Struvite Crystallization Research Articles

Enhanced removal efficiency of nitrogen and phosphorus from swine wastewater using MgO modified pig manure biochar

Pig manure and swine wastewater from livestock and poultry contain high levels of nitrogen and phosphorus, which can seriously threaten ecosystems. In this study, biochar derived from pig manure (PMBC) was modified by various magnesium salts to obtain pig manure biochar modified with MgO (MgO-PMBC), Mg(OH)2 (Mg(OH)2-PMBC) and MgCl2 (MgCl2-PMBC), and their capacities of simultaneous adsorption of NH4+-N and PO43--P were investigated. Results showed that the adsorption quantities for NH4+-N and PO43--P decreased in the order: MgO-PMBC >Mg(OH)2-PMBC > MgCl2-PMBC > PMBC. When the optimal dosage for MgO-PMBC was determined to be 0.6 g/L and the initial solution pH was set to the ideal value of 7, the maximum adsorption quantities for NH4+-N and PO43--P by MgO-PMBC reached 122.01 mg/g and 206.85 mg/g, respectively, which were 49.8 and 85.5 times of those of the PMBC. The specific surface area and total pore volume of MgO-PMBC were 9.4 times and 4.1 times of the PMBC. Removal rate of PO43--P from swine wastewater was 97.57%, and the concentration of PO43--P from treated swine wastewater was lower than 0.5 mg/L, the primary discharge standard of China’s Comprehensive Wastewater Discharge Standard. The enhanced simultaneous adsorption of NH4+-N and PO43--P by modified PMBC (MgO-PMBC) was ascribed to its greater specific surface area and total pore volume, and the reaction of crystallisation of struvite. Our results demonstrated that pig manure biochar modified by MgO can be used to treat swine wastewater effectively.

Differential expression of urease genes and ureolytic activity of uropathogenic Escherichia coli and Pseudomonas aeruginosa isolates in different nutritional conditions.

Uropathogens have adaptation strategies to survive in the host urinary tract by efficiently utilizing and tolerating the urinary metabolites. Many uropathogens harbour the enzyme urease for the breakdown of urea and the enzymatic breakdown of urea increases the pH and facilitate the struvite crystallization. In this study, the differential urease activity of uropathogenic Escherichia coli and Pseudomonas aeruginosa strains was investigated under different nutritional conditions. The experiments included measurement of growth, pH, urease activity, NH4-N generation and urease gene (ureC) expression among the bacterial strains under different conditions. Further, the implications of urea breakdown on the struvite crystallization in vitro and biofilm formation were also assessed. The study included urease positive isolates and for comparison urease negative isolates were included. Compared to the urease negative strains the urease positive strains formed higher biofilms and motility. The urease positive P. aeruginosa showed significantly higher (p < 0.01) pH and urease activity (A557-A630) compared to E. coli under experimental conditions. Further, supplementation of glucose to the growth media significantly increased the urease activity in P. aeruginosa and in contrast, it was significantly lower in E. coli. The expression profile of urease gene (ureC) was significantly higher (p < 0.001) in P. aeruginosa compared to E. coli and was consistent with the biochemical results of the urease activity under the nutritional conditions. The differential urease activity under two nutritional conditions influenced the biogenic struvite crystallization. It correlated with the urease activity showing higher crystallization rate in P. aeruginosa compared to E. coli. The results highlight the differential urease activity in two common uropathogens under different nutritional conditions that may have significant role on the regulation of virulence, pathogenicity and in the kidney stone disease.

Effects of biochar combined with MgO desulfurization waste residue on nitrogen conversion and odor emission in chicken manure composting

