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1.
Chemosphere ; 210: 745-752, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30036822

RESUMO

In this study, the performance of a living machine (LM) system was evaluated for use in the treatment of black water collected from septic tanks with hydraulic retention times (HRTs) of 6, 5, and 4 days. We found that the HRT had little effect on the removal efficiency of chemical oxygen demand (COD). However, the removal rates of total nitrogen (TN) and ammonium nitrogen (NH4+-N) decreased with the reduction of HRT, whereas the removal efficiency of total phosphate (TP) was consistently low because of the long sludge retention time. The working conditions of #1 achieved the highest removal efficiency of COD (85%), NH4+-N (75%), and TN (47%), although the removal efficiency of TP (11%) was slightly lower than that of #2 (12%). The microbial communities in each tank of the LM system were characterized by high-throughput sequencing, which showed that the LM system successfully created more favorable conditions for fermentative bacteria than traditional systems, with relative abundances of 13% (#1), 13% (#2), and 15% (#3) compared to that of the anaerobic/anoxic/oxic (A2O) system (<3%). Smithella was the dominant fermentative bacteria, accounting for 9% (#1), 7% (#2), and 10% (#3) of total bacteria in the LM system. The relative abundances of ammonia oxidizing bacteria (AOB) (12%) and anaerobic ammonium oxidizing bacteria (AnAOB) (7%) in the LM system were much higher than that in the A2O system. Overall, the LM system offered a more sustainable and economical solution for treating black water.


Assuntos
Bactérias Anaeróbias/crescimento & desenvolvimento , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/química , Purificação da Água/métodos , Água/química , Nitrogênio/química
2.
Bioresour Technol ; 249: 175-181, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-29040852

RESUMO

This study assesses the use of vertical greening for blackwater treatment. The effects of hydraulic retention time (HRT) and drip frequency on treatment performance were systematically studied. Additionally, microbial communities in the vertical greening system were characterized. The results show that the removal efficiencies of NH4+-N and total phosphate (TP) increased with an increase in HRT, and the drip frequency had a significant effect on TP. High-throughput sequencing revealed that the diversity of the microbial community did not change significantly along vertical and horizontal directions, but the dominant species shifted. Heterotrophic nitrifying and denitrifying bacteria decreased significantly while autotrophic nitrifying bacteria, especially ammonia oxidizing bacteria, proliferated in a vertical direction. Therefore, it is concluded that vertical greening systems can effectively treat blackwater and lower NH+-N levels.


Assuntos
Reatores Biológicos , Processos Autotróficos , Bactérias
3.
Water Res ; 123: 1-11, 2017 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-28641088

RESUMO

A unique sediment-capping agent consisting of a zeolite/hydrous zirconia composite (ZHZ) was developed and tested for P-immobilization in the overlying water and sediment cores from a freshwater pond. In the ZHZ, NaP1 zeolite was covered with hydrous zirconia, which existed as an amorphous phase. Experimental results in pond water indicated that ZHZ could efficiently remove soluble reactive phosphorus. The 28-day sediment incubation experiments showed that capping sediment with ZHZ resulted in a more efficient, rapid and sustained decrease in P concentration when compared with the traditional alum treatment method. Furthermore, ZHZ increased the sediment stability, resulting in the lowest turbidity, total phosphorus and soluble reactive phosphorus concentrations in overlying water following artificially induced resuspension of sediment. Phosphorus fractionation of sediment showed that the dominant P form transferred from HCl-extractable P to residual P, and the most release-sensitive P (labile P and reductant reactive P) was decreased after ZHZ application. Overall, ZHZ is a highly effective P-immobilization material. ZHZ has high potential as a sediment capping material to control internal P loading in eutrophic water bodies.


Assuntos
Fósforo/química , Poluentes Químicos da Água/química , Sedimentos Geológicos , Zeolitas , Zircônio
4.
Chemosphere ; 144: 1290-8, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26476050

