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1.
PLoS One ; 15(8): e0236745, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32785276

RESUMO

Mineral precipitation via microbial activity is a well-known process with applications in various fields. This relevance of microbially induced calcite precipitation (MICP) has pushed researchers to explore various naturally occurring MICP capable bacterial strains. The present study was performed to explore the efficiency of microbially induced calcite precipitation (MICP) via locally isolated bacterial strains and role of guar gum, which is a naturally occurring polymer, on the MICP process. The strains were isolated from local soil and screened for urease activity Further, the urease positive strain was subjected to urea and calcium chloride based medium to investigate the efficacy of isolated strain for microbial induced precipitation. Among screened isolates, the soil bacterium that showed urease positive behaviour and precipitated calcium carbonate was subjected to 16S rRNA gene sequencing. This strain was identified as Bacillus velezensis. Guar gum-a natural polymer, was used as a sole carbon source to enhance the MICP process. It was observed that the isolated strain was able to breakdown the guar gum into simple sugars resulting in two-fold increase in calcium carbonate precipitate. Major bio-chemical activities of isolated strain pertaining to MICP such as ammonium ion concentration, pH profiling, and total reducing sugar with time were explored under four different concentrations of guar gum (0.25%, 0.5%, 0.75% and 1% w/v). Maximum ammonium ion concentration (17.5 µg/ml) and increased pH was observed with 1% guar gum supplementation, which confirms augmented MICP activity of the bacterial strain. Microstructural analysis of microbial precipitation was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, which confirmed the presence of calcium carbonate in different phases. Further, XRD and SEM based studies corroborated that guar gum supplemented media showed significant increase in stable calcite phase as compared to media without guar gum supplementation. Significant diverse group of nitrogenous compounds were observed in guar gum supplemented medium when subjected to Gas Chromatography-Mass spectrometry (GC-MS) profiling.


Assuntos
Bacillus/metabolismo , Carbonato de Cálcio/química , Carbonato de Cálcio/metabolismo , Galactanos/química , Mananas/química , Gomas Vegetais/química , Precipitação Química
2.
PLoS One ; 15(7): e0235793, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32634162

RESUMO

Extracellular vesicles (EVs) are small vesicles secreted from cells. They have crucial biological functions in intercellular communications and may even be biomarkers for cancer. The various methods used to isolate EVs from body fluid and cell culture supernatant have been compared in prior studies, which determined that the component yield and physical properties of isolated EVs depend largely on the isolation method used. Several novel and combined methods have been recently developed, which have not yet been compared to the established methods. Therefore, the purpose of this study is to compare the physical and functional differences in EVs isolated using a differential centrifugation method, the precipitation-based Invitrogen kit, the ExoLutE kit, and the Exodisc, of which the latter two were recently developed. We investigated the properties of EVs isolated from non-infected and Kaposi's sarcoma-associated herpesvirus-infected human umbilical vein endothelial cells using each method and determined the yields of DNA, RNA, and proteins using quantitative polymerase chain reaction and bicinchoninic acid assays. Additionally, we determined whether the biological activity of EVs correlated with the quantity or physical properties of the EVs isolated using different methods. We found that Exodisc was the most suitable method for obtaining large quantities of EVs, which might be useful for biomarker investigations, and that the EVs separated using Exodisc exhibited the highest complement activation activity. However, we also found that the functional properties of EVs were best maintained when differential centrifugation was used. Effective isolation is necessary to study EVs as tools for diagnosing cancer and our findings may have relevant implications in the field of oncology by providing researchers with data to assist their selection of a suitable isolation method.


Assuntos
Fracionamento Celular/métodos , Células Endoteliais/química , Vesículas Extracelulares/química , Biomarcadores/análise , Centrifugação/métodos , Precipitação Química , DNA/análise , Células Endoteliais/virologia , Vesículas Extracelulares/virologia , Infecções por Herpesviridae/virologia , Herpesvirus Humano 8/isolamento & purificação , Células Endoteliais da Veia Umbilical Humana , Humanos , Proteínas/análise , RNA/análise
3.
Water Sci Technol ; 81(7): 1329-1335, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32616685

