Effect of sodium alginate on phosphorus recovery by vivianite precipitation

Comparative evaluation of phosphorus recovery from sewage sludge thermal products via magnesium ammonium phosphate and hydroxyapatite methods

Shortage of phosphorus resource has become a global concern. Due to the high phosphorus content in sewage sludge, phosphorus recovery can be realized from thermal products of sewage sludge. Phosphorus recovery performance of smoldering ash (SA), incineration ash (IA) and pyrolysis char (PC) was investigated. The precipitate rate of phosphorus in acid and alkali leaching solutions is over 94 % by magnesium ammonium phosphate (MAP) and hydroxyapatite (HAP) methods. For MAP method, the recovered P contents in the precipitations of SA, IA and PC are 23.25 ± 0.35, 31.71 ± 0.79 and 23.76 ± 0.24 mg/g, respectively. For HAP recovery, the phosphorus contents per unit mass of precipitated products are lower than that by MAP, ranging from 13.67 ± 0.10 to 22.89 ± 0.34 mg/g. The purity of the recovered products was evaluated based on the contents of major elements and heavy metals in recovered products. Most of major elements and heavy metals can coprecipitate with phosphorus in the recovery products by acid leaching-MAP method. Due to the low impurity content in the alkali leaching solution and insolubility of most heavy metals in it, the products recovered by alkali leaching-HAP shows higher purity than that by acid leaching-MAP method. The phosphorus recovery performance, reagent consumption and purity of recovered products of the two methods were compared. Acid leaching-MAP recovery is optimal for IA due to its highest P recovery and purity, with lower reagent consumption compared to alkali leaching-HAP. For SA and PC, alkali leaching-HAP recovery is preferable due to its higher P recovery purity and market price of hydroxyapatite products.

Compatibility of vivianite-crystallization pathway of phosphorus recovery with anaerobic digestion systems of thermally hydrolyzed sludge

Phosphorus in sewage is mostly enriched in activated sludge in wastewater treatment plants, making excess sludge an appropriate material for phosphorus recovery. The potential of vivianite (Fe3(PO4)2·8H2O) crystallization-based phosphorus recovery during the anaerobic digestion of thermally hydrolyzed sludge was discussed with influences of organic compounds on the formation of vivianite crystals being investigated in detail. Bovine serum albumin, humic acids and alginate, as model compounds of proteins, humic acids and polysaccharides, all inhibited vivianite crystallization, with the influence of humic acids being the most significant. A sludge retention time of >12 d for effective degradation of organic compounds and a certain degree of FeII excess are suggested to decrease the organics resulting inhibition. The results demonstrate the compatibility of vivianite-crystallization pathway of phosphorus recovery with anaerobic sludge digesters, and reveal the complexity of vivianite formation in the sludge with further research warranted to minimize the inhibitory influences.

Improving nutrients ratio in class A biosolids through vivianite recovery: Insights from a wastewater resource recovery facility

Class A biosolids from water resource recovery facilities (WRRFs) are increasingly used as sustainable alternatives to synthetic fertilizers. However, the high phosphorus to nitrogen ratio in biosolids leads to a potential accumulation of phosphorus after repeated land applications. Extracting vivianite, an FeP mineral, prior to the final dewatering step in the biosolids treatment can reduce the P content in the resulting class A biosolids and achieve a P:N ratio closer to the 1:2 of synthetic fertilizers. Using ICP-MS, IC, UV-Vis colorimetric methods, Mössbauer spectroscopy, and SEM-EDX, a full-scale characterization of vivianite at the Blue Plains Advanced Wastewater Treatment Plant (AWTTP) was surveyed throughout the biosolids treatment train. Results showed that the vivianite-bound phosphorus in primary sludge thickening, before pre-dewatering, after thermal hydrolysis, and after anaerobic digestion corresponded to 8 %, 52 %, 40 %, and 49 % of the total phosphorus in the treatment influent. Similarly, the vivianite-bound iron concentration also corresponded to 8 %, 52 %, 40 %, and 49 % of the total iron present (from FeCl3 dosing), because the molar ratio between total iron and total incoming phosphorus was 1.5:1, which is the same stoichiometry of vivianite. Based on current P:N levels in the Class A biosolids at Blue Plains, a vivianite recovery target of 40 % to ideally 70 % is required in locations with high vivianite content to reach a P:N ratio in the resulting class A biosolid that matches synthetic fertilizers of 1:1.3 to 1:2, respectively. A financial analysis on recycling iron from the recovered vivianite had estimated that 14-25 % of Blue Plain's annual FeCl3 demand can potentially be met. Additionally, model simulations with Visual Minteq were used to evaluate the pre-treatment options that maximize vivianite recovery at different solids treatment train locations.

