粗枝云杉不同径级根系分解过程中4种养分元素的释放特征

植物根系分解是养分元素进入土壤的重要途径之一.为了解径级对根系分解过程中养分元素释放的潜在影响,以川西亚高山针叶林中的粗枝云杉(Picea asperata)为对象,采用原位分解试验,研究云杉3个径级(0-2 mm,2-5 mm和5-10 mm)根系分解过程中钾(K)、钠(Na)、钙(Ca)和镁(Mg)元素的浓度、残留...     

某市给水管网中铁释放现象影响因素与控制对策分析

针对某市管网水中铁浓度的变化规律进行了系统的研究,确定了管垢向管网水中释放出的铁是管网水中铁超标的主要原因.研究中发现铸铁管和镀锌钢管中管垢的主要化学组分为铁.在给水管网中,管网水的溶解氧和余氯浓度低时,对应的管网水中铁释放现象严重,其原因是还原条件使管垢表面的致密钝化层被破坏,造成二价铁的大量释放.根据试验结果提出了给水管网中铁释放和“红水”现象的控制对策.     

水源更换对给水管网水质的影响研究

为了研究水源更换对给水管网水质的影响,对北方A市水源更换过程中管网水质理化指标进行了监测分析.通过33 h的监测发现,由于水源水质不同造成管网水质化学不稳定,管网水水质部分指标发生了明显的下降,pH从7.54降到7.18,碱度从188　mg·L^-1降到117 　mg·L^-1,氯化物从310 　mg·L^-1降到132 　mg·L^-1（以Cl^-计）,电导率从0.176　S·m^-1降到0.087 　S·m^-1,钙离子和镁离子略有下降分别为15 　mg·L^-1和11 　mg·L^-1,这些都是由于滦河水质与黄河水质不同造成的;余氯在换水过程中发生了较复杂的变化,主要是由于水源更换造成耗氯量增加以及夜间用水量少造成管网水输配时间长引起的;pH、碱度、余氯的变化使得管网水中铁的含量增加,最高达到0.4 　mg·L^-1,超出饮用水标准规定的0.3 　mg·L^-1.通过分析水源更换过程中水质的变化,提出了控制管网水质稳定的方法主要有提高pH、增加碱度、投加缓蚀剂和严格保证出厂水及管网水水质指标特别是余氯等.     

湖泊沉积物中磷化氢的释放动力学初探

采用柱状芯样模拟法,研究了太湖沉积物-水界面磷化氢的释放动力学.结果表明:当沉积物-水界面磷化氢的释放达到动态平衡时,水界面中磷化氢的浓度基本不再增大,大约在0.34 pg·l-1左右,此时磷化氢的释放通量约为0.008 pg·dm-2·h-1.根据室内模拟结果,太湖沉积物每年的磷化氢释放量在13.81-49.62 g之间,从而使磷化氢在湖水中的平均浓度达到0.16 pmol·l-1.     

潮间带沉积物/大气Hg的释放的模拟研究

研究了潮间带沉积物中的Hg向大气的释放,结果表明光照造成沉积物中的Hg快速向大气释放.光照8 h后,海泊河口和黄河口沉积物释放到大气中的Hg分别占58%和51%,其释放通量总体上遵循先升高后降低的规律,前者在13:00～14:00达到最大值2 830μg/(m2·h),后者在12:00～13:00达到最大值73μg/(m2·h);海泊河口沉积物Hg的释放通量与大气温度、沉积物温度和光照强度的相关系数分别为0.83(P＜0.05)、0.98(P＜0.01)和0.73(P＜0.05),黄河口沉积物Hg的释放通量与大气温度、沉积物温度和光照强度的相关系数分别为0.73(P＜0.05)、0.80(P＜0.05)和0.81(P＜0.01),温度、光照对沉积物Hg的释放有重要的影响.     