RESUMO

Chemical precipitation with the addition of ferric chloride is commonly used to remove phosphorus from wastewater. However, since its application also involves several disadvantages, alternative solutions are required. The present paper shows the results of a full-scale experimental work aimed at evaluating the efficiency of the ion exchange process using a polymeric anion exchange resin impregnated with aluminum ions in the removal of phosphorus from wastewater. The study compared the results obtained through this process with chemical precipitation, considering both technical and economic issues. At the same dosage of 6 L/hour and influent concentration (about 6 mg/L), total removal efficiency of 95% and 78% (including also that occurring in the mechanical and biological processes) was achieved by means of the anion exchange process and chemical precipitation, respectively. However, in the latter case, this value was insufficient to ensure consistent compliance with the limit of 2 mg/L Ptot set on the effluent; to achieve this goal, the ferric chloride dosage had to be raised to 12 L/hour, thus increasing the related costs. Furthermore, the anion exchange process generated a lower sludge production. Therefore, the ion exchange process represents a valid alternative to chemical precipitation for P removal from wastewater.


Assuntos
Fósforo , Águas Residuárias , Precipitação Química , Troca Iônica , Esgotos , Eliminação de Resíduos Líquidos
4.
Chemosphere ; 258: 127275, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32535445

RESUMO

Clay minerals are widely used to treat sewage containing heavy metals such as zinc and cadmium. In this study, the chemical reactivity of natural serpentine was signally improved through mechanochemical activation, achieving the efficient separation of Zn(Ⅱ) and Cd(Ⅱ) ions in a mixed solution. The activated serpentine would release a large amount of Mg2+ and OH- and thereby selectively precipitate Zn(Ⅱ) ions as an uncommon metamorphic zinc mineral, bechererite, in the presence of SO42-. By adjusting the parameters including grinding intensity, reaction temperature, serpentine dosage and salt species, the optimum conditions were determined and a 92% separation rate of Zn(Ⅱ) and Cd(Ⅱ) ions was achieved. The mechanochemical activation of natural clay minerals expresses a great potential for purification of heavy metal contaminated sewage, as well as the simultaneous separation and recovery of multi-metal secondary resources.


Assuntos
Asbestos Serpentinas/química , Cádmio/isolamento & purificação , Zinco/isolamento & purificação , Precipitação Química , Esgotos/química , Soluções , Sulfatos/química
5.
Sci Total Environ ; 740: 140194, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-32563888

RESUMO

Urea hydrolysis is an initiating step of microbially induced calcium carbonate precipitation (MICP) which can be used as a stabilization technology in heavy metals contaminated soil. In this study, inhibition of urea hydrolysis was investigated in Cu-contaminated soil. At soil Cu concentration from 0 to 1000 mg/kg, the amount of urea hydrolyzed (i.e., initial urea 450 mM) ranged from 449.3 ± 1.4 to 10.5 ± 0.8 mM. Correspondingly, decrease in calcium carbonate precipitation was commensurate with the inhibition of urea hydrolysis. Interestingly, 2.75 times more urea were hydrolyzed in 350 days-aged soil than in freshly spiked soil even at the same soil Cu concentration of 250 mg/kg, suggesting the inhibitory effect of Cu in soil solution. Indeed, the concentrations of Cu in soil solution were 4.9 ± 0.1 and 21.0 ± 0.3 mg/L, respectively. Since MICP application involved an increase in Ca2+ concentration in soil, its effect was also determined. In the freshly spiked soil with 250 mg-Cu/kg, the Cu concentration in the soil solution increased from 7.6 ± 0.1 to 21.0 ± 0.3 mg/L as the calcium concentration increased from 0 to 450 mM. Accordingly, urea hydrolysis was significantly reduced from 217.5 ± 59.0 to 11.9 ± 0.2 mM. The effect of pH was also determined, showing that 32.8 ± 3.4 and 205.9 ± 32.5 mM of urea was hydrolyzed at soil pH of 4.5 and 7.8, respectively. The reason was attributed to the great difference in free Cu concentration in soil solution (i.e., 3.3 and 0.3 mg/L at pH 4.5 and 7.8, respectively). The relationship between amounts of urea hydrolyzed and free Cu concentrations was established and half-maximal inhibition concentration (IC50) of free Cu concentration in soil solution was predicted to be 0.39 mg/L.


