Improving Oxygen Conditions in the Deeper Parts of Bornholm Sea by Pumped Injection of Winter Water

Vertical diffusivity and oxygen consumption in the basin water, the water below the sill level at about 59 m depth, have been estimated by applying budget methods to monitoring data from hydrographical stations BY4 and BY5 for periods without water renewal. From the vertical diffusivity, the mean rate of work against the buoyancy forces below 65 m depth is estimated to about 0.10 mW m⁻². This is slightly higher than published values for East Gotland Sea. The horizontally averaged vertical diffusivity κ can be approximated by the expression κ = a₀N⁻¹ where N is the buoyancy frequency and a₀ ≈ 1.25 × 10⁻⁷ m² s⁻², which is similar to values for a₀ used for depths below the halocline in Baltic proper circulation models for long-term simulations. The contemporary mean rate of oxygen consumption in the basin water is about 75 g O₂ m⁻² year⁻¹, which corresponds to an oxidation of 28 g C m⁻² year⁻¹. The oxygen consumption in the Bornholm Basin doubled from the 1970s to the 2000s, which qualitatively explains the observed increasing frequency and vertical extent of anoxia and hypoxia in the basin water in records from the end of the 1950s to present time. A horizontally averaged vertical advection–diffusion model of the basin water is used to calculate the effects on stratification and oxygen concentration by a forced pump-driven vertical convection. It is shown that the residence time of the basin water may be reduced by pumping down and mixing the so-called winter water into the deepwater. With the present rate of oxygen consumption, a pumped flux of about 25 km³ year⁻¹ would be sufficient to keep the oxygen concentration in the deepwater above 2 mL O₂ L⁻¹.     

Modelling geochemical and microbial consumption of dissolved oxygen after backfilling a high level radiactive waste repository

Dissolved oxygen (DO) left in the voids of buffer and backfill materials of a deep geological high level radioactive waste (HLW) repository could cause canister corrosion. Available data from laboratory and in situ experiments indicate that microbes play a substantial role in controlling redox conditions near a HLW repository. This paper presents the application of a coupled hydro-bio-geochemical model to evaluate geochemical and microbial consumption of DO in bentonite porewater after backfilling of a HLW repository designed according to the Swedish reference concept. In addition to geochemical reactions, the model accounts for dissolved organic carbon (DOC) respiration and methane oxidation. Parameters for microbial processes were derived from calibration of the REX in situ experiment carried out at the Asp? underground laboratory. The role of geochemical and microbial processes in consuming DO is evaluated for several scenarios. Numerical results show that both geochemical and microbial processes are relevant for DO consumption. However, the time needed to consume the DO trapped in the bentonite buffer decreases dramatically from several hundreds of years when only geochemical processes are considered to a few weeks when both geochemical reactions and microbially-mediated DOC respiration and methane oxidation are taken into account simultaneously.     

The use of petroleum coke as fuel in a 10 kWth chemical-looping combustor

Tests were made in a 10 kW_th chemical-looping combustor with a petroleum coke as the solid fuel and the oxygen carrier ilmenite, an iron titanium oxide. The fuel reactor is fluidized by steam and the oxygen carrier reacts with the volatiles released as well as the gasification intermediates CO and H₂. A constant fuel flow corresponding to a thermal power of 5.8 kW was introduced into the fuel reactor and a total of 11 h of operation was reached. The effects of particle circulation and carbon stripper operation on solid fuel conversion, conversion of gas from the fuel reactor and CO₂ capture were investigated. The actual CO₂ capture ranged between 60% and 75% while the solid fuel conversion was in the range of 66–78%. The low values of solid fuel conversion reflect loss of char due to low efficiency of the fuel reactor cyclone. The incomplete conversion of the gas from the fuel reactor is expressed as oxygen demand. The oxygen demand corresponds to the fraction of oxygen lacking to achieve full gas conversion and was typically 25%, due to presence of CH₄, CO and H₂ from the fuel reactor. Typical ratios of CH₄, CO and H₂ over the total gaseous carbon from the fuel reactor are respectively 5, 10 and 25%. Low loss of non-combustible fines from the system indicates very low attrition of the oxygen carrier.     

