Effect of bubble morphology and behavior on power consumption in non-Newtonian fluids’aeration process

Due to a prolonged operation time and low mass transfer efficiency, the primary challenge in the aeration process of non-Newtonian fluids is the high energy consumption, which is closely related to the form and rate of impeller, ventilation, rheological properties and bubble morphology in the reactor. In this perspective, through optimal computational fluid dynamics models and experiments, the relationship between power consumption, volumetric mass transfer rate(kLa) and initial bubble size(d0) was constructed to establish an efficient operation mode for the aeration process of non-Newtonian fluids. It was found that reducing the d0could significantly increase the oxygen mass transfer rate, resulting in an obvious decrease in the ventilation volume and impeller speed. When d0was regulated within 2-5 mm,an optimal kLa could be achieved, and 21% of power consumption could be saved, compared to the case of bubbles with a diameter of 10 mm.

Effect of surfactant frequently used in soil flushing on oxygen mass transfer in micro-nano-bubble aeration system

In-site soil flushing and aeration are the typical synergetic remediation technology for contaminated sites.The surfactant present in flushing solutions is bound to affect the aeration efficiency.The purpose of this study is to evaluate the effect of surfactant frequently used in soil flushing on the oxygen mass transfer in micro-nano-bubble(MNB)aeration system.Firstly,bio-surfactants and chemical surfactants were used to investigate their effects on Sauter mean diameter of bubble(dBS),gas holdup(ε),volumetric mass-transfer coefficient(kLa)and liquid-side mass-transfer coefficient(kL)in the MNB aeration system.Then,based upon the experimental results,the Sardeing's and Frossling's models were modified to describe the effect of surfactant on kL in the MNB aeration.The results showed that,for the twenty aqueous surfactant solutions,with the increase in surfactant concentration,the value of dBS,kLa and kL decreased,while the value ofεand gas-liquid interfacial area(a)increased.These phenomena were mainly attributed to the synergistic effects of immobile bubble surface and the suppression of coalescence in the surfactant solutions.In addition,with the presence of electric charge,MNBs in anionic surfactant solutions were smaller and higher in number than in non-ionic surfactant solutions.Furthermore,the accumulation of surfactant on the gas-liquid interface was more conspicuous for small MNB,so the reduction of kL in anionic surfactant solutions was larger than that in non-ionic surfactant solutions.Besides,the modified Frossling's model predicted the effect of surfactant on kL in MNB aeration system with reasonable accuracy.

Changes in the activities of key enzymes and the abundance of functional genes involved in nitrogen transformation in rice rhizosphere soil under different aerated conditions

Soil microorganisms play important roles in nitrogen transformation. The aim of this study was to characterize changes in the activity of nitrogen transformation enzymes and the abundance of nitrogen function genes in rhizosphere soil aerated using three different methods(continuous flooding(CF), continuous flooding and aeration(CFA), and alternate wetting and drying(AWD)). The abundances of amoA ammonia-oxidizing archaea(AOA) and ammonia-oxidizing bacteria(AOB), nirS, nirK, and nifH genes, and the activities of urease, protease, ammonia oxidase, nitrate reductase, and nitrite reductase were measured at the tillering(S1), heading(S2), and ripening(S3) stages. We analyzed the relationships of the aforementioned microbial activity indices, in addition to soil microbial biomass carbon(MBC) and soil microbial biomass nitrogen(MBN), with the concentration of soil nitrate and ammonium nitrogen. The abundance of nitrogen function genes and the activities of nitrogen invertase in rice rhizosphere soil were higher at S2 compared with S1 and S3 in all treatments. AWD and CFA increased the abundance of amoA and nifH genes, and the activities of urease, protease, and ammonia oxidase, and decreased the abundance of nirS and nirK genes and the activities of nitrate reductase and nitrite reductase, with the effect of AWD being particularly strong. During the entire growth period, the mean abundances of the AOA amoA, AOB amoA, and nifH genes were 2.9, 5.8, and 3.0 higher in the AWD treatment than in the CF treatment, respectively, and the activities of urease, protease, and ammonia oxidase were 1.1, 0.5, and 0.7 higher in the AWD treatment than in the CF treatment, respectively. The abundances of the nirS and nirK genes, and the activities of nitrate reductase and nitrite reductase were 73.6, 84.8, 10.3 and 36.5% lower in the AWD treatment than in the CF treatment, respectively. The abundances of the AOA amoA, AOB amoA, and nifH genes were significantly and positively correlated with the activities of urease, protease, and ammonia oxidase, and the abundances of the nirS and nirK genes were significantly positively correlated with the activities of nitrate reductase. All the above indicators were positively correlated with soil MBC and MBN. In sum, microbial activity related to nitrogen transformation in rice rhizosphere soil was highest at S2. Aeration can effectively increase the activity of most nitrogen-converting microorganisms and MBN, and thus promote soil nitrogen transformation.

