Lanthanum hydroxide engineered sewage sludge biochar for efficient phosphate elimination: Mechanism interpretation using physical modelling

Adsorption recovery of phosphorus in contaminated water by calcium modified biochar derived from spent coffee grounds

Phosphate recovery from water is essential for reducing water eutrophication and alleviating the phosphorus resource crisis. In this study, spent coffee grounds and CaCl2 were used as raw materials and a modifier, respectively, to create a novel calcium modified biochar (MBC) for removing phosphorus from water. The modified biochar (MBC) was the best at removing phosphorous when the modifier concentration was 1.5 M with theoretically maximum adsorption capacity of 70.26 mg/g. MBC also performed well in the wide pH range of 3-11 under different phosphorus concentration gradients, with phosphorus removal efficiency of more than 50 %. According to kinetic analysis, the adsorption process at low phosphorus concentrations (50-100 mg/L) can be more properly described by the pseudo-first-order model, while the pseudo-second-order model best describes the adsorption process at high concentrations (200-600 mg/L). The thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. Characterization results revealed that surface precipitation, complexation, and ligand exchange were the dominant mechanisms of phosphorus adsorption. MBC has great potential to recover phosphorus from wastewater.

Phosphate adsorption on LDHs-biochar composite: Double-layer model for quantifying the contribution of ion exchange and ligand exchange

The adsorption performance of layered double hydroxides (LDHs) is limited owing to self-aggregation. To avoid this and effectively control the eutrophication of water bodies, biochar (BC) was synthesized, herein, by pyrolyzing waste sheep manure at 500°C, and Ca-Al-LDHs were loaded on the surface via a coprecipitation method to obtain Ca-Al-LDHs-BC(CA) composites with varying LDH contents. The fitted maximum adsorption capacities of the CA-5%, CA-10%, CA-15%, and CA-20% samples (corresponding to samples with 5%, 10%, 15%, and 20% LDHs, respectively) were 10.21, 16.14, 22.40, and 28.47 mg g-1, which were (when converted into metal proportions) 1.48, 1.23, 1.15, and 1.13 times of that of single hydrotalcite, respectively. The double-layer model was fitted using the Levenberg-Marquardt iterative algorithm, which when combined with the characterization results, confirmed that the adsorption of phosphate ions by CA-BC occurred via the double-layer adsorption mechanism. Two types of direct adsorption were observed: ion exchange, which resulted in first-layer adsorption, and ligand exchange, which resulted in second-layer adsorption, with first-layer adsorption accounting for a higher proportion. This double-layer adsorption mechanism showed that LDHs-BC could achieve higher ligand exchange performance compared to that achieved using only LDHs.

Significant Improvement of Adsorption for Phosphate Removal by Lanthanum-Loaded Biochar

Due to eutrophication, removing phosphate ions from wastewater has received a lot of attention. In order to improve the phosphorus adsorption capacity of the material, this study used biomass pyrolysis to create a series of biochars modified with metal chloride ions. In accordance with adsorption tests, lanthanum-loaded biochar (LCBC) had a significant phosphorus adsorption capacity of approximately 666.67 mg/g, which was 30 times greater than that of pristine biochar. Adsorption kinetic analysis revealed that the LCBC's adsorption process could be fitted to the pseudo-secondary kinetic equation, indicating that chemical processes were primarily responsible for controlling the adsorption process. Zeta potential, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis showed that the main adsorption mechanism of LCBC for phosphate removal was electrostatic attraction of protonated H+ with negatively charged mono-hydrogen phosphate and dihydrogen phosphate ions and complexation reaction of the C=O on the carboxyl group and P=O on the phosphate group with the oxygen on the phosphate group and hydroxyl group. According to regeneration performance results, LCBC performed relatively better than as-prepared adsorbents, and the phosphate removal rate was approximately 75.1% after the fifth regeneration cycle. The study provided a potential approach for creating and preparing an adsorbent with high adsorption for phosphate removal.

A critical review on the development of lanthanum-engineered biochar for environmental applications

Biochar and lanthanum (La) have been widely used in environment. However, there is a lack of knowledge and perspective on the development of La-engineered biochar (LEB) for environmental applications. This review shows that LEBs with a variety of La species via pre-/post-doping routes are developed for environmental applications. Specifically, precipitation, gelation, and calcination are the common sub-processes involved in the pre-/post-doping of La on the resultant LEB. The dominant La species for LEBs is La(OH)₃, which is formed through precipitation of La ions with various bases. Various La carbonates, e.g., LaOHCO₃, La₂(CO₃)₃, La₂CO₅, and NaLa(CO₃)₂, are also involved in the preparation of LEBs. The LEBs are high-efficient in the adsorption of phosphate, arsenic, antimonate and fluoride ions, attributed to the strong affinity of La to oxyanions and Lewis hard base. Lanthanum is also favorable for co-doping with transition metal species to further enhance the performances in adsorption or catalysis. This review also analyzes the prospects and future challenges for the preparation and application of LEBs in environment. Finally, this review is beneficial to inspire new breakthroughs on the preparation and environmental application of LEBs.