RESUMO

A simple method to functionalize diatomite with hydrous iron oxide was attempted and its performance as a new active filtration material to remove and recover phosphate from water was investigated under varying solution conditions. The Langmuir phosphate adsorption capacity increased from 0.6 mgP/g for raw diatomite to 4.89, 14.71, 25.02 mgP/g for hydrous iron oxide modified diatomite (HIOMD), depending on the amount of iron loaded. Loading of hydrous iron oxide caused the increase in true and bulk density and a decline in filtration rate, but to a lesser extent. It was shown that the HIOMD product with suitable iron content could retain a good filtration performance with a greatly increased adsorption capacity for phosphate. The phosphate adsorption increased by decreasing pH and by increasing ionic strength at high pH levels. The adsorption process was interpreted by ligand exchange. Coexisting oxyanions of sulfate, nitrate, citrate, carbonate, silicate and humic acid showed different effects on phosphate fixation but it was presumed that their influence at their concentrations and pH levels commonly encountered in effluent or natural waters was limited, i.e., HIOMD had a reasonably good selectivity. Results in repeated adsorption, desorption and regeneration experiment showed that the adsorbed phosphate could be recovered and the material could be reused after regeneration. The column test showed that HIOMD could be potentially utilized as an adsorption filtration medium for phosphate removal and recovery from water.


Assuntos
Terra de Diatomáceas/química , Compostos Férricos/química , Nitratos/química , Fosfatos/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Adsorção , Filtração , Substâncias Húmicas/análise
5.
Artigo em Inglês | MEDLINE | ID: mdl-26301857

RESUMO

This study was undertaken to investigate the effectiveness of the hybrid adsorbent, which was synthesized from coal fly ash and was composed of lanthanum hydroxide and zeolite (La-ZFA), for phosphate removal from water. Long-term repeated adsorption tests for 30 days showed that the maximum removal capacity of the material reached 66.09 mg P/g. The fractionation of adsorbed phosphorus indicated that phosphate immobilized by La-ZFA was quite irreversible and was dominated by HCl-P fraction. It was suggested that the immobilization of phosphate was mainly attributed to lanthanum hydroxide and was slightly influenced by coexistence of other anions (Cl(-), NO3(-), SO4(2-), and HCO3(-)). At a La/P molar ratio between 1.5:1 and 2.0:1, a nearly complete removal (above 98%) of phosphate could be achieved. La-ZFA also exhibited great performance for removing phosphate from lake water (97.29%) as well as the effluent from wastewater treatment plant (97.86%), respectively. In addition, based on the results of the present study, it was believed that La-ZFA could be a potential material for phosphate removal in practical application.


Assuntos
Cinza de Carvão/química , Lantânio/química , Fosfatos/isolamento & purificação , Águas Residuárias/química , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Zeolitas/química , Adsorção , Humanos , Lagos/química , Concentração Osmolar , Fosfatos/farmacocinética , Fósforo/isolamento & purificação , Água/química
6.
Huan Jing Ke Xue ; 34(1): 231-6, 2013 Jan.
Artigo em Chinês | MEDLINE | ID: mdl-23487944

RESUMO

Activated alumina was studied for removing phosphate from water, and the recovery of adsorbed phosphate on activated aluminum oxide was also tested. Phosphate solution was prepared using distilled water, tap water and Luoshijiang River water, respectively. All the phosphate adsorption tests using activated alumina were proved to be well fitted with Langmuir isotherm and the respective maximum adsorption amount were 20.88, 32.15 and 29.85 mg x g(-1), respectively. The presence of electrolyte in water could be a positive factor for phosphate removal. As the pH value of phosphate solution became lower the Zeta potential of activated alumina increased, which could enhance the phosphate removal efficiency of activated alumina. The recovery tests indicated that NaOH (0.1 mol x L(-1)) solution could almost completely extract the phosphate adsorbed by activated alumina.


Assuntos
Óxido de Alumínio/química , Fósforo/isolamento & purificação , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Fósforo/química , Hidróxido de Sódio/química , Poluentes Químicos da Água/química , Purificação da Água/métodos
7.
J Hazard Mater ; 231-232: 57-63, 2012 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-22771348