Performance Evaluation of Collard Based Bio-Filter for Treating Fish Tank Effluent for Re-use

The increasing Uganda’s urban population growth has led to limited space coupled with high cost of living, thus making it difficult for the urban poor in congested areas to afford fish protein hence poor nutrition among the low income earners. Therefore this study was conducted to evaluate the performance of collard based bio-filtration system for filtering fish tank effluent for re-use in congested peri-urban areas. Field physical-chemical parameters (ammonia, nitrate, dissolved oxygen, temperature and pH) were measured at various bio-filter lengths in the effluent from both collard based and GBF (Gravel Based Bio-Filter). Differences in mean ammonia and nitrate levels at various lengths were analyzed using one-way ANOVA at p = 0.05. Ammonia levels were significantly reduced (p < 0.05) at various lengths: L0 99.1 mg/L;L1 75.8 mg/L (23.6%);L2 53.1 mg/L (46.4%);L3 25.8 mg/L (74%) and L4 6.6 mg/L (93.4%). Similarly, nitrate levels significantly reduced (p < 0.05): L0 11.8 mg/L;L1 7.2 mg/L (39.4%);L2 3.6 mg/L (69.2%);L3 1.6 mg/L (86.7%) and L4 0.1 mg/L (99.3%). Significant difference (p < 0.05) was obtained in mean ammonia and nitrate removal between collard based and gravel bio-filters. Collard based filter yielded higher ammonia and nitrate removal at L4 by 18.3% and 39.5% respectively, hence L4 is the effective length for collard based bio-filter.

Influence of Stand-Alone Vertical Gas Vents on Aeration and Denitrification of Organic Municipal Waste Assessed by Two-Dimensional (2D) Lysimeters

Landfilled organic waste, in the presence of oxygen, can undergo aerobic decomposition facilitated by heterotrophic microorganisms. Aerobic degradation of solid waste can quickly consume available oxygen thus curtailing further degradation. The aim of this study was the investigation of a low-cost method of replenishing oxygen consumed in landfilled waste. Three 2D lysimeters were established to investigate the effectiveness of stand-alone, vertical ventilation pipes inserted into waste masses. Two different configurations of ventilation were tested with the third lysimeter acting as an unventilated control. Lysimeters were left uninsulated and observed over the course of 6 months with regular collection of gas and leachate samples. Lysimeters were then simulated for Oxygen (O2) and Nitrous oxide (N2O) to analyze the denitrification contributions of each. The experiment revealed that a single ventilation pipe can increase the mean oxygen level of a 1.7 m × 1.0 m area by up to 13.5%. It also identified that while increasing the density of ventilation pipes led to increased O2 levels, this increase was not significant at the 0.05 probability level. A single vent averaged 13.67% O2 while inclusion of an additional vent in the same area only increased the average to 14.59%, a 6.7% increase. Simulation helped to verify that lower ventilation pipe placement density may be more efficient as in addition to the effect on oxygenation, denitrification efficiency may increase. Simulations of N2O production estimated between 8% - 20% more N2O being generated with lower venting density configurations.

