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Solution thermodynamics and kinetic modelling applied to struvite crystallisation–precipitation were reviewed from diverse references to determine proximity between predicted and cited experimental measurements. These simulations show the expected variability range of struvite saturation calculation when only limited solution compositional information is given, showing acceptable agreement between predicted and experimental struvite mass. This work also compares results from struvite crystallisation kinetic studies on liquid phase species depletion, crystallisation induction time, primary nucleation, secondary nucleation, crystal growth, and crystal aggregation. Large inconsistencies between reported kinetics were observed in many scenarios. Variations in species depletion models highlighted that they are only suitably applied to the specific system from which they were regressed. Spontaneous primary nucleation was predicted to occur in the range of SI = 0.237–0.8. Predicted primary nucleation rates vary over at least 10 orders of magnitude (depending on supersaturation) because of uncertainties in interfacial tension and maximum achievable nucleation rate. Secondary nucleation rates are more agreeable, varying over approximately two orders of magnitude. Growth rates varied over five orders of magnitude due to variations in experimental conditions. Aggregation rates are not thoroughly examined enough to make any inferences.

The high concentration of ammonia nitrogen (NH4+) and chemical oxygen demand (COD) in biogas slurry pose great challenges to the efficiency of traditional wastewater treatment systems. Collophanite tailings are solid waste, characterized by significant concentrations of phosphorus (PO43-) and magnesium (Mg2+), represent a potential resource for the reduction and recovery of NH4+ in biogas slurry via struvite precipitation. This study systematically explored the optimal leaching parameters employing sulfuric acid for the extraction of PO43− and Mg2+ from collophanite tailings. The effect of [PO43-]:[NH4+] molar ratio and pH on the recovery of NH4+ in biogas slurry was investigated. The physicochemical properties of the precipitates were confirmed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis. Results suggested that the highest removal efficiency of NH4+ (88.5%) was achieved when employing a [PO43-]:[NH4+] molar ratio of 1.0 at pH 9.5. Evaluation of effluent quality demonstrates a significant enhancement in the biodegradability of the treated biogas slurry, evidenced by an increase in the COD/TN ratio increased from 2.1 to 10.4. Economic analysis shows that the net income would be approximately 21.33 USD/m3 for proposed produces. These findings underscore the potential of utilizing collophanite tailings for NH4+ recovery from biogas slurry.

For soil and environmental remediation, biochar/struvite composites are prepared by the crystallization-adsorption method. The recovery rates of N, P, and Mg in the solution increase to 99.02%, 97.23%, and 95.22%, respectively, by forming 10% biochar/struvite composite. X-ray diffraction (XRD) patterns acquired from the 10% biochar/struvite composite show a crystalline structure of MgNH 4 PO 4 ·6H 2 O (PDF no. 15-0762) and release of the main nutrient elements (N, P, Mg) from the 10% biochar/struvite composite increases significantly compared to struvite. The solubility of the biochar/struvite composite is the highest in 0.5 mol/L HCl, second in 20 g/L citric acid, and lowest in water. The power function equation describes more precisely the cumulative release of N, P, and Mg from the biochar/struvite composite in distilled water, whereas it follows the simple Elovich equation in 20 g/L critic acid and first-order kinetics equation in 0.5 mol/L HCl. Leaching experiments are performed on the biochar/struvite composite in soil, and the results indicate that the biochar/struvite composite has a longer cycle of release of nutrients than traditional chemical fertilizers and has large potential as a slow-release fertilizer.

Struvite crystallization is an interesting method for the recovery of phosphorus (P) from wastewater. However, the struvite crystals obtained are small, which makes them difficult to separate from wastewater. A continuous reactor for enlarging struvite crystals was developed. Batch-scale experiments were conducted to investigate the optimum factors for the enlargement of struvite crystals. The results of pH experiments showed that P recovery efficiency increased with an increase of pH values (7.6 to 10), while the size of struvite crystals decreased. The results of the Mg:P ratios found that the maximum P recovery efficiency occurred at the maximum ratio of Mg:P. The sizes of struvite crystals were not significantly different. For the variation of temperature values, the results showed that P recovery efficiency and crystal sizes decreased when temperature values increased. Therefore, the optimized conditions for P recovery efficiency and enlargement of struvite crystals for the continuous reactor were pH 8.5 and an Mg:P ratio of 1.2:1 at 30 °C (room temperature). The treated swine wastewater and seawater were continuously fed in at the bottom of the reactor. After 30 days, the size of struvite crystals had increased from 125 μm to 0.83 mm (seven times).

