Investigation into lanthanum-coated biochar obtained from urban dewatered sewage sludge for enhanced phosphate adsorption

Scaled-up development of magnetically recyclable Fe3O4/La(OH)3 composite for river water phosphate removal: From bench-scale to pilot-scale study

The use of magnetic lanthanum-based materials for phosphate removal from river water has gained increasing attention. However, challenges to produce and use lanthanum-based materials in large-scale or pilot-scale studies remain. In this work, a kilogram-scale Fe₃O₄/La(OH)₃ magnetically recyclable composite for removing phosphate from river water was developed through a low-temperature precipitation route. The composite was used to remove phosphate from river water at both bench- and pilot-scales. Based on the bench-scale tests, the developed Fe₃O₄/La(OH)₃ composite was found to have excellent magnetic particle separation efficiency (>98%) and a sorption capacity of 11.77 mg/g for phosphate. A 1.0 g/L dosage of the composite in the river water sample was able to selectively reduce the phosphate level from 0.089 to 0.005 mg/L in 60 min over five consecutive adsorption cycles. At the pilot-scale, the Fe₃O₄/La(OH)₃ composite only achieved 36.0% phosphate removal efficiency, which is considerably different from the bench-scale results over an operational time of five months and a total treatment volume of 300 m³. This significantly reduced removal efficiency is mainly attributable to turbidity, suspended solids, and organic matter in the river water and the deteriorated magnetic separation efficiency. This study revealed potential challenges and shed new insights on moving magnetic nanocomposite-based technology from the bench-scale to the pilot-scale, which can inspire new designs for the application of similar technology.

Enhanced recovery of phosphate as a value-added product from wastewater by using lanthanum modified carbon-fiber

The aim of this study is to present the potential of activated carbon fiber (CF) impregnated with lanthanum (La) as a novel adsorbent (La-CF) of phosphate-phosphorus (P) and to assess the value-added due to P-recovery from wastewater using La-CF. The CF were loaded with La and the loaded CF was then calcined at 500 °C. The La-CF adsorbent was used in a series of batch experiments to characterize the adsorption of P at pH of 6-10 and P concentrations of 1-200 mg/L. Physical-chemical properties such as surface morphology, surface charge, surface area, and surface chemistry were determined for the La-CF. The La-CF exhibited adsorption capacity of 196.5 mg/g, fast sorption kinetics and high selectivity for P removal from aqueous solution. La-CF removed 97.3% of P from wastewater and achieved P-level to below 2 mg/L. It was repetitively reused over 10 times in successive cycles to remove P from wastewater. The value-added by recovery of P from wastewater was calculated at around 0.12 US$/L, demonstrating economic benefits of La-CF. In conclusion, the successful removal, recycling, and recovery value-added of P using La-CF adsorbent displayed good potential for developing the technology for treatment of wastewaters to recover valuable compounds such as phosphorus.

Efficient recovery of phosphate from simulated urine by Mg/Fe bimetallic oxide modified biochar as a potential resource

The massive use of phosphate fertilizers in agriculture is costly and induces water pollution, calling for more sustainable phosphate sources in the context of the circular economy. Here we prepared a new adsorbent based on waste straw biochar modified with the Mg/Fe bimetallic oxide, namely the Mg/Fe biochar, to recover phosphate from the simulated urine as an possible phosphate fertilizer. About 90% phosphate was recovered from the simulated urine with a wide pH range of 3.0-9.0 and a maximum adsorption capacity of 206.2 mg/g, using 1 g/L of Mg/Fe modified biochar. A pseudo second-order kinetics and Sips model were proposed to fit the experimental data well, suggesting that the adsorption was controlled by physical and chemical processes, which is driven by electrostatic attraction, intra-particle diffusion, ion exchange and surface ligand exchange. Overall, the Mg/Fe biochar is renewable and can recover more than 70% of phosphate in the simulated urine after 5 cycles of reuse, which appears as a safe and efficient adsorbent to recycle phosphate from urine.