ABSTRACT Aim: Chicken manure is known to produce strong odors during aerobic composting, which not only pollutes the surrounding environment but also leads to the loss of valuable nutrients like nitrogen and sulfur, thus reducing the quality of the fertilizer. Methods: In this study, we explored the use of biochar combined with MgO desulfurization waste residue (MDWR) as a novel composting additive. Our approach involved conducting composting tests, characterizing the compost samples, conducting pot experiments, and examining the impact of the additives on nitrogen retention, deodorization, and compost quality. Results: Our findings revealed that the addition of biochar and MDWR significantly reduced ammonia volatilization in chicken manure compost, demonstrating a reduction rate of up to 60.12%. Additionally, the emission of volatile organic compounds (VOCs) from chicken manure compost treated with biochar and MDWR decreased by 44.63% compared to the control group. Conclusions: The composting product treated with both biochar and MDWR (CMB) exhibited a 67.7% increase in total nitrogen (TN) compared to the blank control group, surpassing the other treatment groups and showcasing the synergistic effect of these two additives on nitrogen retention. Moreover, the CMB treatment facilitated the formation of struvite crystals. Furthermore, our pot experiment results demonstrated that the CMB treatment enhanced vegetable yield and quality while reducing nitrate content. These findings highlight the significant impact of MDWR on nitrogen retention, deodorization, and compost quality enhancement, thereby indicating its promising application prospects.

Baseline Urinalysis of the Fully Marine, Herbivorous Dugong (Dugong dugon)

The dugong (Dugong dugon) is a fully marine mammal that grazes in nearshore seagrass meadows and whose health is vulnerable to human coastal activities. This study establishes urine baseline ranges for apparently healthy dugongs that can be used as health biomarkers. Voluntary urine samples (uncontaminated by seawater) were collected from 71 wild-caught dugongs in Moreton Bay, Australia, that were held out of water during an annual health assessment from 2008 to 2022. Urine was analysed for qualitative characteristics (colour, turbidity, odour), biochemistry through reactive urinalysis test strips, urine specific gravity (USG) by refractometer, electrolytes by flame photometry, sediment by microscopy, and bacterial culture. Urine of dugongs was typically pale yellow, clear to slightly cloudy, and mildly odorous. Urine was usually slightly alkaline (mean pH 8), and USG was low (mean 1.018). Urinalysis from dipstick indicated consistently negative readings for the presence of glucose, urobilinogen, bilirubin, ketones, and nitrites. Urinary protein was detected in 85% of sampled dugongs. Haemolysed red blood cells were recorded in &gt; 85% of urine samples; microscopy indicated light haematuria (intact red blood cells) in 16% of samples. Seven percent of dugongs had detectable levels of leukocytes suggesting the possibility of mild urinary tract infection. Urinary sediment containing epithelial cells, keratinaceous debris, calcium carbonate crystalluria, and rare struvite crystals were typical. Light to moderate levels of bacteria were present in urine samples, with variable mixed growths, including Halomonas aquamarina, Pseudomonas stutzeri, Photobacterium damselae, Psychrobacter spp., and Staphylococcus aureus. Spermatozoa were present in the urine of 32% of the sexually mature males. Physical characteristics and chemistry of dugong urine showed some similarities to those of manatees and other herbivores. These baseline urinalysis data for healthy wild dugongs in a single population are valuable benchmarks against which dugongs of variable health status (including compromised dugongs) and from other localities may be compared.

Removal of Ammonium and Phosphate from Synthetic Wastewater of Complex Fertilizer Industry Through Struvite Crystallization Process

The complex fertilizer industry produces wastewater which contributes to the pollution of water bodies because it contains high levels of phosphate and ammonium concentrations and high TKN (Total Kjeldahl Nitrogen) which contains organic nitrogen. The organic nitrogen contained in the complex fertilizer wastewater is urea so it can be hydrolyzed to ammonium using the urease enzyme. The ammonium formed from the hydrolysis of urea will then react with magnesium and phosphate to form struvite, a crystal of Magnesium Ammonium Phosphate (MAP). The purpose of this study was to determine the effect of aeration and the enzyme urease in the removal of ammonium and phosphate in complex fertilizer synthetic wastewater through struvite precipitation. Struvite precipitation was carried out in a batch reactor which had a working volume of 0.5 L with variations in aeration rate, aeration time, and the addition of urease enzyme from Jack bean peas (Canavalia ensiformis). Residual ammonium and phosphate levels were analyzed and struvite crystal formation (MAP) was determined using Scanning Electron Microscope (SEM) and X-ray diffraction (XRD). The results showed that the aeration reactor was able to form struvite crystals and remove the ammonium and phosphate content in the synthetic wastewater of complex fertilizers. The removal of ammonium with a molar ratio of [Mg2+] : [NH4+] : [PO43-] 1:2:1 reached 61-77% at high aeration rates because a lot of ammonium was released into the air. The phosphate removal reached 99%. The urease enzyme was proven to be able to hydrolyze urea into ammonium and increase the pH value and affect the shape of the resulting struvite crystals. The precipitate product obtained was struvite crystals which were confirmed by analysis using SEM-EDX and XRD.

