【作者】 陈华清；

【导师】 许天福； 李义连；

【作者基本信息】 中国地质大学 ， 地下水科学与工程， 2010， 博士

【摘要】 在石油化工生产区、储备基地、加油站等地,落地油、含油废水排放和输油管道渗漏等很容易造成地下水石油类污染。石油类污染物已被列为环境中应优先控制的潜在危险性大的毒害性污染物,研发性能安全可靠、操作简便、高效廉价的修复技术,是规模化解决浅层地下水石油类污染问题的关键所在。石油类污染物在地下水中通常以非水相流体(Non-Aqueous Phase Liquids, NAPLs)形式存在,主要修复方法有11种,大致可分为异位修复和原位修复2类,地下水原位曝气(In-Situ Air Sparging, AS)修复技术具有成本低、效率高及原位操作的突出优势,已成为地下水NAPLs污染修复技术的首选。它是一项将空气注入到含水层饱和区中通过空气流的吹脱作用去除挥发性有机物(Volatile Organic Compounds, VOCs)并增强微生物降解效果的创新性原位修复技术,国内外众多专家和学者的实验研究和应用均表明AS技术对于地下水NAPLs污染物的去除效果非常明显。我国对于AS技术的研究还处于室内实验研究和小试阶段,急需形成一套简单易行、经济有效的用于治理地下水NAPLs污染的AS技术体系。AS去除地下水NAPLs污染物是一个多相传质过程,影响因素主要包括污染区的地质和水文地质条件、水文地球化学状况、NAPLs污染物性质、气候状况和AS系统操作特性等。本文主要研究了与AS修复系统相关的4个方面的内容：①地下水NAPLs污染物在AS修复过程中的传质过程和修复机理,对于优化AS系统具有重要作用；②各种影响因素对AS系统气流分布模型和AS系统修复效率的影响,对形成明确的AS技术适用标准具有重要意义；③将AS修复过程中的多相流模型与AS技术相结合,对AS系统的现场设计具有指导意义；④目前AS系统的运行设计基本依靠经验方法,往往会造成系统成本大量增加和修复效率低下,因此在实际污染场地调查的基础上结合AS技术集成研究方法为吉林油田坎下屯污染区设计了AS修复方案。除为所依托的项目提供完整的修复方案、污染防治措施和修复效果的预测之外,研究成果还可为大规模推广地下水NAPLs污染AS修复技术提供科学依据和作为标准范例。具体包括以下研究内容和结果：(1)地下水原油污染AS修复实验研究首先采用DO法研究了曝气深度和曝气流量对AS过程中空气流在砂槽含水层中所能到达的范围的影响。AS过程中含水层上部区域DO很容易达到饱和,在300mL/min的空气注入速率的情况下,随着曝气深度的改变,含水层下部的DO饱和度变化较大,普遍情况是曝气深度越大,空气到达的深度越大。在曝气深度相同的情况下,随着曝气流量的改变,含水层下部的DO饱和度变化较大,普遍情况是曝气流量越大,空气到达的宽度越大。实验用的砂土介质分选性较好,空气注入后在含水层中的分布比较均匀,在曝气深度和曝气流量改变的情况下,DO饱和度分布基本上呈以经过曝气点的垂线轴对称分布,表明AS过程中含水层中的空气流大致呈U型轴对称分布。在DO法确定最佳曝气条件的基础上,以吉林扶余油田原油配制的模拟废水为研究对象,从含水层底部以150mL/min的空气注入速率进行AS修复。150天后砂槽含水层中不同区域的TPH浓度均有大幅度降低,最大去除率达到84.3%,最小去除率也达到59.8%。TPH在水平方向上的去除规律是距离曝气点轴线越近,污染物去除速率越快,距离曝气点轴线越远,污染物去除速率越慢；垂直方向上的去除规律是含水层中部区域的污染物最先去除,然后是含水层上部区域,接下来是含水层下部区域。污染物的去除规律与气流分布模型一致,即气流密集区域污染物去除速率较快,气流稀疏区域污染物去除速率较慢。第30天开始周围环境温度降至10℃以下,污染物去除速率明显减缓,说明第1个月内污染物去除是物理挥发和微生物降解共同作用的结果,后4个月主要以微生物降解作用为主,温度降低严重影响了微生物活性。通过曲线拟合发现在温度适宜的情况下,AS修复过程中TPH浓度呈指数式衰减,当TPH浓度降至0.05mg/L以下时,气流分布密集区域大约需要6-7个月完成修复,气流稀疏区域需要7-8个月,气流难以到达的区域则需要2年以上才能完成修复。(2)AS技术的影响因素研究以高温杀菌后的0.075-2.0mm的混砂作为含水介质,蒸馏水配制的甲苯模拟废水为研究对象,对影响AS修复效率的曝气流量、曝气深度和曝气机制等可控因素进行研究。从含水层底部以15mL/min、30mL/min、60mL/min的不同空气注入速率进行AS修复,60min后含水层下部区域的污染物去除率均已达到50%以上,而且空气注入速率越快污染物去除速率越快。以30mL/min的空气注入速率从含水层不同深度进行AS修复时,含水层中曝气点下方区域污染物去除速率极其缓慢,而且离曝气点越远污染物越难以去除,因此实际应用中应从污染晕下方曝气或从含水层底部曝气。与连续曝气方式相比,间歇曝气方式具有节省能耗的优点,但完成修复所需要的时间较长,综合考虑并不具有明显优势。在无微生物降解条件下周围环境温度对AS修复效率的影响比较明显,在混砂介质中以30mL/min的空气注入速率从含水层底部AS修复240min后,8.0℃条件下含水层下部区域污染物浓度降至24.8mg/L,此时在30℃条件下污染物去除率已达99%以上,浓度仅为5.4mg/L,8.0℃条件下污染物去除率达到99%则需要720min以上。在空气注入速率均为5mL/min的相同曝气条件下,由于空气在不同渗透率含水介质中的流动方式不同,粗砂含水层中的污染物去除速率最快,中砂次之,细砂含水层中的污染物去除速率最慢,这是由于空气流动方式不同影响了含水层中的空气饱和度分布,从而影响了气-液相间的传质面积。对各组影响因素实验的有效数据进行拟合,发现无微生物降解条件下含水层中的污染物在AS修复过程中也是呈指数式衰减。17条拟合曲线中有10条曲线的相关系数都在0.95以上,有13条曲线的相关系数在0.9以上,仅有1条曲线的相关系数低于0.85。通过半衰期对比可以看出,当前实验条件下空气注入速率为30mL/min时,AS系统修复的经济效益是最高的；间歇曝气方式在一定程度上的效益比是优于连续曝气方式,但是完成修复所需的时间远远长于连续曝气方式；周围环境温度越低,污染物半衰期λ越大,完成修复所需要的时间也越长；粒径较大的砂土介质最适宜进行AS修复,半衰期最小,完成修复所需要的时间也最短。(3)AS技术集成及修复机理进行AS系统设计之前要在污染场地现场钻孔进行地质和水文地质条件分析、钻探水井取样分析污染物类型和状况,进行水文地球化学特征和气候调查。AS技术适用于没有厚而且连续盖层的岩性为粉土或粉质粘土的中-浅层含水层NAPLs污染场地的修复。一般在地下水埋深小于15米的潜水层中采用AS技术效果较好,适用于渗透率大于10-14m2的土壤条件。污染物饱和蒸汽压大于5mmHg且亨利常数大于1.013(Pa·m3)/mol的NAPLs污染物都是能够通过AS技术去除的。污染区的水文地球化学特征关系到微生物的降解效率,亚铁离子浓度(Fe2+)过高还会影响AS系统的修复效率。要通过资料调研获取污染区环境温度季节性、长期性和短期性的变化规律,以便合理确定AS系统启动的时间。地下水中NAPLs污染物一般分散在土壤空隙、粘土裂隙和隔层里面,这些污染物首先通过高浓度区向低浓度区域的分子扩散作用运动进入空气通道,然后通过对流-弥散作用去除。AS修复初期污染物通过对流和扩散作用从水相传递到气-液界面,然后挥发进入气相被空气流带出含水层是去除污染物的最主要机理。当地下水中存在NAPL相的VOCs时,则NAPL相VOCs向水相的溶解是去除污染物的第二个机理。土壤介质表面和表面的有机质对污染物都有吸附作用,因此AS修复过程中污染物的吸附/解吸是去除污染物的第三个机理。