亚硝酸盐对外碳源反硝化过程N2O还原的影响

本试验通过批次试验考察了亚硝酸盐对外碳源反硝化过程N2O还原的影响.结果表明NO2--N初始浓度为5.92~35.23mg/L时,随着NO2--N浓度的增加,反硝化过程中N2O的积累量逐渐增加;当NO2--N浓度为35.23mg/L时,NO2--N还原量的46.26%被转化为N2O.通过对比试验得出,N2O还原酶与亚硝酸盐还原酶对电子的竞争和游离亚硝酸(FNA)对N2O还原酶的抑制会导致N2O比还原速率下降,造成反硝化过程N2O积累.基于上述试验结果提出,污水处理厂可通过调控运行条件控制NO2--N浓度,降低反硝化过程的N2O的产生与释放;也可以通过短程硝化提高NO2--N浓度,促进反硝化过程N2O的积累,再通过N2O氧化甲烷减少N2O排放,同时提高产能37%.     

昼夜增温对大豆田土壤N2O排放的影响

通过田间试验,用静态箱-气相色谱法测定N2O排放通量,研究昼夜增温对大豆田土壤N2O排放的影响.结果表明,增温没有改变大豆田土壤N2O排放通量的季节性变化规律.整个生长季,与对照相比,增温土壤N2O平均排放通量增加了17.31%(P=0.019),累积排放量显著增加了20.27%(P=0.005).对照与增温处理土壤N2O排放通量与土壤温湿度均呈显著性相关关系,对照与增温土壤的N2O排放温度敏感系数分别为3.75和4.10.整个生育期,增温显著增加了植株地上和总生物量、叶片硝酸还原酶活性和全氮含量,显著降低了叶片NO3--N含量;显著增加了土壤NO3--N含量,但对土壤有机碳及全氮含量没有显著影响.本研究表明,昼夜增温显著增加了大豆田土壤N2O的排放.     

厌氧条件下砂壤水稻土N2、N2O、NO、CO2和CH4排放特征

了解厌氧条件土壤反硝化气体(N2、N2O和NO)、CO2和CH4排放特征,是认识反硝化过程机制的基础,并有助于制定合理的温室气体减排措施.定量反硝化产物组成,可为氮转化过程模型研发制定正确的关键过程参数选取方法或参数化方案.本研究选取质地相同(砂壤土)的两个水稻土为研究对象,通过添加KNO3和葡萄糖的混合溶液,将培养土壤的初始NO-3和DOC含量分别调节到50 mg·kg-1和300 mg·kg-1,采用氦环境培养-气体及碳氮底物直接同步测定方法,研究完全厌氧条件下土壤N2、N2O、NO、CO2和CH4的排放特征,并获得反硝化气态产物中各组分的比率.结果表明,在整个培养过程中,两个供试土壤的N2、N2O和NO累积排放量分别为6~8、20和15~18 mg·kg-1,这些气体排放量测定结果可回收土壤NO-3变化量的95%~98%,反硝化气态产物以N2O和NO为主,其中3种组分的比率分别为15%~19%(N2)、47%~49%(N2O)和34%~36%(NO);但反硝化气体产物组成的逐日动态均显现为从以NO为主逐渐过渡到以N2O为主,最后才发展到以N2为主.以上结果说明,反硝化气体产物组成是随反硝化进程而变化的,在以气体产物组成比率作为关键参数计算各种反硝化气体产生率或排放率的模型中,很有必要重视这一点.     

以甲醇为碳源生物反硝化过程释放一氧化二氮的试验研究

污水生物反硝化脱氮过程是一氧化二氮(N2O)的重要释放源之一.试验采用序批式反应器以甲醇为碳源(电子供体),硝酸盐(NO3--N)为电子受体驯化反硝化菌,并采用批处理试验研究不同电子受体、不同碳氮(C/N)比和不同初始亚硝酸盐(NO2--N)质量浓度条件下N2O释放情况.在典型周期试验和批处理试验中均能检测到N2O的释放.以NO2--N为电子受体时会释放较多的N2O,而以NO3--N为电子受体时释放的N2O相对较少.不同C/N比通过影响反硝化菌的活性进而影响N2O的释放,反硝化菌的活性和N2O的释放量均随着C/N比的降低而降低.N2O的释放量随着初始NO2--N质量浓度的增加而增加,一定浓度范围内的NO2--N会增强反硝化菌的活性.初始NO2--N质量浓度与N2O的释放量具有较好的指数相关性.     

