Insoluble Calcium Phosphate Research Articles

Phosphate solubilization by rhizobacteria isolated from the rhizosphere of <i>Mimosa pudica</i>: an investigation into microbial mobilization of phosphorus

Phosphorus (P), in addition to nitrogen (N) and potassium (K), makes up the essential macronutrients needed by plants for growth and development. P is also one of the most abundant elements present in the Earth’s crust, and it occurs in both organic and inorganic forms. Although present in high concentrations, only a very minute amount is bioavailable to plants because of its poor solubility due to its high binding affinity to calcium, aluminium, and iron in the soil, forming insoluble calcium phosphate, aluminium phosphate, and ferrous phosphate, thereby becoming recalcitrant for plant utilization. In this study, bacteria isolated from the rhizosphere of Mimosa pudica from different locations at Nnamdi Azikiwe University, Awka, were screened for their ability to solubilize phosphate using point inoculation on Pikovskaya (PVK) media agar plates with tricalcium phosphate (Ca3(PO4)2) as a source of phosphate. The result showed that of the twenty-one (21) rhizobacteria screened, four (4) were able to solubilize phosphate with varying phosphate solubilizing index (PSI). The degrees of PSI were in the following order: isolate SVM5 and UBG13 > isolate UBG14> isolate FEA6. Isolate SVM5 and UBG13 had the highest PSI of 4.0, while isolate FEA6 had the lowest PSI of 3.1. The biochemical tests of the isolates revealed that the phosphate-solubilizing bacteria were members of Klebsiella spp. (FEA6, SVM5, and UBG14) and Pseudomonas sp. (UBG13). This study, therefore, suggests the need to include rhizobacteria as part of biofertilizer formulations to improve plant yield via the solubilization of phosphate into forms that are bioavailable for plant growth.

Synergistic Chemical Modification and Physical Adsorption for the Efficient Curing of Soluble Phosphorus/Fluorine in Phosphogypsum

Phosphogypsum (PG), a by-product of phosphoric acid production, contains high levels of fluorine and phosphorus impurities, which negatively impact the strength and setting time of PG-based cement materials and pose environmental risks. This study explores a dual approach combining physical adsorption using zeolite powder and chemical modification with quicklime (CaO) to immobilize these impurities. The composition of 90 wt.% PG, 5 wt.% zeolite powder, and 5 wt.% quicklime reduces the soluble phosphorus to below the detection limits and significantly lowers the free water content in the PG. Through SEM, XRD, and FT-IR analyses, it was found that zeolite powder adsorbs fluorine and phosphorus through encapsulation, while quicklime chemically reacts to form insoluble calcium phosphate and calcium fluoride. This transformation decreases the solubility, mitigating potential environmental contamination. The combination of physical adsorption and chemical conversion provides a sustainable strategy to reduce environmental hazards and enhance PG’s suitability for cement-based materials. The findings from this research offer a promising pathway for the sustainable utilization of PG, providing a mechanism for its safe incorporation into building materials, while addressing both environmental and material performance concerns.

Evaluating the Chemical Stability and Performance of Zinc Phosphate-Coated Steel Fibers in Concrete Corrosion Simulations

This study investigates the impact of zinc phosphate-coated steel fibers on corrosion performance and bond strength within concrete subjected to corrosive environments. Results indicate that the coating enhanced corrosion resistance in various environments, including saturated Ca(OH)2, 10% Na2SO4, and 3.5% NaCl solutions. The zinc phosphate coating resulted in a more positive corrosion potential and a lower corrosion rate, likely due to galvanic coupling between the coating and the steel fiber matrix. Furthermore, the improved corrosion resistance in Ca(OH)2 solution may also be related to the formation of insoluble calcium phosphate compounds. The bond strength and pullout energy in the zinc phosphate-coated fiber-reinforced pre-corrosion specimens enhanced by 19.3% and 90.92%, respectively, compared to the bare fiber-reinforced ones. Upon exposure to a simulated seawater environment that induces corrosion, the interfacial bond strength and pullout energy of zinc phosphate-coated steel fibers and cement mortar experienced marginal decreases of 4.2% and 4.6%. Zinc phosphate coatings demonstrate considerable promise for extensive application in concrete structures exposed to highly corrosive environments.