(4)地下水NAPLs污染AS修复模拟TMVOC模拟程序是美国劳伦斯伯克利国家实验室在TOUGH2模拟程序基础上开发的一种用于变饱和度非均质介质中多组分烃混合物三相非等温流数值模拟程序,具有良好的准确性和可靠性,得到了中国地质调查局的大力推荐。它可以模拟“自然”环境条件下的污染物行为模式,解释不同VOCs在NAPLs中可能出现的水溶性与挥发性的差异,能模拟热修复处理方法,例如蒸气注入或者电阻加热和相关的相变和水流影响等,还包括了一个简单的生物降解半衰期模型。通过二维AS修复实验和数学模拟结果的对比,表明模拟结果在可接受的误差范围之内,TMVOC建立的AS修复模型的可靠性较好,可以较好的预测地下水甲苯污染AS修复过程中的污染物衰减规律。数值模型计算的结果能够满足各种分析的需要,尤其是对研究地下水NAPLs污染AS修复过程中的相态变化、物质传递的微观过程及污染区平衡状态的微观变化等提供了有效手段。数值模拟对地下水NAPLs污染AS修复工程的设计和实施具有重要的指导作用和借鉴意义,有利于节省成本以及AS技术的标准化和大规模推广。(5)AS方案设计实例现场钻探资料表明吉林油田坎下屯污染区第四系孔隙潜水赋存于亚砂土、砂、砂砾石层中。饱和区厚16.6m，含水层上覆厚2.4m的亚砂粘性土层。地表以风化作用生成的细砂为主,厚度约1m。土壤渗透率在10-13m2到10-11m2之间变化。主要接受大气降水入渗补给和地下水侧向径流补给,排泄途径主要有潜水蒸发、地下径流(排向河流)和人工开采等,地下径流方向由东南往西北。平均水位埋深3.52m,平均水力梯度为1.7%,污染区域在石油开采井顺水流方向。污染区属于典型的中温带大陆性季风气候,多年平均气温为4.7℃,年均降雨量约435.9mm,降雨量年际变化于150-350mm之间,年蒸发量为1694mm，其中五月份蒸发量最大,达到318.5mm。钻井资料表明孔隙潜水化学类型为重碳酸钙钠型,部分为重碳酸氯化物钠钙型,含水层均存在不同程度的石油类污染,超标率达到了82%,最大超标倍数达48.6倍,垂向上污染羽最远达到潜水面以下10米左右。现场资料表明该污染区适合采用AS技术进行修复。按照AS技术集成研究成果,结合TMVOC在AS修复模型中表现出的可靠性,根据现场资料数据确定了AS修复方案所需的关键参数。结果表明AS系统以12m3/h的空气注入速率比较合适,此时有效修复半径约为7m,有效修复范围可以达到曝气点下游整个含水层区域。按照等边“三角法”布井时注气井间距为12m,AS系统适宜在春季转暖后启动,此种情况下全年有效修复时间可达8个月左右。油田区域主要以LNAPLs污染物为主,通过模拟BTEX在包气带中泄露后在非饱和-饱和区的迁移规律,表明AS修复完成后可以采用隔离墙和长期AS系统防止落地油造成新污染。AS修复地下水原油污染是一个中长期的过程,至少需要8个月以上才能完成修复,修复期间要周期性监测水样并不断优化AS系统,保证AS系统的稳定运行和保持良好的修复效率。更多还原

【Abstract】 Groundwater is prone to be polluted by petroleum hydrocarbons falling to the ground and leaking from oil pipeline as well as the discharging of oily waste water in the petrochemical production area, reserve base, gas stations and other places. Petroleum hydrocarbons pollutants have been listed as the potentially toxic pollutants which are given to priority in the environment. Research and development of safe and dependable performance, easy operation, high efficiency and low-cost remediation technologies is the key to large-scale solution of petroleum hydrocarbons pollution of shallow groundwater. Petroleum hydrocarbons pollutants usually exist as non-aqueous phase liquids (NAPLs) in the groundwater. The main eleven types of remediation methods can be divided into two classes including en-situ and in-situ remediation methods. In-situ Air Sparging (AS) remediation technology has become the first choice for the NAPLs polluted groundwater due to the outstanding advantages of low cost, high efficiency and in-situ operation over other remediation technologies. AS is an innovative in-situ treatment technology that uses injected air to remove volatile organic compounds (VOCs) and strengthen micro-biological degradation from the saturated zone. A large number of experimental studies and applications from domestic and foreign experts and scholars show that AS technology is obviously to remove the NAPLs pollutants from groundwater. In China, however, AS technology research is still in the laboratory study and small pilot stage, it is urgent to form a simple and cost-effective AS technology system for the treatment of NAPLs polluted groundwater.NAPLs pollutants removal from groundwater by AS is a multi-phase mass transfer process. Influencing factors include the geology and hydrogeology, hydrogeochemistry of polluted areas, and the nature of NAPLs pollutants, climate conditions, as well as the operations characteristics of AS system, etc. This paper mainly studied four aspects associated with AS remediation system:①The mass transfer processes of NAPLs pollutants and remediation mechanisms during the remediation process of AS system play an important role in optimizing system in AS running.