Adsorption and immobilization of phosphorus from eutrophic seawater and sediment using attapulgite - Behavior and mechanism

Phosphorus immobilization in sulfide-ferrous oxidation process driven by nitrate reduction during black-odorous sediment remediation

During remediation of black-odorous sediment, the pathways of phosphorus immobilization require clarification alongside the oxidation of sulfide and ferrous. This study separated the oxidation stages of sulfide and ferrous through controlled sodium nitrate dosing ratios and methods, and analyzed the changes in phosphorus species and immobilization effects throughout these processes. Results showed that iron-bound phosphorus was the primary contributor to the phosphorus immobilization in the oxidation process, with increased 19% in ferrous oxidation stage and affected the transformation between phosphorus sources or sinks in the adsorption experiment. Additionally, the increase in abundance of phosphorus uptake and transport genes, and denitrifying phosphorus accumulation genes in sediment after ferrous oxidation (1 %-18 % and 87 %-164 %, respectively) indicated the potential for biological phosphorus immobilization. These results demonstrated that higher degrees of sediment oxidation correlate with stronger phosphorus immobilization capacities, providing theoretical bases for phosphorus immobilization during the restoration of black-odorous water bodies.

Toward a better understanding of polymeric aluminum-modified attapulgite for the efficient removal of low phosphorus concentration

Attapulgite (ATP) is a biocompatible clay mineral that efficiently absorbs water. It is widely used in water treatment due to its environmental friendliness and cost-effectiveness. This study aimed to develop a volume-expansion structure-based attapulgite flocculant (VES-ATP) using aluminum salt and attapulgite (ATP) under alkaline conditions, specifically for the treatment of water containing low levels of phosphorus. The VES-ATP was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The removal of phosphorus by the VES-ATP was conducted by varying the mass ratio of Al to attapulgite (denoted as RmAl/mATP), ATP dosage, and pH. The results showed that the VES-ATP had a good expansion and dispersibility in the presence of alkalized aluminum species. The basicity as the molar ratio of OH to Al (0.8 or 1.6) determined the expansion feasibility, and the coverage degree of Al onto ATP, as indicated by the mass ratio of Al to attapulgite (denoted as RmAl/mATP), determined Al flocculation efficiency. Higher values such as RmAl/mATP = 4:1 and 2:1 may result in a better flocculation. Low phosphorus treatment was successfully achieved through Al flocculation and ATP adsorption, including complexation, hydrogen bonding, and electrostatic attraction. As expected, the VES-ATP generated larger size flocs with a bigger fractal dimension than that with the sole Al flocculation. As a result, the total phosphorus could be reduced to the level below 5 μg/L. It is more efficient in the pH range of 5-9. Overall, the coupling of aluminum and attapulgite has significantly enhanced both purification capabilities of phosphorus. PRACTITIONER POINTS: Polymeric aluminum-modified attapulgite was efficient for removal of low phosphorus concentration. Phosphorus concentrations can be reduced to below 5 μg/L. Polymeric aluminum and attapulgite are both safe, and this technology is suitable for water treatment.

Enhanced degradation of enrofloxacin in mariculture wastewater based on marine bacteria and microbial carrier

This study aimed to isolate marine bacteria to investigate their stress response, inhibition mechanisms, and degradation processes under high-load conditions of salinity and enrofloxacin (ENR). The results demonstrated that marine bacteria exhibited efficient pollutant removal efficiency even under high ENR stress (up to 10 mg/L), with chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN) and ENR removal efficiencies reaching approximately 88%, 83%, 61%, and 73%, respectively. The predominant families of marine bacteria were Bacillaceae (50.46%), Alcanivoracaceae (32.30%), and Rhodobacteraceae (13.36%). They responded to ENR removal by altering cell membrane properties, stimulating the activity of xenobiotic-metabolizing enzymes and antioxidant systems, and mitigating ENR stress through the secretion of extracellular polymeric substance (EPS). The marine bacteria exhibited robust adaptability to environmental factors and effective detoxification of ENR, simultaneously removing carbon, nitrogen, phosphorus, and antibiotics from the wastewater. The attapulgite carrier enhanced the bacteria's resistance to the environment. When treating actual mariculture wastewater, the removal efficiencies of COD and TN exceeded 80%, TP removal efficiency exceeded 90%, and ENR removal efficiency approached 100%, significantly higher than reported values in similar salinity reactors. Combining the constructed physical and mathematical models of tolerant bacterial, this study will promote the practical implementation of marine bacterial-based biotechnologies in high-loading saline wastewater treatment.

