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Microbial activity related to N cycling in the rhizosphere of maize stressed by heavy metals

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Journal of Environmental Sciences 2005年第3期17卷 448-451页

作者： YANGYe CHENYing-xu TIANGuang-ming ZHANGZi-jian departmentofenvironmentalengineering ZhejiangUniversityHangzhou310029China departmentofenvironmentalengineering ZhejiangUniversityHangzhou310029China

A greenhouse experiment was carried out to compare differences in potential activities of ammonification, nitrification and denitrification in rhizosphere and bulk soil in a heavy-metal-stressed system. Exchangeable fractions of Cd, Cu and Cr were all higher in the rhizosphere of maize than in bulk soil. Results showed that the mineralization of N in soil was stimulated by low concentration of Cd. Addition of Cd at low levels stimulated the ammonifying and nitrifying activity in soil, while inhibitory influences were shown at high levels. Nitrifying bacteria was proved to be the most sensitive one, whilst the effect on denitrifying bacteria was very limited. Comparing Cd, Cu and Cr(VI) at 20 mg/kg soil, Cd was the most effective inhibitor of ammonification and denitrification, while Cr(VI) had the strongest inhibitory influence on nitrifying activity. Root exudates played important roles on the different exchangeable metal fractions and bacterial activities between rhizosphere and non-rhizosphere. Nitrate was the main form of mineral N in soil, as well as the main form of N absorbed by plants, but the formation and relative absorption of ammonium were promoted in response to high Cd exposure.

关键词： heavy metal nitrogen cycle rhizosphere root exudates

Modeling of mass transfer characteristics of bubble column reactor with surfactant present

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Journal of Zhejiang University Science 2004年第6期5卷 714-720页

作者：赵伟荣史惠祥汪大翚 departmentofenvironmentalengineering ZhejiangUniversityHangzhou310027China

Danckwert’s method was used to determine the specific interfacial area, a, and the individual mass transfer coefficient, kL, during absorption of CO2 in a bubble column with an anionic surfactant in the carbonate-bicarbonate buffer solution and NaAsO2 as catalyst, the presence of which decreases the specific interfacial area and the individual mass transfer coefficient. The specific interfacial area and the individual mass transfer coefficient increase with increasing su- perficial gas velocity. The specific interfacial area decreases whereas the individual mass transfer coefficient increases with increasing temperature. The results of experiments were used to determine the dependence of a, kL, and kLa on the surface tension, the temperature of the absorption phase, and the superficial velocity of the gas. The calculated results from the correlation were found to be within 10% deviation from the actual experimental results.

关键词： Mass transfer coefficient Surfactant Bubble column reactor Gas absorption

Heterogeneous UV／Fenton catalytic degradation of wastewater containing phenol with Fe－Cu－Mn－Y catalyst

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Journal of Zhejiang University Science 2004年第2期5卷 206-211页

作者：郑展望雷乐成徐生娟岑沛霖 departmentofenvironmentalengineering ZhejiangUniversityHangzhou310027China

The heterogeneous UV/Fenton process with the appropriate amount of Fe-Mn-Cu-Y as catalyst was developed and various operation conditions for the degradation of phenol were evaluated. The results indicated that by using the het-erogeneous UV/Fenton process, the CODcr removal rate reached almost 100% for wastewater containing phenol. Compared with the homogeneous process, the developed catalyst could be used at wider pH range in the UV/Fenton process. Com-parison of various heterogeneous process showed that heterogeneous UV/Fenton process was best. The heterogeneous UV/Fenton process with Fe-Mn-Cu-Y catalyst is highly efficient in degrading various organic pollutants.

关键词： Heterogeneous catalyst Wastewater treatment UV/Fenton

Biological removal of air loaded with a hydrogen sulfide and ammonia mixture

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Journal of Environmental Sciences 2004年第4期16卷 656-661页

作者： CHENYing-xu YINJun FANGShi departmentofenvironmentalengineering ZhejiangUniversityHangzhou310029China

