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Phosphate microbial mineralization consolidation of waste incineration fly ash and removal of lead ions
Ecotoxicology and Environmental Safety 191 (2020) 110224
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Phosphate microbial mineralization consolidation of waste incineration fly ash and removal of lead ions
T
Xiaoniu Yua,b, Jianguo Jianga,∗ a b
School of Environment, Tsinghua University, Beijing, 100084, China College of Architecture and Civil Engineering, Wenzhou University, Wenzhou, 325035, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Waste incineration fly ash Heavy metal cations Chemical composition Removal efficiency Wind erosion rate
This paper proposes a green environment-friendly Bacillus subtilis to mineralize and consolidate waste incineration fly ash and heavy metal cations, and there is no harmful by-product in the mineralization process. Different phosphate products can be prepared, and are more stable than the microbially-induced carbonate precipitation (MICP) in nature. Typical heavy metal oxides were mainly PbO, ZnO, CdO, NiO, CuO and Cr2O3 in the chemical composition of waste incineration fly ash. Microstructure and chemical composition of waste incineration fly ash before and after treatment were characterized by powder X-ray diffraction (XRD) analysis and scanning electron microscopy. Scanning electron microscopy (SEM) images showed that the morphology of the Bacillus subtilis was mainly a rod-like structure. The optimal hydrolysis dosage of the organic phosphate monoester sodium salt was 0.2mol in the bacterial solution (1L, 20 g/L). The optimum required mass of the bacterial powder was 15 g/kg in treatment process of the waste incineration fly ash. The initial concentration of lead ions was 40.28 mg/L in waste incineration fly ash solution. After the optimum dosage treatment, the removal efficiency of lead ions was 78.15%, 79.64%, 77.70% and 80.14% when curing time was 1, 2, 4 and 6d, respectively. The waste incineration fly ash had a Shore hardness of 22 after the optimum amount of bacterial liquid treatment. Results of wind erosion test showed that the wind erosion rate of waste incineration fly ash was 2.6, 0, 0, 0, 0 and 0 g/h when blank group, deionized water, 100, 200, 300 and 400 mL of bacterial solutions treated, respectively. The bio-mineralization method provides an approach for the safe disposal of heavy metals in the contaminated areas of tailings, electroplating sewage, waste incineration plants, and so on.
1. Introduction The treatment of residues (waste fly ash) generated after incineration is particularly important with the widespread use of municipal solid waste incineration technology (Yan et al., 2019). Waste incineration fly ash contains a large amount of free heavy metals (Cd2+, Pb2+, Cu2+, Hg2+, etc.) and other harmful toxic substances, which eventually lead to ecosystem degradation, soil quality degradation and crop pollution, threatening human health and safety, and thus classified as dangerous materials (Li et al., 2018, 2019; Luo et al., 2019; Huber and Fellner, 2018; Fei et al., 2018; Liu et al., 2019). In addition, leached heavy metal cations can enter biological chain through media such as soil and water, and combine with animal and plant proteins, resulting in poisoning. Therefore, waste incineration fly ash must be consolidated/stabilized before it can be landfilled safely (Shiota et al., 2019). There are three major characteristics of free heavy metal cations pollution in waste incineration fly ash: (1) Covertness, (2) Long-term,
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and (3) Irreversibility (Kushwaha et al., 2018; Yu and Jiang, 2019). Treatment of heavy metals in waste incineration fly ash has become an interesting and challenging topic based on the characteristics and hazards of heavy metals. Therefore, it is necessary to take certain technical measures to effectively dispose of the waste incineration fly ash so as to achieve the purpose of non-toxicity, volume reduction and resource utilization, and avoid secondary pollution caused by waste incineration (Shiota et al., 2019). Treatment technologies of heavy metals pollution can be divided into three categories: chemical methods, physical and chemical methods, and bioremediation methods (Hwang and Jho, 2018; Shen et al., 2018; M. Li et al., 2018; Huang et al., 2018; Wang and Liu, 2018; Efome et al., 2018; Ivanets et al., 2018; Shao et al., 2018; Zhang et al., 2018; Ates and Uzal, 2018; Wang et al., 2018; Shi et al., 2016, 2017). Bioremediation methods are currently a hot research area for heavy metals pollution control, including phytoremediation and microbial adsorption/mineralization technologies (Bind et al., 2018; Kushwaha
Corresponding author. E-mail address: [email protected] (J. Jiang).
https://doi.org/10.1016/j.ecoenv.2020.110224 Received 16 November 2019; Received in revised form 30 December 2019; Accepted 15 January 2020 0147-6513/ © 2020 Elsevier Inc. All rights reserved.
Ecotoxicology and Environmental Safety 191 (2020) 110224
X. Yu and J. Jiang
harvested bacterial solution was stored in a refrigerator (4 ± 1 °C) prior to use. The organophosphate monoester solution (2.5 mol/L) was added to 1L of Bacillus subtilis solution (20 g/L) and allowed to stand for 36h (Yu and Jiang, 2019). 5 parts of waste incineration fly ash (400g) were weighed and added into 2L of beaker. 400 mL of deionized water, 100 mL of bacterial solution+300 mL of deionized water, 200 mL of bacterial solution+200 mL of deionized water, 300 mL of bacterial solution+100 mL of deionized water, and 400 mL of the bacterial solution were uniformly stirred and added to 5 parts of waste incineration fly ash (400g), respectively. After curing for 24h, 600 mL of deionized water was sequentially added to the above-mentioned waste fly ash, and was uniformly stirred. The content of lead ions in the above solution was measured at different time (1, 2, 4 and 6d).