Development of nanofibrous scaffolds containing polylactic acid modified with turmeric and hydroxyapatite/vivianite nanoparticles for wound dressing applications

Damaging the outer layer of the body (the skin) has been a common issue for decades. Fabrication of nanofibrous membranes via the electrospinning technique for the sake of making the wound healing process more facile has caught a lot of interest. For this purpose, a polymeric scaffold of polylactic acid (PLA) was doped with nanoparticles with different concentrations of turmeric/hydroxyapatite/vivianite/graphene oxide. The obtained membrane was tested by XRD, SEM, FTIR, and XPS. The surface topography of the scaffold has experienced changes upon adding different concentrations of the nanoparticles. The contact angle was measured by water droplets. It accentuated change in CA starting from 43.9o for pure condition of PLA to 67.7o for PLA/turmeric/vivianite. The thermogravimetric analysis (TGA) test stated that the PLA scaffold features are thermally stable in relatively high-temperature conditions initiating from room temperature to about 300 °C, meeting the maximum loss in mass of about 5 %. The cell viability was carried out in prepared vitro for the sample which contains PLA/turmeric/vivianite/GO, it was elucidated that the IC50 was around 3060 μg/ml.

Emerging electro-driven technologies for phosphorus enrichment and recovery from wastewater: A review

The recovery of phosphorus from wastewater is a critical step in addressing the scarcity of phosphorus resources. Electro-driven technologies for phosphorus enrichment have gathered significant attention due to their inherent advantages, such as mild operating conditions, absence of secondary pollution, and potential integration with other technologies. This study presents a comprehensive review of recent advancements in the field of phosphorus enrichment, with a specific focus on capacitive deionization and electrodialysis technologies. It highlights the underlying principles and effectiveness of electro-driven techniques for phosphorus enrichment while systematically comparing energy consumption, enrichment rate, and concentration factor among different technologies. Furthermore, the study provides a thorough analysis of the capacity of various technologies to selectively enrich phosphorus and proposes several methods and strategies to enhance selectivity. These insights offer valuable guidance for advancing the future development of electrochemical techniques with enhanced efficiency and effectiveness in phosphorus enrichment from wastewater.

Phosphorus recovery from synthetic anaerobic fermentation supernatant via vivianite crystallization: Coupling effects of various physicochemical process parameters

Recovery of phosphorus (P) via vivianite crystallization is an effective strategy to recycle resources from the anaerobic fermentation supernatant. However, the presence of different components in the anaerobic fermentation supernatant (e.g., polysaccharides and proteins) might alter conditions for optimal growth of vivianite crystals, resulting in distinct vivianite characteristics. In the present study, the effect of different components on vivianite crystallization was explored. Then, the reaction parameters (pH, Fe/P, and stirring speed) for P recovery from synthetic anaerobic fermentation supernatant as vivianite were optimized using response surface methodology, and the relationship between crystal properties and supersaturation was elucidated using a thermodynamic equilibrium model. The optimized values for pH, Fe/P, and stirring speed were found to be 7.8, 1.74, and 500 rpm respectively, resulting in 90.54 % P recovery efficiency. Moreover, the variation of reaction parameters did not change the crystalline structure of the recovered vivianite but influenced its morphology, size, and purity. Thermodynamic analysis suggested the saturation index (SI) of vivianite increased with increasing pH and Fe/P ratio, leading to a facilitative effect on vivianite crystallization. However, when the SI was >11, homogenous nucleation occurred so that the nucleation rate was much higher than the crystal growth rate, causing a smaller crystal size. The findings presented herein will be highly valued for the future large-scale application of the vivianite crystallization process for wastewater treatment.

