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Phosphorus recovery from wastewater using light calcined magnesite, effects of alkalinity and organic acids
Journal of Environmental Chemical Engineering 7 (2019) 103334
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Phosphorus recovery from wastewater using light calcined magnesite, effects of alkalinity and organic acids ⁎
Jinshan Weia,b,d, Jie Geb, Ashaki A. Rouffc, Xianghua Wend, Xiaoguang Mengb, , Yonghui Songa,
T ⁎
a
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China Center for Environmental Engineering, Stevens Institute of Technology, Hoboken, NJ, 07030, USA c Department of Earth and Environmental Sciences, Rutgers University, Newark, NJ, 07102, USA d School of Environment, Tsinghua University, Beijing, 100084, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Wastewater treatment Phosphorus recovery Alkalinity Organic acids Light calcined magnesite Struvite
To solve the problem of phosphorus pollution and resource crisis, phosphorus recovery by struvite crystallization has become a focus of research in recent years. In municipal wastewater, insufficient magnesium content and relatively low pH can be a limitation for struvite formation. A commercial magnesium source, light calcined magnesite (LCM), was used in this study for phosphorus recovery from wastewater without an adjustment of pH. Bench-scale jar test experiments were conducted to study the kinetics of phosphate removal by LCM. The effects of LCM dosage, initial phosphate concentration, carbonate alkalinity and organic acid content on the removal of phosphate was evaluated. Hydrolyzation of LCM released hydroxyl ions (OH−) during the reaction, increasing the solution pH from 7.63 to 8.62. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the composition and morphology of formed precipitates. At an LCM dosage of 200 mg/L, 84.5% of phosphate was removed mainly through the formation of struvite. Increased alkalinity and organic acid concentration in the solution inhibited struvite formation, and higher alkalinity promoted the formation of coarse crystal surfaces. Abundant global reserves of the magnesite ore resource reveal LCM may be a viable and costeffective source of magnesium and hydroxyl reagent for phosphorus recovery from wastewater.
1. Introduction Discharge of excess nutrient elements like phosphorus and nitrogen cause serious environmental problems, such as eutrophication in lakes, reservoirs, estuaries, and oceans, which may deteriorate the ecosystem and the economy associated with tourism [1–3]. The United States Environmental Protection Agency (USEPA) reported that “sewer and septic systems that are responsible for treating large number of waste did not always operate properly or remove enough nitrogen and phosphorus before discharging treated waste to waterways” [4]. Phosphorus mainly exists in the form of inorganic phosphate in wastewater from municipal wastewater treatment plants (WWTPs). Conventional phosphate removal methods, such as enhanced biological phosphorus removal (EBPR) and chemical phosphorous removal, consume a large amount of coagulants and deposit phosphate in the sludge which is a waste of resources. Meanwhile, phosphorus is an essential nutrient for all living organisms and is important for global food production, being a component of nucleic acids, phospholipids, and ATP/ ADP [5,6]. Most of the phosphorus fertilizer applied to agricultural land
⁎
comes from phosphate rock (PR), which is considered to be a non-renewable resource [7]. According to the optimistic estimate, the amount of PR depletion is around 20–35%. In the worst case, about 40–60% of the current reserves will be extracted by 2100 [8]. The distribution of PR reserves and the share of current production are both concentrated in a few countries, notably Morocco, China, and the US [9]. The use of phosphorus on the earth presents a linear law, apart from phosphorus that can be partially recycled by applying manure to agricultural land, with very few recycling routes and inefficiency in its production and use [10]. In addition, various options for recycling waste flows also exist. Increasing the efficiency of phosphorus recovery seems to be worthwhile, even if depletion is not imminent [11]. This situation requires an urgent adoption of a sustainable process to improve nutrient management practices and identify alternative phosphorus sources. Therefore, wastewater “mining” can supplement artificial demand, while reducing dependence on natural and geological reserves. Extensive research has been conducted to find viable materials for the removal of anions, like phosphate, arsenic, selenium, and nitrate.
Corresponding authors. E-mail addresses: [email protected] (J. Wei), [email protected] (X. Meng), [email protected] (Y. Song).
https://doi.org/10.1016/j.jece.2019.103334 Received 15 May 2019; Received in revised form 25 July 2019; Accepted 28 July 2019 Available online 29 July 2019 2213-3437/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Environmental Chemical Engineering 7 (2019) 103334
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[12–29]. Various adsorbents such as zeolite [30], fiber adsorbent [31–33], biochar [34,35], ferrihydrite [36], and clays [37,38], have been investigated for phosphate removal. Among them, metal oxides generally exhibit better performance in phosphate removal than other adsorbents [39]. Pretreated magnesite obtained from different calcination temperature was reported for phosphorus removal in China and Nepal [40,41]. However, many factors (i.e. initial phosphorus concentration, co-existing ions competition) that affect the phosphorus recovery should also need pay attention to. Magnesium oxides, like synthesized nanoscale MgO with high ionicity, simple stoichiometry, and crystal structure have emerged due to versatility in applications, such as adsorption, catalysis, and refraction [42]. In recent years, struvite (Mg(NH4)PO4·6H2O) crystallization and hydroxyapatite (Ca5(PO4)3(OH)) precipitation were recognized as the main techniques for phosphorus recovery [43–46], with several pilot demonstration studies reported in the literature [47]. The chemical formula of struvite contains both nitrogen and phosphorus elements, which can be recovered and reused [48]. It has been concluded that the precipitation of hydroxyapatite occurs at pH values above 9.5, whereas the optimal pH value for struvite precipitation should be at 8.0 and above [49]. Researchers have also conducted a multitude of phosphorus recovery tests involving the addition of chemical reagents, and consumption of large amounts of alkali, therefore increasing the economic cost of the technology [50]. Thus, capital cost is a key limiting factor in the practical application of phosphorus recovery technology. Discovering a cost-efficient phosphorus recovery additive reagent is an urgent issue. Magnesium salts (such as magnesium chloride) are widely used for the production of struvite [51,52], with the advantage of a fast reaction rate and immediate crystallization and precipitation. Seawater can also be used as a source of magnesium, with the drawback of limited access of this source to inland cities [53,54]. Meanwhile, the alkali reagents for pH adjustment are also required in the phosphorus removal process using magnesium chloride and seawater, which drastically escalates the economic cost. To reduce costs associated with the addition of Mg and alkali reagents separately, a single reagent that serves this dual purpose is needed. Light Calcined Magnesite (LCM) obtained from pretreatment of magnesite ore, also known as magnesia powder or magnesia, is commonly used as a fireproof material in the construction industry. The LCM is readily soluble in water, releasing Mg ions while simultaneously increasing pH. In a wastewater application, any undissolved LCM can subsequently act as seed material to accelerate the phosphate crystallization reaction. However, limited studies have been conducted on the use of naturally obtained minerals or LCM materials as a magnesium source for the treatment of phosphate [55]. In this study, LCM was used for phosphorus removal from municipal wastewater. The new reagent light calcined magnesite was closed in the previous applied patent “Method and reagent for treatment of nitrogen and phosphorus in wastewater and resource recovery” in September 2015, with open number CN106554060A [56]. The mineralogy of the ores is dominated by magnesite (> 94%, with variable grain size and crystalloblastic texture) with only small amounts of quartz, dolomite, clinochlore, and talc. The LCM acted as both a magnesium source and a pH adjustment reagent. Factors, potentially affecting the phosphorus removal process, such as alkalinity and dissolved organic content, were investigated. Solids recovered from the treatment process were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM).
Fig. 1. XRD pattern of LCM and the standard synthetic MgO. (PDF#78-0430).
from 40.80% to 47.50% (mass percent, mean = 46.31 ± 3.08%, 2SD, n = 24) and 47.82% to 52.08% (mean = 51.22 ± 2.20%, 2SD, n = 24), respectively. The CaO content ranged from 0.21% to 2.50% (mean = 0.59 ± 0.92%, 2SD, n = 23). The percentage of SiO2, Al2O3, Fe2O3, and MnO2 was relatively low. LCM was obtained through calcination of magnesite ores at 650˜800 ℃ for 2 h. The particle size of the LCM used in the experiment was around 150 μm. XRD pattern of the LCM is shown in Fig. 1, and the main components are listed in Table 1.
2.2. Wastewater solutions The supernatant of anaerobically digested sludge was collected from the sludge digestion reactor in a WWTP in Beijing, China. Synthetic wastewater was prepared by adding potassium phosphate (KH2PO4), ammonium chloride (NH4Cl), sodium bicarbonate (NaHCO3) and sodium acetic (CH3COONa) into tap water, to simulate the composition of the sludge supernatant. All the reagents were analytical purity and purchased from Sigma-Aldrich. The characteristics of real and simulated wastewater are shown in Table 2.
2.3. Batch experiments The batch experiments were carried out at room temperature of 20 ℃, with 1000 mL simulated wastewater. The stirring speed was controlled at 100 r/min using a ZR4-6 Jar Tester. The effect of LCM dosage on phosphate removal was evaluated at concentrations of 50, 100, 200, 300, 400, 500 and 600 mg/L LCM, respectively, at an initial phosphate concentration of 30 mg-P/L. The effect of initial phosphate was determined for concentrations of 28 (real wastewater), 30, 60, 100, 150, and 200 mg-P/L, at an LCM dosage of 200 mg/L. Initial alkalinity (i.e. 10, 15, 20, 25 and 35 mmol-CO32−/L) was adjusted to evaluate the effect of alkalinity on phosphate removal and recovered products. The alkalinity in the solution was simulated using NaHCO3. Three kinds of organic acids, such as formic acid (H2CO2), oxalic acid (H2C2O4), and citric acid (C6H8O7), were used to study the effect of dissolved organic matter. Alkalinity and organic acid experiments were conducted at t a 200 mg/L LCM dosage and 30 mg-P/L phosphate concentration. For all experiments, removal of phosphate and ammonium, as well as pH, were monitored at the reaction times of 0.5, 1, 2, 3, 4, and 6 h. At the predetermined sampling time, 5 mL of sample was collected, and filtered using a 0.45 μm membrane, and then acidified using HNO3.
2. Materials and methods
Table 1 Main composition of LCM. (mass percent, %).