Phosphorus (P), an essential element for living cells, is present in different soluble and adsorbed chemical forms found in soil, sediment, and water. Most species are generally immobile and easily adsorbed onto soil particles. However, P is a major concern owing to its serious environmental effects (e.g., eutrophication, scale formation) when found in excess in natural or engineered environments. Commercial chemicals, fertilizers, sewage effluent, animal manure, and agricultural waste are the major sources of P pollution. But there is limited P resources worldwide. Therefore, the fate, effects, and transport of P in association with its removal, treatment, and recycling in natural and engineered systems are important. P removal and recycling technologies utilize different types of physical, biological, and chemical processes. Moreover, P minerals (struvite, vivianite, etc.) can precipitate and form scales in drinking water and wastewater systems. Hence, P minerals (e.g., struvite, vivianite etc.) are problems when left uncontrolled and unmonitored although their recovery is beneficial (e.g., slow release fertilizers, sustainable P sources, soil enhancers). Sources like wastewater, human waste, waste nutrient solution, etc. can be used for P recycling. This review paper extensively summarizes the importance and distribution of P in different environmental compartments, the effects of P in natural and engineered systems, P removal mechanisms through treatment, and recycling technologies specially focusing on various types of phosphate mineral precipitation. In particular, the factors controlling mineral (e.g., struvite and vivianite) precipitation in natural and engineered systems are also discussed.

The manufacturing of fossil-based fertilizers by extraction of rock phosphate has contributed to carbon emissions and depleted the non-renewable phosphorus reserves. Sewage sludge, which is a waste product from Sewage Treatment Plants (STPs), is rich in phosphorus. The existing techniques for sludge management contribute to carbon emissions and ecological footprint. Struvite (raw fertilizer) and biochar recovery from sludge has emerged as viable methods to reduce carbon emission and ensure economic sustainability of STPs. In this work, the potential for phosphorus recovery and revenue generation is discussed for Rajasthan state in India. The fate of phosphorus and heavy metals in STPs is evaluated which indicates that about 70% of the phosphorus and trace amounts of metals end up in sewage sludge. Further, the power consumption is high in STPs due to industrial wastewater ingress. There is a need to bridge the gap between sewage treatment and generation in Rajasthan, improve STP performance before resource recovery inclusion at policy-level and scale-up. Mixing struvite with biochar can lead to safe application of struvite as raw fertilizer as heavy metals are sequestered by biochar. A business framework is developed to serve as a blueprint and potential model for linking technical and market viability.

This present study investigated the removal of COD and ammoniacal nitrogen (NH 4 + –N) from tannery deliming wastewater (TDLWW) through microbes immobilized carbon consisted a bioreactor (MICCR) and reactive struvite crystallization process. Initially, 90% of the organic content of TDLWW was removed using a MICCR reactor at 24 h retention time. Nanoporous carbon (NPC) was used as the carrier matrix for the MICCR reactor. SEM and AFM images of NPC used in the MICCR reactor identify different microorganisms on its surface. The microbial profile of NPC used in the MICCR was analyzed, and the relative abundance is phyla Firmicutes , 25.64%; Proteobacteria , 43.68%; Bacteroidetes , 6.58%; Cyanobacteria , 2.22%; Actinobacteria , 2.34% reason for organic removal. The removal of organics follows the pseudo-second-order rate kinetics with the rate constant of 1.75 × 10 −3  L COD −1 h −1 . For the reactive struvite crystallization, MgO and Na 2 HPO 4 .2H 2 O were taken as the precipitating agents. The optimum molar ratio for the maximum conversion of NH 4 + –N into struvite was obtained as 1:1.4:1.4 (NH 4 + –N:MgO:Na 2 HPO 4 .2H 2 O). The volume of struvite precipitate was 48.5 mL/L of TDLWW, and the dry weight was 8.89 g/L. More than 93% of NH 4 + –N was converted as the struvite fertilizer. The conversion of NH 4 + –N into struvite follows the pseudo-first-order rate kinetics with the rate constant of 1.67 × 10 −2 min −1 . Despite the conversion of NH 4 + –N into struvite, COD removal was observed, which confirms the conversion of organic nitrogen into struvite. The struvite was evaluated using SEM, XRD, TGA, DSC, and FT-IR spectroscopic analysis. Hence, the integrated MICCR and the reactive struvite crystallization process can be applied to manage tannery deliming wastewater.

