Resource Recovery Research Articles

Real-time non-destructive monitoring of supported liquid membranes using electrochemical impedance spectroscopy

The degradation of supported liquid membranes (SLMs) due to membrane liquid leaching has been a hurdle for their implementation in resource recovery from waste streams. We present a novel approach utilizing four-electrode mode electrochemical impedance spectroscopy (EIS) for real-time, non-destructive monitoring of SLM degradation, providing detailed analysis of SLM's structural changes. We first showed that SLMs may be depicted as an electrical circuit of resistors and capacitors by EIS. The EIS then revealed that SLM degradation progressed over four different phases as a result of varying rates of thickness and area reduction of the SLM. To demonstrate the effectiveness of EIS-based diagnosis, we prepared SLMs designed for selective medium-chain fatty acid (MCFA) extraction in intact, partially, and completely degraded states, determined by the EIS. The intact SLM showed a high selectivity (∼50) for MCFAs over short-chain fatty acids. The selectivity decreased to ∼22 in the partially degraded SLMs, and less than 1 in the completely degraded SLM, indicating the clear linkage between the degree of degradation and the separation performance. Our four-electrode mode EIS method is expected to serve as a key tool for efficient SLM operation and stable SLM development.

Waste Zinc–Carbon Battery Recycling: Focus on Total Material Recovery

Currently, less attention is paid to zinc–carbon batteries, although they are still widely used and are among the major types of batteries collected and recycled. The recycling technologies currently in use do not allow the complete recovery of resources, are not self-sufficient and require additional financing. Therefore, this paper aims to study the possibility of complete recycling of waste zinc–carbon batteries and to suggest the practical use of the final products generated in the recycling process. The possibility of complex processing of spent zinc–carbon batteries using mechanical separation and processing of the battery’s components (steel case, zinc electrode, graphite electrode, polypropylene and paper insulators) is justified. The separation of spent electrolytes from other components of batteries with hydrochloric acid was studied. It was shown that the extraction of Zn2+ and NH4+ cations takes place following the addition of an equivalent amount of Na3PO4 solution and water-insoluble NH4ZnPO4 salt sedimentation. Waste agglomerate (mixture of MnO2, MnO(OH), and graphite) was regenerated to its initial composition (MnO2, graphite) at a temperature of 300–325 °C; manganese (III) hydroxide was oxidized to manganese (IV) dioxide. Thermal destruction of polypropylene and paper insulators with additional introduction of polyethylene into the primary mixture produced pyrolysis liquid, pyrocarbon and pyrolysis gas as products. The practical use of the products obtained and compliance with the environmental requirements of the suggested method of waste batteries recycling were shown.

Enhancing medium-chain fatty acids production via alkyl polyglucose modulation of electron acceptor generation, microbial community and metabolic traits in anaerobic fermentation of waste activated sludge

Production of medium chain fatty acids (MCFAs) through anaerobic fermentation is an essential pathway for efficient resource recovery and utilization of waste activated sludge (WAS). In this study, a novel strategy utilizing polyglucose (APG) to enhance MCFAs production from WAS by anaerobic fermentation was proposed. The results showed that the maximum MCFAs production reached 14745.0 mg COD/L with 0.3 g APG/g TSS, which was 20.2 times of that without APG treatment. The transformation of intermediates demonstrated that APG promoted the generation of electron acceptors (i.e., short-chain fatty acids) and conversion of substrate to MCFAs. Microbial community analysis indicated that APG selectively enriched microbe involved in hydrolysis, acidogenesis and chain elongation (CE). Also, the presence of APG had a negative impact on methanogens and potential excessive ethanol oxidation (EEO) microbe, which were competitors of CE bacteria in mixed-culture system. Metagenomic analysis showed an increase in relative abundance of genes encoding metabolic functions responsible for hydrolysis, acidogenesis, CE and energy generation, thus maintained high microbial activity in MCFAs biosynthesis. These enhanced metabolic functions were accompanied by a reduction in relative abundance of genes encoding methanogenesis and EEO metabolism, which together result in boosting the efficiency of substrate and energy flow to MCFAs production. This study presents a promising approach to improve the biotransformation of polysaccharides and proteins from WAS into MCFAs.