Microstructural properties of alkali-activated mortars prepared from Fenton oxidation and heat-treated dyeing sludge as the substitutions of slag

This study investigates three treatment methods for removing organic residues and enhancing dyeing sludge (DS) activity: high-temperature calcination, Fenton oxidation, and mechanical grinding. The treated DS was used as a substitute for ground granulated blast slag (GGBS) in producing alkali-activated mortars. A comprehensive characterization of the chemical composition and microstructure of DS was conducted to evaluate the effectiveness of these treatment methods. Results showed that DS contains phosphorus oxides, which, upon dissolution, react with calcium and alkaline ions to form insoluble calcium phosphate and fluorine hydroxyapatite. Subsequently, the mechanical properties, micromorphology, and microstructure of alkali-activated mortars with varying DS contents were analyzed to assess the potential of treated DS as a precursor. Test results revealed that mechanical/heat-activated DS (HDS) experienced minimal strength reduction at 10 % doping, achieving a compressive strength of 99 % compared to the control group. However, controlling the amount of alkali used was crucial, as an increase in alkali resulted in decreased compressive strength. DS treated through mechanical/chemical activation (CDS) also showed promising results, with CDS-9 achieving a compressive strength of 78.4 % of the control group after 56 days of curing. Notably, although the early strength of specimens with CDS was lower, a more significant increase in strength was observed at later stages. Mechanical activation (MDS) had the most adverse effect on strength, independent of the curing duration. The pore size distribution of alkali-activated mortars can be optimized by refining the macro-pores in samples and transforming them into harmless gel pores through HDS and CDS integration. This study offers a feasible strategy for DS activation and demonstrates the highly promising utilization of DS as a precursor for alkali-activated materials.

Effect of phosphate impurities on the properties of β-hemihydrate gypsum pastes plasticized by polycarboxylate superplasticizer

This study aims to investigate the effect of HPO42-/PO43- on the working performance and mechanical strength of β-hemihydrate gypsum pastes containing polycarboxylate superplasticizer (PCE) and reveal its underlying mechanism. The results showed that HPO42-/PO43- has a detrimental effect on the fluidity, compressive strength, and softening coefficient of β-hemihydrate gypsum pastes. However, in the presence of PCE, all properties were improved compared to the blank group when the HPO42-/PO43- content was less than 0.3 %. The fluidity and compressive strength of the pastes can be increased by up to 95 % and 32 %, respectively. It was found that HPO42-/PO43- reacted with Ca2+ to form insoluble calcium phosphate salt (ICPS), and the adsorption of PCE on the surface of ICPS increased the total adsorption amount, thereby enhancing the dispersion ability of PCE and increasing the fluidity of fresh slurry. In addition, the adsorption behavior of PCE on the surface of ICPS weakened its inhibitory effect on the hydration of hemihydrate gypsum, which was confirmed by TG-DSC. The increased hydration products and reduced water requirements significantly improved mechanical properties. These findings enhance the understanding of the interaction between phosphorus impurities and PCE, which can guide the improvement of the performance of β-HPG and promote the resource utilization of phosphogypsum.

High-flux electrochemical phosphorus recovery in an undivided electrolytic cell coupled with microfiltration with low energy consumption