2.1. Light calcined magnesite Raw material of LCM, magnesite ore, was obtained from a mining company in Liaoning Province, China. Magnesium oxide and carbon dioxide were the dominant components of raw magnesite ores, ranging 2
Magnesite ignition loss (CO2)
MgO
CaO
SiO2
Fe2O3
Al2O3
others
49.82
46.21
0.72
2.3
0.23
0.22
0.50
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Table 2 Parameters of real wastewater and simulated wastewater. Real wastewater Constituent 3−
PO4 NH4+ Mg2+ COD Alkalinity pH
Simulated wastewater Unit (mg-P /L) (mg-N/L) (mg-Mg/L) (mg/L) (mmol-CO32−/L)
Concentration
Constituent 3−
25.19-32.10 595.24-751.91 12.31-18.63 495.00-582.03 19.10-20.27 7.63
PO4 NH4+ Mg2+ COD Alkalinity pH
Unit
Concentration
(mg-P /L) (mg-N/L) (mg-Mg/L) (mg/L) (mmol-CO32−/L)
30.0/spiked 730 15.0 500 20/spiked 7.63
presented in Fig. 2(b), The results show that the pH of the solution increased rapidly from 7.63 to 8.51, in the first 2 h, followed by a slow increase to 8.62 in the next 4 h. Hydrolysis of MgO as shown in Eq. 1 can produce hydroxyl ions (OH−) to increase the solution pH. Studies have indicated that pH is one of the most important factors affecting the struvite crystallization reaction (Eq. 2), and the optimal solution should be above 8.0 for struvite formation [49]. Eq. (3) obtained from the combination of Eq. (1) and Eq. (2) can be used to trace the overall process of phosphate recovery using LCM.
2.4. Sample analysis The phosphate concentration of the samples was measured by the molybdenum-antimony anti-spectrophotometric method (UV/VIS 4802, Unico, Shanghai), and the ammonium concentration was measured by Nessler reagent spectrophotometry. The solids were collected after 6 h reaction, filtered with 0.45 μm membrane, and air-dried at room temperature for XRD (Bruker, D8 Advanced MAX2RB, Germany) and SEM (Zeiss, EVO18, Germany) analysis.
MgO + H2O → Mg2+ + 2OH− 3. Results and discussion
NH4+
3.1. Effect of LCM dosage and kinetics on phosphate removal
+ Mg
2+
+
HPO42−
(1)
+ OH- + 5H2O ⇔ Mg(NH4)PO4·6H2O (s) (2)
NH4+ + MgO + HPO42− + 6H2O → Mg(NH4)PO4·6H2O (s) + OH(3)
Effects of LCM dosages on phosphate removal were studied, and the results are shown in Fig. 2(a). The residual phosphate concentration decreased with increasing LCM dosage. The phosphate removal efficiency was 24.3% at the dosage of 50 mg/L, and increased to 94.6% at a dosage of 600 mg/L. From the perspective of phosphate removal efficiency and utilization of resources, the optimal dosage is up to 200 mg/ L with a phosphate removal efficiency of 84.5%. At the same time, the amount of Mg2+ released from LCM was enough for the struvite crystallization reaction. The kinetics of phosphate and ammonium removal using LCM are shown in Fig. 2(b). Phosphate removal efficiency increased rapidly to 63.2% after reacting with 200 mg/L of LCM in 1 h and then increased to 83.5% after 2 h. Thereafter, phosphate removal slowly reached equilibrium until 6 h. The phosphate removal can be modeled using the pseudo-second-order model and R2 of the model fitting is 0.989. Kinetics of ammonium removal showed a similar trend as phosphate within 2 h of reaction, after which ammonium removal remained stable and reached an equilibrium. The kinetics results in Fig. 2(b) demonstrate the ability of LCM to remove phosphate. Due to the simultaneous removal of ammonium, the crystallizing phase is likely struvite. Any undissolved LCM, as well as impurities and micro-particles, may act as nucleating material to accelerate the crystallization reaction. Solution pH was also measured throughout the reaction and is
3.2. LCM as a pH adjuster and struvite formation model The effect of LCM on solution pH was further measured by the pH changes of deionized (DI) water after adding different dosages of LCM, and the results are shown in Fig. 3(a). The initial pH of the DI water was around 7.00 and it increased to 10.34 and 10.55 at the LCM dosage of 100 and 200 mg/L, respectively. The dramatic increase in solution pH after adding LCM illustrates the good ability of LCM to release OH−, accompanied by the release of Mg2+, as shown in Eq. (1). The soluble Mg2+ would be further precipitated in the form of Mg(OH)2 at a higher solution pH, which can be modeled by Visual Minteq. Fig. 3(b) shows the percentage of Mg species as a function of solution pH. The free Mg2+ in water could transform to Mg(OH)2 precipitate at pH 10.1, and 99% of Mg precipitated at pH greater than 11.2. A pC{log(total Mg)}-pH diagram of Mg precipitation in the absence of co-existing ions(i.e. PO43−, NH4+) was calculated and showed in Fig. 3(c). The Ksp of Mg(OH)2 was calculated at 5.6 × 10-12 [57]. The simulation yielded a sharp decreasing trend of Mg(OH)2 in the pH range of 9–14, which translated to a lower Mg solubility. The 99% precipitation curve means that most of the total Mg precipitated in the
Fig. 2. (a) Effect of LCM dosage on phosphate removal; (Initial phosphate concentration 30 mg-P/L, 6 h) and (b) kinetics of phosphate and ammonium removal, and the changes of pH. (Initial Phosphate concentration 30 mg-P/L, LCM dosage 200 mg/L). 3
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Fig. 3. (a) Changes of solution pH by functional of solubility time of LCM in DI water; (b) percentage of Mg species as a function of solution pH modeled by Visual Minteq; (c) pC-pH diagram of Mg; (total Mg concentration 1 mM, 25 ℃) (d) modeling struvite formation in PO43−-NH4+-Mg2+ system. (PO43−, Mg2+ and NH4+ concentration 1 mM, ionic strength 0.01 M, 25 ℃).
system. At pH 9 and 10, precipitation occurs at Mg2+ concentrations higher than 7000 and 40.1 mg/L, respectively. As shown in Fig. 2(b), the equilibrium solution pH was around 8.6 in the phosphate removal test using 200 mg/L LCM. The ion product of struvite is 2.51 × 10−13 at room temperature, and the mineral is precipitated at saturated conditions [58]. The formation of struvite consumes free Mg2+ in the water, thus promoting a forward movement of the equilibrium in Eq. (1). The formation of struvite was modeled at the experimental conditions, and the results are shown in Fig. 3(d). The model results illustrate that PO43-, Mg2+, and NH4+ precipitated as struvite as the pH increased from 8.5 to 9.5. Figure S1 showed the changes of point of struvite formation as a function of NH4+ and Mg2+ concentration in the solution. It is validated that under conditions of excessive Mg2+ and NH4+, phosphate can be precipitated through the formation of struvite at the pH of 8.0˜8.5. To some extent, the optimum pH for struvite crystallization varies when treating different types of wastewater. Studies have shown that the optimum pH is in the range of 9.0–10.5 [59]. In this experiment, phosphorus could be immobilized in struvite in great quantities in the viable pH range of 8.0–8.5 and good efficiency of the phosphate removal was achieved.
Fig. 4. Removal of phosphate at different initial phosphate concentrations. (real wastewater 28 mg-P/L, simulated wastewater 30, 60, 100, 150 and 200 mg-P/L, LCM dosage 200 mg/L, 6 h).
to 200 mg-P/L, the phosphate removal efficiency dropped to 69.6%, which can be interpreted by the insufficient LCM dose applied. As a result, different LCM dosages can be considered based on the initial phosphate concentration in the raw wastewater, as well as the removal efficiency. Characterization of the recovered products at different initial phosphorus concentrations was performed by analysis of the XRD patterns (Fig. 5a). The XRD patterns of recovered solids were analyzed through the PDF diffraction database CARD (PDF#77-2303). The main component was assigned as struvite, mixed with the unreacted magnesium oxide. With the increase of initial phosphorus concentration
3.3. Effect of initial P concentration Phosphorus removal at various initial phosphate concentrations was investigated at the LCM dosage of 200 mg/L and the results are summarized in Fig. 4. The real wastewater and simulated wastewater at 5 different concentrations were used in the experiment. The phosphate removal of 86.6% was obtained for the real wastewater system. In the simulated wastewater treatment, the phosphate removal efficiency was 84.5% at the initial phosphate concentration of 30 mg-P/L while it rose to 91.3% at 60 mg-P/L. As the initial phosphate concentration increased 4
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the increase of alkalinity in the wastewater. At the alkalinity of 20 mmol/L, which was the alkalinity content in real wastewater, the phosphate removal efficiency reached 84.5%. However, only 60.9% of phosphate was removed at the alkalinity content of 35 mmol/L, indicating a competitive effect of the carbonate with phosphate during the precipitation reaction. The co-existing carbonate can react with the Mg2+ and form magnesite. (Eq. 4) Mg2+ + CO32− → MgCO3 (s)
Dissolved organic material especially organic acids may have great effects on the phosphate removal during struvite crystallization [61]. The effects of three organic acids (citric acid, oxalic acid, and formic acid) on P removals efficiency were investigated, and the results are shown in Fig. 6(b). P removal can be affected by the co-existed organic acid, due to the complexation between organic acid and Mg2+/NH4+, i.e. the binding constant for Mg2+ with citric acid is 13.5 × 103 [62]. The presence of all three organic acids inhibited the P removal at the outset of the reaction, and a positive correlation between inhibition and organic acid concentration was observed. Meanwhile, when the three organic acids were present at the same concentration, the inhibition effects followed the order: citric acid > oxalic acid > formic acid, which can be related to the number of carboxyl groups carried by these three organic acids. The number of carboxyl groups on citric acid, oxalic acid, and formic acid can be calculated as 3:2:1 at the same mole of the organic acid. The high concentration of citric acid significantly interrupted the struvite crystallization reaction, and phosphate removal was reduced from 84.5% to 47.8% in the presence of 4 mM citric acid. Overall, the experimental results demonstrate that phosphate can be removed by LCM in the presence of different kinds and concentrations of organic acids. The SEM images of recovered products under different alkalinity conditions are shown in Fig. 7. The morphology of the precipitates was irregular short rods, lump crystals, including crystals with smooth polygon surfaces, and was different from the familiar needle-like morphology. In general, the shape of crystals in Fig. 7(a) and (b) is typical of struvite crystals, corresponding with our previous study [63]. Specifically, the crystal shape in Fig. 7(a) was most similar to the standard struvite crystal, without any interference of basicity, showing a good crystal structure [64]. Some flocculent attachments on the crystal surface can be seen in Fig. 7(b), and the crystals were much more irregular. Fig. 7(c) shows the presence of massive flocs attached to the surface of the crystal. It has been reported that when alkalinity is within a certain range, such as concentrations less than 5 mmol/L CO32−, increase of basicity reduces the phosphate removal efficiency, but has little effect on the crystal morphology and composition of the crystallization product [65]. In this study, it was found that alkalinity within a concentration range 2–35 mmol/L has a great effect on the crystallization precipitation process, and more floccule and crystal precipitate co-polymers were generated with the increase of alkalinity in the LCM treatment. For example, the shape of the crystals was changed significantly at up to 35 mmol/L alkalinity.
