Search Results (60)

Rice is a globally important food crop, and its production is often affected by extreme climates such as drought and high temperatures. This study investigated how drought applied at different growth stages affects cadmium (Cd) uptake and accumulation in rice, as well as the underlying mechanisms. The results showed that drought treatments generally increased soil organic matter and alkali-hydrolyzed nitrogen content but decreased pH and available phosphorus content. The available Cd content in soil under the grain-filling stage drought treatment was lower than that under other treatments. Speciation analysis showed that under grain-filling stage drought, exchangeable Cd decreased by 3.04%, and residual Cd increased by 2.67%. Furthermore, drought treatments significantly enhanced soil urease and sucrase activities. Rice plant height and yield were significantly affected by the timing of drought, with the grain-filling stage drought treatment yielding the highest, while full growth stage and tillering stage drought treatments resulted in significantly lower yields. Cd content in various organs followed the order: root > stem > leaf > brown rice, with the brown rice Cd content being the lowest under grain-filling stage drought. In conclusion, drought treatment during the grain-filling stage had the least effect on Cd content in various rice tissues while maintaining a relatively high yield, providing a theoretical basis for water management in Cd-contaminated paddy fields. Full article

Organic phosphorus (OP) constitutes an important and chemically diverse fraction of total phosphorus (TP) in aquatic environments, yet its removal mechanisms in substrate-based treatment systems remain insufficiently understood. In particular, the relative contributions of adsorption and microbial transformation to OP removal and their coupling effects are still unclear. To address this issue, gravel-, sludge-, and sludge biochar-based biofilters were operated under controlled phosphorus inputs with varying OP/inorganic phosphate (IP) compositions. Phosphorus removal performance, effluent phosphorus speciation, phosphatase activity, and microbial community characteristics were systematically analyzed to distinguish physicochemical and biological pathways. Results indicated that phosphorus removal was dominated by adsorption at early operational stages, with comparable performance across substrates. As the operation progressed, sludge-based substrates exhibited more stable removal than gravel, attributable to stronger Fe/Al-associated adsorption. Biologically active sludge biochar systems consistently maintained higher TP removal efficiencies (87.1–93.3%) than abiotic systems. Phosphatase-mediated OP mineralization governed phosphorus speciation transformation, while effective removal depended on subsequent immobilization of transformation products. Overall, the results demonstrate that efficient OP removal relies on a coupled bio–physicochemical mechanism, in which microbial transformation and substrate adsorption act synergistically. This insight offers guidance on optimizing phosphorus control in biofilters and constructed wetlands (CWs), especially for robust biofilters and CWs designed to treat OP-rich wastewaters. Full article

Phosphogypsum (PG) and phosphorus tailings (PT) are bulk solid wastes generated by the phosphorus chemical industry whose stockpiling poses significant environmental risks and represents a waste of resources. To achieve the goals of “treating waste with waste” and large-scale disposal, this study proposes a technical pathway involving the co-pyrolysis of phosphogypsum and phosphorus tailings to produce artificial soil-like materials. The effects of raw material ratio, pyrolysis temperature and duration, and biomass addition on the speciation transformation, leaching toxicity, and matrix characteristics of phosphorus (P) and fluorine (F) in the products were systematically investigated. Characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), were employed to elucidate the synergistic immobilization mechanism. The results indicate that under optimized conditions (PG:PT mass ratio of 6:4, pyrolysis temperature of 800 °C, duration of 2–3 h, and biomass addition of 20%–30%), the active forms of harmful elements in the product were significantly reduced. The proportion of water-soluble fluorine decreased from ~39% in raw phosphogypsum to less than 3%, with apatite phosphorus becoming the dominant form of phosphorus. Mechanistic studies reveal that the immobilization process follows a “multi-pathway synergy” mechanism: thermal activation promotes the in situ formation of thermodynamically stable fluorapatite through the reaction of Ca²⁺, PO₄³⁻, and F⁻ (chemical fixation); iron/aluminum oxides in phosphorus tailings and the biochar derived from added biomass provide adsorption sites for surface complexation (physicochemical fixation); and the melting of silicon–aluminum components forms an amorphous silicate network that physically encapsulates pollutant microcrystals. This study provides crucial theoretical foundations and process parameters for the synergistic disposal and soil-like resource utilization of phosphogypsum and phosphorus tailings, demonstrating significant environmental and economic benefits. Full article