Assuntos
Carbonato de Cálcio , Solo , Precipitação Química , Concentração de Íons de Hidrogênio , Hidrólise , Ureia
6.
World J Microbiol Biotechnol ; 36(6): 90, 2020 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-32524202

RESUMO

A chitinolytic bacterium Chitinophaga sp. S167 producing extracellular chitinases was isolated from a soil sample in India. The extracellular chitinases produced by S167 were concentrated by ammonium sulphate precipitation (AS70) and seven bands corresponding to chitinases were observed by zymography. Optimum temperature and pH of AS70 were between 40 and 45 °C and pH 6.0 respectively with high stability at 20-40 °C and pH 5-7. AS70 inhibited the growth of Fusarium oxysporum, Alternaria alternata and Cladosporium sp. in vitro. The culture conditions for the high level production of extracellular chitinases were optimized resulting in 48-folds higher chitinase production. As the combination of chitinases could be more potent in biocontrol of plant diseases, it was checked if AS70 could control postharvest fungal infection caused by Fusarium oxysporum on tomatoes. AS70 treated tomatoes showed significant lower incidence of infection (11%) by F. oxysporum as compared with 100% in the control at 5 days post inoculation. Further, AS70 caused significant mortality in second stage juveniles of root knot nematode, Meloidogyne incognita, a major agriculture pest responsible for economic losses in agriculture. This study highlights the antifungal and nematicidal activity of chitinases produced by Chitinophaga sp. S167. To the best of our knowledge, this is the first report of the biocontrol potential of the chitinases produced by Chitinophaga sp.


Assuntos
Antifúngicos/farmacologia , Bacteroidetes/isolamento & purificação , Quitinases/farmacologia , Doenças das Plantas/prevenção & controle , Alternaria/efeitos dos fármacos , Sulfato de Amônio , Bacteroidetes/enzimologia , Precipitação Química , Quitinases/metabolismo , Cladosporium/efeitos dos fármacos , Estabilidade Enzimática , Fusarium/efeitos dos fármacos , Concentração de Íons de Hidrogênio , Microbiologia do Solo , Temperatura
7.
J Chromatogr A ; 1624: 461258, 2020 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-32540083

RESUMO

Lithium ion batteries are essential power sources in portable electronics, electric vehicles and as energy storage devices for renewable energies. During harsh battery cell operation as well as at elevated temperatures, the electrolyte decomposes and inter alia organo(fluoro)phosphates are formed due to hydrolysis of the conducting salt lithium hexafluorophosphate (LiPF6). Since these phosphorus-containing decomposition products possess a potential toxicity based on structural similarities compared to chemical warfare agents, quantification is of high interest regarding safety estimates. In this study, two comprehensive approaches for the precipitation of highly concentrated PF6¯ were investigated, allowing the separation from target analytes (organo(fluoro)phosphates) and improving mass spectrometry-based quantification techniques. Trimethyl phosphate was used as a polar, non-acidic organophosphate reference substance for method development via liquid chromatography-mass spectrometry. Six solvents were examined regarding precipitation reaction and selectivity. Thermally degraded electrolytes were analyzed after precipitation by means of gas chromatography-flame ionization detector, demonstrating the applicability of the developed sample preparations. The optimized method was applied successfully without influencing any volatile and non-acidic decomposition products. Using optimized conditions, a precipitation rate of 98% PF6¯ was achieved. Consequently, a fast and easy sample preparation for gas chromatographic investigations on lithium ion battery electrolytes was implemented, applicable for routine analysis.


Assuntos
Cromatografia Gasosa/métodos , Fontes de Energia Elétrica , Eletrólitos/química , Lítio/química , Organofosfatos/análise , Precipitação Química , Cromatografia Líquida de Alta Pressão , Íons , Organofosfatos/química , Solventes/química
8.
Water Sci Technol ; 81(6): 1130-1136, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32597400

RESUMO

Heavy metal pollution has become one of the most serious environmental problems today. The preparation of magnesium hydroxy carbonate from low-grade magnesite, and the chemical precipitation of heavy metal wastewater with magnesium hydroxy carbonate as precipitating agent were undertaken. The removal efficiencies of heavy metals were improved by increasing the dose of magnesium hydroxy carbonate, and the applicable dose of magnesium hydroxy carbonate was 0.30 g for 50 mL of the wastewater (6,000 mg/L). The precipitation reactions proceeded thoroughly within 20 min. At this time, the removal efficiencies of heavy metals were above 99.9%. The final pH value was 7.1, the residual VO2+, Cr3+ and Fe3+ concentrations were 0.01, 0.05 and 1.12 mg/L, respectively, which conformed to the limit of discharge set by China (0.5-2.0 mg/L, GB 8978-1996). The precipitate was mainly composed of Fe2O3, V2O5 and Cr2O3, which can be recycled as secondary raw material for metallurgical industry. The treatment of the heavy metal wastewater with magnesium hydroxy carbonate was successful in decreasing the concentrations of VO2+, Cr3+ and Fe3+ in wastewater.


