市场机制在白色污染物回收处置中的应用探讨——以上海一次性塑料餐具废弃物为例

近10年来上海城市生活垃圾组分中,以塑料为代表的包装废物的组分份额上升趋势尤为显著;上海GDP持续高速增长,但单位GDP城市废弃物清运量的下降率却显著低于GDP的年均增长率,一定程度上说明环卫行业的投资渠道较为单一,缺乏竞争和优化配置的市场机制;上海各类废弃塑料主要流向江浙一带,进行小规模低技术层次的加工处理,容易形成隐蔽的废品交易暗流;造成“白色污染”屡禁不止的重要原因是忽视了基于生产者责任的市场调控机制,社会化的回收体系薄弱;上海从2000年10月起,对一次性塑料餐具的回收处置建立了基于生产者责任的市场机制,由于一次性塑料饭盒的区域回收网络建设滞后,实施的效果有效但仍有限.     

冬小麦中轻度水分胁迫的增产节水效应研究

利用大型水分试验场的防雨棚遮挡自然降水,采用人工定量补水进行冬小麦土壤含水量占田间持水量40%～50%、45%～50%、50%～55%、50%～60%、55%～60%、60%～70%持续时间分别为5、10、15天水分胁迫处理的控制试验。试验结果表明:50%～70%的中轻度水分胁迫处理,冬小麦具有显著的增产节水效果;2年平均,增产6.3%～7.4%,节水28.2%～34.1%。中轻度水分胁迫下,冬小麦增产节水作用机制的实现,主要是通过水分胁迫效应诱发增强:①冬小麦根系的找水功能;②产量构成因子的优化;③复水后光合速率的提高。冬小麦水分胁迫效应的最佳利用时间为返青-拔节期,此时进行水分胁迫效应利用最有利于冬小麦稳产增产。     

复合生物滤池处理H2S和NH3的研究:生物相机理分析

采用天然斜发沸石和木屑作为复合生物滤池(生物滴滤池+生物过滤池)的填料,研究了该工艺处理含H₂S和NH₃混合恶臭气体的生物相机理.结果表明:生物滴滤池中形成了由细菌、藻类及原生动物组成的复杂生态系统,而生物过滤池中真菌为优势微生物.生物滴滤池的下层优势菌种主要为葡萄球菌属和球形芽孢杆菌等细菌,中层主要为梨形四膜虫属和肾形虫属,上层主要为钟虫和舟形藻属;生物过滤池优势菌种主要是聚多曲霉菌种.据对复合生物滤池的生物相机理探讨推论,生物滴滤池去除H₂S和NH₃机理主要是生物链的分级捕食和沸石的吸附-生物再生机理;生物过滤池去除H₂S和NH₃机理主要是真菌降解.因此,通过控制生物滴滤池和生物过滤池处于不同的环境条件,可使复合生物滤池能高效地同时处理H₂S和NH₃组成的混合恶臭气体.      

用复极固定床电解槽处理硝基苯废水

用复极固定床电解槽处理模拟硝基苯废水,考察了电解电压、N2SO4质量浓度、pH、硝基苯的初始质量浓度等条件对电解效果的影响。在Na2SO4质量浓度为1000mg／t、电解电压为40V、初始pH为10的条件下,复极固定床电解槽对硝基苯初始质量浓度为120mg／L的废水有较好的处理效果,硝基苯去除率可达到82．8％。探讨了复极固定床电解槽电化学降解硝基苯的机理。     

淹没式膜生物反应器中膜污染机理的研究

为减小微生物絮体对膜的污染,设计了一种具有沉降室的膜生物反应器,膜A与膜B分别淹没在上清液和污泥混合液中以相同的抽吸方式运行,与预期结果相反,膜A比膜B的污染速度还快．为探讨膜污染机理,考察了污泥混合液中不同组分对膜污染的影响,利用扫描电镜和原子力显微镜分析了膜面污染层的特征．结果发现,在污泥混合液与上清液中膜面污染层在微观结构上存在显差异,其方差平均粗糙度Rms分别为132．3nm和75．2nm．经膜污染机理分析认为：微生物絮体和大分子有机物会在膜面形成污染层,该污染层作为“二次膜”影响膜过滤性能．上清液中细小的微生物絮体和大分子有机物形成的污染层相对致密,会加剧膜污染．     