et al., 2017; Goswami et al., 2017; Yu and Jiang, 2019). Bioremediation technology is used by the absorption, mineralization, degradation, enrichment of heavy metals by specific organisms (plants, microorganisms or protozoa) to restore the normal ecological functions of soil, wastewater and waste fly ash systems (Kushwaha et al., 2018; Goswami et al., 2019; Singh et al., 2019; Yu and Jiang, 2019). Heavy metals cations are usually converted into insoluble precipitation and removing them from soil, wastewater, and waste fly ash by bioremediation method. The biotechnology is environmental-friendly for treatment of heavy metals pollution and can achieve environmental purification and ecological effects recovery (Bind et al., 2018; Kushwaha et al., 2017, 2018; Goswami et al., 2017, 2019; Singh et al., 2019; Yu and Jiang, 2019). Different microorganisms have been applied and reported at home and abroad to control heavy metals contamination. For examples, Pseudomonas aeruginosa can biosorb lead ions in aqueous solution (Chang et al., 1997). Lead ions can also be removed by microbially-inducing PbCO3 precipitation (Qian et al., 2018). Microbial mineralization is a type of bio-mineralization function that converts free heavy metal cations into solid phase minerals (Hwang and Jho, 2018; Chen and Wang, 2007; Podda et al., 2000; Li and Qian, 2010; Yu and Qian, 2016; Jiang et al., 2019; Wang et al., 2019; Mwandira et al., 2017). Lead ions can affect the functions of the central and peripheral nervous system, cardiovascular system, reproductive system, and immune system, causing diseases of the gastrointestinal tract, liver, kidney, and brain. However, the body is damaged from high concentration of lead ions is fatal. Therefore, lead ions in waste fly ash need to be passivated before waste fly ash can be safely landfilled. There are certain shortcomings in the process of treating waste incineration fly ash based on traditional cement and microbially-induced carbonate precipitation (MICP). Urease produced-bacteria (UPB) was usually selected and used to mineralize free heavy metal cations and were converted into carbonate minerals of solid state can reduce the risk of heavy metals in water and soil (Li and Qian, 2010; Jiang et al., 2019; Qian et al., 2017, 2018). Ammonia will be prepared as a by-product during the UPB mineralization process, according to literature reported (Yu et al., 2016, 2019; Li et al., 2015). Therefore, the environmentallyfriendly of phosphate bacteria (Bacillus subtilis) was selected and used to mineralize heavy metals in waste incineration fly ash. Bacillus subtilis can secrete alkaline phosphatase (ALP), during the growth and reproduction process, to hydrolyze the substrate to form PO43− ions, which immediately combine with free heavy metal cations. Finally, free heavy metal cations are reduced and converted into phosphate precipitation in the Bacillus subtilis solution. A schematic diagram of experimental technological flows is showed in Fig. S1 (see Supplementary information). The bio-mineralization method provides an approach for the safe disposal of heavy metals in waste incineration fly ash, which has a certain practical value (Yu et al., 2018; Zhan et al., 2016).
2.2. Characterization Chemical composition of samples was determined by powder X-ray diffraction analysis (10-85°) (XRD, Bruker D8-Advance, λ = 1.5406 Å, Bruker Company, Karlsruhe, Germany). Morphological analysis of specimens was performed by scanning electron microscopy (SEM, JEOL-7800Prime, operating voltage 5 kV, JEOL, Tokyo, Japan). The particle size distribution of the waste incineration fly ash was analyzed by particle size analysis (Mastersizer Micro, Malvern Instruments Ltd., United Kingdom). The concentration of phosphate ions (PO43−) was determined by the colorimetric method of molybdenum blue (Heimann and Jakobsen, 2007; Kowalenko and Babuin, 2007). The concentration of lead ions in the solution was determined by atomic absorption spectrophotometer (AA6880, Shimadzu Corporation, Japan) (Zhan and Qian, 2016). In the wavelength of 283.3 nm, the concentration of lead ions can be calculated using the standard curve Equation (1):
Abs = 0.014687Conc − 0.0027800
(1)
where, Abs is the absorbance, and Conc represents the concentration of lead ions, mg/L. 3. Results and discussion 3.1. Chemical composition and particle size distribution of waste incineration fly ash The contents of PbO, ZnO, CdO, NiO, CuO and Cr2O3 were found to be < 0.01%, 0.07%, 0.01%, < 0.01%, 0.01% and 0.01%, respectively, by analyzing the chemical constituents of waste incineration fly ash, as shown in Table S1 (see Supplementary information). Among them, the highest content of chemical component in waste incineration fly ash was CaO (36.14%), followed by Cl (11.66%) (Table S1) (see Supplementary information). It showed that the waste incineration fly ash had higher alkali and chloride content. Fig. S2 showed that the particle size of waste incineration fly ash was mainly distributed between 1 and 100 μm. When particle size was less than 10, 52, and 98 μm, the volume fraction was 35.33%, 79.30%, and 93.90%, respectively (see Supplementary information).