Pilot-scale biogas and in-situ struvite production from pig slurry: A novel integrated approach

Excess ammonia produced during the decomposition of nitrogen-rich substrates inhibits the anaerobic digestion (AD) process while it increases the concentration of ammonium nitrogen (NH4+) in the digestate. Digestate is commonly applied to farmland, causing nitrogen loss via runoff and volatilization. Therefore, developing an integrated strategy to promote the overall efficiency of AD systems susceptible to ammonia toxicity events, is worthy of consideration. Herein, a step-feeding approach to combat ammonia toxicity in AD process in which, intermittent rather than continuous substrate feeding was tested. A pilot-scale, mesophilic (37 ± 1 °C), fed-batch AD reactor (working volume ∼ 6.67 m3), was operated as the biomethanation step in a novel biorefinery concept, to recover bioenergy and nutrients (struvite) from pig slurry. The results showed that methane production yield achieved was 89.7 % of the theoretical at high ammonia levels (4.44 g NH4+-N L−1), indicating an efficient AD process under strong ammonia stress. The production rate of precipitate was 4.0 kg t−1 feedstock, while X-Ray Diffraction analysis revealed that purity of struvite crystal was 98 % w/w. Orthorhombic crystals and homogeneous distribution of significant elements (O, P, N, and Mg) in the precipitate were observed through scanning electron microscopy coupled with energy dispersive X-ray analysis. Recoveries of nitrogen and phosphorus were 48.5 % and 68.5 % from the digestate, respectively. Furthermore, the chemical and sanitary (i.e., Escherichia coli, Enterobacteriaceae and Salmonella) indicators of the precipitate were in line with the EU Fertilizer Regulation. Overall, the obtained results indicate that it is possible to establish an integrated efficient nutrient and energy recovery process for the simultaneous production of high-yield biogas and high-purity struvite fertilizer from pig slurry, which could yield a gross profit of 5.79 € t−1 feedstock.

Phosphate removal from wastewater for the manufacture of struvite fertilizer

One of the non-renewable natural resources is phosphate rock. Phosphate is currently a lot necessity, while the need for phosphate is estimated to last within 30 to 300 years. Therefore, it is necessary to strive for the development of new sustainable sources of phosphate to maintain phosphate stability. Stirring is an efficient method in the crystallization process where the stirring speed affects the growth of struvite crystals. The purpose of this study was to study the growth of struvite crystals with the struvite crystallization process with the influence of stirring rotations of 100, 150 and 200 rpm at a temperature of 30oC. The experiment was carried out by mixing the two solutions in a 1000 ml glass beaker. The reaction time and pH of struvite crystallization were evaluated in this experiment. The crystals obtained were characterized using a scanning electron microscope (SEM) with energy dispersion x-ray (EDX) and x-ray fluorescence (XRF). From the results of the study, it was found that the highest P2O5 content at a stirring speed of 100 rpm and a temperature of 30oC was 47.5%, and was included in the quality of triple superphosphate fertilizer.The morphology of the irregular flake crystals was a typical form of struvite crystals with a size of 20 m.

Characterization, kinetics and thermodynamic evaluation of struvite produced using ferrochrome slag as a magnesium source