Synthesis and application of biomass-based graphene oxide using microwave-assisted pyrolysis method

Graphene and related materials have excellent potential to revolutionise many emerging fields, but the large quantity synthesis using environmentally sustainable methods is still challenging. This work studies the synthesis of graphene oxide from food waste biochar with negatively charged properties, which is initially produced using microwave pyrolysis. The synthesised graphene oxide achieved 64.53 % carbon content, 345.79 m2/g surface area, 0.074 cm3/g micropore volume, large reactive surface area, and ribbon/banded organisation. The performance of carbon-based material is evaluated in the fabrication of a modified screen-printed carbon electrode (SPCE) for selective dopamine (DA) detection in the coexistence of ascorbic acid (AA) and uric acid (UA). The electrostatic interactions between the negatively charged biochar-based graphene oxide (BBGO) on the surface SPCE and opposite-charged dopamine assisted the oxidation potential with interfering species by electrostatic repulsion of AA and UA. This manuscript substantiates the resource recovery from organic materials and sustainable graphene oxide synthesis, underscoring their application in detecting positively charged species.

Comprehensive geophysical, geotechnical, and geochemical assessments of an offshore landfill in Singapore

Comprehensive site investigation techniques, including Electrical Resistivity Tomography (ERT), Induced Polarization (IP), Multichannel Analysis of Surface Waves (MASW), and Microtremor Array Method (MAM), were integrated with geotechnical and geochemical tests of retrieved waste samples from Singapore’s operational offshore landfill. The properties of landfill wastes vary widely, including shear-wave velocities 127–248 m/s, densities 1.2–2.1 Mg/m3, resistivity 3.0–25.3 Ω∙m, and chargeability 48–82 mV/V. The natural clay layer underneath was clearly delineated and effectively mitigated leachate leakage. K-means clustering of the geophysical data facilitates precise mapping of waste distribution and quantities of recoverable metals based on quantitative criteria. This study illustrates a thorough case study adopting the new site investigation and characterization paradigm for an offshore landfill, which provides insights into leachate leakage detection and evaluations of landfill mining and resource recovery.

Multifaceted Impact of Lipid Extraction on the Characteristics of Polymer-Based Sewage Sludge towards Sustainable Sludge Management.

Dewatered sludge (DS) is a sewage sludge with a unique property due to extracellular polymeric substances (EPSs) and polymer flocculants. These components form a stable 3D polymer network to increase dewatering efficiency, leaving behind valuable materials such as lipids. This article explored the influences of DS particle size on lipid yield and the effects of extraction on the chemical, morphological, and thermal properties of the residual dewatered sludge (RDS). Lipid yields with unimodal distribution were observed across the particle size ranges (<0.5, 0.5-1.0, 1.0-2.0, 2.0-4.0, and 4.0 mm). The highest lipid yield of 1.95% was extracted from 1.0-2.0 mm after 4 h at 70 °C and 0.1 g/mL sludge-to-solvent ratio. Efficiency was influenced by the DS's morphology, facilitating solvent infiltration and pore diffusion. The extraction process reduced water and organic fractions, resulting in higher thermal stability. Bibliometric analysis of "extraction*" and "sewage sludge" shows increasing research interest from 1973 to 2024. Five research clusters were observed: heavy metal speciation and stabilization, sludge and its bioavailability, extraction techniques and resource recovery, contaminants remediation, as well as phosphorus recovery and agricultural applications. These clusters highlight the diverse approaches to researching DS and RDS while promoting sustainable waste management.

Hydrophobic and positively charged magnetic nanoparticles for enhanced oil recovery from concentrated emulsion wastewaters