Rising concentrations of organic carbon (OC), phosphorus, and nitrogen in liquid waste from urban, industrial, and agricultural sources pose persistent challenges for environmental protection and resource recovery. Despite extensive application of microfiltration (MF) and ultrafiltration (UF) in wastewater treatment, their role in selective organic carbon and nutrient fractionation remains insufficiently clear-cut and is often interpreted solely through nominal pore size. This review was guided by the hypothesis that the reported limitations of MF and UF for nutrient separation are not intrinsic to the technologies but arise from simplified interpretations of separation mechanisms. A unified analytical framework was developed by synthesizing recent studies, linking membrane surface charge, pore structure, solute speciation, fouling-induced secondary layers, and operating conditions to the observed separation behavior. The analysis shows that MF fractionates particulate OC and suspended solids, whereas UF extends separation to macromolecular OC and phosphorus mainly via indirect retention mechanisms. Dissolved nitrogen species largely permeate both membranes unless they are transformed into retainable forms. Performance differences between MF and UF are conditional and system-dependent, with enhanced selectivity emerging through process integration. MF and UF can thus be repositioned as strategic fractionation interfaces within integrated treatment systems supporting circular economy–oriented wastewater management. Full article

The transition toward sustainable and circular bioeconomies in Agriculture 4.0 demands fertilization strategies that reduce environmental impacts while maintaining agronomic productivity. This article presents a structured narrative review of peer-reviewed literature integrating evidence across waste management, soil science, food safety, and regulatory frameworks to evaluate the potential of seafood processing byproducts including fish offal, shellfish residues, and aquaculture effluents as nutrient-rich fertilizers. These materials provide nitrogen, phosphorus, calcium, and essential micronutrients and may contribute to nutrient recycling within precision and resource-efficient agricultural systems. Evidence from diverse cropping contexts indicates that seafood waste-derived fertilizers can improve crop yield, nutrient use efficiency, and soil biological activity under site-specific conditions. Biological processing methods, including composting, enzymatic hydrolysis, and fermentation, are examined for their roles in enhancing nutrient bioavailability and reducing undesirable constituents. Particular emphasis is placed on food safety considerations, including heavy metals, persistent organic pollutants, antimicrobial resistance, pathogens, and microplastics, with discussion of speciation-based risk assessment and mitigation strategies such as thermal treatment, microbial screening, and compliance with international standards. Regulatory fragmentation, economic feasibility, and lifecycle environmental implications are also critically assessed. Emerging digital tools, including Internet of Things (IoT)-enabled nutrient monitoring and artificial intelligence (AI)-assisted compost optimization, are discussed as enabling technologies for integrating seafood-derived biofertilizers into smart farming systems. Overall, this interdisciplinary synthesis highlights the potential contribution of seafood waste valorization to circular nutrient management, environmental stewardship, and sustainable food production. Full article

Understanding the short-term availability of legacy phosphorus (P) in soils is important for improving fertilizer management and reducing unnecessary P inputs. This study evaluated whether soil legacy P could temporarily support rice growth under continuous cultivation and assessed the short-term potential for reducing P fertilizer applications. Field experiments were conducted over two consecutive rice cropping seasons in paddy soils located in Taoyuan (TY) and Changhua (CH), Taiwan. Rice grain yield, grain P concentration, and soil P dynamics were compared between plots receiving chemical fertilizers (CF) and those without chemical P fertilization (NCF). Results showed no significant differences in grain yield or grain P concentration between CF and NCF treatments over the two cropping seasons. Sequential P extraction and P K-edge X-ray absorption near-edge structure (XANES) analyses of soils collected before planting and after harvest revealed a redistribution of soil P from moderately and slowly labile pools to more labile fractions during rice cultivation. These changes suggest that legacy P contributed to maintaining plant-available P during the short experimental period. Overall, this study provides short-term (two-season) field evidence that, in P-enriched paddy soils, legacy P can partially supply rice P demand without additional P fertilization. However, the long-term sustainability of this strategy and its applicability under different soil and management conditions require further investigation. Full article