2. Materials and methods 2.1. Materials Bacillus subtilis powder was selected to mineralize removal of heavy metal cations (Yancheng shenwi Microorganism Strain Co., Ltd.). Beef extract and peptone were purchased from Sinopharm Chemical Reagent Co., Ltd. Organic phosphate monoester sodium salt (Substrate, ROP) was purchased from TCI (Shanghai) Development Co., Ltd.. Deionized water was self-made. Cultivation of Bacillus subtilis: 3g of peptone and 5g of beef extract peptone were added to 1L of deionized water, stirred evenly, and the pH of the solution was adjusted to 7 in order to prepare medium solution. 1L of medium solution was divided equally and poured into 2 Erlenmeyer flasks (500 mL each). 10g of Bacillus subtilis powder was added to a medium solution, and the flask was wrapped with six layers of gauze (Yu and Jiang, 2019). Bacillus subtilis was cultured in the oscillation incubator (170 rpm, 29.0 ± 1 °C) for 24h. After 24h, the
3.2. SEM images and the powder XRD pattern of waste incineration fly ash The powder XRD pattern of waste incineration fly ash showed that the compounds in the waste fly ash were mainly Sylvite (KCl), Halite (NaCl), Cordierite (Mg2 (Al4Si5O18)), Calcium Chloride Hydroxide (CaClOH) and Portlandite (Ca(OH)2), corresponding to PDF Card No. were 99–0101, 99–0059, 99–0035, 36–0938 and 72–0156, respectively, as shown in Fig. S3 (see Supplementary information). SEM images showed that the particles structure of waste incineration fly ash was mainly irregular spheres and block morphology, and the surface of the particles was rough (Fig. 1a). Fig. 1a showed that the particle size of the waste incineration fly ash was mainly distributed between 2
Ecotoxicology and Environmental Safety 191 (2020) 110224
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Fig. 2. Catalytic mechanism of alkaline phosphatase (ALP) in Bacillus subtilis solution (Stec et al., 2000).
Fig. 3. Variation of lead ions concentration in waste incineration fly ash solution with time. Table 1 Lead ions concentration in waste incineration fly ash solid after treatment.
Fig. 1. SEM images of waste incineration fly ash (a) and Bacillus subtilis powder (b). 3
Water/Bacterial solution (mL)
Water
100
200
300
400
Concentration (mg/L)
1.02
0.98
1.02
0.65
0.74
Ecotoxicology and Environmental Safety 191 (2020) 110224
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Fig. 4. XRD patterns of the waste incineration fly ash after treatment: 100 mL (a), 200 mL (b), 300 mL (c), 400 mL (d).
10–50 μm. SEM images showed that a rod-shaped morphology was observed in the Bacillus subtilis powder was possibly bacterial body, which was identical with literature reported, as shown in Fig. 1b (Mamou et al., 2016).
Bacillus subtilis powder was selected according to literature reported (Wang, 2014). The bacteria can secrete ALP to hydrolyze organic phosphomonoester, and then obtaining PO43− ions (Wang, 2014). 3.4. Concentration change of lead ions in waste incineration fly ash solution
3.3. Hydrolyzing process of Bacillus subtilis Fig. 3 showed the concentration change of lead ions in the waste incineration fly ash at different curing time. The average concentration of lead ions after treatment with deionized water, 100, 200, 300 and 400 mL of bacterial solution was 40.28, 22.20, 13.80, 8.80 and 12.00 mg/L for 1d, respectively. It can be seen that the initial concentration of lead ions was 40.28 mg/L. The average concentration of lead ions was 21.80, 10.60, 8.20 and 10.78 mg/L for 2d, respectively. The average concentration of lead ions was 16.90, 12.20, 8.98, and 12.00 mg/L for 4d, respectively. The average concentration of lead ions was 13.85, 12.12, 8.00 and 11.90 mg/L for 6d, respectively. The optimum dosage of bacterial solution was 300 mL. Initial concentration of lead ions was 1.80 mg/L in waste incineration fly ash solid (National Environmental Protection Agency, The environmental protection industry standards of China, 2007). Lead ions concentration in waste incineration fly ash solid after treated by 100, 200, 300, and 400 mL of bacterial solution, and water, was 0.98, 1.02, 0.65, 0.74 mg/L, and 1.02 mg/L, as shown in Table 1 (National Environmental Protection Agency, The environmental protection industry standards of China, 2007). It further confirmed the optimum content of bacterial solution was 300 mL. After curing for 1, 2, 4 and 6d, removal efficiency of lead
The concentration of phosphate ions was determined to be 1.88 × 103 mg/L by the colorimetric method of molybdenum blue. Therefore, the optimal molar mass of the substrate was 0.2mol in 1L of Bacillus subtilis solution, which was consistent with the literature reported (Yu and Jiang, 2019). The catalytic process of alkaline phosphatase (ALP) is shown in Fig. 2 (Stec et al., 2000; Yu et al., 2015). The proposed mechanism and structure of alkaline phosphatase (ALP) have been reported according to literature reported (Stec et al., 2000). (1) The alkaline phosphatase-organic phosphomonoester complex (ALPROP) can be formed and coordinating oxygen atom in the ester with Zn1 (Stec et al., 2000). (2) The covalent formation of alkaline phosphatase-phosphate (ALP-P) intermediate, results in structural inversion of the phosphorus center, and then the group (RO−) is released to the solution (Stec et al., 2000). (3) A nucleophilic hydroxide ion is coordinated with Zn1 and attacking the ALP-P intermediate, forming the non-covalent alkaline phosphatase-phosphate complex (ALP-Pi) (Stec et al., 2000). (4) The water molecule is coordinated with Mg atom, which acts as a general acid, donating a proton to Or in Ser102, and then PO43− ions are obtained (Stec et al., 2000). The appropriate 4
Ecotoxicology and Environmental Safety 191 (2020) 110224
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Fig. 5. SEM images of the waste incineration fly ash after treatment: 100 mL (a, b), 200 mL (c, d), 300 mL (e, f), 400 mL (g, h).
