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Microscope images of struvite crystal populations produced from water solutions containing 0.2 mass % of phosphate(V) ions, magnesium and ammonium ions in stoichiometric proportions and 0.03 mass % (a) and 0.06 mass % (b – d) of lactic acid. Correspond - ing parameter values of struvite continuous reaction crystallization process: a and b) pH 9, t 900 s, c) pH 10, t 900 s and d) pH 9, t 3600 s. Mean size of struvite product crystals L m : a) 50.3 m m, b) 42.5 m m, c) 32.1 m m and d) 80.0 m m. Magnification 1000 ́. Scanning electron microscope JEOL JSM 5800LV
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Introduction In the present day waste liquids containing phosphate(V) ions become inexpensive, widespread and relatively easily accessible secondary sources of phosphorus. These are particularly municipal, industrial and agricultural liquid wastes (e.g. liquid manure, ground leachates from fertilized and cultivated fields, etc.). Purification of su...
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... parameter values of struvite product crystal size distributions are presented in Table 1. From these data it results, that in presence of lactic acid in a process system under study the properly shaped struvite crystals of mean size L m from 28.6 to 80.0 m m were produced. Generally larger values of L m corresponded to lower values of lactic acid concentration in a feed solution. For example, at concentration 0.03 mass % of lactic acid in this solution, struvite crystals of mean size L m 50.3 m m were produced, while at 2–time higher initial concentration of this acid – 42.5 m m (assuming constant pH 9 and t 900 s). Lactic acid, however, did not favor homogeneity within the population of struvite product crystals. In most cases the CV coefficient value, quantitatively representing size homogeneity within the product particles, exceeded 90% (CV = 90÷107%). These are relatively high values, suggesting high inhomogeneity within struvite population (CV for the ideal theoretical MSMPR crystallizer is 50% [21]). Some exemplary microscope images of product crystal populations are presented in Figure 2. Mainly some individual, practically undamaged struvite crystals can be observed. Only in selected cases one can notice surface defects and destructed edges. Their agglomeration degree was also low. One can also conclude, that crystal attrition and breakage within mixed and circulated suspension was restrained. It may be supposed, that the process parameter values defining hydrodynamic conditions in the crystallizer construction used were selected properly, affecting thus the process course and its results advantageously. Presence of lactic acid resulted, that struvite product crystals were long and thin. In respect to their habit they significantly deviated from typical struvite crystals produced in comparable conditions from pure solutions of phosphates(V) [16], in the presence of inorganic impurities (selected metal ions) [6 ÷ 15], or from liquid wastes from the phosphorus mineral fertilizer industry [22, 23]. Based on planimetric measurements covering 50 randomly selected crystals from each product crystal population it was concluded, that their length L a to their width L b ratio was in average 10.7 and 11.1 in the presence of 0.03 and 0.06 mass % of lactic acid, appropriately (at pH 9 and t 900 s – Fig. 2a and b). At pH 8.5 ( t 900 s, [C 3 H 6 O 3 ] RM 0.06 mass %) struvite crystals were significantly better shaped and more proportional geometrically ( L / L ca. 5.1). On the other hand at higher pH 10 crystal lengths L a visibly decreased, whereas its width L b decreased only insignificantly, resulting that average L a / L b ratio was 6.8 ±0.2 (Fig. 2c). Elongation of mean residence time of crystal suspension in a crystallizer working volume, thus decrease of mean working supersaturation in struvite reaction crystallization environment resulted in significant increase in crystal size (Tab.1), which habit significantly altered, L a / L b : 11.1, 8.2 and 5.9 appropriately for t 900, 1800 and 3600 s at pH 9 in presence of 0.06 mass % of lactic acid (Fig. 2b and d). Struvite crystals became longer and wider, thus product quality increased clearly. From the solutions of phosphate(V) ions of their five–time higher initial concentration (1.0 mass %), in presence of 0.03 ÷ 0.06 mass % of lactic acid, the struvite crystals of similar size proportions L / L were produced [24]. From Table 1 it also results that increase in crystallizer environ ment’s pH did not favor production of uniform struvite crystals of relatively large sizes. Increase in pH from 8.5 to 10 caused decrease of mean crystal size L m from 52.8 to 28.6 m m (by ca. 46%) and from 51.7 to 32.1 m m (by ca. 38%) for t 900 s in the presence of 0.03 and 0.06 mass % of lactic acid, respectively. Similarly, CV coefficient value increased from 86.4 up to 107% and from 79.2 to 93.5%. Crystal line products corresponding to pH 10 characterized, compared to solid products manufactured at pH 8.5 ÷ 9, not only smaller particle sizes, but also higher size dispersion. With the pH parameter increase the struvite solubility decreases (its minimal value corresponds to pH 10.3 [25] or 10.7 [26]), thus its precipitation potential increases [2, 3]. Also induction time, indispensable for initiation of nucleation process, shortens [27]. In result of these phenomena action nuclei population density n 0 increases (Tab. 2), producing shift of mean or median crystal size towards smaller values (Tab. 1). Elongation of mean residence time of suspension in a crystallizer resulted in significant increase in product crystal size, even by 90%. Struvite crystals reached mean size L m 80.0 m m at mean residence time of suspension in a crystallizer t 3600 s, pH 9 and in presence of 0.06 mass % of lactic acid. With the elongation of mean residence time average super saturation in solution decreased, producing in effect gradual decrease of both kinetic process parameter values: nucleation rate of solid phase and its linear growth rate (Tab. 2). However, prolonged contact time of crystal suspension with supersaturated solution caused, that product crystal size increased significantly. In solution of lower mean working supersaturation crystals grew slower, however in more stable process conditions. Longer contact time of crystalline phase with supersaturated mother solution influenced other product parameter advantageously, as well. Homogeneity within crystal population in respect to its linear size increased significantly. CV coefficient decreased from 95.1 to 65.9%, thus approached the value theoretically predicted as a standard for ideal MSMPR crystallizer products. It should be noticed, that this value was reached in spite of simultaneously prolonged exposition of crystal phase to the action of co–occurring processes of attrition and agglomeration in intensively mixed and circulated suspension. From more concentrated water solutions of phosphate(V), magnesium and ammonium ions containing 0.03 - 0.06 mass % of lactic acid, in comparable process conditions, struvite ...
Citations
... During the experiments we compared two molar ratios of PO 4 3-:Mg 2+ as the ratios represent an important part of phosphorus precipitation into the form of struvite [31]. In comparison with Sýkorová et al. in [19] when at best, they obtained a precipitate in the amount of 0.54 g/L of "raw" dewatering liquor (without concentration), of which 40% were struvite crystals. ...
Wastewater contains resources, which can be recovered for secondary use if treated properly. Besides research in zero liquid discharge solutions, the aim of the study was a simultaneous recovery of products from a wastewater treatment plant’s dewatering liquor. To be specific, we investigated a simultaneous recovery of struvite and irrigation water using electrodialysis (ED) in laboratory experiments. Two products were obtained from ED—concentrate and diluate. The concentrate was precipitated to obtain struvite. On average, 11 g of wet precipitate (including 17.58% of dry solids) were obtained from 1 L of concentrate. Crystal phases were confirmed by powder X-ray diffraction (XRD), with showing 94–97% recovery of struvite, while the remaining 3–6% were identified as hazenite. The average yield of crystal struvite was 1.76 g. Both struvite and hazenite may further be used as a fertilizer. Next, we suggest using the second ED product, the diluate, as irrigation water if it meets the irrigation water requirements. Attention was paid to the concentrations of dissolved solids (DS) in diluate, which decreased by an average of 93% compared to the input values in the dewatering liquor. In line with the observed Czech or EU standards indicators, we can say that the diluate can be used in agriculture, namely as irrigation water (Category I—water suitable for irrigation).
... Ca 2+ , Na + , SO4 2-). They significantly affect the homogeneity and structure of the obtained crystals [4,11]. The pH range from 7.5 to 9.5 is recommended for struvite precipitation [12]. ...