②The factors, which have an effect on air flow distribution and the remediation efficiency of AS system, is of great significance to forming the definite applicable standards for the AS technology.③Consequently, it will be of importance in guiding the site design of AS system to integrate the multiphase flow model of the AS remediation process into the AS system.④However, the current design and operation of AS system relying on empirical method often result in a substantial cost increase and low remediation efficiency of the system. Therefore, on the basis of the field investigation of the polluted sites, an AS remediation program is designed for polluted area of Jilin oilfield Kanxiatun, coupling with the AS Technology Integration Research Methods. In addition to provide a complete remediation program, pollution prevention and control measures, and remediation effects of forecasts for the relied projects, research results can also provide a scientific basis and act as a standard example for large-scale remediation of the NAPLs polluted groundwater by AS technology.The research contents and results in detail are as follows:(1) Experimental study on remediation of crude oil polluted groundwater by ASFirstly, DO methods is used to study the AS depth and AS flow rate influencing on the range of air flow in the sand aquifer during the AS process. DO in the upper aquifer is easy to reach saturation during the AS process. However, DO saturation in the lower aquifer changes greatly with the AS depth changes at the air injection rate of 300 ml/min. As a general rule, the greater the AS depth, the deeper the air flow can reach. Even at the same AS depth, DO saturation varies widely with the AS flow rate. The experimental results show that the larger AS flow rate, the wider the air flow can reach. Because the well-sorted sand medium is used in the experiment, the air distribution is relatively homogeneous in the aquifer as air is injected. DO saturation was basically symmetrical distributed to the axis line through the AS point when the AS depth and AS flow rate changed, which indicates that the air flow was roughly symmetrical distributed of U-axis in the aquifer during AS process.As the best AS conditions is determined by DO methods, remediation by AS is carried out at the air injection rate of 150 ml/min from the bottom of the aquifer, taken the simulated wastewater confected by crude oil from Jilin Fuyu oilfield as the research object.150 days later, the TPH concentrations in different parts of the sand aquifer are significantly reduced. The maximum removal rate is up to 84.3%, and the minimum removal rate reaches 59.8%. The removal law of TPH in the horizontal direction is that the closer from the axis through AS point, the faster the removal rate of pollutants is; the farther from the axis, the slower the removal rate of pollutants is. The removal law of TPH in the vertical direction is that the pollutants in the central part of the aquifer remove first, and then the upper part of the aquifer, following by the lower part of the aquifer. The removal law of pollutants is consistent with the airflow distribution model, i.e. the removal rate of pollutants is fast in the dense airflow region, and the