Phosphorus removal from urban wastewater through adsorption using biogenic calcium carbonate

Phosphorus (P) removal from urban wastewater is increasingly relevant in the wastewater treatment sector. The present work aims to contribute to the study of the adsorption process as a P removal technology. Biogenic calcium carbonate from industrial eggshell waste prepared by milling and calcination was used as an adsorbent. Batch adsorption experiments were conducted using real wastewater with 40 mg P/L (orthophosphate), original pH 7.33, under stirring conditions (100 rpm). The adsorbent was characterized using SEM-EDS, XRD, and FTIR-ATR before and after adsorption. From an initial screening of calcination times (15, 30, 60, and 120 min) and considering a balance between P removal and energy saving, the adsorbent selected was eggshell calcined at 700 °C for 60 min. The Langmuir isotherms describe the experimental data with a maximum adsorption capacity of 4.57 mg P/g at 25 °C. The adsorption process reached equilibrium within 120 min for different dosages (5, 10, and 20 g/L at 25 °C). Batch experiments showed that SO42-, at a concentration of 2689 mg/L reduced the P adsorption selectivity for dosages ≤10 g/L at 25 °C. Characterization of the loaded adsorbent shows that P adsorption from real wastewater is mostly electrostatic attraction, with the contribution of ligand exchange and microprecipitation. The adsorption capacity and behavior of the selected adsorbent seem promising for P removal from urban wastewater compared with other low-cost adsorbents.

Quaternary ammonium-functionalized rosin-derived resin for the high-performance capture of caramels: Experiments and quantum chemical theory simulations

Water contamination caused by discharge of spent washes containing colorants remains controversial. In this study, rosin-derived strongly basic macroporous anion-adsorption resin (RSBMAR) was designed as an advanced adsorbent for scavenging caramel, the most recalcitrant colorant in spent washes. Toxicity tests suggest that RSBMAR is environmentally friendly and hardly threatens aquatic organisms. RSBMAR exhibits outstanding caramel capture efficiency because of its rich target quaternary ammonium (-R4N+) and protonated tertiary amine (-R3NH+) groups, abundant porous structure, large specific surface area, excellent thermal stability, and good sphericity. The caramel adsorption capacity of RSBMAR was 165.86 mg/g and the decolorization efficiency reached 96.75%. After five cycles, the spent RSBMAR maintained a high decolorization rate, indicating excellent renewability. Multiple characterizations indicated that caramel capture was largely mediated by charge interaction between -R4N+/-R3NH+ (RSBMAR) and -RCOO-/-RCOOH (caramel), followed by H-bonds. Quantum chemical theory simulations, including electrostatic potential, local ionization energy, frontier molecular orbitals, and independent gradient model analyses, further visualized caramel capture mechanisms at atomic level. Hirshfeld surface analysis revealed that RSBMAR acts as both an H-bond donor and acceptor during caramel uptake. Dynamic adsorption was performed to treat real wastewater, laying the foundation for the industrial application of RSBMAR.

Super-amphiphobic arabic gum-based coatings on textile for on-demand oily and dye wastewater treatment

Different membrane materials have broadly been constructed for oil-containing water separation, but most of preparation routes involve corrosive or toxic chemicals and especially many materials have only single superwetting property. Herein, a novel and eco-friendly cellulose-based textile membrane is developed by incorporating the composite coating consisting of arabic gum (AG), attapulgite (APT), and iron (Fe) onto cellulose textiles. The functionalized textile is superoleophobic underwater and superhydrophobic underoil. As a result, the textile prewetted with water or oil can be employed to separate light oil layer/water and heavy oil layer/water mixtures, respectively, and the separation efficiency to the two types of mixtures is larger than 98.3 %. Results also reveal that the decorated textile possesses superior stability and recyclability in purifying oily wastewater. More importantly, such coated textile is capable of filtrating water-soluble contaminants (dyes) from polluted water. Due to the versatility and environmental compatibility of product as well as the accessibility as agricultural and forestry product as raw materials, the advanced textiles may offer effective solutions to oily wastewater purification and water-soluble contaminant removal.

Exploration of the Compressive Strength and Microscopic Properties of Portland Cement Taking Attapulgite and Montmorillonite Clay as an Additive

The effects of attapulgite and montmorillonite calcinated at 750 °C for 2 h as supplementary cementing materials (SCMs) on the working properties, mechanical strength, phase composition, morphology, hydration and heat release of ordinary Portland cement (OPC) were studied. The results show that pozzolanic activity increased with time after calcination, and with the increase in content of calcined attapulgite and calcined montmorillonite, the fluidity of cement paste exhibited a downward trend. Meanwhile, the calcined attapulgite had a greater effect on the decrease in the fluidity of cement paste than calcined montmorillonite, and the maximum reduction was 63.3%. Within 28 days, the compressive strength of cement paste with calcined attapulgite and montmorillonite was higher than that of the blank group in the later stage, and the optimum dosages of calcined attapulgite and montmorillonite were 6% and 8%, respectively. In addition, the compressive strength of these samples reached 85 MPa 28 days later. The introduction of calcined attapulgite and montmorillonite increased the polymerization degree of silico-oxygen tetrahedra in C-S-H gels during cement hydration, thereby contributing to accelerating the early hydration process. In addition, the hydration peak of the samples mixed with calcined attapulgite and montmorillonite was advanced, and the peak value was lower than that of the control group.