Simple model of sludge thickening process in secondary settlers

In wastewater treatment plants (WWTPs), a secondary settler acts as a clarifier, sludge thickener, and sludge storage tank during peak flows and therefore plays an important role in the performance of the activated sludge process. Sludge thickening occurs in the lower portions of secondary clarifiers during their operation. In this study, by detecting the hindered zone from the complete thickening process of activated sludge, a simple model for the sludge thickening velocity, u _s = aX ^b (a = 0.9925SSVI _3.5, b = 3.541ln(SSVI _3.5)+12.973), describing the potential and performance of activated sludge thickening in the hindered zone was developed. However, sludge thickening in the compression zone was not studied because sludge in the compression zone showed limited thickening. This empirical model was developed using batch settling data obtained from four WWTPs and validated using measured data from a fifth WWTP to better study sludge thickening. To explore different sludge settling and thickening mechanisms, the curves of sludge thickening and sludge settling were compared. Finally, it was found that several factors including temperature, stirring, initial depth, and polymer conditioning can lead to highly concentrated return sludge and biomass in a biologic reactor.     

煤层瓦斯压力测定的合理封孔注浆压力研究

煤层瓦斯压力测定是煤矿安全生产基础参数测定的重要内容之一,测压成功的关键是封孔技术。当围岩裂隙较发育时需要采用压力注浆封孔,注浆压力就成为封孔的技术关键。为了确定一定围岩岩性条件下的合理封孔注浆压力,采用数值模拟的方法对测压钻孔塑性区大小进行了仿真模拟,并根据浆液渗流规律和钻孔围岩性质之间的关系建立了浆液流动数学模型,得出了合理的注浆压力为4MPa,结合新型“两堵一注”囊袋式封孔装置与CPD8M型煤层瓦斯压力自动测定仪进行了现场应用,结果表明4MPa的注浆压力满足平煤十三矿试验现场围岩条件下的封孔要求,对同类条件下瓦斯压力测定具有一定的指导意义。     

论湖滨带的结构与生态功能

湖滨带作为陆地和湖泊之间的过渡带,是健康湖泊生态系统不可缺少的有机组成部分,属于生态交错带的一种. 明晰湖滨带的结构与生态功能对湖滨带及湖泊的水环境改善与生态修复十分重要. 随着水环境因子的梯度变化,湖滨带的空间结构在横向、纵向和轴向分布上都表现出明显的圈层结构特点. 横向结构由陆向辐射带、水位变幅带和水向辐射带组成;纵向结构由空气、水体、底泥构成;轴向结构则是不同岸段湖滨带的景观变化和层次结构,体现整个湖滨带的全貌和湖滨带类型的组合. 湖滨带的时间结构体现在湖滨带生物及其生境条件随着时间推移的演化规律上,并在“时-空结构”中和人的积极存在紧密联系在一起. 影响时间结构的因素包括生物节律、气候因子、水动力等. 湖滨带在生态环境方面的功能可归纳为6项:污染物截留与净化、捕集和抑制藻类、提高湖滨带的生物多样性、提供野生动植物栖息地、控制沉积和侵蚀、调蓄洪水.      

池杉在三峡水库消落带生态修复中的适应性

冬季淹没和夏季干旱的交替作用会导致三峡水库消落带生态系统质量下降. 为了探索有效的生态系统修复方式,选用池杉树种开展了消落带林泽工程试验,并采用统计分析和RDA(冗余分析)排序对水淹胁迫下池杉的生长响应进行了研究. 结果表明:种植在海拔169 m以上的池杉经历两轮冬季淹水后成活率约为84.52%;树高、冠幅和枝叶密度平均变化量较小,分别为0.10 m、0.04 m和-0.11%,而胸径和枝下高变化明显,平均改变量分别为0.78 cm和-0.64 m;树高、胸径、冠幅和枝叶密度等指标变化率在没顶和部分淹水情况下存在显著差异. 部分淹水时,池杉对水淹胁迫的适应能力较强,随着淹水深度的增加,各生长指标变化量均呈下降趋势,部分植株有枯梢,没顶和部分淹水情况下枯梢率分别为43.56%和11.76%. RDA结果表明,水力条件和初始生长特征共同对淹水后池杉生长变化产生影响,二者对池杉生长指标变化的总体解释率为31.20%,独立解释率分别为11.90%、14.40%,共同解释率为4.90%. 池杉作为适应三峡水库消落带水位变动的本土耐淹树种,其经历水淹后的生长变化不仅与水位变动有关,同时也与其淹水前的生长状态有关. 研究结果有助于三峡水库消落带类似生态修复工程的进一步深入开展.      

不同河岸带修复策略对氮磷非点源污染的净化作用

选择北江的重要支流流溪河流域为研究对象,基于现有河岸带对非点源污染削减作用的模拟结果,采用情景分析法,预测不同河岸带修复策略对非点源污染的削减作用,使用效益-成本指数表征TN和TP削减率提高幅度与增加河岸带面积的关系,比较不同河岸带修复策略的效率.结果表明:河岸带对TN和TP的削减能力具有较大的空间差异性.各修复情景都在不同程度上提高了河岸带对TN和TP的削减率(TN:23.36%~30.72%;TP:27.19%~39.86%),河岸带增加总面积与削减率呈现对数增长关系(P<0.05).选择综合考虑了流域非点源负荷量以及河岸带状况的优先修复子流域进行河岸带修复时,效益-成本指数达最高为1.19%.     

