Repeatedly using the decomposition product of struvite by ultrasound stripping to remove ammonia nitrogen from landfill leachate

In this study, the decomposition of struvite by ultrasound stripping and the recycle use of the decomposition product for the treatment of landfill leachate were investigated. The results indicated that when the decomposition of struvite by ultrasound stripping was performed at 55 °C for 40 min, the ammonium in the struvite could be almost completely eliminated from the solution system. The characterization analysis showed that magnesium phosphate and the dissolved phosphate ions were the main active derivatives. Approximately 90% of the total ammonia nitrogen (TAN) in landfill leachate can be removed by reusing the decomposition product at pH 9 for 60 min. Repeated use of the struvite decomposition product revealed that the TAN removal efficiency decreased with an increase in the number of recycles. However, in the process of multiple recycling, about 90% of TAN removal could be maintained by supplementing a certain amount of the preformed struvite to the solution for every recycle. An economic analysis demonstrated that 79.3% of the treatment cost could be saved by the proposed process compared to the non-recycling process.     

垃圾渗滤液中溶解性有机物组分的三维荧光特性

运用三维荧光光谱技术研究了垃圾渗滤液中六种DOM组分的荧光特性。结果表明:类富里酸、类色氨酸和腐殖酸类物质是垃圾渗滤液DOM的主要组成,其中大量紫外区类富里酸物质的存在,是导致其可生化性差的主要原因。HOA含有较多紫外区类富里酸和较少可见区类富里酸,HIA正好相反;HIN组分主要包括紫外区和可见区类富里酸;HOB、HIB和HIN三种组分在各区域荧光信号都较强,包括HON组分在内,这四种组分荧光峰位置主要集中在类腐殖酸、紫外区类富里酸及可见区类富里酸三个区域;但不同组分的荧光强度差别较大,HOB和HIB在紫外区类富里酸有较强荧光强度,HIN在紫外区类富里酸、可见区类富里酸区域均有较强荧光强度;与这三者相比,HON在各位置的荧光信号中等;而HOA和HIA的荧光强度相对较弱,说明有机酸类物质的荧光特性较差。     

717树脂吸附渗滤液中有机物的荧光特性研究

利用同步荧光光谱和三维荧光光谱技术分析了717树脂处理卫生填埋场渗滤液过程中有机质的组成变化。同步荧光光谱显示,在开始10 min内,波长较长的特征荧光峰强度急剧下降,波长较短的荧光峰升高,其后变化不大。三维荧光光谱扫描发现,渗滤液中只有两个类富里酸荧光峰,随时间的增长,荧光峰强度下降,紫外和可见类富里酸荧光强度比值降低,发射波长明显蓝移。结果表明,717树脂对渗滤液中有机物的吸附速度快,主要吸附分子量较大、复杂程度较高的有机物,这可能有利于后续的生物处理。     

Independence of alpine meadow plants from soil organic matter for nitrogen supply: evidence from stable nitrogen isotopes

Stable nitrogen isotope signatures of major sources of mineral nitrogen (mineralization of soil organic nitrogen, biological N(2) fixation by legumes, annual precipitation and plant litter decomposition) were measured to relatively define their individual contribution to grass assimilation at the Haibei Alpine Meadow Ecosystem, Qinghai, China. The results indicated that delta(15)N values (-2.40 per thousand to 0.97 per thousand) of all grasses were much lower than those of soil organic matter (3.4+/-0.18 per thousand) and mineral nitrogen (ammonium and nitrate together, 7.8+/-0.57 per thousand). Based on the patterns of stable nitrogen isotopes, soil organic matter (3.4+/-0.18 per thousand), biological N(2) fixation (0 per thousand), and precipitation (-6.34+/-0.24 per thousand) only contributed to a small fraction of nitrogen requirements of grasses, but plant litter decomposition (-1.31+/-1.01 per thousand) accounted for 67 %.     

Effects of ultrasound on Microcystis aeruginosa cell destruction and release of intracellular organic matter