Operational guidance for aeration and flow augmentation for the Chicago Area Waterway System—A case study

The Chicago Area Waterway System(CAWS)is a 133.9 km branching network of navigable waterways controlled by hydraulic structures,in which the majority of the flow is treated wastewater effluent and there are periods of substantial combined sewer overflows.The CAWS comprises a network of effluent dominated streams.More stringent dissolved oxygen(DO)standards and a reduced flow augmentation allowance have been recently applied to the CAWS.Therefore,a carefully calibrated and verified one-dimensional flow and water quality model was applied to the CAWS to determine emission-based real-time control guidelines for the operation of flow augmentation and aeration stations.The goal of these guidelines was to attain DO standards at least 95%of the time.The“optimal”guidelines were tested for representative normal,dry,and wet years.The finally proposed guidelines were found in the simulations to attain the 95%target for nearly all locations in the CAWS for the three test years.The developed operational guidelines have been applied since 2018 and have shown improved attainment of the DO standards throughout the CAWS while at the same time achieving similar energy use at the aeration stations on the Calumet River system,greatly lowered energy use on the Chicago River system,and greatly lowered discretionary diversion from Lake Michigan,meeting the recently enacted lower amount of allowed annual discretionary diversion.This case study indicates that emission-based real-time control developed from a well calibrated model holds potential to help many receiving water bodies achieve high attainment of water quality standards.

水产养殖中传统增氧设备增氧能力差异分析

为了解水产养殖中应用广泛的叶轮式增氧机、水车式增氧机、涌浪式增氧机和曝气式增氧机4种型式的增氧机的增氧性能水平,统计和分析了国内主要增氧设备生产企业2020年以来生产的145台不同型式增氧机的增氧能力试验数据。结果显示:1)部分企业生产的叶轮增氧机的增氧性能有所下降;2)水车式增氧机增氧性能有大幅提高,部分产品超过了SC/T 6010—2018《叶轮式增氧机通用技术条件》中规定同规格叶轮式增氧机的要求;3)涌浪式增氧机增氧性能总体呈上升趋势;4)曝气式增氧机具有较强的增氧性能,但配套风机形式不同、相同配套功率但曝气管不同的配置,其增氧性能存在较大差异。本研究为养殖用户在水产养殖系统增氧设备的配置时提供技术参考。

滚筒式堆肥反应器通风搅拌系统设计与试验

针对有机废弃物堆肥过程中物料溶氧效率低导致的堆体起温速率慢、发酵不彻底等问题,设计了一种高效堆肥通风搅拌系统,该系统由分段式通风系统和组合式搅拌装置构成,通过对两个主要装置进行理论设计和DEM-FEM耦合仿真,实现堆肥通风和搅拌工艺优化。结果显示,通风系统中的最大应力出现在通风管上,为13.064 MPa,最大形变量为0.038126 mm,搅拌装置中最大应力出现在抄板上,为190.31 MPa,最大形变量为0.34417 mm,符合设计要求。在此基础上,以食物垃圾和梧桐叶为原料,进行为期14 d的堆肥试验,监测堆肥过程中关键参数变化并测定发酵产物相关指标,完成通风搅拌系统性能验证试验。试验结果表明:使用该通风搅拌系统的滚筒式堆肥反应器,其内部堆体温度在3 d时达到53.34℃,堆肥过程中堆体最高温度可达69.56℃,堆体高温期(大于50℃)可持续6 d以上;试验结束后其产物含水率降至27.21%、pH值升至8.4、种子发芽指数最高可达131.4%,符合有机肥料测定标准(NY/T 525—2021),滚筒反应器运行成本仅65.51元/t。

AOA后置短时低氧曝气实现短程硝化反硝化除磷

为培养亚硝酸盐型反硝化聚磷菌实现好氧颗粒污泥(AGS)短程硝化内源反硝化除磷,设置3组同规格以厌氧/好氧/缺氧后置短时曝气(AO_(1)A-O_(2))模式运行的SBR,各反应器好氧段/后置好氧段(O_(1)/O_(2))的曝气强度和曝气时间均不同,通过对比3组反应器60 d的运行情况,探究各系统污染物处理性能和功能菌活性。结果表明,后置短时低氧曝气10 min且O_(1)、O_(2)的曝气强度分别为5、2.5 L/(h·L)的R2脱氮除磷效果最佳,其COD、TP、NH^(+)_(4)-N、TN去除率达95.49%、95.57%、100%、95.52%。通过短时好氧饥饿和低溶解氧可以创造出短程硝化内源反硝化除磷的最适环境,R2中约60%的除磷菌为DPAOs,且亚硝酸盐型聚磷菌最多,可达38.76%,其反应器好氧段的亚硝酸盐积累率(R_(NA))为74.19%,实现了较高的NO^(-)_(2)-N积累,游离亚硝酸(FNA)为1.03μg/L,可抑制PAOs和NOB,同时富集出更多的AOB和DPAOs。

