Drinking water treatment residue recycled to synchronously control the pollution of polycyclic aromatic hydrocarbons and phosphorus in sediment from aquatic ecosystems

Depletion of crude oil and fuel in the Arctic. Summer and winter field studies with immobilized oil in seawater at Svalbard

Seasonal dynamics can vastly influence the natural depletion of oil spilled into the ocean and the Arctic regions are characterized by large seasonal changes, especially in temperature and daylight. To determine the influences of seasonal variation on natural oil depletion processes like dissolution, photooxidation and biodegradation, we deployed thin films of three oils in natural seawater during the Arctic summer and winter in Svalbard, Norway. The extent of oil depletion varied with season and the type of the oil, however, considerable depletion of n-alkanes and polycyclic aromatic compounds were observed during both summer and winter. The influence of temperature on depletion of components was not consistent between the three oils and only small effects of photooxidation were found during the summer. We further found variations in the composition of bacterial communities associated with the oil films between the seasons with an apparently delayed succession during the winter. The bacterial communities generally contained high abundances of previously reported oil degrading taxa which displayed distinct seasonal patterns in their relative abundance. Oleispira and Oleibacter were dominantly found during the summer and Colwellia during the winter, while Cycloclasticus and C1-B045 were highly abundant during both seasons. While the environmental factors were likely the cause for variations in oil depletion between the seasons and oils, the seasonal differences in the bacterial community composition did not seem to affect their biodegradation potential.

New insights into sustainable in-situ fixation of heavy metals in disturbed seafloor sediments

To address the issues of plume formation and heavy metal ion release during deep-sea mining operations, this study employed multi-sourced mineral composite roasting materials (MMCCM) of varying sizes. An in-situ capping technique was applied within a simulated system to immobilize heavy metals in contaminated sediments. The results demonstrated that capping with MMCCM of different sizes significantly suppressed the upward migration of Cu, Co, and Ni from sediments into the overlying seawater following disturbance. Ion diffusion was identified as a key mechanism driving heavy metal migration. By calculating the release rates of heavy metals during both the disturbed and undisturbed phases, it was found that the application of MMCCM induced a negative diffusion of heavy metals, indicating that the MMCCM-sediment layer functioned as a "sink" for heavy metals. FTIR and XPS analysis showed that the primary mechanisms for heavy metal removal by MMCCM were electrostatic attraction and complexation-precipitation. Additionally, capping with MMCCM facilitated the transition of heavy metals from labile to stable forms within the sediments. Through comprehensive evaluation, the long-term effectiveness of the fixed effects was demonstrated as follows: large MMCCM (L@MCM) > medium MMCCM (M@MCM) > small MMCCM (S@MCM) > powder MMCCM (P @ MCM). Finally, we proposed future research directions and introduced the DQSE framework for the sustainable application of MMCCM. Based on the above findings, this study provides new insights and research references for the in-situ immobilization of heavy metals and plume reduction during future deep-sea mining processes.

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.

Making waves: Breaking the bottleneck of recycling drinking water treatment residue for practical engineering applications in water pollution control

Drinking water treatment residue (DWTR), an inevitable byproduct of water treatment plants, is typically recycled to control water pollution. DWTR poses a low environmental risk and has the potential to function as a functional material for various applications. However, the practical engineering applications of DWTR are limited. These limitations arise from a disconnect between fundamental research and the practical needs of engineering applications, creating a bottleneck for the effective recycling of DWTR. Previous studies have primarily focused on exploring potential DWTR recycling methods that reuse Al, Fe, Mn, Ca, Si, and organic C. However, the varying properties of DWTR obtained from different water treatment plants tend to differ with respect to potential recycling methods, confusing managers and engineers in using relevant knowledge to guide practical engineering applications. To address this challenge, the author advocates for a shift in research toward establishing guidelines that provide direct guidance for practical engineering applications of DWTR. The key components of these guidelines should include risk assessment, capability evaluation, and environmental application procedures with sustainability assessment to break the bottleneck associated with the recycling of DWTR.