Assuntos
Metais Pesados , Águas Residuárias , Carbonatos , Precipitação Química , China , Magnésio
9.
Food Chem ; 327: 126998, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32438264

RESUMO

Cold-pressed rapeseed meal with high protein content (38.76% protein dry weight basis) was used to prepare rapeseed protein isolates (RPIs) by alkaline extraction (pH 8.0, 9.0, 10.0, 11.0, 12.0 and 13.0) and acid precipitation (pH 3.0, 3.5, 4.0, 4.5, 5.0 and 5.5). The protein with an intact structure and the highest yield (65.08%) was obtained at extraction pH 9.0 and precipitation pH 4.5, accompanied by the lowest D-amino acid content, the lightest colour and the lowest contents of glucosinolates (2.85 mmol/kg), phytic acid (1.05 mg/g) and sinapine (0.68 mg/g). Additionally, water/oil absorption, foaming and emulsifying capacities decreased with decreasing precipitation pH, while the solubility showed the reverse trend. During gastric simulation digestion, the α-polypeptide of cruciferin and napin in the RPIs showed digestive resistance. Overall, pH regulation might be an effective method to isolate high quality RPIs for use in the food processing industry.


Assuntos
Brassica napus/química , Proteínas de Plantas/isolamento & purificação , Proteínas de Plantas/farmacocinética , Albuminas 2S de Plantas/farmacocinética , Aminoácidos/análise , Aminoácidos/química , Antígenos de Plantas , Precipitação Química , Cor , Digestão , Emulsificantes/química , Indústria de Processamento de Alimentos/métodos , Glucosinolatos/análise , Concentração de Íons de Hidrogênio , Ácido Fítico/análise , Proteínas de Plantas/química , Óleo de Brassica napus/química , Proteínas de Armazenamento de Sementes/farmacocinética , Solubilidade
10.
Chemosphere ; 255: 126977, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32402891

RESUMO

The simultaneous removal of nitrate (15 mg N-NO3- L-1) and phosphate (12 mg P-PO43- L-1) from nutrient-polluted synthetic water was investigated in a recirculated pyrite-packed biofilter (RPPB) under hydraulic retention time (HRT) ranging from 2 to 11 h. HRT values ≥ 8 h resulted in nitrate and phosphate average removal efficiency (RE) higher than 90% and 70%, respectively. Decrease of HRT to 2 h significantly reduced the RE of both nitrogen and phosphorus. The RPPB showed high resiliency as reactor performance recovered immediately after HRT increase to 5 h. Solid-phase characterization of pyrite granules and backwashing material collected from the RPPB at the end of the study revealed that iron-phosphate, -hydroxide and -sulfate precipitated in the bioreactor. Thermodynamic modeling predicted the formation of S0 during the study. Residence time distribution tests showed semi-complete mixing hydrodynamic flow conditions in the RPPB. The RPPB can be considered an elegant and low-cost technology coupling biological nitrogen removal to the recovery of phosphorus, iron and sulfur via chemical precipitation.


Assuntos
Reatores Biológicos , Desnitrificação , Filtração/métodos , Ferro , Fósforo/isolamento & purificação , Sulfetos , Precipitação Química , Filtração/instrumentação , Ferro/isolamento & purificação , Nitrogênio/isolamento & purificação , Enxofre/química , Enxofre/isolamento & purificação
11.
J Environ Sci (China) ; 93: 164-169, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32446452

RESUMO

There are good prospects for phosphorus recovery from excess sludge by vivianite crystallization while a large number of extracellular polymeric substances in sludge will have impact on vivianite precipitation. In this study, as a representative of extracellular polymeric substance, the effect of sodium alginate (SA) on phosphorus recovery by vivianite precipitation under different initial SA concentrations (0-800 mg/L), pH values (6.5-9.0) and Fe/P molar ratios (1:1-2.4:1) was investigated using synthetic wastewater. The results showed that SA in low concentrations (≤400 mg/L) had little inhibitory effect on the phosphorus recovery rate. However, when the concentration of SA was larger than 400 mg/L, the phosphorus recovery rate decreased significantly with increasing SA concentrations. The inhibition rate of 800 mg/L SA was about 3 times as large as that of 400 mg/L SA. It was worth noting that the inhibitory effect of SA on vivianite precipitation decreased with increasing initial pH and Fe/P molar ratios. Additionally, SA has no obvious influence on the composition of products, but the morphology of harvested crystals was transformed from branches to plates or rods in uneven sizes.


