Search Results (1,356)

Adsorption is a promising technology for phosphate removal to alleviate eutrophication. In this study, thermally modified calcium aluminate decahydrate (TCAH) was prepared via low-temperature thermal treatment of calcium aluminate decahydrate (CAH₁₀) to develop a cost-effective and high-performance phosphate adsorbent. The optimal modification temperature was determined to be 120 °C, which reduced the crystallinity of CAH₁₀, enhanced its porosity, and induced the formation of amorphous calcium aluminate phases. Batch adsorption experiments showed that TCAH exhibited a maximum adsorption capacity of 199.80 mg P/g at 25 °C. The adsorption kinetics followed the pseudo-second-order model, while the adsorption isotherms were well fitted by the Redlich–Peterson model. TCAH maintained high removal efficiency over a wide pH range of 3.0–11.0 and showed high selectivity against common coexisting anions. Characterizations using SEM-EDS, XRD, FTIR and XPS suggested that phosphate removal by TCAH was dominated by synergistic amorphous precipitation and inner-sphere complexation. In tests with real phosphorus-releasing liquor derived from excess sludge, TCAH achieved nearly complete phosphate removal at a dosage of 5 g/L within 6 h. Owing to its readily available raw materials, low preparation temperature, and outstanding phosphate capture performance, TCAH is a promising candidate for efficient phosphate capture and recovery from wastewater. Full article

Surfactant-enhanced soil washing is a promising strategy for the remediation of organochlorine pesticide (OCPs) contaminated sites. In this study, we constructed a comprehensive evaluation framework integrating efficient parameter optimization, effluent recovery and ecological restoration assessment. Among the 14 evaluated washing agents, the non-ionic surfactant Triton X-100 exhibited superior solubilization capacity for highly hydrophobic OCPs. Under an optimal dosage of 2.0%, Triton X-100 achieved near-complete extraction of γ-chlordane and over 75% removal of mirex in both moderately and severely contaminated soils. Powdered activated carbon (PAC) demonstrated exceptional selective adsorption performance, significantly outperforming activated carbon fiber (ACF). The optimal PAC dosages (20 g/L) could extract over 90% of OCPs from the soil washing effluents, facilitating potential washing agent recycling. Furthermore, community-level physiological profiling (BIOLOG-AWCD) revealed distinct ecological trajectories post-washing. While nitrogen and phosphorus (N/P) bio-stimulation successfully restored and even surpassed the microbial diversity in moderately contaminated soils, it only partially alleviated the ecological vulnerability in severely contaminated soils (Simpson index < 0.45). These findings underscore that while surfactant-enhanced soil washing combined with selective adsorption constitutes a powerful physicochemical remediation cycle, restoring heavily degraded microhabitats necessitates an integrated approach coupling bio-stimulation with phytoremediation. Full article

Eutrophication remains a persistent water-quality problem in shallow lakes, where external inputs interact with internal loading and biogeochemical cycling. Although floating treatment wetlands (FTWs) are increasingly promoted as nature-based solutions for water remediation, their field-scale interpretation in hydrologically complex eutrophic lakes remains challenging. This study examined the spatial organization of water quality during the operation of a floating-island system in a eutrophic urban lake affected by polluted tributary inflow. The study was not designed to quantify isolated FTW removal efficiency, but to evaluate spatial water quality organization during FTW operation under real-use field conditions. Water quality was monitored over two growing seasons across six functionally defined zones, and spatial and temporal patterns were analyzed using descriptive statistics and linear mixed-effects models. The results showed parameter-specific spatial structuring rather than a uniform treatment response. The clearest inlet-lake contrasts were observed for electrical conductivity (EC), suspended matter (SM), and nitrate nitrogen (NO₃-N), whereas biochemical oxygen demand (BOD₅), ammonium nitrogen (NH₄-N), and total organic carbon (TOC) showed lower values at the inlet and higher values in downstream zones. Dissolved oxygen (DO), oxygen saturation (SO), chemical oxygen demand (COD), nitrite nitrogen (NO_2-N), and orthophosphate phosphorus (PO₄-P) showed moderate or non-robust zonal effects. These findings indicate that FTWs in shallow eutrophic lakes should be evaluated through functional zoning and parameter-specific interpretation rather than as isolated units with uniform removal responses. Full article