Fig. 5. (a) XRD patterns of recovered solids from different initial phosphorus concentrations. (Initial phosphate concentration 30, 60, 100, and 150 mg-P/L, LCM content 200 mg/L, 6 h) (b) XRD pattern of recovered product in the real wastewater system using LCM and the standard struvite. (Initial phosphate concentration 28 mg-P/L, LCM content 200 mg/L, PDF#77-2303). Table 3 Semi-quantitative analysis of recovered products under different phosphorus concentration determined by XRD. Initial concentration of phosphate (mg-P/L)
Struvite(%)
MgO(%)
real 30 60 100 150
30.9 33.7 54.2 70.5 84.4
69.1 67.3 45.8 29.5 15.6
(4)
Note: % for a mass fraction.
from 30 to 150 mg-P/L, the peak intensity of magnesium oxide decreased gradually, while the peak intensity of struvite increased. This observation corresponds to an increase in the struvite content of the products. Semi-quantitative analysis of these three products (Table 3) was consistent with the results in Fig. 5. The MgO content in the sediments declined with the increase of the initial concentration of phosphate, displaying an increasing tendency of LCM utilization. A similar XRD pattern of the recovered product (Fig. 4b) was obtained in the phosphate removal experiment using real wastewater at the LCM dose of 200 mg/L. The XRD pattern also showed the formation of struvite in the real wastewater system, when compared the standard struvite pattern showed in Fig. 4(b).
3.5. Cost estimation and LCM resource estimation Technology costs are significant in the nutrient recycling process. Calculating the cost of LCM in the phosphorus recycling process and comparing it with the cost of adding sodium hydroxide and magnesium chloride is of great importance to assess the practical value of employing the technology. As magnesite is the main source of LCM, further research was conducted on the magnesite resources. Based on various quality requirements of LCM powder, different grades were defined according to the MgO content ranging from 75% to 96% (wt). As reported in relevant statistics, the proven magnesite reserves were about 100 × 108 t on the earth by the end of 2000, and the main distribution
3.4. Effects of alkalinity and organic acid The foregoing research shows that alkalinity has a great influence on the struvite crystallization process [60]. The effects of alkalinity and organic acids on phosphate removals using LCM are shown in Fig. 6. From Fig. 6(a), it shows a decreasing trend of phosphate removal with 5
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Fig. 6. Effects of alkalinity (a) and dissolved organic acid (b) on phosphate removal. (LCM dosage 200 mg/L, equilibrium pH 8.5 ± 0.1, 6 h).
is listed in Table 4. China has the largest magnesite resources in the world, and most of the deposits are located in Liaoning Province, accounting for 85.6% of the national reserve [67]. Meanwhile, the Liaoning mining area is famous for its high quality of magnesite. Overall, relatively sufficient magnesite can be found for LCM production. The treatment of 1 m3 wastewater was taken as a study case. The initial phosphorus concentration in the wastewater was 60 mg/L and the dosage of 200 mg/L LCM was employed. In this scenario, 0.20 kg of LCM was required per ton of wastewater, resulting in a chemical reagent cost of 0.135 Chinese Yuan per ton. The previous study has shown that in the technique of using lye and magnesium chloride, the consumption of alkali was 0.33 kg, which is equivalent to a cost of 0.828 Chinese Yuan per ton, when treating wastewater containing 77.5 mg/L phosphate under the conditions with N:Mg:P mole ratio 5:1.2:1 and pH of the 9.20 [49]. The consumption of magnesium chloride (including 6 water of crystallization) was 0.61 kg and the cost was 0.396 Chinese Yuan, total cost was 1.224 Chinese Yuan per ton in the technique of simultaneously using magnesium chloride and alkali. The cost of alkali accounted for 67.6% of the total cost, which was a large proportion [50]. Compared to the above conventional technology of dosing lye and magnesium chloride, the LCM technology exhibited a significant advantage of low reagent cost, at a cost of only 11% of the conventional technology. Hence, using LCM was much more cost-efficient, indicating it a promising agent in the phosphorus recovery process.
Table 4 The main distributed countries and regions of magnesite deposits [66]. (×108 t). Countries and regions
reserves
Countries and regions
reserves
China North Korea The former Soviet Union New Zealand Former Czech India
31.2 30 22 6 5 1
Austria The United States Canada Brazil The Greek Former Yugoslavia
0.75 0.66 0.6˜1 0.4 0.3 0.14
formation of struvite, which was associated with the chemical immobilization of ammonium and phosphate from the solution. Additionally, an amount of 15–67% unreacted magnesium oxide was found in the products at phosphate concentrations lower than 150 mgP/L. A higher phosphorus concentration in the wastewater enhanced the percentage of struvite in the product. The phosphate could be removed at different solution alkalinity and in the presence of different organic acids. However, the SEM images showed high alkalinity (35 mmol/L of carbonate) could cause the formation of flocs on the crystal surfaces. 5. Environmental implications To improve the conventional WWTP into an environmental-friendly modern plant, installing the struvite phosphorus recovery unit at the side-stream of anaerobic digestion wastewater will be a practical method for phosphorus recovery. The original pH of wastewater is usually lower than 8.0 and not conducive to the formation of struvite, as a result, the addition of lye for adjusting pH is demanded in many phosphorus recovery techniques using chemical additives in the foregoing reports, and it accounts for a large proportion of the total investment. Another limitation for struvite formation is the insufficient magnesium content in wastewater. Owing to the costly investment of the pH adjustment and magnesium source, sustainable technologies are
4. Conclusions This study provided an efficient and low-cost reagent LCM for phosphorus recovery. Lye addition was not included throughout the phosphate treatment process. The optimum dosage of LCM was 200 mg/L, the solution pH rose from 7.63 to 8.62 automatically, and 84.5% phosphate was removed from the synthetic P-contaminated wastewater containing 30 mg/L within 6 h by struvite formation. The XRD characterization of the recovered products confirmed the
Fig. 7. SEM images of the recovered products at different alkalinity. (×1000; alkalinity content: a. 2 mmol/ L, b. 15 mmol/L, c. 35 mmol/L). 6
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needed. The use of LCM solved this problem because it does not require lye addition and the solution pH could be increased automatically. In addition, residual LCM, and any impurities and micro-particles could function as the crystal nuclei, to induce the crystallization reaction. However, the technology may be limited to regions with readily available magnesite ore resources, which is the source of LCM. The costs of acquiring magnesite ore may be mitigated by the high phosphorus removal efficiency and no necessary pH adjustment when using LCM. Furthermore, the recovered struvite product can be used commercially as a slow-release fertilizer in the agricultural field.
Res. 45 (2011) 4592–4600. [22] A. Shahat, H.M.A. Hassan, H.M.E. Azzazy, M. Hosni, M.R. Awual, Novel nanoconjugate materials for effective arsenic(V) and phosphate capturing in aqueous media, Chem. Eng. J. 331 (2018) 54–63. [23] M.R. Awual, Efficient phosphate removal from water for controlling eutrophication using novel composite adsorbent, J. Clean. Prod. 228 (2019) 1311–1319. [24] M.R. Awual, T. Yaita, S. Suzuki, H. Shiwaku, Ultimate selenium(IV) monitoring and removal from water using a new class of organic ligand based composite adsorbent, J. Hazard. Mater. 291 (2015) 111–119. [25] M.R. Awual, M.M. Hasan, M.A. Khaleque, Efficient selenium(IV) detection and removal from water by tailor-made novel conjugate adsorbent, Sens. Actuators B Chem. 209 (2015) 194–202. [26] X.Y. Liu, Z.H. Xu, J.F. Peng, Y.H. Song, X.G. Meng, Phosphate recovery from anaerobic digester effluents using CaMg(OH)4, J. Environ. Sci. 44 (2016) 260–268. [27] M.R. Awual, M.M. Hasan, T. Ihara, T. Yaita, Mesoporous silica based novel conjugate adsorbent for efficient selenium(IV) detection and removal from water, Microporous Mesoporous Mater. 197 (2014) 331–338. [28] M.R. Awual, M.M. Hasan, A.M. Asiri, M.M. Rahman, Cleaning the arsenic(V) contaminated water for safe-guarding the public health using novel composite material, Compos. Part B Eng. 171 (2019) 294–301. [29] M.R. Awual, M.M. Hasan, A. Islam, M.M. Rahman, A.M. Asiri, M.A. Khalequed, M.C. Sheikhe, Introducing an amine functionalized novel conjugate material for toxic nitrite detection and adsorption from wastewater, J. Clean. Prod. 228 (2019) 778–785. [30] D. Guaya, C. Valderrama, A. Farran, C. Armijos, J.L. Cortina, Simultaneous phosphate and ammonium removal from aqueous solution by a hydrated aluminum oxide modified natural zeolite, Chem. Eng. J. 271 (2015) 204–213. [31] M.R. Awual, M.A. Shenashen, A. Jyo, H. Shiwaku, T. Yaita, Preparing of novel fibrous ligand exchange adsorbent for rapid column-mode trace phosphate removal from water, J. Ind. Eng. Chem. 20 (2014) 2840–2847. [32] M.R. Awual, A. Jyo, S.A. El-Safty, M. Tamada, N. Seko, A weak-base fibrous anion exchanger effective for rapid phosphate removal from water, J. Hazard. Mater. 188 (2011) 164–171. [33] M.R. Awual, A. Jyo, Assessing of phosphorus removal by polymeric anion exchangers, Desalination 281 (2011) 111–117. [34] A.A. Rouff, A.R.O. Goswami, M.V. Ramlogan, D. Kalderis, D. Ntarlagiannis, P. Soupios (Eds.), Biochar as Sorbent for the Treatment of Inorganic Pollutants in Water and Wastewater In Non-Soil Biochar Applications, Nova Science Publishers, Inc., Hauppauge, NY, U.S.A, 2018. [35] F. Yang, S.S. Zhang, Y.Q. Sun, D.C.W. Tsang, K. Cheng, S.Y. Ok, Assembling biochar with various layered double hydroxides for enhancement of phosphorus recovery, J. Hazard. Mater. 365 (2019) 665–673. [36] H. Wang, J. Zhu, Q.L. Fu, J.W. Xiong, C. Hong, H.Q. Hu, A. Violante, Adsorption of phosphate onto ferrihydrite and ferrihydrite-humic acid complexes, Pedosphere 25 (2015) 405–414. [37] J. Chen, L.G. Yan, H.Q. Yu, S. Li, L.L. Qin, G.Q. Liu, Y.F. Li, B. Du, Efficient removal of phosphate by facile prepared magnetic diatomite and illite clay from aqueous solution, Chem. Eng. J. 287 (2016) 162–172. [38] N. Hamdi, E. Srasra, Removal of phosphate ions from aqueous solution using Tunisian clays minerals and synthetic zeolite, J. Environ. Sci. 24 (2012) 617–623. [39] Y. Liu, Q. Li, S. Gao, J.K. Shang, Exceptional As(III) sorption capacity by highly porous magnesium oxide nanoflakes made from hydrothermal synthesis, J. Am. Ceram. Soc. 94 (2011) 217–223. [40] R. Yu, H. Ren, J. Wu, X. Zhang, A novel treatment processes of struvite with pretreated magnesite as a source of low-cost magnesium, Environ. Sci. Pollu. Res. 24 (2017) 22204–22213. [41] M. Krähenbühl, B. Etter, K.M. Udert, Pretreated magnesite as a source of low-cost magnesium for producing struvite from urine in Nepal, Sci. Total Environ. 