due to the high solubility of ammonium salts. Among these techniques, chemical precipitation and ammonia stripping/ absorption have achieved full commercialization, with estimated recovery costs of 6.0-10.0 EUR kgP-1 and 4.4-4.8 £ kgN-1, respectively. Multiple technologies integrating biomass thermo-chemical processing and P and/or N have also reached technology readiness level TRL = 9. However, due to maturing regulatory of waste-derived products, not all of their products are commercially available. The non-homogenous nature of wastewater introduces impurities into nutrient recovery products. While calcium and iron impurities may impact product bioavailability, some full-scale P recovery technologies deliver products containing this admixture. Recovered mineral nutrient forms have shown up to 60 % higher yield biomass growth compared to synthetic fertilizers. Life cycle assessment studies confirm the positive environmental outcomes of nutrient recycling from wastewater to agricultural applications. Integration of novel technologies may increase wastewater treatment costs by a few percent, but this can be offset through renewable energy utilization and the sale of recovered products. Moreover, simultaneous nutrient recovery and energy production via bio-electrochemical processes contributes to carbon neutrality achieving. Interdisciplinary cooperation is essential to offset both energy and chemicals inputs, increase their cos-efficiency and optimize technologies and understand the nutrient release patterns of wastewater-derived products on various crops. Addressing non-technological factors, such as legal and financial support, infrastructure redesign, and market-readiness, is crucial for successfully implementation and securing the global food production.

Minimization of heavy metal adsorption in struvite through effective separation and manipulation of flow field

The admixture of heavy metals on struvite during the P recovery process from wastewater will affect its value for safe agricultural application, but it is not clear how to effectively separate heavy metals from struvite. Herein, a two-stage separation reactor (static and dynamic) has been developed to achieve efficient separation of heavy metals and struvite. The generation of struvite from real swine wastewater would naturally precipitate to the lowest layer under static conditions, leading to an enrichment of heavy metals (75 % Cu and 84 % Zn) in suspension. Meanwhile, phosphorus recovery from real swine wastewater results in the generation of a large amount of fines flowing out of the reactor due to the effects of suspended solids (SS), etc., making it necessary to recover phosphorus by static separation. For the dynamic separation step, we also analyzed the characteristics of struvite formation at different rotational speeds in a continuous reaction system. The results demonstrated that the shear rate of the fluid affects the particle size of struvite, which in turn determines the rate and the distribution of struvite in either primary or secondary recovery tanks. The implementation of zonal regulation in the flow field can produce a higher phosphorus efficiency (from 85.8 to 95.5 % at pH=8.1-8.2, from 93.8 to 98.5 % at pH=9.0-9.1) and a lower alkali consumption (55.56 % of alkali cost), which is favorable for the separation of struvite crystals and heavy metals (the amount of Cu and Zn metals separated increased by more than 50 %), and ultimately yield high quality of struvite. The findings in this study will provide insights for the separation and reduction of heavy metals through a combined method with dynamic and static in a continuous system, providing a reference for the safe application of struvite in agriculture.

Study on the occurrence state of main components of phosphogypsum dihydrate and its impurity distribution

The dihydrate phosphoric acid process is the mainstream technique. However, the phosphogypsum (PG) produced contains high levels of impurities such as phosphorus and fluorine, severely constraining its valorization. In order to elucidate the occurrence patterns of phosphorus and fluorine impurities in PG, this study employed analytical methods including XRF, XRD, AMICS (Automated Mineralogy Integrated with Chemistry System), XPS, and chemical element balance analysis. We investigated the occurrence states of phosphorus, fluorine, silicon, iron, and aluminum elements in PG from wet-process phosphoric acid production, as well as the distribution characteristics of phosphorus and fluorine impurities. Additionally, we utilized Density Functional Theory (DFT) calculations to determine the binding energies of major minerals with water-soluble phosphate and fluoride groups, and analyzed the zeta potentials of gypsum and quartz mineral surfaces. The results indicate that the main mineral phases in PG are gypsum, quartz, potassium silicate minerals, aluminosilicate minerals, and hematite, predominantly occurring in monomineralic forms. Phosphorus impurities primarily exist in calcium silicate and hematite minerals, while fluorine is mainly associated with gypsum and potassium silicate minerals. DFT calculations demonstrate strong binding energies between calcium silicate and hematite minerals with PO4 3-, as well as between gypsum and quartz minerals with F-. The acidic conditions in the separation tank during wet-process phosphoric acid production may contribute to the distinctive distribution characteristics of phosphorus and fluorine impurities in PG.