The algae-based landfill leachate (LL) treatment system has been proved promising for nutrient recycling and biomass production at lab- or small-scale photobioreactors (PBRs). However, many assessment tools such as techno-economic analyses (TEAs) usually utilize parameters from small-scale experiments as input data to predict the potential performance of commercial large-scale or full-scale bioreactors. Reliability of using data from lab-scale for commercial large-scale estimation is still uncertain. This study compared the performance of three photobioreactor systems that differed simultaneously in scale, geometry, light intensity, mixing mode, and aeration: 0.125 L small-scale flask, 1 L medium-scale tubular PBR, and 15 L wall-shaped PBR for real LL treatment. The 1 L medium-scale tubular photobioreactor outperformed the other two systems in biomass growth rate and the rates of nitrogen and phosphorus removal, even though all three systems removed nearly all NH₄-N and PO₄-P (≈100%) within two weeks. Possible reasons for this better performance include stronger illumination, a bubbling aeration mode, the reactor shape (which improves mixing), and higher surface area to volume ratio × light intensity. According to these results, using relatively small-scale flask experimental data for predictive analysis of industrial-scale algal systems could be inadequate. In this study, volumetric optical radiation (VOR) serves as a promising preliminary descriptive indicator to reflect the overall performance of an algal-based treatment system. Full article

A complex curved reflector made from a 40% silicon–aluminum alloy (AlSi40) can meet the requirements of optical systems operating across the infrared, near-infrared, and visible bands. It enables an athermalization design with simplified alignment and assembly, while offering high manufacturing efficiency and low costs. This makes it ideal for widespread use in high-end optical systems. As an enabling technology for the fabrication of AlSi40 freeform mirrors, error compensation in ultra-precision (UP) diamond turning is currently a research hotspot; however, current error compensation methods still have considerable room for improvement in terms of both accuracy and manufacturing efficiency. To address this issue, this study proposes an efficient and highly accurate method: a polar grid is defined in the machining coordinate system, and the corresponding surface point cloud is calculated. Using measured point clouds from reference spheres and freeform form error in the measurement coordinate system, mounting pose errors and form error with measurement error removed are determined via least squares. Machining error at grid points is then calculated via coordinate transformations and bicubic spline interpolation, and applied to correct cutter contact points (CCPs). Cutter location points (CLPs) are finally obtained using piecewise cubic spline fitting and a bisection method. With this method, average form error of four AlSi40 substrates improved from RMS 114.8 nm to 47.9 nm, and for four AlSi40 substrates with nickel–phosphorus (NiP)-plated surfaces, from RMS 71.3 nm to 31.1 nm. The compensated accuracy meets near-infrared stellar tracker requirements without polishing, greatly enhancing freeform mirror manufacturing efficiency. Full article

Water scarcity and increasing environmental pressures have intensified the need for sustainable water management, including the reuse of treated wastewater. This study evaluated the continuous up-flow sand filter as a tertiary treatment process for secondary wastewater effluent. A pilot-scale filtration unit was installed downstream of the secondary treatment at Qaha Wastewater Treatment Plant (QWWTP), Egypt and operated at influent flow rates of 3.9–8.5 m³/h. Performance was assisted for removing turbidity, total suspended solids (TSS), biochemical oxygen demand (BOD₅), E. coli, total nitrogen (TN), and total phosphorus (TP), under three phases: baseline operation, variable influent quality produced by mixing secondary effluent with raw wastewater, and coagulant-assisted filtration using alum or ferric chloride. During baseline and variable influent conditions, the maximum removal efficiencies were 67.0%, 62.1% and 37.3% for turbidity, TSS and BOD₅, respectively. Alum improved the corresponding removals to 94.5%, 71.7% and 55.5%, while ferric chloride achieved 81.4%, 83.8%, and 87.5%, respectively. Overall, the results demonstrate that coagulant-assisted continuous up-flow sand filtration is a robust and practical tertiary treatment approach for upgrading secondary effluents to meet stringent wastewater reuse standards. Full article

