Bubble performance of a novel dissolved air flotation(DAF) unit

ES-DAF, a novel DAF with low cost, high reliability and easy controllability, was studied. Without a costly air saturator, ES-DAF consists of an ejector and a static mixer between the pressure side and suction side of the recycle rotary pump. The bubble size distribution in this novel unit was studied in detail by using a newly developed CCD imagination through a microscope. Compared with M-DAF under the same saturation pressure, ES-DAF can produce smaller bubble size and higher bubble volume concentration, especially in lower pressure. In addition, the bubble size decreases with the increase of reflux ratio or decrease of superficial air-water ratio. These results suggested that smaller bubbles will be formed when the initial number of nucleation sites increases by enhancing the turbulence intensity in the saturation system.

Dissolved Air Flotation in Combination with Ultrafiltration Membrane Modules in Surface Water Treatment

The primary purpose of this research is to evaluate the feasibility of dissolved air flotation(DAF) as pretreatment process for membrane modules in river water treatment.The performances of DAF in combination with an up-flow membrane biofilter(MBF) and a hollow-fiber ultrafiltration membrane(UFM) were investigated respectively.Removal efficiency of ultraviolet absorbance at 254 nm(UV254),ammonia nitrogen(NH3-N),particle counts and microbial index were measured for both systems.Results showed that DAF was a robust pretreatment process for floc particles separation despite of raw water quality fluctuations.For DAFUFM system,the monitoring data indicated bacteria breeding,nitrite accumulation in membrane vessel and the ammonia concentration of permeate water even exceeded regulatory limits.By contrast,DAF-MBF system was established via the introduction of multilayer filter media between DAF and curtain type ultrafiltration membrane.In MBF,the matured biological activated carbon(BAC) and zeolite particles guaranteed the efficient removal of both organic matters and ammonia.Moreover,the high dissolved oxygen levels in DAF effluent significantly improved bio-adsorption and degradation of pollutants in MBF.The retention of microorganisms by the membrane not only ensured a high concentration of biomass,but also eliminated the risk of microbes leaking out from MBF.In addition,compared with UFM,the curtain membrane exhibited obviously slower fouling development.These results suggested that the DAF-MBF system was more suitable for purifying raw waters seriously polluted by dissolved contaminants.

Strategy for Controlling the Level in a Dissolved Air Flotation Chamber

The aim of the present study was to implant an efficient strategy for controlling the level of the effluent-oily foam interface in a DAF （dissolved air flotation） chamber of a pilot-scale prototype. DAF has been successfully used in the treatment of oily water, which is one of the main environmental problems in different industrial facilities. Along with important operational parameters, such as microbubble size and flow rate, the control strategy for the automation of a DAF chamber may be an important tool for increasing efficiency. Controlling the level was the strategy chosen to enhance the separation efficiency in a pilot-scale DAF prototype, with monitoring performed using a computational program in LabVIEW （laboratory virtual instrument engineering workbench）. The findings demonstrate that it is possible to maintain the level of the fluid at a reference value established by the operator using the software program through the application of classic proportional integral derivative controllers. Using this control tool, the efficiency of water-oil separation in the pilot flotation chamber prototype was increased to nearly 98%.

Treatment of Wastewater Containing Heavy Metals Using Dissolved Air Released Flotation Column

A new type of dissolved air released flotation column is developed to treat wastewater containing Cr（Ⅵ） based on advantages of both dissolved air floatation and column floatation. By using a column with a diameter of 50 mm and a specially made dissolved air releaser, micro-bubbles inside the column can be formed. N2H4H2O was used as reductant, AlCl3 as flocculant, C12H25SO3Na（SDS） as surfactant in the experiment. The effects of pH of wastewater, pressure of dissolved air, ratio of return water, and concentration of flocculant and surfactant on the removal efficiency are studied. The results show that the efficiency of dissolved air released flotation column is much higher than that of other approaches after the operation parameters are optimized, with the reduction ratio of Cr（Ⅵ ） in wastewater reaching 98%. So this technique can be widely used in wastewater treatment