Magnetic field-assisted adsorption of phosphate on biochar loading amorphous Zr-Ce (carbonate) oxide composite

For metal-based phosphate adsorbents, the dispersity and utilization of surface metal active sites are crucial factors in their adsorption performance and synthesis cost. In this study, a biochar material modified with amorphous Zr-Ce (carbonate) oxides (BZCCO-13) was synthesized for the phosphate uptake, and the adsorption process was enhanced by magnetic field. The beside-magnetic field was shown to have a better influence than under-magnetic field on adsorption, with maximum adsorption capacities (123.67 mg P/g) 1.14-fold greater than that without magnetic field. The beside-magnetic field could also accelerate the adsorption rate, and the time to reach 90% maximum adsorption capacity decreased by 83%. BZCCO-13 has a wide range of application pHs from 5.0 to 10.0, with great selectivity and reusability. The results of XPS and ELNES showed that the "magnetophoresis" of Ce3+ under the magnetic field was the main reason for the enhanced adsorption performance. In addition, increased surface roughness, pore size and oxygen vacancies, enhanced mass transfer by Lorentz force under a magnetic field, all beneficially influenced the adsorption process. The mechanism of phosphate adsorption by BZCCO-13 could be attributed to electrostatic attraction and CO32-dominated ligand exchange. This study not only provided an effective strategy for designing highly effective phosphate adsorbents, but also provides a new light on the application of rare earth metal-based adsorbent in magnetic field.

Sludge reduction, nitrous oxide emissions, and phosphorus removal by oxic-settling-anaerobic (OSA) process: the effect of hydraulic retention time

This paper presents a study on reducing sewage sludge by an oxic-settling-anaerobic (OSA) pilot plant compared to the conventional activated sludge (CAS) process in view of resource recovery and moving towards plant carbon neutrality. The OSA plant was supplied with real wastewater and the anaerobic reactor was operated under two hydraulic retention times (HRT) (4 and 6 h). Greenhouse gas (GHG) emissions were monitored for the first time to determine the OSA process's production mechanism. The results highlighted that under the lowest HRT (4 h), the removal efficiencies of COD and PO4-P, increased from 75 to 89% and from 39 to 50% for CAS and OSA configurations, respectively. The observed yield coefficient was reduced from 0.58 gTSS gCOD-1 (CAS period) to 0.31 gTSS gCOD-1 (OSA period). A remarkable deterioration of nitrification efficiency under OSA configuration was obtained from 79% (CAS) to 27% (OSA with HRT of 6 h). The huge deterioration of nitrification significantly affected the GHG emissions, with the N2O-N fraction increasing from 1% (CAS) to 1.55% (OSA 4 h HRT) and 3.54% (OSA 6 h HRT) of the overall effluent nitrogen, thus suggesting a relevant environmental implication due to the high global warming potential (GWP) of N2O.

Multi-criteria analysis of strategies towards sustainable recycling of phosphorus from sewage sludge in Austria

To promote optimal phosphorus (P) recovery from municipal wastewater and sewage sludge with viable legal instruments, it is imperative to understand the regional and national consequences of different legal requirements for recycling. In this study we develop a scenario-based analysis to assess the environmental and economic impact of different national P recovery strategies in the context of a detailed representation of the existing Austrian wastewater infrastructure. This assessment combines material flow analysis, life cycle assessment and life cycle costing and includes the indicators P recycling rate, P utilization degree, heavy metal removal rate, share of heavy metals' content in wastewater redirected to agricultural soils, global warming potential, cumulated energy demand, terrestrial acidification potential, volume of freight transport and annual costs. The following main conclusions can be drawn. P recovery from ash shows the highest potential regarding the utilization of P from wastewater. A high P utilization from wastewater should rely on recovery technologies that decontaminate products, otherwise pollutant loads to agricultural soils might increase. P recovery to the extent of 60-85 % of P in WWTPs influent can be achieved by savings/costs of -0.8 to +4.7 EUR inhabitant-1 yr-1 in addition to current cost of the wastewater treatment/sludge disposal system. Key factors to be considered for costs are the choice of recovery process, revenues from products, and the use of existing incineration infrastructure. P recovery can lead to the reduction of greenhouse gas emissions in Austria if nitrous oxide emissions from sludge incineration are limited and efficient heat utilization strategies are implemented. There is a trade-off in terms of environmental and economic costs in choosing a more centralized or decentralized mono-incineration strategy.