Metal and nutrients can be extracted and recovered from sediments for beneficial use. The aim of the current study is to extract phosphorus (P) from dredged sediments from Malmfjärden bay through chemical extraction, targeting the determination of the best conditions to extract P from the studied sediments with minimal contamination from metals. The chemicals used for the extractions include citric acid (C₆H₈O₇), sulphuric acid (H₂SO₄), sodium hydroxide (NaOH) and ethylenediaminetetraacetic acid (EDTA) at 0.01 M or 0.1 M. The acids were at pH 5, and NaOH at pH 12. The pH was also varied for 0.01 M EDTA at pH 2, and 0.1 M H₂SO₄ at pH 1. A single extraction was carried out with each reagent at the varying concentrations and pH. One test had a sequential two-step extraction of EDTA as the first step, followed by H₂SO₄ as the second step. The elements were analysed using inductively coupled plasma sector field mass spectrometry (ICP-SFMS). The results showed that the extraction efficiencies were significantly higher at 0.1 M than 0.01 M of the reagents, as well as at more acidic conditions for the reagents with a varied pH, in most cases. H₂SO₄ at pH 1 extracted the most P (46.4%), together with most of the other elements. EDTA also exhibited a high extraction efficiency for the elements and can be used as a pre-step to remove metal before extraction with H₂SO₄. Alternatively, although it had lower P extraction efficiencies, NaOH can be used as the extractant, since it extracted less of the other elements. The P/metal extraction ratios further indicated that NaOH achieved high selectivity, as well as the second step sequential extraction H₂SO_4. Hence, the recovered P will be less contaminated. P extraction from sediments can indeed become one way of recovering the finite element, which would otherwise be normally lost as waste with the sediments. Full article

As eutrophication worsens, countries including China, the US, France, Sweden, and South Korea have tightened phosphorus (P) discharge limits for wastewater treatment plants (WWTPs). This paper first reviews China’s evolving P regulations, then classifies P removal technologies into physical, chemical, biological, and combined methods. Analysis of current WWTPs in China shows that biological P removal alone is insufficient, making chemical P removal (CPR) a necessary supplement or primary approach. Thus, the review focuses on CPR technologies: chemical precipitation, ion exchange, adsorption, electrocoagulation, magnetic methods, hybrid biological-chemical methods, and P recovery technologies. For each, the principles, materials, application conditions, advantages, and disadvantages are discussed. This review aims to guide the selection, application, and future research of CPR processes. Full article

This paper presents a mechanistic model for a thin-layer microalgal bioreactor cultivating Stigeoclonium nanum, with a comprehensive analysis of its dynamics and stability. Unlike most bioreactor studies that assume simple Monod or linear growth, our model rigorously explores the nonlinear interplay between logistic constraints and multiple nutrient limitations. We introduce a coupled Logistic–Monod system of nonlinear ordinary differential equations that captures sigmoidal transitions and steady states of Stigeoclonium nanum under simultaneous nitrogen and phosphorus depletion and incorporates abiotic nutrient removal to ensure mass conservation. Qualitative analysis proves positive invariance and boundedness of solutions using the Localization of Compact Invariant Sets method. Asymptotic stability of the biologically relevant equilibrium is established. Experimental validation in a thin-layer photobioreactor using three-fold cross-validation yielded high correlation coefficients (0.78–0.96) for biomass, nitrate, and phosphate concentrations, confirming predictive accuracy. The model thus provides a robust framework for process control and optimization in industrial-scale applications. Full article

Accurate effluent-quality prediction is essential for improving nitrogen and phosphorus removal performance and reducing energy consumption in wastewater treatment plants (WWTPs). However, the strong coupling, high noise, and time-lag effects in wastewater treatment processes pose significant challenges to existing prediction models. In this study, we propose a GAT-CNN-LSTM(GCL) model for the prediction of effluent total nitrogen (TN) and total phosphorus (TP). The GCL model first uses a graph attention network (GAT) to adaptively learn inter-variable relationships, and then applies a convolutional neural network (CNN) and long short-term memory (LSTM) network to extract local and long-term temporal features. The GCL model is trained and evaluated using real operational data from a municipal WWTP in northern China. Based on the best run of each model, GCL improves the $R^2$ by 13.7% and 6.4% over LSTM and Transformer for TN prediction, while reducing MAPE by 39.4% and 30.4%, respectively. For TP prediction, the corresponding improvements in $R^2$ are 70.7% and 59.1%, with MAPE reductions of 37.1% and 36.0%. Ablation experiments further demonstrate the complementary contributions of the three modules, showing that graph-based feature fusion enhances subsequent temporal modeling. The temporal variation in neighbor attention weights and one-at-a-time (OAT) sensitivity analysis provide interpretability consistent with A²/O process mechanisms. These findings provide a preliminary validation based on a limited dataset from a single WWTP, and broader applicability under more diverse operating conditions warrants further investigation. Full article