With the development of petroleum industry, a large amount of oil-in-water (O/W) emulsion wastewaters were produced, resulting in serious environmental pollution and resource waste. Up till now, magnetic nanoparticles (MNPs) were frequently reported in emulsion wastewater treatment and mainly focused on the water purification, but little effort was devoted to the facile recovery of oil resource. In the present work, a class of hydrophobic and positively charged MNPs, namely dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DOTAC)-coated MNPs (M−DOTAC), was carefully synthesized by regulating DOTAC anchoring density on Fe3O4@SiO2, and then employed to treat the concentrated emulsion wastewaters stabilized by anionic sodium dodecyl benzene sulfonate (SDBS) or nonionic Tween-80. M−DOTAC with relatively high DOTAC density (M−DOTAC 1.8) exhibited higher positive charge density and hydrophobicity, and hence could significantly promote the oil droplet coalescence and mergence via the electrostatic attraction and hydrophobic adsorption bridging as well as the hydrophilic-lipophilic transition of interfacial adsorption layer. Accordingly, with addition of moderate dosage of M−DOTAC 1.8, the emulsion was broken and divided into three layers: (1) a continuous oil layer was formed in the upper layer which could be directly recycled; (2) the middle layer was composed of MNPs-tagged oil droplets/flocs; (3) the bottom layer was the clearer water phase. The optimal recovery rate of oil resource reached ∼ 60 % in SDBS stabilized system, and further increased to ∼ 98 % in Tween-80 stabilized system. However, the oil recovery rate was declined at an excessive dosage of M−DOTAC 1.8 due the formation of double emulsion. Besides, M−DOTAC 1.8 exhibited good reusability. These results indicated the fabricated M−DOTAC had great application prospect in treating emulsion wastewaters containing high oil content.

Thermal activation of basic oxygen furnace slag as a heterogeneous catalyst in transesterification: Characterization and catalytic activity studies

The valorization of industrial by-products has garnered significant attention in recent years due to its potential to enhance sustainability and economic efficiency within various sectors. Basic Oxygen Furnace slag (BOF-S), a by-product generated in the steelmaking process characterized by its complex composition, presents an opportunity for waste management and resource recovery. This study investigates the potential of BOF-S as a catalyst in converting waste cooking oil to biodiesel via the transesterification reaction. To improve its efficiency, BOF-S was calcined at 850 °C (BOF-S 850), and 1000 °C (BOF-S 1000), for 5 h. The BOF-S was characterized using XRF, N2 sorption, XRD, TGA-DSC, SEM-EDS and FTIR. The characterization techniques showed that the BOF-S 850 had superior characteristics as a catalyst: rough surface, increased pore size and more active basic sites compared to the BOF-S and the BOF-S 1000 slag samples. The transesterification reaction was conducted at a methanol: oil ratio of 20:1, a catalyst loading of 20 wt %, a reaction time of 12 h, a reaction temperature of 60 °C, and a stirring speed of 750 rpm. The findings established that the BOF-S 850 was the best catalyst, with a 90.77 % biodiesel yield and was able to sustain a maximum of two transesterification cycle runs.

Upcycling Post-Consumer Paint Pail Plastic Waste.

The need for ending plastic waste and creating a circular economy has prompted significant interest in developing a new family of composite materials through recycling and recovery of waste resources (including bio-sourced materials). In this work, a family of natural fiber-reinforced plastic composites has been developed from paint pail waste recycled polypropylene (rPP) and waste wool fibers of different diameter and aspect ratio. Composites were fabricated by melt processing using polypropylene-graft-maleic anhydride as a compatibilizer. The internal morphology, interfacial and thermal characteristics, viscoelastic behavior, water sorption/wettability, and mechanical properties of composites were studied using electron microscopy, high-resolution synchrotron Fourier transform infrared microspectroscopy, thermal analysis, rheology, immersion test, contact angle measurement, tensile test and flexural test. The composite matrix exhibited an internal morphology of coalescent micro-droplets due to the presence of polyethylene and dry paint in the rPP phase. In general, the rheological and mechanical properties of the composites comprising higher-aspect-ratio (lower diameter) fibers exhibited relatively superior performance. About an 18% increase in tensile strength and a 39% increase in flexural strength were measured for composites with an optimal fiber loading of 10 wt.%. Interfacial debonding and fiber pull-out were observed as the main failure mechanism of the composites. The developed composites have potential for applications in automotive, decking, and building industries.