30% I-nZVI and biosorbent (Hydrilla verticillata), respectively (Cai et al., 2019; Chathuranga et al., 2014). Lead ions can also be removed by other bio-mineralization method (microbially-induced PbCO3 precipitation) in soil and wastewater (Qian et al., 2018). The removal
ions was 78.15%, 79.64%, 77.70% and 80.14% in the optimum dosage of bacterial solution. Therefore, the optimal curing time was 1d. Compared with chemical/bio-adsorption method, the removal efficiency of Pb(II) from aqueous solution can reach 99% and 85.7% using 5
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could be effectively cured and reduced to a safe level. The waste incineration fly ash will be landfilled after treatment. Powder XRD analysis showed that compounds contained in the waste fly ash were mainly Sylvite, Halite, Cordierite, Calcium Chloride Hydroxide and Portlandite. The results of particle size analysis showed that the particles size of waste incineration fly ash was mainly distributed between 1 and 100 μm. Composition of waste incineration fly ash was complicated and crystallized poorly in XRD patterns after treatment. SEM images showed that the particles morphology of the fly ash after treatment was mainly irregular spheres and block structure, and the particle size was mainly distributed between 5–50 μm. The optimum amount of the bacterial solution was 300 mL when 400g of waste incineration fly ash were treated. The waste incineration fly ash treated by the optimum amount of bacterial solution had the highest Shore hardness of 22. The wind erosion rate of waste incineration fly ash was 0 g/h after spraying bacterial solution. Therefore, the bio-mineralization technology can be easily used for repairing heavy metals contaminated areas of tailings, electroplating sewage, waste incineration plants, and so on.
Table 2 Shore hardness of the waste incineration fly ash after treatment. Water/Bacterial solution (mL)
Blank
Water
100
200
300
400
Shore Hardness
0
12
13
16
22
18
efficiency of lead ions is 72%, when the mass of Sporosarcina pasteurii is 9.28g (Qian et al., 2018). The removal efficiency of lead ions can reach 90% more when the mass of Sporosarcina pasteurii is 12.06g (Qian et al., 2018). Lead ions can also be removed by microbially-induced lead phosphate precipitation (MIPP). In this process, no harmful by-product (ammonia gas) is released compared with microbially-induced PbCO3 precipitation. Phosphates are more stable than carbonates in nature. Therefore, the bio-mineralization method can remove effectively lead ions from waste incineration fly ash. As can be seen from Fig. 3, the concentration of lead ions was decreased with time in the waste incineration fly ash solution made by deionized water and 100 mL of bacterial solution. Because the solution was alkaline, carbon dioxide could be absorbed from the air in the alkali solution, formed carbonates, combined with lead ions formed lead carbonate precipitation, resulting in concentration decrease of lead ions. However, the concentration of lead ions in the waste incineration fly ash solution made by 200, 300 and 400 mL of bacterial solution was remained substantially unchanged with different time. Because the alkaline substance in the solution reacted with excess phosphate ions to form a calcium phosphate compound, which caused a decrease in alkalinity and a weakening ability to absorb carbon dioxide in the air. Therefore, the concentration of lead ions was remained substantially unchanged.
CRediT authorship contribution statement Xiaoniu Yu: Data curation, Formal analysis, Writing - original draft. Jianguo Jiang: Methodology, Writing - review & editing, Supervision, Validation. Declaration of competing interest The authors declare no conflict of interest. Acknowledgements
3.5. Chemical composition and microstructure of waste incineration fly ash after treatment
This work is supported by the China Postdoctoral Science Foundation (2019M650715), the National Nature Science Foundation of China (51702238), and the Opening Funds of Jiangsu Key Laboratory of Construction Materials (CM2018-02), the financial support is gratefully acknowledged.
Powder XRD patterns of the waste incineration fly ash after 100, 200, 300, and 400 mL of bacterial solution treatment showed that the composition of waste fly ash was complicated, as shown in Fig. 4. Heavy metal phosphates were not found because they crystallized poorly in XRD patterns, as shown in Fig. 4a, b, c and d. SEM images showed that the morphology of the waste incineration fly ash after treatment was irregular spheres and block structure, and the surface of particles was rough, as shown in Fig. 5. Particles size of waste incineration fly ash after 100, 200, 300, and 400 mL of bacterial solution treatment was mainly distributed between 5 and 50 μm, which was similar with the size of waste incineration fly ash before treatment (Fig. 5a, c, e and g).
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3.6. Shore hardness and wind erosion rate of the waste incineration fly ash after treatment The waste incineration fly ash was treated by 100, 200, 300, and 400 mL of bacterial liquid, water, blank had a Shore hardness of 13, 16, 22, 18, 12, and 0, respectively, as shown in Table 2. The waste incineration fly ash after treatment has the highest Shore hardness of 22 in the optimum content of bacterial solution. Results of wind erosion test were shown in Table S2 and Fig. S4 (see Supplementary information). The wind speed was 5.7–6.3 m/s. The wind erosion rate was 0, 0, 0, 0, and 2.6 g/h when the waste incineration fly ash was treated by 100, 200, 300, and 400 mL of bacterial liquid, water, blank, respectively. The wind erosion rate of the waste incineration fly ash treated by spraying deionized water and bacterial liquid was 0 g/h due to the calcium hydroxide and gypsum had a certain gelation property. 4. Conclusions Heavy metals cations contained in the waste incineration fly ash 6
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Phosphate microbial mineralization consolidation of waste incineration fly ash and removal of lead ions
T
Xiaoniu Yua,b, Jianguo Jianga,∗ a b
School of Environment, Tsinghua University, Beijing, 100084, China College of Architecture and Civil Engineering, Wenzhou University, Wenzhou, 325035, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Waste incineration fly ash Heavy metal cations Chemical composition Removal efficiency Wind erosion rate
This paper proposes a green environment-friendly Bacillus subtilis to mineralize and consolidate waste incineration fly ash and heavy metal cations, and there is no harmful by-product in the mineralization process. Different phosphate products can be prepared, and are more stable than the microbially-induced carbonate precipitation (MICP) in nature. Typical heavy metal oxides were mainly PbO, ZnO, CdO, NiO, CuO and Cr2O3 in the chemical composition of waste incineration fly ash. Microstructure and chemical composition of waste incineration fly ash before and after treatment were characterized by powder X-ray diffraction (XRD) analysis and scanning electron microscopy. Scanning electron microscopy (SEM) images showed that the morphology of the Bacillus subtilis was mainly a rod-like structure. The optimal hydrolysis dosage of the organic phosphate monoester sodium salt was 0.2mol in the bacterial solution (1L, 20 g/L). The optimum required mass of the bacterial powder was 15 g/kg in treatment process of the waste incineration fly ash. The initial concentration of lead ions was 40.28 mg/L in waste incineration fly ash solution. After the optimum dosage treatment, the removal efficiency of lead ions was 78.15%, 79.64%, 77.70% and 80.14% when curing time was 1, 2, 4 and 6d, respectively. The waste incineration fly ash had a Shore hardness of 22 after the optimum amount of bacterial liquid treatment. Results of wind erosion test showed that the wind erosion rate of waste incineration fly ash was 2.6, 0, 0, 0, 0 and 0 g/h when blank group, deionized water, 100, 200, 300 and 400 mL of bacterial solutions treated, respectively. The bio-mineralization method provides an approach for the safe disposal of heavy metals in the contaminated areas of tailings, electroplating sewage, waste incineration plants, and so on.