Recycling drinking water treatment sludge in construction and building materials: A review

Drinking water treatment sludge (DWTS) is a by-product of water treatment, and it is difficult to recycle to high value and poses potential environmental risks. Recycling DWTS into cement-based materials is an effective measure to achieve its high-volume utilization and reduce its environmental load. DWTS is rich in silica-alumina phases and has potential pozzolanic activity after drying, grinding and calcination, giving it similar properties to traditional supplementary cementitious materials. Adjusting the sludge production process and coagulant type will change its physical and chemical properties. Adding a small amount of DWTS can generate additional hydration products and refine the pore structure of the cement sample, thus improving the mechanical properties and durability of the sample. However, adding high-volume DWTS to concrete causes microstructural deterioration, but it is feasible to use high-volume DWTS to produce artificial aggregates, lightweight concrete, and sintered bricks. Meanwhile, calcined DWTS has similar compositions to clay, which makes it a potential raw material for cement clinker production. Cement-based materials can effectively solidify heavy metal ions in DWTS, and alkali-activated binders, magnesium-based cement, and carbon curing technology can further reduce the risk of heavy metal leaching. This review provides support for the high-value utilization of DWTS in cement-based materials and the reduction of its potential environmental risks.

Dual-emission Tb-based coordination polymer as a ratiometric fluorescence probe for the detection of phosphate

A simple, sensitive dual-emission probe was developed for the detection of phosphate (Pi). The probe Tb-BTB/DPA was synthesized by mixing dual-ligand, 1,3,5-tri(4-carboxyphenyl) benzene (H3BTB) and dipicolinic acid (DPA), with metal ions Tb3+ in ethanol-water solution at 40℃ for 2 h. Tb-BTB/DPA exhibits two emission peaks, the emission at 362 nm is attributed to H3BTB, an energy transfer between Tb3+ nodes, and DPA further enhances the fluorescence of Tb3+ at 544 nm. Pi competes with ligand H3BTB to coordinate Tb3+, resulting in partial collapse of the Tb-BTB/DPA structure and interrupting the electron transfer between H3BTB and Tb3+. Therefore, the emission at 362 nm is enhanced, while the emission at 544 nm is unchanged, and a ratiometric fluorescence method is developed to detect Pi. Tb-BTB/DPA exhibits good linearity within the Pi concentration range (0.1-50 µmol/L), and the detection limit was 25.8 nmol/L. This study provides a new way to prepare probes with dual emission sensing properties.

New insights into the sustainable use of co-pyrolyzed dredged sediment for the in situ remediation of Cd polluted sediments in coastal rivers

The remediation of Cd-polluted sediment in coastal rivers is essential because of its potential hazards to river and marine ecosystems. Herein, a co-pyrolysis product of contaminated dredged sediment (S@BC) was innovatively applied to cap and immobilize Cd-contaminated sediment in coastal rivers in situ, and their remediation efficiencies, mechanisms, and microbial responses were explored based on a 360 d incubation experiment. The results showed that although S@BC immobilization and capping restrained sediment Cd release to the overlying water, S@BC capping presented a high inhibitory efficiency (66.0% vs. 95.3% at 360 d). Fraction analysis indicated that labile Cd was partially transformed to stable fraction after remediation, with decreases of 0.5%- 32.7% in the acid-soluble fraction and increases of 5.0%- 182.8% in the residual fraction. S@BC immobilization and capping had minor influences on the sediment bacterial community structure compared to the control. S@BC could directly adsorb sediment mobile Cd (precipitation and complexation) to inhibit Cd release and change sediment properties (e.g., pH and cation exchange capacity) to indirectly reduce Cd release. Particularly, S@BC capping also promoted Cd stabilization by enhancing the sediment sulfate reduction process. Comparatively, S@BC capping was a priority approach for Cd-polluted sediment remediation. This study provides new insights into the remediation of Cd-contaminated sediments in coastal rivers.

Effects of switching redox conditions on sediment phosphorus immobilization by calcium/aluminum composite capping: Performance, ecological safety and mechanisms

There many materials were used in lake restoration to immobilize phosphorus (P) and reduce the effect of eutrophication. Among them, calcium/aluminum composite (CAC) showed a good capacity of P adsorption. However, a comprehensive of its performance, ecological safety, and the mechanism of P passivation in the aluminum-bound P (Al -P) dominated sediments under varying redox conditions remains incomplete. In the current study, both unwashed CAC (UCAC) and washed CAC (WCAC) showed good P adsorption properties, and the greatest maximum capacity for P adsorption (Qmax) reached 206.8 mg/g at pH 8.5 for UCAC. The SRP and TP in the overlying water of the uncapped sediments showed a decrease-increase-decrease trend in a sequence of transition from aerobic to anaerobic to re-aerobic stages. In contrast, the SRP and TP of the two CACs-capped sediments were maintained low. Phosphorus forms in the uncapped sediment also underwent significant changes during continuous variation of dissolved oxygen (DO) levels. In particular, the decrease in iron-bound P (Fe-P) and Al-P was significantly promoted in the anaerobic phase, and the released P was reabsorbed to form mainly Fe-P in the re-aerobic phase. The CACs-capping promoted the transformation of Fe-P to residual P (Res-P), forming a thick static layer in the surface sediment, thus significantly inhibiting sediment P release. Moreover, the CACs-capping did not induce the Al3+ leaching and significant changes of the microbial community in sediments, and their performances of P immobilization could keep stable to resist the redox variation, which promised to be a good choice for P passivation in eutrophic lake sediments dominated by Al/Fe-P. These findings also confirmed that the risk of P release from Al/Fe-P (mainly Al-P)-dominated sediments was strongly influenced by continuously changing redox conditions, and was probably enhanced by the formation of Fe-P from the resorption of the released P.

Pollutants reduction via artificial mixing in a drinking water reservoir: Insights into bacterial metabolic activity, biodiversity, interactions and co-existence of core genera

Endogenous pollution due to long periods of hypolimnetic anoxia in stratified reservoirs has become a worldwide concern, which can threaten metabolic activity, biodiversity, water quality security, and ultimately human health. In the present study, an artificial mixing system applied in a drinking water reservoir was developed to reduce pollutants, and the biological mechanism involved was explored. After approximately 44 days of system operation, the reservoir content was completely mixed resulting in the disappearance of anoxic layers. Furthermore, the metabolic activity estimated by the Biolog-ECO microplate technique and biodiversity was enhanced. 16S rRNA gene sequencing indicated a great variability on the composition of bacterial communities. Co-occurrence network analysis showed that interactions among bacteria were significantly affected by the proposed mixing system. Bacteria exhibited a more mutualistic state and >10 keystone genera were identified. Pollutants, including nitrogen, phosphorus, organic matter, iron, and manganese decreased by 30.63-80.15 %. Redundancy discriminant analysis revealed that environmental factors, especially the temperature and dissolved oxygen, were crucial drivers of the bacterial community structure. Furthermore, Spearman's correlation analysis between predominant genera and pollutants suggested that core genus played a vital role in pollutant reduction. Overall, our findings highlight the importance and provide insights on the artificial mixing systems' microbial mechanisms of reducing pollutants in drinking water reservoirs.

Coal slime as a good modifier for the restoration of copper tailings with improved soil properties and microbial function

In recent years, the solid wastes from the coal industry have been widely used as soil amendments. Nevertheless, the impact of utilizing coal slime for copper tailing restoration in terms of plant growth, physicochemical characteristics of the tailing soil, and microbial succession remains uncertain.Herein, the coal slime was employed as a modifier into copper tailings. Their effect on the growth and physiological response of Ryegrass, and the soil physicochemical properties as well as the bacterial community structure were investigated. The results indicated that after a 30-day of restoration, the addition of coal slime at a ratio of 40% enhanced plant growth, with a 21.69% rise in chlorophyll content, and a 62.44% increase in peroxidase activity. The addition of 40% coal slime also increased the content of nutrient elements in copper tailings. Following a 20-day period of restoration, the concentrations of available copper and available zinc in the modified tailings decreased by 39.6% and 48.51%, respectively, with 40% of coal slime added. In the meantime, there was an observed augmentation in the species diversity of the bacterial community in the modified tailings. The alterations in both community structure and function were primarily influenced by variations in pH value, available nitrogen, phosphorus, potassium, and available copper. The addition of 40% coal slime makes the physicochemical properties and microbial community evolution of copper tailings reach a balance point. The utilization of coal slime has the potential to enhance the physicochemical characteristics of tailings and promote the proliferation of microbial communities, hence facilitating the soil evolution of two distinct solid waste materials. Consequently, the application of coal slime in the restoration of heavy metal tailings is a viable approach, offering both cost-effectiveness and efficacy as an enhancer.