542 (2016) 1155–1161. [42] Y.Y. Pei, M. Wang, D. Tian, X.F. Xu, L.J. Yuan, Synthesis of core−shell SiO2@MgO with flower like morphology for removal of crystal violet in water, J. Colloid Interface Sci. 453 (2015) 194–201. [43] L. Yang, H. Ipan, S. Michel, D.V. Renatavan, J.N.B. Cees, Fate of calcium, magnesium and inorganic carbon in electrochemical phosphorus recovery from domestic wastewater, Chem. Eng. J. 362 (2019) 453–459. [44] A. Rabinovich, A.A. Rouff, B. Lew, M.V. Ramlogan, Aerated fluidized bed treatment for phosphate recovery from dairy and swine wastewater, ACS Sustain. Chem. Eng. 6 (2018) 652–659. [45] F.H. John, L. Cheryl, A.C. Mackowiak, W.G.H. Wilkie, Struvite phosphorus recovery from aerobically digested municipal wastewater, Sustainability 11 (2019) 376. [46] A.A. Rouff, M.V. Ramlogan, A. Rabinovich, Synergistic removal of zinc and copper in greenhouse waste effluent by struvite, ACS Sustain. Chem. Eng. 4 (2016) 1319–1327. [47] L. Pastor, D. Mangin, R. Barat, A. Seco, A pilot-scale study of struvite precipitation in a stirred tank reactor: conditions influencing the process, Bioresour. Technol. 99 (2008) 6285–6291. [48] N. Ma, A.A. Rouff, B.L. Phillips, A 31P NMR and TG/DSC-FTIR investigation of the influence of initial pH on phosphorus recovery as struvite, ACS Sustain. Chem. Eng. 2 (2014) 816–822. [49] D.D. James, A. Simon, Struvite formation, control and recovery, Water Res. 36 (2002) 3925–3940. [50] Y.S. Zhang, C.Q. Li, J.Q. Lin, Amount of alkali needed and variation patternsin phosphorus recovery process by struvite, CIESC Journal 07 (2012) 2217–2223. [51] M.S. Rahaman, D.S. Mavinic, A. Meikleham, N. Ellis, Modeling phosphorus removal and recovery from anaerobic digester supernatant through struvite crystallization in a fluidized bed reactor, Water Res. 51 (2014) 1–10.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jece.2019.103334. References [1] R.A. Duce, J. Laroche, K. Altieri, et al., Impacts of atmospheric anthropogenic nitrogen on the open ocean, Science 320 (2008) 893–897. [2] D.J. Conley, H.W. Paerl, R.W. Howarth, et al., Controlling eutrophication: nitrogen and phosphorus, Science 323 (2009) 1014–1015. [3] M.B. Rothenberger, A.J. Calomeni, Complex interactions between nutrient enrichment and zooplankton in regulating estuarine phytoplankton assemblages: microcosm experiments informed by an environmental dataset, J. Exp. Mar. Biol. Ecol. 480 (2016) 62–73. [4] United States Environmental Protection Agency, https://www.epa.gov/ nutrientpollution/sources-and-solutions. (Accessed March 16, 2019). [5] P. Wilfert, P.S. Kumar, L. Korving, G.J. Witkamp, M.C.M. Loosdrecht, The relevance of phosphorus and iron chemistry to the recovery of phosphorus from wastewater: a review, Environ. Sci. Technol. 49 (2015) 9400–9414. [6] Y.V. Nancharaiah, S.V. Mohan, P.N.L. Lens, Recent advances in nutrient removal and recovery in biological and bioelectrochemical systems, Bioresour. Technol. 215 (2016) 173–185. [7] J. Cooper, R. Lombardi, D. Boardman, The future distribution and production of global phosphate rock reserves, Resour. Conserv. Recycl. 57 (2011) 78–86. [8] D.P.V. Vuuren, A.F. Bouwman, A.H.W. Beusen, Phosphorus demand for the 1970−2100 period: a scenario analysis of resource depletion, Global Environ. Change 20 (2010) 428–439. [9] S.M. Jasinski, Phosphate rock, U.S. Geological Survey, Mineral Commodity Summaries, (2012) (accessed March 16, 2019), http://minerals.usgs.gov/minerals/ pubs/commodity/phosphaterock/mcs-2012-phosp.pdf. [10] L. Reijnders, Phosphorus resources, their depletion and conservation, a review, Resour. Conserv. Recycl. 93 (2014) 32–49. [11] X.D. Hao, F. Hiroaki, G.H. Chen, Resource recovery: efficient approaches to sustainable water and wastewater treatment, Water Res. 86 (2015) 83–84. [12] S. Karaca, A. Gurses, M. Ejder, M. Açıkyıldız, Kinetic modeling of liquid-phase adsorption of phosphate on dolomite, J. Colloid Interface Sci. 277 (2004) 257–263. [13] P. Wilfert, A. Mandalidis, A.I. Dugulan, K. Goubitz, L. Korving, H. Temmink, G.J. Witkamp, M.C.M. Van Loosdrecht, Vivianite as an important iron phosphate precipitate in sewage treatment plants, Water Res. 104 (2016) 449–460. [14] S. Wang, J. An, Y. Wan, Q. Du, X. Wang, X. Cheng, N. Li, Phosphorus competition in bioinduced vivianite recovery from wastewater, Environ. Sci. Technol. 52 (2018) 13863–13870. [15] M.R. Awual, S. Urata, A. Jyo, M. Tamada, A. Katakai, Arsenate removal from water by a weak-base anion exchange fibrous adsorbent, Water Res. 42 (2008) 689–696. [16] M.R. Awual, M.A. Hossain, M.A. Shenashen, T. Yaita, S. Suzuki, A. Jyo, Evaluating of arsenic(V) removal from water by weak-base anion exchange adsorbents, Environ. Sci. Pollut. Res. - Int. 20 (2013) 421–430. [17] M.R. Awual, A. Jyo, Rapid column-mode removal of arsenate from water by crosslinked poly (allyamine) resin, Water Res. 43 (2009) 1229–1236. [18] L. Yan, Y. Xu, H. Yu, X. Xin, Q. Wei, B. Du, Adsorption of phosphate from aqueous solution by hydroxy-aluminum, hydroxy-iron and hydroxy-iron–aluminum pillared bentonites, J. Hazard. Mater. 179 (2010) 244–250. [19] M.R. Awual, S.A. El-Safty, A. Jyo, Removal of trace arsenic(V) and phosphate from water by a highly selective ligand exchange adsorbent, J. Environ. Sci. 23 (2011) 1947–1954. [20] M.R. Awual, M.A. Shenashen, T. Yaita, H. Shiwaku, A. Jyo, Efficient arsenic(V) removal from water by ligand exchange fibrous adsorbent, Water Res. 46 (2012) 5541–5550. [21] M.R. Awual, A. Jyo, T. Iharaa, N. Seko, M. Tamada, K.T. Lim, Enhanced trace phosphate removal from water by zirconium(IV) loaded fibrous adsorbent, Water
7
Journal of Environmental Chemical Engineering 7 (2019) 103334
J. Wei, et al.
swine wastewater, Chemosphere 69 (2007) 319–324. [61] Y.H. Song, Y.R. Dai, Q. Hua, X.H. Yu, F. Qian, Effects of three kinds of organic acids on phosphorus recovery by magnesium ammonium phosphate (MAP) crystallization from synthetic swine wastewater, Chemosphere 101 (2014) 41–48. [62] D. Wyrzykowski, J. Czupryniak, T. Ossowski, L. Chmurzynski, Thermodynamic interactions of the alkaline earth metal ions with citric acid, J. Therm. Anal. Calorim. 102 (2010) 149–154. [63] X.Y. Liu, L.C. Xiang, Y.H. Song, F. Qian, X.G. Meng, The effects and mechanism of alkalinity on the phosphate recovery from anaerobic digester effluent using dolomite lime, Environ. Earth Sci. 73 (2015) 5067–5073. [64] N. Hutnik, A. Kozik, A. Mazienczuk, K. Piotrowski, B. Wierzbowska, A. Matynia, Phosphates (V) recovery from phosphorous mineral fertilizers industry wastewater by continuous struvite reaction crystallization process, Water Res. 47 (2013) 3635–3643. [65] P. Yuan, Y.H. Song, F. Yuan, J.F. Peng, Nutrient removal and recovery from swine wastewater by crystallization of magnesium ammonium phosphate, Acta Sci. Circ. 27 (2007) 1127–1134. [66] Z.M. Wang, Current situation and trend of development of magnesite in China, China Non-Metall. Mining Industry Herald 57 (2006) 6–8+23. [67] X.Y. Zhang, Ways of improving utilization level of magnesite resource in China, Conserv. Util. Miner. Resour. 04 (2008) 23–25.
[52] E. Ariyanto, K.S. Tushar, M.A. Ha, The influence of various physic-chemical process parameters on kinetics and growth mechanism of struvite crystallization, Adv. Powder Technol. 25 (2) (2014) 682–694. [53] F.J. Rubio-Rincón, C.M. Lopez-Vazquez, M. Ronteltapa, Seawater for phosphorus recovery from urine, Desalination 348 (2014) 49–56. [54] J. Dai, W.T. Tang, Y.S. Zheng, H.R. Mackeya, H.K. Chuia, M.C.M. van Loosdrecht, G.H. Chen, An exploratory study on seawater-catalysed urine phosphorus recovery (SUPR), Water Res. 66 (2014) 75–84. [55] L.A. Wendling, P. Blomberg, T. Sarlin, O. Priha, M. Arnold, Phosphorus sorption and recovery using mineral-based materials: Sorption mechanisms and potential phytoavailability, Appl. Geochem. 37 (2013) 157–169. [56] J. S. Wei; Y. H. Song, X. G. Meng, X.Y. Liu, F. Qian, Method and reagent for treatment of nitrogen and phosphorus in wastewater and resource recovery. Chinese patent (2015) open number CN106554060A. [57] C.X. Dong, G.H. He, W.J. Zheng, T.F. Bian, M. Li, D.W. Zhang, Study on antibacterial mechanism of Mg(OH)2 nanoparticles, Mater. Lett. 134 (2014) 286–289. [58] K. Bube, Uber magnesium ammonium phosphate, Anal. Bioanal. Chem. 49 (1910) 525–596. [59] Y. Jaffer, T.A. Clark, P. Pearce, S.A. Parsons, Potential phosphorus recovery by struvite formation, Water Res. 36 (2002) 1834–1842. [60] Y.H. Song, P. Yuan, B.H. Zheng, J.F. Peng, F. Yuan, Y. Gao, Nutrients removal and recovery by crystallization of magnesium ammonium phosphate from synthetic
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Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece
Phosphorus recovery from wastewater using light calcined magnesite, effects of alkalinity and organic acids ⁎
Jinshan Weia,b,d, Jie Geb, Ashaki A. Rouffc, Xianghua Wend, Xiaoguang Mengb, , Yonghui Songa,
T ⁎
a
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China Center for Environmental Engineering, Stevens Institute of Technology, Hoboken, NJ, 07030, USA c Department of Earth and Environmental Sciences, Rutgers University, Newark, NJ, 07102, USA d School of Environment, Tsinghua University, Beijing, 100084, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Wastewater treatment Phosphorus recovery Alkalinity Organic acids Light calcined magnesite Struvite
To solve the problem of phosphorus pollution and resource crisis, phosphorus recovery by struvite crystallization has become a focus of research in recent years. In municipal wastewater, insufficient magnesium content and relatively low pH can be a limitation for struvite formation. A commercial magnesium source, light calcined magnesite (LCM), was used in this study for phosphorus recovery from wastewater without an adjustment of pH. Bench-scale jar test experiments were conducted to study the kinetics of phosphate removal by LCM. The effects of LCM dosage, initial phosphate concentration, carbonate alkalinity and organic acid content on the removal of phosphate was evaluated. Hydrolyzation of LCM released hydroxyl ions (OH−) during the reaction, increasing the solution pH from 7.63 to 8.62. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the composition and morphology of formed precipitates. At an LCM dosage of 200 mg/L, 84.5% of phosphate was removed mainly through the formation of struvite. Increased alkalinity and organic acid concentration in the solution inhibited struvite formation, and higher alkalinity promoted the formation of coarse crystal surfaces. Abundant global reserves of the magnesite ore resource reveal LCM may be a viable and costeffective source of magnesium and hydroxyl reagent for phosphorus recovery from wastewater.