This study investigated the effects of calcium (Ca²⁺) and iron (II) Fe²⁺ concentrations (0–500 mg/L) on the heterogeneous nucleation and crystallization behavior of struvite (MgNH₄PO₄·6H₂O) through controlled batch precipitation experiments. Struvite formed under different Ca²⁺ and Fe²⁺ concentrations were systematically characterized using XRD, SEM, FTIR, and XPS, while real-time pH and redox potential (Eh) monitoring was employed to elucidate reaction dynamics and thermodynamic speciation and saturation indices were calculated, and classical nucleation theory (CNT) was applied to interpret nucleation behavior. The results show that Ca²⁺ primarily suppresses struvite formation through bulk-phase competition with Mg²⁺ for phosphate, diverting phosphate into Ca–P phases and progressively reducing struvite supersaturation, which leads to decreased crystallinity and distorted Crystal habit. In contrast, Fe²⁺ does not form detectable crystalline Fe-P phases but inhibits struvite crystallization mainly through surface-mediated processes. Surface analyses indicate that Fe-bearing species adsorb onto struvite surfaces and promote amorphous Fe-P deposition, increasing interfacial resistance to nucleation and growth. CNT analysis further reveals that Ca²⁺ inhibition is governed by reduced thermodynamic driving force, whereas Fe²⁺ inhibition is dominated by surface-related kinetic barriers. This study provides mechanistic insight into ion-specific interference during struvite crystallization and offers guidance for optimizing phosphorus recovery in ion-rich wastewater systems. Full article

Phosphate fertilizer is essential for crop production but poses environmental risks in agriculture. The agronomic and environmental thresholds for phosphorus application in Southwest China’s purple soils (Luvic Xerosols) remain poorly defined. We combined soil phosphorus fractionation, root phenotyping, and microbial community analysis (16S rRNA and ITS amplicon sequencing) to explore soil–microbe–plant interactions in a 12-year field experiment with five P application rates (0, 37.5, 75, 112.5 and 150 kg P₂O₅ ha⁻¹ yr⁻¹). Results showed that beyond 75 kg ha⁻¹, the medium-soluble phosphorus pool increased significantly while stable phosphorus decreased. Fungal diversity was more sensitive to high phosphorus than bacterial diversity. Maize yield plateaued at 75–150 kg ha⁻¹, mainly due to increased grain weight and optimized root architecture. An environmental risk threshold was identified at 83.54 kg ha⁻¹ and an optimal yield threshold at 84.65 kg ha⁻¹, enabling high yield with low environmental risk via microbially mediated phosphorus activation. Therefore, this research reveals that the phosphorus input threshold can provide a basis for reducing phosphorus application, regulating phosphorus components, and maintaining microbial diversity and network complexity in purple soil dryland farming systems, thereby ensuring maize yield. Full article

Most of the phosphorus (P) input from feed ends up accumulating in the pond water or sediment, ultimately harming the environment. Rice demonstrates remarkable bioremediation potential. However, the mechanisms by which long-term rice impacts the sediment P cycle in aquaculture environments remain unclear. This study investigated the effects of a six-year rice–fish co-culture on sediment resuspension-driven P release, P speciation, and removal efficiency in intensive aquaculture. Our results indicated that the rice–fish co-culture (RF) system enhanced the P utilization efficiency by 128.36% while decreasing P residue in water and sediment by 77.42% and 34.62%, compared to the monoculture (F) system. The RF system reduced labile P pool (H₂O-IP, NaHCO₃-IP) contents, leading to a 74.89% and 82.20% reduction in sediment resuspension and P release rates, respectively. Concurrently, stable P pool (NaOH-IP, NaOH-OP) contents increased by 14.21% and 52.99%. Microbial mineralization in the 5–10 cm layer was enhanced, with acid phosphatase activity and relative abundance of functional gene phoC increasing by 19.69% and 327.61%. Our results showed that the six-year RF system enhanced sediment P cycling, reducing P release risk and improving P utilization. These findings inform eco-efficient aquaculture optimization, with future research needing isotope tracing and metagenomics to explore microbial roles. Full article

