Biochar triggers methanogenesis recovery of a severely acidified anaerobic digestion system via hydrogen-based syntrophic pathway inhibition

Rapid methanogenesis recovery of an acidified anaerobic digestion (AD) system is a challenging issue in engineering application, due to the unfavorably thermodynamics of volatile fatty acids (VFA) syntrophic oxidation process with hydrogen as electron transfer mediator. To breakthrough this bottleneck, in this study, we developed the strategy with biochar as an additive for rapid methanogenesis recovery of a severely acidified AD system is elucidated. First, with VFA as substrate, it was found that biochar addition shortened lag time and promoted maximum methane production rate, confirming the role of biochar to enhance VFA syntrophic oxidation. Moreover, the addition of biochar to the acidified sludge significantly decreased hydrogen partial pressure, which thermodynamically stimulated VFA oxidation by reducing Gibbs free energy. Microbial community analysis delivered that biochar addition largely altered the dominant microbes. The enrichment of electro-active Syntrophomonas and Methanosarcina suggested the role of biochar as potential redox-active mediator to stimulate potential direct interspecies electron transfer between syntrophic microorganisms, and inhibit hydrogen-based syntrophic pathway simultaneously. Further stable operation confirms that biochar is a promising additive for the rapid methanogenic recovery of acidified AD systems.     

Methane and nitrous oxide measured throughout Lake Erie over all seasons indicate highest emissions from the eutrophic Western Basin

Eutrophication has been linked to increased greenhouse gas emissions from inland waters. Phytoplankton blooms in Lake Erie have increased since the 1990s, although its greenhouse gas emissions are not well characterized. We measured CH₄ and N₂O concentrations and diffusive fluxes in four seasons around the entire lake, and CO₂ fluxes in one summer season. Lake Erie is a source of CH₄ all year across the lake, concentrated in spring and summer in the Western Basin. Methane emissions ranged from 0.03 to 14.87 mg C m⁻² d^-1. Methane is predominantly biogenic, and natural gas leaks are an insignificant source. While Lake Erie is an overall N₂O source, it is an N₂O sink in winter and occasionally during summer. Emissions of N₂O ranged from −0.08 to 1.22 mg N m⁻² d^-1. We also measured CO₂ fluxes in summer only, when Lake Erie is a small atmospheric CO₂ sink. While areal fluxes of CH₄ and N₂O are similar to those observed elsewhere, total fluxes from Lake Erie are higher due to its surface area. Lake Erie emits ~ 6300 (±19%) metric tons of CH₄-C yr⁻¹ and ~600 (±37%) metric tons N₂O-N yr⁻¹: almost 500,000 metric tons CO₂-eq yr⁻¹ total. This is the first comprehensive dataset of CH₄ and N₂O concentrations and diffusive emissions in a very large lake. More measurements and monitoring are needed to determine whether increased eutrophication in the Great Lakes is tied to increased emissions of these powerful climate forcers in a possible positive feedback to climate warming.     

关中地区实际蒸散发量年际变化成因分析

为提供陕西关中地区水资源配置和开发利用的合理依据,亟需对关中地区未来主要气象因素进行分析和预报,研究蒸散发量的时空变化是关键。基于近50年7个气象站点资料,应用加拿大互补相关模型(CRAE)计算分析了关中地区实际蒸散发量的年内变化与其影响因素,获得了实际蒸散发量年内变化与气象因素变化的特点及影响实际蒸散发量变化的气候要素的变化趋势。     

2024铝合金氟铝酸盐转化膜的制备及其防腐蚀性能

为了寻找替代传统铬酸盐转化的处理工艺,采用由NaF,(NH4)2SiF6,(NaPO3)6和钛盐促进剂组成的转化液,在2024铝合金表面制备了一种氟铝酸盐化学转化膜,优化了转化液组分及转化工艺条件。结果表明:最优工艺为5.0 g/L NaF,5.0 g/L(NH4)2SiF6,0.9 g/L(NaPO3)6,0.5 g/L钛盐促进剂,pH值为4.7,室温,20 min;最优工艺所得氟铝酸盐转化膜由排列紧密且形状规则的晶体颗粒组成,表面覆盖有胶状物,膜层连续而致密、呈亚光,组成(质量分数)为7.53%O,48.87%F,19.11%Na,20.78%Al,0.79%Si,1.66%P,1.26%Cu;氟铝酸盐转化膜耐蚀性优良,最优工艺所得转化膜耐盐雾腐蚀达285 h,其使铝合金在3.5%NaCl溶液中的腐蚀电位增加了58 mV,腐蚀电流密度降为钝化前的1/9。     

