曝气策略对膜面剪切力的影响机制及其优化

曝气冲刷是浸没式MBR工艺不同于常规活性污泥法工艺的关键特征,然而现行规范的曝气系统设计与运行比较粗放,缺乏气泡尺寸模拟优化方法。以可直接观测的工程规模 (500 m³·d⁻¹) 膜生物反应器为研究对象,对穿孔管角度进行了优化研究,并用群体平衡模型(Population Balance Model,PBM)模型模拟污泥混合液不同粘度下的内部气泡分布情况。结果表明：穿孔管角度垂直向下、60°、45°、30°、垂直向上在膜面产生的平均剪切力分别为1.74、1.46、1.19、1.38、1.67 Pa,这表明曝气角度最优为垂直向下。0.3%、0.5%和0.8%浓度的羧甲基纤维素钠(Carboxymethyl cellulose, CMC)下产生的平均剪切力分别是1.51、1.92、2.24 Pa,气泡直径逐渐增大。且气泡尺寸越大、流速越大,分布越均匀。基于0.3%、0.5% CMC的速度实验结果与 PBM模拟结果基本吻合。该研究结果可为MBR技术的工艺优化和系统控制方法提升提供参考。     

污泥厌氧消化的热预处理研究进展

热预处理能够提高后续厌氧消化效率,改善污泥脱水性能。对国内外污泥热预处理的研究进行了归纳,包括热与碱、超声波和氧化法的联合预处理,重点介绍了热预处理对污泥溶解作用、厌氧消化、脱水性和流变性的影响,分析了热处理与厌氧消化整体的能量平衡。最后提出了热预处理研究中存在的问题,并展望了今后的发展趋势。     

有机污染土壤异位直接热脱附装置节能降耗方案

以异位直接热脱附技术的原理、适用范围、工艺流程、优缺点等为基础,建立了输入、输出能量平衡关系式并进行了热平衡计算;针对该工艺能耗过高的问题,分析了系统各部分能耗,提出了节能降耗方案。通过烟气热回用装置,将二燃室后高温烟气余热能量经循环管道输送给土壤预干燥装置,将有机污染土壤含水率降低,从而减少系统总能耗。结果表明：经过热力计算,土壤水分预干燥量越大,系统节能效果越好;烟气余热足够用于土壤预干燥减少17%左右土壤水分的要求。通过土壤预干燥装置将土壤水分从20%降低到15%,可使直接热脱附装置降低能耗20%以上。     

蒸发塔技术用于脱硫废水的处理

脱硫废水水质复杂、含有重金属,处理难度很大,为此开发了一种新型的脱硫废水处理技术——蒸发塔技术,可以实现脱硫废水的零排放。在实验室搭建了小型蒸发塔实验台,对脱硫废水的蒸发特性、热量衡算进行了研究。研究表明：导流板角度一定的情况下,脱硫废水主蒸发区在塔体中心位置,随着脱硫废水处理量的增加,主蒸发区域向塔壁和塔体下部偏移;导流板角度减小,高温区下移;雾矩受给液量和雾化器转速的双重影响,给液量越大,雾矩越大,转速越大,雾矩越小;塔径一定的条件下,适当调节进风量和导流板角度可增加脱硫废水的处理量;模拟计算表明,蒸发系统抽取热烟气量较少,不会对电厂热系统产生明显影响。     

Tuning the fill percentage in the hydrothermal synthesis process to increase catalyst performance for ozone decomposition

The performance of Ce-OMS-2 catalysts was improved by tuning the fill percentage in the hydrothermal synthesis process to increase the oxygen vacancy density.The Ce-OMS-2 samples were prepared with different fill percentages by means of a hydrothermal approach(i.e.80%,70%,50% and 30%).Ce-OMS-2 with 80% fill percentage(Ce-OMS-2-80%)showed ozone conversion of 97%,and a lifetime experiment carried out for more than20 days showed that the activity of the catalyst still remained satisfactorily high(9...     