There is limited data on studies that have focused on the kinetics, thermodynamics, and characterization of struvite crystallization from alternative magnesium sources. This study focused on thermal analysis of struvite (produced using ferrochrome slag as a magnesium source) and the results indicated that the residual quantities of struvite were lower than the theoretical mass loss of struvite of 51.42%. When using ferrochrome slag (FCS) as the magnesium source, 47.9%, 47.4%, and 46.9% losses in mass were observed for heating rates of 5°C/min; 10°C/min and 15°C/min respectively. The mean activation energies for struvite produced using FCS were deduced using isoconversional kinetic methods and ranged from 49.81to 56.20 kJ/mol which is very similar to the activation energies deduced using MgCl2. The study also focused on the surface morphology, and particle size of the final product at different pH and N:P ratios. The final particle size distribution of the product was significantly influenced by the solution pH. To improve the crystal growth kinetics for both MgCl2 and FCS, a high ratio of N:P molar ratios should be adopted. The product's highest median particle size was obtained using FCS as the magnesium source at a low pH. Median particle size increased with decrease in pH, at a pH of 7.5 the recorded median particle size was 96 µm whilst, the lowest was 31 µm at a pH of 9.5. The highest percent of fines (<10 µm) was recorded at a pH of 9.5 using FCS as magnesium source in the metastable region of struvite precipitation whereas at a pH of 7.5 no fines (<10 µm) were recorded. SEM images confirmed that the struvite underwent morphological changes when prepared with FCS in comparison to that produced using MgCl2. The surface morphology of the finished product demonstrated the presence of irregular shaped particles, due to presence of impurities. The kinetic data showed that struvite precipitation was limited by the chemical reaction step. Model fitting was used to determine the reaction control mechanism and the average activation energies obtained by four model free methods were FWO (56.2), KAS (51.67) Starink (49.61) and Tang (49.81) kJ/mol, indicating that the FWO method was the least accurate method. The thermodynamic data indicated that the thermal degradation of struvite crystals has a high degree of disorder, and the process is endothermic, irreversible, and non-spontaneous.

Hydrothermal Carbonization of Sewage Sludge: New Improvements in Phosphatic Fertilizer Production and Process Water Treatment Using Freeze Concentration

In recent years, promising developments in the hydrothermal carbonization (HTC) of sewage sludge, as well as the potential to reclaim phosphorus and nitrogen, have emerged. In this study, the HTC of digested sewage sludge (DSS) was investigated for the downstream production of heavy metal (HM)-free fertilizer and the use of freeze concentration (FC) as a novel technology for process water treatment. To obtain clean fertilizer, phosphatic acid extracts were first treated with ion-exchange resins to remove dissolved HM, as well as phosphorus precipitating agents (i.e., aluminum and iron). Over 98% of the aluminum (Al) and 97% of the iron (Fe) could be removed in a single treatment step. The purified extract was then used for the precipitation of HM-free struvite crystals, with P-recovery rates exceeding 89%. Process water (PW) makes up the largest share of the two main HTC-products (i.e., hydrochar and PW) and is very rich in organic compounds. Compared to evaporation or membrane separation, FC is a promising technology for concentrating solutes from PW. Separation experiments resulted in the recovery of over 90% of the dissolved compounds in the concentrate. In our study, the concentrate was later utilized as an ammonium source for struvite precipitation, and the subsequent aerobic digestion of the remaining ice water resulted in an 85% reduction in chemical oxygen demand (COD) in 15 days.

Nitrogen and phosphorus recovery from cow digestate by struvite precipitation: Process optimization to maximize phosphorus recovery

The combination of the anaerobic digestion of waste biomass (e.g., livestock manure, energy crops and organic wastes) and the digestate treatment allows green energy to be obtained (starting from biogas/biomethane) and nutrients to be returned to the soil, satisfying the principles of the circular economy. Digestate has valuable potential as an organic fertilizer and soil amendment, as it can be an important source of nutrients, nitrogen and phosphorus (N and P), essential for crop growth. However, digestate production sometimes exceeds the capacity of nearby lands to use the nutrients. Therefore, the recovery of nutrients from digestate has become an important task for anaerobic digestion plants, to meet current regulations. In this study, a method combining struvite precipitation and ammonia stripping was tested in the laboratory to better understand the nutrient removal/recovery efficiency of the two nutrients. Results indicate that more than 60% of total P was removed as struvite, which can be used in N–P fertilizer, substituting synthetic mineral fertilizers.The recovery of N and P from digestate by struvite crystallization allows the removal of nutrient excess at farm level, reducing the environmental impacts of using slurry/digestate in agriculture. The recovery of struvite allows the production of a fertilizer that can be easily exported from farms, promoting the circular economy.

Evidence for liquid-liquid phase separation during the early stages of Mg-struvite formation.