The nuisance impact of air pollutant emissions from wastewater pumping stations is a major issue of concern to China. Hydrogen sulfide and ammonia are commonly the primary odor and are important targets for removal. An alternative control technology, biofiltration, was studied. The aim of this study is to investigate the potential of unit systems packed with compost in terms of ammonia and hydrogen sulfide emissions treatment, and to establish optimal operating conditions for a full-scale conceptual design. The laboratory scale biofilter packed with compost was continuously supplied with hydrogen sulfide and ammonia gas mixtures. A volumetric load of less than 150 gH 2S/(m3·d) and 230 gNH 3/(m3·d) was applied for about fifteen weeks. Hydrogen sulfide and ammonia elimination occurred in the biofilter simultaneously. The removal efficiency, removal capacity and removal kinetics in the biofilter were studied. The hydrogen sulfide removal efficiency reached was very high above 99%, and ammonia removal efficiency was about 80%. Hydrogen sulfide was oxidized into sulphate. The ammonia oxidation products were nitrite and nitrate. Ammonia in the biofilter was mainly removed by adsorption onto the carrier material and by absorption into the water fraction of the carrier material. High percentages of hydrogen sulfide or ammonia were oxidized in the first section of the column. Through kinetics analysis, the presence of ammonia did not hinder the hydrogen sulfide removal. According to the relationship between pressure drop and gas velocity for the biofilter and Reynolds number, non-Darcy flow can be assumed to represent the flow in the medium.

关键词： biological removal hydrogen sulfide ammonia mixture

Electrokinetic characteristic and coagulation behavior of flocculant polyaluminum silicate chloride (PASiC)

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Journal of Environmental Sciences 2003年第1期15卷 69-74页

作者： YUEQin－yan GAOBao－yu 等 departmentofenvironmentalengineering SchoolofEnvironmentalShangdongUniversityJina250100China

The electrokinetic characteristics and coagulation behaviors of polyaluminum silicate chloride (PASiC) and polyaluminum chloride (PAC) were studied and compared by streaming current (SC) measurement and jar test method. The experimental results showed that the interaction between polysilicic acid characterized negative charge and hydrolyzed aluminum species result in a decrease of the charge neutralizing ability of PASiC, compared to PAC. The decrease has a close relationship with the basicity ( B ) and Al/Si molar ratio in PASiC. The less the B value and the Al/Si molar ratio, the lower the charge neutralizing ability of PASiC is. In contrast, the preparation technique for PASiC affects the charge-neutralization of PASiC to a smaller extent. In addition, compared with PAC, PASiC may enhance aggregating efficiency and give better coagulating effects.

关键词： flocculant polyaluminum chloride (PASiC) streaming current (SC) electrokinetic characteristics coagulation effect

Stability of expanded granular sludge bed process for terylene artificial silk printing and dyeing wastewater treatment

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Journal of Environmental Sciences 2005年第3期17卷 419-424页

作者： GUANBao-hong departmentofenvironmentalengineering ZhejiangUniversityHangzhou310027China

Terylene artificial silk printing and dyeing wastewater(TPD wastewater), containing averaged 710 mg/L terephthalic acid(TA) as the main carbon source and the character pollutant, was subjected to expanded granular sludge bed(EGSB) process. The stability of the EGSB process was firstly conducted by laboratory experiment. TA ionization was the predominated factor influencing the acid-base balance of the system. High concentration of TA in wastewater resulted in sufficient buffering capacity to neutralize the volatile fatty acids(VFA) generated from substrate degradation and provided strong base for anaerobic system to resist the pH decrease below 6.5. VFA and UFA caused almost no inhibition on the anaerobic process and biogas production except that pH was below 6.35 and VFA was at its maximum value. Along with the granulating of the activated sludge, the efficiency of organic removal and production rate of biogas increased gradually and became more stable. After start-up, the efficiency of COD removal increased to 57%—64%, pH stabilized in a range of 7.99—8.04, and production rate of biogas was relatively high and stable. Sludge granulating, suitable influent of pH and loading were responsible for the EGSB stability. The variation of VFA concentration only resulted in neglectable rebound of pH, and the inhibition from VFA could be ignored in EGSB. The EGSB reactor was stable for TPD wastewater treatment.

