A new approach to removing and recovering phosphorus from livestock wastewater using dolomite

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.

Recovery of ammonia nitrogen and phosphate from livestock farm wastewater by iron-magnesium oxide coupled lignite and its potential for resource utilization

A new adsorbent called iron-magnesium oxide coupled lignite (CIMBC) was developed to address the challenges of recovering high concentrations of ammonia nitrogen and phosphate in livestock farm wastewater and improving the inefficient use of lignite (BC) with low calorific value. CIMBC was synthesized using the modified ferromagnesium salt double-coating method. The experiments demonstrated that Fe2O3 and MgO could be effectively loaded onto the surface of BC at a Fe/Mg molar ratio of 1:2 and pyrolysis temperature of 500 °C. The optimal conditions for adsorption were determined to be an N/P concentration ratio of 2:1, adsorbent dosage of 1 g/L, and pH of 7. The presence of coexisting cations (Ca2+ and Mg2+) inhibited the removal of ammonia nitrogen but enhanced the removal of phosphate. Likewise, the presence of coexisting anions (CO32- and SO42-) hindered the removal of both ammonia nitrogen and phosphate. The adsorption behavior followed the pseudo-second-order model and the Langmuir model, with a maximum adsorption capacity of 95.69 mg N/g for ammonia nitrogen and 101.32 mg P/g for phosphate. The adsorption process was a spontaneous endothermic process controlled by multiple levels. The main mechanisms of adsorption involved electrostatic attraction, intra-particle diffusion, ion exchange, chemical precipitation, and coordination exchange. After 5 times of adsorption-desorption, the recovery rate of CIMBC is less than 50%, and the removal rate of phosphate is less than 40%. Although the RCIMBC exhibited low reusability, but also it showed potential in removing heavy metals (Pb) from wastewater and for use as a slow-release fertilizer. CIMBC is a promising new adsorbent, which can realize resource utilization of lignite with low calorific value while removing nitrogen and phosphorus.

Konjac glucomannan/pectin/Ca-Mg hydrogel with self-releasing alkalinity to recover phosphate in aqueous solution

The combination of polysaccharides can obtain stable, degradable, and environmentally friendly hydrogels, which have broad application prospects in adsorbents assembly. With Ca2+ and Mg2+ as crosslinkers, a new pectin/Konjac glucomannan/Ca-Mg composite hydrogel was prepared for phosphate adsorption by the alkali-thermal co-reaction method. Since Mg(OH)2 can create a suitable pH condition for phosphate adsorption by Ca, Ca and Mg synergistically promoted phosphate adsorption and remained stable in the pH range of 4 to 10. FTIR, SEM-EDS, XRD, XPS, and zero potential analysis corroborated that the hydrogel used Ca and Mg as active sites to trap pollutants by electrostatic adsorption and fix phosphate through complexation to form Mg3(PO4)2·8H2O and CaPO3(OH)2·H2O. Furthermore, it is unnecessary to separate the recovered phosphate from the hydrogel, and it can be used directly as a fertilizer. By being reused in the soil, it promoted seed germination and seedling growth. This adsorbent has the potential for recovery as a phosphorus-containing organic fertilizer after phosphorus adsorption.

Phosphorus recovery from wastewater via calcium phosphate precipitation: A critical review of methods, progress, and insights

Phosphorus (P) is one of the important elements for human, animal, and plant life. Due to the development of the circular economy in recent years, the recovery of P from wastewater has received more attention. Recovery of P from domestic, industrial, and agricultural wastewater in the form of calcium phosphate (CaP) by precipitation/crystallization process presents a low-cost and effective method. Recovered CaP could be used as P fertilizer and for other industrial applications. This review summarizes the effects of supersaturation, pH, seed materials, calcium (Ca) source, and wastewater composition, on the precipitation/crystallization process. The recovery efficiency and value proposition of recovered CaP were assessed. This in-depth analysis of the literature reports identified the process parameters that are worth further optimization. The review also provides perspectives on future research needs on expanding the application field of recovered CaP and finding other more economical and environmentally friendly Ca sources.