中国七大河流水资源开发利用率阈值

从二元水循环角度分析地表水资源开发利用率的影响因素,说明地表水资源开发利用率与河道生态需水、回归水及其污染物浓度之间有着密切的关系。以河道生态需水、污径比为约束条件,分析了水资源开发利用率与消耗系数之间的关系,其呈现出logistic曲线增长趋势,随着消耗系数的增加,允许水资源开发利用率经历逐渐增加→最大值→下降的趋势,波动的范围从20%→50%→40%。以我国七大河流为例,估算了在当前水资源消耗水平下地表水资源允许开发利用率的阈值。结果表明:松花江、辽河、海河、黄河、淮河、长江、珠江的阈值分别是34%、38%、45%、36%、38%、31%、32%。与现状水资源开发利用率比较的结果是,松花江、长江、珠江等3条河流的水资源开发利用率在其阈值范围之内,辽河、海河、黄河、淮河等4条河流的开发利用率均超过了最大允许开发利用率。     

紫外吸收光谱法直接测定化学需氧量的研究进展

利用紫外吸收光谱法直接测定COD是一种不用化学试剂、对样品无须加热消解、快速、简洁、元二次污染的绿色技术。本文对此技术的原理、相关概念、特点、进展、技术难点及应用前景作了较全面的评述。     

水质的生化需氧量(BOD5)稀释与接种法测定结果不确定度评定

在实际工作中，运用测量过程的合并样本标准差来评定A类不确定度比较客观。本文根据JJF1059—1999《测量不确定度评定与表示》，通过实例，阐述了用稀释接种法测定水中生化需氧量不确定度的评定方法。     

活性污泥耗氧速率的测定及其影响因素试验分析

本文首先介绍了活性污泥净化能力判别指标——耗氧速率的原电池氧测定法,继而通过试验研究了一些相关的影响因素同比耗氧速率的关系,最后分析说明了比耗氧速率在监控活性污泥系统运行中所起的作用。     

Defect-enhanced photocatalytic removal of dimethylarsinic acid over mixed-phase mesoporous TiO2

Much attention has been paid to the pollutant dimethylarsenic acid(DMA),because of its high toxicity even at very low doses.Although TiO_2 photocatalytic oxidation(PCO) is one of the few effective methods for treating DMA-containing water,the efficient decomposition of DMA and simultaneous removal of toxic arsenic species remains a significant but challenging task.Here,defective mesoporous TiO_2 with mixed-phase structure was synthesized and used as both photocatalyst and adsorbent for DMA removal.Due to the reduced band-gap and enhanced separation of photogenerated charge carriers, the oxygen-deficient TiO_2 nanostructures exhibited 4.2 times higher PCO efficiency than commercial TiO_2(P25).More importantly,the high surface area of the mesoporous TiO_2 provided sufficient active sites for in-situ adsorption and reaction,resulting in the efficient removal of as-formed As(V).Combining the experimental and characterization results,the different roles of reactive species during PCO reactions were clarified.In the presence of hole(h~+) as the dominant oxidation species,DMA was demethylated and transformed into MMA.Thereafter,MMA was subsequently reduced to As(Ⅲ) by photo-generated electrons.Superoxide radicals(O_2~(·-)) played a significant role in oxidizing As(Ⅲ) into As(Ⅴ),which was finally adsorptively removed by the mesoporous TiO_2.     

河道最小环境需水量确定方法及其应用研究(Ⅰ)--理论

从水污染问题出发，探讨河道环境需水的内涵，指出河道最小环境需水量是指维系河流的最基本环境功能不受破坏，所必须在河道中常年流动着的最小水量的阈值，在此概念的基础上，提出了一种适用于污染比较严重河流的河道最小环境需水量的确定方法－－段首控制方法，该方法为河流生态系统的环境需水量研究提供了一种思路和可借鉴的方法。     

Safety parameters for oxygen-enriched flames

The utilization of low-quality gaseous fuel from biomass gasification and the abundance of oxygen-rich streams obtained as a by-product of nitrogen-air separation by membrane technology has incentivized the development of sustainable oxygen-enriched combustion technologies in the last decades. However, a dearth of experimental and numerical analysis addressing the reactivity and safety aspects of these mixtures at initial low temperatures can be observed in the current literature.In this work, the heat flux burner was adopted for the measurement of the laminar burning velocity of methane in oxygen enriched air at different equivalence ratios. Results were compared with numerical data obtained by means of detailed kinetic mechanisms developed at the University of Bologna and the Gas Research Institute (GriMech3.0). Simplified correlations for the estimation of the laminar burning velocity with respect to the oxygen content at any equivalence ratio were developed, tested and evaluated.An elemental reaction-based function was found appropriate for the estimation of the overall reactivity of the investigated mixtures. Besides, numerical analyses were performed to characterize the flame structures in terms of temperature and product distribution under several initial conditions. These results gave further insights into the reaction mechanisms of gaseous fuels in the case of oxygen-enriched air, highlighting potential bottlenecks for kinetic model refinements. Eventually, relevant safety parameters were estimated, in particular the flammability range of the fuel/oxidant mixture, in terms of lower and upper flammability limits.