A novel strategy for enhancing high solid anaerobic digestion of fecal slag and food waste using percolate recirculation and dosage of nano zero-valent iron

To speed up reaching UN Sustainable Development Goal 6 for safe sanitation by 2030, integrating high-solid anaerobic digestion (HSAD) into decentralized systems could recycle fecal slag (FS) and food waste (FW), aiding a circular economy and toilet revolution. In this study, a percolate recirculation system and conductive material were used to improve mass transfer, stability, and enhance methane production in HSAD of FS and FW. This setup consists of a percolate tank and a digester tank, where nano-zero valent iron (nZVI) was dosed in the percolate tank (PnZVI in P) and the digester tank (PnZVI in D) and compared with a control with no additive (PControl). The highest cumulative methane yield of 519.43 mL/gVS was achieved in PnZVI in D, which was 4.52 and 3.59 times higher than that of PControl (144.59 mL/gVS) and PnZVI in P (114.96 mL/gVS). This finding demonstrates that the dosing strategy of PnZVI in D facilitated effective interaction among organic matter, microbial communities, and nZVI, resulting in organics removal efficiencies of 67.42 % (total solid) and 77.22 % (volatile solid). Moreover, microbial community analysis supported the efficacy of the PnZVI in D strategy, revealing the enrichment of Clostridium sensu stricto 1 (46.91 %), which potentially engaged in interspecies electron transport (Interspecies hydrogen transfer (IHT) and direct interspecies electron transfer (DIET)) with Methanobacterium (81.19 %) and Methanosarcina (17.11 %). These interactions contribute to enhanced methane yield and stability maintenance in the HSAD system with percolate recirculation. The findings of this study demonstrate that the implementation of HSAD of FS and FW, coupled with percolate recirculation and the addition of nZVI, holds promise for enabling sustainable sanitation practices in developing regions. Moreover, this approach not only facilitates resource recovery but also eliminates the requirement for water.

Recycling of e-waste power cables using microwave-induced pyrolysis - process characteristics and facile recovery of copper metal.

This article reports on recycling e-wastes using a VVF power cable as a model through a rapid pyrolytic process following exposure to microwave radiation. This occurred via three possible pathways: (i) discharges at the copper wire on exposure to microwaves, with heat produced causing the thermal decomposition of the covering material - a relationship exists between the length of the copper wire and the wavelength of the microwaves; (ii) microwave heating softened the wire's covering material and ultimately led to its decomposition - in addition, the coating material carbonized by the discharge is rapidly heated by microwaves; (iii) the carbonaceous component present in the covering material absorbed the microwaves, causing the thermal decomposition. On the other hand, for VVF cables longer than 12 cm canceled the wavelength-dependent process, and the longer the VVF cable was, the more efficient was the microwave-induced pyrolysis, therefore eliminating the need to pre-cut the waste VVF cable into smaller pieces. The microwave-induced pyrolysis showed that chlorine could be recycled as HCl and the carbon and activated carbon produced could be recovered as carbon black. While conventional pyrolysis might produce tar substances and polycyclic aromatic compounds, microwave pyrolysis has been shown to enable extremely rapid resource recovery, with only C6 to C12 linear alcohols produced as intermediates; no formation of tar-like substances, polycyclic aromatic compounds, or dioxins were detected. Clearly, microwave-induced pyrolysis has proven suitable for recycling/recovery of e-waste containing metals and requires no pre-treatment to separate the plastics from the metals.

A review of the engineered treatment of red mud: Construction materials, metal recovery, and soilization revegetation

