The cause and influence of self-cementing properties of fine recycled concrete aggregates on the properties of unbound sub-base

The use of coarse recycled concrete aggregates (CRCA) in conjunction with fine recycled concrete aggregates (FRCA) as sub-base materials has been widely studied. Although research results indicate that it is feasible to employ both CRCA and FRCA as granular sub-base, the influence of the unhydrated cement in the adhered mortar of the RCA on the properties of the sub-base materials has not been thoroughly studied. Generally, it is known that the strength of the sub-base materials prepared with RCA increases over time. However, this mechanism, known as the self-cementing properties, is not well understood and is believed to be governed by the properties of the fine portion of the RCA (<5mm). This paper presents an investigation on the cause of the self-cementing properties by measuring X-ray diffraction patterns, pH values, compressive strength and permeability of various size fractions of the FRCA obtained from a commercially operated construction and demolition waste recycling plant. Their influence on the overall sub-base materials was determined. The results indicate that the size fractions of <0.15 and 0.3-0.6mm (active fractions) were most likely to be the principal cause of the self-cementing properties of the FRCA. However, the effects on the properties of the overall RCA sub-base materials were minimal if the total quantity of the active fractions was limited to a threshold by weight of the total fine aggregate.     

生态足迹计算模型应用中热点问题及探讨

简要介绍了生态足迹计算模型,论述了近年国际上争论的几个主要热点问题,数据的准确完整性,初级产品与二级产品,均衡因子与产量因子,全球产量与本地产量,以及能源足迹计算等,并对其进行了探讨和指出今后研究发展的方向。     

利用阈值浮动技术实现机场周围飞机噪声的自动测量

介绍一种自动、高效测量机场周围飞机噪声的技术方法"阈值浮动技术",即噪声测量仪的运行阈值随环境背景噪声的高低而自主浮动的技术。利用该技术,当被测飞机噪声声级高于运行阈值时,噪声测量仪启动"记录、分析、录音"等程序的运行;当被测飞机噪声声级低于运行阈值时,停止相关程序的运行。由于运行阈值是浮动的,因而实现了机场周围飞机噪声的自动、高效和准确测量。给出了实现"阈值浮动技术"的计算机算法,并列举了测量实例对该项技术加以验证,证明了该技术方法行之有效。     

湖南省红色村落空间分布格局及公路可达性研究

基于“红色村落”概念内涵界定,以湖南省262个乡村红色旅游景区(点)为数据样本,综合运用数理建模和GIS空间分析方法,定量刻画了全省红色村落空间分布格局及可达性特征。结果表明：(1)全省红色村落呈集聚型分布状态,不同空间板块或行政单元红色村落分布非均衡性特征突出,集聚强度具有随尺度距离增加而不断弱化的“空间衰减”规律;(2)红色村落整体呈“大分散、小集聚”分布格局,全省存在三大高密度集聚区以及多个红色村落跨界连绵集群组团,长征沿线、湘鄂赣及湘粤赣边区等形成多个“中低密度”集聚片区;(3)红色村落通行时间平均值为221.58 min,标准差为42.75,可达性整体状况不理想,且内部差异显著,可达性水平稳健性欠佳,不同可达时段内红色村落数理分布近似于呈“金字塔”状结构;(4)红色村落可达性空间分布呈现“中心-外围”结构特征,省际边缘区形成多个交通可达性低谷,与其核密度格局存在“空间错位性”,且具有沿交通干线分布的指向特征。最后,提出了优化红色村落可达性格局、驱动交通区位重构和推进红色旅游开发的对策建议。     

酸析-Fenton试剂氧化-混凝法处理制浆废水

用酸析-Fenton试剂氧化-混凝法对自偶氧化清洁制浆废水进行预处理,考察了各种因素对处理效果的影响。最佳处理条件：酸析时的废水pH为3．0;酸析后上层清液无需调节pH,加水稀释至COD为2000mg／L后进行Fenton试剂氧化,H2O2加入量为84．56mmol／L,FeS04加入量为8．44mmol／L,反应时间60min;混凝时Ca（OH）：加入量为2g／L。最终出水的COD为577．20mg／L（COD去除率为71．14％）,色度为36倍,pH为8．60。     