Electrochemical systems are promising for phosphorus (P) removal and recovery from wastewater. However, its industrial application still faces some challenges, including relatively low P recovery efficacy, high energy consumption, and complex configuration of the reactors. This work, developed an undivided electrolytic cell with H+ or OH− extraction from its corresponding electrode surface for P recovery. The experimental results and models validated the superiority of continuously and precisely extracting H+ from the tubular Ti porous anode surface for H+–OH− separation over OH− extraction from the cathode surface. In the electrolytic cell, alkaline effluent with H+ extraction, the P could be precipitated with Ca2+ in the form of insoluble calcium phosphate (Ca-phosphate), which could then be separated from the wastewater by microfiltration. Under the conditions of a current density of 4 mA cm−2, an initial P concentration of 0.6 mM, a influent flow rate of 500 mL min−1, and H+ extraction rate of 50 mL min−1, the P recovery efficiency reached 81 % with the alkaline effluent pH of 10.5. The calculated P recovery rate and treatment capacity were 18.3 g P (m2 h)-1 and 1194 L (m2 h)-1, respectively, at energy consumption of 8.75 kWh (kg P)-1, which were superior over the cutting-edge divided electrolytic systems and the conventional undivided electrolytic systems. The recovered precipitates are composed principally of hydroxyapatite in the minor presence of amorphous calcium phosphate, showing a Ca/P molar ratio of 1.8. Generally, the established undivided electrolytic cell coupled with microfiltration exhibited significant prospects for recovering P from wastewater without acid-base reagents.

Erratum: Deposition of insoluble calcium phosphate layers by combining finely dispersed calcium hydroxide sols with soluble phosphates

The proceedings editor, while fixing formatting issues, inadvertently introduced inaccuracies within the chemical formulas and the authors names. A corrected version of the article has been published.

Deposition of insoluble calcium phosphate layers by combining finely dispersed calcium hydroxide sols with soluble phosphates

Carbonate containing materials are subject to severe weathering. Traditional formulations of stone strengtheners have low compatibility with the original material and further they contain VOCs (volatile organic compounds), which endanger human health and the environment. This study explores the high potential of novel treatments based on water-soluble phosphates used as an agent to react with calcium carbonate (CaCO3) to form an insoluble film of calcium phosphate in the pore space of the treated material. Pretreatments with nanolime suspensions ensure greater availability of calcium ions and reduce the consumption of the original material in the reactions. An alkaline environment is required to promote the conversion of the CaCO3 components to hydroxyapatite-like compounds. Based on experiments in aqueous solutions, different sources of phosphate ions could be examined and compared for the development of effective treatments to apply on different test specimens. To implement the treatments, barium phosphate solutions were investigated. Important aspects of this research are the use of green solvents and the search of components that avoid the formation of byproducts, to increase the efficiency of the chemical reactions and reduce possible negative effects on the operator, the environment and the very same built heritage material. The developed treatments are a valuable alternative to the traditional methods, as it follows an improvement in the material properties without affecting the moisture transport within it and allows the evenly reaction of the strengthened material to external physical and mechanical stresses without creating internal tension between the grains.

Study of a new potassium phosphate-based waste as an alkaline activator in alkali-activated binders: The açai seed ash

Açai seed ash (ASA) was assessed as a new alkaline activator in alkali-activated binders (AAB) based on blast-furnace slag (BFS). ASA was produced by calcination of açai seed in the laboratory, and it is mainly composed of K2O (33.75 wt%) and P2O5 (22.59 wt%), with a pH of 12.3 and solubility in water of over 35 wt%. Due to the harmful soluble phosphate, ASA was combined with Ca(OH)2 (CH) to form insoluble calcium phosphate. Four AAB mixtures were assessed after 1 day of curing at 60 °C: BFS/water, BFS/CH/water, BFS/ASA/water, and BFS/ASA/CH/water. Microstructural studies of pastes showed that the BFS/ASA/CH/water mixture presented the formation of insoluble hydroxylapatite by X-ray diffraction, the highest reaction product content (26.52 %) by Fourier transform infrared spectroscopy, and densest microstructure by scanning electron microscopy. The compressive strength of mortars showed that BFS/ASA/CH/water mixture presented the highest value of 8.7 MPa.

Measuring insoluble calcium content in curds during cheesemaking

A rapid water‐soluble calcium (WSC) extraction was evaluated as an in‐process method to quickly quantify insoluble calcium (ICa) phosphate content during cheesemaking and compare it with existing methods for finished cheese, that is cheese juice and acid–base titration. Although there were some differences in methods when evaluated using string cheese and Mozzarella, results for ICa obtained from the WSC method were consistent with the cheese juice. This WSC method was successful in measuring the ICa in curds during manufacture of Mozzarella made with varying pH values at whey drainage. Meltability of cheese correlated with ICa content at 1 month of storage.

