Removal and recovery of phosphorus from solution by bifunctional biochar

Effective phosphorus removal using transformed water hyacinth: Performance evaluation in fixed-bed columns and practical applications

This study introduces calcined water hyacinth (CWH), processed at 650°C, as a novel and environmentally friendly adsorbent for phosphorus (P) removal from wastewater. Building on previous findings that identified CWH as a rich source of metal oxides and hydroxides (e.g., Ca(OH)₂, Al₂O₃, MgO, Fe₃O₄), this research explores its application in fixed-bed column systems for continuous adsorption processes. The study demonstrates that CWH effectively removes phosphorus through apatite formation, showcasing its potential for real-world water treatment. The phosphorus adsorption capacity increased from 23.64 to 26.55 mg/g when the flow rate was reduced from 1.5 to 0.5 mL/min. Breakthrough curves fitted to the Thomas, Adams-Bohart, and Yoon-Nelson models provided critical insights into column performance, while the Bed Depth Service Time (BDST) model confirmed the feasibility of employing CWH in continuous-flow systems. The practical tests on synthetic municipal wastewater, which revealed a maximum adsorption capacity of 5.20 mg/g, further demonstrated CWH's effectiveness for treating wastewater with low phosphorus concentrations, providing reassurance about its real-world applicability. Furthermore, the study found that increasing the adsorbent height improved column performance by extending breakthrough and exhaustion times, whereas higher flow rates led to faster saturation and reduced capacity. The exhausted CWH material can be repurposed as a soil amendment or fertilizer feedstock, supporting nutrient recycling.

Efficient Adsorption of Nitrogen and Phosphorus in Wastewater by Biochar

Nitrogen and phosphorus play essential roles in ecosystems and organisms. However, with the development of industry and agriculture in recent years, excessive N and P have flowed into water bodies, leading to eutrophication, algal proliferation, and red tides, which are harmful to aquatic organisms. Biochar has a high specific surface area, abundant functional groups, and porous structure, which can effectively adsorb nitrogen and phosphorus in water, thus reducing environmental pollution, achieving the reusability of elements. This article provides an overview of the preparation of biochar, modification methods of biochar, advancements in the adsorption of nitrogen and phosphorus by biochar, factors influencing the adsorption of nitrogen and phosphorus in water by biochar, as well as reusability and adsorption mechanisms. Furthermore, the difficulties encountered and future research directions regarding the adsorption of nitrogen and phosphorus by biochar were proposed, providing references for the future application of biochar in nitrogen and phosphorus adsorption.

Phosphorus recovery from agricultural waste via cactus pear biomass

In this study, the potential of cactus pear pruning waste (CPPW) as a low-cost adsorbent biomass for phosphorus (P) removal from aqueous solutions was investigated in batch mode. Biomass samples derived from cactus pear were collected and analyzed to investigate their properties when enriched with either calcium (Ca) or iron (Fe). The examination focused on the capacity of these samples to remove P. The P removal capacities were determined to be 2.27 mg g-1, 1.33 mg g-1, and 1.87 mg g-1 for Ca2+-enriched, Fe2+-loaded, and Fe3+-loaded biomass respectively. Among the various models studied, the Langmuir isotherm model was identified as the most appropriate for accurately describing the P adsorption the enriched biomass. The kinetics of the adsorption process were analyzed by applying the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The pseudo-second-order model provided the best fit to the experimental data. Furthermore, the desorption and regeneration process was investigated, revealing minimal P desorption (less than 8%) from Ca or Fe-loaded biomass, indicating the strong stability of the biomass-cation-P system. The estimated cost ranged from 8 to 161 euros per tonne, with an additional 230 euros when considering the pruning costs inherent to the crop. These costs fall below the threshold (320 euros per tonne) for the economically viable P reuse at the farm level. Consequently, CPPW, when reduced to powder and loaded with ions, emerges as an affordable adsorbent with good removal performance, offering a promising avenue for direct utilization in agriculture as both soil conditioner and fertiliser.