Struvite is regarded as a promising phosphorus fertilizer alternative to mineral fertilizers; however before fertilizing, soil tests should be undertaken to determine fertilizer recommendations. In May 2022, soil was sampled from a pot experiment with the application of phosphorus set up at the Wroclaw University and Environmental and Life Sciences. Chemical analysis of the soil included total and available phosphorus, potassium, magnesium determined by the Egner–Riehm, Mehlich 3 and Yanai methods. The purpose of the article is to compare soil element extraction by three different methods under struvite fertilization and its use in soybean cultivation. The application of these methods indicated an unambiguous increase in soil Mg content after struvite application. Broadcast soybean fertilization affected the phosphorus content of the soil. The results of the study indicated that different extraction methods presented different contents of P from soil. The content of available phosphorus was circa 122–156 mg kg −1  dm, 35.4–67.5 mg kg −1  dm and 100–159 mg kg −1  dm according to the Mehlich, Yanai and Egner–Riehm methods, respectively. A positive correlation was found between the content of Mg and K in soil determined by the Mehlich 3 and Yanai methods, which may suggest that the Yanai method could be introduced into standard soil chemical analysis in Poland. Such a correlation was not found for phosphorus, which is a difficult element to determine due to the multitude of factors affecting its availability.

Wastewater-recovered phosphorus (P), in the form of the mineral struvite (MgNH 4 PO 4 ⋅6H 2 O), may provide a sustainable alternative to decreasing rock-phosphate reserves. Struvite can be generated via precipitation methods, potentially reducing the amount of P runoff to aquatic ecosystems. The objective of this greenhouse tub study was to evaluate the effects of chemically- and electrochemically precipitated struvite (CPST and ECST, respectively) on above- and belowground plant response in a hybrid rice ( Oryza sativa ) cultivar grown using furrow-irrigation compared to other common fertilizer-P sources [i.e., triple super phosphate (TSP) and diammonium phosphate (DAP)]. Rice was grown in tubs in controlled environmental conditions in a greenhouse for a full growing season in a P-deficient, silt-loam soil (Typic Glossaqualfs). Plant nutrients (i.e., N. P. K. Mg, Zn) were determined at the end of the growing season through Mehlich-3 extraction. Below- and aboveground rice dry matter (DM), root-P concentration and uptake, aboveground tissue-P uptake, total aboveground and total plant DM, grain yield, and grain P uptake from CPST and ECST did not differ from DAP or TSP. However, aboveground tissue-P concentration was greater ( P  < 0.05) from TSP (0.05%) than from ECST, CPST, and the unamended control (UC). Total aboveground (i.e., vegetative plus grain) tissue-P uptake was largest ( P  < 0.05) from TSP (4.8 g m − 2 ), which did not differ from DAP or CPST, and was at least 1.1 times greater than from ECST and the UC. Despite only a few differences from the UC, the many similar rice responses among struvite and other common fertilizer-P sources suggest that struvite, especially ECST, is a potential alternative fertilizer-P source that warrants further research into struvite’s role in food production.

Typical biological processing is often challenging for removing ammonia nitrogen and phosphate from swine wastewater due to inhibition of high ammonia on activity of microorganisms, exhaustion of time, and low efficiency. In this study, a physicochemical process by combining ammonia stripping with struvite precipitation has been tested to simultaneously remove ammonia nitrogen, phosphate, and chemical oxygen demand (COD) from digested swine wastewater (DSW) with high efficiency, low cost, and environmental friendliness. The pH, temperature, and magnesium content of DSW are the key factors for ammonia removal and phosphate recovery through combining stripping with struvite precipitation. MgO was used as the struvite precipitant for NH 4 + and PO 4 3− and as the pH adjusted for air stripping of residual ammonia under the condition of 40 °C and 0.48 m 3  h −1  L −1 aeration rate for 3 h. The results showed that the removal efficiency of ammonia, total phosphate, and COD from DSW significantly increased with increase of MgO dosage due to synergistic action of ammonia stripping and struvite precipitation. Considering the processing cost and national discharge standard for DSW, 0.75 g L −1 MgO dosage was recommended using the combining technology for nutrient removal from DSW. In addition, 88.03% NH 4 + -N and 96.07% TP could be recovered from DSW by adsorption of phosphoric acid and precipitation of magnesium ammonium phosphate (MAP). The combined technology could effectively remove and recover the nutrients from DSW to achieve environmental protection and sustainable and renewable resource of DSW. An economic analysis showed that the combining technology for nutrient removal from DSW was feasible.