Functionality of process cheese made from Cheddar cheese with various rennet levels and high-pressure processing treatments

Due to its versatility and shelf stability, process cheese is gaining interest in many developing countries. The main structural component (base) of most processed cheese formulations is young Cheddar cheese that has high levels of intact casein. Exporting natural Cheddar cheese base from the United States to distant overseas markets would require the aging process to be slowed or reduced. As Cheddar cheese ripens, the original structure is broken down by proteolysis and solubilization of insoluble calcium phosphate. We explored the effect of varying rennet levels (we also used a less proteolytic rennet) and application of high-pressure processing (HPP) to Cheddar cheese, as we hoped these treatments might limit proteolysis and concomitant loss of intact casein. To try to retain high levels of insoluble Ca, all experimental cheeses were made with a high-draining pH and from concentrated milk. To compare our intact casein results with current practices, we manufactured a Cheddar cheese that was prepared according to typical industry methods (i.e., use of unconcentrated milk, calf chymosin [higher levels], and low draining pH value [∼6.2]). All experimental cheeses were made from ultrafiltered milk with protein and casein contents of ∼5.15% and 4.30%, respectively. Three (low) rennet levels were used: control (38 international milk clotting units/mL of rennet per 250 kg of milk), and 25% and 50% reduced from this level. All experimental cheeses had similar moisture contents (∼37%) and total Ca levels. Four days after cheese was made, half of the experimental samples from each vat underwent HPP at 600 MPa for 3 min. Cheddar cheese functionality was monitored during aging for 240 d at 4°C. Cheddar cheese base was used to prepare process cheese after aging for 14, 60, 120, 180, and 240 d. Loss tangent (LT) values of cheese during heating were measured by small strain oscillatory rheology. Intact casein levels were measured using the Kjeldahl method. Acid or base titrations were used to determine the buffering capacity and insoluble Ca levels as a percentage of total Ca. The LTmax values (an index of meltability) in process cheese increased with aging for all the cheese bases; the HPP treatment significantly decreased LTmax values of both base (natural) and process cheeses. All experimental cheeses had much higher levels of intact casein compared with typical industry-make samples. Process cheese made from the experimental treatments had visually higher stretching properties than process cheese made from Cheddar with the typical industry-make procedure. Residual rennet activity was not affected by rennet level, but the rate of proteolysis was slightly slower with lower rennet levels. The HPP treatment of Cheddar cheese reduced residual rennet activity and decreased the reduction of intact casein levels. The HPP treatment of Cheddar cheese resulted in process cheeses that had slightly higher hardness values, lower LTmax values, and retained higher storage modulus values at 70°C. We also observed that the other make procedures we used in all experimental treatments (i.e., using a less proteolytic chymosin, using a concentrated cheese milk, and maintaining a high draining pH value) had a major effect on retaining high levels of intact casein.

Avoiding and allowing apatite precipitation in oxygenic photolithotrophs.

The essential elements Ca and P, taken up and used metabolically as Ca2+ and H2 PO4 - /HPO4 2- respectively, could precipitate as one or more of the insoluble forms calcium phosphate (mainly apatite) if the free ion concentrations and pH are high enough. In the cytosol, chloroplast stroma, and mitochondrial matrix, the very low free Ca2+ concentration avoids calcium phosphate precipitation, apart from occasionally in the mitochondrial matrix. The low free Ca2+ concentration in these compartments is commonly thought of in terms of the role of Ca2+ in signalling. However, it also helps avoids calcium phosphate precipitation, and this could be its earliest function in evolution. In vacuoles, cell walls, and xylem conduits, there can be relatively high concentrations of Ca2+ and inorganic orthophosphate, but pH and/or other ligands for Ca2+ , suggests that calcium phosphate precipitates are rare. However, apatite is precipitated under metabolic control in shoot trichomes, and by evaporative water loss in hydathodes, in some terrestrial flowering plants. In aquatic macrophytes that deposit CaCO3 on their cell walls or in their environment as a result of pH increase or removal of inhibitors of nucleation or crystal growth, phosphate is sometimes incorporated in the CaCO3 . Calcium phosphate precipitation also occurs in some stromatolites.