Recent progress on the functionalization of white phosphorus in China

Direct synthesis of organophosphorus compounds from white phosphorus represents a significant but challenging subject, especially in the context of ongoing efforts to comprehensively improve the phosphorus-derived chemical industry driven by sustainability and safety concerns. China is the world's largest producer of white phosphorus, creating a significant demand for the green transformation of this crucial feedstock. This review provides an overview of advancements in white phosphorus activation by Chinese research teams, focusing on the direct construction of P‒C/N/O/S/M bonds from white phosphorus. Additionally, we offer some insights into prospective directions for the activation and transformation of white phosphorus in the future. This review paper aims to attract more researchers to engage in this area, stimulating follow-up exploration and fostering enduring advances.

Assessment of three different approaches for integrating phosphorus recovery from sewage sludge and derived products in existing wastewater treatment plants

Three different technological solutions, namely acidogenic fermentation and chemical extraction (alkaline or acidic), followed by precipitation with 1% Ca(OH)2, were investigated in the view of integrating phosphorus recovery into existing wastewater treatment plants. Experiments were conducted at the lab-scale using (i) sludge taken from biologically and chemically promoted phosphorus removal activated sludge processes and (ii) ashes obtained from sludge muffle incineration. Results highlighted the benefits of enhanced biological phosphorus removal (EBPR) systems rather than chemically promoted phosphorus removal in not only phosphorus extraction (up to 40% with EBPR) and recovery directly from secondary sludge (P precipitation between 66 and 92%), but after sludge incineration as well (P extraction up to 96% and precipitation above 96%). Acidogenic fermentation ensured the highest phosphorus release from EBPR sludge (equal to a concentration in solution of 122 mg/L P-PO43-), while the derived ashes had a lower level of metal contamination (particularly Fe and Al content < 2%). The phosphorus-rich product obtained by means of the recovery process showed relevant metal contamination (Cu, Zn, and Ni) under some operating conditions, suggesting the need for further treatments.

Combined Computational and Experimental Study Reveals Complex Mechanistic Landscape of Brønsted Acid-Catalyzed Silane-Dependent P═O Reduction

The reaction mechanism of Brønsted acid-catalyzed silane-dependent P═O reduction has been elucidated through combined computational and experimental methods. Due to its remarkable chemo- and stereoselective nature, the Brønsted acid/silane reduction system has been widely employed in organophosphine-catalyzed transformations involving P(V)/P(III) redox cycle. However, the full mechanistic profile of this type of P═O reduction has yet to be clearly established to date. Supported by both DFT and experimental studies, our research reveals that the reaction likely proceeds through mechanisms other than the widely accepted "dual activation mode by silyl ester" or "acid-mediated direct P═O activation" mechanism. We propose that although the reduction mechanisms may vary with the substitution patterns of silane species, Brønsted acid generally activates the silane rather than the P═O group in transition structures. The proposed activation mode differs significantly from that associated with traditional Brønsted acid-catalyzed C═O reduction. The uniqueness of P═O reduction originates from the dominant Si/O═P orbital interactions in transition structures rather than the P/H-Si interactions. The comprehensive mechanistic landscape provided by us will serve as a guidance for the rational design and development of more efficient P═O reduction systems as well as novel organophosphine-catalyzed reactions involving P(V)/P(III) redox cycle.

An up-scaled biotechnological approach for phosphorus-depleted rye bran as animal feed

Side streams from the milling industry offer excellent nutritional properties for animal feed; yet their use is constrained by the elevated phosphorus (P) content, mainly in the form of phytate. Biotechnological P recovery fosters sustainable P management, transforming these streams into P-depleted animal feed through enzymatic hydrolysis. The enzymatic P mobilization not only enables P recovery from milling by-products but also supports the valorization of these streams into P-depleted animal feeds. Our study presents the scalability and applicability of the process and characterizes the resulting P-depleted rye bran as animal feed component. Batch mode investigations were conducted to mobilize P from 100 g to 37.1 kg of rye bran using bioreactors up to 400 L. P reductions of 89% to 92% (reducing from 12.7 gP/kg to 1.41-1.28 gP/kg) were achieved. In addition, High Performance Ion Chromatography (HPIC) analysis showed complete depletion of phytate. The successful recovery of the enzymatically mobilized P from the process wastewater by precipitation as struvite and calcium hydrogen phosphate is presented as well, achieving up to 99% removal efficiency. Our study demonstrates a versatile process that is easily adaptable, allowing for a seamless implementation on a larger scale.