Mechanistic insights of removing pollutant in adsorption and advanced oxidation processes by sludge biochar

With the accelerated industrialization, more and more sewage sludge (SS) needs to be treated properly. The conversion of sludge into harmless biochar material with dual utilization value of adsorption and catalysis by pyrolysis is in line with the concept of sustainable development. However, the reaction mechanisms of pristine sludge biochar (SDBC) and its composites (SDBCs) in adsorption, persulfate (PS), and Fenton-like advanced oxidation processes (AOPs) are very closely related to its adsorption performance and catalytic efficiency. In this paper, from the application mechanisms of SDBC in adsorption and AOPs, we review in detail the common methods for synthesizing SDBC and their characteristics. We discuss the synthesis techniques that affect the structural, chemical, and catalytic properties of SDBC, including gasification, pyrolysis, and hydrothermal carbonation (HTC). The pyrolysis temperature, environmental factors, and sludge characteristics have important effects on the properties of SDBC, leading to different mechanisms in adsorption and catalytic processes. Furthermore, this paper systematically generalizes the mechanisms of SDBCs in adsorption, where π-π interactions and electrostatic attractions are the main adsorption mechanisms. Then, activation mechanisms of SDBCs in PS and Fenton-like AOPs systems are discussed, including free radical pathways and non-free radical pathways. Finally, we present several challenges and perspectives for the application of SDBC and SDBCs in the field of adsorption, PS, and Fenton-like AOPs from the mechanistic point of views.

Recycling of Waste Cotton Sheets into Three-Dimensional Biodegradable Carriers for Removal of Methylene Blue

Waste cotton sheets (WCS) are promising cellulose sources due to their high content of cellulose and large amount of disposal every year, which could be recycled and employed as low-cost structural materials. The present work aims at investigating the efficacy of hydrogel adsorbents prepared from regenerated WCS as the carriers of activated carbon (AC) for treating the dye-contaminated water. Activated WCS was directly dissolved in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) solvent and then regenerated into cellulose hydrogels, which were employed as three-dimensional biodegradable matrices for loading an extremely high content of AC (up to 5000%). The morphology and properties of resultant adsorbents were studied in detail. The results showed that different washing methods and contents of AC and cellulose had obvious effects on water contents, mechanical properties, and adsorption capacities of AC/WCS hydrogels. Especially, the hydrogels containing high AC content washed by gradient ethanol solvent exhibited outstanding compressive strengths of up to 3.0 MPa at 60% strain, while the adsorption capacity of 5000%AC/0.3CS toward a model dye methylene blue (MB, initial concentration of 200 mg/L) reached 174.71 mg/g at pH 6.9 and 35 °C. This was comparable to the adsorption capacity of original AC powders, while no AC powders were released from hydrogels to water. The adsorption of MB followed the Dubinin-Astakhov model and pseudo-first-order mechanism. Thermodynamic studies showed the spontaneous and endothermic nature of the overall physical adsorption process. Therefore, this work demonstrates the feasibility to recycle WCS into biodegradable carriers of functional compounds, and the AC/regenerated cellulose hydrogels have a high potential as a promising adsorbent with low-cost and convenient separation for dye removal from wastewater.

Removal of phosphate from aqueous solution by chitosan coated and lanthanum loaded biochar derived from urban dewatered sewage sludge: adsorption mechanism and application to lab-scale columns

A lanthanum modified sludge biochar chitosan (La-SBC-CS) microsphere was successfully synthesized by dropping sludge biochar (BC) and chitosan into a lanthanum chloride solution. Batch adsorption experiments were conducted to investigate the adsorption kinetics and isotherm. Application of continuous phosphate removal was achieved via lab-scale column reactors. The phosphate adsorption equilibrium data of the La-SBC-CS fitted well with the Freundlich isotherm, with a maximum adsorption amount of 81.54 mg p/g at 25 °C. Characterization of the adsorbent using scanning electron microscopy analysis (SEM), X-ray energy spectrum analysis (EDS), X-ray diffraction analysis (XRD) and Fourier infrared analysis (FTIR) techniques suggested that the possible adsorption mechanisms were electrostatic interaction, ligand exchange and complexation. The La-SBC-CS kept 76.37% phosphate removal efficiency after eight recycles. The results of continuous column reactor experiment demonstrated that the breakthrough time increased with an increase in adsorbent filling height, while it decreased with an increase in initial phosphate concentration or flow velocity. The Yoon model was applied to the continuous experimental data to predict breakthrough curves and determined the characteristic adsorption parameters for process design. This study indicated the potential for the practical application of La-SBC-CS in phosphate removal from wastewater.