空气吹脱法模拟去除地下水中三氯乙烯研究

三氯乙烯(TCE)是地下水中的典型有机污染物，其有效治理技术的开发一直是环境领域热点。本文研究了四种曝气流量和三种曝气模式下空气吹脱法对溶液中TCE的去除效果，以及空气吹脱结合热修复法去除TCE时三种因素曝气流量、溶液浓度和温度的影响程度。结果表明：0.5 L/min是最佳的曝气流量，同一流量下浓度越高的溶液中TCE去除速率越大，脉冲曝气模式比连续曝气模式对溶液中TCE的去除效率更高，曝气流量是最重要的影响因素。论文研究结果为后续开展空气吹脱在实际地下水污染场地的应用提供了基础数据和技术支持。     

华东某地块场地调查与土壤地下水污染评价

针对华东某重金属与有机复合污染场地,为全面了解其污染程度,重新进行场地规划,开展了土壤及地下水环境调查、污染识别与特征分析及健康风险评估。根据调查结果,土壤样品中重金属砷(As)超过《土壤环境质量建设用地土壤污染风险管控标准(试行)》(GB 36600—2018)中第一类用地风险筛选值,污染主要分布在0～0.5 m的浅层土壤中;地下水样品中铅(Pb)、砷(As)等重金属及苯、苯并(a)芘等有机物超过《地下水质量标准》(GB/T 14848—2017) Ⅲ类标准,其中MW4点位苯并(a)芘超标17 400倍。经健康风险评估,为排除污染隐患,确保场地安全利用,确定土壤中As风险控制值为20 mg·kg^-1,待修复方量301 m³;地下水中As、苯并(a)芘、总石油烃风险控制值分别为10,0.01,600μg·L^-1,待修复方量3 544 m³。     

低膜面流速下曝气对管式膜水力特性及膜污染影响

采用曝气强化管式膜超滤高岭土混合液,考察了低膜面流速下曝气对强化膜分离过程影响,探讨了曝气对膜面水力特征及膜污染过程影响,并对过滤介质影响及膜污染阻力构成进行了研究。结果表明,在低膜面流速下,通过向管式膜引入曝气使膜表面形成气液两相流,可实现膜通量稳定保持在15L/(m²·h)以上。不仅如此,曝气的引入使膜表面雷诺数由1800~2500增至3300~4500,显著增强了膜表面湍流程度,并且实现了低膜面流速下使膜污染指数控制在较低水平,节省了运行能耗。此外,曝气的引入主要减轻了膜表面滤饼污染,使膜过滤总阻力减小且对高岭土截留效率影响不大,但强烈的膜面传质使高岭土粒径有减小趋势,并且膜表面形成污染阻力以不可逆污染层为主,不利于膜污染长周期控制。     

间歇低氧曝气下CANON工艺处理生活污水的启动

利用序批式反应器（SBR）接种短程硝化和厌氧氨氧化污泥处理实际生活污水,在间歇低氧曝气条件下实现了CANON工艺的启动。同时,保证适宜的温度和污泥浓度对处理效果及系统的稳定也很重要。该运行模式下,可实现对亚硝酸盐氧化菌（NOB）的抑制淘洗,短程硝化和厌氧氨氧化为主导反应,自养脱氮体系稳定。系统稳定运行后污染物去除效果良好：进水总氮和氨氮质量浓度为63.9 mg·L^-1和62.7 mg·L^-1,出水总氮和氨氮质量浓度为12.3 mg·L^-1和7.6 mg·L^-1,总氮和氨氮去除率为77.8%和86.7%,总氮去除负荷达0.16 kg N·（m³·d）^-1。试验研究为间歇低氧曝气运行模式推广应用于城市污水自养脱氮提供了参考。     

江苏某关停精细化工企业地块土壤和地下水环境调查及风险评估研究

江苏某关停精细化工企业地块在企业关闭搬迁后多年处于闲置状态,现将规划开发为一类工业用地。因发生土地流转,该地块先需开展土壤污染状况调查,以明确土壤地下水环境质量是否满足规划利用需求。经调查,地块内土壤地下水均存在不同程度的有机物污染物超标情况,且污染情况与企业历史生产经营存在较大关联性。根据风险评估结果,最终明确该地块需开展修复的土壤污染物为氯乙烯、苯、乙苯、1,2-二氯乙烷、1,2-二氯丙烷、1,1,2-三氯乙烷、1,2,3-三氯丙烷、双(2-氯乙基)醚,整体修复区域面积2600 m²,修复污染土壤方量6400 m³。     