Modification of Hardwood Derived Biochar to Improve Phosphorus Adsorption

The excessive application of phosphorus in agricultural lands leads to serious environmental issues. Efficient application is beneficial from an economic and environmental perspectives. Biochar can be used as a carrier for slow release of phosphate. However, its adsorption capacity is limited. In this work, biochar was prepared at different pyrolysis temperatures (350–550 °C). The biochar prepared at 550 °C had the highest adsorption capacity and was selected for modification by magnesium impregnation. Magnesium modification enhanced the adsorption capacity by 34% to a theoretical max adsorption capacity of 463.5 mg·g−1. The adsorbed phosphate can be desorbed. The desorption was bi-phasic with fast- and slow-release fractions. The distribution of the phosphate fractions was pH dependent with slow release being most prominent in neutral conditions. Mg modified biochar can be used to recover phosphate and then used as a carrier for slow release of phosphate. The bi-phasic desorption behaviour is useful as the fast release fraction can provide the immediate phosphate needed during plant establishment, while the slow-release fraction maintains steady supply over extended periods.

Phosphate-lanthanum coated sewage sludge biochar improved the soil properties and growth of ryegrass in an alkaline soil

The reclamation of alkaline soils remains challenging while the application of biochar has been proposed as a viable measure to rehabilitate soil fertility. The objective of the current pot study was to evaluate the efficacy of various P-La modified sewage sludge biochars (SSBC, La-SSBC, SSBC-P, La-SSBC-P) on soil phosphate-retention and ryegrass (Lolium perenne L.) growth in an alkaline soil (excess CaCO3). The results revealed that germination percentage, plant dry biomass, plant height, and the total amount of P in the ryegrass leaves were significantly (P < 0.05) improved under La-SSBC-P treatment as compared to other treatments. La-SSBC-P treatment significantly altered the chemical characteristics of post-harvest alkaline soil, such as pH, electrical conductivity (EC), cation exchange capacity (CEC), soil organic matter (SOM), limestone (CaCO3), phosphate, and lanthanum contents. In comparison to the SSBC treatment, soil available phosphorous (AP) contents under La-SSBC-P were enhanced by 6.7 times after loading biochar with P and La (La-SSBC-P). After the plantation of ryegrass, concentration of lanthanum in the soil was negligible. The contents of CaCO3 reduced by 76.2% after La-SSBC-P biochar treatment, compared to the cultivated control. This phenomenon clearly indicated that lanthanum was reduced due to the precipitation with limestone, which was proposed based on the data of X-ray diffraction (XRD) analysis. Overall, results showed that the P-loaded lanthanum decorated biochar (La-SSBC-P) could be used as a potential substitute for P-fertilizer under the experimental conditions. However, field experiments are required to confer the efficiency of La-SSBC-P as P fertilizer in different soils.

New insights into interactions of organic substances in poultry slurry with struvite formation: An overestimated concern?

The high content of organic substances in strength agro-industrial wastewater has been documented to be among the major barriers hampering nutrient recovery efficiency of struvite precipitation. However, our results in this study show that the previously reported negative impacts of organic substances in high-strength agricultural wastewater on struvite precipitation might be overestimated. This study is the first to test the influence of three forms of organic substances from real high-strength wastewater that contains a complex of particulate, colloidal and soluble organic substances, on nutrient recovery efficiency and product quality through struvite precipitation at varying pH conditions. Our results demonstrated that the inhibition of organic substances on struvite formation only happens at the pH levels of <9.0 with recovery reduction of PO₄^3- (5-15%) and NH₄⁺ (6-13%). The inhibitory effect of the organic substances at the optimal pH range (9.5-10) reported from the literature review is only ≤5%. Moreover, the transformation in the contents of humic- and protein-like substances with an increment in pH was characterized and may contribute to mitigate the inhibition of nutrient recovery. Even though the particulate and colloidal organic substances slowed the precipitation reaction, they substantially increased the particle size (i.e., 70% and 40%, respectively) of the formed struvite. The presence of organic substances in all tested forms does not significantly influence the purity and crystalline structure of struvite which can still be used as a slow-releasing fertilizer. Regarding the relocation process of organic substances during struvite precipitation under varying pH conditions, understanding the interaction between organics and heavy metals which in turn affect the dynamics of heavy metals in solution and precipitates remains limited; thus, additional research is needed.