1. Introduction Discharge of excess nutrient elements like phosphorus and nitrogen cause serious environmental problems, such as eutrophication in lakes, reservoirs, estuaries, and oceans, which may deteriorate the ecosystem and the economy associated with tourism [1–3]. The United States Environmental Protection Agency (USEPA) reported that “sewer and septic systems that are responsible for treating large number of waste did not always operate properly or remove enough nitrogen and phosphorus before discharging treated waste to waterways” [4]. Phosphorus mainly exists in the form of inorganic phosphate in wastewater from municipal wastewater treatment plants (WWTPs). Conventional phosphate removal methods, such as enhanced biological phosphorus removal (EBPR) and chemical phosphorous removal, consume a large amount of coagulants and deposit phosphate in the sludge which is a waste of resources. Meanwhile, phosphorus is an essential nutrient for all living organisms and is important for global food production, being a component of nucleic acids, phospholipids, and ATP/ ADP [5,6]. Most of the phosphorus fertilizer applied to agricultural land
⁎
comes from phosphate rock (PR), which is considered to be a non-renewable resource [7]. According to the optimistic estimate, the amount of PR depletion is around 20–35%. In the worst case, about 40–60% of the current reserves will be extracted by 2100 [8]. The distribution of PR reserves and the share of current production are both concentrated in a few countries, notably Morocco, China, and the US [9]. The use of phosphorus on the earth presents a linear law, apart from phosphorus that can be partially recycled by applying manure to agricultural land, with very few recycling routes and inefficiency in its production and use [10]. In addition, various options for recycling waste flows also exist. Increasing the efficiency of phosphorus recovery seems to be worthwhile, even if depletion is not imminent [11]. This situation requires an urgent adoption of a sustainable process to improve nutrient management practices and identify alternative phosphorus sources. Therefore, wastewater “mining” can supplement artificial demand, while reducing dependence on natural and geological reserves. Extensive research has been conducted to find viable materials for the removal of anions, like phosphate, arsenic, selenium, and nitrate.
Corresponding authors. E-mail addresses: [email protected] (J. Wei), [email protected] (X. Meng), [email protected] (Y. Song).
https://doi.org/10.1016/j.jece.2019.103334 Received 15 May 2019; Received in revised form 25 July 2019; Accepted 28 July 2019 Available online 29 July 2019 2213-3437/ © 2019 Elsevier Ltd. All rights reserved.
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[12–29]. Various adsorbents such as zeolite [30], fiber adsorbent [31–33], biochar [34,35], ferrihydrite [36], and clays [37,38], have been investigated for phosphate removal. Among them, metal oxides generally exhibit better performance in phosphate removal than other adsorbents [39]. Pretreated magnesite obtained from different calcination temperature was reported for phosphorus removal in China and Nepal [40,41]. However, many factors (i.e. initial phosphorus concentration, co-existing ions competition) that affect the phosphorus recovery should also need pay attention to. Magnesium oxides, like synthesized nanoscale MgO with high ionicity, simple stoichiometry, and crystal structure have emerged due to versatility in applications, such as adsorption, catalysis, and refraction [42]. In recent years, struvite (Mg(NH4)PO4·6H2O) crystallization and hydroxyapatite (Ca5(PO4)3(OH)) precipitation were recognized as the main techniques for phosphorus recovery [43–46], with several pilot demonstration studies reported in the literature [47]. The chemical formula of struvite contains both nitrogen and phosphorus elements, which can be recovered and reused [48]. It has been concluded that the precipitation of hydroxyapatite occurs at pH values above 9.5, whereas the optimal pH value for struvite precipitation should be at 8.0 and above [49]. Researchers have also conducted a multitude of phosphorus recovery tests involving the addition of chemical reagents, and consumption of large amounts of alkali, therefore increasing the economic cost of the technology [50]. Thus, capital cost is a key limiting factor in the practical application of phosphorus recovery technology. Discovering a cost-efficient phosphorus recovery additive reagent is an urgent issue. Magnesium salts (such as magnesium chloride) are widely used for the production of struvite [51,52], with the advantage of a fast reaction rate and immediate crystallization and precipitation. Seawater can also be used as a source of magnesium, with the drawback of limited access of this source to inland cities [53,54]. Meanwhile, the alkali reagents for pH adjustment are also required in the phosphorus removal process using magnesium chloride and seawater, which drastically escalates the economic cost. To reduce costs associated with the addition of Mg and alkali reagents separately, a single reagent that serves this dual purpose is needed. Light Calcined Magnesite (LCM) obtained from pretreatment of magnesite ore, also known as magnesia powder or magnesia, is commonly used as a fireproof material in the construction industry. The LCM is readily soluble in water, releasing Mg ions while simultaneously increasing pH. In a wastewater application, any undissolved LCM can subsequently act as seed material to accelerate the phosphate crystallization reaction. However, limited studies have been conducted on the use of naturally obtained minerals or LCM materials as a magnesium source for the treatment of phosphate [55]. In this study, LCM was used for phosphorus removal from municipal wastewater. The new reagent light calcined magnesite was closed in the previous applied patent “Method and reagent for treatment of nitrogen and phosphorus in wastewater and resource recovery” in September 2015, with open number CN106554060A [56]. The mineralogy of the ores is dominated by magnesite (> 94%, with variable grain size and crystalloblastic texture) with only small amounts of quartz, dolomite, clinochlore, and talc. The LCM acted as both a magnesium source and a pH adjustment reagent. Factors, potentially affecting the phosphorus removal process, such as alkalinity and dissolved organic content, were investigated. Solids recovered from the treatment process were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM).
Fig. 1. XRD pattern of LCM and the standard synthetic MgO. (PDF#78-0430).
from 40.80% to 47.50% (mass percent, mean = 46.31 ± 3.08%, 2SD, n = 24) and 47.82% to 52.08% (mean = 51.22 ± 2.20%, 2SD, n = 24), respectively. The CaO content ranged from 0.21% to 2.50% (mean = 0.59 ± 0.92%, 2SD, n = 23). The percentage of SiO2, Al2O3, Fe2O3, and MnO2 was relatively low. LCM was obtained through calcination of magnesite ores at 650˜800 ℃ for 2 h. The particle size of the LCM used in the experiment was around 150 μm. XRD pattern of the LCM is shown in Fig. 1, and the main components are listed in Table 1.
2.2. Wastewater solutions The supernatant of anaerobically digested sludge was collected from the sludge digestion reactor in a WWTP in Beijing, China. Synthetic wastewater was prepared by adding potassium phosphate (KH2PO4), ammonium chloride (NH4Cl), sodium bicarbonate (NaHCO3) and sodium acetic (CH3COONa) into tap water, to simulate the composition of the sludge supernatant. All the reagents were analytical purity and purchased from Sigma-Aldrich. The characteristics of real and simulated wastewater are shown in Table 2.
2.3. Batch experiments The batch experiments were carried out at room temperature of 20 ℃, with 1000 mL simulated wastewater. The stirring speed was controlled at 100 r/min using a ZR4-6 Jar Tester. The effect of LCM dosage on phosphate removal was evaluated at concentrations of 50, 100, 200, 300, 400, 500 and 600 mg/L LCM, respectively, at an initial phosphate concentration of 30 mg-P/L. The effect of initial phosphate was determined for concentrations of 28 (real wastewater), 30, 60, 100, 150, and 200 mg-P/L, at an LCM dosage of 200 mg/L. Initial alkalinity (i.e. 10, 15, 20, 25 and 35 mmol-CO32−/L) was adjusted to evaluate the effect of alkalinity on phosphate removal and recovered products. The alkalinity in the solution was simulated using NaHCO3. Three kinds of organic acids, such as formic acid (H2CO2), oxalic acid (H2C2O4), and citric acid (C6H8O7), were used to study the effect of dissolved organic matter. Alkalinity and organic acid experiments were conducted at t a 200 mg/L LCM dosage and 30 mg-P/L phosphate concentration. For all experiments, removal of phosphate and ammonium, as well as pH, were monitored at the reaction times of 0.5, 1, 2, 3, 4, and 6 h. At the predetermined sampling time, 5 mL of sample was collected, and filtered using a 0.45 μm membrane, and then acidified using HNO3.
2. Materials and methods
Table 1 Main composition of LCM. (mass percent, %).