Assuntos
Fósforo , Eliminação de Resíduos Líquidos , Alginatos , Precipitação Química , Matriz Extracelular de Substâncias Poliméricas , Compostos Ferrosos , Fosfatos , Esgotos
12.
J Environ Manage ; 264: 110419, 2020 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-32250884

RESUMO

The stability of carbonate products resulting from microbially induced carbonate precipitation (MICP) under acid rain is under question. The present study investigated the stability of CaCO3 precipitated by MICP in soil under simulated acid rain (SAR). Soils were treated continuously for two months with four SAR pH levels: 3.5, 4.5, 5.5, and 7.0. During SAR, biostimulation using nutrient broth containing urea and calcium chloride was adopted to ensure CaCO3 precipitation. At the end of treatments, soil samples from top and bottom layers were analyzed for bacterial diversity by Illumina MiSeq sequencing, Fourier transform infrared (FTIR) spectroscopy for identification of chemical functional groups related to calcite precipitation, and X-ray diffraction (XRD) for identification of the main crystalline phases. The analysis identified several ureolytic bacteria mainly from Arthrobacter and Sporosarcina genera in SAR-treated soils accelerated with biostimulation, and urease quantities of greater than 300 mg NH4+ per kg soil at all pH levels. The precipitation of CaCO3 was pronounced and its stability was maintained even when the pH was as low as 3.5. The results obtained in this study are helpful to the scientific community to ensure the immobilization of heavy metals with microbial carbonate precipitation in soil under acid rain.


Assuntos
Chuva Ácida , Sporosarcina , Carbonato de Cálcio , Carbonatos , Precipitação Química , Solo
14.
J Environ Manage ; 259: 109783, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32072952

RESUMO

Large volume of wastewater consisting complex forms of organics, lipids and nutrients, is discharged from the abattoir (red meat) processing industry. In this study, nutrient rich pre-Anaerobic Membrane Bioreactor (AnMBR) treated abattoir effluent was fed to a struvite (MgNH4PO4.6H2O) precipitator to evaluate the possibility of developing an innovative environmentally sustainable treatment technology to produce nutrient free high-quality treated effluent. A series of continuous and batch experiments were conducted to investigate the influence of pH and presence of Ca2+ on struvite precipitation. The study found that Mg2+:Ca2+ molar ratio of 0.8 (or high Ca2+) impacts on the production and quality of struvite significantly. Pre-AnMBR treated abattoir wastewater with negligible Ca2+ (Mg2+:Ca2+ molar ratio > 20) showed over 80% removal of phosphorus via struvite precipitation. The highest removal rates of both nitrogen and phosphorus were achieved at pH 9.5 with Mg2+:PO43- molar ratio of 2:1.


Assuntos
Matadouros , Águas Residuárias , Reatores Biológicos , Precipitação Química , Nutrientes , Fosfatos , Fósforo , Estruvita , Eliminação de Resíduos Líquidos
15.
Environ Sci Technol ; 54(6): 3618-3627, 2020 03 17.
Artigo em Inglês | MEDLINE | ID: mdl-32049503

RESUMO

Source separation of urine can enable nutrient recycling, facilitate wastewater management, and conserve water. Without stabilization of the urine, urea is quickly hydrolyzed into ammonia and (bi)carbonate, causing nutrient loss, clogging of collection systems, ammonia volatilization, and odor nuisance. In this study, electrochemically induced precipitation and stabilization of fresh urine was successfully demonstrated. By recirculating the urine over the cathodic compartment of an electrochemical cell, the pH was increased due to the production of hydroxyl ions at the cathode. The pH increased to 11-12, decreasing calcium and magnesium concentrations by >80%, and minimizing scaling and clogging during downstream processing. At pH 11, urine could be stabilized for one week, while an increase to pH 12 allowed urine storage without urea hydrolysis for >18 months. By a smart selection of membranes [anion exchange membrane (AEM) with a cation exchange membrane (CEM) or a bipolar membrane (BPM)], no chemical input was required in the electrochemical cell and an acidic stream was produced that can be used to periodically rinse the electrochemical cell and toilet. On-site electrochemical treatment, close to the toilet, is a promising new concept to minimize clogging in collection systems by forcing controlled precipitation and to inhibit urea hydrolysis during storage until further treatment in more centralized nutrient recovery plants.