Nutritional content of pastures with phosphate fertilization in 2 calcareous soils

ABSTRACT Alkaline soils present large amounts of calcium carbonates, with precipitation of insoluble calcium phosphate. The objective of the research was to determine the effects of the P application on the nutrient levels of the foliar tissue of Pennisetum pastures in calcareous soils in Córdoba-Colombia. Soil samples were collected from two locations in the Department of Córdoba. A completely randomized design with a 2 x 3 x 6 factorial arrangement (Vista Hermosa and Carolina), there Pennisetum species (king grass, Cuba OM-22, and Pennisetum purpureum), and six P doses (0, 80, 150, 250, 400, and 650 kg ha-1), applied as P2O5, was used. The addition of P did not increase the contents of N, K, Ca, and Mg in the king grass, Pennisetum purpureum, and Cuba OM-22 pastures. However, in the calcareous soils of Carolina, king grass, Pennisetum purpureum, and Cuba, OM-22 absorbed higher amounts of P.

Induction of citrate transporter gene expression in soybean roots by sulfur application

ABSTRACT Organic acid secretion from the roots enables plants to acquire phosphorus (P) which is poorly soluble in soil. We previously reported that when soybeans were cultivated in vermiculite in the presence of insoluble calcium phosphate, as a phosphorus source, sulfur (S) fertilization increased organic acid secretion from the roots and improved P acquisition in soybeans. In the present study, we confirmed that S fertilization increased secretion of organic acids such as citric acid when soybeans were cultivated in Andosols having a strong P fixation capacity. In contrast, concentration of citric acid in soybean roots did not increase by S fertilization. Therefore, the relationship between S nutrition and gene expression of citric acid exporters was investigated to understand the mechanisms of induction of citric acid secretion by S. Further, we verified whether the expression of citric acid transporter genes, GmMATE13 and GmMATE47, is involved in the induction of citric acid secretion from the roots by S fertilization. The expression level of GmMATE13 in roots was significantly increased by S fertilization compared to that without S fertilization. Therefore, our results suggest that S nutrition is involved in inducing GmMATE13 expression and contributes to the excretion of citric acid from the soybean roots.

Influence of phosphorus impurities on the structure and performance of cellulose-ether-modified gypsum

This study examined the influence mechanism of phosphorus impurities in phosphogypsum on the structure and properties of gypsum. The influence of four phosphorus impurities, namely Ca3(PO4)2, CaHPO4, H3PO4, and Ca(H2PO4)2 on the hydration process, water retention, and mechanical properties of hydroxypropyl methyl cellulose ether (HPMC)-modified gypsum was examined through inductive coupled plasma emission spectrometer, scanning electron microscopy, and nanoparticle size testing. The soluble phosphorus impurities exert a significant retarding effect on HPMC-modified gypsum, which decreases the heat of hydration in the early stage. Moreover, soluble phosphorus impurities significantly decrease the water retention and compressive and flexural strengths of modified gypsum. Although slightly soluble CaHPO4 exerts a similar adverse influence on the structure and properties of modified gypsum, the effect is weaker than that of soluble phosphorus impurities. Insoluble Ca3(PO4)2 does not affect the properties of modified gypsum. Soluble phosphorus in the liquid phase decreases the supersaturation of the gypsum solution and metathesises with the Ca2+ in the solution to produce insoluble calcium phosphate. This product covers the surface of the crystal nucleus, delays the hydration reaction of gypsum, and decreases the amount of heat released in the early hydration process. Moreover, a coarse overlap of the crystal growth and loose structure of the hardened body is observed, and the flexural and compressive strengths decrease. Increase in the amount of soluble phosphorus in the solution decreases the polarity of the hydroxyl group in the HPMC molecule and strength of the hydrogen bond within the association complex. This phenomenon leads to the disintegration of the large colloidal association and the less swelling, owing to which the HPMC molecule cannot effectively block the water transmission channel in the mixture, resulting in decreased water retention of the HPMC-modified gypsum.