1. Introduction The treatment of residues (waste fly ash) generated after incineration is particularly important with the widespread use of municipal solid waste incineration technology (Yan et al., 2019). Waste incineration fly ash contains a large amount of free heavy metals (Cd2+, Pb2+, Cu2+, Hg2+, etc.) and other harmful toxic substances, which eventually lead to ecosystem degradation, soil quality degradation and crop pollution, threatening human health and safety, and thus classified as dangerous materials (Li et al., 2018, 2019; Luo et al., 2019; Huber and Fellner, 2018; Fei et al., 2018; Liu et al., 2019). In addition, leached heavy metal cations can enter biological chain through media such as soil and water, and combine with animal and plant proteins, resulting in poisoning. Therefore, waste incineration fly ash must be consolidated/stabilized before it can be landfilled safely (Shiota et al., 2019). There are three major characteristics of free heavy metal cations pollution in waste incineration fly ash: (1) Covertness, (2) Long-term,
∗
and (3) Irreversibility (Kushwaha et al., 2018; Yu and Jiang, 2019). Treatment of heavy metals in waste incineration fly ash has become an interesting and challenging topic based on the characteristics and hazards of heavy metals. Therefore, it is necessary to take certain technical measures to effectively dispose of the waste incineration fly ash so as to achieve the purpose of non-toxicity, volume reduction and resource utilization, and avoid secondary pollution caused by waste incineration (Shiota et al., 2019). Treatment technologies of heavy metals pollution can be divided into three categories: chemical methods, physical and chemical methods, and bioremediation methods (Hwang and Jho, 2018; Shen et al., 2018; M. Li et al., 2018; Huang et al., 2018; Wang and Liu, 2018; Efome et al., 2018; Ivanets et al., 2018; Shao et al., 2018; Zhang et al., 2018; Ates and Uzal, 2018; Wang et al., 2018; Shi et al., 2016, 2017). Bioremediation methods are currently a hot research area for heavy metals pollution control, including phytoremediation and microbial adsorption/mineralization technologies (Bind et al., 2018; Kushwaha
Corresponding author. E-mail address: [email protected] (J. Jiang).
https://doi.org/10.1016/j.ecoenv.2020.110224 Received 16 November 2019; Received in revised form 30 December 2019; Accepted 15 January 2020 0147-6513/ © 2020 Elsevier Inc. All rights reserved.
Ecotoxicology and Environmental Safety 191 (2020) 110224
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harvested bacterial solution was stored in a refrigerator (4 ± 1 °C) prior to use. The organophosphate monoester solution (2.5 mol/L) was added to 1L of Bacillus subtilis solution (20 g/L) and allowed to stand for 36h (Yu and Jiang, 2019). 5 parts of waste incineration fly ash (400g) were weighed and added into 2L of beaker. 400 mL of deionized water, 100 mL of bacterial solution+300 mL of deionized water, 200 mL of bacterial solution+200 mL of deionized water, 300 mL of bacterial solution+100 mL of deionized water, and 400 mL of the bacterial solution were uniformly stirred and added to 5 parts of waste incineration fly ash (400g), respectively. After curing for 24h, 600 mL of deionized water was sequentially added to the above-mentioned waste fly ash, and was uniformly stirred. The content of lead ions in the above solution was measured at different time (1, 2, 4 and 6d).