黄河上游灌区连作稻田N2O排放特征及影响因素

黄河上游灌区高产连作稻田氮肥的过量施用引起土壤氮素盈余,进而导致稻田N2O排放量增大.为了探明水稻连作模式下稻田N2O排放特征及影响因素,采用静态箱-气相色谱法,开展了为期2年的连作水稻田试验研究.试验共设置3个施氮处理,包括常规氮肥300kg.hm-2(N300)、优化氮肥240kg.hm-2(N240)和对照不施氮肥(N0),并在稻田连作的第2年,对N240处理灌溉节水30%.2年连作试验结果表明,水稻生长季稻田N2O排放主要发生在水稻施基肥后及水稻生长的中后期,在稻田灌水泡田后N2O排放速率达最大值.稻田高氮肥(300kg.hm-2)施用显著增加N2O的排放量,优化氮肥(240kg.hm-2)处理可有效降低土壤N2O排放量(p<0.01).水稻生长季稻田淹水状态时N2O排放量极低,稻田灌溉节水会相应增加土壤N2O排放量.土壤温度变化对稻田N2O的生成和排放会产生较大影响,但受稻田肥水管理等因素的影响,温度与N2O排放量相关性不显著.灌区稻田土壤N2O排放通量与田面水NO3--N含量变化及耕层0～40cm土壤NO3--N积累量变化有显著的相关性.稻田连作显著增加了耕层土壤剖面0～40cm土层NO3--N的积累量,耕层土壤NO3--N积累量的增加进而加大了土壤N2O排放的风险.在宁夏黄灌区稻田常规灌水和高氮肥(300kg.hm-2)水平下,2年连作稻田水稻生长季土壤N2O总排放量分别达55.98×104kg.a-1和51.48×104kg.a-1,在100a时间尺度上的全球增温潜势(GWPs)均值为16.02×107kg.hm-2(以CO2计),表明黄灌上游灌区高氮肥施用导致稻田N2O排放量增大,由此引起的增温潜势严重.     

碳源对反硝化过程中一氧化二氮释放的影响

碳源种类及其浓度影响污水处理反硝化过程中一氧化二氮(N2O)的释放。以往关于碳源对反硝化过程中N2O释放特性的研究多采用单一碳源驯化活性污泥,采用混合碳源条件驯化的研究尚少。利用序批式反应器,以蔗糖和乙酸钠为混合碳源驯化反硝化菌。采用批处理试验研究了不同碳源(乙酸钠、葡萄糖和两者混合)在不同碳氮比(COD/N)条件下,利用硝酸盐氮(NO3--N)或亚硝酸盐氮(NO2--N)进行反硝化时N2O的释放。以NO2--N为电子受体进行反硝化时,N2O释放量远大于以NO3--N为电子受体进行反硝化时的释放量。碳源种类影响N2O释放,其释放比从低到高依次为乙酸钠、混合碳源和葡萄糖。以乙酸钠为碳源且当COD/N较低时,由于NO2--N积累和内源反硝化,导致较多N2O的释放,而在碳源相对充足情况下释放量较少。以葡萄糖为碳源时,由于反硝化速率较低,N2O释放量大于利用乙酸钠时的释放量,同时释放量随COD/N比的增加而增加。在混合碳源条件下,反硝化菌优先利用乙酸钠进行反硝化,N2O释放量随COD/N比的增加而降低。     

Characteristics and factors of the N20 emission from the continuous cropping paddyfield in irrigation area of the Yellow River

黄河上游灌区高产连作稻田氮肥的过量施用引起土壤氮素盈余,进而导致稻田N2O排放量增大.为了探明水稻连作模式下稻田N2O排放特征及影响因素,采用静态箱-气相色谱法,开展了为期2年的连作水稻田试验研究.试验共设置3个施氮处理,包括常规氮肥300kg.hm-2（N300）、优化氮肥240kg.hm-2（N240）和对照不施氮肥（N0）,并在稻田连作的第2年,对N240处理灌溉节水30%.2年连作试验结果表明,水稻生长季稻田N2O排放主要发生在水稻施基肥后及水稻生长的中后期,在稻田灌水泡田后N2O排放速率达最大值.稻田高氮肥（300kg.hm-2）施用显著增加N2O的排放量,优化氮肥（240kg.hm-2）处理可有效降低土壤N2O排放量（p〈0.01）.水稻生长季稻田淹水状态时N2O排放量极低,稻田灌溉节水会相应增加土壤N2O排放量.土壤温度变化对稻田N2O的生成和排放会产生较大影响,但受稻田肥水管理等因素的影响,温度与N2O排放量相关性不显著.灌区稻田土壤N2O排放通量与田面水NO3--N含量变化及耕层0～40cm土壤NO3--N积累量变化有显著的相关性.稻田连作显著增加了耕层土壤剖面0～40cm土层NO3--N的积累量,耕层土壤NO3--N积累量的增加进而加大了土壤N2O排放的风险.在宁夏黄灌区稻田常规灌水和高氮肥（300kg.hm-2）水平下,2年连作稻田水稻生长季土壤N2O总排放量分别达55.98×104kg.a-1和51.48×104kg.a-1,在100a时间尺度上的全球增温潜势（GWPs）均值为16.02×107kg.hm-2（以CO2计）,表明黄灌上游灌区高氮肥施用导致稻田N2O排放量增大,由此引起的增温潜势严重.     