The influence of microplastics (MPs) on the availability of soil heavy metals (HMs) is a current research hotspot, but how MPs regulate HM availability via soil properties and the bacterial community remains unclear. This study investigated the effects of polyethylene (PE) MP concentrations on soil properties, bacterial communities, surface chemistry, and the speciation of cadmium (Cd) and lead (Pb) through soil incubation. Results indicated that as PE MP concentration increased, soil pH and cation exchange capacity declined, while organic carbon concentration increased. Available phosphorus and alkali–hydrolyzable nitrogen concentrations increased at 0.1% and 1% PE MPs, but decreased at 10% PE MPs. Bacterial community indices, including Simpson, ACE, and Chao1, increased at 0.1% and 1% PE MPs but decreased at 10% PE MPs. PE MPs (0.1% and 1%) reduced DTPA–Cd/Pb, promoting their transformation into stable forms and surface complexation with oxygen–containing groups. In contrast, 10% PE MPs disrupted the formation of PbO, PbCO₃, and Cd(OH)₂, producing the opposite effect. The random forest model revealed that soil organic carbon and available phosphorus were the primary factors influencing DTPA–Pb and DTPA–Cd, respectively. Partial least squares path modeling demonstrated that PE MPs altered the physicochemical characteristics of soil and structure of bacterial communities, ultimately impacting transformation of Cd and Pb speciation, with these changes being highly dependent on PE MP concentration. Full article

High levels of phosphorus cause eutrophication, leading to water blooms and making the water undesirable in aquatic environments. Surface water pollution by phosphorus (P) is caused by both point and diffuse sources. Despite the recent technological advancements in wastewater phosphorus removal, this element persists in aquatic ecosystems, particularly in sediments, often in non-bioavailable forms (in the case of precipitation by aluminum salts) or within biomass associated with high concentrations of heavy metals, rendering it unsuitable for reuse. In this paper, we review the measures and methods commonly used for reducing or removing bioavailable phosphorus, with a focus on the strategies and methods for direct in situ phosphorus removal or reuse, including the use of microbial biofilms and aquatic macrophytes, natural and constructed wetlands, and biotised (biologically enhanced) solid-phase sorbents or woodchip bioreactors. This paper also highlights the significance of bioavailable phosphorus from both the hydrochemical perspectives, examining phosphorus speciation, solubility, and the geochemical interactions influencing mobility in water and sediments, and the biological perspectives, which consider phosphorus uptake, bioaccumulation in aquatic organisms, and the role of microbial and plant communities in modulating phosphorus cycling. This overview presents sustainable phosphorus management approaches that are key to reducing eutrophication and supporting ecosystem health. Full article

Lake eutrophication, often driving harmful algal blooms (HABs) and ecosystem degradation, involves complex biogeochemical shifts within sediments. Changes in the sedimentary dissolved organic matter (DOM) composition during transitions from macrophyte to algal dominance are thought to critically regulate internal phosphorus (P) loading, yet the underlying mechanisms, especially in vulnerable plateau lakes like Qilu Lake, require further elucidation. This study investigated the coupled cycling of carbon (C) and P in response to historical ecosystem succession and anthropogenic activities using a 0–24 cm sediment core from Qilu Lake. We analyzed the total organic carbon (TOC), total phosphorus (TP), sequential P fractions, and DOM fluorescence characteristics (EEM-PARAFAC), integrated with chronological series data. The results revealed an asynchronous vertical distribution of TOC and TP, reflecting the shift from a submerged macrophyte-dominated, oligotrophic state (pre-1980s; high TOC, low TP, stable Ca-P dominance) to an algae-dominated, eutrophic state. The eutrophication period (~1980s–2010s) showed high TP accumulation (Ca-P and NaOH85 °C-P enrichment), despite a relatively low TOC (due to rapid mineralization), while recent surface sediments (post-2010s) exhibited a high TOC, but a lower TP following input controls. Concurrently, the DOM composition shifted from microbial humic-like dominance (C1) in deeper sediments to protein-like dominance (C3) near the surface. This study demonstrates that the ecosystem shift significantly regulates P speciation and mobility by altering sedimentary DOM abundance and chemical characteristics (e.g., protein-like DOM correlating negatively with Ca-P), reinforcing a positive feedback mechanism that sustains internal P loading and potentially exacerbates HABs. DOM molecular characteristics emerged as a key factor controlling the internal P cycle in Qilu Lake, providing critical insights for managing eutrophication in plateau lakes. Full article