Atomic force microscopy to assess the mechanical properties of individual casein micelles

Casein micelles (CMs) are ∼100 nm natural colloids found in milk resulting from the complex and unresolved association of casein monomers, phosphorus, and calcium; the latter being either directly bound to the phosphoserine residues of caseins or present as nanoclusters of insoluble micellar calcium phosphate (MCP). Dairy products such as cheese or yogurt are colloidal gels formed by CMs destabilization, for which texture and ability to be processed are essentially determined by rheological properties. Those properties depend on the physico-chemical conditions used during gel formation (e.g., pH, temperature, ionic content). However, questions remain about the origin of this dependence at the microscopic scale. In particular, we still do not have a clear picture of the specific contributions of the rigidity of the elementary bricks (CMs) in comparison with the inter-particles interactions or their spatial distribution. In this work, Atomic Force Microscopy (AFM) is used to evaluate changes in the nanomechanical properties of single CMs following physico-chemical modifications that are known to affect the MCP content and the rheology of the enzymatic milk gel (i.e. decrease of pH and CaCl2 addition). AFM is used as a direct indenter that assesses the CMs’ elastic deformation and gives an estimate of their Young modulus. We show that for a ±18–24% w/w depletion or enrichment in MCP content, the Young modulus of CMs significantly decreases or increases, respectively. This correlation suggests that variations in the modulus of individual CMs could explain the changes in the macroscopic properties of the enzymatic milk gel upon variations of physico-chemical conditions.

A transcription factor STOP1-centered pathway coordinates ammonium and phosphate acquisition in Arabidopsis

Phosphorus (P) is an indispensable macronutrient required for plant growth and development. Natural phosphate (Pi) reserves are finite, and a better understanding of Pi utilization by crops is therefore vital for worldwide food security. Ammonium has long been known to enhance Pi acquisition efficiency in agriculture; however, the molecular mechanisms coordinating Pi nutrition and ammonium remains unclear. Here, we reveal that ammonium is a novel initiator that stimulates the accumulation of a key regulatory protein, STOP1, in the nuclei of Arabidopsis root cells under Pi deficiency. We show that Pi deficiency promotes ammonium uptake mediated by AMT1 transporters and causes rapid acidification of the root surface. Rhizosphere acidification-triggered STOP1 accumulation activates the excretion of organic acids, which help to solubilize Pi from insoluble iron or calcium phosphates. Ammonium uptake by AMT1 transporters is downregulated by a CIPK23 protein kinase whose expression is directly modulated by STOP1 when ammonium reaches toxic levels. Taken together, we have identified a STOP1-centered regulatory network that links external ammonium with efficient Pi acquisition from insoluble phosphate sources. These findings provide a framework for developing possible strategies to improve crop production by enhancing the utilization of non-bioavailable nutrients in soil.

Effect of lactose standardization of milk using low-concentration factor ultrafiltration: Effect of reducing the lactose-to-casein ratio on the properties of milled-curd Cheddar cheese