Thermodynamic analysis and application for extracting valuable components from iron-phosphorus residue of spent catalysts

The method of extracting valuable metals from spent catalysts has been developed in recent years. In this paper, the solid waste produced in the treatment of spent catalyst was studied and named iron-phosphorus residue (IPR). IPR was composed of FePO4·2H2O, Fe3(PO4)2·3H2O, Fe5(PO4)4(OH)3·2H2O, and SiO2. Appreciable quantities of Ni, Co, V, Mo, and W were detected in IPR. Based on E-pH diagrams, different atmospheric leaching strategies were used to extract valuable components from IPR. Both the HCl and NaOH leaching are appropriate for treating IPR. An in-depth investigation on HCl atmospheric leaching showed that >95% of Fe, Ni, Co, V, and Mo, 76.9% of W, and 89.3% of P were extracted efficiently and SiO2 was enriched into the leach residue, at leaching temperature of 90 ℃, leaching time of 180 min, initial HCl concentration of 5 mol/L and liquid to solid ratio of 8:1 mL/g. The leaching mechanism was discussed via XRD, XPS, and FTIR. An efficient and green process for the recovery of valuable components in IPR has been developed. This research achieves the sufficient extraction of valuable components in IPR and provides significant guidance for the management of similar solid waste.

Inter-basin water diversion homogenizes microbial communities mainly through stochastic assembly processes

Inter-basin water transfer is an effective manner to achieve the optimal allocation of water resources, while accompanied by some ecological effects. The responses of microorganisms to water diversion and the ecological processes in regulating the community assembly are still unclear. Taking the eastern route of South-to-North Water Diversion Project as the study area, we investigated the microbial community patterns and the underlying assemblage processes in habitats with different hydrological connectivity, including isolated lakes, connected lakes and man-made canal. The results showed that microbial communities in the canal had higher diversity, lower dissimilarity, weaker compositional variation, and stronger co-occurrence patterns compared with that in the connected and isolated lakes. These findings suggested that the increase of connectivity among natural aquatic habitats due to water diversion can homogenize microbial communities and reduce microbial heterogeneity. The neutral and null models demonstrated the importance of stochastic processes in shaping microbial community assembly. Dispersal limitation and variable selection were the predominant mechanisms structuring microbial communities in the isolated lakes. Due to the homogenized environmental condition and the enhanced hydrologic connectivity in the canal and the connected lakes, microbial communities had higher dispersal capability and ecological drift occurred more frequently in these lotic habitats. The variations in microbial community structure were mainly driven by biotic ecological succession than abiotic factors, with positive and negative cohesion explained 63% and 25% of variability, respectively. Six taxa were considered as the potential introduced microorganisms, which may favor the nutrient biogeochemical cycling and the organic matter degradation, but may also bring ecological risks. Overall, this study provides a deeper understanding of the ecological consequences of inter-basin water diversion, and helps the regulation and management of these projects.

The microbial community and functional indicators response to flow restoration in gradient in a simulated water flume

Flow reduction has greatly affected the river ecological systems, and it has attracted much attention. However, less attention has been paid to response to flow restoration, especially flow restoration in gradient. Flow regime of rivers may affect river functional indicators and microbial community structure. This study simulated the ecological restoration of the flow-reduced river reach by gradiently controlling the water flow and explores the ecological response of environmental functional indicators and microbial community structure to the water flow. The results showed that gross primary productivity (GPP), ecosystem respiration rate (ER) and some water quality indices such as chemical oxygen demand, total nitrogen, and total phosphorus (TP), exhibited positive ecological responses to flow restoration in gradient. GPP and ER increased by 600.1% and 500.2%, respectively. The alpha diversity indices of the microbial community increased significantly with a flow gradient restoration. Thereinto, Shannon, Simpson, Chao1, and Ace indices, respectively, increased by 16.4%, 5.6%, 8.6%, and 6.2%. Canonical correspondence analysis indicated that water flow, Dissolved oxygen and TP were the main influencing factors for changes in bacterial community structure. Microbial community structure and composition present a positive ecological response to flow restoration in gradient. This study reveals that the main variable in the restoration of the flow-reduced river reach is the flow discharge, and it provides a feasible scheme for its ecological restoration.