Nitrogen and phosphorus are the primary pollutants responsible for eutrophication in water bodies, and their effective removal is crucial for water environmental protection. Biochar, owing to its porous structure and surface functional groups, exhibits excellent adsorption performance for nitrogen and phosphorus, which can be significantly enhanced through metal modification. In this study, magnetic biochar (MBC) was prepared from spent mushroom substrate via FeCl₃ impregnation and microwave pyrolysis, and its adsorption performance for NH₄⁺ and PO₄³⁻ was systematically evaluated. The physicochemical properties of MBC were characterized using scanning electron microscopy, thermogravimetric analysis, specific surface area and pore structure analysis, vibrating sample magnetometry, and Fourier transform infrared spectroscopy. The results showed that the saturated magnetization of MBC was 7.86 emu/g, the specific surface area was 37 m²/g, and the material exhibited a mesoporous structure with high thermal stability. The adsorption process followed pseudo-second-order kinetics, and the mechanisms involved electrostatic interactions, surface complexation, and pore filling. Isotherm studies indicated that the maximum adsorption capacities of MBC for NH₄⁺ and PO₄³⁻ were 16.25 mg/g and 14.99 mg/g, respectively. Thermodynamic analysis revealed that the adsorption of NH₄⁺ was exothermic, whereas that of PO₄³⁻ was endothermic. Furthermore, MBC maintained an adsorption efficiency of up to 93% after ten adsorption–desorption cycles, demonstrating excellent reusability. Full article

In this study, a sustainable calcium-rich biochar was synthesized via co-pyrolysis at 800 °C of marble waste, animal manure, and lignocellulosic biomass. This biochar (MWM–B) was comprehensively characterized and then valorized for phosphorus (P) removal from real effluent and synthetic solutions in both batch and continuous stirred tank reactor (CSTR) modes. Characterization results confirm the formation and deposition of significant amounts of calcium oxides and calcium hydroxides on the biochar surface, which enhance the biochar’s surface chemistry and textural properties. In batch mode, MWM–B efficiently removes P with a removal capacity (108.4 mg g⁻¹) that is 5.3 times higher than that observed in the CSTR system. This efficiency drop is due to the limited contact time between phosphate species and the biochar particles. Interestingly, the presence of calcium and magnesium in the continuously renewed real effluent in the CSTR system increases P removal efficiency by approximately 136% compared with synthetic solutions. A detailed analysis of MWM–B before and after P removal suggests that this process occurs mainly through precipitation as hydroxyapatite, complexation with hydroxyl functional groups, electrostatic interactions, and hydrogen bonding. This work confirms that MWM–B generated at 800 °C is an attractive material for P removal from effluents. Full article

Anaerobic digestion (AD) is an important method for sewage sludge (SS) stabilization and methane recovery. Fe compounds are widely present in SS because they are commonly used for phosphorus removal and organic matter (OM) capture in wastewater treatment plants. Endogenous Fe occurs in different forms, but the roles of these forms in SS AD remain unclear. This study systematically compared the effects of FeCl₃, Poly-FeCl₃, Fe₃O₄, FeOOH, and Fe₅HO₈·4H₂O on AD. The results showed that FeCl₃ and Poly-FeCl₃ decreased methane yield by 9.90% and 11.92%, respectively, whereas Fe₃O₄, FeOOH, and Fe₅HO₈·4H₂O increased it by 18.54%, 15.23%, and 15.09%. The analysis suggested that flocculating salts FeCl₃ and Poly-FeCl₃ groups increased sludge particle size, decreased SCOD concentrations by 10.21% and 12.41%, as well as F₄₂₀ by 16.88% and 28.63%, respectively, thereby inhibited the methanogenesis process. In contrast, Fe₃O₄, FeOOH, and Fe₅HO₈·4H₂O enhanced methane production by promoting OM hydrolysis, with SCOD concentrations increased by 12.71%, 8.99%, and 7.47%, respectively. XRD, CV, and EIS results showed that Fe₃O₄ likely promoted methanogenesis through a stable Fe(III)/Fe(II) cycle and electron transfer. Although FeOOH and Fe₅HO₈·4H₂O also underwent Fe(III)/Fe(II) conversion, their promoting effects were weaker than that of Fe₃O₄, possibly because the lack of a bulk mixed-valence structure reduced the efficiency of continuous electron transfer. This study highlights that the chemical form of Fe in SS fundamentally determines its effects on AD performance. Full article