Comparison of Dissolved Air Flotation and Sedimentation in Treatment of Typical North China Source Water

The treatment of typical north China water by dissolved air flotation(DAF)and sedimentation process was examined.A pilot plant with a water treatment capacity of 120 m^3/d constructed in the Jieyuan Water Treatment Plant(JWTP) of Tianjin,China,was utilized for the comparison of the two processes.The results show that during the pilot test,DAF process can remove particles and organic mater more efficiently than sedimentation process.The removal rate for turbidity by DAF process is 5.5% higher than that by sedimentation in normal turbidity period,and 40% higher in low turbidity period,it is 5%～10% higher for removals of algae,total organic carbon(TOC),trihalomethane formation potential(THMFP)and bacteria in all periods.The removal rates for turbidity,TOC,THMFP,algae and bacteria by DAF process can reach 95%,30%, 20%,94% and 97% respectively.From the results of the pilot test,it can be concluded that DAF is a feasible clarification process,especially for source water with low turbidity and high algal blooming.

Feasibility of bubble surface modification for natural organic matter removal from river water using dissolved air flotation

A novel, functionalized bubble surface can be obtained in dissolved air flotation （DAF） by dosing chemicals in the saturator. In this study, different cationic chemicals were used as bubble surface modifiers, and their effects on natural organic matter （NOM） removal from river water were investigated. NOM in the samples was fractionated based on molecular weight and hydrophobicity. The disinfection byproduct formation potentials of each fraction and their removal efficiencies were also evaluated. The results showed that chitosan was the most promising bubble modifier compared with a surfactant and a synthetic polymer. Tiny bubbles in the OAF pump system facilitated the adsorption of chitosan onto microbubble surfaces. The hydrophobic NOM fraction was preferentially removed by chitosan-modified bubbles. Decreasing the recycle water pH from 7.0 to 5.5 improved the removal of hydrophilic NOM with low molecular weight. Likewise, hydrophilic organic compounds gave high dihaloacetic acid yields in raw water. An enhanced reduction of haloacetic acid precursors was obtained with recycle water at pH values of 5.5 and 4.0. The experimental results indicate that NOM fractions may interact with bubbles through different mechanisms. Positive bubble modification provides an alternative approach for OAF to enhance NOM removal.

常减压装置电脱盐污水治理的工艺改造与优化

针对常减压装置电脱盐污水中H2S和可燃气体含量高、水质因含油含渣的影响不能稳定达标的突出问题。采用常压闪蒸和高效旋流溶气气浮(CDFU)相结合技术路线配套原有重力沉降除油技术工艺,有效解决电脱盐污水中高含油含渣、可燃气和硫化氢含量较高的问题,改造后石油类降低73.6%,COD(化学需氧量)降低32.7%,H2S、可燃气体和VOCS体积浓度分别下降56.85%、57.93%和38.25%。电脱盐污水水质明显改善,减少对下游污水系统的影响,消除安全隐患。

铁路站段含油废水处理模式的碳排放研究

为提高铁路站段含油废水的去除效果,同时达到节能降耗减排的目的,以某铁路局车辆段含油废水为研究对象,对比研究传统方案“加压溶气气浮法”与新方案“平板陶瓷膜法”的去除效果和碳排放效果。此外,将传统方案中含油污泥的直接外运处理更改为掺入燃煤中焚烧,探讨其产生的环境效益。结果表明,平板陶瓷膜的整体碳排放强度仅占加压溶气气浮法的35.47%,年碳减排量可达70.2 tCO_(2)。平板陶瓷膜法电耗和药耗的碳排放量相较传统方案而言大幅降低,是因为处理过程所需能耗较小且反应无需添加药剂,仅需使用次氯酸钠对反应装置定期进行反冲洗,物耗使用量也大大降低。将含油污泥直接外运更改为掺入燃煤中焚烧法处理,能够在有效回收资源、实现污泥资源化利用的同时节约成本。整体而言,使用平板陶瓷膜法对铁路站段含油废水进行处理在碳减排方面具有明显优势,同时能够带来更好的处理效益和经济效益,是一项可行的方案,可以进行大范围推广使用。

