A national critical loads framework for atmospheric deposition effects assessment: IV. Model selection,applications, and critical loads mapping

The critical loads approach is emerging as an attractive means for evaluating the effects of atmospheric deposition on sensitive terrestrial and aquatic ecosystems. Various approaches are available for modeling ecosystem responses to deposition and for estimating critical load values. These approaches include empirical and statistical relationships, steady-state and simple process models, and integrated-effects models. For any given ecosystem, the most technically sophisticated approach will not necessarily be the most appropriate for all applications; identification of the most useful approach depends upon the degree of accuracy needed and upon data and computational requirements, biogeochemical processes being modeled, approaches used for representing model results on regional bases, and desired degree of spatial and temporal resolution. Different approaches are characterized by different levels of uncertainty. If the limitations of individual approaches are known, the user can determine whether an approach provides a reasonable basis for decision making. Several options, including point maps, grid maps, and ecoregional maps, are available for presenting model results in a regional context. These are discussed using hypothetical examples for choosing populations and damage limits. The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract #68-C8-0006 with ManTech Environmental Technology, Inc., and Interagency Agreement #1824-B014-A7 with the U.S. Department of Energy and at Oak Ridge National Laboratory managed by Martin Marietta Energy Systems, Inc., under Contract DE-AC05-84OR21400 with the US Department of Energy. Environmental Sciences Division Publication No. 3904. It has been subjected to the agency’s peer and administrative review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

间歇曝气系统中硝酸盐氮负荷对脱氮效率的影响

本试验主要考察间歇反应器缺氧阶段硝酸盐氮负荷ＮＮＯ－ｘ－Ｎ（ＫｇＮＯ－ｘ－Ｎ／ＫｇＭＬＳＳｄ）对脱氮效率的影响。试验结果表明：在一定水温和ＢＯＤ５／ＮＯｘ－Ｎ下,ＮＮＯｘ－Ｎ负荷对脱氮效率有显著影响。在反应器中采用高浓度污泥是降低ＮＮＯｘ－Ｎ的有效途径,有利于反应器脱氮速率ＶＤＮ（ｍｇ／ｌ·ｍｉｎ）的提高。此外,通过正交试验得出了在ＢＯＤ５／ＮＯ－ｘ一定时,ＮＮＯ－ｘ－Ｎ、Ｔ℃与脱氮效率ηＮＯ－ｘ－Ｎ之间的数量关系式     

同分异构体喹啉和异喹啉的缺氧降解性能比较

研究了同分异构体的含氮杂环化合物喹啉和异喹啉在缺氧条件下的降解情况,发现两者表现出不同的缺氧降解特性。喹啉可以在缺氧条件下得到有效降解,其缺氧降解的最佳碳氮比为8。在最佳碳氮比条件下,喹啉的缺氧降解过程符合一级动力学规律,在其降解过程中首先以硝酸盐为电子受体,当硝酸盐氮浓度为零时,亚硝酸盐氮浓度达到最高,此后喹啉的降解主要以亚硝酸盐为电子受体,并和亚硝酸盐氮同时达到最低浓度。异喹啉对硝酸盐的利用甚微,其降解主要表现为厌氧降解特征,降解过程符合零级动力学规律。     

连续流系统中好氧段及沉淀段对污泥及其缺氧段脱氮能力的影响

在好氧段3种溶解氧(DO)[3. 0～3. 5 mg·L~(-1)(Ⅰ阶段)、2. 0～2. 5 mg·L~(-1)(Ⅱ阶段)和1. 5～2. 0 mg·L~(-1)(Ⅲ阶段)]的A~2/O实验系统,考察了本段及后续沉淀阶段污泥的变化,以及对系统缺氧段反硝化的影响,并与DO为1. 5～2. 0 mg·L~(-1)的缺氧-好氧(A/O)系统进行了对比.结果表明,沉淀阶段污泥开始发生反硝化作用,脱氮碳源由内、外碳源同时提供;沉淀污泥优先利用外碳源进行反硝化;好氧段DO为1. 5～2. 0 mg·L~(-1)时,沉淀阶段污泥的硝酸盐还原酶活力及反硝化活性最强,此时A~2/O系统缺氧段的反硝化效果也最佳;在与A~2/O系统相同污泥负荷下的A/O系统中,好氧段后污泥中细菌胞内残留的PHB含量要高于A~2/O系统; A~2/O系统沉淀段污泥的反硝化活性高于A/O系统,其硝酸盐还原酶活力是A/O系统的1. 08倍;该污泥回流后,尽管硝态氮充分但A/O系统缺氧段反硝化效果却较A~2/O系统差;沉淀阶段污泥的脱氮性能直接关系到缺氧段反硝化效果.因此,本研究认为在保证沉淀污泥反硝化不严重影响泥水分离的前提下,污水生物脱氮工程中应适当控制好氧段运行、维持沉淀池污泥适当反硝化来提升系统的脱氮效能,而不能仅仅是考虑控制缺氧段.     