This study evaluates the performance of natural plant-derived coagulants as sustainable alternatives to conventional chemical coagulants in water treatment. Surface water samples were collected from the Meda Ela stream in Karadiyana, Sri Lanka, which is an urban water body impacted by leachate from the Karadiyana dumpsite, industrial discharges, and urban runoff. Grab samples were analyzed for key water quality parameters, including pH, conductivity, turbidity, dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), settleable solids, total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), total nitrogen, and total phosphorus. Several parameters exceeded permissible standards established by the Central Environmental Authority (CEA) of Sri Lanka, including turbidity (35 NTU; limit: 20 NTU), COD (80 mg/L; limit: 15 mg/L), TDS (1000 mg/L; limit: 500 mg/L), and TSS (100 mg/L; limit: 40 mg/L), indicating significant pollution levels. Jar test experiments were conducted to compare the coagulation efficiency of cowpea seeds (75.8%), fenugreek seeds (69.2%), papaya seeds (72.5%), okra pods (84.6%), and Moringa oleifera (drumstick) leaves (87%) with conventional alum (94.2%) at an optimum dosage of 12 mL/L. Among the tested plant-derived coagulants, Moringa oleifera leaves demonstrated the highest turbidity removal efficiency, reducing residual turbidity to 4.54 NTU. A low-cost integrated treatment system incorporating coagulation, flocculation, sedimentation, and filtration using sawdust and cotton wool was developed, achieving average removal efficiencies of 90.13% for turbidity, 88.57% for COD, 83.46% for TDS, and 74.83% for TSS, with all effluent parameters maintained within CEA permissible limits. The results confirm that locally available plant-derived coagulants, particularly Moringa oleifera leaves, offer an effective, environmentally friendly, and economically viable approach for sustainable water treatment, highlighting the potential of nature-based solutions in strengthening climate-resilient water management strategies. Full article

Plant detritus plays a pivotal role in regulating soil nutrient dynamics within forest ecosystems. Understanding short-to-medium-term responses of soil-available nitrogen (AN) and phosphorus (AP) to altered detritus inputs is important for forest nutrient management. In this study, we investigated the effects of changing detritus inputs on soil AN and AP in two representative forest types in Northeast China—Korean pine (Pinus koraiensis Siebold et Zucc.) forest (KP) and Aspen (Populus ussuriensis Kom.)−birch (Betula platyphylla Sukaczev) forest (AB). Using the detritus input and removal treatments (DIRTs) method, we established six experimental treatments and measured soil ammonium nitrogen (NH₄⁺-N), soil nitrate nitrogen (NO₃⁻-N), and AP contents monthly from May to October. The results showed that significant differences in NH₄⁺-N, NO₃⁻-N, and AP contents were observed among treatments. Under the six DIRTs, the fluctuation ranges of NH₄⁺-N, NO₃⁻-N, and AP contents in KP soil were 1.16–12.52 mg/kg, 7.34–35.40 mg/kg, and 9.63–31.72 mg/kg, respectively. For AB soil, the fluctuation ranges of the above three nutrients under the six DIRTs were 2.94–13.17 mg/kg, 3.45–28.47 mg/kg, and 1.77–25.60 mg/kg, respectively. Root treatments exerted stronger effects on AN and AP than litter: root exclusion generally reduced NH₄⁺-N but increased NO₃⁻-N and AP, with the direction and magnitude of the response to this treatment varying with month and forest type, whereas litter treatments showed no consistent trends. The soil-available N:P ratio was lower in the KP forest than in the AB forest; root exclusion significantly reduced the N:P ratio in the AB forest but had no significant effect on that in the KP forest. In terms of seasonal dynamics, the study found that AN peaked in May and AP in July. In conclusion, these findings reflect the short-to-medium-term effects of plant detritus, forest type, and month on soil-available nitrogen and phosphorus, providing scientific insights into how detritus changes alter soil nutrients in temperate forests. Full article