et al., 2017; Goswami et al., 2017; Yu and Jiang, 2019). Bioremediation technology is used by the absorption, mineralization, degradation, enrichment of heavy metals by specific organisms (plants, microorganisms or protozoa) to restore the normal ecological functions of soil, wastewater and waste fly ash systems (Kushwaha et al., 2018; Goswami et al., 2019; Singh et al., 2019; Yu and Jiang, 2019). Heavy metals cations are usually converted into insoluble precipitation and removing them from soil, wastewater, and waste fly ash by bioremediation method. The biotechnology is environmental-friendly for treatment of heavy metals pollution and can achieve environmental purification and ecological effects recovery (Bind et al., 2018; Kushwaha et al., 2017, 2018; Goswami et al., 2017, 2019; Singh et al., 2019; Yu and Jiang, 2019). Different microorganisms have been applied and reported at home and abroad to control heavy metals contamination. For examples, Pseudomonas aeruginosa can biosorb lead ions in aqueous solution (Chang et al., 1997). Lead ions can also be removed by microbially-inducing PbCO3 precipitation (Qian et al., 2018). Microbial mineralization is a type of bio-mineralization function that converts free heavy metal cations into solid phase minerals (Hwang and Jho, 2018; Chen and Wang, 2007; Podda et al., 2000; Li and Qian, 2010; Yu and Qian, 2016; Jiang et al., 2019; Wang et al., 2019; Mwandira et al., 2017). Lead ions can affect the functions of the central and peripheral nervous system, cardiovascular system, reproductive system, and immune system, causing diseases of the gastrointestinal tract, liver, kidney, and brain. However, the body is damaged from high concentration of lead ions is fatal. Therefore, lead ions in waste fly ash need to be passivated before waste fly ash can be safely landfilled. There are certain shortcomings in the process of treating waste incineration fly ash based on traditional cement and microbially-induced carbonate precipitation (MICP). Urease produced-bacteria (UPB) was usually selected and used to mineralize free heavy metal cations and were converted into carbonate minerals of solid state can reduce the risk of heavy metals in water and soil (Li and Qian, 2010; Jiang et al., 2019; Qian et al., 2017, 2018). Ammonia will be prepared as a by-product during the UPB mineralization process, according to literature reported (Yu et al., 2016, 2019; Li et al., 2015). Therefore, the environmentallyfriendly of phosphate bacteria (Bacillus subtilis) was selected and used to mineralize heavy metals in waste incineration fly ash. Bacillus subtilis can secrete alkaline phosphatase (ALP), during the growth and reproduction process, to hydrolyze the substrate to form PO43− ions, which immediately combine with free heavy metal cations. Finally, free heavy metal cations are reduced and converted into phosphate precipitation in the Bacillus subtilis solution. A schematic diagram of experimental technological flows is showed in Fig. S1 (see Supplementary information). The bio-mineralization method provides an approach for the safe disposal of heavy metals in waste incineration fly ash, which has a certain practical value (Yu et al., 2018; Zhan et al., 2016).
2.2. Characterization Chemical composition of samples was determined by powder X-ray diffraction analysis (10-85°) (XRD, Bruker D8-Advance, λ = 1.5406 Å, Bruker Company, Karlsruhe, Germany). Morphological analysis of specimens was performed by scanning electron microscopy (SEM, JEOL-7800Prime, operating voltage 5 kV, JEOL, Tokyo, Japan). The particle size distribution of the waste incineration fly ash was analyzed by particle size analysis (Mastersizer Micro, Malvern Instruments Ltd., United Kingdom). The concentration of phosphate ions (PO43−) was determined by the colorimetric method of molybdenum blue (Heimann and Jakobsen, 2007; Kowalenko and Babuin, 2007). The concentration of lead ions in the solution was determined by atomic absorption spectrophotometer (AA6880, Shimadzu Corporation, Japan) (Zhan and Qian, 2016). In the wavelength of 283.3 nm, the concentration of lead ions can be calculated using the standard curve Equation (1):
Abs = 0.014687Conc − 0.0027800
(1)
where, Abs is the absorbance, and Conc represents the concentration of lead ions, mg/L. 3. Results and discussion 3.1. Chemical composition and particle size distribution of waste incineration fly ash The contents of PbO, ZnO, CdO, NiO, CuO and Cr2O3 were found to be < 0.01%, 0.07%, 0.01%, < 0.01%, 0.01% and 0.01%, respectively, by analyzing the chemical constituents of waste incineration fly ash, as shown in Table S1 (see Supplementary information). Among them, the highest content of chemical component in waste incineration fly ash was CaO (36.14%), followed by Cl (11.66%) (Table S1) (see Supplementary information). It showed that the waste incineration fly ash had higher alkali and chloride content. Fig. S2 showed that the particle size of waste incineration fly ash was mainly distributed between 1 and 100 μm. When particle size was less than 10, 52, and 98 μm, the volume fraction was 35.33%, 79.30%, and 93.90%, respectively (see Supplementary information).
2. Materials and methods 2.1. Materials Bacillus subtilis powder was selected to mineralize removal of heavy metal cations (Yancheng shenwi Microorganism Strain Co., Ltd.). Beef extract and peptone were purchased from Sinopharm Chemical Reagent Co., Ltd. Organic phosphate monoester sodium salt (Substrate, ROP) was purchased from TCI (Shanghai) Development Co., Ltd.. Deionized water was self-made. Cultivation of Bacillus subtilis: 3g of peptone and 5g of beef extract peptone were added to 1L of deionized water, stirred evenly, and the pH of the solution was adjusted to 7 in order to prepare medium solution. 1L of medium solution was divided equally and poured into 2 Erlenmeyer flasks (500 mL each). 10g of Bacillus subtilis powder was added to a medium solution, and the flask was wrapped with six layers of gauze (Yu and Jiang, 2019). Bacillus subtilis was cultured in the oscillation incubator (170 rpm, 29.0 ± 1 °C) for 24h. After 24h, the
3.2. SEM images and the powder XRD pattern of waste incineration fly ash The powder XRD pattern of waste incineration fly ash showed that the compounds in the waste fly ash were mainly Sylvite (KCl), Halite (NaCl), Cordierite (Mg2 (Al4Si5O18)), Calcium Chloride Hydroxide (CaClOH) and Portlandite (Ca(OH)2), corresponding to PDF Card No. were 99–0101, 99–0059, 99–0035, 36–0938 and 72–0156, respectively, as shown in Fig. S3 (see Supplementary information). SEM images showed that the particles structure of waste incineration fly ash was mainly irregular spheres and block morphology, and the surface of the particles was rough (Fig. 1a). Fig. 1a showed that the particle size of the waste incineration fly ash was mainly distributed between 2
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Fig. 2. Catalytic mechanism of alkaline phosphatase (ALP) in Bacillus subtilis solution (Stec et al., 2000).
Fig. 3. Variation of lead ions concentration in waste incineration fly ash solution with time. Table 1 Lead ions concentration in waste incineration fly ash solid after treatment.