Mechanistic study of ozonation of p-nitrophenol in aqueous solution

Introduction p Nitrophenolhasbeenwidelyusedintheproductionof pesticides,herbicides,dyes,andotherindustrialchemicals.Asaresultofthesewidespreadapplications,wastewatersandwaterresources,includinggroundwaterandsurfacewaters,havebecomecontaminatedwiththiscomp…     

饮用水水源保护区划分问题探讨

阐述了国内外划定饮用水水源保护区的方法和原则,并举例说明了辽宁省水库水源保护区的划分情况以及相关的技术发展趋势、法律程序等。     

Modeling of a cryogenic liquid pool boiling by CFD simulation

A boiling model is developed by Computational Fluid Dynamics (CFD) code to calculate the source term of a cryogenic liquid spill. The model includes the effect of the changing ground temperature on the vaporization rate of the cryogenic liquid. Simulations are performed for liquid nitrogen. The model can describe different boiling regimes (film, transition and nucleate). The heat flux calculated for each boiling regimes are compared to the experimental data from literature. The developed numerical model seems to have a good ability to predict the heat flux for the film boiling stage. Model development is still necessary to improve the prediction of the nucleate boiling regime. Overall, the approach shows very promising results to model the complex physical phenomena involved in in the vaporization of cryogenic liquid pool spilled on ground.     

Phosphorus resources,their depletion and conservation,a review

Yearly, about 22 × 10¹² g phosphorus (P) from mined fossil phosphate resources are added to the world economy. The size of remaining fossil phosphate resources is uncertain but practically finite. Thus, fossil P resources may become depleted by ongoing mining. Despite calls for resource conservation, fossil P resources have been depleted at an increasing rate. Geographically, fossil P supply and demand are distributed in an increasingly uneven way, which has geopolitical consequences and may well affect security of supply. Current use of P gives rise to negative environmental impacts due to P losses from the economy and contaminants derived from fossil P resources. There may also be negative impacts on human health. Reducing the demand for fossil phosphorus may reduce environmental burdens and may improve the future security of supply. Technically speaking, there is much scope for the reduction of current demand for fossil P resources. Limiting consumption of P to essential uses, increased efficiency of agricultural use and increased recycling of P may substantially contribute to the reduction of demand for fossil P resources. Recycling of P has to face concerns regarding the efficiency of P recovery, pathogenic organisms and contaminating substances. Much work remains to be done to effectively address those concerns.     

Comparative study of explosion processes controlled by homogeneous and heterogeneous combustion mechanisms

The dust explosion behaviors induced by two different combustion mechanisms (homogeneous and heterogeneous mechanisms) were comparatively investigated, based on the experiments under different dust concentrations, particle sizes and initial pressures in Siwek 20-L chamber. Based on the thermo-gravimetric analysis (TGA), sweet potato dust and magnesium dust were selected as the representative dusts with homogeneous and heterogeneous combustion mechanisms, respectively. Experiments find that these two dusts have different behaviors in the explosion kinetics due to different combustion mechanisms. For sweet potato dust, the explosion pressure p_max, the pressure rise rate (dp/dt)_max and the combustion fraction η exhibit similar variation trends as dust concentration increases and they all reach to the maximum values at the worst-case concentration; while for magnesium dust, the variation of (dp/dt)_max is somewhat different from that of p_max, that is, the (dp/dt)_max will achieve the maximum at the concentration higher than the worst-case and keep stabilized with further increase of dust concentration. As the particle size decreases, the (dp/dt)_max for sweet potato dust will increasingly rise and gradually approach to a stabilized value, but for magnesium dust, the increase of (dp/dt)_max becomes pronounced only in the range of smaller particle sizes. To account the effect of initial pressure on p_max under different combustion mechanisms, a dimensionless pressure P_R was introduced to denote the relative intensity of explosion. It is found that, for sweet potato dust, the increased initial pressure will promote the explosion process (or with high P_R) for the dust cloud with high concentration due to the augmented oxygen concentration, but for the dust cloud with low concentration, the increased initial pressure will suppress the explosion process due to the increased resistance in devolatilization. For magnesium dust, the rise of initial pressure will generally promote the explosion process even for the dust cloud with low concentration; however, in the case of small particle size, the promotion of increased initial pressure to the explosion process is not so pronounced.