2.1. Light calcined magnesite Raw material of LCM, magnesite ore, was obtained from a mining company in Liaoning Province, China. Magnesium oxide and carbon dioxide were the dominant components of raw magnesite ores, ranging 2
Magnesite ignition loss (CO2)
MgO
CaO
SiO2
Fe2O3
Al2O3
others
49.82
46.21
0.72
2.3
0.23
0.22
0.50
Journal of Environmental Chemical Engineering 7 (2019) 103334
J. Wei, et al.
Table 2 Parameters of real wastewater and simulated wastewater. Real wastewater Constituent 3−
PO4 NH4+ Mg2+ COD Alkalinity pH
Simulated wastewater Unit (mg-P /L) (mg-N/L) (mg-Mg/L) (mg/L) (mmol-CO32−/L)
Concentration
Constituent 3−
25.19-32.10 595.24-751.91 12.31-18.63 495.00-582.03 19.10-20.27 7.63
PO4 NH4+ Mg2+ COD Alkalinity pH
Unit
Concentration
(mg-P /L) (mg-N/L) (mg-Mg/L) (mg/L) (mmol-CO32−/L)
30.0/spiked 730 15.0 500 20/spiked 7.63
presented in Fig. 2(b), The results show that the pH of the solution increased rapidly from 7.63 to 8.51, in the first 2 h, followed by a slow increase to 8.62 in the next 4 h. Hydrolysis of MgO as shown in Eq. 1 can produce hydroxyl ions (OH−) to increase the solution pH. Studies have indicated that pH is one of the most important factors affecting the struvite crystallization reaction (Eq. 2), and the optimal solution should be above 8.0 for struvite formation [49]. Eq. (3) obtained from the combination of Eq. (1) and Eq. (2) can be used to trace the overall process of phosphate recovery using LCM.
2.4. Sample analysis The phosphate concentration of the samples was measured by the molybdenum-antimony anti-spectrophotometric method (UV/VIS 4802, Unico, Shanghai), and the ammonium concentration was measured by Nessler reagent spectrophotometry. The solids were collected after 6 h reaction, filtered with 0.45 μm membrane, and air-dried at room temperature for XRD (Bruker, D8 Advanced MAX2RB, Germany) and SEM (Zeiss, EVO18, Germany) analysis.
MgO + H2O → Mg2+ + 2OH− 3. Results and discussion
NH4+
3.1. Effect of LCM dosage and kinetics on phosphate removal
+ Mg
2+
+
HPO42−
(1)
+ OH- + 5H2O ⇔ Mg(NH4)PO4·6H2O (s) (2)
NH4+ + MgO + HPO42− + 6H2O → Mg(NH4)PO4·6H2O (s) + OH(3)
Effects of LCM dosages on phosphate removal were studied, and the results are shown in Fig. 2(a). The residual phosphate concentration decreased with increasing LCM dosage. The phosphate removal efficiency was 24.3% at the dosage of 50 mg/L, and increased to 94.6% at a dosage of 600 mg/L. From the perspective of phosphate removal efficiency and utilization of resources, the optimal dosage is up to 200 mg/ L with a phosphate removal efficiency of 84.5%. At the same time, the amount of Mg2+ released from LCM was enough for the struvite crystallization reaction. The kinetics of phosphate and ammonium removal using LCM are shown in Fig. 2(b). Phosphate removal efficiency increased rapidly to 63.2% after reacting with 200 mg/L of LCM in 1 h and then increased to 83.5% after 2 h. Thereafter, phosphate removal slowly reached equilibrium until 6 h. The phosphate removal can be modeled using the pseudo-second-order model and R2 of the model fitting is 0.989. Kinetics of ammonium removal showed a similar trend as phosphate within 2 h of reaction, after which ammonium removal remained stable and reached an equilibrium. The kinetics results in Fig. 2(b) demonstrate the ability of LCM to remove phosphate. Due to the simultaneous removal of ammonium, the crystallizing phase is likely struvite. Any undissolved LCM, as well as impurities and micro-particles, may act as nucleating material to accelerate the crystallization reaction. Solution pH was also measured throughout the reaction and is
3.2. LCM as a pH adjuster and struvite formation model The effect of LCM on solution pH was further measured by the pH changes of deionized (DI) water after adding different dosages of LCM, and the results are shown in Fig. 3(a). The initial pH of the DI water was around 7.00 and it increased to 10.34 and 10.55 at the LCM dosage of 100 and 200 mg/L, respectively. The dramatic increase in solution pH after adding LCM illustrates the good ability of LCM to release OH−, accompanied by the release of Mg2+, as shown in Eq. (1). The soluble Mg2+ would be further precipitated in the form of Mg(OH)2 at a higher solution pH, which can be modeled by Visual Minteq. Fig. 3(b) shows the percentage of Mg species as a function of solution pH. The free Mg2+ in water could transform to Mg(OH)2 precipitate at pH 10.1, and 99% of Mg precipitated at pH greater than 11.2. A pC{log(total Mg)}-pH diagram of Mg precipitation in the absence of co-existing ions(i.e. PO43−, NH4+) was calculated and showed in Fig. 3(c). The Ksp of Mg(OH)2 was calculated at 5.6 × 10-12 [57]. The simulation yielded a sharp decreasing trend of Mg(OH)2 in the pH range of 9–14, which translated to a lower Mg solubility. The 99% precipitation curve means that most of the total Mg precipitated in the
Fig. 2. (a) Effect of LCM dosage on phosphate removal; (Initial phosphate concentration 30 mg-P/L, 6 h) and (b) kinetics of phosphate and ammonium removal, and the changes of pH. (Initial Phosphate concentration 30 mg-P/L, LCM dosage 200 mg/L). 3
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Fig. 3. (a) Changes of solution pH by functional of solubility time of LCM in DI water; (b) percentage of Mg species as a function of solution pH modeled by Visual Minteq; (c) pC-pH diagram of Mg; (total Mg concentration 1 mM, 25 ℃) (d) modeling struvite formation in PO43−-NH4+-Mg2+ system. (PO43−, Mg2+ and NH4+ concentration 1 mM, ionic strength 0.01 M, 25 ℃).
system. At pH 9 and 10, precipitation occurs at Mg2+ concentrations higher than 7000 and 40.1 mg/L, respectively. As shown in Fig. 2(b), the equilibrium solution pH was around 8.6 in the phosphate removal test using 200 mg/L LCM. The ion product of struvite is 2.51 × 10−13 at room temperature, and the mineral is precipitated at saturated conditions [58]. The formation of struvite consumes free Mg2+ in the water, thus promoting a forward movement of the equilibrium in Eq. (1). The formation of struvite was modeled at the experimental conditions, and the results are shown in Fig. 3(d). The model results illustrate that PO43-, Mg2+, and NH4+ precipitated as struvite as the pH increased from 8.5 to 9.5. Figure S1 showed the changes of point of struvite formation as a function of NH4+ and Mg2+ concentration in the solution. It is validated that under conditions of excessive Mg2+ and NH4+, phosphate can be precipitated through the formation of struvite at the pH of 8.0˜8.5. To some extent, the optimum pH for struvite crystallization varies when treating different types of wastewater. Studies have shown that the optimum pH is in the range of 9.0–10.5 [59]. In this experiment, phosphorus could be immobilized in struvite in great quantities in the viable pH range of 8.0–8.5 and good efficiency of the phosphate removal was achieved.
Fig. 4. Removal of phosphate at different initial phosphate concentrations. (real wastewater 28 mg-P/L, simulated wastewater 30, 60, 100, 150 and 200 mg-P/L, LCM dosage 200 mg/L, 6 h).
to 200 mg-P/L, the phosphate removal efficiency dropped to 69.6%, which can be interpreted by the insufficient LCM dose applied. As a result, different LCM dosages can be considered based on the initial phosphate concentration in the raw wastewater, as well as the removal efficiency. Characterization of the recovered products at different initial phosphorus concentrations was performed by analysis of the XRD patterns (Fig. 5a). The XRD patterns of recovered solids were analyzed through the PDF diffraction database CARD (PDF#77-2303). The main component was assigned as struvite, mixed with the unreacted magnesium oxide. With the increase of initial phosphorus concentration
3.3. Effect of initial P concentration Phosphorus removal at various initial phosphate concentrations was investigated at the LCM dosage of 200 mg/L and the results are summarized in Fig. 4. The real wastewater and simulated wastewater at 5 different concentrations were used in the experiment. The phosphate removal of 86.6% was obtained for the real wastewater system. In the simulated wastewater treatment, the phosphate removal efficiency was 84.5% at the initial phosphate concentration of 30 mg-P/L while it rose to 91.3% at 60 mg-P/L. As the initial phosphate concentration increased 4
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the increase of alkalinity in the wastewater. At the alkalinity of 20 mmol/L, which was the alkalinity content in real wastewater, the phosphate removal efficiency reached 84.5%. However, only 60.9% of phosphate was removed at the alkalinity content of 35 mmol/L, indicating a competitive effect of the carbonate with phosphate during the precipitation reaction. The co-existing carbonate can react with the Mg2+ and form magnesite. (Eq. 4) Mg2+ + CO32− → MgCO3 (s)
Dissolved organic material especially organic acids may have great effects on the phosphate removal during struvite crystallization [61]. The effects of three organic acids (citric acid, oxalic acid, and formic acid) on P removals efficiency were investigated, and the results are shown in Fig. 6(b). P removal can be affected by the co-existed organic acid, due to the complexation between organic acid and Mg2+/NH4+, i.e. the binding constant for Mg2+ with citric acid is 13.5 × 103 [62]. The presence of all three organic acids inhibited the P removal at the outset of the reaction, and a positive correlation between inhibition and organic acid concentration was observed. Meanwhile, when the three organic acids were present at the same concentration, the inhibition effects followed the order: citric acid > oxalic acid > formic acid, which can be related to the number of carboxyl groups carried by these three organic acids. The number of carboxyl groups on citric acid, oxalic acid, and formic acid can be calculated as 3:2:1 at the same mole of the organic acid. The high concentration of citric acid significantly interrupted the struvite crystallization reaction, and phosphate removal was reduced from 84.5% to 47.8% in the presence of 4 mM citric acid. Overall, the experimental results demonstrate that phosphate can be removed by LCM in the presence of different kinds and concentrations of organic acids. The SEM images of recovered products under different alkalinity conditions are shown in Fig. 7. The morphology of the precipitates was irregular short rods, lump crystals, including crystals with smooth polygon surfaces, and was different from the familiar needle-like morphology. In general, the shape of crystals in Fig. 7(a) and (b) is typical of struvite crystals, corresponding with our previous study [63]. Specifically, the crystal shape in Fig. 7(a) was most similar to the standard struvite crystal, without any interference of basicity, showing a good crystal structure [64]. Some flocculent attachments on the crystal surface can be seen in Fig. 7(b), and the crystals were much more irregular. Fig. 7(c) shows the presence of massive flocs attached to the surface of the crystal. It has been reported that when alkalinity is within a certain range, such as concentrations less than 5 mmol/L CO32−, increase of basicity reduces the phosphate removal efficiency, but has little effect on the crystal morphology and composition of the crystallization product [65]. In this study, it was found that alkalinity within a concentration range 2–35 mmol/L has a great effect on the crystallization precipitation process, and more floccule and crystal precipitate co-polymers were generated with the increase of alkalinity in the LCM treatment. For example, the shape of the crystals was changed significantly at up to 35 mmol/L alkalinity.