Ashes from challenging fuels in the circular economy

In line with the objectives of the circular economy, the conversion of waste streams to useful and valuable side streams is a central goal. Ash represents one of the main industrial side-products, and using ashes in other than the present landfilling applications is, therefore, a high priority. This paper reviews the properties and utilization of ashes of different biomass power plants and waste incinerations, with a focus on the past decade. Possibilities for ash utilization are of uttermost importance in terms of circular economy and disposal of landfills. However, considering its applicability, ash originating from the heat treatment of chemically complex fuels, such as biomass and waste poses several challenges such as high heavy metal content and the presence of toxic and/or corrosive species. Furthermore, the physical properties of the ash might limit its usability. Nevertheless, numerous studies addressing the utilization possibilities of challenging ash in various applications have been carried out over the past decade. This review, with over 300 references, surveys the field of research, focusing on the utilization of biomass and municipal solid waste (MSW) ashes. Also, metal and phosphorus recovery from different ashes is addressed. It can be concluded that the key beneficial properties of the ash types addressed in this review are based on their i) alkaline nature suitable for neutralization reactions, ii) high adsorption capabilities to be used in CO2 capture and waste treatment, and iii) large surface area and appropriate chemical composition for the catalyst industry. Especially, ashes rich in Al2O3 and SiO2 have proven to be promising alternative catalysts in various industrial processes and as precursors for synthetic zeolites.

Electrochemical route outperforms chemical struvite precipitation in mitigating heavy metal contamination

Electrochemically mediated struvite precipitation (EMSP) offers a robust, chemical-free process towards phosphate and ammonium reclamation from nutrients-rich wastewater, i.e., swine wastewater. However, given the coexistence of heavy metal, struvite recovered from wastewater may suffer from heavy metal contamination. Here, we systematically investigated the fate of Cu2+, as a representative heavy metal, in the EMSP process and compared it with the chemical struvite precipitation (CSP) system. The results showed that Cu2+ was 100% transferred from solution to solid phase as a mixture of copper and struvite under pHi 9.5 with 2-20 mg/L Cu2+ in the CSP system, and varying pH would affect struvite production. In the EMSP system, the formation of struvite was not affected by bulk pH, and struvite was much less polluted by co-removed Cu2+ (24.4%) at pHi 7.5, which means we recovered a cleaner and safer product. Specifically, struvite mainly accumulates on the front side of the cathode. In contrast, the fascinating thing is that Cu2+ is ultimately deposited primarily to the back side of the cathode in the form of copper (hydro)oxides due to the distinct thickness of the local high pH layer on the two sides of the cathode. In turn, struvite and Cu (hydro)oxides can be harvested separately from the front and back sides of the cathode, respectively, facilitating the subsequent recycling of heavy metals and struvite. The contrasting fate of Cu2+ in the two systems highlights the merits of EMSP over conventional CSP in mitigating heavy metal pollution on recovered products, promoting the development of EMSP technology towards a cleaner recovery of struvite from waste streams.

Beyond Triphenylphosphine: Advances on the Utilization of Triphenylphosphine Oxide

Triphenylphosphine oxide is a well-known industrial waste byproduct, and thousands of tons of it are generated every year. Due to its chemical stability and limited applications, settlement of this waste issue has drawn extensive attention from chemists. The reduction of triphenylphosphine oxide to triphenylphosphine is heretofore the most employed solution, and is well reviewed. In view of our recent studies on the selective and efficient conversion of Ph3P(O) to other valuable organophosphorus chemicals by using sodium, the present perspective mainly highlights the advances on the utilization of Ph3P(O) to prepare a diverse range of functional organophosphorus compounds, except Ph3P, via selective P-C, C-H, and P-O bond cleavages.