Red mud, known as bauxite residue, is an alkaline solid waste generated during alumina production. Globally, the stockpile of red mud is about 3 billion tons and is increasing at a rate of 150 million tons per year. The global production of red mud is mainly distributed in China (28.2 %), Oceania region (22.4 %), South America (14.6 %), Europe (12.9 %), and North America (8.8 %). The increasing stockpile of red mud has posed a huge challenge to safe disposal while restricting the development of the alumina industry. The comprehensive utilization of red mud still needs green, efficient, and massive consumption methods. This work gives a review of the engineered treatment of red mud, including the characteristics and threats, as well as the engineered application through construction materials, metal recovery, and soilization revegetation. For red mud with a high content of metals, resource recovery of valuable metals and rare earth elements is a preferred choice, meeting the circular economy concept. Recovery of valuable metals from red mud can be achieved by magnetic separation, hydrometallurgy, and bioleaching. Hydrometallurgy is promising for recovering valuable metals such as Fe, Al, V, Ti, and rare earth elements, and the recovery is up to 99 %. Construction materials such as cement, geopolymers, and ceramics is an efficient alternative for the massive consumption of red mud, and the high-performance concrete with the compressive strength (129.5 MPa) can be obtained. This strategy is limited by the low price of construction materials, the lowered quality by alkaline components, and potential threats of toxic elements in red mud. Soilization of red mud with ecological restoration is promising for the sustainable management of red mud dam. To accelerate the process of red mud soilization, amendments such as gypsum, organic matter, and microorganisms can be added to neutralize red mud (lowering pH from 10 to 12 to near 7), promote the formation of agglomerates, and provide nutrients, promote the conversion of red mud into soil-like substrate. The phytoremediation of red mud can be realized after effective regulation, finally realizing vegetation establishment of red mud. This work provides technological and practical guidance for the engineered disposal of red mud.

Facile fabrication of robust and tight PIMs-based TFC hollow fiber membranes with a semi-interpenetrating polymer network via liquid phase cross-linking for organic solvent nanofiltration

Resource recovery and reuse are essential for sustainable development, particularly for high-value resources such as homogeneous (photo)catalysts, active pharmaceutical ingredients, and high-value natural compounds, which can offer economic benefits. Recently, organic solvent nanofiltration (OSN) for resource recovery has gained significant attention owing to its advantages including low energy consumption and seamless integration with other processes. Polymers of intrinsic microporosity (PIMs) have great potential as membrane materials for OSN, owing to their excellent pore properties and solution processability. However, swelling and dissolution of PIMs in organic solvents can impede the filtration performance of PIMs-based OSN membranes. In this study, we fabricated thin-film composite hollow fiber membranes for OSN based on PIMs with improved organic solvent stability using a semi-interpenetrating polymer network (semi-IPN) formed by cross-linking Matrimid with 1,6-hexanediamine within the PIMs through the liquid phase cross-linking method. Semi-IPNs mitigate swelling and tighten the pores of PIMs-based membranes, enabling excellent filtration and molecular separation performance. Furthermore, the fabricated PIMs with a semi-IPN membrane exhibited excellent rejection performance (>96 %) for homogeneous photocatalysts, allowing successful concentration and recovery via OSN. Therefore, PIMs-based membranes with a semi-IPN hold great promise as OSN membranes for the recovery of valuable resources.

Underpinning the Role of Nanofiltration and Other Desalination Technologies for Water Remediation and Brine Valorization: Mechanism and Challenges for Waste‐to‐Wealth Approach

Desalination brine can negatively impact the marine environment in several ways, although there are ongoing discussions regarding the severity and magnitude of environmental effects. A fascinating strategy to lessen any adverse effects is to undertake resource recovery from the brine, which also has the potential for additional revenue generation. More recently, the increasing demand for secure and less geographically restricted sources of precious or rare earth minerals, integrated with growing awareness of waste management and environmental sustainability, is driving the development of economically viable technologies to recover valuable materials from waste streams. This article provides an overview of different methods and technologies, including reverse osmosis (RO), electrodialysis (ED), and distillation, that can be used to recover precious materials, including Li, Mg, Na, and Rb and valuable blends from various waste sources and thus create a more sustainable and circular economy. The mechanisms are discussed in detail, including electrochemical processes (electrolysis, ED, and capacitive deionization), thermal desalination (multistage flash distillation and membrane distillation), pressure‐driven desalination (RO and nanofiltration), and microbial desalination cells. Challenges associated with recovering precious materials from waste streams, such as fouling, scaling, and environmental impact, along with further research directions and potential applications of desalination technologies, are also addressed.