Removal of nutrients from wastewater with simultaneous recovery of phosphorus (P) and nitrogen (N) in the form assimilable by plants is possible by the precipitation of ammonium magnesium phosphate (struvite). This method benefits environmental protection but has not been widely implemented in Wastewater Treatment Plants (WWTPs). One of the reasons is the high costs of available technologies. The aim of the work is to investigate the low-cost methods of reduction and recovery of nutrients from wastewater. It involves the precipitation of struvite from phosphate-rich leachate from WWTP fermentation chambers. The reaction was carried out in the prototype of a simple horizontal reactor, ensuring the possibility of collecting sediment in the funnel. A cheap waste magnesium salt was used to precipitate the struvite, which significantly reduced the costs of its acquisition. The reduction of P exceeded 80% in most of performed tests in leachate waters. The precipitant removed from the reactor has the character of sludge with a significant degree of hydration (85%). After drying, it is a dusty powder with an average P content of 40% and a total N content of 8% and a trace of heavy metals. It was proposed to mix the obtained aqueous form of struvite sediments with compost produced from excessive sludge, without drying it. Studies have shown that one percent of struvite admixture in compost results in an increase of P and N content by 13% and 2.7%, respectively.
... As a result, a source of magnesium must be added to the wastewater before struvite precipitation can occur, and studies have found magnesium chloride (MgCl) to be the best source of magnesium as it assists with ammonium nitrogen (NH 4 -N) removal . It has been shown that increasing the molar ratio to 1.2:1:1 for Mg 2+ , NH 4 + , and PO 4 3ions respectively yields the maximum amount of struvite precipitation (Kozik et al., 2011). ...
This chapter reviews the alternative approaches for removing and recovering nitrogen (N) and phosphorus (P) from animal manure using both on‐farm and off‐farm management. It first provides a flow diagram on alternative approaches to traditional land application of manures, and shows desirable characteristics of the recovered products. The chapter then presents solids separation and dewatering methods to concentrate nutrients, and reviews technologies for separation of phosphate concentrates. It also shows technologies for recovery of the nitrogen, and describes biological N and P removal processes. Aside from the technologies necessary for isolation, extraction, and recovery of manure nutrients, the agronomic efficacy of recovered nutrient materials for use as plant fertilizers is an important consideration in the selection of the best approach for N and P removal and recovery from manure. Recovery of P in the form of salts or phosphate crystals has been a major area of focus for recovery of manure nutrients.
... It was found that the Mg 2+ :NH 4 + :PO 4 3− P molar ratio of 1:1:1 is enough for struvite precipitation. Generally, the average crystal size is 42 μm at pH 9 and a PO 4 :Mg 2+ molar ratio of 1:1, but it was observed that the crystal size increases with a molar ratio of 1:1.2 within 30 min (Kozik et al. 2011). Moreover, larger crystals were found at higher molar ratio of Mg 2+ to PO 4 3of 1.2:1 of the waste effluent (Koralewska et al. 2009;Matynia et al. 2013). ...
Phosphorus, 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, effect, 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. However, this can be an inexpensive way to remove excess P from polluted environments. Although P minerals (e.g. struvite and vivianite) are problems when left uncontrolled and unmonitored, their recovery is beneficial (e.g., slow release fertilizers, sustainable P sources, soil enhancers). Sources like wastewater, human waste, waste nutrient 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 discussed.
... Liu et al. 16 reported that K + and Ca 2+ in the swine wastewater can influence the formation of struvite crystals. Through experimental study, Anna KOZIK et al. 17 pointed out that the presence of organic impurities may affect the final size and shape of struvite crystals. Hao et al. 18 indicated that when the pH range was 7.5-9.5, the yield of precipitated products was the largest. ...