Fig. 5. (a) XRD patterns of recovered solids from different initial phosphorus concentrations. (Initial phosphate concentration 30, 60, 100, and 150 mg-P/L, LCM content 200 mg/L, 6 h) (b) XRD pattern of recovered product in the real wastewater system using LCM and the standard struvite. (Initial phosphate concentration 28 mg-P/L, LCM content 200 mg/L, PDF#77-2303). Table 3 Semi-quantitative analysis of recovered products under different phosphorus concentration determined by XRD. Initial concentration of phosphate (mg-P/L)
Struvite(%)
MgO(%)
real 30 60 100 150
30.9 33.7 54.2 70.5 84.4
69.1 67.3 45.8 29.5 15.6
(4)
Note: % for a mass fraction.
from 30 to 150 mg-P/L, the peak intensity of magnesium oxide decreased gradually, while the peak intensity of struvite increased. This observation corresponds to an increase in the struvite content of the products. Semi-quantitative analysis of these three products (Table 3) was consistent with the results in Fig. 5. The MgO content in the sediments declined with the increase of the initial concentration of phosphate, displaying an increasing tendency of LCM utilization. A similar XRD pattern of the recovered product (Fig. 4b) was obtained in the phosphate removal experiment using real wastewater at the LCM dose of 200 mg/L. The XRD pattern also showed the formation of struvite in the real wastewater system, when compared the standard struvite pattern showed in Fig. 4(b).
3.5. Cost estimation and LCM resource estimation Technology costs are significant in the nutrient recycling process. Calculating the cost of LCM in the phosphorus recycling process and comparing it with the cost of adding sodium hydroxide and magnesium chloride is of great importance to assess the practical value of employing the technology. As magnesite is the main source of LCM, further research was conducted on the magnesite resources. Based on various quality requirements of LCM powder, different grades were defined according to the MgO content ranging from 75% to 96% (wt). As reported in relevant statistics, the proven magnesite reserves were about 100 × 108 t on the earth by the end of 2000, and the main distribution
3.4. Effects of alkalinity and organic acid The foregoing research shows that alkalinity has a great influence on the struvite crystallization process [60]. The effects of alkalinity and organic acids on phosphate removals using LCM are shown in Fig. 6. From Fig. 6(a), it shows a decreasing trend of phosphate removal with 5
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Fig. 6. Effects of alkalinity (a) and dissolved organic acid (b) on phosphate removal. (LCM dosage 200 mg/L, equilibrium pH 8.5 ± 0.1, 6 h).
is listed in Table 4. China has the largest magnesite resources in the world, and most of the deposits are located in Liaoning Province, accounting for 85.6% of the national reserve [67]. Meanwhile, the Liaoning mining area is famous for its high quality of magnesite. Overall, relatively sufficient magnesite can be found for LCM production. The treatment of 1 m3 wastewater was taken as a study case. The initial phosphorus concentration in the wastewater was 60 mg/L and the dosage of 200 mg/L LCM was employed. In this scenario, 0.20 kg of LCM was required per ton of wastewater, resulting in a chemical reagent cost of 0.135 Chinese Yuan per ton. The previous study has shown that in the technique of using lye and magnesium chloride, the consumption of alkali was 0.33 kg, which is equivalent to a cost of 0.828 Chinese Yuan per ton, when treating wastewater containing 77.5 mg/L phosphate under the conditions with N:Mg:P mole ratio 5:1.2:1 and pH of the 9.20 [49]. The consumption of magnesium chloride (including 6 water of crystallization) was 0.61 kg and the cost was 0.396 Chinese Yuan, total cost was 1.224 Chinese Yuan per ton in the technique of simultaneously using magnesium chloride and alkali. The cost of alkali accounted for 67.6% of the total cost, which was a large proportion [50]. Compared to the above conventional technology of dosing lye and magnesium chloride, the LCM technology exhibited a significant advantage of low reagent cost, at a cost of only 11% of the conventional technology. Hence, using LCM was much more cost-efficient, indicating it a promising agent in the phosphorus recovery process.
Table 4 The main distributed countries and regions of magnesite deposits [66]. (×108 t). Countries and regions
reserves
Countries and regions
reserves
China North Korea The former Soviet Union New Zealand Former Czech India
31.2 30 22 6 5 1
Austria The United States Canada Brazil The Greek Former Yugoslavia
0.75 0.66 0.6˜1 0.4 0.3 0.14
formation of struvite, which was associated with the chemical immobilization of ammonium and phosphate from the solution. Additionally, an amount of 15–67% unreacted magnesium oxide was found in the products at phosphate concentrations lower than 150 mgP/L. A higher phosphorus concentration in the wastewater enhanced the percentage of struvite in the product. The phosphate could be removed at different solution alkalinity and in the presence of different organic acids. However, the SEM images showed high alkalinity (35 mmol/L of carbonate) could cause the formation of flocs on the crystal surfaces. 5. Environmental implications To improve the conventional WWTP into an environmental-friendly modern plant, installing the struvite phosphorus recovery unit at the side-stream of anaerobic digestion wastewater will be a practical method for phosphorus recovery. The original pH of wastewater is usually lower than 8.0 and not conducive to the formation of struvite, as a result, the addition of lye for adjusting pH is demanded in many phosphorus recovery techniques using chemical additives in the foregoing reports, and it accounts for a large proportion of the total investment. Another limitation for struvite formation is the insufficient magnesium content in wastewater. Owing to the costly investment of the pH adjustment and magnesium source, sustainable technologies are
4. Conclusions This study provided an efficient and low-cost reagent LCM for phosphorus recovery. Lye addition was not included throughout the phosphate treatment process. The optimum dosage of LCM was 200 mg/L, the solution pH rose from 7.63 to 8.62 automatically, and 84.5% phosphate was removed from the synthetic P-contaminated wastewater containing 30 mg/L within 6 h by struvite formation. The XRD characterization of the recovered products confirmed the
Fig. 7. SEM images of the recovered products at different alkalinity. (×1000; alkalinity content: a. 2 mmol/ L, b. 15 mmol/L, c. 35 mmol/L). 6
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needed. The use of LCM solved this problem because it does not require lye addition and the solution pH could be increased automatically. In addition, residual LCM, and any impurities and micro-particles could function as the crystal nuclei, to induce the crystallization reaction. However, the technology may be limited to regions with readily available magnesite ore resources, which is the source of LCM. The costs of acquiring magnesite ore may be mitigated by the high phosphorus removal efficiency and no necessary pH adjustment when using LCM. Furthermore, the recovered struvite product can be used commercially as a slow-release fertilizer in the agricultural field.
Res. 45 (2011) 4592–4600. [22] A. Shahat, H.M.A. Hassan, H.M.E. Azzazy, M. Hosni, M.R. Awual, Novel nanoconjugate materials for effective arsenic(V) and phosphate capturing in aqueous media, Chem. Eng. J. 331 (2018) 54–63. [23] M.R. Awual, Efficient phosphate removal from water for controlling eutrophication using novel composite adsorbent, J. Clean. Prod. 228 (2019) 1311–1319. [24] M.R. Awual, T. Yaita, S. Suzuki, H. Shiwaku, Ultimate selenium(IV) monitoring and removal from water using a new class of organic ligand based composite adsorbent, J. Hazard. Mater. 291 (2015) 111–119. [25] M.R. Awual, M.M. Hasan, M.A. Khaleque, Efficient selenium(IV) detection and removal from water by tailor-made novel conjugate adsorbent, Sens. Actuators B Chem. 209 (2015) 194–202. [26] X.Y. Liu, Z.H. Xu, J.F. Peng, Y.H. Song, X.G. Meng, Phosphate recovery from anaerobic digester effluents using CaMg(OH)4, J. Environ. Sci. 44 (2016) 260–268. [27] M.R. Awual, M.M. Hasan, T. Ihara, T. Yaita, Mesoporous silica based novel conjugate adsorbent for efficient selenium(IV) detection and removal from water, Microporous Mesoporous Mater. 197 (2014) 331–338. [28] M.R. Awual, M.M. Hasan, A.M. Asiri, M.M. Rahman, Cleaning the arsenic(V) contaminated water for safe-guarding the public health using novel composite material, Compos. Part B Eng. 171 (2019) 294–301. [29] M.R. Awual, M.M. Hasan, A. Islam, M.M. Rahman, A.M. Asiri, M.A. Khalequed, M.C. Sheikhe, Introducing an amine functionalized novel conjugate material for toxic nitrite detection and adsorption from wastewater, J. Clean. Prod. 228 (2019) 778–785. [30] D. Guaya, C. Valderrama, A. Farran, C. Armijos, J.L. Cortina, Simultaneous phosphate and ammonium removal from aqueous solution by a hydrated aluminum oxide modified natural zeolite, Chem. Eng. J. 271 (2015) 204–213. [31] M.R. Awual, M.A. Shenashen, A. Jyo, H. Shiwaku, T. Yaita, Preparing of novel fibrous ligand exchange adsorbent for rapid column-mode trace phosphate removal from water, J. Ind. Eng. Chem. 20 (2014) 2840–2847. [32] M.R. Awual, A. Jyo, S.A. El-Safty, M. Tamada, N. Seko, A weak-base fibrous anion exchanger effective for rapid phosphate removal from water, J. Hazard. Mater. 188 (2011) 164–171. [33] M.R. Awual, A. Jyo, Assessing of phosphorus removal by polymeric anion exchangers, Desalination 281 (2011) 111–117. [34] A.A. Rouff, A.R.O. Goswami, M.V. Ramlogan, D. Kalderis, D. Ntarlagiannis, P. Soupios (Eds.), Biochar as Sorbent for the Treatment of Inorganic Pollutants in Water and Wastewater In Non-Soil Biochar Applications, Nova Science Publishers, Inc., Hauppauge, NY, U.S.A, 2018. [35] F. Yang, S.S. Zhang, Y.Q. Sun, D.C.W. Tsang, K. Cheng, S.Y. Ok, Assembling biochar with various layered double hydroxides for enhancement of phosphorus recovery, J. Hazard. Mater. 