Effect of alkaline earth metal promoter on catalytic activity of MnO2 for the complete oxidation of toluene

Herein, Na⁺ and Ca²⁺ are introduced to MnO₂ through cation-exchange method. The presence of Na⁺ and Ca²⁺ significantly enhance the catalytic activity of MnO₂ in toluene oxidation. Among them, the Ca-MnO₂ catalyst exhibits the best catalytic activity (T₅₀ = 194°C, T₉₀ = 215°C, E_a = 57.2 kJ/mol, reaction rate 8.40 × 10^?10 mol/(sec?m²) at 210°C. T₅₀ and T₉₀: the temperature of 50% and 90% toluene conversion; E_a: apparent activation energy) and possess high tolerance against 2.0 vol.% water vapor. Results reveal that the increased acidic sites of the MnO₂ sample can enhance the adsorption of gaseous toluene, and the mobility of oxygen species and the content of reactive oxygen species in the catalyst are significantly improved due to the formed oxygen vacancy. Thus these two factors result in excellent catalytic performance for toluene oxidation combining with the weak CO₂ adsorption ability.     

我国生态环境资产负债表编制框架研究*

本文根据生态环境资产负债表的基本概念和理论,提出了生态环境资产负债表编制的总体框架,同时,针对环境容量资产、环境质量产品、生态产品资产的特点,分别建立了相应框架体系,提出了环境资产负债表的应用决策方向。本文研究成果对于确立统一的生态环境资产核算标准和方法、使我国生态环境资产负债核算工作逐步规范化、制度化的轨道具有重要的现实意义。     

关于耕地总量动态平衡的思考

中国是一个人多地少的国家，伴随着80年代经济高速增长而加剧的人地矛盾已经成为区域可持续发展面临的一个重要问题。本文以大量的数据分析了自耕地总量动态平衡实施以来的1999-2001年耕地数量和质量的变化，其中用播面单产和复种指数来度量耕地质量，得出了我国总体耕地质量下降的结论，指出仅仅从数量上实施耕地总量动态平衡，保证不了我国粮食安全的需要。并在此基础上提出了相关的建议。     

A SENSITIVITY ANALYSIS OF THE PALMER HYDROLOGIC DROUGHT INDEX1

ABSTRACT: The sensitivity of the Palmer Hydrologic Drought Index to departures from average temperature and precipitation conditions is examined. A time series of zero index values was calculated and then one monthly temperature or precipitation value was perturbed. The resulting time series shows the effects on the index of one anomalous value. Independent series were calculated for temperature anomalies of plus and minus 1, 3, 5, and 10F and for precipitation anomalies of 25, 50, 75, 125, 150, and 200 percent of normal for each calendar month for Colorado, Indiana, Nevada, New York, Oklahoma, South Carolina, South Dakota, Washington, and Wisconsin. Analysis of the time series showed that the period of time required for the index to reflect actual rather than artificial initial conditions could be more than four years. It was also found that the effects of temperature anomalies are insignificant compared to the effects of precipitation anomalies. In some cases, one anomalous precipitation value could result in established wet or dry spells that last for up to two years. Although not examined in detail, the time series suggest that distributions of index values may be asymmetrical and possibly bimodal.     

Effects of soil properties, mulch and NPK fertilizer on maize yields and nutrient budgets on ferralitic soils in southern Benin

Four on-farm experiments examined whether modest applications of fertilizers in combination with prunings from native agroforestry trees would be an alternative to maintain the fertility of ferralitic soils in Benin. An application of about 1.9 t ha⁻¹ dry matter of mulch of Senna siamea combined with 30 kg N ha⁻¹, 22 kg P ha⁻¹ and 25 kg K ha⁻¹ as compound fertilizer was compared with (1) 60 kg N ha⁻¹, 43 kg P ha⁻¹ and 50 kg K ha⁻¹ as compound fertilizer alone, (2) mulch of S. siamea alone (about 3.2 t ha⁻¹ dry matter), and (3) a control treatment. Criteria were soil properties, yields, nutrient uptakes, and nutrient budgets. Application of sole mulch had no significant effects (P>0.05) on maize yields, while combined application of prunings and NPK fertilizers or sole NPK increased yields significantly (P<0.05). The most limiting nutrient was P. The local maize cultivar was efficient in P uptake, but not in internal nutrient utilization efficiency; mulch increased significantly the internal P utilization efficiency (P<0.05). Soil properties were interpreted with the QUEFTS (quantitative evaluation of the fertility of tropical soils) computer program. The predicted and measured yields were almost the same for maize without NPK. The measured responses to NPK were much lower than the responses calculated by QUEFTS. The calculated nutrient budgets were split into balances for available nutrients and for those not immediately available (NIA). Nutrient budgets were negative for the control and sole mulch treatments, and positive for the NPK treatments. Mulch improved the balances of NIA nutrients. The present experiment could not prove that combining NPK with mulch is the best option for sustainable agriculture. It may be more economical to apply lower rates of fertilizer to local maize than those applied in the two NPK treatments in the present study.