The precipitation of struvite, a magnesium ammonium phosphate hexahydrate (MgNH4PO4 · 6H2O) mineral, from wastewater is a promising method for recovering phosphorous. While this process is commonly used in engineered environments, our understanding of the underlying mechanisms responsible for the formation of struvite crystals remains limited. Specifically, indirect evidence suggests the involvement of an amorphous precursor and the occurrence of multi-step processes in struvite formation, which would indicate non-classical paths of nucleation and crystallization. In this study, we use synchrotron-based in situ x-ray scattering complemented by cryogenic transmission electron microscopy to obtain new insights from the earliest stages of struvite formation. The holistic scattering data captured the structure of an entire assembly in a time-resolved manner. The structural features comprise the aqueous medium, the growing struvite crystals, and any potential heterogeneities or complex entities. By analysing the scattering data, we found that the onset of crystallization causes a perturbation in the structure of the surrounding aqueous medium. This perturbation is characterized by the occurrence and evolution of Ornstein-Zernike fluctuations on a scale of about 1nm, suggesting a non-classical nature of the system. We interpret this phenomenon as a liquid-liquid phase separation, which gives rise to the formation of the amorphous precursor phase preceding actual crystal growth of struvite. Our microscopy results confirm that the formation of Mg-struvite includes a short-lived amorphous phase, lasting >10s.

URINARY TRACT DISEASES IN MALE PERISAN CAT

Urinary tract diseases are one of the various problems that can occur in pets, especially cats. Urolithiasis, kidney failure, urinary tract infections are examples of disorders of the urinary tract which are often a problem in cats. This treatment aims to discuss diagnostic and treatment techniques in Persian cats with urinary tract disorders. A 3-year-old male Persian cat came to the Teaching Animal Hospital, Udayana University, because he had dysuria and had hematuria 3 months ago before being examined. Supporting examinations include a complete blood count, ultrasound examination, dipstick test and urine sedimentation examination. Blood tests showed that the cat had leukocytosis, ultrasonography showed hyperechoic crystalline particles of urine in the lumen of the urinary bladder, thickening of the muscularis part of the bladder wall and results of urine sedimentation showed crystals of magnesium ammonium phosphate (struvite) and calcium oxalate. The diagnosis is LUTD due to thickening of the muscularis wall of the VU and the presence of struvite and calcium oxalate crystals. with a faustal prognosis. The treatment given was insertion of a urinary catheter, administration of the antibiotic ciprofloxacin (PO) and dexamethasone (PO) anti-inflammatory drugs, as well as the herbal medicine Kejibeling® orally for 5 days. After a week of treatment, the cat can urinate smoothly. The diagnostic and therapeutic methods provided help treat cases of urinary tract disorders. Good condition monitoring and maintenance management are required during the maintenance period.

Effect of recirculation and hydraulic loading rate on ammonium and phosphate recovery from fertilizer industry wastewater

This study aimed to determine the optimum recirculation ratio and hydraulic loading rate for the recovery process of ammonium and phosphate, and study the formation, morphology, and structure of struvite crystals. This study provides a crystallization method to treat fertilizer wastewater using a continuous system and recirculation, including a fluidized bed reactor (FBR). Ammonium and phosphate were recovered from fertilizer industry wastewater using a continuous FBR under different recirculation ratios (3, 6, and 9) and loading rates (0.39 L/min, 0.59 L/min, and 0.79 L/min). MgCl2 was used as the precipitant with a 1.5:1 molarity ratio [Mg2+]:[PO43−]. The results showed that 55.71% phosphate and 49.69% ammonium could be recovered at recirculation ratio and hydraulic loading rate were 9 and 0.39 L/min, respectively. Scanning electron microscopy-energy diffraction X-ray analysis showed that the formed crystals comprised 80% struvite. Further, a high recirculation ratio and low loading rate resulted in higher ammonium and phosphate recovery efficiencies. These results indicated that a long detention time of treated wastewater can increase the nutrient recovery.