Fig. 1. SEM images of waste incineration fly ash (a) and Bacillus subtilis powder (b). 3
Water/Bacterial solution (mL)
Water
100
200
300
400
Concentration (mg/L)
1.02
0.98
1.02
0.65
0.74
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Fig. 4. XRD patterns of the waste incineration fly ash after treatment: 100 mL (a), 200 mL (b), 300 mL (c), 400 mL (d).
10–50 μm. SEM images showed that a rod-shaped morphology was observed in the Bacillus subtilis powder was possibly bacterial body, which was identical with literature reported, as shown in Fig. 1b (Mamou et al., 2016).
Bacillus subtilis powder was selected according to literature reported (Wang, 2014). The bacteria can secrete ALP to hydrolyze organic phosphomonoester, and then obtaining PO43− ions (Wang, 2014). 3.4. Concentration change of lead ions in waste incineration fly ash solution
3.3. Hydrolyzing process of Bacillus subtilis Fig. 3 showed the concentration change of lead ions in the waste incineration fly ash at different curing time. The average concentration of lead ions after treatment with deionized water, 100, 200, 300 and 400 mL of bacterial solution was 40.28, 22.20, 13.80, 8.80 and 12.00 mg/L for 1d, respectively. It can be seen that the initial concentration of lead ions was 40.28 mg/L. The average concentration of lead ions was 21.80, 10.60, 8.20 and 10.78 mg/L for 2d, respectively. The average concentration of lead ions was 16.90, 12.20, 8.98, and 12.00 mg/L for 4d, respectively. The average concentration of lead ions was 13.85, 12.12, 8.00 and 11.90 mg/L for 6d, respectively. The optimum dosage of bacterial solution was 300 mL. Initial concentration of lead ions was 1.80 mg/L in waste incineration fly ash solid (National Environmental Protection Agency, The environmental protection industry standards of China, 2007). Lead ions concentration in waste incineration fly ash solid after treated by 100, 200, 300, and 400 mL of bacterial solution, and water, was 0.98, 1.02, 0.65, 0.74 mg/L, and 1.02 mg/L, as shown in Table 1 (National Environmental Protection Agency, The environmental protection industry standards of China, 2007). It further confirmed the optimum content of bacterial solution was 300 mL. After curing for 1, 2, 4 and 6d, removal efficiency of lead
The concentration of phosphate ions was determined to be 1.88 × 103 mg/L by the colorimetric method of molybdenum blue. Therefore, the optimal molar mass of the substrate was 0.2mol in 1L of Bacillus subtilis solution, which was consistent with the literature reported (Yu and Jiang, 2019). The catalytic process of alkaline phosphatase (ALP) is shown in Fig. 2 (Stec et al., 2000; Yu et al., 2015). The proposed mechanism and structure of alkaline phosphatase (ALP) have been reported according to literature reported (Stec et al., 2000). (1) The alkaline phosphatase-organic phosphomonoester complex (ALPROP) can be formed and coordinating oxygen atom in the ester with Zn1 (Stec et al., 2000). (2) The covalent formation of alkaline phosphatase-phosphate (ALP-P) intermediate, results in structural inversion of the phosphorus center, and then the group (RO−) is released to the solution (Stec et al., 2000). (3) A nucleophilic hydroxide ion is coordinated with Zn1 and attacking the ALP-P intermediate, forming the non-covalent alkaline phosphatase-phosphate complex (ALP-Pi) (Stec et al., 2000). (4) The water molecule is coordinated with Mg atom, which acts as a general acid, donating a proton to Or in Ser102, and then PO43− ions are obtained (Stec et al., 2000). The appropriate 4
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Fig. 5. SEM images of the waste incineration fly ash after treatment: 100 mL (a, b), 200 mL (c, d), 300 mL (e, f), 400 mL (g, h).
30% I-nZVI and biosorbent (Hydrilla verticillata), respectively (Cai et al., 2019; Chathuranga et al., 2014). Lead ions can also be removed by other bio-mineralization method (microbially-induced PbCO3 precipitation) in soil and wastewater (Qian et al., 2018). The removal
ions was 78.15%, 79.64%, 77.70% and 80.14% in the optimum dosage of bacterial solution. Therefore, the optimal curing time was 1d. Compared with chemical/bio-adsorption method, the removal efficiency of Pb(II) from aqueous solution can reach 99% and 85.7% using 5
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could be effectively cured and reduced to a safe level. The waste incineration fly ash will be landfilled after treatment. Powder XRD analysis showed that compounds contained in the waste fly ash were mainly Sylvite, Halite, Cordierite, Calcium Chloride Hydroxide and Portlandite. The results of particle size analysis showed that the particles size of waste incineration fly ash was mainly distributed between 1 and 100 μm. Composition of waste incineration fly ash was complicated and crystallized poorly in XRD patterns after treatment. SEM images showed that the particles morphology of the fly ash after treatment was mainly irregular spheres and block structure, and the particle size was mainly distributed between 5–50 μm. The optimum amount of the bacterial solution was 300 mL when 400g of waste incineration fly ash were treated. The waste incineration fly ash treated by the optimum amount of bacterial solution had the highest Shore hardness of 22. The wind erosion rate of waste incineration fly ash was 0 g/h after spraying bacterial solution. Therefore, the bio-mineralization technology can be easily used for repairing heavy metals contaminated areas of tailings, electroplating sewage, waste incineration plants, and so on.