Fabrication of thermoresponsive metal-organic nanotube sponge and its application on the adsorption of endocrine-disrupting compounds and pharmaceuticals/personal care products: Experiment and molecular simulation study

Thermoresponsive metal-organic nanotube modified (MONT-pNIPAM, pNIPAM = poly N-isopropylacrylamide) sponge was synthesized using the dip-coating method and served as an adsorbent for endocrine-disrupting compounds (EDCs) and pharmaceuticals/personal care products (PPCPs) removal. The material was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and N2 sorption-desorption. Nonlinear regression-based equations were derived to optimize pH and ionic strength during process. Though thermoresponsive polymer phase transition between dissolve and aggregate, realizing the adsorption tunnel "ON-OFF" under the temperature control. Adsorption kinetics and isotherms were investigated on the basis of a static experiment. The pseudo-second-order kinetic model and the Langmuir isotherm were fitted well to characterize adsorption. At an initial concentration of 50 mg L-1, maximum adsorption capacity were 128 mg/g, 184 mg/g and partition coefficient were 1.09 mg g-1 μM-1, 1.13 mg g-1 μM-1 for dibutyl phthalate (DBP) and parachlorometaxylenol (PCMX), respectively. The density-functional theory (DFT) was applied to calculate the interaction energy and investigate the possible mechanism. Combining the experimental data with theoretical calculation, results demonstrated that the MONT-pNIPAM sponge was a highly efficient adsorbent material that was suitable for the removal of EDCs/PPCPs from water.

Phosphate removal from river water using a highly efficient magnetically recyclable Fe3O4/La(OH)3 nanocomposite

Lanthanum based nanocomposites have attracted much attention for their efficiency and capacity in removing phosphate from water. This study developed a Fe₃O₄/La(OH)₃ nanocomposite through a precipitation route at room temperature and used the nanocomposite to remove phosphate from river water. Performance of the Fe₃O₄/La(OH)₃ nanocomposite was evaluated in terms of sorption kinetics, sorption isotherms, different solution pH values, competing ions, and regenerative ability. The Fe₃O₄/La(OH)₃ nanocomposite showed a nanosphere-like morphology with 97% magnetic separation efficiency, excellent phosphate removal capacity of 253.83 mg/g, 99% phosphate selectivity in the presence of chloride, nitrate, sulfate, fluoride, and calcium as competing ions and excellent reusability in ten cycles. Based on these findings, the Fe₃O₄/La(OH)₃ nanocomposite was used to remove phosphate from river water. It was found that, in 60 min, a 0.1 g/L dosage of the nanocomposite was able to reduce the phosphate in the water from 0.087 mg/L to 0.002 mg/L. Moreover, studying of the removal mechanism of the nanocomposite revealed that surface complexation and the electrostatic interaction between phosphate species and lanthanum hydroxide played a prominent role in the sorption of phosphate.

Efficient removal of Pb(II) through recycled biochar-mineral composite from the coagulation sludge of swine wastewater

Zeolite-Mg/Fe chloride dual enhanced coagulation is a cost-effective method for advanced treatment of swine wastewater, but the sludge generated after the enhanced coagulation remains to be a problem. In this study, the precipitate from a swine wastewater coagulation unit was regenerated by pyrolysis treatment in an O₂-limited environment to develop a high efficient adsorbent (biochar-mineral composite, BMC) for the removal of Pb(II) from wastewater. SEM images indicate that complex Mg/Fe oxides and sludge biochar gathered around zeolite particles. Effects of different influencing factors such as Pb(II) initial concentration, pH, adsorption time and ion concentration on the adsorption performance were investigated. The results show that the Langmuir isotherm model can better express the adsorption of Pb(II) on BMC than Freundlich model and Temkin model. BMC pyrolyzed at 500 °C showed the maximum adsorption capacity of 450.58 mg/g under experimental condition of 25 °C, 100 mg/L Pb(II) initial concentration and the initial pH of 5.6. The adsorption mechanisms on BMC mainly include ion exchange, electrostatic interaction. Therefore, it is a cost-effective and environmental-friendly strategy to obtain biochar-mineral composite from recycled sludge, which can efficiently remove Pb(II) from wastewater.