RESUMO

The aim of this study was to examine the adsorption capability and mechanism of hexadecyltrimethylammonium modified zeolite, which was synthesized from coal fly ash, for the removal of ionizable phenolic compounds (phenol, p-chlorophenol and bisphenol A, with different pK(a)) and non-ionizable organic compounds (aniline, nitrobenzene, and naphthalene, with different hydrophobicity). The obtained zeolite was identified as type Na-P1 (Na(6)Al(6)Si(10)O(32)·12H(2)O, JCPDS code 39-0219), which is classified into the gismondine group with a pore size of 3.1 Å × 4.5 Å [100] and 2.8 Å × 4.8 Å [101]. The adsorption of the two kinds of organic compounds was due to loaded surfactant bilayer because modified zeolite showed great ability for the removal of organic chemicals while little adsorption by zeolite was observed. The isotherm data of ionizable compounds fitted well to the Langmuir model but those of non-ionizable chemicals followed a linear equation. Uptake of ionizable compounds depended greatly on pH, increasing at alkaline pH conditions. In contrary, adsorption of non-ionizable chemicals was essentially the same at all pH levels studied. The adsorption of both kinds of organic compounds correlated well to k(ow) value, suggesting that more hydrophobic organic contaminants are more easily retained by modified zeolite. Based on the different adsorption behavior, the uptake of non-ionizable pollutants was thought to be a single partitioning process into the surfactant bilayer. For ionizable compounds, however, interaction of the phenol group(s) with the positively charged "head" of surfactant additionally functions.


Assuntos
Compostos de Cetrimônio/química , Poluentes Ambientais/química , Fenóis/química , Zeolitas/síntese química , Adsorção , Compostos de Anilina/química , Cetrimônio , Concentração de Íons de Hidrogênio , Naftalenos/química , Nitrobenzenos/química
8.
Bioresour Technol ; 102(22): 10480-5, 2011 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-21967710

RESUMO

This study evaluated the influences of inoculum-substrate ratio (ISR), volatile fatty acids (VFAs) and nicotinamide adenine dinucleotide, the reduced form (NADH) on hydrogen production during the anaerobic fermentation of Chlorella sp. in batch tests at 35 °C. The results indicated that the hydrogen concentration and lag time increased when ISR decreased, and the maximum hydrogen production and hydrogen content, 7.13 mL/g VS and 45.3%, respectively, were obtained when ISR was equal to 0.3. On the other hand, VFAs concentrations increased with the increase of hydrogen. The NADH increased while the daily output of hydrogen decreased as the fermentation carried on. The results suggested that ISR, VFAs, and NADH were important parameters for effective anaerobic hydrogen production using Chlorella sp. as substrate.


Assuntos
Biocombustíveis/análise , Chlorella/efeitos dos fármacos , Chlorella/metabolismo , Ácidos Graxos Voláteis/farmacologia , Fermentação/efeitos dos fármacos , Hidrogênio/metabolismo , NAD/farmacologia , Anaerobiose/efeitos dos fármacos , Técnicas de Cultura Celular por Lotes , Espectrometria de Fluorescência , Fatores de Tempo
9.
Biomed Environ Sci ; 23(1): 48-52, 2010 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-20486436

RESUMO

OBJECTIVE: To investigate the effect of iron on the growth, physiology and photosynthesis of cyanobacteria. METHODS: A gradient of iron concentrations was employed to investigate the growth, photo-pigments (chlorophyll A and phycocyanin), and cell chemical contents (C, N, P) of Microcystis aeruginosa in response to different iron additions. RESULTS: The specific growth rate during the exponential growth phase, as well as the cell chlorophyll A and the phycocyanin content, was limited by iron below 12.3 tmol Fe x L(-1). The growth was inhibited when the iron concentration was at 24.6 micromol Fe x L(-1). The cell chlorophyll A and the phycocyanin content were saturated when the iron concentration was above 12.3 micromol Fe x L(-1) and declined slightly at 24.6 micromol Fe x L(-1). At a low iron concentration (about 6.15 micromol Fe x L(-1) and less), the cell nitrogen and carbohydrate content were iron limited, and the variation of the cell phosphorus content was similar to that of the nitrogen and carbohydrate, with a transition point of 12.3 micromol Fe x L(-1). CONCLUSION: The variation of cynobacteria growth is synchronous with that of the photo-pigments or the cell chemical content, and there exist relationships among photosynthesis, growth and internal chemical content, which could be useful for the growth estimation from the cell characteristics.


Assuntos
Ferro/farmacologia , Microcystis/efeitos dos fármacos , Microcystis/fisiologia , Carboidratos/análise , Meios de Cultura/química , Relação Dose-Resposta a Droga , Microcystis/química , Microcystis/citologia , Nitrogênio/análise , Fósforo/análise
10.
Water Sci Technol ; 60(11): 2929-38, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19934515