Harmful algal blooms negatively impact ecosystems and threaten drinking water sources. One potential method to effectively counteract algal blooms is ultrasonication. However, ultrasonication can easily lead to the release of intracellular organic matter (IOM). The purpose of this study was to investigate the relationship between the destruction of algal cells and IOM release at different ultrasound frequencies. Microcystis aeruginosa cells were ultrasonicated at 20 kHz with an intensity of 0.038 W/mL, 740 kHz with an intensity of 0.113 W/mL, and 1120 kHz with an intensity of 0.108 W/mL. The IOM release was detected by fluorescence spectroscopy in addition to the more commonly used haemocytometry and optical density. After ultrasonication for 15 min, the removal rate of algal cells reached 10.5% at 20 kHz, 9.46% at 740 kHz, and 35.4% at 1120 kHz. The 20 kHz and 740 kHz ultrasound caused local damage to algal cells and then disrupted them, whereas the 1120 kHz ultrasound directly disrupted most algal cells. The extracellular organic matter (EOM), which was increased by ultrasonication, mainly consisted of protein-like compounds, chlorophyll, and a small amount of humic-like substances. Gas vacuoles had been destructed before the cells were broken, as indicated by the decrease of cell size and the wrinkles on the cell surface. Moreover, the removal of algae cells while upholding integrity is more conducive to the safety of the water environment.     

Electrocatalytic synthesis of ammonia from steam and nitrogen at atmospheric pressure

The electrocatalytic synthesis of ammonia from steam and nitrogen was studied in oxygen ion (O^2?) and proton (H⁺) conducting solid electrolyte cells at 450–700 °C and at atmospheric total pressure. A Ru-based industrial catalyst was used as the working electrode. In the H⁺ cell, steam was electrolyzed at the anode to produce protons and oxygen. Protons, transported to the cathode, reacted with nitrogen to produce ammonia. In the O^2? cell, H₂O and N₂ were fed in together at the cathode. Steam was electrolyzed and the produced hydrogen reacted with nitrogen. Ammonia formation was observed at temperatures between 500 and 700 °C. The conversions with respect to nitrogen or steam were low, primarily because of the poor conductivity of the working electrode. Both cells, however, exhibit promising features that make this alternative approach of ΝΗ₃ synthesis worthy of further investigation.     

Removal of dinitrotoluenes and trinitrotoluene from industrial wastewater by ultrasound enhanced with titanium dioxide

Oxidative degradation of dinitrotoluenes (DNTs) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using ultrasonic irradiation combined with titanium dioxide (TiO(2)). The batch-wise experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, including power intensity, TiO(2) dosage, acidity of wastewater, reaction temperature and oxygen dosage. It is worthy to note that the nitrotoluene contaminants could be almost completely eliminated by sonochemical oxidation enhanced significantly with the addition of TiO(2) due to the supply of adsorbent and/or excess nuclei. High destruction rate of nitrotoluenes could be achieved by increasing the acidity of wastewater and decreasing the reaction temperature. According to the result given by pyrolysis/gas chromatograph-mass spectrometer (Pyrolysis/GC-MS), it is postulated that DNTs adsorbed on TiO(2) preliminarily undergo denitration pathway to o-mononitrotoluene (MNT) or oxidation pathway to 1,3-dinitrobenzene (DNB), respectively. Further, based on the spectra obtained from GC-MS, it is proposed that DNTs dissolved in wastewater proceed with similar reaction pathways as those adsorbed on TiO(2). Besides, oxidative degradation of 2,4,6-TNT results in the formation of 1,3,5-trinitrobenzene (TNB). Apparently, the sonolytic technique established is promising for direct treatment of wastewater from TNT manufacturing process.     

Removal of disperse blue 2BLN from aqueous solution by combination of ultrasound and exfoliated graphite

This paper reports an efficient and convenient removal of disperse blue 2BLN from aqueous solution by the combination of ultrasound and exfoliated graphite. The various affecting factors were studied. The removal ratio of disperse blue 2BLN is 96.9% for the initial concentration of 200 mg/L using 600 mg/L exfoliated graphite (exfoliation volume of 300 mL/g) at 45 degrees C within 120 min under ultrasound. The combination method was more effective than sonolysis or exfoliated graphite treatment individually.     

Removal of pesticide residues from fresh vegetables by the coupled free chlorine/ultrasound process

Pesticide residue in vegetables has been considered as a serious food safety problem across the whole world. This study investigates a novel advanced oxidation process (AOP), namely the coupled free chlorine/ultrasound (FC/US) process for the removal of three typical pesticides from lettuce. The removal efficiencies of dimethoate (DMT), trichlorfon (TCF) and carbofuran (CBF) from lettuce reached 86.7%, 79.8% and 71.3%, respectively by the FC/US process. There existed a synergistic effect in the coupled FC/US process for pesticide removal and the synergistic factors reached 22.3%, 19.0% and 36.4% for DMT, TCF and CBF, respectively. Based on the analysis of mass balance of pesticides, the synergistic effect was probably attributed to the efficient oxidation of pesticides both in vegetables and in water by the generated free radicals and FC. The surface area and surface structure of vegetables strongly affected the removal of pesticides by FC/US. The removal efficiency of DMT increased from 80.9% to 88.1% as solution pH increased from 5.0 to 8.0, and then decreased to 84.1% when solution pH further increased to 9.0. When the ultrasonic frequency changed from 20 to 40 kHz, a remarkable improvement in pesticide removal by FC/US was observed. As the FC concentration increased from 0 to 15 mg L^–l, the removal efficiencies of pesticides increased firstly, and then became stagnant when the FC concentration further increased to 25 mg L^–l. The pesticide degradation pathways based on the identified intermediates were proposed. The total chlorophyll content was reduced by less than 5% after the FC/US process, indicating a negligible damage to the quality of vegetables. It suggests that the FC/US process is a promising AOP for pesticides removal from vegetables.     

