Performance of novel Ca-biocomposites produced from banana peel and eggshell for highly efficient removal and recovery of phosphate from domestic wastewater

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.

Calcium silicate hydrate complex konjac glucomannan-based hydrogel selectively adsorbed phosphate in low alkalinity solution

The selective recovery of phosphate from wastewater can manage nutrients and realize the recycling of phosphorus resources. In this study, a novel konjac glucomannan/pectin/calcium silicate composite hydrogel (KP-CSH) was developed for efficient recovery of phosphate in aqueous solution. The amount of alkali released after the reaction of KP-CSH in a neutral solution was small (the pH of the solution after the reaction was < 9). In a wide initial pH range (3-10), the adsorption capacity of KP-CSH in 50 mg-P/L phosphate solution reached 39∼45 mg-P/g. Besides, even if the pH of the solution after the reaction was less than 8, it could still well adsorb phosphate. The kinetic and isothermal adsorption experiments indicated that the adsorption process of phosphate by KP-CSH was chemical adsorption, and the maximum adsorption capacity was 61.2 mg-P/g. KP-CSH preferentially adsorbed phosphate even in the presence of high concentrations of competitive ions. In the actual biogas slurry, KP-CSH also exhibited the strongest selectivity/affinity for phosphate, and its distribution coefficient (Kd) was significantly higher than that of other co-existing anions and cations. The adsorption mechanism analysis indicated that Ca was the main adsorption site of KP-CSH, and that the adsorption process of target pollutants mainly involved ligand exchange and the intra-sphere complexation. Further plant seed germination and seedling growth experiments suggested that KP-CSH after phosphate recovery did not exert a negative effect on the growth of plant seedlings, and increased the chlorophyll content of seedling leaves. These results demonstrate that KP-CSH is a potential adsorbent for efficient phosphate recovery, which can be used as a slow-release phosphate fertilizer after recovering phosphate.

Molecular insights and thermodynamic feasibility of phosphate adsorption on Ca-biocomposites using a simplified carbon structure

The removal of phosphorous from water sources is a critical challenge in mitigating water eutrophication. Adsorption using Ca-biocomposite-derived materials has proven to be highly effective for phosphorus removal. These biocomposites contain Ca, CaO, and Ca-(hydr)oxide species, which form Ca-P apatite phases, a potential fertilizer, holding promise for phosphorus recycling and promoting a circular economy. Density Functional Theory calculations were conducted to gain molecular insights into the thermodynamic feasibility of calcium-based adsorbents. Four models were used, viz. Ca2+, CaO monomer and dimmer, and Ca-(hydr)oxide, all embedded in a carbon matrix. Several binding modes were evaluated for [H2PO4]- and [H2PO4.6H2O]-, including monodentate mononuclear, bidentate mononuclear, and bidentate binuclear denticities. Adsorption, enthalpy, and Gibbs free energy changes were used as descriptors, together with Natural Bond Orbitals analysis. The findings indicate that [H2PO4.6H2O]- adsorption is thermodynamically favored primarily on the CaO dimmer, followed by the CaO monomer, and finally on Ca2+, suggesting a preference for binding phosphate through a monodentate mononuclear mode. The [H2PO4]- adsorption on the Ca-(hydr)oxide model was found to resemble the system's pH considering the H2O/OH ratio, an approximation of acid, intermediate, and basic pH conditions. Our research demonstrated the phosphate adsorption feasibility across a range of pH conditions, providing a solid foundation for further analysis such as infrared and X-ray photoelectron spectroscopy. The Ca-(hydr)oxide model effectively simulates interactions between phosphate species and calcium-based adsorbents, approximating real environments. It enhances understanding of adsorption across various chemical environments, including the pH effect, and aligns with observed structural changes during phosphate adsorption. By combining theory with practical applications, this model aids in comprehending phosphate removal processes, guiding adsorbent optimization, and environmental strategies like eutrophication mitigation.

Study on the removal efficacy and mechanism of phosphorus from wastewater by eggshell-modified biochar

The excessive discharge of phosphorus from rural domestic sewage is a problem that worthy of attention. If the phosphorus in the sewage were recovered, addressing this issue could significantly contribute to mitigating the global phosphorus crisis. In this study, corn straw, a common agricultural waste, was co-pyrolytically modified with eggshells, a type of food waste from university cafeterias. The resulting product, referred to as corn straw eggshell biochar (EGBC) was characterized using SEM, XRD, XPS, XRF, and other methods. Batch adsorption experiments were conducted to determine the optimal preparation conditions of EGBC and to explore its adsorption characteristics. EGBC showed strong adsorption effectiveness within a pH range of 5-12. The adsorption isotherm closely followed the Sips model (R2  > 0.9011), and the adsorption kinetics were more consistent with the pseudo-second-order model (R2  > 0.9899). The process was found to be both spontaneous and endothermic. Under optimal conditions, the phosphorus adsorption capacity of EGBC was measured to be 288.83 mg/g. This demonstrates the high efficiency of EGBC for phosphorus removal and illustrates an effective method of utilizing food waste for environmental remediation. PRACTITIONER POINTS: Biochar prepared from waste eggshell was used to removal and recovery phosphorus in wastewater treatment. EGBC has an impressive adsorption capacity that can reach up to 288.83 mg/g. EGBC has excellent adsorption and filtration capabilities, and there is a sudden increase in concentration at 900 min in the breakthrough curve of EGBC. EGBC has good regeneration performance, with an adsorption effect of 65% and an adsorption capacity of 121 mg/g after four desorption and regeneration cycles.