Persulfate oxidation for alternative sludge treatment and nutrient recovery: An assessment of technical and economic feasibility

The introduce of tighter waste disposal regulations and increasing resource scarcity make the re-utilization of waste activated sludge a hot and crucial research topic. Compared with traditional sludge disposal technologies (e.g. landfill and incineration), advanced oxidation processes have been proven to be an environmentally friendly method for sludge stabilization and disintegration. However, the effectiveness of persulfate oxidation for sludge degradation, and the re-utilization of its embedded nutrients have been rarely reported. Therefore, this work is to investigate the technical and economic feasibility of using persulfate oxidation and struvite precipitation for sludge degradation and nutrient recovery. The results show that with the assistance of ultraviolet radiation, released phosphate and ammonia nitrogen from sludge could reach 233.4 and 265.6 mg/L. Besides, 92.8% phosphate and 32.6% ammonia-nitrogen could be recovered by struvite precipitation at a pH of 9.5, with an Mg: P molar ratio of 1.1:1. The economic analysis shows that the operational cost of the proposed process was 25% higher than traditional sludge disposal (267.5 $/ton), but its capital investment is much lower. Investigations on chemical dosage minimization, energy reclamation and process optimization are suggested to reduce the process's operating cost in the future.

Control of internal phosphorus release from sediments using magnetic lanthanum/iron-modified bentonite as active capping material

The non-magnetic capping materials are difficult to be recycled from the water bodies after their application, leading to the increase in the cost of the sediment remediation. To address this issue, a capping material, i.e., magnetic lanthanum/iron-modified bentonite (M-LaFeBT) was prepared by loading lanthanum onto a magnetic iron-modified bentonite (M-FeBT) and used to control the internal phosphorus (P) loading in this study. To determine the capping efficiency and mechanism of M-LaFeBT, the impact of M-LaFeBT and M-FeBT capping on the mobilization of P in sediments was investigated, and the stabilization of P bound by the M-LaFeBT and M-FeBT capping layers was evaluated. Results showed that M-LaFeBT possessed good magnetic property with a saturated magnetization of 14.9 emu/g, and exhibited good phosphate adsorption ability with a maximum monolayer sorption capacity (Q_MAX) of 14.3 mg P/g at pH 7. Moreover, M-LaFeBT capping tremendously reduced the concentration of soluble reactive P (SR-P) in the overlying water (OL-water), and the reduction efficiencies were 94.7%-97.4%. Furthermore, M-LaFeBT capping significantly decreased the concentration of SR-P in the pore water and DGT (diffusive gradient in thin films)-labile P in the profile of OL-water and sediment. Additionally, most of P bound by the M-LaFeBT capping layer (approximately 77%) was stable under natural pH and reducing conditions. The phosphate adsorption ability for M-LaFeBT was much higher than that for M-FeBT, and the Q_MAX value for the former was 4.86 times higher than that for the latter. M-LaFeBT capping gave rise to a higher reduction of DGT-labile concentration in the profile of OL-water and sediment than M-FeBT capping. The P adsorbed by the M-LaFeBT capping layer was more stable than that by the M-FeBT capping layer. Results of this study demonstrate that M-LaFeBT is promising for utilization as an active capping material to intercept sedimentary P release into OL-water.

Elimination of humic acid in water: comparison of UV/PDS and UV/PMS

Humic substances are polyelectrolytic macromolecules; their presence in water leads to many environmental problems without effective treatment. In this work, the elimination of humic acid (HA), a typical humic substance, has been examined through ultraviolet (UV) activation systems in the presence of peroxydisulfate (PDS) and peroxymonosulfate (PMS), respectively. The results indicated that 92.9% and 97.1% of HA were eliminated with rate constants of 0.0328 ± 0.0006 and 0.0436 ± 0.0011 min⁻¹ with 180 and 60 min treatment times at pH 6 and 3 when adding 3 and 1 mmol L⁻¹ oxidant during UV/PDS and UV/PMS, respectively; the corresponding electric energies per order were 0.0287 and 0.0131 kW h m⁻³. The HA removal was systematically investigated by varying different reaction parameters, including radical scavengers, persulphate dose, solution pH, and initial HA concentration, and by addition of various common ions. Moreover, the decomposition details were identified through the changes in the dissolved organic carbon, unique UV absorbances, and UV spectroscopic ratios. Furthermore, the destruction mechanism was verified by fluorescence spectroscopy, demonstrating that the HA structure was decomposed to small molecular fractions in the two UV/persulphate systems. In addition, the purification of HA by the two UV/persulphate processes was assessed in actual water matrices.

In this work, UV-activated persulphate treatment (UV/PDS and UV/PMS) was found to be an effective method for HA removal.

Mechanism of phosphate removal from aqueous solutions by biochar supported nanoscale zero-valent iron

The purpose of this study was to investigate the removal mechanism of phosphate by rape straw biochar (RSBC) supported nanoscale zero-valent iron (nZVI).