耦合初雨调蓄处理设施的半地下污水处理厂设计案例

国内近年来的研究表明，除了污水直排带来的污染，初期雨水排放和合流污水溢流造成的河道污染也比较严重。在心圩江下游污水处理厂设计中，采用半地下建设形式，耦合了1.5万m³初期雨水调蓄池和一级强化处理设施，有效提升了心圩江流域内的污水处理水平，同时考虑了应对近远期合流溢流污染及初期雨水污染的控制措施。污水处理采用“改良厌氧缺氧好氧(AAO)生化池→矩形周进周出二沉池→加砂高速沉淀池→紫外线/次氯酸钠联合消毒”组合工艺，系统抗冲击负荷能力强，运行稳定，出水水质达到并优于国标一级A排放标准。初期雨水处理采用“调蓄池→细格栅+曝气沉砂池→加砂高速沉淀池”组合工艺，具有运行灵活、启动速度快的特点，处理后出水可稳定达到设计水质。项目占地指标为0.62 m²/(m³·d^-1),运行电耗为0.33 kW·h/m³,为同类项目较低水平。     

光伏光热一体化系统流量的分析与优化

建立水冷型PV/T热水系统模型并搭建实验台,从发电量、集热量和水泵耗电量各方面考虑,模拟计算流量变化对系统性能的影响,并结合相对应工况下的实验数据进行对比分析。结果表明：存在最佳流量值使得水冷型PV/T系统综合效率最大,最佳流量值大小与太阳辐射值为正系数线性关系,南京夏季典型工况下系统的最佳流量在0.02kg/（s·m²）左右。以此为基础,本文提出了变流量运行方式优化系统性能,即根据太阳辐射强度调整系统运行流量使水冷型PV/T全天运行时刻处于最高综合效率,结果表明：以实际工程0.072m³/（h·m²）定流量运行为参照实验,全天运行变流量系统实际能量比其多收益19808J。因此,对PV/T系统流量的分析和优化是极有意义的,变流量运行有实际应用前景。     

曝气人工湿地深度处理污水处理厂尾水中四环素的研究

采用陶粒、沸石和矿渣复合基质的人工湿地系统处理污水处理厂的尾水。考察了不同曝气位置、曝气量和水力负荷对系统运行效果的影响，研究了不同进水浓度对四环素的去除效果以及三种基质对四环素的吸附特性。结果表明，人工湿地的中段采用2.55 m³/h的曝气量，水力负荷0.48 m³/(m²·d)、四环素进水浓度200μg/L时，四环素的去除效率高达97.36%。三种基质中炉渣对四环素的吸附效果最佳，吸附平衡量约为2 943 mg/kg，吸附过程符合拟一级动力学，等温吸附过程符合Freudlich模型。     

运行背压变化对低压缸零出力技术安全性及经济性的影响分析

介绍了“低压缸零出力技术”的工作原理及热力系统,并针对运行背压变化对低压缸零出力技术安全性及经济性的影响进行了详细分析。结果表明：机组在低压缸零出力工况下运行时,在主蒸汽流量为1961.0t/h情况下,运行背压由0.0049MPa降到0.0029MPa,低压缸容积流量则由3387137m³/h增长到5449587m³/h,供热负荷由862.4MW增长到899.0MW,机组发电煤耗由198.7g/(kW·h)降低到186.0g/(kW·h);在主蒸汽流量为1861.3t/h情况下,运行背压由0.0049MPa降到0.0029MPa,低压缸容积流量则由3391026m³/h增长到5446086m³/h,供热负荷由821.9MW增长到858.6MW,机组发电煤耗由201.7g/(kW·h)降低到187.0g/(kW·h)。可见机组在低压缸零出力工况下运行时,通过增加低压缸的容积流量,会增强低压缸运行的安全性,因此通过适当降低机组运行背压,有利于改善机组运行的安全性,并且能够降低机组的发电煤耗,提高机组的经济效益。     