Impacts of urban form on air quality in metropolitan areas in the United States

Among 221 metropolitan areas (MAs) in the United States (US), this study explored the impact of urban form, either urban compactness or urban sprawl, on two types of air quality in 2014: NO_x emissions from road traffic and annual average NO2 concentrations. Urban form was quantified using Smart Growth America (SGA) sprawl indexes with density, land use mixing, centeredness, and street connectivity. NO_x emissions from road traffic were derived from the National Emissions Inventory (NEI). Through modeling NO2 concentrations using land use regression (LUR), with satellite-based estimates and kriging, this study measured NO₂ concentrations within MAs in the US The study results showed that higher levels of urban form scores (i.e., higher compactness) and land use mixing were associated with lower per-person NO_x emissions from road traffic. In addition, higher levels of centeredness were associated with lower NO₂ concentrations, but the effect was moderate. On the other hand, regional rainfall and solar insolation had more significant associations with NO₂ concentrations than metropolitan urban form. Meanwhile, localized emissions sources had significant associations with local-level NO₂ concentrations. This study provides additional evidence on the relationship between urban form and air quality in the US MAs. The study suggests that high compactness-oriented development and the reduction of localized emission sources may be effective in reducing NO_x emissions from road traffic and local NO₂ concentrations, respectively. However, future studies need to explore the impact of urban form at both the MA and local levels on NO₂ concentrations and develop a more accurate national NO₂ concentration prediction model.     

Continuous simulation of CSO emissions

Modelling is an essential method to predict the behaviour of various water systems in urban areas. A common problem of modelling these systems is that it is hardly possible to model them fully in a detailed way. The applications of existing hydrodynamic models are very data-intensive and time-consuming, particularly for continuous simulation using a long rainfall record. It is thus necessary to develop a new modelling approach which is correct in representing and efficient in dealing with the processes involved in urban water systems. SewSim is such a conceptual combined sewer overflow (CSO) emission model. SewSim has been developed using a dynamic programming package MATLAB and its toolbox SIMULINK. This paper presents some case studies using this model for continuous simulation.     

黄河三角洲暗管排水系统排水效果模拟研究

我国黄河三角洲地区地势平坦,地下水埋深浅、含盐量高,夏季降雨集中,农业生产受到土壤盐渍化与涝渍灾害的威胁.因此排水系统建设是保证粮棉生产的一个重要条件.由于现行的排水设计规范依据的是农田水分调节的平均情况,忽略了水文过程的随机性与地区水文要素的特点.本文使用田间水文模型DRAINMOD模拟研究了黄河三角洲地区暗管排水系统布置的排水效果.模拟结果显示:在有效控制土壤盐分的前提下,采用“浅密型”暗管布置能够更好地调控农田水分,保证作物的正常生长;该布置能够显著减少地下排水输出,增蓄雨季淡水,有利于三角洲地区农业非点源污染控制及生态环境保护.“浅密型”暗管布置在防涝排渍以及防止海水入侵方面均优于当地现有的深沟型明排系统.本研究成果可为黄河三角洲地区农业生产发展与生态环境保护提供技术支撑.     

基于物元分析理论的再生水价值评价

针对再生水价值认识不足而导致利用步伐缓慢的现状,建立再生水资源价值评价模型,研究其在不同区域存在的潜在价值,为促进推广利用提供依据.以陕西省内7个城市的再生水资源为应用实例,基于粗糙集理论及物元分析模型建立了再生水资源价值评价模型,结合再生水回用标准、经济社会发展、天然水资源状况等数据,选用天然水体综合污染指数、水贫乏指数、经济综合指数和再生水水质综合指数共4项复合指标建立了综合评价指标体系,对再生水资源的潜在价值进行了估算.将估算结果与模糊综合评价的结果进行了对比,验证了物元分析模型在再生水价值评价中的可行性.结果表明,除商洛市因天然水资源条件较好、经济欠发达而使再生水资源价值较低外,各地再生水均有较大潜在价值,尤其以水资源与水生态条件较差的咸阳市为最高.     

额济纳绿洲生态需水研究

基于遥感解译和实测径流资料,分析了额济纳绿洲生态状况与水资源的关系,结果表明,无论从时间尺度上还是从空间尺度上,额济纳绿洲生态演变和水资源之间均具有明显的正相关关系,水资源减少是生态退化的决定性因素。在此基础上,结合西北内陆河产水和用水特点,认为产流较弱的绿洲区生态需水量是为维持一定规模绿洲所需区外补给水量。随后建立了额济纳绿洲生态需水计算的"正切"模型,通过与其他方法的比较,验证了模型的合理性,该方法可为北方缺水地区绿洲生态需水分析计算和水资源管理方案的合理制定提供决策依据。