Aerobic degradation of methyl tert-butyl ether by a Proteobacteria strain in a closed culture system

The contamination of methyl ten-butyl ether （MTBE） in underground waters has become a widely concerned problem all over the world. In this study, a novel dosed culture system with oxygen supplied by H2O2 was introduced for MTBE aerobic biodegradation. After 7 d, almost all MTBE was degraded by a pure culture, a member of β-Proteobacteria named as PMI, in a closed system with oxygen supply, while only 40% MTBE was degraded in one without oxygen supply. Dissolved oxygen （DO） levels of the broth in closed systems respectively with and without H2O2 were about 5-6 and 4 mg/L. Higher DO may improve the activity of monooxygemase, which is the key enzyme of metabolic pathway from MTBE to tert-butyl alcohol and finally to CO2, and may result in the increase of the degrading activity of PM1 cell. The purge and trap GC-MS result of the broth in closed systems showed that tea-butyl alcohol, isopronol and acetone were the main intermediate products.     

Applying the Kuhn–Tucker model to estimate the value of recreational ecosystem services in Sicily

This paper applies the Kuhn–Tucker model to estimate recreation demand of parks in Sicily. We estimate a fixed coefficient specification and a random coefficient specification to take into account heterogeneity across visitors. Estimates suggest a diversity of preferences across the population and that parks with higher level of quality attributes are more likely to be visited. We also simulate two sets of hypothetical policy scenarios to evaluate and compare the recreational value of each park and the welfare impacts of changes in a quality attribute.     

A conceptual approach to model sand–gravel extraction from rivers based on a game theory perspective

Sand–gravel mining is a significant parameter of economic development and social welfare function in modern societies. As demand for aggregate increases in construction industry, conflicts for the availability of the resource and environmental impacts become more intense. The present paper describes the contested status quo in riverbed sand–gravel mining activities with an example from Greece, as a case study. The scope is to propose a methodology about good governance of the mining sector that promotes a sustainable sharing of aggregate resource by securing environment and safekeeping revenues in the mining trade market.     

Photovoltaic-thermal (PV/t) panel to minimize electrical and air conditioning energy consumption of a typical office in Beirut

A combined photovoltaic–thermal (PV/t) panel is proposed to produce simultaneously electricity and heat from one integrated unit. The unit utilizes effectively the solar energy through achieving higher PV electrical efficiency and using the thermal energy for heating applications. To predict the performance of the PV/t at a given environmental conditions, a transient mathematical model was developed. The model was integrated in a heating application for a typical office space in the city of Beirut to provide the office needs for electricity, heating during winter season, and dehumidification and evaporative cooling during the summer season. To minimize the yearly office energy (electrical and heat) needs, the PV/t panel cooling air flow rate and the dehumidification regeneration temperature were determined for opimal unit operation. Thermal energy savings of up to 85% in winter and 71% in summer were achived compared to conventional systems at a payback period of 8 years for the panels.     

Numerical simulation of hydrogen–air detonation for damage assessment in realistic accident scenarios

An accidental hydrogen release within an equipment enclosure may result in the presence of detonable mixture in a confined environment. From a safety standpoint, it is then useful to assess the potential for damage. In that context, numerical simulation of the sequence of events subsequent to detonative ignition provides a useful tool, although with obvious limitations. This article describes the procedure, summarizes two case studies, and reviews the limitations. First, a hydrogen dispersion pattern is obtained from numerical simulation of dispersion, using a commercial package designed primarily for incompressible flow. This dispersion cloud is then used as the initial condition in an inviscid, compressible, reactive flow simulation. To force detonative ignition, a sufficiently large amount of energy is deposited in a small region that corresponds to the ignition location. Chemistry is modeled using a single step Arrhenius model. Because the wave thickness is small compared with the computational domain, a fine mesh is needed, limiting the practicality of the process to two-dimensional geometries. This is the most significant limitation; it is conservative. The two cases described in the paper include an electrolyzer, in which a small release occurs, leading potentially to some damage to the enclosure, and a reformer, in which the consequences are potentially more serious.