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

Near-complete recovery of phosphorus from fresh human urine: Combining magnesium-air fuel cells with modified granular attapulgite

In light of the urge demand for sustainable development and environmental protection, the recovery of phosphorus from source-separated urine holds great significance. This study proposed a novel approach combining magnesium-air fuel cells (MAFC) with modified granular attapulgite (GAT) to recover phosphorus from urine, producing a bulk blending fertilizer and soil amendment. The phosphorus adsorption capacity of GAT was enhanced by more than threefold following modification. The combined process attained a phosphorus recovery efficiency of 99.97 %, with the effluent phosphorus concentration decreased to 0.18 mg L-1, which complies with the discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002). In practical implementation, the process effectively treated real urine, yielding artificial phosphate ores (APOs) with a struvite content exceeding 88 % and a phosphate purity over 98 %. The pilot-scale assessment indicated a net benefit of 11.29 $·m-3 of urine, demonstrating significant economic feasibility. This work presents an innovative strategy for the efficient recovery of phosphorus from complex wastewater, showcasing its promising potential for practical applications.

Use of corn carbon as an additive to enhance magnesium metal self-corrosion and recover phosphorus from swine wastewater in the form of struvite

Recovery of phosphate from swine wastewater is significant for alleviating eutrophication in aquatic ecosystems and addressing the increasing scarcity of phosphorus resources. In this study, a method for phosphate recovery from swine wastewater using corn carbon as an additive and non-dynamic magnesium metal self-corrosion was studied. The effects of reaction time, C:Mg mass ratio, stirring rate, and aeration rate on phosphate recovery were discussed, and eight experimental models were explored. The results demonstrated that when the optimal reaction time was 7 h, the mass ratio of corn carbon to the magnesium plate was 5:1. When the stirring rate was 800 rpm/min and the aeration rate was 0.48 m3/L·h, the pH value of wastewater was 9.24, and the phosphate recovery rate was 95.61%. The recovered precipitate was characterized by SEM-EDS and XRD as struvite with excellent crystal shape. This method not only successfully achieved waste treatment but also recovered phosphorus from swine wastewater.

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.

Microalgae-derived hydrogels/membranes for phosphorus removal and recovery from aquaculture tailwater: Waste utilization and phosphorus recycling

Efficient removal and recovery of phosphorus from aquaculture tailwater is challenging due to increasing strict water environment restrictions. This study presents a sustainable approach by using microalgae-waste-derived hydrogels/membranes for phosphorus adsorption and microalgae cultivation. Waste from Euglena gracilis (or Haematococcus pluvialis), modified with magnesium, was converted into biochars (abbreviated as MEBC or MHBC). This biochars were then combined with sodium alginate to fabricate hydrogels and with polyvinyl chloride to create membranes. Due to the almost 100 % phosphorus removal of MEBC (or MHBC) biochar, the as-obtained hydrogels/membranes demonstrated excellent phosphate adsorption, reducing total phosphorus in real aquaculture tailwater from 11 mg/L to 0. Additionally, the phosphorus-saturated hydrogel served as a phosphorus source for microalgae cultivation, while the membranes facilitated microalgae harvesting with a water flux over 40 L/m2/h. This study provides an eco-friendly solution for using microalgae-waste-derived materials to effectively address phosphorus removal and recovery challenges in aquaculture tailwater.

Soil adsorption potential: Harnessing Earth's living skin for mitigating climate change and greenhouse gas dynamics

Soil adsorption, which could be seen as a crucial ecosystem service, plays a pivotal role in regulating environmental quality and climate dynamics. However, despite its significance, it is often undervalued within the realms of research and policy frameworks. This article delves into the multifaceted aspects of soil adsorption, incorporating insights from chemistry and material science, ecological perspectives, and recent advancements in the field. In exploring soil components and their adsorption capacities, the review highlights how organic and inorganic constituents orchestrate soil's aptitude for pollutant mitigation and nutrient retention/release. Innovative materials and technologies such as biochar are evaluated for their efficacy in enhancing these natural processes, drawing a link with the sustainability of agricultural systems. The symbiosis between soil microbial diversity and adsorption mechanisms is examined, emphasizing the potential for leveraging this interaction to bolster soil health and resilience. The impact of soil adsorption on global nutrient cycles and water quality underscores the environmental implications, portraying it as a sentinel in the face of escalating anthropogenic activities. The complex interplay between soil adsorption mechanisms and climate change is elaborated, identifying research gaps and advocating for future investigations to elucidate the dynamics underpinning this relation. Policy and socioeconomic aspects form a crucial counterpart to the scientific discourse, with the review assessing how effective governance, incentivization, and community engagement are essential for translating soil adsorption's functionality into tangible climate change mitigation and sustainable land-use strategies. Integrating these diverse but interconnected strata, the article presents a comprehensive overview that not only charts the current state of soil adsorption research but also casts a vision for its future trajectory. It calls for an integrated approach combining scientific inquiry, technological innovation, and proactive policy to leverage soil adsorption's full potential to address environmental challenges and catalyze a transition towards a more sustainable and resilient future.

