两种填料曝气池氧传质特性的比较研究

通过改变曝气量和空气扩散方式,采用中试对比研究了网格填料和蜂窝管填料对提高曝气过程中氧转移系数和氧转移效率的影响。结果表明,当空气扩散器的初始逸出气泡直径为3 mm、曝气量由2.2 m3/h增至6.2 m3/h时,网格填料曝气池的氧转移系数的平均增长速率是蜂窝管填料曝气池的2.07倍;而且,当曝气量为6.2 m3/h时,前者的氧转移效率是后者的1.6倍。当空气扩散器的初始逸出气泡直径降至80~100μm后,网格填料池的氧转移系数和氧转移效率仍高于蜂窝管填料池的,但优势明显减弱。     

曝气量分配和填料填充率对MBBR氧转移效率的影响

针对曝气量分配方式及填料填充率对移动床生物膜反应器（MBBR）氧转移能力的影响问题，以青岛市某污水处理厂的MBBR单元为研究对象，以标准氧转移效率（αSOTE）为评价指标，通过正交试验确定了最优曝气量分配方式；在特定曝气系统阀门开启度工况下，采用尾气法对不同填料填充率（28%、33%、38%、43%）条件下好氧池沿程各测点处的αSOTE进行了连续72 h测试，最后通过整池平均αSOTE指标评价填料填充率对MBBR氧转移能力的影响。结果表明，在高长宽比（2.6∶1）MBBR反应器和高水流行进流速（36 m/h）条件下，当MBBR进水端、中部区域、出水端的曝气量分别采用中气量、低气量、高气量时，可在反应器内形成反向推流流态，避免填料堵塞；同时，在低填料填充率条件下可关闭穿孔曝气，降低曝气强度，节省能耗。随着填料填充率由43%逐渐降低至28%,MBBR整池平均αSOTE可由19.3%提高至30.2%。     

生物接触氧化预处理池的运行管理

1 生化处理简况 宁波市自来水总公司梅林水厂原有一座Q=40000m~3/d的斜管悬浮澄清池,由同济大学协同宁波市自来水总公司改建成我国第一座弹性立体填料和微孔曝气的生物接触氧化预处理池,于1996年6月初投产运行,其平面和剖面见图1。     

检查井内污水跌落充氧试验研究

检查井是污水管道内水流与外界空气接触的重要场所,管内氧含量对污水自净能力有明显影响。对西安市城区部分检查井内氧含量的调查发现,井内氧组分稀缺现象较普遍,而跌落水流可有效改善此现象。利用竖桶试验模拟研究检查井内跌水充氧的影响因素,结果表明:增大竖桶顶部孔径时,跌落水流的复氧效率和顶部小孔卷吸气量均增加,但随着孔径的增大此影响逐渐变小;随着跌水流量的增加,水垫层复氧效率与小孔卷吸气量缓慢增加;当水流跌落高度为0.6 m时,复氧效率约为0.4 m时的2倍;顶部小孔位置在跌落水流正上方且水平距离入口最远时,水垫层复氧效率最大,当小孔在桶盖边缘处时,水垫层复氧效率均低于小孔在水流正上方的复氧效率。     

A/O-MBBR工艺处理低浓度城镇污水研究

采用A/O-MBBR工艺处理低浓度、低C/N值城镇污水,着重考察了载体投加位置及温度对硝化及反硝化的影响。当生化系统的水力停留时间为12 h、回流比为300%、好氧池DO为2.7～7.0 mg/L、K3型生物悬浮载体投加量为好氧池总池容的11%时,在正常水温下,投加在好氧池前端和后端的装置对氨氮的平均去除率分别为95.7%和92.6%,对总氮的平均去除率分别为22.4%和9.1%,且投加在好氧池前端比投加在后端的抗氨氮冲击负荷能力强;在6.3～10.5℃低温下,系统仍保持了较高的氨氮去除率,载体投加在好氧池前端时对氨氮的平均去除率为82.9%,比投加在后端高8%左右。     