removal rate of pollutants is slow in the sparse airflow region.The removal rate of pollutants has slowed down significantly since the ambient temperature dropped to below 10℃from the 30th day. It indicates that the volatilization and microbial degradation of the physical interaction results in the removal of pollutants at the first month. The microbial degradation becomes the main mechanism at the last 4 months. The fall of ambient temperature has a serious impact on microbial activity. It is found that the TPH concentration decays on an exponential model by plotting fitting curve at the moderate temperature during the AS remediation process. If the TPH concentration goes down to 0.05 mg/L below, it will takes about 6-7 months to complete remediation in the airflow dense region and 7-8 months in the airflow sparse region, and more than 2 years in the region that airflow hard to reach.(2) Study on the factors of AS technologyThe factors including AS flow rate, AS depth and AS operation mechanism is investigated to indentify the impacts on the remediation efficiency of AS system. Mixed sand with the size ranging from 0.075 mm to 2.0 mm after the high-temperature sterilization was chose as the aquifer medium, and the simulated wastewater confected by toluene with pure-water was taken as the research object. The air is injected into the bottom of the aquifer for AS remediation, at the rate of 15 ml/min,30 ml/min and 60 ml/min, respectively. The pollutants in the lower part of the aquifer have been removed more than 50% in the different three air injection rate after 60 minutes. And the faster of air injection rate, the greater the removal rate of pollutants is. AS remediation are carried out repeatedly at different depths of the toluene polluted aquifer at the same air injection rate of 30 ml/min. The results show that the part below the AS point of the aquifer are extremely slow to remove, and the farther away from the AS point the pollutants are more difficult to remove. Therefore, it is better to inject air below the pollution plume or at the bottom of the aquifer for actual application of AS system. Compared with continuous AS mode, Intermittent AS mode has the advantage of saving energy, but requires longer time to complete remediation, which make it not obvious advantage taken the two factors into consideration.The environment ambient temperature has an obvious influence on the efficiency of AS system under the absence of microbial degradation. AS remediation from the bottom of the aquifer which is composed of mixing sand medium in the air injection rate of 30 ml/min.240 minutes later, the pollutants concentration decay to 24.8 mg/L in the lower part of the aquifer when the environment ambient temperature is 8.0℃. At this time the pollutants removal rate has reached more than 99% when the environment ambient temperature is 30.0℃, and the concentration is only 5.4 mg/L. It will need more than 720 minutes for the pollutants removal rate reach above 99% when the environment ambient temperature is 8.0℃. At the same AS conditions with the air injection rate of 5 ml/min, the air flow ways vary with the permeability of aquifer medium. The pollutants removal rate in the coarse sand aquifer is fastest, followed by the medium sand aquifer, and the pollutants removal rate in the fine sand aquifer is