亚热带土壤反硝化过程中NO3--N对CH4排放的影响

研究了发育于不同成土母质和不同土地利用方式下的45个亚热带土壤样本,在反硝化严格厌氧培养条件下(密闭、淹水、充N2),加入KNO3的处理(加入N量为200 mg·kg-1)和不加KNO3的空白对照对CH4产生和排放的影响.结果表明,厌氧培养条件下无论加入KNO3与否,CH4的产生和排放首先取决于土壤有机碳总量水平及其有效性.对照土壤中花岗岩母质发育的土壤和KNO3处理土壤中稻田利用方式下的土壤CH4排放量最高.加入KNO3显著抑制了CH4的产生和排放,NO3--N对CH4,产生的抑制效应可能较N2O对CH4产生的抑制效应更大.加入KNO3处理中厌氧培养第1周内的NO3-反硝化量和降低速率是决定CH4排放量的关键因素.不加KNO3的对照土壤中,73%的土样表现为Fe2+的产生和CH4的排放之间呈指数关系增长,表明Fe3和CO2的还原可同步进行.NO3--N不仅显著抑制了CH4的产生和排放,也抑制了Fe3+的还原.     

厌气条件下百菌清对土壤N2O和CH4排放的影响

在密闭、淹水、充N2的严格厌氧条件下对土壤进行了14d的培养试验,研究了杀菌剂百菌清在添加水平为田间施用量（FR）(5.5 mg·kg-1),20倍(20FR)和40倍田间施用量(40FR)时对强酸性、酸性、中性和碱性土壤N2O和CH4排放的影响.结果表明,20FR和40 FR的百菌清能够显著促进N2O向N2的还原,降低N2O排放,在酸性、中性和碱性土壤中培养14d后,对照处理的N2O排放量为0.076~0.46mg·kg-1,而20FR和40FR处理的N2O排放量为0.004~0.06mg·kg-1,降低了１个数量级.反硝化作用和有机氮矿化作用强的土壤中,百菌清减少N2O排放作用更明显.反硝化底物NO-3的存在对CH4的产生与排放具有显著的抑制作用.在加入百菌清未对NO-3浓度产生显著影响的土壤中,百菌清对CH4排放量没有明显影响,在对NO-3浓度产生显著影响的土壤中,CH4排放量随着NO-3的增加而减少,说明百菌清可能通过影响反硝化过程中NO-3的消耗而影响CH4排放.     

外源氮输入对不同土地利用排水沟底泥反硝化和N2O排放影响

农田排水沟通过底泥硝化-反硝过程可消纳部分农业面源氮.水稻、蔬菜和水果是太湖地区种植业的主要土地利用类型,各种植区排水河沟密布,且不同种植区沟道接受外源氮差异明显,直接影响沟道消纳氮能力.分别采集太湖地区果园、稻田和菜地种植区排水沟道沉积物,设计上覆水N0、N1、N2、N3和N4这5个外源NO-3-N输入梯度,净氮输入量分别为0、0.5、1.0、5.0和10 mg·L~(-1),开展室内培养试验,研究外源氮输入对不同土地利用区排水沟道底泥反硝化和N2O排放的影响.结果表明,外源氮输入激发了排水沟底泥反硝化作用,3条沟道底泥反硝化速率均随上覆水NO-3-N输入浓度增大显著增大(P0.05),底泥累积反硝化量与输入NO-3-N浓度呈显著线性正相关关系(R20.75);除菜地外,沟道底泥N2O排放速率和累积排放量随外源NO-3-N输入浓度增大均无显著增大趋势(P0.05).在无外源氮或低外源氮输入时(N0和N1),果园、菜地和稻田种植区3种沟道之间底泥反硝化和N2O排放累积损失氮量的差异不显著(P0.05).随NO-3-N输入浓度增大,特别是高外源氮输入(N3和N4)条件下,果园和稻田排水沟道底泥反硝化消纳氮量显著高于菜地沟道底泥反硝化损失氮量(P0.05),而菜地排水沟底泥N2O排放损失氮量显著高于其它2条沟道底泥的N2O排放损失氮量(P0.05).排水沟底泥有机碳矿化速率与反硝化损失速率成正相关关系(n=15),微生物矿化(CO2-C)作用促进了沟道底泥硝化反硝过程.     