Latitudinal distribution of nitrogen isotopic composition in suspended particulate organic matter in tropical/subtropical seas

Natural nitrogen isotopic composition (δ(15)N) of suspended particulate organic matter (POM) and nitrogen fixation rates via (15)N(2) assay were measured in surface waters along 120° E from 30° N to 30° S in the Asian marginal seas (the East/South China Seas and the Sulu/Celebes/Java Seas) and the northeastern Indian Ocean in November-December 2005 and March 2006. The POM δ(15)N values ranged from-1.8 to 12.2‰ with an average of 3.6‰ and showed a decreasing trend towards the equator in both hemispheres. In parallel, the measured N(2) fixation rates showed an increase from the subtropical to the tropical seas. This implies that a higher contribution of (15)N-depleted POM was derived from enhanced N(2) fixation. Water temperature and the stability of water column were partly responsible for the observed variations in nitrogen fixation. The large-scale spatial variations in suspended POM δ(15)N and N(2) fixation rates suggest that the suspended POM δ(15)N may be a potential indicator of nitrogen fixation in surface waters in tropical/subtropical seas.     

Removal of particle matter from dust-vapor-gas mixture in condenser with inclined tubes

The article presents results of the research of particulate matter and droplets removal on inclined tubes of the flue gas cleaning condenser in the process of vapor condensation of vapor-and-gas emissions from kraft pulp production.     

Latitudinal distribution of nitrogen isotopic composition in suspended particulate organic matter in tropical/subtropical seas

Natural nitrogen isotopic composition (δ¹⁵N) of suspended particulate organic matter (POM) and nitrogen fixation rates via ¹⁵N₂ assay were measured in surface waters along 120° E from 30° N to 30° S in the Asian marginal seas (the East/South China Seas and the Sulu/Celebes/Java Seas) and the northeastern Indian Ocean in November–December 2005 and March 2006. The POM δ¹⁵N values ranged from?1.8 to 12.2‰ with an average of 3.6‰ and showed a decreasing trend towards the equator in both hemispheres. In parallel, the measured N₂ fixation rates showed an increase from the subtropical to the tropical seas. This implies that a higher contribution of ¹⁵N-depleted POM was derived from enhanced N₂ fixation. Water temperature and the stability of water column were partly responsible for the observed variations in nitrogen fixation. The large-scale spatial variations in suspended POM δ¹⁵N and N₂ fixation rates suggest that the suspended POM δ¹⁵N may be a potential indicator of nitrogen fixation in surface waters in tropical/subtropical seas.     

Sonochemical and photochemical oxidation of organic matter

Recent developments in sonochemistry have led us to study its use to treat water and wastewater. The effects of ultrasound wave in hydrophilic chemical oxidations are mainly due to hydroxyl radical production during the cavitation-induced water decomposition. Currently, the sonochemical destruction of aromatic compounds in water solution is obtained with low rates. The aim of this work is to evaluate the efficiency of the sonochemical effect in conjunction with a photochemical irradiation. Taking phenol as an example, the combined action of sonochemistry and photochemistry has been considered in a ‘sonuv’ reactor. An important enhancement of the degradation rate of phenol has been observed. It may be the result of three different oxidative processes: direct photochemical action, high frequency sonochemistry and reaction with ozone (produced by UV irradiation of air). The process has been successfully tested to lower the chemical oxygen demand of a municipal wastewater.     

Degradation pathways of dissolved carbon in landfill leachate traced with compound-specific 13C analysis of DOC

The isotopic compositions of carbon compounds in landfill leachate provide insights into the biodegradation pathways that dominate the different stages of waste decomposition. In this study, the carbon geochemistry of different carbon pools, environmental stable isotopes and compound-specific isotope analysis (CSIA) of leachate dissolved organic carbon (DOC) fractions and gases show distinctions in leachate biogeochemistry and methane production between the young area of active waste emplacement and the old area of historical emplacement at the Trail Road Landfill (TRL).