溶气气浮中CFD方法发展和应用的研究进展

溶气气浮(DAF)工艺是水处理行业中一项重要的处理方法,其具有适应范围广、运营成本低等优势,但其复杂的三相体系使得对其内部研究较为困难。计算流体力学(CFD)技术采用数值模拟方式指导反应器设计,计算成本低,数据准确性高。通过对DAF工艺发展过程中CFD应用的文献全面综述,主要对浮选过程的原理、CFD方法的发展和气浮反应器优化等多方面进行研究,以突出目前使用的CFD方法特点和数值模拟工具的最新发展,并根据研究内容的总结,对今后的研究提出一些建议。

水解酸化+MBBR+气浮+反硝化深床滤池工艺在半地下式污水处理厂的应用

贵州某半地下式生活污水处理厂设计规模为10000 t/d,对现行工艺经过出水水质、技术优缺点、经济分析等方面的对比,最终采用了“水解酸化+MBBR+气浮+反硝化深床滤池”的组合工艺处理。实际工程结果表明,“水解酸化+MBBR+气浮+反硝化深床滤池”的组合工艺能够稳定实现COD,TN、氨氮、TP、SS的去除,污水厂排放水质比《城镇污水处理厂污染物排放标准》(GB18918-2002)中一级A的排放标准更佳,且污水处理厂设备运行稳定,维护简便。工程总投资额为17624.14万元,污水处理厂的运行总成本1.03元/吨水,本工程设计的成功运行为城镇中半地下式污水处理厂的设计运行提供了实际指导经验。

某地下式污水处理厂工艺设计及经验总结

为应对稀缺的城市土地资源和高标准出水排放要求,某地下式污水处理厂采用曝气沉砂池-多段AAO生物池-反硝化深床滤池-气浮池-紫外消毒的组合工艺,出水水质执行DB34/2710—2016《巢湖流域城镇污水处理厂和工业行业主要水污染物排放限值》要求,BOD_(5)、NH_(3)-N、TP达到GB 3838—2002《地表水环境质量标准》中Ⅳ类标准,且可实现TP质量浓度不超过0.1 mg/L的目标。介绍了该地下式污水处理厂的工艺选择、工艺流程、工艺布置及主要构筑物设计参数等,对工艺设计特点进行了总结。实际运行结果表明,该污水处理厂工艺技术合理,运行稳定,出水水质满足设计要求。

等静压石墨生产过程中洗烟废水处理技术分析

石墨烯生产过程中,碱洗塔会产生大量高浓度洗烟废水,其中COD>1000mg/L,TDS约14000mg/L,经过"混凝-气浮"+碟管式反渗透(DTRO)+机械式蒸汽再压缩(MVR)工艺进行处理后,一部分水可回用至生产车间,剩下的废水COD<500mg/L,TDS<1500mg/L,达到当地产业园区接管指标要求,直接排入园区污水管网。

溶气气浮法采收盐藻(Dunalilla salina)细胞

初步探讨了不添加絮凝剂和表面活性剂时用溶气气浮法采收盐藻细胞的工艺条件,结果表明,藻液pH值、溶气压(PS)、溶气水进水流量(QW)、溶气水/原料藻液体积比(水液比αWF)对采收效果有重要影响. 本实验条件下,调节藻液pH值为11.5, 在PS＝0.39 MPa, QW＝7 ml/s, αWF＝1.5的气浮操作条件下,细胞采收率和浓缩倍数分别达86.4%～96.4%和2.38～5.57. 表明气浮法可以安全、高效地从培养液中采收盐藻细胞,无需添加絮凝剂.