关键词： expanded granular sludge bed stability anaerobic treatment dyeing and printing wastewater

Desulfurization of dibenzothiophene by a newly isolated Corynebacterium sp. ZD-1 in aqueous phase

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Journal of Environmental Sciences 2004年第6期16卷 1011-1015页

作者： WANGMiao-dong LIWei WANGDa-hui SHIYao departmentofenvironmentalengineering ZhejiangUniversityHangzhou310027China

Sulfur emission through fuel combustion is a global problem because it is a major cause of acid rain. Crud oil contains many heterocyclic organic sulfur compounds, among which dibenzothiophene(DBT) and DBTs bearing alkyl substitutions usually are representative compounds. A strain was isolated from refinery sludge and identified as Corynebacterium ZD-1. The behavior of DBT degradation by ZD-1 in aqueous phase was investigated. Corynebacterium ZD-1 could metabolize DBT to 2-hydroxybiphenyl(2-HBP) as the dead-end metabolite through a sulfur-specific pathway. In shake flask culture, ZD-1 had its maximal desulfurization activity in the late exponential growth phase and the specific production rate of 2-HBP was about 0.14(mmol·kg dry cell -1·min -1, mmol·KDC -1·min -1). Active resting cells for desulfurization should be prepared only in this period. 2-HBP inhibited the growth of strain ZD-1, the production of DBT degradation enzymes, and the activity of enzymes. Sulfate inhibited the production of dibenzothiophene(DBT) degradation enzymes but had no effect on the enzymes' activity. The production rates of 2-HBP at lower cell densities were higher and the maximum amount conversion of DBT to 2-HBP(0.067 mmol/L) after 8 h was gained at 9.2 g dry cell/L rather higher cell density. The results indicated that this newly isolated strain could be a promising biocatalyst for DBT desulfurization.

关键词： biodesulfurization dibenzothiophene Corynebacterium

Degradation of chlorophenol by in－situ electrochemically generated oxidant

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Journal of Zhejiang University Science 2004年第2期5卷 180-185页

作者：丛燕青吴祖成叶倩谭天恩 departmentofenvironmentalengineering ZhejiangUniversityHangzhou310027China

A novel in-situ electrochemical oxidation method was applied to the degradation of wastewater containing chlorophenol. Under oxygen sparging, the strong oxidant, hydrogen dioxide, could be in-situ generated through the reduction of oxygen on the surface of the cathode. The removal rate ofchlorophenol could be increased 149% when oxygen was induced in the electrochemical cell. The promotion factor was estimated to be about 82.63% according to the pseudo-first-order reaction rate constant (min^-1). Important operating parameters such as current density, sparged oxygen rate were investigated. Higher sparged oxygen rate could improve the degradation of chlorophenol. To make full use of oxygen, however, sparged oxygen rate of 0.05 m3/h was adopted in this work. Oxidation-reduction potential could remarkably affect the generation of hydrogen peroxide. It was found that the removal rate of chlorophenol was not in direct proportion to the applied current density. The optimum current density was 3.5 mA/cm^2 when initial chlorophenol concentration was 100 mg/L and sparged oxygen rate was 0.05 m^3/h.

关键词： In-situ electrochemical oxidation Chlorophenol Oxygen Hydrogen peroxide

Catalytic oxidation of calcium sulfite in solution/aqueous slurry

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Journal of Environmental Sciences 2004年第6期16卷 973-977页

作者： WUXiao-qin WUZhong-biao WANGDa-hui departmentofenvironmentalengineering ZhejiangUniversityHangzhou310027China

Forced oxidation of calcium sulfite aqueous slurry is a key step for the calcium-based flue gas desulfurization(FGD) residue. Experiments were conducted in a semi-batch system and a continuous flow system on lab scales. The main reactor in semi-batch system is a 1000 ml volume flask. It has five necks for continuous feeding of gas and a batch of calcium sulfite solution/aqueous slurry. In continuous flow system, the main part is a jacketed Pyrex glass reactor in which gas and solution/aqueous slurry are fed continuously. Calcium sulfite oxidation is a series of complex free-radical reactions. According to experimental results and literature data, the reactions are influenced significantly by manganese as catalyst. At low concentration of manganese and calcium sulfite, the reaction rate is dependent on 1.5 order of sulfite concentration, 0.5 order of manganese concentration, and zero order of oxygen concentration in which the oxidation is controlled by chemical kinetics. With concentrations of calcium sulfite and manganese increasing, the reactions are independent gradually on the constituents in solution but are impacted by oxygen concentration. Manganese can accelerate the free-radical reactions, and then enhances the mass transfer of oxygen from gas to liquid. The critical concentration of calcium sulfite is 0.007 mol/L, manganese is 10 -4 mol/L, and oxygen is of 0.2—0.4 atm.

关键词： calcium-based FGD calcium sulfite manganese catalyzed oxidation