Table 2 Shore hardness of the waste incineration fly ash after treatment. Water/Bacterial solution (mL)
Blank
Water
100
200
300
400
Shore Hardness
0
12
13
16
22
18
efficiency of lead ions is 72%, when the mass of Sporosarcina pasteurii is 9.28g (Qian et al., 2018). The removal efficiency of lead ions can reach 90% more when the mass of Sporosarcina pasteurii is 12.06g (Qian et al., 2018). Lead ions can also be removed by microbially-induced lead phosphate precipitation (MIPP). In this process, no harmful by-product (ammonia gas) is released compared with microbially-induced PbCO3 precipitation. Phosphates are more stable than carbonates in nature. Therefore, the bio-mineralization method can remove effectively lead ions from waste incineration fly ash. As can be seen from Fig. 3, the concentration of lead ions was decreased with time in the waste incineration fly ash solution made by deionized water and 100 mL of bacterial solution. Because the solution was alkaline, carbon dioxide could be absorbed from the air in the alkali solution, formed carbonates, combined with lead ions formed lead carbonate precipitation, resulting in concentration decrease of lead ions. However, the concentration of lead ions in the waste incineration fly ash solution made by 200, 300 and 400 mL of bacterial solution was remained substantially unchanged with different time. Because the alkaline substance in the solution reacted with excess phosphate ions to form a calcium phosphate compound, which caused a decrease in alkalinity and a weakening ability to absorb carbon dioxide in the air. Therefore, the concentration of lead ions was remained substantially unchanged.
CRediT authorship contribution statement Xiaoniu Yu: Data curation, Formal analysis, Writing - original draft. Jianguo Jiang: Methodology, Writing - review & editing, Supervision, Validation. Declaration of competing interest The authors declare no conflict of interest. Acknowledgements
3.5. Chemical composition and microstructure of waste incineration fly ash after treatment
This work is supported by the China Postdoctoral Science Foundation (2019M650715), the National Nature Science Foundation of China (51702238), and the Opening Funds of Jiangsu Key Laboratory of Construction Materials (CM2018-02), the financial support is gratefully acknowledged.
Powder XRD patterns of the waste incineration fly ash after 100, 200, 300, and 400 mL of bacterial solution treatment showed that the composition of waste fly ash was complicated, as shown in Fig. 4. Heavy metal phosphates were not found because they crystallized poorly in XRD patterns, as shown in Fig. 4a, b, c and d. SEM images showed that the morphology of the waste incineration fly ash after treatment was irregular spheres and block structure, and the surface of particles was rough, as shown in Fig. 5. Particles size of waste incineration fly ash after 100, 200, 300, and 400 mL of bacterial solution treatment was mainly distributed between 5 and 50 μm, which was similar with the size of waste incineration fly ash before treatment (Fig. 5a, c, e and g).
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.ecoenv.2020.110224. References Ates, N., Uzal, N., 2018. Removal of heavy metals from aluminum anodic oxidation wastewaters by membrane filtration. Environ. Sci. Pollut. Res. 25, 22259–22272. Bind, A., Goswami, L., Prakash, V., 2018. Comparative analysis of floating and submerged macrophytes for heavy metal (copper, chromium, arsenic and lead) removal: sorbent preparation, characterization, regeneration and cost estimation. Geol. Ecol. Landscap. 2, 61–72. Cai, X.Q., Yu, X.H., Yu, X.N., Wu, Z.X., Li, S.Q., Yu, C., 2019. Synthesis of illite/iron nanoparticles and their application as an adsorbent of lead ions. Environ. Sci. Pollut. Res. 26, 29449–29459. Chang, J.S., Law, R., Chang, C.C., 1997. Biosorption of lead, copper and cadmium by biomass of Pseudomonas aeruginosa PU21. Water Res. 31, 1651–1658. Chathuranga, P.D., Dissanayake, D.M.R.E.A., Priyantha, N., Iqbal, S.S., Mohamed Iqbal, M.C., 2014. Biosorption and desorption of lead (II) by Hydrilla verticillata. Bioremediat. J. 18, 192–203. Chen, C., Wang, J.Y., 2007. Influence of metal ionic characteristics on their bio-sorption capacity by Saccharomyces cerevisiae. Appl. Microbiol. Biotechnol. 74, 911–917. Efome, J.E., Rana, D., Matsuura, T., Lan, C.Q., 2018. Insight studies on metal-organic framework nanofibrous membrane adsorption and activation for heavy metal ions removal from aqueous solution. ACS Appl. Mater. Interfaces 10, 18619–18629 2018. Fei, F., Wen, Z., Huang, S., De Clercq, D., 2018. Mechanical biological treatment of municipal solid waste: energy efficiency, environmental impact and economic feasibility analysis. J. Clean. Prod. 178, 731–739. Goswami, L., Kumar, R.V., Pakshirajan, K., Pugazhenthi, G., 2019. A novel integrated biodegradation—microfiltration system for sustainable wastewater treatment and energy recovery. J. Hazard Mater. 365, 707–715. Goswami, L., Manikandan, N.A., Pakshirajan, K., Pugazhenthi, G., 2017. Simultaneous heavy metal removal and anthracene biodegradation by the oleaginous bacteria Rhodococcus opacus. Biotech 7, 37.
3.6. Shore hardness and wind erosion rate of the waste incineration fly ash after treatment The waste incineration fly ash was treated by 100, 200, 300, and 400 mL of bacterial liquid, water, blank had a Shore hardness of 13, 16, 22, 18, 12, and 0, respectively, as shown in Table 2. The waste incineration fly ash after treatment has the highest Shore hardness of 22 in the optimum content of bacterial solution. Results of wind erosion test were shown in Table S2 and Fig. S4 (see Supplementary information). The wind speed was 5.7–6.3 m/s. The wind erosion rate was 0, 0, 0, 0, and 2.6 g/h when the waste incineration fly ash was treated by 100, 200, 300, and 400 mL of bacterial liquid, water, blank, respectively. The wind erosion rate of the waste incineration fly ash treated by spraying deionized water and bacterial liquid was 0 g/h due to the calcium hydroxide and gypsum had a certain gelation property. 4. Conclusions Heavy metals cations contained in the waste incineration fly ash 6
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