Hypolimnetic aeration: practical design and application

Hypolimnetic aeration is becoming increasingly important as a fisheries management and water quality improvement technique, however its application has been restricted by a paucity of practical reference material. Hypolimnetic aeration includes partial and full lift designs and several air/oxygen injection systems. Positive displacement compressors flanged to three phase electric motors are the preferred air supply and power for most lake aeration projects. Internal combustion power is adequate for short term use and wind power is in the developmental stage. Rubber compressed air hose is recommended for lake aeration applications. Free air delivery is the air volume taken into the compressor at standard temperature and pressure however actual output volume is regulated by discharge pressure. Performance specifications of full lift hypolimnetic aerators are based on water:air ratios, oxygen increase, transfer efficiencies and oxygenation capacity. An empirical sizing method is proposed using hypolimnetic volume, hypolimnetic oxygen consumption, water flow, air flow and inflow tube radius. Outflow tube radius should equal or exceed inflow tube radius to achieve high flow rates and allow efficient removal of residual bubbles. Floatation requirements are calculated from the total weight of the separator box, inflow and outflow tubes and the theoretical water head.     

Hypolimnetic aeration and dissolved gas concentrations: Enclosure experiments

Two large circular enclosures, each containing approx. 550 m³ of water, 14 m deep, and open to the mud-water interface, were used to monitor the effects of hypolimnetic aeration. One enclosure was held as a control, the other aerated every 3 or 4 days for a period long enough (usually < 2 h) to maintain hypolimnetic O₂ levels at > 4 mg 1⁻¹. Nutrient additions (10 g of 90% H₃ PO₄ and 250 g NaNO₃ per week) to each enclosure were controlled from the commencement of the experiment (17 June 1980) until its completion (2 November 1981). Temperatures in both enclosures were identical. Hypolimnetic O₂ levels in the control fell to zero during both summers, but remained at > 4 mg 1⁻¹ in the aerated enclosure. Free N₂ concentrations in the hypolimnion of the aerated enclosure was higher than in the control. Concentrations of H₂S in the control hypolimnion increased to > 5 mg 1⁻¹ and concentrations of CH₄ increased to > 18 mg 1⁻¹. Both remained at or near zero in the aerated enclosure. Tests of aerator efficiency suggested that the full air-lift design that was employed had an average O₂ exchange efficiency of 42% which is higher than the values reported for most other designs.     

隧道施工的通风技术和粉尘治理方法

通过浙江温州赵山渡引水隧道工程的施工实践,对施工中的通风方式选择、通风量的计算及通风设备的选择和布置进行了较系统地总结,并对粉尘治理方法进行了介绍,为其他类似工程提供参考借鉴。     

Factors influencing oxygen transfer in fine pore diffused aeration

A bench-scale experiment was conducted in a 701. tank of tap water to examine the effect of four design variables on oxygen transfer in a fine pore diffused aeration system. The experiment used non-steady state gas transfer methodology to examine the effect of air flow rate, air flow rate per diffuser, orifice diameter and reduced tank surface area on the overall oxygen transfer coefficient (K_La₂₀, h⁻¹); standard oxygen transfer rate (OT₂, g O₂ h⁻¹); energy efficiency (E_p, g O₂ kWh⁻¹) and oxygen transfer efficiency (E_o, %). The experiments demonstrated that K_La₂₀ and OT_s increased with air flow rate (9.4–18.8 1 min⁻¹) in the 40 and 140 μ diameter orifice range; however, E_p and E₀ were not affected. Reducing the air flow rate per fine pore diffuser (40 and 140 μ diameter pore size) significantly increased K_La₂₀, OT_s, E_p and E₀. A decrease in orifice diameter from 140 to 40 μ had no effect on K_La₂₀, OT_s, E_p and E₀. A reduction in tank surface area had a marginally significant inverse effect on K_La₂₀ and OT_s, and no effect on E_p and E_o. The mean bubble size produced by the 40 and 140 μ diffusers was 4.0 and 4.2 mm, respectively. There was no consistent effect of air flow rate on bubble size within the range of air flow rates used in this experiment. In clean water aeration applications, the optimum system efficiency will be obtained using the largest number of fine pore diffusers operated at low air flow rates per diffuser. In wastewater treatment plants, higher air flow rates per diffuser should be used to prevent diffuser biofouling and keep biological solids in suspension. Wastewater systems are purposely operated at less than optimum transfer efficiencies in exchange for reduced diffuser maintenance and improved mixing. In either situation, changes in tank surface area and diffuser pore size (provided that pore diameter remains between 40 and 140 μ) are unlikely to have any significant effect on aeration system efficiency.     