Denitrification and microbial community in MBBR using A. donax as carbon source and biofilm carriers for reverse osmosis concentrate treatment

In this study,raw Arundo donax(A.donax)pieces were applied as carbon source and biofilm carriers for denitrification in a lab-scale moving bed biofilm reactor(MBBR)for the treatment of reverse osmosis concentrate gathered from local wastewater reuse plant.At stable phase(about 60 days),efficient denitrification performance was obtained with73.2%±19.5%NO_(3-)~-N average removal and 8.10±3.45 g N/(m~3·day)NO_(3-)~-N average volumetric removal rate.Mass balance analysis showed that 4.84 g A.donax was required to remove 1 g TN.Quantitative real-time PCR analysis results showed that the copy numbers of 16S r-RNA,narG,nirS,nosZ and anammox gene of carrier biofilm and suspended activated sludge in the declination phase(BF2 and AS2)were lower than those of samples in the stable phase(BF1 and AS1),and relatively higher copy numbers of nirS and nirK genes with lower abundance of narG and nosZ genes were observed.High-throughput sequencing analysis was conducted for BF2 and AS2,and similar dominant phyla and classes with different abundance were obtained.The class Gammaproteobacteria affiliated with the phylum Proteobacteria was the most dominant microbial community in both BF2(52.6%)and AS2(41.7%).The PICRUSt prediction results indicated that 33 predictive specific genes were related to denitrification process,and the relative abundance of 18 predictive specific genes in BF2 were higher than those in AS2.     

A strategy for enhancing anaerobic digestion of waste activated sludge: Driving anodic oxidation by adding nitrate into microbial electrolysis cell

Cathodic reduction of CO₂ and anodic oxidation of organic matters are crucial to methane-producing microbial electrolysis cell (MEC) applied in anaerobic digestion of waste activated sludge. However, cathodic CO₂ reduction is usually restrained by slow metabolism rates of H₂-utilizing methanogens and low electron-capturing capacity of CO₂, which consequently slows down the anodic oxidation that participates to sludge disintegration. Herein, a strategy with adding nitrate as electron acceptor to foster electronic transfer between the anode and cathode was proposed to improve anodic oxidation. Results showed that the average efficiency of anodic oxidation in the nitrate-added MEC increased by 55.9%. Accordingly, volatile suspended solid removal efficiency in the nitrate-added MEC was 21.9% higher than that of control MEC. Although the initial cumulative methane production in the nitrate-added MEC was lower than that of control MEC, the cumulative methane production in 24?days was 8.9% higher. Fourier transform infrared spectroscopy analysis indicated that anodic oxidation of MEC with nitrate accelerated the disintegration of sludge flocs and cell walls. Calculation on current signal further revealed that anodic oxidation driven by cathodic nitrate reduction was the main mechanism responsible for the improved sludge digestion.     

有机复肥对作物品质的影响初报

对小白菜、茶叶和番茄的大田及盆栽试验表明,与无机肥相比,有机复肥对作物的品质有良好的影响。施用有机复肥使小白菜和茶叶的硝酸盐含量下降,番茄的次果率减少而贮藏期延长。推广有机复肥,对于发展高产、优质、高效农业意义重大。     

Evaluation of a fetus at risk for dihydropteridine reductase deficiency by direct mutation analysis using denaturing gradient gel electrophoresis

Dihydropteridine reductase (DHPR) is an enzyme involved in the recycling of tetrahydrobiopterin (BH₄), which is an obligate co-factor of the aromatic amino acid hydroxylases. DHPR deficiency is a rare, autosomal recessive disorder caused by mutations in the QDPR gene. DHPR-deficient patients are diagnosed by a lack of response to a low phenylalanine diet and by severe neurological symptoms. Final diagnosis is made by measurements of neurotransmitters and pterin metabolites in cerebrospinal fluid (CSF) and urine, in addition to DHPR enzyme activity, which can be assessed in whole red blood cells. Treatment of DHPR deficiency can be difficult and the outcome is not always satisfying, even if all treatment strategies are followed. Therefore prenatal diagnosis is of great importance in affected families. Prenatal diagnosis is possible by measuring DHPR activity in different cell types but this is time consuming. More than 25 different mutations have to date been identified in the QDPR gene and direct identification of a mutation in a fetus would be easy and rapid. We have developed a method based on denaturing gradient gel electrophoresis (DGGE) for the analysis of the QDPR gene. The method is useful for rapid and simultaneous scanning of all exons and flanking intronic sequences of the QDPR gene. We describe the first prenatal diagnosis conducted using this method. Copyright © 2001 John Wiley & Sons, Ltd.     

不同氮源对利玛原甲藻(Prorocentrum lima)生长和产毒的影响

采用单因子实验,设置4个浓度梯度:12μmol·L-1、25μmol·L-1、50μmol·L-1和lOOp.mol·L-1,研究了NaNO3、NH4Cl和尿素对利玛原甲藻(Prorocentrum lima)的生长、硝酸还原酶(nitrate reductase,NR)活性以及腹泻性贝毒(diarrhetic shellfish poisoning,DSP)产生的影响.对比分析了利玛原甲藻对3种不同氮源的利用特征.结果发现,以NaNO3、NH4Cl和尿素分别作为氮源时,利玛原甲藻最大生长速率(μmax)相差不大;NaNO3组和尿素组之间最大生物量(X)和硝酸还原酶活性也相近;NH4Cl组最大生物量(X)和硝酸还原酶活性明显低于NaNO3组和尿素组.平台期NaNO3组单位藻细胞OA含量明显高于NH4Cl组和尿素组,NH4Cl组和尿素组之间无显著性差异.这些结果表明,利玛原甲藻可以利用无机氮(NaNO3、NH4Cl)和有机氮盐尿素,利玛原甲藻中可能存在尿素酶;NaNO3和尿素比NH4Cl可能更有利于维持利玛原甲藻的生长;利玛原甲藻毒素的合成与营养盐的形态有关,其中NaNO3最有利于毒素的合成.