RESUMO

The aim of this study was to investigate the effects of current density, gap between electrodes, urine dosage, dilution and hydrolysis on phosphate removal from human urine by electrocoagulation technique using iron as electrodes. It was shown that, although a high current density and a long electrolysis time favored the removal of phosphate, an appropriate value for these two parameters can be obtained by taking into account the consumption of energy and iron in addition to P removal. In this study, current density 40 mA/cm2 and electrolysis time 20 min were shown to be optimal for 1.0 L pure urine to achieve nearly a complete removal (98%) efficiency of phosphate under the conditions of electrode area 160 cm2, the stirring speed 150 rpm, and the gap between electrodes 5 mm. Increase of gap between electrodes had little effect on phosphate removal, although it increased the energy consumption dramatically. The use of a high urine dosage reduced the efficiency of phosphate removal but increased the amount of removed phosphate. When pure urine was diluted with tap water, use of a higher tap water proportion for dilution expedited the electrolysis to achieve a nearly complete removal of phosphate in solution, but dilution caused the increase in energy consumption. It was also revealed that the hydrolysis of urine prior to electrocoagulation treatment impeded phosphate removal.


Assuntos
Eletrocoagulação/métodos , Fosfatos/isolamento & purificação , Urina/química , Eletrodos , Desenho de Equipamento , Humanos , Hidrólise , Técnicas de Diluição do Indicador , Ferro , Cinética , Masculino , Fosfatos/química , Fósforo/isolamento & purificação , Urinálise/métodos , Água/análise
11.
Chemosphere ; 77(8): 1143-5, 2009 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-19765796

RESUMO

Chromite Ore Processing Residue (COPR) is the byproduct of chromate production process, which contains a large amounts of Cr(VI). The present work developed a new technique to treat COPR, and the process involved mixing the COPR with rice straw followed by pyrolysis. It was found that the gaseous organic fraction generated during pyrolysis of straw was beneficial to Cr(VI) reduction. In the study, process variables, such as the amount of straw added to COPR, heating temperature and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were all investigated. After pyrolysis, Cr(VI) decreased greatly, from 3400 for untreated COPR to less than 30 mg kg(-1) for treated COPR at 600 degrees C.


Assuntos
Cromatos/química , Cromatos/isolamento & purificação , Calefação , Resíduos Industriais , Oryza/química , Biomassa , Tamanho da Partícula , Temperatura
12.
J Hazard Mater ; 172(2-3): 1597-601, 2009 Dec 30.
Artigo em Inglês | MEDLINE | ID: mdl-19765898

RESUMO

The effect of pyrolysis process with sewage sludge on the chromium behavior of chromite ore processing residue (COPR) was examined in this study. The behavior of chromium was characterized in term of chromium oxidation test, pH-static leaching tests, column leaching test and sequential extraction test. As a sequence of pyrolysis process, the Cr(VI) in COPR was effectively reduced from 5057 mg kg(-1) for untreated COPR to 8.6 mg kg(-1) for treated COPR at temperature over 600 degrees C, which is far below the New Jersey Department of Environmental Protection regulatory limit of 240 mg kg(-1). As a result, the amount of exchangeable and carbonate-bound Cr fractions, the most mobile for the environment, were largely reduced. At the same time, the amount of the other three Cr fractions which are much less mobile become augmented. pH static test showed that the chromium in the treated COPR at pyrolysis temperature above 400 degrees C was quite stable at pH>7. Column study also indicated that only negligible amount of chromium of the treated COPR at above 600 degrees C can be released by the acid rain.


Assuntos
Cromo/química , Incineração , Concentração de Íons de Hidrogênio , Esgotos/química
13.
J Environ Sci (China) ; 21(4): 424-8, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19634414

RESUMO

The conversion of glucose to hydrogen was evaluated using continuous stirred tank reactor at pH 5.5 with various hydraulic retention times (HRT) at 30 degrees C. Furthermore, the population dynamics of hydrogen-producing bacteria was surveyed by fluorescence in-situ hybridization using probe Clost IV targeting the genus Clostridium based on 16S rRNA. It was clear that positive correlation was observed between the cells quantified with probe Clost IV and hydrogen yield of the respective sludge. The numbers of hydrogen-producing bacteria were decreased gradually with increasing HRT, were 9.2 x 10(8), 8.2 x 10(8), 2.8 x 10(8), and 6.2 x 10(7) cell/mL at HRT 6, 8, 12, and 14 h, respectively. The hydrogen yield was 1.4-1.5 mol H2/mol glucose at the optimum HRT range 6-8 h. It is considered that the percentage of the hydrogen-producing bacteria to total bacteria is useful parameter for evaluation of hydrogen production process.