移动床生物膜反应器中微生物呼吸对氧传质的影响

为研究移动床生物膜反应器(MBBR)中微生物呼吸对氧传质的影响,于体积为13 L的玻璃装置中,采用聚乙烯生物载体(填充率为40%)培养生物膜,经过20 d后,MBBR对NH3-N的去除率达97%。采用off-gas尾气分析方法测定MBBR的氧传质效率(αSOTE),结果表明生物膜的耗氧速率(OUR)对αSOTE有明显的促进作用。在曝气量为40 L/h条件下,当OUR由11 mg/(L·h)增大至28 mg/(L·h)时,αSOTE可提高近一倍。αSOTE与OUR有较好的线性相关性,其拟合曲线的R2约为0.96。在不同曝气量下,OUR对αSOTE的促进程度不同。在试验所调节的60、80和100 L/h三个曝气量下,60 L/h时OUR对αSOTE的促进作用最大,可使αSOTE提高近一倍;而曝气量为100 L/h时,αSOTE可提高约40%。此外,利用OUR与αSOTE的线性关系,通过测定OUR可获得实际工艺状态下的αSOTE。     

生物接触氧化/气浮处理微污染源水中试

开展了生物接触氧化/气浮工艺处理微污染源水的中试研究(规模为20 m3/h),考察了生物接触氧化池的气水比、水力停留时间、悬浮生物填料填充率和气浮池混凝剂投加量、表面负荷对污染物去除效果的影响。结果表明,当生物接触氧化池的气水比为1.0、水力停留时间为60m in、填料填充率为40%与气浮池的硫酸铝投加量为30 mg/L、表面负荷为7.5 m3/(m2.h)时,工艺除污效果良好,对CODMn的去除率为23%,出水NH3-N及TP达到了地表水Ⅱ类水水质标准。     

接触氧化+人工湿地处理小区污水的试验研究

介绍了采用"接触氧化 人工湿地"组合工艺处理小区污水的试验研究。组合工艺的试验运行分两个阶段:前阶段生物接触氧化池连续运行,后阶段生物接触氧化池间歇运行。试验结果表明,间歇运行的生物接触氧化池与人工湿地组合,其运行效果优与连续运行的工艺组合。组合工艺的最佳运行工况为曝气强度为4.0 m3/(m2.h),进水0.25 h,曝气2 h,沉淀1 h,排水0.25 h,此时出水水质可达到《城镇污水处理厂污染物排放标准》(GB18918-2002)的一级A标准,经过消毒后可以回用。同时针对不同浓度的小区污水,还可以通过调整组合工艺的运行方式以满足排放标准要求。     

SBR工艺污泥沉降性能的影响因素研究

分别研究了运行方式、运行时间、硝酸盐浓度、曝气量、污泥负荷及曝气时间对SBR工艺中污泥沉降性能的影响.试验结果表明,以厌氧/好氧方式运行时,厌氧≥1 h且好氧≥3h可获得沉降性良好的污泥;以缺氧/好氧方式运行时,缺氧段硝酸盐浓度过高会导致污泥膨胀,缺氧段时间宜控制在1h左右;当有机负荷较高时,曝气量较高或较低均可能导致污泥膨胀,通过降低有机负荷可有效改善污泥沉降性能;在污泥负荷较低、曝气量适当且氮磷充足的条件下,曝气6h时污泥的沉降性较差,将曝气时间延长至10 h,污泥浓度保持稳定,沉降性较好.     

竹制填料的充氧性能试验研究

在相同试验条件下,采用间歇式非稳态曝气法进行清水充氧性能研究,通过测定氧的总转移系数、氧的转移速率、充氧能力、氧的利用率和充氧动力效率5项指标来考察弹性塑料填料、竹丝填料和竹球填料3种不同填料对反应器充氧能力的影响.试验结果表明:与弹性塑料填料相比,竹制填料在对反应器充氧性能的影响方面占有优势,可替代传统的塑料类填料作为生物接触氧化工艺的载体填料.     