A study of optimum aeration efficiency of a lab‐scale air‐diffused system

Up to now, tremendous efforts have been devoted to modelling the oxygen transfer coefficient (k_La) for diffused aeration systems, while not considering the corresponding energy consumption. Enhancing k_La is favorable for an exemplary oxygenation process, but may come at the cost of greater energy withdrawal, an unwelcome tradeoff. Assessing the aeration efficiency (the rate of oxygen delivered per unit energy) reflects the overall effectiveness of an aeration process and guarantees a superior system performance. Presented here is a lab‐scale study that investigates the effect of the orifice diameter, the airflow rate and the water column on the aeration efficiency. Various combinations of the studied parameters were tested using a cylindrical tank with a single orifice for air injection. An optimal performance of the aeration efficiency was observed at an orifice diameter of 0.3 mm when tested under 0.91 m water column and an airflow rate of 0.05 SLPM. Furthermore, a new empirical formula of aeration efficiency was established with a high correlation index (R² = 0.97) to allow preliminary prediction of aeration efficiency.     

A model for the design of hypolimnetic aerators

Diffusor depth, air flow rates, rise velocity and cross-sectional area of the riser tube are the major variables considered in the simple empirical model presented for use in the design of hypolimnetic aerators. Water flow values predicted by the model were correlated with those observed in twenty published field experiments (r = 0.893). The model determined that some aerators are inefficient and their design could be improved. A discussion of required oxygen input during aeration is presented in which the problems of hypolimnetic oxygen depletion rates and oxygen transfer efficiencies (observed and absolute) are considered.     

Etude de la circulation dans les bassins d'aeration a boues activeesStudy of the circulation pattern in aeration tanks

Keeping the mixed liquor in suspension is one of the critical problems in aeration tanks. This can only be assured by adequate circulation of the liquid. A hydrodynamic study in different laboratory and industrial scale aeration tanks, has been carried out to characterise the circulation (bottom velocity, V_f, mean circulation velocity) using the following parameters i.e. tank geometry and air flow rate G. This study also proposes a scale-up criterion for aeration tanks. All the dimensions of these tanks are given in Table 1.     

冻土融沉系数的经验确定方法

冻土融沉系数是计算冻土融化后沉降量的重要参数,也是多年冻土融沉性分类的一个指标.本文根据345个冻土原状样品融沉压缩试验数据资料,对细砾土、砂土、粉土、粘性土、泥炭化粘性土和泥炭质土这六类土,分别得出了估计其融沉系数a0的回归分析方程.同时还简单论述了采用超塑含水量(w-wp)因子估计山区粘性土融沉性的效果及原因,分析...     

钢筋混凝土开洞深梁拉压杆模型方法与经验方法试验对比研究

针对不同的洞口尺寸和洞口位置,按拓扑优化中的遗传演化算法构造拉压杆模型和我国规范推荐的经验方法,设计了4组共8个钢筋混凝土开洞深梁试件。通过静载试验对两种方法设计的试件进行对比,结果表明：按拉压杆模型方法设计的试件不仅具有较高的受剪承载力、较充分的裂缝开展和较好的延性,而且有效解决了按经验方法设计的试件纵筋不能充分利用的问题。通过比较实测的受剪承载力和按材料标准值计算的设计受剪承载力,结果表明：拉压杆模型方法可以得到偏于安全的承载力预测值,而经验方法的预测结果偏差较大;开洞深梁的破坏形态,洞口尺寸较小时由“瓶形”斜压杆两侧的斜裂缝开展起控制作用,而洞口尺寸较大时,虽然也由斜裂缝控制破坏,但显现一定的弯曲破坏特征。     

真空预压法现场试验研究分析

真空预压法的处理深度和加固机理目前还存在一些不同认识,为探索真空预压加固软基的应用效果,特别其加固的有效深度问题,本文通过对实体工程的大量现场试验和理论分析对真空预压加固机理和效果进行了分析和阐述。     

消防水系统的验收测试方法

分别介绍了室内消火栓灭火系统,室外消火栓灭火系统等的验收测试方法,通过对消防水系统应该达到的功能进行分析,提出了在消防验收时正确测试消防水系统功能的方法,以确保系统安全可靠。     

Membrane properties change in fine-pore aeration diffusers: full-scale variations of transfer efficiency and headloss