Comparison of phosphorus species in livestock manure and digestate by different detection techniques

Phosphorus (P) species characterize the effectiveness of the P fertilizer. In this study, the P species and distribution in different manures (pig manure, dairy manure and chicken manure) and their digestate were systematically investigated through combined characterization methods of Hedley fractionation (H₂OP, NaHCO₃-P, NaOH-P, HCl-P, and Residual), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) techniques. The results from Hedley fractionation showed that >80 % of P in the digestate was inorganic and the HCl-P content in manure increased significantly during anaerobic digestion (AD). XRD manifested that insoluble hydroxyapatite and struvite belonging to HCl-P were presented during AD, which was in agreement with the result of Hedley fractionation. ³¹P NMR spectral analysis revealed that some orthophosphate monoesters were hydrolyzed during AD, meanwhile the orthophosphate diester organic phosphorus like DNA and phospholipids content has increased. After characterizing P species by combining these methods, it was found that chemical sequential extraction could be an effective way to fully understand the P in livestock manure and digestate, with other methods used as auxiliary tool depending on the purpose of studies. Meanwhile, this study provided a basic knowledge of utilizing digestate as P fertilizer and minimizing the risk of P loss from livestock manure. Overall, applying digestates can minimize the risk of P loss from directly applied livestock manure while satisfying plant demands, and is an environmentally friendly P fertilizer.

Phosphorus recovery and reuse in water bodies with simple ball-milled Ca-loaded biochar

The demand to control eutrophication in water bodies and the risk of phosphorus scarcity have prompted the search for treatment technologies for phosphorus recovery. In this study, ball-milled Ca-loaded biochar (BMCa@BC) composites were prepared with CaO and corn stover biochar as raw materials by a new ball-milling method to recover phosphorus from water bodies. Experimental results demonstrated that BMCa@BC could efficiently adsorb phosphorus in water bodies with an excellent sorption capacity of 329 mg P/g. Hydrogen bonding, electrostatic attraction, complexation, and surface precipitation were involved in adsorption process. In addition, phosphorus recovered by BMCa@BC had high bioavailability (86.7 % of TP) and low loss (3.3 % of TP) and was a potential slow-release fertilizer. P-laden BMCa@BC significantly enhanced seed germination and growth in planting experiments, proving that it could be used as a substitute for P-based fertilizer. After five cycles of regeneration, BMCa@BC still showed good adsorption recovery and the P-enriched desorption solution could be recovered as Ca-P products with the fertilizer value. Overall, BMCa@BC has good cost-effectiveness and practical applicability in phosphorus recovery. This provides a new way to recover and reuse phosphorus effectively.

Precipitation of struvite using MgSO4 solution prepared from sidestream dolomite or fly ash

Struvite (NH₄MgPO₄∗6H₂O) is a slow-release fertilizer produced from phosphorus and nitrogen-containing wastewater in the presence of Mg salts. Commercial Mg salts are the single most significant cost of struvite precipitation. In this study, H₂SO₄ formed as an industrial sidestream was used to prepare MgSO₄ solution from waste dolomite (DOL) and fly ash (FA). MgSO₄ solution was then used to precipitate struvite from a synthetic (NH₄)₂HPO₄ solution and from actual industrial process waters. The best results were obtained with real process waters where over 99% of phosphate and about 80% ammonium removals were achieved with both MgSO4 solutions after 30 min of reaction time. A higher molar ratio between Mg and P improved the phosphate removal efficiency, especially with DOL-based MgSO4 solutions; however, it had no practical effect on ammonium removal. The struvite content of precipitates was 75.49% with an FA-based chemical and 60.93% with a DOL-based chemical; other valuable nutrients (Ca, K, S, Fe, Mn, and Cl) were captured in the precipitates. The results indicate that both sidestream-based reagents perform well in struvite precipitation and that the formed precipitates could be used as fertilizers.

Production of struvite by magnesium anode constant voltage electrolytic crystallisation from anaerobically digested chicken manure slurry

Nitrogen and phosphorus levels in livestock manure and digestive fluid are high, posing a threat to soil and water quality and necessitating nutrient removal and recovery. Phosphorus recovery has the potential to alleviate the global phosphorus resource crisis. This study proposed a magnesium anode constant voltage electrolysis method to crystallise struvite (magnesium ammonium phosphate hexahydrate, MgNH₄PO₄·6H₂O) from anaerobically digested chicken manure slurry using reaction kinetics at variable constant voltages ranging from 2 V to 12 V. The recovery of nitrogen and phosphorus was shown to be effective over a wide initial pH range (3.00 ± 0.03-7.90 ± 0.10) using synthetic digestion fluids. Moreover, the pH gradually increased during the reaction without any external chemical adjustments. The phosphorus recovery rates conformed to the first-order kinetic model, with a maximum rate constant of 2.13 h^-1. When the best voltage of 2 V was used at 25 ± 1 °C, the recovery rate reached 5.24 mg P h^-1cm^-2 in the synthetic digestion fluids during 90 min and 4.60 mg P h^-1cm^-2 in the anaerobically digested chicken manure slurry. The crystalline products recovered were identified as high-purity struvite by XRD and XPS. The purity of recovered struvite with an initial pH of 3.00 and 7.90 was 96.5% and 98.9%, respectively. These results demonstrated that the magnesium electrode could rapidly react with nitrogen and phosphorus to generate high-purity struvite.