Occurrence of arsenic in brown rice and its relationship to soil properties from Hainan Island, China

The acquaintance of arsenic concentrations in rice grain is vital in risk assessment. In this study, we determined the concentration of arsenic in 282 brown rice grains sampled from Hainan Island, China, and discussed its possible relationships to the considered soil properties. Arsenic concentrations in the rice grain from Hainan Island varied from 5 to 309 μg/kg, with a mean (92 μg/kg) lower than most published data from other countries/regions and the maximum contaminant level (MCL) for As_i in rice. The result of correlation analysis between grain and soil properties showed that grain As concentrations correlated significantly to soil arsenic speciation, organic matter and soil P contents and could be best predicted by humic acid bound and Fe-Mn oxides bound As fractions. Grain arsenic rises steeply at soil As concentrations lower than 3.6 mg/kg and gently at higher concentrations.     

Toxicity profile of labile preservative bronopol in water: the role of more persistent and toxic transformation products

Transformation products usually differ in environmental behaviors and toxicological properties from the parent contaminants, and probably cause potential risks to the environment. Toxicity evolution of a labile preservative, bronopol, upon primary aquatic degradation processes was investigated. Bronopol rapidly hydrolyzed in natural waters, and primarily produced more stable 2-bromo-2-nitroethanol (BNE) and bromonitromethane (BNM). Light enhanced degradation of the targeted compounds with water site specific photoactivity. The bond order analysis theoretically revealed that the reversible retroaldol reactions were primary degradation routes for bronopol and BNE. Judging from toxicity assays and the relative pesticide toxicity index, these degradation products (i.e., BNE and BNM), more persistent and higher toxic than the parent, probably accumulated in natural waters and resulted in higher or prolonging adverse impacts. Therefore, these transformation products should be included into the assessment of ecological risks of non-persistent and low toxic chemicals such as the preservative bronopol.     

Air pollution perception in ten countries during the COVID-19 pandemic

As largely documented in the literature, the stark restrictions enforced worldwide in 2020 to curb the COVID-19 pandemic also curtailed the production of air pollutants to some extent. This study investigates the perception of the air pollution as assessed by individuals located in ten countries: Australia, Brazil, China, Ghana, India, Iran, Italy, Norway, South Africa and the USA. The perceptions towards air quality were evaluated by employing an online survey administered in May 2020. Participants (N = 9394) in the ten countries expressed their opinions according to a Likert-scale response. A reduction in pollutant concentration was clearly perceived, albeit to a different extent, by all populations. The survey participants located in India and Italy perceived the largest drop in the air pollution concentration; conversely, the smallest variation was perceived among Chinese and Norwegian respondents. Among all the demographic indicators considered, only gender proved to be statistically significant.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01574-2.     

大庆石化公司化工三厂中水回用探讨

中水回用是企业普遍采用的节水减排方式之一。大庆石化公司化工三厂中水回用装置采用目前国内较为先进的工艺,中水主要经过曝气生物滤池、水处理生化系统、臭氧尾气回收处理——预臭氧化系统、二氧化氯发生系统等单元的处理得以回用。装置投用后满负荷生产每年可减排污水约80多万吨,减排COD约80t。文章针对存在的问题进行了分析并提出了对策措施。     

城市地表污染物累积和降雨径流冲刷过程研究进展

城市地表污染物是城市降雨径流污染的主要来源,其累积和降雨冲刷过程分别是沉降-悬浮-再沉降以及悬浮-沉淀-再悬浮的动态过程。描述累积过程的模型主要有线性、指数、对数等形式,其中以指数及一些变形形式发展相对成熟并得到了广泛的应用。这些模型都将雨前干期天数（ADWP）作为主要的影响因子。而描述冲刷过程的模型主要基于一级反应动力学假设,这类模型已被人们广泛接受。为使冲刷模型更接近实际,人们进一步在其中引入了雨天排污因素,并取得较好的成效。虽然城市地表径流的研究取得了较大的进步,但是目前的模型基本属于经验型或基于大量监测数据的统计学模型,尚缺对污染物输移过程的机理性描述。因此,从城市地表污染物输移过程的机理出发,建立城市地表污染物累积和降雨冲刷过程的物理模型是今后城市降雨径流污染研究工作中一个亟待解决的问题.