Nutrient recovery from wastewater for hydroponic systems: A comparative analysis of fertilizer demand, recovery products, and supply potential of WWTPs

Nutrient recovery from wastewater treatment plants (WWTPs) for hydroponic cultivation holds promise for closing the nutrient loop and meeting rising food demands. However, most studies focus on solid products for soil-based agriculture, thus raising questions about their suitability for hydroponics. In this study, we address these questions by performing the first in-depth assessment of the extent to which state-of-the-art nutrient recovery processes can generate useful products for hydroponic application. Our results indicate that less than 11.5% of the required nutrients for crops grown hydroponically can currently be recovered. Potassium nitrate (KNO3), calcium nitrate (Ca(NO3)2), and magnesium sulfate (MgSO4), constituting over 75% of the total nutrient demand for hydroponics, cannot be recovered in appropriate form due to their high solubility, hindering their separated recovery from wastewater. To overcome this challenge, we outline a novel nutrient recovery approach that emphasizes the generation of multi-nutrient concentrates specifically designed to meet the requirements of hydroponic cultivation. Based on a theoretical assessment of nutrient and contaminant flows in a typical municipal WWTP, utilizing a steady-state model, we estimated that this novel approach could potentially supply up to 56% of the nutrient requirements of hydroponic systems. Finally, we outline fundamental design requirements for nutrient recovery systems based on this new approach. Achieving these nutrient recovery potentials could be technically feasible through a combination of activated sludge processes for nitrification, membrane-based desalination processes, and selective removal of interfering NaCl. However, given the limited investigation into such treatment trains, further research is essential to explore viable system designs for effective nutrient recovery for hydroponics.

Phosphorus recovery from domestic wastewater: A review of the institutional framework

Phosphorus (P) is an essential element for life that must be managed sustainably. The institutional framework for P recovery from wastewater includes policies, regulations, plans, and actions that promote the recovery, recycling, and safe use of this element, aimed at moving toward more sustainable nutrient management and environmental protection. This review analyzes the status of the institutional framework for P recovery from wastewater in different countries around the world. Europe is the continent where the most progress has been made in terms of legislation. Countries such as Germany, the Netherlands, Austria, and Denmark have already implemented policies and regulations that promote environmental protection, as well as P recovery and reuse. In other parts of the world, such as the United States, China, and Japan, there have also been significant advances in promoting the closure of the P cycle, with the implementation of advanced recovery technologies in wastewater treatment plants and regional/national action plans. By contrast, in Latin America there has been little progress in P treatment and recovery, with a weak regulatory framework, unclear goals, and insufficient allocation of techno-economic resources. In this context, it is necessary to reinforce the comprehensive institutional framework, which covers technological aspects, economic incentives, political agreements, and regulations, to promote the sustainable management of this valuable resource.

A novel scalable polycationic melamine sponge-based filtration matrix for continuous ultrafast adsorption of anionic pollutants

Effective capturing of anionic pollutants from wastewater under industrial operating conditions, which requires high processing flux and fast adsorption rate remains a challenge. Here, a commercially available melamine sponge (MS) with reticulated 3D macroporous structures was covalently modified with positively charged moieties using a single step functionalization under mild conditions. The developed novel polycationic melamine sponge (MS+) was formed by a nucleophilic addition reaction between glycidyltrimethylammonium chloride (GMTA) and MS, followed by a self-propagation of GMTA. The produced MS+ possessed strong electrostatic interactions with different anions such as Rose Bengal (RB) and phosphates (P) under a wide pH range (3-11). The MS+ exhibited promoted static adsorption efficiencies of 400 mg g-1 (P) and 600 mg g-1 (RB), within 5 min and 60 s, respectively. Furthermore, the MS+ showed high stability and recyclability for up to 15 cycles of uses, and the recycling process was environmentally friendly by using 1 M NaCl as a releasing solution. Benefiting from fast flow through the macroporous MS+ and highly positive charged skeleton, the MS+ was applied for rapid dynamic enrichment process of P from real manure wastewater with an enrichment factor of 4.4. Utilization of the MS+ as the substrate brings additional advantages such as low cost, availability, and flexibility to fit into existing filtration devices. The developed MS+ could be expanded for enrichments of other anionic species from various polluted water sources.

Direct Synthesis of Phosphoryltriacetates from White Phosphorus via Visible Light Catalysis

Organophosphorus compounds (OPCs) are widely used in many fields. However, traditional synthetic routes in the industry usually involve multistep and hazardous procedures. Therefore, it's of great significance to construct such compounds in an environmentally-friendly and facile way. Herein, a photoredox catalytic method has been developed to construct novel phosphoryltriacetates. Using fac-Ir(ppy)3 (ppy=2-phenylpyridine) as the photocatalyst and blue LEDs (456 nm) as the light source, white phosphorus can react with α-bromo esters smoothly to generate phosphoryltriacetates in moderate to good yields. This one-step approach features mild reaction conditions and simple operational process without chlorination.