我国海岛潮间带贝类体中重金属含量及其评价

以2007年5月~2008年10月我国典型海岛潮间带贝类体内重金属检测结果为基础,探讨了我国海岛潮间带贝类体中重金属(Cu、Pb、Zn、Cd、Cr、Hg)含量水平.结果表明,研究区各海岛潮间带贝类体内以Zn、Cu较高, Pb、Cd和Cr较低, Hg最低;与上世纪九十年代初的数据比较,变化不明显.根据《海洋生物质量》标准,评价了各海岛潮间带贝类体中重金属污染水平.分析表明各种重金属含量均有一定程度的超标, Zn超标较严重, Cu和Cd次之,其余较轻.原因可能与陆源污染物排放和贝类对不同金属的富集能力有关.     

超限结构无缝法施工在污水处理工程中的应用

介绍了一种在超限混凝土结构中取消伸缩缝或增大伸缩缝最大间距的新型施工方法——超限混凝土结构无缝法施工。论述无缝法施工的原理及膨胀加强带的设置,探讨UEA膨胀混凝土的配制,在实践的基础上总结了无缝法施工的方法、注意事项及优点。     

Remediation of 2,4-dichlorophenol-contaminated groundwater using nano-sized CaO2 in a two-dimensional scale tank

• Nano CaO₂ is evaluated as a remediation agent for 2,4-DCP contaminated groundwater. • 2,4-DCP degradation mechanism by different Fe²⁺ concentration was proposed. • 2,4-DCP was not degraded in the system for solution pH>10. • The 2,4-DCP degradation area is inconsistent with the nano CaO₂ distribution area. This study evaluates the applicability of nano-sized calcium peroxide (CaO₂) as a source of H₂O₂ to remediate 2,4-dichlorophenol (2,4-DCP) contaminated groundwater via the advanced oxidation process (AOP). First, the effect and mechanism of 2,4-DCP degradation by CaO₂ at different Fe concentrations were studied (Fenton reaction). We found that at high Fe concentrations, 2,4-DCP almost completely degrades via primarily the oxidation of •OH within 5 h. At low Fe concentrations, the degradation rate of 2,4-DCP decreased rapidly. The main mechanism was the combined action of •OH and O₂^•−. Without Fe, the 2,4-DCP degradation reached 13.6% in 213 h, primarily via the heterogeneous reaction on the surface of CaO₂. Besides, 2,4-DCP degradation was significantly affected by solution pH. When the solution pH was>10, the degradation was almost completely inhibited. Thus, we adopted a two-dimensional water tank experiment to study the remediation efficiency CaO₂ on the water sample. We noticed that the degradation took place mainly in regions of pH<10 (i.e., CaO₂ distribution area), both upstream and downstream of the tank. After 28 days of treatment, the average 2,4-DCP degradation level was ≈36.5%. Given the inadequacy of the results, we recommend that groundwater remediation using nano CaO₂: (1) a buffer solution should be added to retard the rapid increase in pH, and (2) the nano CaO₂ should be injected copiously in batches to reduce CaO₂ deposition.     

非饱和带柴油入渗实验研究及HSSM模拟

通过土柱模拟实验研究了柴油在不同含水率、不同粒径砂土中的入渗及残留特征,并采用HSSM(Hydrocarbon Spill Screening Model)模拟了柴油在含水率为6%中砂介质中的入渗过程.结果表明:随着介质含水率增加,柴油在介质中湿润锋推进速度先增大后减小,最快速度对应含水率处于相应介质最大残余含水率40%~50%范围内,残余柴油量随介质含水率增大而减小.在细砂、中砂和粗砂3种介质,柴油入渗平均湿润锋推进速度分别为0.42,0.52,0.73cm/min;平均残余柴油量分别为98.10,68.70,48.79mL. 湿润锋推进速度及残余柴油量均与介质粒径呈负相关.HSSM拟合柴油在含水率为6%中砂介质中的湿润锋推进速度为0.5832cm/min,与实验值0.5689cm/min相比,相对误差为2.51%.HSSM能较好的模拟柴油在非饱和带入渗过程,对于土壤及地下水污染预报具有重要意义.     

Applicability of Montreal Process Criterion 4 — soil and water conservation — to rangeland sustainability

SUMMARY

Criterion 4 of the Montreal Process addresses the conservation of soil and water resources as a way to assess the sustainability of a nation's forests. For the most part, the indicators under this criterion are relevant to rangelands. The area and percent of rangeland with significant soil erosion apply equally well to both biomes. Percent of streams with flow rates and timing outside its range of historical variation is also equally important, although a measure of proper functioning and condition may provide a better measure of the indicator. The area and percent of rangeland with diminished soil productive capability because of a loss of reduced organic matter or changed physical characteristics can be useful indicators locally and regionally.