Toxic effects of acetochlor, methamidophos and their combination on nifH gene in soil

Toxic effects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel electrophoresis （DGGE） and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene diversity （both in gene richness and diversity index values） and caused changes in the nifH gene composition. The effects of acetochlor on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed that nifH gene composition which had been affected by low concentration of acetochlor （50 mg/kg） recovered firstly. Methamidophos reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos （150 mg/kg） caused the most apparent changes in nifH gene diversity at the first week while the high concentration of methamidophos （250 mg/kg） produced prominent effects on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found at 1 week and maximal changes at 4 weeks. Toxic effects of acetochlor and methamidophos combination on nifH gene were also apparent. Different nifH genes （bands） responded differently to the impact of agrochemicals： four individual bands were eliminated by the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 different nifH sequences, which were used for phylogenetic reconstructions. All sequences were affiliated with the alpha- and beta-proteobacteria, showing higher similarity to eight different diazotrophic genera.     

Arsenic uptake by arbuscular mycorrhizal maize （Zea mays L.） grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment.Non-mycorrhizal and zero-P addition controls were included.Plant biomass and concentrations and uptake of As,P,and other nutrients,AM colonization,root lengths,and hyphal length densities were determined.The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium.Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments,but shoot and root biomass of AM plants was depressed by P application.AM fungal inoculation decreased shoot As concentrations when no P was added,and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition,respectively.Shoot and root uptake of P,Mn,Cu,and Zn increased,but shoot Fe uptake decreased by 44.6%,with inoculation, when P was added.P addition reduced shoot P,Fe,Mn,Cu,and Zn uptake of AM plants,but increased root Fe and Mn uptake of the nonmycorrhizal ones.AM colonization therefore appeared to enhance plant tolerance to As in low P soil,and have some potential for the phytostabilization of As-contaminated soil,however,P application may introduce additional environmental risk by increasing soil As mobility.     

Degradation of metabolites accumulated of benzo[a]pyrene by coupling Penicillium Chrysogenum with KMnO4

Several main metabolites of benzo[a]pyrene （BaP） formed by Penicillium chrysogenum, Benzo[a]pyrene-1,6-quinone （BP 1,6- quinone）, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene （BP 7,8-diol）, 3-hydroxybenzo[a]pyrene （3-OHBP）, were identified by high-performance liquid chromatography （HPLC）. The three metabolites were liable to be accumulated and were hardly further metabolized because of their toxicity to microorganisms. However, their further degradation was essential for the complete degradation of BaP. To enhance their degradation, two methods, degradation by coupling Penicillium chrysogenum with KMnO4 and degradation only by Penicillium chrysogenum, were compared; Meanwhile, the parameters of degradation in the superior method were optimized. The results showed that （1） the method of coupling Penicillium chrysogenum with KMnO4 was better and was the first method to be used in the degradation of BaP and its metabolites; （2） the metabolite, BP 1,6-quinone was the most liable to be accumulated in pure cultures; （3） the effect of degradation was the best when the concentration of KMnO4 in the cultures was 0.01% （w/v）, concentration of the three compounds was 5 mg/L and pH was 6.2. Based on the experimental results, a novel concept with regard to the bioremediation of BaP-contaminated environment was discussed, considering the influence on environmental toxicity of the accumulated metabolites.     