Simultaneous adsorption of phosphate and tetracycline by calcium modified corn stover biochar: Performance and mechanism

It is important to solve the problems of biomass treatment and combined contaminants removal in environmental remediation. In this study, a calcium (Ca) modified biochar (CaBC800) was fabricated using corn stover (CS) as a raw material to remove phosphate and tetracycline (TC). The experimental results indicate that CaBC800 can adsorb both inorganic phosphate and organic TC. The entire adsorption process corresponds to pseudo-second-order kinetics and Langmuir adsorption isotherm. The maximum adsorption capacities of phosphate and TC were 33.944 and 33.534 mg/g, respectively. The phosphate adsorption was demonstrated to mainly depend on the chemical precipitation by Ca²⁺ and ligand exchange by hydroxyl groups from CaBC800. Meanwhile, hydrogen bonding from oxygen functional groups and π-π interactions from aromatic rings are the main adsorption mechanisms of TC. This study provides a new adsorbent to efficiently remove phosphate and TC, and the simultaneous adsorption indicates the application potential of CaBC800 in wastewater remediation.

Electrified nanohybrid filter for enhanced phosphorus removal from water

Phosphorus (P) has been identified as a major cause of eutrophication. One feasible way to deal with P-containing wastewater is to employ advanced adsorbents with high P affinity. Towards this end, the loading of these sorbents onto a conductive scaffold would facilitate the introduction of an electric field into the reaction system thereby permitting a continuous-flow operation and improved P sorption kinetics. Here, the preparation and evaluation of an electroactive carbon nanotube (CNT) filter functionalized with cerium-based metal organic frameworks (Ce-MOF) is reported. Various advanced characterization techniques confirmed the successful fabrication of the Ce-MOF/CNT nanohybrid filter. The results suggested that the nanohybrid filter had a maximum P adsorption capacity of 22.41 mg g^-1, which compared favorably with other state-of-the-art P sorbents. Ce-MOF loading, applied voltage and flow rate each increased the rate constants for phosphate removal by factors of 1.6, 2.1 and 5.8 times relative to the absent states. The underlying P sorption mechanisms involved outer-sphere surface complexation (electrostatic attraction), inner-sphere surface complexation (Ce-O-P) and diffusion. The performance was tolerant of a wide operational pH range and different water matrices. The Ce-MOF/CNT electrochemical filter described in this study provides a viable strategy to address the challenging issues associated with aqueous P pollution.

A Novel Ca-Modified Biochar for Efficient Recovery of Phosphorus from Aqueous Solution and Its Application as a Phosphorus Biofertilizer

Recovery phosphorus (P) from P-contaminated wastewater is an efficient and environmentally friendly mean to prevent water pollution and alleviate the P shortage crisis. In this study, oyster shell as calcium sources and peanut shells as carbon sources (mass ratio 1:1) were used to prepare a novel Ca-modified biochar (OBC) via co-pyrolysis, and its potential application after P adsorption as a P biofertilizer for soil was also investigated. The results shown that OBC had a remarkable P adsorption capacity from wastewater in a wide range of pH 4−12. The maximum P adsorption capacity of OBC was about 168.2 mg/g with adsorbent dosage 1 g/L, which was about 27.6 times that of the unmodified biochar. The adsorption isotherm and kinetic data were better described by Langmuir isotherm model (R2 > 0.986) and the pseudo second-order model (R2 > 0.975), respectively. Characterization analysis of OBC before and after P adsorption by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and specific surface area and porosity analyzer (BET) indicated that the remarkable P adsorption capacity of OBC was mainly ascribed to chemical precipitation, electrostatic adsorption, and hydrogen bonding. Pot experiment results showed that OBC after P adsorption could significantly promote the germination and growth of Spinacia, which manifested that OBC after P adsorption exhibited a good ability to be reused as P fertilizer for soil.