热处理污泥联合间歇梯度曝气实现短程硝化

提出了一种结合热处理污泥和间歇梯度曝气的新策略.在为期120d的实验中,探索了联合策略对氨氧化细菌(AOB)和亚硝酸盐氧化细菌(NOB)的影响.并在此基础上,以排泥比为主要变量,进一步优化短程硝化运行的长期稳定性.结果显示,在未添加外部碳源的条件下,间歇梯度曝气(DO:2.0mg/L//DO:1.2mg/L//DO:0.5mg/L)可以快速恢复因热处理而活性降低的AOB,并在5d内亚硝酸盐氮积累率(NAR)达到80%以上.在稳定运行阶段,比氨氧化速率(SAOR)和比亚硝酸盐氧化速率(SNPR)分别为30.12和6.69mg N/(gVSS⋅h),氨氮出水浓度低于0.1mg/L,亚硝酸盐和硝酸盐的出水浓度分别为53.42和8.01mg/L.进一步研究表明,排泥比设置为1%的反应器相较于排泥比分别为0.5%和1.5%的反应器,展现出更高的NAR(88.96%)和稳定性.

减水剂改性固废基蒸压加气混凝土的制备与性能研究

以花岗岩石粉、黄河特细砂为硅质材料,以电石渣为钙质材料,以聚羧酸减水剂为改性剂,制备固废基蒸压加气混凝土(AAC)。研究了聚羧酸减水剂掺量对AAC料浆流动性、发气过程、抗压强度、干密度、孔隙率和孔径分布的影响。结果表明,减水剂掺量由0.15%增大到0.30%,料浆初始流动度、发气速率、发气量和孔隙率逐渐增大,制品抗压强度和干密度逐渐降低。减水剂掺量为0.25时,料浆初始流动性270 mm,发气量208 mL,孔隙率82.54%,抗压强度2.9 MPa,干密度509 kg/m^(3),AAC综合性能最优。减水剂掺量大于0.2%时,2 mm以上的大孔基本消失,孔隙率和孔壁无害孔含量对AAC抗压强度影响更明显。

废水泥浆对陶粒加气混凝土砌块性能的影响研究

在废水泥浆中的水取代全部拌合水的条件下,探究废水泥浆中的粉体以等量取代或系数为0.65~1.05折算取代部分粉煤灰时,对陶粒加气混凝土和易性及陶粒加气混凝土砌块抗压强度、干密度、干燥收缩、导热系数的影响。研究表明,水胶比为0.45,当废水泥浆浓度为0~18%时,按等量取代后,砌块28 d平均抗压强度为5.51~5.54 MPa,干密度为728~730 kg/m~3,干燥收缩值为0.28~0.41 mm/m,导热系数为0.137~0.145 W/(m·K);当废水泥浆浓度为20%时,按系数为0.75~0.95折算取代后,砌块28 d平均抗压强度为5.18~5.43MPa,干密度为732~743 kg/m~3,干燥收缩值为0.35~0.42 mm/m,导热系数为0.146~0.178 W/(m·K),此时,砌块符合JG/T 504—2016对CA5.0B07砌块要求。