Predicting oxygen transfer of fine bubble diffused aeration systems--model issued from dimensional analysis

The standard oxygenation performances of fine bubble diffused aeration systems in clean water, measured in 12 cylindrical tanks (water depth from 2.4 to 6.1m), were analysed using dimensional analysis. A relationship was established to estimate the scale-up factor for oxygen transfer, the transfer number (N(T)) The transfer number, which is written as a function of the oxygen transfer coefficient (k(L)a(20)), the gas superficial velocity (U(G)), the kinematic viscosity of water (nu) and the acceleration due to gravity (g), has the same physical meaning as the specific oxygen transfer efficiency. N(T) only depends on the geometry of the tank/aeration system [the total surface of the perforated membrane (S(p)), the surface of the tank (S) or its diameter (D), the total surface of the zones covered by the diffusers ("aerated area", S(a)) and the submergence of the diffusers (h)]. This analysis allowed to better describe the mass transfer in cylindrical tanks. Within the range of the parameters considered, the oxygen transfer coefficient (k(L)a(20)) is an increasing linear function of the air flow rate. For a given air flow rate and a given tank surface area, k(L)a(20) decreases with the water depth (submergence of the diffusers). For a given water depth, k(L)a(20) increases with the number of diffusers, and, for an equal number of diffusers, with the total area of the zones covered by the diffusers. The latter result evidences the superiority of the total floor coverage over an arrangement whereby the diffusers are placed on separate grids. The specific standard oxygen transfer efficiency is independent of the air flow rate and the water depth, the drop in the k(L)a(20) being offset by the increase of the saturation concentration. For a given tank area, the impact of the total surface of the perforated membrane (S(p)) and of the aerated area (S(a)) is the same as on the oxygen transfer coefficient.     

Study the effect of recycled pressurized air on oxygen transfer design parameters in sequencing batch reactor technology

Aeration process consumes more than 60% of the total energy required for wastewater treatment. The present study aims to save power consumption within wastewater treatment aeration process through recycling of the air flow. A new technique of aeration is used to increase oxygen transfer efficiency via exploiting recycled pressurized air. A pilot plant has been constructed to study the effect of using recycled pressurized air within sequencing batch reactor (SBR) model. The results showed that the new technique comparing with the conventional SBR model improved Standard oxygen transfer rate (SORT), Standard oxygen transfer efficiency (SOTE) and Standard aeration efficiency (SAE). In particular, the new technique enhanced (SAE) with 10 and 4% at gauge pressure values 0.5 atm. and 2 atm. respectively. On the other hand, intermittent aeration enhanced (SAE) with 15 and 5% at gauge pressure values 0.5 atm. and 2 atm. respectively.     

On the reoxygenation efficiency of diffused air aeration

One technique used to increase the dissolved oxygen concentration of polluted waters is the bubbling of air through a diffuser pipe located at depth, thereby producing a bubble curtain from which oxygen transfer to the water occurs.

The results of laboratory studies on the aeration efficiency of a diffuser placed along the entire width of a flume, perpendicular to a cross flow are presented (two dimensional aeration). Parameters investigated include (1) diffuser type-porous materials with mean pore sizes of 40, 90 and 180 μm and perforated pipes with 0.4, 0.6 and 1.0 mm diameter ports (2) air flow rate per unit width 3–53 m³ (m h)⁻¹ and (3) cross flow velocity (2.5–15 cm s⁻¹. The effect of variation from the two dimensional situation is also discussed as well as the consequence of using oxygen instead of air, and the sensitivity to discharge angle, port spacing and the free surface. The measured efficiencies are compared with theory as well as available laboratory and field data.