The pyrolysis of sewage sludge into biochar, enhanced by incorporating agriculture waste rich in inorganic minerals and lignocellulosic compounds, provides an effective approach for achieving sludge-harmless treatment and resourceful utilization. In this study, sewage sludge and maize straw-based biochar (SMB) was prepared using the co-pyrolysis method, and the effects of different application ratios (0%, 1%, 3%, and 5%, w/w) of SMB on soil properties, ryegrass growth, microbial community structure, and Pb content and speciation in the contaminated soil of constructed wetlands were investigated. The results showed that SMB had a high carbon content (28.58%) and was rich in functional groups (e.g., -C-O, -C-N). The results indicated that increasing SMB dosage (0–5% w/w) in Pb-contaminated soil elevated soil pH from 6.40 to 7.93, cation-exchange capacity (CEC) from 30.59 to 79.03 cmol/kg (+158%), and organic carbon content by 65% (from 176.79 mg/kg to 107.3 mg/kg), while reducing available phosphorus and potassium by 20% and 30%, respectively, resulting in a 6% decline in ryegrass leaf length. SMB application enriched Pb-resistant bacteria (e.g., Sphingomonas abundance increased from 10.3% to 11.2%) and enhanced Pb immobilization. After 55 days, the total soil Pb increased by 33%, and the residual fraction Pb significantly increased by 7.3% to 21.7%, driven by functional group complexation, ion exchange, pH, and CEC improvements. Full article

A comprehensive investigation into sustainable agriculture and environmental health was conducted in the Baotou region, encompassing analyses of 90 vegetable samples across 12 varieties and their corresponding rhizosphere soil samples. The physical and chemical properties of the soil, along with the content and chemical speciations of heavy metals, were studied. Results indicated that the study area soil is alkaline to strongly alkaline, with significant heterogeneity in the organic carbon and phosphorus contents, affecting the uptake of heavy metals by these vegetables. The balance of Ca, K, Mg, and P is crucial for soil nutrient equilibrium and reducing heavy metal uptake. The heavy metal contents in the twelve vegetables were below the national food contaminant limit values, with notable accumulations of Cd, Zn, Cu, and Hg. There was a curvilinear correlation between the rhizosphere soil and vegetable contents of Cd and Hg, but differences in uptake were observed. Cd, Zn, Cu, and Hg contents in vegetables were significant, correlating curvilinearly with soil heavy metal content. Soil chemical forms influenced bioavailability, with Cd exhibiting the highest bioactivity. Thus, element migration variations in vegetables reflect the combined influence of the soil’s physical and chemical properties, heavy metal content, and chemical forms. This study validates food safety protocols and soil management practices. Results demonstrate key relationships between soil properties, metal behavior, and plant uptake, enabling targeted solutions for heavy metal contamination and soil remediation. Findings advance sustainable agriculture while protecting ecosystems and food security. Full article

Existing studies have demonstrated the positive effects of nano-sized iron oxide on compost maturity, yet the impact of nano-sized iron oxide on phosphorus speciation and bacterial communities during the composting process remains unclear. In this study, pig manure and straw were used as raw materials, with biochar-supported nano-sized iron oxide (BC-Fe₃O₄NPs) as an additive and calcium peroxide (CaO₂) as a co-agent, to conduct an aerobic composting experiment with pig manure. Four treatments were tested: CK (control), F1 (1% BC-Fe₃O₄NPs), F2 (5% BC-Fe₃O₄NPs), and F3 (5% BC-Fe₃O₄NPs + 5% CaO₂). Key findings include the following. (1) BC-Fe₃O₄NPs increased compost temperatures, with F3 reaching 61℃; F1 showed optimal maturity (C/N ratio: 12.90). (2) BC-Fe₃O₄NPs promoted stable phosphorus forms; Residual-P proportions were higher in F1, F2, and F3 (25.81%, 51.16%, 51.68%) than CK (19.32%). (3) Bacterial phyla Firmicutes, Actinobacteria, and Proteobacteria dominated. BC-Fe₃O₄NPs altered community composition, especially on day 7. Firmicutes dominated CK, F1, and F3; Proteobacteria dominated F2. At the genus level, day 7 showed Corynebacterium (CK), Clostridum (F1, F3), and Caldibacillus (F2) as predominant. (4) Pearson correlation analysis revealed shifted correlations between phosphorus forms and bacterial phyla after BC-Fe₃O₄NPs addition. Firmicutes positively correlated with NaOH-OP in F1 during the thermophilic phase, facilitating phosphate release and adsorption by BC-Fe₃O₄NPs. The significance of correlations diminished with increasing additive concentration; in F3, all phyla positively correlated with various phosphorus forms. Full article