Fine-pore diffusers are the most common aeration system in municipal wastewater treatment. Punched polymeric membranes are often used in fine-pore aeration due to their advantageous initial performance. These membranes are subject to fouling and scaling, resulting in increased headloss and reduced oxygen transfer efficiency, both contributing to increased plant energy costs. This paper describes and discusses the change in material properties for polymeric fine-pore diffusers, comparing new and used membranes. Three different diffuser technologies were tested and sample diffusers from two wastewater treatment facilities were analysed. The polymeric membranes analysed in this paper were composed of ethylene-propylene-diene monomer (EPDM), polyurethane, and silicon. Transfer efficiency is usually lower with longer times in operation, as older, dilated orifices produce larger bubbles, which are unfavourable to mass transfer. At the same time, headloss increases with time in operation, since membranes increase in rigidity and hardness, and fouling and scaling phenomena occur at the orifice opening. Change in polymer properties and laboratory test results correlate with the decrease in oxygen transfer efficiency.     

坦桑尼亚供水四期项目长输管线阶段试压方法

以坦桑尼亚供水四期项目长输管线阶段性水压试验为例,详细阐述了在非洲地区进行长输管线阶段性水压试验的全过程和注意事项,为中国公司在非洲地区进行长输管线阶段性水压试验提供了一个范例。     

ETFE气枕力学性能试验研究及有限元分析

对1个乙烯-四氟乙烯共聚物（ETFE）气枕足尺模型进行形态测试、加载测试及自振测试,研究了气枕的静力性能和动力特性。建立了ETFE气枕有限元模型,进行了形态、荷载及模态分析,验证了有限元分析方法的有效性。结果表明：气枕内压对外荷载较为敏感,荷载作用下内压变化幅度随初始内压增加而非线性减小;作用于气枕中部或单侧的荷载较对称荷载会引起更大的变形和内压变化;相同荷载作用下,气枕变形随初始内压增加而非线性减小;在试验内压范围内,测试气枕的基本自振频率位于6～10Hz之间,前两阶自振频率间隔较大,2～5阶自振频率分布更为密集,气枕各阶频率均随初始内压升高而非线性增加;在低阶模态中,气枕上、下层膜面呈对称振动;ETFE气枕为低阻尼结构,各阶模态阻尼比随初始内压增加而减小;形态、荷载及模态分析的有限元结果均与试验结果吻合良好,验证了共同作用有限元模型在ETFE气枕静、动力分析中的准确性和适用性。     

水冷式表冷器传热研究（4）：表冷器总传热系数的一个新实验公式

认为目前使用的表冷器总体传热系数实验公式中未考虑管壁及助片的导热,故利用接触因数和表冷器外表面换热系数的关系,提出了一个新的实验公式,对该公司进行了实验验证,拟合精度较高。     

吉林省小流域水文计算方法

对以水科所法为基础的吉林省小流域水文计算方法从计算公式、流域特征、计算过程三个方面进行了详细的介绍.通过实例分别对流域面积、河道长度和河道坡度对设计流量的影响进行了对比分析,通过分析得出流域面积对设计流量的影响最大,河道长度对设计流量的影响相对也较大,河道坡度对设计流量的影响相对较小.     

高层建筑空调工程水系统调试方法

根据高层空调水系统的特点，提出了针对高层空调水系统的调试方法，其中还列出了其质量要求和安全措施，以保证高层建筑空调系统的使用效果。     

空调大温差研究（5）：空调冷水大温差系统设计方法

就冷水机组、空调机组、水泵等的选择,介绍了空调冷水大温差系统的设计方法,指出空调冷水大温差系统与常规温差的空调系统有本质区别,应选用大温差专用空调机组,采用定露点设计法,水力计算宜采用优化设计,以使冷水大温差系统获得更佳的经济性。     

浅析建筑物抗震设计方法

为了更好地从结构抗震原理上认识和理解结构抗震设计方法,分别对静力法、反应谱法、基于反应谱和构造保证延性的设计方法、基于损伤和能量的设计方法、能力设计方法、基于性能/位移的抗震设计方法进行了详细阐述.     

牛顿迭代法在水面线计算中的运用及程序设计

针对天然河流复杂的水力特性,使得传统的水面线推算方法存在着不足,从能量方程着手,采用牛顿迭代法,以河道水深为变量,并用计算机编程实现了对天然水面线的推算,得出推算结果精确且易实现的结论。