沿海地区台风荷载下陶粒加气混凝土砌块填充墙斜裂缝试验研究

为研究沿海地区低抗震设防烈度条件下陶粒加气混凝土砌块填充墙的开裂原因,采用PKPM软件分析了某13层框架结构住宅在台风荷载和6度抗震设防烈度下结构的层间位移,结果表明:在该地区基本风压下,该工程的最大层间位移角与6度抗震设防烈度时基本相当。同时进行了一榀足尺框架模型试验,结果表明,当主体结构还在弹性阶段时,模型的整体刚度就急剧下降,填充墙就已经开裂。当试件的位移角达到1/1 092时,填充墙开裂严重,此时相当于刚度修正后的13层框架住宅案例在1.27kN/m^(2)的风压下的表现。因此按照目前的结构设计参数取值和施工构造措施,沿海地区陶粒加气混凝土砌块填充墙的开裂在所难免。为避免该斜裂缝发生,应在设计和施工阶段采取新的设计方法和构造措施。

竹纤维增强金尾矿砂加气混凝土性能研究

以竹纤维为增强材料制备B06级金尾矿砂加气混凝土,分析了竹纤维掺量和长度对竹纤维砂加气混凝土(BFAAC)料浆流动性、发气高度、干密度和抗压强度等的影响;采用XRD及SEM分析了BFAAC的物相组成和微观结构。结果表明:随着竹纤维掺量的增加,BFAAC的料浆流动性、发气高度逐渐下降,试样干密度逐渐增大,抗压和抗折强度先提高后降低,竹纤维的最佳掺量为0.3%。竹纤维长度对BFAAC浆料性能和制品基本物理力学性能影响不明显。XRD和SEM分析表明,BFAAC的水化产物主要是托贝莫来石和少量C-S-H;竹纤维不参与基体材料之间的水化反应,而是通过物理作用达到增强效果。

砖混建筑垃圾制备蒸压加气混凝土性能及水化机理

以砖混建筑垃圾为主要原料制备蒸压加气混凝土(AAC),考察了废弃混凝土(WC)、废弃黏土砖(CB)及其复配掺量对蒸压加气混凝土抗压强度和干体积密度的影响,并利用X射线衍射(XRD)和扫描电子显微镜(SEM)分析了不同砖混配比加气混凝土样品的物相组成和微观形貌。结果表明,当建筑垃圾的掺量为50%~60%(质量分数,下同)时,以废弃混凝土或废弃黏土砖为原料制备的蒸压加气混凝土的抗压强度和干体积密度均能达到《蒸压加气混凝土砌块》(GB11968-2020)中A5.0 B07级别的要求。复配能进一步提升样品性能,随着废弃混凝土、废黏土砖质量比(m(WC)∶m(CB))的降低,所得样品的抗压强度不断升高,而干体积密度先降低后上升,当质量配比为2∶3~3∶2时,试样性能达到《蒸压加气混凝土砌块》(GB11968-2020)中A5.0 B06级别的要求。蒸压养护过程中,坯体中的SiO_(2)、Al_(2)O_(3)、Ca(OH)2、长石、富钙型水化硅酸钙(α-C_(2)SH)共同作用,生成大量片状托贝莫来石、半结晶的CSH(I)、CSH凝胶和少量水化石榴石、硬石膏,与原料中残留的石英、方解石一起填充在孔壁中,相互交织成网状,提高样品强度的同时降低其密度。砖混复配的样品含有更多结晶完整的托贝莫来石、CSH(I)以及适量的CSH凝胶,形成良好的网状致密结构,使样品综合性能更优。

复杂管道浓差腐蚀机制深入分析

在关于管道的流动加速腐蚀研究中,浓差腐蚀这一机制一直被忽视,这是因为这种腐蚀的出现需要一定的条件,即流体中的氧的分布存在较大的差异。为了揭示这种机制的腐蚀过程,本文以复杂形状管道为例,采用数值模拟技术建立了关于浓差腐蚀的数学模型。将管道壁面附近的流体粘性底层作为研究对象,对其进行离散化处理,然后根据基尔霍夫第二定律建立了关于极化后的腐蚀电流的离散方程组,并对其进行求解,得到了浓差腐蚀条件下,离子导电层的电流分布。结果表明:浓差腐蚀会引起腐蚀电流的极大的改变,使管路各部位的腐蚀情况有所改变,如果不考虑浓差腐蚀,对管路的腐蚀情况会产生错误判断。