The pH of cheese is determined by the amount of lactose fermented and the buffering capacity of the cheese. The buffering capacity of cheese is largely determined by the protein contents of milk and cheese and the amount of insoluble calcium phosphate in the curd, which is related to the rate of acidification. The objective of this study was to standardize both the lactose and casein contents of milk to better control final pH and prevent the development of excessive acidity in Cheddar cheese. This approach involved the use of low-concentration factor ultrafiltration of milk to increase the casein content (∼5%), followed by the addition of water, ultrafiltration permeate, or both to the retentate to adjust the lactose content. We evaluated milks with 4 different lactose-to-casein ratios (L:CN): 1.8 (control milk), 1.4, 1.1, and 0.9. All cheesemilks had similar total casein (2.3%) and fat (3.4%) contents. These milks were used to make milled-curd Cheddar cheese, and we evaluated cheese composition, texture, functionality, and sensory properties over 9 mo of ripening. Cheeses made from milks with varying levels of L:CN had similar moisture, protein, fat, and salt contents, due to slight modifications during manufacture (i.e., cutting the gel at a smaller size than control) as well as control of acid development at critical steps (i.e., cutting the gel, whey drainage, salting). As expected, decreasing the L:CN led to cheeses with lower lactic acid, residual lactose, and insoluble Ca contents, as well as a substantial pH increase during cheese ripening in cheeses. The L:CN ratio had no significant effect on the levels of primary and secondary proteolysis. Texture profile analysis showed no significant differences in hardness values during ripening. Maximum loss tangent, an index of cheese meltability, was lower until 45 d for the L:CN 1.4 and 0.9 treatments, but after 45 d, all reduced L:CN cheeses had higher maximum loss tangent values than the control cheese (L:CN 1.8). Sensory analyses showed that cheeses made from milks with reduced L:CN contents had lower acidity, sourness, sulfury notes, and chewdown cohesiveness. Standardization of milk to a specific L:CN ratio, while maintaining a constant casein level in the milk, would allow Cheddar cheese manufacturers to have tighter control of pH and acidity.

Synchronous anodic oxidation-cathodic precipitation strategy for efficient phosphonate wastes mineralization and recovery of phosphorus in the form of hydroxyapatite

• Electrochemical “oxidation-precipitation” system can recover phosphorus from phosphonates. • Phosphorus was electrochemically recovered in the form of hydroxyapatite (HAP) within 120 min. • BDD( OH) led to the fastest orth-P yield, medium TOC attenuation and slowest nitrate formation. • The HAP formation proceeded via brushite, octacalcium phosphate and amorphous calcium phosphate. To make up the gap of wasted phosphonates being too much as pollutants and phosphorus being too little as a natural resource, electrochemical “oxidation-precipitation” system was rationally developed to recover phosphorus with simultaneous mineralization of ethylenediamine tetra(methylene phosphonic acid) (EDTMP), a typical phosphonate. In this process, BDD( OH) was the primary oxidative species for EDTMP degradation, which led to the bond cleavage in the sequence of C-N, C-P and C-C. Increasing current density from 3 to 30 mA cm −2 improved the mineralization efficiency of EDTMP from 14% to 72% within 120 min, accompanying 65–95% of EDTMP conversion to orth-P. With the presence of 50 mg L −1 Ca 2+ , 21–83% of phosphorus was recovered as insoluble calcium phosphate at the cathode surface. High initial Ca 2+ concentration favored the phosphorus recovery, whereas it was negatively influenced with the presence of Mg 2+ and HCO 3 – . In addition, phosphorus recovery was negligibly affected by solution pH in the range of 3.0 to 12.0 because the locally alkaline condition was well maintained at the cathode surface. Phosphorus was electrochemically recovered mainly in the form of thermodynamically most stable hydroxyapatite, which proceeded via the formation of brushite, octacalcium phosphate, and amorphous calcium phosphate with Δ[Ca]/Δ[P] molar ratio increasing from 1.0 to 1.67. Based on the results of phosphorus recovery from the real wastewater, we envision that this synchronous anodic oxidation-cathodic precipitation process can be applied as an environmentally compatible and feasible strategy for phosphorus recovery from the phosphonate wastewaters.

Temperature Tolerant Rhizobium leguminosarum bv. viciae Strains with Plant Growth Promotion Traits

Rhizobacteria (PGPR) that promote the plant growth are essential component of sustainable agriculture. Pea (Pisum sativum L.) root nodule Rhizobium leguminosarum bv. viciae ten strains were cultured at two different temperatures (28°C and 45°C). Out of eight strains screened the three N25, N30 and N40 were temperature tolerant while only one strain (N40) showed tolerance to pH11. The growth of Rhizobium strain N40 at 45 °C was 96.8 percent as compared to the growth of the at 28°C. The temperature tolerant strain N40 produced maximum IAA and solubilized insoluble tri calcium phosphate compared to other strains and thus can be used microbial inoculant in biofertilizer technology.