Assuntos
Clostridium/metabolismo , Fermentação , Glucose/metabolismo , Hidrogênio/metabolismo , Clostridium/genética , Hibridização in Situ Fluorescente , RNA Ribossômico 16S/genética , Esgotos
14.
Chemosphere ; 76(9): 1303-7, 2009 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-19596134

RESUMO

The occurrence of harmful algal bloom in water source poses a serious water safety problem to local water supply systems. In order to ensure the raw water quality, the feasibility of reducing harmful algae by light-shading plus aeration was investigated. The batch test showed that algal biomass reduced rapidly under light-shading condition, and the reduction efficiency was further increased when light-shading was accompanied by aeration. The continuous flow experiment showed that the algal reduction efficiency increased with the increase of residence time. At residence time of 5 d, when treated with light-shading plus aeration, algal biomass could be reduced by more than 65%, with raw water quality improved simultaneously. Furthermore, considering that some harmful algae such as Microcystis tend to float upwards under light-limited condition, an integrated light-shading system consisting of pre-separation process and light-shading plus aeration treatment was suggested to treat naturally high algal water. The result showed that pre-separation process could remove more than 40% of algal biomass, and the total reduction efficiency of the integrated system increased to above 80%.


Assuntos
Eucariotos/crescimento & desenvolvimento , Abastecimento de Água , Ar , Biomassa , Eutrofização , Luz , Fatores de Tempo
15.
Bioresour Technol ; 100(11): 2874-7, 2009 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-19217773

RESUMO

The present work developed a novel technique to treat chromite ore processing residue (COPR). The process involved mixing the COPR with sewage sludge followed by pyrolysis. The gaseous organic fraction generated during pyrolysis of sludge was beneficial to Cr(VI) reduction. Process variables, such as the amount of sludge added to COPR (sludge-to-COPR (S/C) ratio), heating temperature, reaction time and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were investigated. Cr(VI) content had decreased greatly, from 3384 mg kg(-1) for untreated COPR to less than 30 mg kg(-1) for COPR treated at 600 degrees C.


Assuntos
Bactérias Anaeróbias/metabolismo , Cromo/isolamento & purificação , Cromo/metabolismo , Resíduos Industriais/prevenção & controle , Mineração/métodos , Esgotos/microbiologia , Gerenciamento de Resíduos/métodos , Biodegradação Ambiental
16.
J Hazard Mater ; 167(1-3): 244-9, 2009 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-19185993

RESUMO

Zeolitic materials were synthesized from thermally treated sediment by alkali treatment using different NaOH/sediment ratios. Characterization of the materials was done by XRD, FTIR, cation exchange capacity and specific surface area. Use of high NaOH/sediment ratio favored the formation of zeolite. The potential value of the zeolitic materials for the retention of trivalent chromium from water was examined. The maximum of Cr(III) sorption by the zeolitic materials, determined by a repeated batch equilibration method, ranged from 38.9 to 75.8 mg/g which was much greater than that of the thermally treated sediment (6.3 mg/g). No release of sorbed Cr(III) by 1.0M MgCl(2) at pH 7 was observed but Cr(III) desorption by ionic electrolyte increased with decreasing pH. The zeolitic materials could completely remove Cr(III) from wastewater even in the presence of Na(+) and Ca(2+) with high concentrations with a dose above 2.5 g/L. The pH-dependent desorption behavior and the high selectivity of zeolitic material for Cr(III) were explained by sorption at surface hydroxyl sites and formation of surface precipitates.


Assuntos
Cromo/isolamento & purificação , Resíduos Industriais/prevenção & controle , Poluentes Químicos da Água/isolamento & purificação , Zeolitas/química , Adsorção , Sedimentos Geológicos , Temperatura Alta , Concentração de Íons de Hidrogênio
17.
J Environ Sci (China) ; 21(12): 1632-8, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-20131591

RESUMO

A cyanobacterial (Arthrospira platensis) bloom was induced in situ by nutrient manipulation in an enclosure. The succession of the phytoplankton community and the water chemistry variations before the appearance of bloom, as well as their relationship, were investigated. The cell pigment variations were studied simultaneously. The Pearson's correlation analysis showed that there was no significant correlation between water chemistry and green algal or cyanobacterial composition, indicating that water chemistry variations were not suitable to be used as indicators for cyanobacterial-bloom early-warning. However, the diversity index of the phytoplankton community decreased sharply before the bloom appeared. Therefore, the dynamics of phytoplankton community was put forward to be an indicator for cyanobacterial-bloom early-warning. In addition, the cell pigment variations represented the changes of community structure, which should be useful for studying the dynamics of phytoplankton community.