365 (2019) 665–673. [36] H. Wang, J. Zhu, Q.L. Fu, J.W. Xiong, C. Hong, H.Q. Hu, A. Violante, Adsorption of phosphate onto ferrihydrite and ferrihydrite-humic acid complexes, Pedosphere 25 (2015) 405–414. [37] J. Chen, L.G. Yan, H.Q. Yu, S. Li, L.L. Qin, G.Q. Liu, Y.F. Li, B. Du, Efficient removal of phosphate by facile prepared magnetic diatomite and illite clay from aqueous solution, Chem. Eng. J. 287 (2016) 162–172. [38] N. Hamdi, E. Srasra, Removal of phosphate ions from aqueous solution using Tunisian clays minerals and synthetic zeolite, J. Environ. Sci. 24 (2012) 617–623. [39] Y. Liu, Q. Li, S. Gao, J.K. Shang, Exceptional As(III) sorption capacity by highly porous magnesium oxide nanoflakes made from hydrothermal synthesis, J. Am. Ceram. Soc. 94 (2011) 217–223. [40] R. Yu, H. Ren, J. Wu, X. Zhang, A novel treatment processes of struvite with pretreated magnesite as a source of low-cost magnesium, Environ. Sci. Pollu. Res. 24 (2017) 22204–22213. [41] M. Krähenbühl, B. Etter, K.M. Udert, Pretreated magnesite as a source of low-cost magnesium for producing struvite from urine in Nepal, Sci. Total Environ. 542 (2016) 1155–1161. [42] Y.Y. Pei, M. Wang, D. Tian, X.F. Xu, L.J. Yuan, Synthesis of core−shell SiO2@MgO with flower like morphology for removal of crystal violet in water, J. Colloid Interface Sci. 453 (2015) 194–201. [43] L. Yang, H. Ipan, S. Michel, D.V. Renatavan, J.N.B. Cees, Fate of calcium, magnesium and inorganic carbon in electrochemical phosphorus recovery from domestic wastewater, Chem. Eng. J. 362 (2019) 453–459. [44] A. Rabinovich, A.A. Rouff, B. Lew, M.V. Ramlogan, Aerated fluidized bed treatment for phosphate recovery from dairy and swine wastewater, ACS Sustain. Chem. Eng. 6 (2018) 652–659. [45] F.H. John, L. Cheryl, A.C. Mackowiak, W.G.H. Wilkie, Struvite phosphorus recovery from aerobically digested municipal wastewater, Sustainability 11 (2019) 376. [46] A.A. Rouff, M.V. Ramlogan, A. Rabinovich, Synergistic removal of zinc and copper in greenhouse waste effluent by struvite, ACS Sustain. Chem. Eng. 4 (2016) 1319–1327. [47] L. Pastor, D. Mangin, R. Barat, A. Seco, A pilot-scale study of struvite precipitation in a stirred tank reactor: conditions influencing the process, Bioresour. Technol. 99 (2008) 6285–6291. [48] N. Ma, A.A. Rouff, B.L. Phillips, A 31P NMR and TG/DSC-FTIR investigation of the influence of initial pH on phosphorus recovery as struvite, ACS Sustain. Chem. Eng. 2 (2014) 816–822. [49] D.D. James, A. Simon, Struvite formation, control and recovery, Water Res. 36 (2002) 3925–3940. [50] Y.S. Zhang, C.Q. Li, J.Q. Lin, Amount of alkali needed and variation patternsin phosphorus recovery process by struvite, CIESC Journal 07 (2012) 2217–2223. [51] M.S. Rahaman, D.S. Mavinic, A. Meikleham, N. Ellis, Modeling phosphorus removal and recovery from anaerobic digester supernatant through struvite crystallization in a fluidized bed reactor, Water Res. 51 (2014) 1–10.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jece.2019.103334. References [1] R.A. Duce, J. Laroche, K. Altieri, et al., Impacts of atmospheric anthropogenic nitrogen on the open ocean, Science 320 (2008) 893–897. [2] D.J. Conley, H.W. Paerl, R.W. Howarth, et al., Controlling eutrophication: nitrogen and phosphorus, Science 323 (2009) 1014–1015. [3] M.B. Rothenberger, A.J. Calomeni, Complex interactions between nutrient enrichment and zooplankton in regulating estuarine phytoplankton assemblages: microcosm experiments informed by an environmental dataset, J. Exp. Mar. Biol. Ecol. 480 (2016) 62–73. [4] United States Environmental Protection Agency, https://www.epa.gov/ nutrientpollution/sources-and-solutions. (Accessed March 16, 2019). [5] P. Wilfert, P.S. Kumar, L. Korving, G.J. Witkamp, M.C.M. Loosdrecht, The relevance of phosphorus and iron chemistry to the recovery of phosphorus from wastewater: a review, Environ. Sci. Technol. 49 (2015) 9400–9414. [6] Y.V. Nancharaiah, S.V. Mohan, P.N.L. Lens, Recent advances in nutrient removal and recovery in biological and bioelectrochemical systems, Bioresour. Technol. 215 (2016) 173–185. [7] J. Cooper, R. Lombardi, D. Boardman, The future distribution and production of global phosphate rock reserves, Resour. Conserv. Recycl. 57 (2011) 78–86. [8] D.P.V. Vuuren, A.F. Bouwman, A.H.W. Beusen, Phosphorus demand for the 1970−2100 period: a scenario analysis of resource depletion, Global Environ. Change 20 (2010) 428–439. [9] S.M. Jasinski, Phosphate rock, U.S. Geological Survey, Mineral Commodity Summaries, (2012) (accessed March 16, 2019), http://minerals.usgs.gov/minerals/ pubs/commodity/phosphaterock/mcs-2012-phosp.pdf. [10] L. Reijnders, Phosphorus resources, their depletion and conservation, a review, Resour. Conserv. Recycl. 93 (2014) 32–49. [11] X.D. Hao, F. Hiroaki, G.H. Chen, Resource recovery: efficient approaches to sustainable water and wastewater treatment, Water Res. 86 (2015) 83–84. [12] S. Karaca, A. Gurses, M. Ejder, M. Açıkyıldız, Kinetic modeling of liquid-phase adsorption of phosphate on dolomite, J. Colloid Interface Sci. 277 (2004) 257–263. [13] P. Wilfert, A. Mandalidis, A.I. Dugulan, K. Goubitz, L. Korving, H. Temmink, G.J. Witkamp, M.C.M. Van Loosdrecht, Vivianite as an important iron phosphate precipitate in sewage treatment plants, Water Res. 104 (2016) 449–460. [14] S. Wang, J. An, Y. Wan, Q. Du, X. Wang, X. Cheng, N. Li, Phosphorus competition in bioinduced vivianite recovery from wastewater, Environ. Sci. Technol. 52 (2018) 13863–13870. [15] M.R. Awual, S. Urata, A. Jyo, M. Tamada, A. Katakai, Arsenate removal from water by a weak-base anion exchange fibrous adsorbent, Water Res. 42 (2008) 689–696. [16] M.R. Awual, M.A. Hossain, M.A. Shenashen, T. Yaita, S. Suzuki, A. Jyo, Evaluating of arsenic(V) removal from water by weak-base anion exchange adsorbents, Environ. Sci. Pollut. Res. - Int. 20 (2013) 421–430. [17] M.R. Awual, A. Jyo, Rapid column-mode removal of arsenate from water by crosslinked poly (allyamine) resin, Water Res. 43 (2009) 1229–1236. [18] L. Yan, Y. Xu, H. Yu, X. Xin, Q. Wei, B. Du, Adsorption of phosphate from aqueous solution by hydroxy-aluminum, hydroxy-iron and hydroxy-iron–aluminum pillared bentonites, J. Hazard. Mater. 179 (2010) 244–250. [19] M.R. Awual, S.A. El-Safty, A. Jyo, Removal of trace arsenic(V) and phosphate from water by a highly selective ligand exchange adsorbent, J. Environ. Sci. 23 (2011) 1947–1954. [20] M.R. Awual, M.A. Shenashen, T. Yaita, H. Shiwaku, A. Jyo, Efficient arsenic(V) removal from water by ligand exchange fibrous adsorbent, Water Res. 46 (2012) 5541–5550. [21] M.R. Awual, A. Jyo, T. Iharaa, N. Seko, M. Tamada, K.T. Lim, Enhanced trace phosphate removal from water by zirconium(IV) loaded fibrous adsorbent, Water
7
Journal of Environmental Chemical Engineering 7 (2019) 103334
J. Wei, et al.
swine wastewater, Chemosphere 69 (2007) 319–324. [61] Y.H. Song, Y.R. Dai, Q. Hua, X.H. Yu, F. Qian, Effects of three kinds of organic acids on phosphorus recovery by magnesium ammonium phosphate (MAP) crystallization from synthetic swine wastewater, Chemosphere 101 (2014) 41–48. [62] D. Wyrzykowski, J. Czupryniak, T. Ossowski, L. Chmurzynski, Thermodynamic interactions of the alkaline earth metal ions with citric acid, J. Therm. Anal. Calorim. 102 (2010) 149–154. [63] X.Y. Liu, L.C. Xiang, Y.H. Song, F. Qian, X.G. Meng, The effects and mechanism of alkalinity on the phosphate recovery from anaerobic digester effluent using dolomite lime, Environ. Earth Sci. 73 (2015) 5067–5073. [64] N. Hutnik, A. Kozik, A. Mazienczuk, K. Piotrowski, B. Wierzbowska, A. Matynia, Phosphates (V) recovery from phosphorous mineral fertilizers industry wastewater by continuous struvite reaction crystallization process, Water Res. 47 (2013) 3635–3643. [65] P. Yuan, Y.H. Song, F. Yuan, J.F. Peng, Nutrient removal and recovery from swine wastewater by crystallization of magnesium ammonium phosphate, Acta Sci. Circ. 27 (2007) 1127–1134. [66] Z.M. Wang, Current situation and trend of development of magnesite in China, China Non-Metall. Mining Industry Herald 57 (2006) 6–8+23. [67] X.Y. Zhang, Ways of improving utilization level of magnesite resource in China, Conserv. Util. Miner. Resour. 04 (2008) 23–25.
[52] E. Ariyanto, K.S. Tushar, M.A. Ha, The influence of various physic-chemical process parameters on kinetics and growth mechanism of struvite crystallization, Adv. Powder Technol. 25 (2) (2014) 682–694. [53] F.J. Rubio-Rincón, C.M. Lopez-Vazquez, M. Ronteltapa, Seawater for phosphorus recovery from urine, Desalination 348 (2014) 49–56. [54] J. Dai, W.T. Tang, Y.S. Zheng, H.R. Mackeya, H.K. Chuia, M.C.M. van Loosdrecht, G.H. Chen, An exploratory study on seawater-catalysed urine phosphorus recovery (SUPR), Water Res. 66 (2014) 75–84. [55] L.A. Wendling, P. Blomberg, T. Sarlin, O. Priha, M. Arnold, Phosphorus sorption and recovery using mineral-based materials: Sorption mechanisms and potential phytoavailability, Appl. Geochem. 37 (2013) 157–169. [56] J. S. Wei; Y. H. Song, X. G. Meng, X.Y. Liu, F. Qian, Method and reagent for treatment of nitrogen and phosphorus in wastewater and resource recovery. Chinese patent (2015) open number CN106554060A. [57] C.X. Dong, G.H. He, W.J. Zheng, T.F. Bian, M. Li, D.W. Zhang, Study on antibacterial mechanism of Mg(OH)2 nanoparticles, Mater. Lett. 134 (2014) 286–289. [58] K. Bube, Uber magnesium ammonium phosphate, Anal. Bioanal. Chem. 49 (1910) 525–596. [59] Y. Jaffer, T.A. Clark, P. Pearce, S.A. Parsons, Potential phosphorus recovery by struvite formation, Water Res. 36 (2002) 1834–1842. [60] Y.H. Song, P. Yuan, B.H. Zheng, J.F. Peng, F. Yuan, Y. Gao, Nutrients removal and recovery by crystallization of magnesium ammonium phosphate from synthetic
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