A dual-cycle regeneration to recover high-value and high-purity FePO4 from real wastewater for Li-battery application

The recovery of high-purity and high-value FePO4 raw materials from wastewater has great prospects in LiFePO4 battery industry due to the huge demand for new energy vehicle. However, the conventional in-situ FePO4 precipitation, as well as ex-situ PO43- adsorption-alkali regeneration, was incapable of efficiently obtaining high-purity products. To solve these problems, a dual-cycle regeneration method of Fe-NH2-polyacrylonitrile (PAN) adsorbent and H2SO4 desorbing solution was proposed to ex-situ FePO4 recovery from wastewater for Li-battery application. Benefitted from coordination interaction and electrostatic attraction, the maximum PO43- adsorption capacity of Fe-NH2-PAN reached 73.1 ± 0.4 mg/g. The average PO43- removal rate of continuous flow devices were 88.5% and 91.3% when treating low-P-concentration (0.22 mg/L) municipal wastewater (MW) and high-P-concentration (48.9 mg/L) slaughterhouse wastewater (SW) respectively. Furthermore, high-purity FePO4 analyzed by XRD spectra was achieved from the desorption solution at pH ∼1.6, resulting in the ultrahigh P recovery efficiencies of 91.4 ± 3.2%-96.3 ± 2.5% for SW and 82.7 ± 3.5% for MW. Besides, the LiFePO4/C electrodes made of recycled FePO4 exhibited a better discharge capacity (37.3 - 55.8 mAh/g) than that of commercial FePO4 agent (32.2 - 35.1 mAh/g) from 80 to 132 cycles, which showed the promising feasibility of recovering FePO4 from wastewater for Li-battery application.

Efficient removal and recovery of phosphorus from industrial wastewater in the form of vivianite

With the shortage of phosphorus resources, the concept of phosphorus recovery from wastewater is generally proposed. Recently, phosphorus recovery from wastewater in the form of vivianite has been widely reported, which could be used as a slow-release fertilizer as well as the production of lithium iron phosphate for Li-ion batteries. In this study, chemical precipitation thermodynamic modeling was applied to evaluate the effect of solution factors on vivianite crystallization with actual phosphorus containing industrial wastewater. The modeling results showed that the solution pH influences the concentration of diverse ions, and the initial Fe²⁺ concentration affects the formation area of vivianite. The saturation index (SI) of vivianite increased with the initial Fe²⁺ concentration and Fe:P molar ratio. pH 7.0, initial Fe²⁺ concentration 500 mg/L and Fe:P molar ratio 1.50 were the optimal conditions for phosphorus recovery. Mineral Liberation Analyzer (MLA) accurately determined the purity of vivianite was 24.13%, indicating the feasibility of recovering vivianite from industrial wastewater. In addition, the cost analysis showed that the cost of recovering phosphorus by the vivianite process was 0.925 USD/kg P, which can produce high-value vivianite products and realize "turn waste into treasure".

Human urine: A novel source of phosphorus for vivianite production

Human urine contributes up to 50 % of the phosphorus load in domestic wastewater. Decentralized sanitation systems that separately collect urine provide an opportunity to recover this phosphorus. In this study, we leveraged the unique and complex chemistry of urine in favor of recovering phosphorus as vivianite. We found that the type of urine affected the yield and purity of vivianite, but the kind of iron salt used, and reaction temperature, did not affect the yield and purity. Ultimately, it was the urine pH that affected the solubility of vivianite and other co-precipitates, with the highest yield (93 ± 2 %) and purity (79 ± 3 %) of vivianite obtained at pH 6.0. Yield and purity of vivianite were both maximized when Fe:P molar ratio was >1.5:1, but <2.2:1. This molar ratio provided sufficient iron to react with all available phosphorus, while exerting a competitive effect that suppressed the precipitation of other precipitates. Vivianite produced from fresh urine was less pure than vivianite produced from synthetic urine, because of the presence of organics in real urine, but washing the solids with deionized water improved the purity by 15.5 % at pH 6.0. Overall, this novel work adds to the growing body of literature on phosphorus recovery as vivianite from wastewater.