曝气生物滤池同步除铁锰和氨氮

在实验室条件下,采用双层陶粒滤料曝气生物滤池工艺,以受氨氮污染的原生铁锰地下水作为研究对象,研究了模拟微污染地下水中铁、锰和氨氮的去除,分析了滤速变化对滤池中铁、锰和氨氮同步去除的影响及铁、锰和氨氮浓度沿滤层深度的变化。结果发现当滤速突然增加时,滤池经过2～3 d的培养后,出水铁、锰和氨氮均可达标;当滤速由0.74 m·h^-1逐渐增加到3 m·h^-1时,水中铁与氨氮的浓度一般都在滤层深度0.75 m处即可达标,但锰浓度达标的滤层深度却由0.75 m增加到1.60 m。     

Groundwater Cleanup by In-Situ Sparging. VIII. Effect of Air Channeling on Dissolved Volatile Organic Compounds Removal Efficiency

Abstract

A mathematical model for removal of dissolved volatile organic compounds (VOCs) from contaminated aquifers by in-situ air sparging is described. The model assumes that the sparging air moves through persistent channels in the aquifer, and that VOC transport to the sparging air is by diffusion/dispersion and airinduced circulation of the water in the vicinity of the sparging well. The dependence of model results on the parameters of the model is explored. The use of pulsed air flow in sparging as a means to increase VOC transport by dispersion is suggested. An extension and modification of the Sellers-Schreiber preliminary screening model for in-situ air sparging is also described. The revised model includes an improved method for calculating bubble residence times in the aquifer, and also permits the modeling of nonaqueous phase liquid (NAPL) removal.     

Ultrafiltration Fouling: Impact of Backwash Frequency and Air Sparging

A bench-scale study was performed to optimize backwash frequency and air sparging conditions during ultrafiltration (UF) for drinking water treatment in order to minimize hydraulically irreversible fouling as well as operating and maintenance costs. Surface shear stress representing different air sparging conditions (continuous coarse bubble, intermittent coarse bubble, and large pulse bubble) was applied in combination with various backwash frequencies (0.5, 2, and 6 hours) during UF of two natural surface waters. Results indicated that air sparging during permeation with intermittent coarse or large pulse bubbles significantly reduced the rate of irreversible fouling. This allowed for longer permeation times (up to 6 hours) between backwashing, when compared to a baseline condition which assumed a 0.5 h-backwash frequency with no air sparging during permeation. As a result, operation and maintenance cost savings estimated at > $350,000/year for a 29 MLD membrane train could be realized. This study demonstrates that optimized air sparging could serve as a cost-effective UF fouling control strategy for drinking water production.     

Groundwater Cleanup by In-Situ Sparging. XIII. Random Air Channels for Sparging of Dissolved and Nonaqueous Phase Volatiles

Abstract

A mathematical model is developed to simulate the sparging of dissolved volatile organic compounds (VOCs) and nonaqueous phase liquid (NAPL) from contaminated aquifers. The sparging air moves through the aquifer in persistent, random channels, to which VOC must move by diffusion/dispersion to be removed. The dependence of the rate of remediation on the various model parameters is investigated and some practical conclusions are reached regarding the operation of air sparging wells for aquifer remediation. VOCs of low water solubility (such as alkanes) and present as NAPL are found to be removed by air sparging much more slowly than VOCs of higher water solubility (such as benzene, toluene, ethylbenzene and xylenes) and present as NAPL, due to the very small maximum concentration gradients which can be maintained around droplets of the former. These small concentration gradients result in very slow rates of NAPL solution.     

地下水曝气过程中空气流场的数学模拟

地下水曝气（AS）过程中空气流场的数学模拟是现场过程研究的必要手段。利用饱和度与相对渗透率、毛细压力间的关系建立了AS二维非稳态流场的数学模型,用有限元法模拟了复杂流场非稳态二维气相饱和度场、速度场和稳态压力场分布,结果显示气相饱和度随着曝气时间和距曝气井位置的不同而变化。在曝气5 h左右,流场区域稳定。由饱和度的分布确定了空气在地下水中流型为下部U形,上部水平。在本模拟条件下,单井AS的影响区半径为9 m,若修复大面积污染的地下水,宜采用多井曝气的方式,增大其影响区半径。     