Impact of atrazine and nitrogen fertilizers on the sorption of chlorotoluron in soil and model sorbents

Sorption of chlorotoluron in ammonium sulfate, urea and atrazine multi-solutes system was investigated by batch experiments. The results showed application of nitrogen fertilizers to the soil could affect the behavior of chlorotoluron. At the same concentration of N, sorption of chlorotoluron decreased as the concentration of atrazine increased on the day 0 and 6 in soil, respectively. The sorption of chlorotoluron increased from 0 to 6 d when soils were preincubated with deionized water, ammonium sulfate and urea solution for 6 d. That indicated incubation time was one of the most important factors for the sorption of chlorotoluron in nitrogen fertilizers treatments. The individual sorption isotherms of chlorotoluron in rubbery polymer and silica were strictly linear in single solute system, but there were competition sorption between pesticides or between pesticides and nitrogen fertilizers. That indicated the sorption taken place by concurrent solid-phase dissolution mechanism and sorption on the interface of water-organic matter or water-mineral matter.     

Distribution and ecological effect of mercury in Laogang landfill, Shanghai, China

Laogang landfill near Shanghai is the largest landfill in China, and receives about 10000 t of daily garbage per day, Samples of topsoil and plants were analyzed to evaluate mercury pollution from the landfill. For topsoil samples, there were significant correlations among total mercury （HgT）, combinative mercury （Hgc） and gaseous mercury （HgG）, and content of total organic carbon （TOC）, but, no significantly relationship was found between Hg content and filling time. Hg content changes in vertical profiles with time showed that the average Hgv of profiles 1992, 1996, and 2000 was similar, but their average HgG was quite different. HgT was significantly correlated with Hgc in profile 1992 and 2000, and Hgv was significantly correlated with Hg6 in profile 1996. HgG/Hgv ratio in profile samples decreased in the order of （HgG,/HgT）1992〉（HgG/HgT）1996〉〉（HgG/HgT）2000. A simple outline of Hg release in landfill could be drawn： with increasing of filling time, degradation undergoes different biodegradation, accordingly, gaseous mercury goes through small, more, and small proportion to total mercury. Distribution of Hg in plants was inhomogeneous, following the order of leaf〉root〉stem. The highest value of leaf may be associated with higher atmospheric Hg from landfill. Ligneous plants （e.g. Phyllostachys glanca, Prunus salicina and Ligustrum lucidum） are capable of enriching more Hg than herbaceous plants.     

EDTA-enhanced phytoremediation of lead contaminated soil by Bidens maximowicziana

Phytoremediation is a potential cleanup technology for the removal of heavy metals from contaminated soils.Bidens maximowicziana is a new Pb hyperaccumulator,which not only has remarkable tolerance to Pb but also extraordinary accumulation capacity for Pb.The maximum Pb concentration was 1509.3 mg/kg in roots and 2164.7 mg/kg in overground tissues.The Pb distribution order in the B. maximowicziana was:leaf>stem>root.The effect of amendments on phytoremediation was also studied.The mobility of soil Pb and the Pb concentrations in plants were both increased by EDTA application.Compared with CK(control check),EDTA application promoted translocation of Pb to overground parts of the plant.The Pb concentrations in overground parts of plants was increased from 24.23-680.56 mg/kg to 29.07-1905.57 mg/kg.This research demonstrated that B.maximowicziana appeared to be suitable for phytoremediation of Pb contaminated soil,especially,combination with EDTA.     

Potential of plant polyphenol oxidases in the decolorization and removal of textile and non-textile dyes

In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.     

Decomposition of alachlor by ozonation and its mechanism

Decomposition and corresponding mechanism of alachlor, an endocrine disruptor in water by ozonation were investigated. Results showed that alachlor could not be completely mineralized by ozone alone. Many intermediates and final products were formed during the process, including aromatic compounds, aliphatic carboxylic acids, and inorganic ions. In evoluting these products, some of them with weak polarity were qualitatively identified by GC-MS. The information of inorganic ions suggested that the dechlorination was the first and the fastest step in the ozonation of alachlor.     

Enzymatic oxidation of aqueous pentachlorophenol

The influence of the nonionic surfactant Tween 80 on pentachlorophenol （PCP） oxidation catalyzed by horseradish peroxidase was studied. The surfactant was tested at concentrations below and above its critical micelle concentration （CMC）. Enhancement of PCP removal was observed at sub-CMCs. The presence of Tween 80 in the reaction mixture reduced enzyme inactivation which occurred through a combination of free radical attack and sorption by precipitated products. A simple first-order model was able to simulate time profiles for enzyme inactivation in the presence or absence of Tween 80. At supra-CMCs, the surfactant caused noticeable reductions in PCP removal, presumably through micelle partitioning of PCP which precluded the hydrophobic PCP molecule from interacting with the enzyme.     

Removal of heavy metals from sewage sludge by low costing chemical method and recycling in agriculture

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