Recovery of phosphorus from wastewater containing humic substances through vivianite crystallization: Interaction and mechanism analysis

Vivianite crystallization has been regarded as a suitable option for recovering phosphorus (P) from P-containing wastewater. However, the presence of humic substances (HS) would inevitably affect the formation of vivianite crystals. Therefore, the influences of HS on vivianite crystallization and the changes in the harvested vivianite crystals were investigated in this study. The results suggested the inhibition effect of 70 mg/L HS on vivianite crystallization reached 12.24%, while it could be attenuated by increasing the pH and Fe/P ratio of the solution. Meanwhile, the addition of HS altered the size, purity, and morphology of recovered vivianite crystals due to the blockage of the growth sites on the crystal surface. Additionally, the formation of phosphate ester group, hydrogen bonding, and COOH-Fe²⁺ complexes are the potential mechanisms of HS interaction with vivianite crystals. The results obtained herein will help to elucidate the underlying mechanism of HS on vivianite crystallization from P-containing wastewater.

Acid/alkali pretreatment enhances the formation of vivianite during anaerobic fermentation of waste activated sludge

Phosphorus (P) recovery from waste activated sludge (WAS) of wastewater treatment plants is significant in the world suffering from P shortage. Recently, vivianite crystallization has been regarded as an essential method of recovering P from anaerobic fermentation (AF) of WAS. This study performed acid/alkali pretreatment (pH 3/pH 10) on AF of WAS to improve iron reduction and vivianite formation. The results showed that the maximum iron reduction rate (R_max) in the pH 3 and pH 10 groups was increased by 1.9 and 1.7 times compared with that in the Control-Fe group, and the iron reduction efficiency (E_Fe) was increased by 17.5% and 12.0% respectively. The Fe bound P (Fe-P) proportion in the sludge in the pH 3 and pH 10 groups increased by 50.0% and 33.7%, respectively. Furthermore, the relative abundance of the iron-reducing bacteria Clostridium_sensusensu in the pH 3 group was higher; and the Fe-P proportion in the sludge and the size of vivianite crystal after AF were larger. With these results, pH 3 pretreatment was preferred for promoting Fe²⁺ release and vivianite formation during AF.

Unravelling key factors controlling vivianite formation during anaerobic digestion of waste activated sludge

As a product of phosphorous recovery from anaerobic digestion (AD) of waste activated sludge (WAS), vivianite has received increasing attention. However, key factors controlling vivianite formation have not yet been fully addressed. Thus, this study was initiated to ascertain key factors controlling vivianite formation. A simulation of chemical equilibriums indicates that interfering ions such as metallic ions and inorganic compounds may affect vivianite formation, especially at a PO₄^3-concentration lower than 3 mM. The experiments demonstrated that the rate of ferric bio-reduction conducted by dissimilatory metal-reducing bacteria (DMRB) and the competition of methane-producing bacteria (MPB) with DMRB for VFAs (acetate) were not the key factors controlling vivianite formation, and that ferric bio-reduction of DMRB can proceed when a sufficient amount of Fe³⁺ exists in WAS. The determined affinity constants (K_s) of both DMRB and MPB on acetate revealed that the K_HAc constant (4.2 mmol/g VSS) of DMRB was almost 4 times lower than that of MPB (15.67 mmol/g VSS) and thus MPB could not seriously compete for VFAs (acetate) with DMRB. As a result, vivianite formation was controlled mainly by the amount of Fe³⁺ in WAS. In practice, a Fe/P molar ratio of 2:1 should be enough for vivianite formation in AD of WAS. Otherwise, exogenously dosing Fe³⁺ or Fe²⁺ into AD must be applied in AD.

Recovery of phosphorus from eutrophic water using nano zero-valent iron-modified biochar and its utilization