Struvite precipitation electrolyzers are interesting environmental electrochemical reactors with potential applications for efficient phosphate recovery from wastewater, such as swine wastewater. In this paper, effects of phosphate concentration and pH on the struvite precipitation reaction rate were investigated. When phosphate concentration decreased from 100 to 20 mg/L, the precipitation reaction rate decreased from 396.65 mg/L·h to 70.46 mg/L·h, indicating that the reaction rate of struvite crystallization can be controlled by adjusting pH according to the change of phosphate concentration. Numerical simulation of different currents and flow rates on pH in the electrolyzer was developed and validated, and pH in the electrolyzer was dynamically measured along the distribution point of the flow field. We aimed to test the treatment effect of the electrolyzer on actual swine wastewater. When the flow rate was 20 L/h and constant voltage was 4 V, the electrolyzer was run continuously for 5 hours with the volume of 50 L. The phosphate recovery efficiency reached 99.51%, and the time-space yield of the struvite precipitation electrolyzer was 0.0219 kg/m2·h. The harvested struvite particles were identified by XRD and SEM-EDS, which presented orthorhombic structure and high purity. Economic analysis demonstrated that the proposed electrolyzer was cost-effective and technologically convenient.
... Struvite might be described as a soft mineral due to its low specific gravity (1.7 g cm⁻³) and orthorhombic structure (Lee et al., 2009). It can occur as an elongated structure, a tight aggregate of fine crystals, star-like particles, or coarse crystals in white, yellowish or brownishwhite colors (Rahman et al., 2011;Kozik et al., 2011;Hutnik et al., 2013;Matynia et al., 2013). The size of struvite crystals can vary from 15 μm to 3.5 mm in length depending upon the production conditions (Adnan et al., 2003;Zhang et al., 2009). ...
To meet the needs of a fast growing global population, agriculture and livestock production have been intensified, resulting in environmental pollution, climate change, and soil health declining. Closing the nutrient circular loop is one of the most important sustainability factors that affect these issues. Apart from being a serious environmental issue, the discharge of N and P via agricultural wastewater is also a major factor that disturbs nutrient cycling in agriculture. In this study, the performance, in terms of recovery, of N and P (individually, as well as simultaneously) from agricultural wastewaters via struvite has been comparatively summarized. Details on the hindrances to nutrient recovery through struvite formation from agricultural effluents, along with strategies to overcome these hindrances, are provided. In addition, various strategies for recovery performance intensification and operational cost reduction are comprehensively discussed. This work will provide scientists and engineers with a better idea on how to solve the bottlenecks of this technique and integrate it successfully into their treatment systems, which will ultimately help close the nutrient loop in agriculture.
... Struvite might be described as a soft mineral due to its low specific gravity (1.7 g cm⁻³) and orthorhombic structure (Lee et al., 2009). It can occur as an elongated structure, a tight aggregate of fine crystals, star-like particles, or coarse crystals in white, yellowish or brownishwhite colors (Rahman et al., 2011;Kozik et al., 2011;Hutnik et al., 2013;Matynia et al., 2013). The size of struvite crystals can vary from 15 μm to 3.5 mm in length depending upon the production conditions (Adnan et al., 2003;Zhang et al., 2009). ...
To meet the needs of a fast growing global population, agriculture and livestock production have been intensified, resulting in environmental pollution, climate change, and soil health declining. Closing the nutrient circular loop is one of the most important sustainability factors that affect these issues. Apart from being a serious environmental issue, the discharge of N and P via agricultural wastewater is also a major factor that disturbs nutrient cycling in agriculture. In this study, the performance, in terms of recovery, of N and P (individually, as well as simultaneously) from agricultural wastewaters via struvite has been comparatively summarized. Details on the hindrances to nutrient recovery through struvite formation from agricultural effluents, along with strategies to overcome these hindrances, are provided. In addition, various strategies for recovery performance intensification and operational cost reduction are comprehensively discussed. This work will provide scientists and engineers with a better idea on how to solve the bottlenecks of this technique and integrate it successfully into their treatment systems, which will ultimately help close the nutrient loop in agriculture.