Assuntos
Aparelho Sanitário , Águas Residuárias , Amônia , Precipitação Química , Hidrólise , Reciclagem , Urina
16.
Chemosphere ; 247: 125963, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32069729

RESUMO

Lead (Pb) pollution in the soil is becoming more and more serious, and lead poisoning incidents also constantly occur. Therefore, the remediation of lead pollution in the soil has attracted widespread attention. In this study, heavy metal lead in soil was remediated by mechanochemical methods. The effects of different ball milling conditions on the toxic leaching concentration and morphological distribution (BCR sequential extraction procedure) of lead in contaminated soil were analyzed, including the addition of calcium dihydrogen phosphate (Ca(H2PO4)2), ball milling time, and ball milling speed. The reaction mechanism was analyzed by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and a laser particle size analyzer. The results show that the optimal conditions for mechanochemical immobilization were 10% additive (Ca(H2PO4)2), milling speed of 550 rpm, and ball milling time for 2 h. Under this condition, the toxic leaching concentration of lead from contaminated soil was 4.36 mg L-1, and in the BCR sequential extraction procedure, Pb was mainly present in the residual fraction (54.96%). The mechanism of mechanochemical solidification of heavy metal lead in soil is that, during the ball milling process, the lead precipitates with Ca(H2PO4)2 to produce dense agglomerates (Pb3(PO4)2 and PbxCa10-x(PO4)6(OH)2), which fixes the lead in the soil and hampers its leaching.


Assuntos
Fosfatos de Cálcio/química , Recuperação e Remediação Ambiental/métodos , Chumbo/isolamento & purificação , Poluentes do Solo/química , Pirofosfato de Cálcio/química , Precipitação Química , Chumbo/química , Metais Pesados/química , Metais Pesados/isolamento & purificação , Microscopia Eletrônica de Varredura , Poluentes do Solo/análise , Poluentes do Solo/isolamento & purificação
17.
Water Res ; 173: 115572, 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32062222

RESUMO

Seawater, as an alternative magnesium source, has the potential to improve the overall economics and environmental footprint of struvite production compared to the use of pure magnesium salts. However, the dilution effect and the presence of other ions in seawater can reduce the phosphorus recovery potential and the simultaneous precipitation of other compounds may reduce the quality of the produced struvite. This work presents a comparative study of seawater and MgCl2 by performing a series of thermodynamic equilibrium modeling and crystallization experiments. The results revealed that acceptable phosphorus recovery (80-90%) is achievable by using seawater as the magnesium source for struvite precipitation. Further, the simultaneous precipitation of calcium phosphates was successfully controlled and minimized by optimum selection of reaction pH and seawater volume (i.e. Mg:P and Mg:Ca molar ratios). The increase of temperature from 20 °C to 30 °C reduced the phosphorus recovery by 15-20% while it increased the particle size by 30-35%. The presence of suspended solids in reject water did not have significant effects on phosphorus recovery but it made the struvite separation difficult as the obtained struvite was mixed with suspended solids. The experimental results and economic evaluation showed that the use of seawater can reduce the chemical costs (30-50%) and the CO2-footprint (8-40%) of struvite production. It was concluded that seawater is a potential alternative to pure magnesium sources in struvite production, while studies in larger scale and continuous mode are needed for further verification before full-scale applications.