Assuntos
Cianobactérias , Ecossistema , Proliferação Nociva de Algas , Fitoplâncton , Água/química , Clorofila/análise
18.
Ying Yong Sheng Tai Xue Bao ; 20(11): 2813-9, 2009 Nov.
Artigo em Chinês | MEDLINE | ID: mdl-20136021

RESUMO

Harmful algal bloom (HAB) occurs frequently and causes serious damage. To study the early-warning and prediction technology of HAB is of significance for the early-warning and prediction, ecological control, and disaster prevention and mitigation of HAB. This paper reviewed the research progress in the early-warning and prediction technologies of HAB, including transport prediction, specific factors critical value prediction, data-driven model, and ecological math model, and evaluated the advantages and disadvantages of these four types of technologies. Some new ideas were brought forward about the prediction of cyanobacterial growth rate based on cell characteristics, and the early-warning of cyanobacterial bloom based on algal community characteristics.


Assuntos
Monitoramento Ambiental/métodos , Proliferação Nociva de Algas , Modelos Teóricos , Poluentes da Água/análise , Cianobactérias/crescimento & desenvolvimento , Ecossistema , Previsões , Água Doce/microbiologia , Modelos Biológicos
19.
J Environ Sci (China) ; 21(5): 575-80, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-20108657

RESUMO

Xonotlite was synthesized and tested for phosphate removal and recovery from synthetic solution in a batch mode. The effects of pH, initial calcium concentration, bicarbonate concentration on phosphate removal through crystallization were examined. The morphology and X-ray diffraction (XRD) pattern of xonotlite before and after crystallization confirmed the formation of crystalline hydroxyapatite. The results indicated that the crystallization product had a very high P content (> 10%), which is comparable to phosphate rock at the dosage of 50-200 mg xonotlite per liter, with a maximum P content of 16.7%. The kinetics of phosphate removal followed the second-order reaction equation. The phosphate removal ability increased with increasing pH. The precipitation of calcium phosphate took place when pH was higher than 7.2, whereas the crystallization occurred at pH 6.0. A high calcium concentration could promote the removal of phosphate via crystallization, while a high bicarbonate concentration also enhanced phosphate removal, through that the pH was increased and thus induced the precipitation process. When xonotlite was used to remove phosphate from wastewater, the removal efficiency could reach 91.3% after 24 h reaction, with removal capacity 137 mg/g. The results indicated that xonotlite might be used as an effective crystal seed for the removal and recovery of phosphate from aqueous solution.


Assuntos
Compostos de Cálcio/química , Durapatita/química , Fosfatos/isolamento & purificação , Silicatos/química , Cristalização , Cristalografia por Raios X , Concentração de Íons de Hidrogênio , Microscopia Eletrônica de Varredura
20.
Chemosphere ; 73(7): 1071-7, 2008 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-18782640

RESUMO

Constructed wetlands are considered to be important sources of nitrous oxide (N(2)O). In order to investigate the contribution of nitrification in N(2)O formation, some environmental factors, plant species and ammonia-oxidizing bacteria (AOB) in active layers have been compared. Vegetation cells indicated remarkable effect of seasons and different plant species on N(2)O emission and AOB amount. Nitrous oxide data showed large temporal and spatial fluctuations ranging 0-52.8 mg N(2)O m(-2)d(-1). Higher AOB amount and N(2)O flux rate were observed in the Zizania latifolia cell, reflecting high potential of global warming. Roles of plants as ecosystem engineers are summarized with rhizosphere oxygen release and organic matter transportation to affect nitrogen transformation. The Phragmites australis cell contributed to keeping high T-N removal performance and lower N(2)O emission. The distribution of AOB also supported this result. Statistical analysis showed several environmental parameters affecting the strength of observed greenhouse gases emission, such as water temperature, water level, TOC, plant species and plant cover.


Assuntos
Óxido Nitroso/análise , Áreas Alagadas , Amônia/metabolismo , Bactérias/metabolismo , Ecossistema , Efeito Estufa , Hibridização in Situ Fluorescente , Óxido Nitroso/metabolismo , Poaceae/metabolismo , Estações do Ano , Microbiologia do Solo , Poluentes Químicos da Água/análise
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