Technological Advancements and Prospects for Near-Zero-Discharge Treatment of Semi-Coking Wastewater

This review examines the technological bottlenecks, potential solutions, and future development directions in the treatment and resource utilization of semi-coking wastewater (SCOW) in China. By comprehensively investigating the semi-coking industry and analyzing wastewater treatment research hotspots and existing projects, this study systematically explores the current status and challenges of each treatment unit, emphasizing the necessity for innovative wastewater treatment technologies that offer high efficiency, engineering feasibility, environmental friendliness, and effective resource recovery. This review highlights prospects and recommendations, including the development of novel extractants for phenol and ammonia recovery, a deeper understanding of biological enhancement mechanisms, exogenous bio-enhancement materials, and the creation of cost-effective advanced oxidation process (AOP)-based combined processes. Additionally, it underscores the potential for repurposing SCOW as a valuable resource through appropriate treatment, whether recycling for production or other applications.

Impacts of Polyvinyl Alcohol and Chitosan-Modified Biochar on the Anaerobic Digestion of Sewage Sludge and Valuable Resource Recovery

The accumulation of organic dyes and heavy metals (HMs) in sewage sludge (SS) after wastewater treatment is a significant problem due to the non-degradable nature of these pollutants. Moreover, the simultaneous removal of HMs and dyes in the complex process of SS treatment, such as anaerobic digestion (AD), has become attractive. HMs and dyes present in SS can have a detrimental effect on anaerobic digesters. These pollutants not only inhibit the production of methane, which is crucial for biogas generation, but also affect the stability of AD treatment, which can result in failure or inadequate performance of the AD process. This review highlights a novel method of removing HMs and dyes from the AD process of SS through the use of biochar modified with polyvinyl alcohol (PVA) and chitosan (CTS). The applications of conventional biochar have been limited due to poor adsorption capacity. However, modification using PVA/CTS composites enhances properties such as surface functional groups, adsorption capacity, porosity, surface area selectivity, and stability. Furthermore, this modified version can function as an additive in AD of SS treatment to boost biogas production, which is a viable source for heat generation or electricity supply. In addition, the digestates can be further processed through plasma pyrolysis for the removal of HMs and dyes bound to the modified biochar. Plasma pyrolysis generates two major products: syngas and slag. The syngas produced can then be used as a source of hydrogen, heat, and electricity, while the slag can potentially be reused as an AD additive or as a biofertilizer in the agricultural sector. Additionally, this study addresses the challenges associated with this integration and biochar modifications, and offers an outlook on understanding the interactions between the modified biochar properties, microbial dynamics, and the presence of micropollutants to ensure the economic viability and scalability of this technology. This comprehensive review provides insights into the potential of PVA/CTS-modified biochar as an effective additive in AD systems, offering a sustainable approach to SS treatment and valuable resource recovery.

Development of Dust Emission Prediction Model for Open-Pit Mines Based on SHPB Experiment and Image Recognition Method

Open-pit coal mining offers high resource recovery, excellent safety conditions, and large-scale production. However, the process generates significant dust, leading to occupational diseases such as pneumoconiosis among miners and adversely affecting nearby vegetation through dust deposition, which hinders photosynthesis and causes ecological damage. This limits the transition of open-pit mining to a green, low-carbon model. Among these processes, blasting generates the most dust and has the widest impact range, but the specific amount of dust generated has not yet been thoroughly studied. This study integrates indoor experiments, theoretical analyses, and field tests, employing the Split Hopkinson Pressure Bar (SHPB) system to conduct impact loading tests on coal–rock samples under pressures ranging from 0.13 MPa to 2.0 MPa. The results indicate that as the impact load increases, the proportion of large-sized blocks decreases while smaller fragments and powdered samples increase, signifying intensified sample fragmentation. Using stress wave attenuation theory, this study translates indoor impact loadings to field blast shock waves, revealing the relationship between blasting dust mass fraction and impact pressure. Field tests at the Haerwusu open-pit coal mine validated the formula. Using image recognition technology to analyze post-blast muck-pile fragmentation, the estimated dust production closely matched the calculated values, with an error margin of less than 10%. This formula provides valuable insights for estimating dust production and improving dust control measures during open-pit mine blasting operations.