Critical flux aspect of air sparging and backflushing on membrane bioreactors

Membrane bioreactors (MBR) combine biological processes with membrane filtration. The main obstacle to efficient operation remains the deterioration of membrane permeability with time. One possible approach to the fouling issue is sub-critical flux operation. Other options are air sparging and backflushing. This study investigated the impact of air sparging and backflushing on flux enhancement, as well as exploring the relationship between use of these strategies and critical flux. The research was accomplished in pilot plant scale using a 70 L reactor fed with glucose-based synthetic wastewater at temperatures around 20°C and MLSS of approximately 10 g/L. Results showed that air sparging and backflushing each increased the flux in the MBR. Using both strategies at low transmembrane pressures (TMP) yielded the most substantial flux enhancement (factor 2) at sub-critical conditions. Without enhancement, no critical flux could be identified for permeate flow rates of less than 2/3 of the limiting flux, and the flux dropped to 20% of the limiting flux after 8 days in pseudo-steady state. With a combination of air sparging and backflushing at low TMP (38 kPa), it was possible to maintain flux for the same time frame at about 40% of the limiting flux. The fact that no fouling occurred indicates (by definition) sub-critical flux.     

Groundwater Cleanup by in-situ Sparging. III. Modeling of Dense Nonaqueous Phase Liquid Droplet Removal

Abstract

Microcomputer models for describing the removal of dispersed DNAPL (dense nonaqueous phase liquid) droplets from contaminated aquifers by air sparging are presented, and the dependence of cleanup times on the model parameters is explored. Diffusion transport is assumed to take place from spherical DNAPL droplets through a thick stagnant water layer in a porous medium to the advecting mobile water. Single sparging wells and single sparging curtains are modeled.     

Groundwater Cleanup by In-Situ Sparging. IX. Air Channeling Model for Nonaqueous Phase Liquid Removal

Abstract

A mathematical model is developed to simulate the removal of dissolved and nonaqueous phase liquid (NAPL) volatile organic compounds (VOCs) from contaminated aquifers by sparging. The model assumes that the sparging air moves through the aquifer in persistent channels and that NAPL must dissolve and move to these channels by diffusion and dispersion processes. The dependence of the model results on model parameters is explored, and practical implications for sparging well operation are discussed.     

Groundwater Cleanup by in-situ Sparging. IV. Removal of Dense Nonaqueous Phase Liquid by Sparging Pipes

Abstract

Mathematical models for describing the removal of dense nonaqueous phase liquid (DNAPL) droplets dispersed in a contaminated aquifer by air sparging are described. The sparging configurations considered are 1) a single air pipe discharging at the bottom of the aquifer and 2) a single horizontal slotted pipe discharging at the bottom of the aquifer. Diffusion transport of VOC is assumed to take place from spherical DNAPL droplets through a thick stagnant water layer in a porous medium to the moving aqueous phase. The dependence of removal rates on model parameters is explored.     

寒区石油污染场地浅层地下水原位增温强化空气扰动修复

原位空气扰动技术（air sparging,AS）常被用在治理地下水与土壤的有机污染,在寒区,由于低温环境,污染物传质过程的多种基本参数受到影响,导致修复结果不理想。本文基于野外原位空气扰动实验结果,以甲苯为代表性污染物,进行室内土柱模拟实验,并构建增温空气扰动下污染物迁移模型,对野外场地增温强化空气扰动效果进行模拟,以预测采用增温方式时寒区污染物的去除效果。结果表明,甲苯的挥发速率与温度之间存在正比例关系;在室内柱实验中,高温注气条件下甲苯浓度衰减速率更快;野外数值模拟中的增温强化空气扰动修复过程中温度传导半径为2~4 m,曝气场污染物去除半径达10 m,比非增温强化条件污染物去除范围扩大3~5 m,进而将去除率有效提高40%~50%。     

Long-term flux improvement by air sparging and backflushing for a membrane bioreactor, and modeling permeability decline

Fouling remains a major issue for all membrane applications. This study investigated anti-fouling applications for a side-stream membrane bioreactor (MBR) fed with glucose-based synthetic wastewater. Air sparging, backflushing and high cross flow velocity (CFV) were investigated as anti-fouling strategies. For better comparison of longer test runs, an equation to model effects of MLSS and temperature on viscosity was developed. This study showed that for backflushing with a CFV of 5.2 m/s, the permeability is about 3 times higher than for air sparging with CFV of 2 m/s. Long-term investigations of combined air sparging and backflushing compared to conventional membrane filtration at equal CFVs of 2 m/s showed 4 times higher permeability. The long-term permeability decline can be estimated by a power function of the type P= a tⁿ whereby the factor a is related to the initial permeability and the parameter n indicates how rapidly the flux declines. In most cases it was possible to predict the long term flux decline (over a one week or 8 week period) from data for the first two days of filtration with errors of less than 10%.