... Meanwhile, Mg dosage posed a less effect on crystal size compared with solution pH. Kozik et al. (2011) observed an increased crystal size from 67 to 80 mm at an increase of Mg/P ratio from 1.0 to 1.2, but in our study, the increase in Mg/P ratio did not result in an obvious variation of particle size. The difference might be correlated with the continuous reaction crystallization adopted in their study. ...
... Precipitation of struvite needs the presence of three ionic species, magnesium (Mg 2+ ), ammonium (NH 4 + ), and orthophosphate (PO 4 3À ) in an alkaline solution in equimolar (1:1:1) concentrations ( Rahaman et al. 2008). pH, ionic strength of participating molecules, the presence of impurities or nonparticipating ions, mixing energy, residence time for crystallization, and the type of crystallization reactor are the factors that govern the precipitation of struvite in P-rich sources (Doyle and Parson 2002;Nelson et al. 2003;Le Corre et al. 2007;Koralewska et al. 2009;Hutnik et al. 2011) (Fig. 3). The basic chemical reaction to form struvite can be expressed using Eq. 1. ...
... Crystal size can be decreased by up to 46% in the presence of impurities like calcium, iron, and nitrates ( Hutnik et al. 2011). The ions can affect negatively the growth rate and can lengthen the induction time preceding the first occurrence of crystals ( Koutsoukos et al. 2003;Kabdasli et al. 2006). ...
Finite resources of non-substitutable plant nutrient like phosphorus (P) make recovery of it an attractive option of renewed interest from alternative waste sources. In this context, feasibility of struvite recovery (MgNH4PO4. 6H2O), an alternative P fertilizer, is already established from different waste streams with reasonably high ortho-P recovery efficiency (~90%). Feasibility of struvite recovery has been established at laboratory scale for a range of sources of farm, municipal, and industrial origin. Municipal wastewater is the most common struvite recovery source, whereas farm wastes represent easily accessible stock with reliable availability. Depending on the source characteristics, the recovery of struvite may require some process modifications such as addition of P and NH4 + salt and incorporation of pretreatments. However, except for municipal sludge and urine, development of cost-effective, targeted, and environmentally friendly full-scale recovery of struvite is limited due to inherently heterogeneous nature of the sources and unfavorable economics. In recent years, an increasing research concern can be seen toward the techno-economical aspects of the process for development of competent and energy-efficient process from alternative potential struvite sources with incorporation of more efficient method, Mg source, and seed material. Studies on struvite’s application aspect identify its favorable impact on crop though with variation attributed to soil type, plant type, and climate; however, its field-scale long-term impact, its applicability within regulatory limits of fertilizer, and users’ perception remain other concerns. Nevertheless, considering the related benefits of recovery process, struvite recovery appears to be an attractive and feasible pathway provided uncertain aspects are addressed through appropriate research and development.
... The input Fe redox states, e.g., Fe(þIII)Cl 3 and Fe(þII)SO 4 , can optionally be specified, if such data are available. As it is well-known that the presence of organic compounds may influence the purity of recovered products (Kozic et al., 2011), relevant interactions between inorganic and organic components were also accounted for. Among the organic biological components considered (see Section 2.2.3), volatile fatty acids (VFAs) up to valerate were included as individual components in the physicochemical models. ...
The reported research developed a generic nutrient recovery model (NRM) library based on detailed chemical solution speciation and reaction kinetics, with focus on fertilizer quality and quantity as model outputs. Dynamic physicochemical three-phase process models for precipitation/crystallization, stripping and acidic air scrubbing as key unit processes were developed. In addition, a compatible biological-physicochemical anaerobic digester model was built. The latter includes sulfurgenesis, biological N/P/K/S release/uptake, interactions with organics, among other relevant processes, such as precipitation, ion pairing and liquid-gas transfer. Using a systematic database reduction procedure, a 3-to 5-fold improvement of model simulation speeds was obtained as compared to using full standard thermody-namic databases. Missing components and reactions in existing standard databases were discovered. Hence, a generic nutrient recovery database was created for future applications. The models were verified and validated against a range of experimental results. Their functionality in terms of increased process understanding and optimization was demonstrated.