Effective removal and recovery of phosphorus (P) from the aquatic environment was of great significance for eutrophication control and P recovery. This study investigated the effects of different environmental conditions on P adsorption by biochar (BC) and the feasibility of applying the P-laden BC as a fertilizer for plant growth. The nano zero-valent iron (nZVI) modified reeds BC prepared at 700 °C (Fe-700-BC) had the maximum P adsorption capacity of 95.2 mg g^-1, which was higher than those prepared at 300, 500, and 900 °C. The addition of Fe-700-BC reduced the concentration of total phosphorus (TP) in the overlying water, in which the soluble reactive phosphorus (SRP) almost completely removed, as well as had a certain inhibitory effect on the growth of algae. Simultaneously, Fe-700-BC reduced the contents of different fractions of P (weakly adsorbed inorganic phosphorus (WA-Pi), potential active inorganic phosphorus (PA-Pi), and Fe/Al-bound inorganic phosphorus (Fe/Al-Pi)) by adsorbing the soluble P released from the sediments, especially in the case of disturbance. Fe-700-BC had no significant effect on the diversity and richness of the microbial community in the sediment. Moreover, P-laden BC was safe and environmentally friendly for application in the soil and tended to increase stem and root length, fresh and dry weight at low doses (0.5 wt%) in wheat planting experiments. The present work could provide a reference for solving the problems related to eutrophication and P deficiency.

Phosphorus recovery from waste activated sludge by sponge iron seeded crystallization of vivianite and process optimization with response surface methodology

As a novel phosphorus recovery product, vivianite (Fe₃(PO₄)₂·8H₂O) has attracted much attention due to its enormous recycling potential and foreseeable economic value. Taking sponge iron as seed material, the effect of different reaction conditions on the recovery of phosphorus in waste activated sludge by vivianite crystallization was studied. Through single factor tests, the optimal conditions for vivianite formation were in the pH range of 5.5-6.0 with Fe/P molar ratio of 1.5. Scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) were used to analyze the components of the crystals. The results showed that the vivianite produced by sponge iron as the seed crystal were larger and thicker (300-700 μm) than other seed (200-300 μm) and without seed (50-100 μm). Moreover, vivianite, which was synthesized with sponge iron as seed, was obviously magnetic and could be separated from the sludge by rubidium magnet. The Box-Behnken design of the response surface methodology was used to optimize the phosphorus-recovery process with sponge iron (maximum phosphorus recovery rate was 83.17%), and the interaction effect of parameters was also examined, pH had a significant effect on the formation of vivianite. In summary, this research verifies the feasibility of using sponge iron as the seed crystal to recover phosphorus in the form of vivianite from waste activated sludge, which is conducive to the subsequent separation and utilization of vivianite.

Organic matter affects phosphorus recovery during vivianite crystallization

Vivianite crystallization is a promising route for phosphorus (P) recovery from P-rich wastewater. However, organic matter (OM) in wastewater may influence vivianite formation. In this study, the effects of four representative OMs, glucose, bovine serum albumin (BSA), humic acid (HA) and sodium alginate (SA), on P recovery by vivianite were investigated. The results showed that P recovery efficiency was inhibited by HA and SA, declining by 3.7% and 12.1% under HA (100 mg/L) and SA (800 mg/L), respectively. BSA, HA and SA affected the aggregated form of vivianite crystals. Vivianite particle size decreased in the presence of HA and SA. Subsequent mechanistic exploration indicated that the complexation between the OM and Fe²⁺ was the main cause of P recovery efficiency reduction. The coprecipitation of HA and SA with vivianite could reduce the zeta potential on the crystal surface, resulting in a smaller particle size. The nucleation sites provided by BSA and SA could transfer vivianite from single plate-like agglomerate to multilayer plate-like agglomerate. This study provided a better understanding of P recovery by vivianite from OM-rich wastewater.

Phosphate substances transformation and vivianite formation in P-Fe containing sludge during the transition process of aerobic and anaerobic conditions

Excess sludge was considered as a promising raw material for phosphorus recovery. In this study, the P-Fe containing sludge came from the aerobic membrane bioreactor with electrocoagulation (EC), which was refluxed to the anaerobic unit for iron reduction. Under anaerobic condition, the ORP and pH maintained at -350 mV and 7.5, which exactly met the conditions for vivianite formation. According to the analysis of X-ray polycrystalline diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), the final product of the sludge after anaerobic condition was mainly vivianite. Microbial analysis showed that there were iron reducing bacteria (IRB) in sludge before and after anaerobic process, including Dechloromonas, Desulfovibrio. Aeromonas and Methanobacterium. During the transition process of aerobic and anaerobic conditions, amorphous phosphate substances in P-Fe containing sludge could be transformed vivianite just with long term standing, which could promote the recovery of phosphate resource from wastewater.