Recent developments in metallic-nanoparticles-loaded biochars synthesis and use for phosphorus recovery from aqueous solutions. A critical review

Phosphorus (P) represents a major pollutant of water resources and at the same time a vital element for human and plants. P recovery from wastewaters and its reuse is a necessity in order to compensate the current important depletion of P natural reserves. The use of biochars for P recovery from wastewaters and their subsequent valorization in agriculture, instead of synthetic industrial fertilizers, promotes circular economy and sustainability concepts. However, P retention by pristine biochars is usually low and a modification step is always required to improve their P recovery efficiency. The pre- or post-treatment of biochars with metal salts seems to be one of the most efficient approaches. This review aims to summarize and discuss the most recent developments (from 2020- up to now) in: i) the role of the feedstock nature, the metal salt type, the pyrolysis conditions, and the experimental adsorption parameters on metallic-nanoparticles-loaded biochars properties and effectiveness in recovering P from aqueous solutions, as well as the dominant involved mechanisms, ii) the effect of the eluent solutions nature on the regeneration ability of P-loaded biochars, and iii) the practical challenges facing the upscaling of P-loaded biochars production and valorization in agriculture. This review shows that the synthesized biochars through slow pyrolysis at relatively high temperatures (up to 700-800 °C) of mixed biomasses with Ca- Mg-rich materials or impregnated biomasses with specific metals in order to from layered double hydroxides (LDHs) biochars composites exhibit interesting structural, textural and surface chemistry properties allowing high P recovery efficiency. Depending on the pyrolysis's and adsorption's experimental conditions, these modified biochars may recover P through combined mechanisms including mainly electrostatic attraction, ligand exchange, surface complexation, hydrogen bonding, and precipitation. Moreover, the P-loaded biochars can be used directly in agriculture or efficiently regenerated with alkaline solutions. Finally, this review emphasizes the challenges concerning the production and use of P-loaded biochars in a context of circular economy. They concern the optimization of P recovery process from wastewater in real-time scenarios, the reduction of energy-related biochars production costs and the intensification of communication/dissemination campaigns to all the concerned actors (i.e., farmers, consumers, stakeholders, and policymakers) on the benefits of P-loaded biochars reuse. We believe that this review is beneficial for new breakthroughs on the synthesis and green application of metallic-nanoparticles-loaded biochars.

Thermally modified bamboo-eggshell adsorbent for phosphate recovery and its sustainable application as fertilizer

Phosphate recovery from wastewater using readily available biowaste-based adsorbents is beneficial for both eutrophication control and waste management. Bamboo char has a high-density porous structure and eggshell contains CaCO₃ with high affinity for phosphate. The combination of calcined bamboo and eggshell is a potential adsorbent for P recovery that has not been tested previously. Because bamboo char and eggshell both are popular for soil amendment, a P-loaded bamboo and eggshell composite is a promising fertilizer for long-term soil improvement. In this work, the feasibility of calcined bamboo and eggshell (BE) for P recovery and its use as fertilizer were investigated. The adsorption capacity and mechanism were examined using adsorption kinetic, isotherm, and thermodynamic analysis. The kinetic study showed that the experimental data sets were fitted best by a pseudo second-order model, indicating chemisorption. The Langmuir isotherm model estimated maximum adsorption capacities of 95.14 and 98.40 mg/g for BE 1:1 and 2:1 adsorbent. Monolayer adsorption occurred on a homogenous surface. The adsorption reaction was non-spontaneous at 298 K and exothermic for the BE 1:1 and 2:1 adsorbent, and the calculated Langmuir separation factor indicated favorable conditions for P adsorption. The desorption study showed lower P desorption capacity in water than in neutral ammonium citrate. P-loaded eggshell-modified bamboo char was an effective slow-release fertilizer for Japanese mustard spinach cultivation, which is a sustainable and environment friendly use of P-loaded materials.