Pure water and resource recovery from municipal wastewater using high-rate activated sludge, reverse osmosis, and mainstream anammox: A pilot scale study

In response to the escalating global water scarcity and the high energy consumption associated with traditional wastewater treatment plants, there is a growing demand for transformative wastewater treatment processes that promise greater efficiency and sustainability. This study presents an innovative approach for municipal wastewater treatment that integrates high-rate activated sludge with membrane bio-reactor (HRAS-MBR), reverse osmosis (RO) and partial nitrification-anammox (PN/A). With an influent of 8.4 m³/d, the HRAS-MBR demonstrated a removal efficiency of approximately 85 % for chemical oxygen demand (COD), with over 70 % of it being recovered for energy production. The RO system achieved a recovery rate of 75 % for the influent, producing pure water with an electrical conductivity of 50 μS/cm. Concurrently, it concentrated ammonia, thereby enhancing the effectiveness of the PN/A process for nitrogen removal in the mainstream, resulting in a removal efficiency exceeding 85 %. Notably, the HRAS-MBR achieved significant phosphorus removal without chemical additives, attributed to the presence of influent calcium and magnesium ions. Overall, this integrated system reduced the net energy consumption for reclaimed water production by about 26 % compared to conventional methods. Additionally, the new process produced a revenue of 0.75 CNY/m³, demonstrating considerable economic and environmental benefits. This pilot-scale study offers a viable alternative for wastewater treatment and water reuse in water-scarce regions, contributing to sustainable water resource management.

Molecular understanding of speciation transformation of phosphorus and sulfur in food waste digestate during hydrothermal treatment

Recovering phosphorus (P) and sulfur (S) from biowaste is a key strategy to address the current P resources shortage and soil S deficiency. Food waste digestate (FWD) contains high contents of P and S, while its direct application is severely limited by available nutrient leaching loss and pollutant exposure. Hydrothermal treatment (HT) is an effective technique for biowaste disposal, enabling detoxification and resource recovery. The study systematically investigated the speciation transformation of P and S in FWD during HT, using chemical extraction and in-situ X-ray absorption near-edge structure (XANES) spectroscopy. The results revealed that up to 98% of P in FWD was enriched in the solid product (hydrochar) after HT, with organic P and labile P being converted into stable Ca-bound forms, predominantly hydroxyapatite. This transformation reduced the risk of P leakage loss compared to untreated FWD. Interestingly, the S speciation evolution exhibited more complexity. The highest S proportion in hydrochar of 73.6% was observed at 140 °C under HT. As the temperature increased from 140 °C to 180 °C, S in the hydrochar gradually dissolved into the liquid phase, attributed to unstable aliphatic compounds (mercaptan) and the sulfides oxidizing to sulfates. Above 180 °C, intermediate oxidation states and sulfates were reduced and formed metal sulfides. These findings have important implications for understanding the viability of HT for FWD disposal and the value-added utilization of FWD.

Optimization of Leaching Recovery of Zinc, Iron and Manganese from Selected Solid Waste Ashes in Zaria, Kaduna State, Nigeria

The increasing environmental burden of toxic heavy metal-concentrated ash from solid waste incineration, particularly from burnt tires and contraband drugs, poses significant challenges for waste management and resource recovery. This study aims to optimize the leaching recovery of zinc, iron, and manganese from these solid waste ashes in Zaria, Kaduna State, Nigeria, using Response Surface Methodology (RSM). The ashes were analyzed for their metal content using atomic absorption spectroscopy (AAS), with additional characterization by X-ray diffraction (XRD) and X-ray fluorescence (XRF). Among the leaching agents tested, hydrochloric acid (HCl) exhibited the highest efficiency, particularly under optimized conditions determined through central composite design (CCD). The optimal conditions for leaching from burnt tire ash were found to be 2.97 mol/l acid concentration, 97.7 minutes leaching time, and 68.85°C temperature, yielding recoveries of 32,009 mg/kg zinc, 4,553 mg/kg iron, and 137 mg/kg manganese. For contraband drug ash, the optimal conditions were 2.83 mol/l acid concentration, 97.7 minutes leaching time, and 68.85°C temperature, resulting in recoveries of 70.55 mg/kg zinc, 5,771 mg/kg iron, and 676 mg/kg manganese. This study successfully developed a multiple linear regression model to express the relationship between the leaching parameters and metal recovery, providing a reliable and sustainable method for metal recovery from solid waste ashes. The findings offer valuable insights into waste management practices, contributing to the circular economy and reducing the environmental impact of waste disposal.