Impact of Magnesium Sources for Phosphate Recovery and/or Removal from Waste

As the population continues to rise, the demand for resources and environmentally friendly management of produced wastes has shown a significant increase in concern. To decrease the impact of these wastes on the environment, it is important to utilize the wastes in producing and/or recovering usable products to provide for the sustainable management of resources. One non-renewable and rapidly diminishing resource is phosphorus, which is used in several products, the most important being its use in manufacturing chemical fertilizer. With the increase in demand but reduction in availability of naturally occurring mineral phosphorus, it is important to investigate other sources of phosphorus. Phosphorus is most commonly recovered through struvite (magnesium ammonium phosphate) precipitation. The recovery of phosphorus from various wastewater has been well established and documented with recovery rates mostly above 90%. However, one of the major drawbacks of the recovery is the high cost of chemicals needed to precipitate the phosphorus. Since the external magnesium needed to achieve struvite precipitation accounts for around 75% of the total chemical cost, applicability of low-cost magnesium sources, such as bittern or seawater, can help reduce the operational cost significantly. This paper investigates the different magnesium sources that have been used for the recovery of phosphorus, highlighting the different approaches and operating conditions investigated, and their corresponding phosphorus recovery rates. An investigation of the economic aspects of the magnesium sources used for removal/recovery show that costs are dependent on the raw waste treated, the source of magnesium and the location of treatment. A review of published articles on the economics of phosphorus removal/recovery also indicates that there is a lack of studies on the economics of the treatment processes, and there is a need for a comprehensive study on life cycle assessment of such processes that go beyond the technical and economical aspects of treatment processes.

Microalgae-based livestock wastewater treatment (MbWT) as a circular bioeconomy approach: Enhancement of biomass productivity, pollutant removal and high-value compound production

The intensive livestock activities that are carried out worldwide to feed the growing human population have led to significant environmental problems, such as soil degradation, surface and groundwater pollution. Livestock wastewater (LW) contains high loads of organic matter, nitrogen (N) and phosphorus (P). These compounds can promote cultural eutrophication of water bodies and pose environmental and human hazards. Therefore, humanity faces an enormous challenge to adequately treat LW and avoid the overexploitation of natural resources. This can be accomplished through circular bioeconomy approaches, which aim to achieve sustainable production using biological resources, such as LW, as feedstock. Circular bioeconomy uses innovative processes to produce biomaterials and bioenergy, while lowering the consumption of virgin resources. Microalgae-based wastewater treatment (MbWT) has recently received special attention due to its low energy demand, the robust capacity of microalgae to grow under different environmental conditions and the possibility to recover and transform wastewater nutrients into highly valuable bioactive compounds. Some of the high-value products that may be obtained through MbWT are biomass and pigments for human food and animal feed, nutraceuticals, biofuels, polyunsaturated fatty acids, carotenoids, phycobiliproteins and fertilizers. This article reviews recent advances in MbWT of LW (including swine, cattle and poultry wastewater). Additionally, the most significant factors affecting nutrient removal and biomass productivity in MbWT are addressed, including: (1) microbiological aspects, such as the microalgae strain used for MbWT and the interactions between microbial populations; (2) physical parameters, such as temperature, light intensity and photoperiods; and (3) chemical parameters, such as the C/N ratio, pH and the presence of inhibitory compounds. Finally, different strategies to enhance nutrient removal and biomass productivity, such as acclimation, UV mutagenesis and multiple microalgae culture stages (including monocultures and multicultures) are discussed.

A global meta-analysis of animal manure application and soil microbial ecology based on random control treatments

The processes involved in soil domestication have altered the soil microbial ecology. We examined the question of whether animal manure application affects the soil microbial ecology of farmlands. The effects of global animal manure application on soil microorganisms were subjected to a meta-analysis based on randomized controlled treatments. A total of 2303 studies conducted in the last 30 years were incorporated into the analysis, and an additional 45 soil samples were collected and sequenced to obtain 16S rRNA and 18S rRNA data. The results revealed that manure application increased soil microbial biomass. Manure application alone increased bacterial diversity (M-Z: 7.546 and M-I: 8.68) and inhibited and reduced fungal diversity (M-Z: -1.15 and M-I: -1.03). Inorganic fertilizer replaced cattle and swine manure and provided nutrients to soil microorganisms. The soil samples of the experimental base were analyzed, and the relative abundances of bacteria and fungi were altered compared with no manure application. Manure increased bacterial diversity and reduced fungal diversity. Mrakia frigida and Betaproteobacteriales, which inhibit other microorganisms, increased significantly in the domesticated soil. Moreover, farm sewage treatments resulted in a bottleneck in the manure recovery rate that should be the focus of future research. Our results suggest that the potential risks of restructuring the microbial ecology of cultivated land must be considered.