The major conclusions are (1) aeration efficiencies using diffused air aeration are on the order of 2–13%m⁻¹ (2) the aeration efficiency increases with increasing cross flow velocity and decreasing air flow rate per unit width (3) aeration efficiencies using porous filters, for air flow rates less than 40 m³ (m h)⁻¹, are significantly higher (a factor of 2–3) than those achieved using perforated pipes (4) changing the pore size from 40 to 180 μm, the port size from 0.4 to 1.0 mm or the port spacing does not significantly effect the aeration efficiency (5) aeration using oxygen is somewhat less efficient than that using air. However, since equivalent oxygen bubbles contain approximately five times more oxygen than air bubbles, more oxygen is transferred on an absolute basis at the same gas flow rate using compressed oxygen as opposed to air (6) aeration efficiency resulting from aeration over a portion of the entire width can be reasonably predicted using the results of the two dimensional studies and (7) the available laboratory and field data compare well with the results of these laboratory studies.     

Promotion and inhibition of oxygen transfer under fine bubble aeration by activated sludge

The promotion and inhibition of inactivated and activated sludge on oxygen mass transfer (OMT) were studied using lab‐scale experiments. The results showed that the α‐values and oxygen transfer efficiency (OTE) decreased with increasing mixed liquor suspended solids (MLSS) concentration (1–10 g/L). Although OMT promotion rate by microbial respiration in activated sludge system increased from 39.8–97.5% for the α‐values and OTE, the two parameters were found to fall sharply when MLSS concentration was over 5 g/L. This indicated that the sludge concentration is a major influence factor on OMT in activated sludge system. Such results provide valuable knowledge for the operating optimization of the aeration system in wastewater treatment process.     

中空纤维膜无泡曝气氧传质性能试验研究

为探究中空纤维膜无泡曝气技术水体充氧性能,使用聚四氟乙烯(PTFE)和聚丙烯(PP)两种材质的中空纤维膜组件,分别在曝气压强为2、4、6 kPa,曝气流量为18、36、54 L/h条件下进行清水曝气测试,并对两种中空纤维膜的氧传质系数、氧传质速率以及曝气效率等进行分析。结果表明,PTFE和PP两种中空纤维膜组件均能实现无泡曝气,且PP中空纤维膜组件的充氧效果相比PTFE组件要好;当曝气压强为4 kPa、曝气流量为36 L/h时,PTFE和PP膜组件的氧传质速率分别为0.326、0.550 g/(m^2·h)。中空纤维膜无泡曝气技术具有操作压力小、氧传质速率高等特点,充氧效果优于传统曝气。     

Hydrodynamic parameters of diffused air systems

The influence of hydrodynamic parameters of diffused air systems on the oxygen transfer efficiency and the longitudinal dispersion of liquid in diffused air aeration wastewater treatment tanks have been evaluated using dimensional analysis, which involved the identification of significant parameters, development of equations to relate the dimensionless mass transfer and dispersion criteria with dimensionless hydrodynamic and geometric variables, and experimentation to determine the necessary numerical values for these equations. The developed relationships can be used as a guide for the design and optimization of aeration tanks.     

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.     

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.     

悬浮填料生物系统处理炼油废水试验

为了提高A／O工艺的脱氮效果，采用悬浮填料生物系统来处理炼油废水。试验结果表明，当装填30％反应器容积的悬浮填料、进水NH3-N和COD分别为54～75mg／L和420～570mg／L、水力停留时间为24h时，对NH3-N和COD的去除率分别达96％和88％以上，出水水质达到了排放标准。此外，在悬浮填料曝气池中还发生了同步硝化反硝化现象。     

Aeration Performance of Triangular-Notch Weirs

Hydraulic structures have an impact on the concentration of dissolved oxygen in a river system, even though the water is in contact with the structure for only a short period of time. The same oxygen transfer that would normally occur over several kilometres in a river can occur at a single hydraulic structure, because the flow over a structure is typically highly turbulent, resulting in increased interfacial renewal. Plunging overfall jets from weirs are a good example of this fact, and the aeration properties of such structures have been studied widely in the laboratory and field over a number of years. This technical note (a) describes triangular-notch weirs having a different weir angle α and how they affect aeration performance, and (b) demonstrates that aeration efficiency decreases with increasing weir angle.