The active area leachate has low DOC concentrations (<200 mg l^?1) dominated by fulvic acid (FA=160 mg l^?1), and produces CH₄ dominantly by CO₂ reduction (D? excess=20.6‰). Leachate generated in the area of older waste has high DOC (>4770 mg l^?1) dominated by FA (4482 mg l^?1) and simple fatty acids (acetic=1008 mg l^?1 and propionic=608 mg l^?1), and produces CH₄ by the acetate fermentation pathway (D? excess=9.8‰). CSIA shows an advanced degradation and a progressive accumulation of ¹³C of fatty acids in leachate from the older area. The enriched ¹³C value of FA (?20 and?26‰ for the older and active parts, respectively,) and of low molecular weight DOC (?8 and?27‰) as well as of the bulk DOC (?21 and?25‰) shows more advanced degradation in the older part of the landfill, which is consistent with the shift in the humic/FA ratios (0.05 and 0.18). The ¹³C enrichment of acetate (?12‰) above the ¹³C of DOC (?21‰) and of propionic acid (?19‰), in older leachate, suggests that this acetate has not evolved from the simple degradation of larger organic molecules, but by homoacetogenesis from the enriched dissolved inorganic carbon (DIC) pool (8‰) and H_2, which produce a more enriched ¹³C of acetate. In contrast, the ¹³C of the minor acetate in the active area (?17‰) indicates that CO₂-reducing bacteria must be the primary consumers of H₂, which has resulted in enriched ¹³C_DIC (10‰) and depleted ¹³C_CH4 (?58‰).     

The application of high frequency ultrasound waves to remove ammonia from simulated industrial wastewater

This article aims at applying the ultrasound technique in the field of clean technology to protect environment. The principle of ultrasound was conducted here to remove and recover ammonia from industrial wastewater. Three different concentrations of ammonia namely 5%, 15% and 25% (vol.%) were used to study the efficiency of removing ammonia from water. These concentrations are exactly similar to what may be found in wastewater resulting from strippers at petroleum refinery. High ultrasound frequency device with 2.4 and 1.7 MHz was conducted to study the effect of waves on the removal of ammonia. It was found that the ultrasound has the ability to remove ammonia with 5% concentration to meet the local standard of treated wastewater within less than 2 h for 0.080 L solution. It was also found that as the concentration of the ammonia increases the removing of ammonia within 2 h decreases, still the concentration of the ammonia meets the standard of the treated wastewater. The ability of the ultrasound to remove the ammonia failed to produce any mist when the height of the liquid solution increased, namely when the height reached (0.0337 m). This is equivalent to liquid volume of 0.150 L. It means that the device capacity to remove ammonia has certain limitations based on liquid heights. The best condition for ammonia removal was obtained at 5% concentration and 0.080 L liquid volume (equivalent to 0.0165 m).     

Removal of organic contaminants from aqueous solution by cattle manure compost (CMC) derived activated carbons

The activated carbons (ACs) prepared from cattle manure compost (CMC) with various pore structure and surface chemistry were used to remove phenol and methylene blue (MB) from aqueous solutions. The adsorption equilibrium and kinetics of two organic contaminants onto the ACs were investigated and the schematic models for the adsorptive processes were proposed. The result shows that the removal of functional groups from ACs surface leads to decreasing both rate constants for phenol and MB adsorption. It also causes the decrement of MB adsorption capacity. However, the decrease of surface functional groups was found to result in the increase of phenol adsorption capacity. In our schematic model for adsorptive processes, the presence of acidic functional groups on the surface of carbon is assumed to act as channels for diffusion of adsorbate molecules onto small pores, therefore, promotes the adsorption rate of both phenol and MB. In phenol solution, water molecules firstly adsorb on surface oxygen groups by H-bonding and subsequently form water clusters, which cause partial blockage of the micropores, deduce electrons from the π-electron system of the carbon basal planes, hence, impede or prevent phenol adsorption. On the contrary, in MB solution, the oxygen groups prefer to combine with MB⁺ cations than water molecules, which lead to the increase of MB adsorption capacity.     

Applications of ultrasound to organic chemistry

Ultrasound promotes efficient mixing in solid-liquid and liquid-liquid mixtures and it has also been used in several phase transfer catalysed reactions, e.g. N-alkylation of amines, synthesis of ethers and esters and hydrolysis of esters. In this Paper preliminary results are presented which support the view that the presence of oxygen in a cavitating liquid generates singlet oxygen in addition to peroxy radicals.     