Advanced treatment of phosphorus-containing tail water by Fe-Mg-Zr layered double hydroxide beads: Performance and mechanism

The adsorption process for low concentration phosphorus wastewater treatment has advantages of simple convenience, stable performance and less sludge, while most of current adsorbents fail to be separated for reuse. Meanwhile, few people pay attention to the removal of low concentration phosphorus from tail water by adsorbents. In this study, a newly efficient Fe-Mg-Zr layered double hydroxide beads were prepared by simple in-situ crosslinking method and applied for low concentration phosphorus adsorption from real tail water. The maximum adsorption capacity of Fe-Mg-Zr beads was 21.61 mg/g, showing more practical application value for phosphorus removal. Fixed bed experiments showed that 5.0 g adsorbent could removed 2.12 mg phosphorus from tail wastewater containing 1.03 mg/L phosphorus. The beads adsorbent can be reused with excellent adsorption performance even after five cycles of adsorption-desorption operation. After detailed analyses, it was found that ligand exchange and ion exchange were the dominant mechanisms for phosphorus adsorption by this beads. Overall, the material has the advantages of simple preparation, good adsorption performance, easy separation and recycle, indicating a great potential for low concentration phosphorus wastewater treatment.

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.

Recovery phosphate and ammonium from aqueous solution by the process of electrochemically decomposing dolomite

The cost-effective recovery of phosphate is of great significance to the mitigation of phosphorus resource depletion crisis. The electrochemical-decomposition of dolomite was developed to recover phosphate and ammonium from aqueous solution. The dolomite ore is mainly composed of CaMg(CO₃)₂ (53.73%), CaCO₃ (28.93%) and SiO₂ (16.59%). The continuous release of Mg²⁺ and Ca²⁺ were achieved by electrochemically decomposing dolomite ore, accompanied by the generation of base solution (9.0-10.5). The main factors affecting the recovery performance of phosphate (PO₄-P) and ammonium (NH₄-N) are current, initial concentration of PO₄-P and NH₄-N, initial pH of feed solution and feed rate. For a 30-d operation, the recovery rate of PO₄-P was maintained at 90-97% and that of NH₄-N at 50-60% under optimized operating conditions. The recovered product had low water solubility but high citric-acid-soluble, and was proposed as a slow-release fertilizer for crops. The proposed process as a simple, effective and green route may serve as a new strategy for recovering PO₄-P and NH₄-N from wastewaters.

Phosphorus removal from secondary wastewater effluent using copper smelter slag

This study investigated the use of copper smelter slag for the removal of phosphorus from secondary wastewater effluent through batch tests. The media was physically and chemically characterized and showed presence of Fe2O3 (45.22%), SiO2 (14.98%), Al2O3 (3.21%), CaO (1.99%), SO3 (1.77%) and MgO (1.33%). Scanning electron microscopy monographs revealed smooth and flat surface and no heterogeneity on the surface of the slag with visible micro pores before the experiment and less visible after the experiment. The point of zero charge of the media was 5.0. Equilibrium was reached after 4 h at 29.5 ± 0.71% phosphorus removal efficiency and media dosage of 0.4/100 mL. The kinetic data was best described by Pseudo second order equation. More than one mechanisms were involved in the adsorption of phosphorus onto copper smelter slag as suggested by multi-linearity of intra particle diffusion model. Ninety seven percent (97.5 ± 0.0%) removal efficiency was achieved at an equilibrium dosage of 160 gL-1. The equilibrium isotherm was described better by Langmuir equation with observed maximum adsorption capacity of 0.16 mg P g-1 media and the experimental maximum adsorption capacity was 0.26 mg P g-1 media. Regeneration studies showed low performance with maximum efficiency of 11.7% revealed during the first regeneration trial therefore low practical benefits. Copper smelter slag is a poor adsorbent for phosphorus and further studies on the media should be conducted.