花岗岩石粉蒸压加气混凝土的制备及性能

【目的】实现以大掺量(质量分数,下同)低品位硅质固废制备蒸压加气混凝土(autoclaved aerated concrete,AAC)。【方法】研究不同掺量花岗岩石粉对AAC料浆发气、抗压强度和干密度等的影响,确定优化掺量配比;通过X射线衍射(X-ray diffractometer,XRD)、傅里叶转换红外光谱(fourier transform infrared spectrometer,FTIR)、场发射扫描电镜(scanning electron microscope,SEM)等表征手段对AAC微观性能进行分析。【结果】花岗岩石粉掺量为60%时,AAC抗压强度为3.02 MPa,干密度为523㎏/m^(3),性能较优;主要矿物成分为托贝莫来石、水化硅酸钙和残留的石英等;托贝莫来石、水化硅酸钙等水化产物与未反应的石英相互交织形成坚固的网状结构,使AAC致密并具有强度。【结论】花岗岩石粉主要含低活性SiO_(2),属于低品位硅质固废,以花岗岩石粉60%替代黄河特细砂制备AAC,物理力学性能可满足GB11968-2020中混凝土砌块抗压强度A 3.5、 B 05级的性能要求。

加气混凝土复合保温外墙板连接节点试验研究

通过对钢管锚节点、套筒节点和新型F型节点进行的6组加气混凝土板四分点加载节点极限承载力试验,分析不同板厚下3种节点的节点强度、节点刚度等性能指标。研究表明:新型F型节点力学性能良好,连接可靠,节点极限承载力随板厚增加而增大。新型F型节点可较好地适用在加气混凝土复合保温外墙板体系中。

持续负温(-5℃)养护条件下含气混凝土性能劣化及孔结构发展规律试验研究

通过对比负温养护、标准养护条件下5种不同含气混凝土试块在不同龄期下的抗压强度值及内部孔结构,分析持续负温(-5℃)养护条件下含气混凝土抗压强度的发展规律,针对持续负温(-5℃)养护条件,对少害孔的范围进一步明确;并从混凝土内部孔隙分布状况对引气类混凝土普遍存在的强度缺失进行研究。试验结果表明:持续负温(-5℃)条件养护对含气混凝土抗压强度的增长有明显的抑制作用,相同引气剂掺量下混凝土试块强度均小于标准养护试块的强度;同种养护条件下,受引气剂影响,混凝土的强度与引气剂掺量间均呈现负相关;在负温养护环境条件下,实验中设置的最高掺量(0.2%引气剂掺量组别)含气混凝土结构整体密实性因浆体内部孔隙数量的增加而减弱,对混凝土自身的强度有一定影响,但引气剂的加入对负温环境混凝土的抗冻作用不可忽视。为了分析负温环境与引气剂掺量之间的平衡性,通过对含气混凝土在不同养护条件下孔结构发展规律的研究,在保证含气混凝土抗压强度劣化程度低、孔径结构相对优化的前提下,明确了负温(-5℃)条件下含气混凝土引气剂的最优掺量。

稳定段曝气时间对高负荷接触稳定法碳捕获影响及微生物群落结构分析

为探究高负荷接触稳定法(HiCS)中稳定段曝气时间(ts)对废水碳捕获的影响,分析不同ts下HiCS系统的碳捕获率及污泥性质的差异,同时分析微生物群落结构差异。结果表明:当ts为1.0、2.0、3.0 h时,碳捕获率分别为43.0%、42.4%、39.2%,显著高于ts为0.5、4.0 h的20.3%和25.3%;污泥粒径较小且分布集中、微观结构粗糙多孔,有利于污泥和有机物接触絮凝。微生物群落结构分析表明,与接种污泥相比,ts为0.5 h的HiCS污泥中变形菌门(Proteobacteria)和拟杆菌门(Bacteroidetes)的相对丰度由24.7%、25.8%上升至40.0%、30.8%。FAPROTAX功能预测结果显示,与碳循环代谢相关的微生物丰度最高,占比达到60%以上,其相对丰度受ts影响显著,在1.0~3.0 h时高于0.5、4.0 h时。