Assuntos
Compostos de Magnésio , Fósforo , Precipitação Química , Cristalização , Fosfatos , Água do Mar , Estruvita , Eliminação de Resíduos Líquidos
18.
Water Environ Res ; 92(8): 1162-1172, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32072707

RESUMO

As a promising strategy to remove and recover phosphorus from wastewater, optimization of the struvite (MgNH4 PO4 .6H2 O) precipitation parameters is required to achieve desirable phosphorus removal efficiency. To tackle the challenges upon the precipitation optimization methods as three-level full factorial designs, and central composite design as well, Box-Behnken design was implemented to optimize different reaction parameters for phosphorus removal and recovery during struvite precipitation in the current study. Moreover, the reaction orders and the rate equation were all determined to reveal the reaction kinetics parameters of struvite precipitation. The results showed that the optimal operating parameters of pH, Mg/P ratio and N/P ratio were 9.82, 1.45, and 4.00, respectively, by which more than 95% of phosphorus removal efficiency could be achieved. In addition, it was found that pH and pH/(N/P) had the most influence on phosphorus removal efficiency among different individual factors and interactive items, respectively. The partial orders of PO4 -P, Mg2+ , and NH 4 + in kinetic rate equation were determined as 1.586, 0.930, and 1.236 while the rate constant k was 0.0167 ± 0.0014 mM-2.752 per minute by differential method. PRACTITIONER POINTS: Different reaction parameters were optimized by Box-Behnken design. pH and pH/(N/P) had the most influence on phosphorus removal efficiency among different individual factors and interactive items. The reaction orders and the rate equation were all determined to reveal the reaction kinetics parameters.


Assuntos
Compostos de Magnésio , Fósforo , Precipitação Química , Cinética , Fosfatos , Estruvita
19.
Appl Microbiol Biotechnol ; 104(5): 2029-2037, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31940083

RESUMO

Crack propagation is one of the issues associating with dental composites which can significantly affect their performance. Current solutions for preventing and stopping the cracks include maximizing the filler to matrix ratio as well as fiber reinforcing of composites which are not always reliable. The precipitation of calcium carbonate (CaCO3) minerals by the generally recognized as safe (GRAS) bacteria can be seen as a novel approach to address this shortcoming. In the present study, the effect of microbially induced calcium carbonate precipitation (MICP) on filling dental composites' cracks and cavities was studied. In this first step, the capability of different GRAS bacteria to induce CaCO3 precipitation was investigated. In the next step, the capability of potent bacteria to initiate MCIP in solid matrix was evaluated. For this purpose, the CaCO3-bacteria along with necessary nutrients were introduced into different dental composites in two ways, namely, powder and paste form. The light-cured composites were analyzed using optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDS) to identify and characterize the precipitated CaCO3 crystals. It was shown that the incorporation of powder healing compound in two composites resulted in precipitation of CaCO3, while no crystals were formed when a paste form of healing compound was mixed with composites. The results evidently show that MICP can be a feasible alternative to current inefficient approaches to address microcracking issues in dental composites.


Assuntos
Bactérias/metabolismo , Carbonato de Cálcio/química , Materiais Dentários/química , Carbonato de Cálcio/metabolismo , Precipitação Química , Materiais Dentários/metabolismo
20.
Environ Sci Pollut Res Int ; 27(7): 7720-7728, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31900769

RESUMO

The production of fertilizer magnesium ammonium phosphate (MAP, Mg.NH4PO4.6H2O), commonly known as struvite, has been investigated in this study by mixing waste effluents of different sources. Effluents form pigment preparation industry rich in ammonium carbonate and poly phosphoric acid have been used as source of nitrogen (N) and phosphorus (P), respectively, whereas sea bittern has been used as a source of Mg. The stoichiometric mole ratio of the Mg2+ to NH4+ to PO43- in the mixed reaction liquid was maintained as 1:0.5:1 and 1:1:1, and the pH value of the reaction liquid was adjusted to 8.5 using sodium hydroxide. Struvite formation has been confirmed by using FTIR and P-XRD techniques. Thermal stability and morphology of the product were characterized employing thermo-gravimetric analysis (TGA) and field emission scanning electron microscopy (FE-SEM). The method reported is easy to implement and cost-effective. The adoption of the method will not only help in waste management but also in controlling environment hazards of P and N discharge in water bodies with economic benefits. The method is particularly useful for solar works which are in vicinity of industries releasing P- and N-containing effluents. After precipitation of struvite, the left out liquor can be further recycled into the salt works for enhanced recovery of common salt.


Assuntos
Compostos de Amônio , Fertilizantes , Resíduos Industriais , Estruvita/química , Precipitação Química , Magnésio , Compostos de Magnésio , Nitrogênio , Fosfatos , Fósforo , Sais , Eliminação de Resíduos Líquidos , Águas Residuárias
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