Efficient simultaneous phosphate and ammonia adsorption using magnesium-modified biochar beads and their recovery performance

Phosphate and ammonia as important sources of eutrophication in water bodies, their removal and recovery are crucial for environmental management. In this study, magnesium-modified biochar beads (Ca/MgBC) capable of adsorbing PO3–4 and NH+4 simultaneously were prepared, the size of the biochar materials was successfully enlarged to realize recycling. Ca/MgBC has excellent simultaneous adsorption properties, compared to single PO3–4 or NH+4 solution, the adsorption capacity of PO3–4 was increased almost twice and that of NH+4 was increased almost 1.5 times in simultaneous adsorption solution. The Qmax,PO3–4 was 253.95 mg/g and Qmax, NH+4 was 177.25 mg/g. Characterization results indicated that struvite crystallization was the main adsorption mechanism of PO3–4 and NH+4 in the simultaneous solution, which was also the reason for the promotion effect of simultaneous adsorption. Besides, ion exchange, surface precipitation and electrostatic attraction were also the other mechanisms for the adsorption. NP-loaded Ca/MgBC has a better slow-release potential of N and P under neutral condition. The adsorbed saturated Ca/MgBC still had good removal effects on seven common soil heavy metals (Cd, Hg, Cu, Pb, Cr, Zn and Ni). These results suggest that Ca/MgBC is a kind of promising adsorbent for phosphate and ammonia with safe, green, and sustainable properties, and offers the possibility of soil fertilization and remediation for carbon neutrality.

Feasibility of high-magnesium nickel slag-fly ash as precursor of magnesium phosphate cement and its hydration mechanism

The aim of this study was to investigate the process conditions, hydration reaction products and mechanism of high-magnesium nickel slag (HMNS)-fly ash (FA) as a precursor of magnesium phosphate cement (MPC). The relationships between properties, hydration products, hydration processes, and micromorphology were investigated by engineering properties, XRD, TG-DSC, FT-IR, Raman, and SEM/EDS. The results showed that the optimal process (HMNS/FA = 1.0/0, NH4H2PO4 dosing of 25 wt%, water-cement ratio of 0.26, the maintenance condition is air maintenance, and 200 mesh particle size of raw materials) prepared the cementitious material with 28 d compressive strength of 58.00 MPa and linear expansion rate of only 2.5 %. The hydration process was a multi-stage process, including the dissolution of NH4H2PO4 and pre-treated HMNS (WHMNS), the precipitation of intermediate hydration products and the formation of struvite, and the formation of gelling phases such as -Si-O-P-, -Al-O-P-, and -Si-O-Al-O-P-. Eventually, a high-strength gel-crystal phase structure consisting of gelling phases such as struvite wrapped around unreacted raw materials and struvite crystals was formed. FA was harmful for cementitious material, and impurities and high levels of Ca in FA reacted with phosphate to form hydration products with a loose porous structure (e.g., brushite). The optimal process sample complies with the 52.5R grade of ordinary Portland cement (GB175-2007); its embodied energy was reduced by more than 73.4 % compared to magnesium phosphate cement (MPC), and the corresponding CO2 emission was reduced by more than 74.2 %. Therefore, it has the potential to partially replace MPC from the environmental and feasibility point of view.

Recovering phosphorus and lithium separately from wastewater and brine using a novel coupled biofilm-precipitation system

Phosphorus (P) and lithium (Li) are scarce resources. To address the situation of resource scarcity, a novel coupled biofilm-precipitation system was proposed to recover P and Li separately from wastewater and brine. The results indicated the denitrifying polyphosphate accumulating organisms (DPAOs) suitable for this operating process promoted their denitrifying phosphorus removal (DPR) capabilities at the aerobic phase, increasing the total P content in the biofilm (TPbiofilm) to 60.7 ± 2.7 mg/g SS. Moreover, the DPAOs performed a metabolic shift from glycogen accumulation metabolism (GAM) to polyphosphate accumulation metabolism (PAM) when TPbiofilm increased, which caused more P being released by DPAOs, and the P concentration of the enriched stream to rise to 185.8 ± 3.4 mg/L. Furthermore, the quadratic regression model was suitable for the struvite crystallization (R2 = 0.87–0.88) in the P recovery stage, and the pure struvite was obtained with a P recovery efficiency was 96.3–97.2 %. The pure lithium carbonate crystals were created with a Li recovery efficiency was 93.3–97.2 % in the Li recovery stage. Additionally, the enriched P stream was applied to natural brine, and pure struvite and lithium carbonate crystals were produced with the P and Li recovery efficiency was 94.7 % and 93.5 %, respectively. In general, using enriched P stream as P source to separate magnesium from brine and thus recover Li was a feasible option. This study provided support for the recovery of P and Li.