Electrochemically mediated phosphorus and energy recovery from digested effluent

The growing global concern over the high phosphorus concentration in discharged wastewaters has driven the demand for exploring the means to recover it from wastewater. We previously demonstrated the possibility of phosphorus recovery by iron-air fuel cells from digested effluent. The present study focused on further optimizing the performance of the fuel cell by adjusting the wastewater properties (initial pH) and device parameters (anode/cathode area ratio, electrode spacing). Under neutral or slightly alkaline conditions, the HCO3- ions accelerated the formation of iron anode passivation layer, resulting in a decreased phosphate removal efficiency and vivianite yield. Additionally, the occurrence of oxygen crossover with small electrode spacing and anode/cathode area ratio significantly influenced the efficiency of fuel cells in terms of phosphate removal, vivianite production, and electricity generation. The results showed that an acidic pH (5.78), an adequate anode/cathode area ratio (1.3), and an appropriate electrode spacing (5 cm) were prone to increase vivianite yield. Furthermore, the fuel cell achieved the highest electric energy output with an initial pH of 5.78, an anode/cathode area ratio of 0.4, and an electrode spacing of 7.5 cm. As far as operational cost was concerned, the iron-air fuel cell system exhibited a potential cost-saving advantage of about 65.6% compared to the traditional electrochemical crystallization system.

Phosphate recovery from sludge-incinerated ash by adsorption with hydrotalcite synthesized by metals in the ash

Selective adsorption of phosphorus (P) from the acidic leachate of sludge-incinerated ash (SIA) becomes more attractive due to avoiding removing heavy metals. Especially, layered double hydroxides (LDHs) as an anion adsorbent could be applied into this area owing to their good capacity on P-adsorption and low cost on preparation. Interestingly, SIA contains more aluminum (Al) and iron (Fe) needed to be removed prior to P-recovery, and removed Al and Fe could be utilized to synthesize LDHs, like Mg/Al-LDH and Mg/Fe-LDH. With this study, Mg/Al-LDH-r and Mg/Fe-LDH-r were economically synthesized with Al and Fe removed from SIA, which were similar in their chemical structures to commercial LDHs. The synthesized LDHs had a high P-adsorption capacity, up to 95.0%. The maximal phosphate capacity of the recovered LDHs (Mg/Al-LDH-r and Mg/Fe-LDH-r) was 239.0 and 199.8 mg P/g LDHs, respectively. "NaOH + desalinated brine" as a new desorption solution could achieve a desorption ratio at about 80%, which could reduce the liquid-solid ratio by at least 60%, greatly decreasing the desorption cost. Pot trials demonstrated that the desorbed and precipitated CaP could promote the growth of maize as well as a commercial P-fertilizer. Furthermore, the adsorbed phosphate by LDHs could be directly used as a slow-released P-fertilizer and also improve the pH value of acidic soil, completely deleting the desorption process.

Integration of molecular and computational approaches paints a holistic portrait of obscure metabolisms

Microorganisms are essential drivers of earth's geochemical cycles. However, the significance of elemental redox cycling mediated by microorganisms is often underestimated beyond the most well-studied nutrient cycles. Phosphite, (per)chlorate, and iodate are each considered esoteric substrates metabolized by microorganisms. However, recent investigations have indicated that these metabolisms are widespread and ubiquitous, affirming a need to continue studying the underlying microbiology to understand their biogeochemical effects and their interface with each other and our biosphere. This review focuses on combining canonical techniques of culturing microorganisms with modern omic approaches to further our understanding of obscure metabolic pathways and elucidate their importance in global biogeochemical cycles. Using these approaches, marker genes of interest have already been identified for phosphite, (per)chlorate, and iodate using traditional microbial physiology and genetics. Subsequently, their presence was queried to reveal the distribution of metabolic pathways in the environment using publicly available databases. In conjunction with each other, computational and experimental techniques provide a more comprehensive understanding of the location of these microorganisms, their underlying biochemistry and genetics, and how they tie into our planet's geochemical cycles.