Removal of colloidal precipitation plugging with high-power ultrasound

Petroleum is a continuous and dynamically stable colloidal system. In the process of oil extraction, transportation, and post-treatment, the stability of the petroleum sol system is easily destroyed, resulting in asphaltenes precipitation that can make pore throat, oil wells, and pipelines blocked, thereby damaging the reservoir and reducing oil recovery. In this paper, removing near-well plugging caused by asphaltene deposition with high-power ultrasound is investigated. Six PZT transducers with different parameters were used to carry out the experimental study. Results show that ultrasonic frequency is one important factor for removing colloidal precipitation plugging in cores, it could not be too high nor too low. The optimum ultrasonic frequency is 25 kHz; Selecting transducers with a higher power is an effective way to improve the removal efficiency. The optimum ultrasonic power is 1000 W. With the increase of ultrasonic treatment time, the recovery rate reaches the maximum and tends to be stable. ultrasonic processing time should be controlled within 120 min. Besides, three methods — ultrasonic treatment alone, chemical injection alone, and ultrasound-chemical method — for removing colloidal precipitation plugging are compared. Results indicate that the ultrasound-assisted chemical method is better than chemical injection alone or ultrasonic treatment alone to remove colloidal sediment in the core. Finally, the mechanism of the ultrasonic deplugging technique is analyzed from three aspects: cavitation effect, the thermal effect, and mechanical vibration.     

Elemental quantitation of natural organic matter by CPMAS 13C NMR spectroscopy

Cross-polarized magic-angle-spinning NMR (CPMAS-NMR) techniques are assumed to be only semi-quantitative in the assessment of carbon distribution in humic substances or natural organic matter, due to a number of interferences such as spinning side bands (SSB) in spectra, paramagnetic species in samples, and low or remote protonation of aromatic carbons. Fast rotor spin rates or direct polarization NMR techniques are normally applied to improve quantitative signal detectability. Variable contact time pulse sequences were used here to obtain CPMAS-NMR spectra of organic compounds of known structure and different humic substances. Integration of spectral areas, previously subtracted of SSB, and relative stoichiometric factors were used for mathematical elaboration to calculate the elemental content in samples. These values did not significantly differ from those obtained by direct determination of elemental content with quantitative elemental analysis. Our results showed that the carbon observed CPMAS-NMR provides a quantitative representation of the whole carbon content in humic substances.     

Degradation pathways of dissolved carbon in landfill leachate traced with compound-specific (13)C analysis of DOC

The isotopic compositions of carbon compounds in landfill leachate provide insights into the biodegradation pathways that dominate the different stages of waste decomposition. In this study, the carbon geochemistry of different carbon pools, environmental stable isotopes and compound-specific isotope analysis (CSIA) of leachate dissolved organic carbon (DOC) fractions and gases show distinctions in leachate biogeochemistry and methane production between the young area of active waste emplacement and the old area of historical emplacement at the Trail Road Landfill (TRL). The active area leachate has low DOC concentrations (<200 mg l(-1)) dominated by fulvic acid (FA=160 mg l(-1)), and produces CH(4) dominantly by CO(2) reduction (D- excess=20.6 per thousand). Leachate generated in the area of older waste has high DOC (>4770 mg l(-1)) dominated by FA (4482 mg l(-1)) and simple fatty acids (acetic=1008 mg l(-1) and propionic=608 mg l(-1)), and produces CH(4) by the acetate fermentation pathway (D- excess=9.8 per thousand). CSIA shows an advanced degradation and a progressive accumulation of (13)C of fatty acids in leachate from the older area. The enriched (13)C value of FA (-20 and-26 per thousand for the older and active parts, respectively,) and of low molecular weight DOC (-8 and-27 per thousand) as well as of the bulk DOC (-21 and-25 per thousand) shows more advanced degradation in the older part of the landfill, which is consistent with the shift in the humic/FA ratios (0.05 and 0.18). The (13)C enrichment of acetate (-12 per thousand) above the (13)C of DOC (-21 per thousand) and of propionic acid (-19 per thousand), in older leachate, suggests that this acetate has not evolved from the simple degradation of larger organic molecules, but by homoacetogenesis from the enriched dissolved inorganic carbon (DIC) pool (8 per thousand) and H(2,) which produce a more enriched (13)C of acetate. In contrast, the (13)C of the minor acetate in the active area (-17 per thousand) indicates that CO(2)-reducing bacteria must be the primary consumers of H(2), which has resulted in enriched (13)C(DIC) (10 per thousand) and depleted (13)C(CH4) (-58 per thousand).