Modulation of struvite composition in full-scale nutrient recovery system using source-separated urine.

Using urine collected from a public restroom at a highway rest stop in Northern California, a full-scale nutrient recovery system involving a two-part system consisting of urine distillation followed by the precipitation of struvite crystals was characterized. The study examined the effects of different operational parameters of the coupled ammonium distillation and struvite process (CADSP) on the composition of struvite crystals and the overall nutrient recovery rates. System inputs that were investigated included the feed:steam (F:S), alkalinity source, and urinary pH. Overall, the findings demonstrate that the composition of the struvite produced can be varied by adjusting the preceding distillation unit process. Low F:S distillation operations result in high ammonium distillation rates which coincided with increased formation of magnesium potassium phosphate (MPP) while higher F:S operations led to conditions favorable to magnesium ammonium phosphate (MAP) precipitation. Therefore, low energy distillation operations (high F:S) are more conducive to MAP formation and high phosphorus recovery rates while high energy operations (Iow F:S) are more conducive to MPP formation. Sodium-based alkalinity sources should also be avoided in instances of low ammonium concentrations in the struvite precipitation tank to minimize the co-precipitation of magnesium sodium phosphate (MSP) with MPP.

Modelling and experimentation of a continuous nutrient recovery reactor – an assessment of mixing on reactor operation

Phosphorus recovery from human waste will help assure global food security, reduce environmental impact, and ensure effective stewardship of this limited and valuable resource. This can be accomplished by the precipitation of struvite (MgNH4PO4·6H2O) in a two-zone reactor, continuously fed with nutrient-rich hydrolysed urine and a magnesium solution. The solid struvite crystals are periodically “harvested”, removing accumulated crystal mass – and therefore recovered nutrients – from the process, and the operating campaign can, in principle, be continuously operated in a batch-continuous operating mode. A previously developed process model is augmented, incorporating two well-mixed volumes (upper zone and lower zone) that are coupled by intermixing forward and back flows. The intermixing back flow is parametrised and, therefore, adjusted for analysis. Crystal linear growth rate is modelled by a simple power-law kinetic, driven by the nutrient solution's saturation index (SI) of struvite. The instantaneous mass transfer rate of struvite constituents from liquid to solid phase is predicted, using the total interfacial area of the crystal population exposed to the well-mixed solution. This model describes a 12-L, laboratory reactor operated in the hybrid batch-continuous mode, although larger reactors could easily be accommodated, subject to their mixing behaviours. Experiments were performed at a 10-hour hydraulic residence time (HRT), which, importantly, is based on the volume of the well-mixed lower zone, since this is the volume of liquid that actively interacts with the suspended struvite crystals. The Mg/P feed molar ratio was varied (0.34, 0.64 and 1.29) to assess Mg feed rate-limiting behaviour. The concentration profiles of elemental P and Mg agree with experimentation, while P and Mg composition in the solid and X-ray diffraction support the production of struvite.

Effect of struvite (Crystal Green) fertilization on soil element content determined by different methods under soybean cultivation

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.

Nitrogen and phosphorus recovery from sludge treatment by supercritical water gasification coupled with struvite crystallization

To recover nitrogen and phosphorus in the process water from the treatment of sewage sludge using supercritical water gasification (SCWG), struvite crystallization was coupled into the process. K2CO3 was added in SCWG to increase syngas production, and improve the migration of N and P into the aqueous phase, which was favorable for the subsequent struvite crystallization. The effect of MgCl2 and pH on the removal of N, P, and COD as well as the purity of struvite was studied during the struvite crystallization process. The results showed that the syngas yield significantly increased from 9.1 mol/kg to 14.2 mol/kg with K2CO3 addition. In the struvite crystallization process, pH had significant impact on the crystallization and the purity of struvite, while MgCl2 had only a slight effect. The highest N and P removal of 94.8 % and 99.5 % from the aqueous phase was achieved by struvite crystallization at pH 8. The obtained struvite had a high purity of 93.3 %, and the heavy metal content in struvite was lower than the value of standard, so that the obtained struvite sample can be used as fertilizer. This research could be a guideline to utilize the process water with high nutrients from sludge treatment.