THK引气气浮系统的研制与应用

在引进美国THK系统基础上 ,通过对THK系统的研究、消化和吸收 ,已实现THK的国产化生产 ,目前 ,国产化水平已达到 80 % - 90 %。工业废水处理应用表明 ,THK是一种简单、节能和高效的气浮设备 。

微藻细胞的连续气浮法采收

以螺旋藻为模型藻 ,较为详细地研究了藻细胞的絮凝行为以及回流比、藻液浓度、溶气时间和溶气压力因素等对藻细胞连续气浮采收效率的影响。结果表明 ,调节pH值为 11— 12可使藻液产生良好的絮凝性能 ;增大回流比、提高溶气压力、延长溶气时间和接触停留时间 ,可有效地提高气浮采收效率 ;藻液浓度较低时 ,气浮采收效率较高。所提出的连续气浮采收动力学模型可较好地拟合实验结果。

微气泡气浮与溶气气浮预处理餐饮含油废水的研究

采用新型以微气泡发生器为核心的微气泡气浮工艺与普通压力溶气气浮工艺对比,对含油餐饮废水进行预处理,考察了在不同絮凝剂投药量、水力停留时间、工作压力、回流比条件下,两种工艺对水中主要污染物油,有机物(COD)的去除效率。结果表明,在相同或相近条件下,新型微气泡气浮工艺对水中污染物的去除率高于普通溶气气浮工艺。

新型气浮装置ES-DAF中气泡粒径分布的表征

对ES DAF气浮装置进行了研究 .该装置取消了溶气灌 ,在循环泵的压水管和吸水管之间装有一个射流器和一个静态混合器进行吸气和溶气 .采用显微摄像系统 ,对该装置中气泡粒径分布进行了探讨 .结果表明 ,当环流比由 10 %增加到 4 0 %时气泡平均粒径由 5 2 9μm降低到 4 0 9μm ,当表观气水比由 12 %降低到 4 %时 ,气泡平均粒径由 5 5 9μm降低到 4 0 1μm .这说明提高溶气系统中的紊流强度能够形成更多的原始气泡核位 ,从而可以形成更小的气泡 .随着溶气压力由 30 0kPa增加到6 0 0kPa ,气泡粒径分布曲线变低变宽说明压力的升高加剧了气泡的碰撞与并聚作用 .

加压溶气气浮微气泡产生机理及工程应用研究

目前广泛应用的加压溶气气浮设备的最主要问题是运行能耗过大。通过对加压溶气气浮设备微气泡产生机理的研究,得出了加压溶气系统在微气泡产生过程中的两个耗能关键点,并提出降低能耗的改进措施。指出了压力溶气罐内空气溶解过程中气体分散成核步骤中最小能量Δf的存在及其理论表达式。阐述了叶轮散气和气浮泵气浮装置在微气泡发生机理方面的转变和节能方面的优势。

低溶气压力下微藻细胞的气浮法采收

从理论和实验两方面探讨了通过添加微量表面活性剂以实现在较低溶气压力下进行微藻气浮采收的可行性。结果表明 :添加适量的非离子型表面活性剂Tween 2 0可降低待分离体系的表面张力 ,改善微气泡的质量 ,在较低溶气压力下 (≤ 0 .2 5MPa)可获得良好的采收效果。无论是批式过程还是连续操作 ,当溶气水中含有浓度为 10 0mg/kg的Tween 2 0时 ,采收性能都得到较大改善。

微藻细胞的气浮法采收

实验以螺旋藻为模型藻种,较为系统地研究了气固比、气浮塔构造特性、溶气压力和溶气时间等操作条件对微藻气浮采收效率的影响。结果表明,调节藻液值为可使藻液产生良好的絮凝性能; pH 12.0 高径比较大的气浮塔具有更优越的采收效能;气浮采收率随气固比、溶气压力的增加以及溶气时间的延长而上升。提出的气浮采收动力学模型与实验数据拟合良好。