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.

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

Using biowaste-based adsorbents to remove phosphorus (P) from wastewater offers significant benefits concerning eutrophication mitigation and addressing waste management challenges. In this work, Ca-biocomposites were prepared by pyrolysis (700 °C) of a mixture of banana peel (BP) and eggshell (ES). The mass ratio of BP to ES was varied in 2:1, 1:1, and 1:2 ratios. Among the tested mixtures, the BPES-1:2 sample exhibited excellent P removal performance, reaching a maximum P adsorption capacity (Qmax) of 214 ± 5 mg P/g. The adsorption process fitted well with the Avrami order kinetic model (R2 > 0.996) and the Liu isotherms model (R2 > 0.997). The excellent fit of the experimental data to the Avrami model suggests that chemisorption is the dominant interaction mechanism, leading to precipitation through the formation of calcium phosphates. Additionally, the Liu model anticipates that the energetic characteristics of the adsorbent's active sites cannot be identical. This is in agreement with the presence of Ca(OH)2 and CaCO3 in the adsorbent material, where the Ca(OH)2 active sites are preferred by the adsorbate molecules (PO43-) for occupation. Furthermore, thermodynamic analysis revealed that P adsorption is a spontaneous process of exothermic nature (ΔH° < 0). The calculated activation energy for the process (72.81 kJ/mol) suggests the P adsorption mechanism involves strong chemical bonding between the adsorbent and P species. In addition, precipitation of apatite (Ca5(PO4)3OH), a vital component in fertilizer production, was observed during the adsorption process. In tertiary treated wastewater applications, the BPES-1:2 biocomposite demonstrated a P removal efficiency of 90%. The solubility of P in a 2% formic acid solution was 100%, while the water-soluble P content was measured at 5.6%. These findings highlight the product's sustainable and environmentally beneficial nature by demonstrating its potential as a slow-release fertilizer, contributing to the application of the 3R slogan: Reduce, Reuse, Recycle. This value-added product is promising in supplying nutrients to plants over an extended period while minimizing the risk of nutrients leaching into the environment.

Enhanced soil P immobilization and microbial biomass P by application of biochar modified with eggshell

Phosphate fertilizers have been excessively applied in agricultural production, bringing the risk of phosphorus (P) loss to nearby river systems and low utilization efficiency. In this study, eggshell-modified biochars prepared by pyrolysis of eggshell and corn straw or pomelo peel were applied to soil for enhancing P immobilization and utilization. The structure and properties of modified biochars before and after P adsorption were analyzed using the Brunauer-Emmett-Teller (BET) nitrogen adsorption method, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The eggshell-modified biochar performed an excellent adsorption performance for P (up to 200 mg/g), which was well described by the Langmuir model (R2 > 0.969), showing monolayer chemical adsorption with homogenous surface. The Ca(OH)2 appeared on the surface of eggshell modified biochars and changed to Ca5(PO4)3(OH) and CaHPO4(H2O)2 after P adsorption. The release of immobilized P by modified biochar increased with decreased pH. In addition, pot experiments of soybean indicated that the combined application of modified biochar and P fertilizer significantly increased the content of microbial biomass P in soil, raising from 4.18 mg/kg (control group) to 51.6-61.8 mg/kg (treatment group), and plants height increased by 13.8-26.7%. Column leaching experiments showed that P concentration in the leachate decreased by 97.9% with the modified biochar application. This research provides a new perspective that the eggshell-modified biochar could serve as a potential soil amendment for enhancing P immobilization and utilization.

Cycling of phosphorus from wastewater to fertilizer using wood ash after energy production

Quercus wood was used for thermal energy production, and wood bottom ash (WDBA) was used as a medium for water purification and soil fertilizer in accordance with the recently proposed food-water-energy nexus concept. The wood contained a gross calorific value of 14.83 MJ kg^-1, and the gas generated during thermal energy production has the advantage of not requiring a desulfurization unit due to its low sulfur content. Wood-fired boilers emit less CO2 and SOX than coal boilers. The WDBA had a Ca content of 66.0%, and Ca existed in the forms of CaCO3 and Ca(OH)2. WDBA absorbed P by reacting with Ca in the form of Ca5(PO4)3OH. Kinetic and isotherm models revealed that the results of the experimental work were in good agreement with the pseudo-second-order and Langmuir models, respectively. The maximum P adsorption capacity of WDBA was 76.8 mg g^-1, and 6.67 g L^-1 of WDBA dose could completely remove P in water. The toxic units of WDBA tested using Daphnia magna were 6.1, and P adsorbed WDBA (P-WDBA) showed no toxicity. P-WDBA was used as an alternative P fertilizer for rice growth. P-WDBA application resulted in significantly greater rice growth in terms of all agronomic values compared to N and K treatments without P. This study proposed the utilization of WDBA, obtained from thermal energy production, to remove P from wastewater and replenish P in the soil for rice growth.