slowest. This is because the different air flow ways affect the air saturation distribution in the aquifer, thus affect the gas-liquid mass transfer area.By plotting the fitting curve based on the availability of the experimental data in each group, the result indicted that the pollutants in the aquifer also exist exponentially decay under the absence of microbial degradation during the AS remediation process. There are 10 curves correlation coefficient above 0.95 in all of the 17 fitting curves, and 13 curves correlation coefficient above 0.9, only one curve correlation coefficient below 0.85. Comparing the half-life, it can be seen that the AS system at the air injection rate of 30 ml/min appears the highest economic benefits under the current experimental conditions. The efficiency ratio of intermittent AS mode is better than the continuous AS mode to a certain degree, but intermittent AS mode required far longer time than the continuous AS mode to complete remediation. The lower of the ambient temperature, the greater the half-lifeλof pollutants is, and much longer time it requires to complete remediation. The larger size sand aquifer is most appropriate to remediate by AS system; its half-life is smallest and required shortest time to complete remediation.(3) AS technology integration and remediation mechanismBefore AS system is designed, it is necessary to bore a hole on site and analysis the geology and hydrology conditions of the polluted sites; take water sample from drilling wells to analysis the type of pollutants and polluted condition; and investigate the hydro-geochemical characteristics and climate surveys. AS technology is applicable to the remediation of the NAPLs polluted shallow aquifer whose rock lithology is silt or silty clay soil and do not have thick and continuous pink cap. AS technology always preferably uses in the unconfined aquifer layer whose groundwater depth of burial is less than 15 m, and the soil permeability is greater than 10-14 m2. NAPLs pollutants can be removed through AS technology when the pollutants saturated vapor pressure is greater than 5 mmHg and the Henry’s constant is greater than 1.013 (Pa·m3)/mol. The efficiency of microbial degradation related to the hydro-geochemical characteristics of the polluted area. If the concentration of ferrous ions is too high, it will affect the remediation efficiency of AS system. In order to rationally determine the AS system startup time, we have to obtain the seasonal, long-term and short-term changes law of the ambient temperature of the polluted area.NAPLs pollutants in groundwater generally dispersed inside of the soil interspaces, clay cranny and interlayer. Firstly, these pollutants move into the air channel from high concentration area to low concentration area through molecule diffusion, and then removed by convection-dispersion. The main mechanism of pollutants removal at the initial stage is that the pollutants transfer from the water phase into the gas-liquid interface by convection and diffusion, and then evaporate into the gas phase flowing out of the aquifer with air. The second mechanism of pollutants removal is that the NAPL phase VOCs dissolution into the aqueous phase if there is NAPL phase VOCs pollutants in the aquifer. The third mechanism of pollutants removal is the pollutants adsorption/desorption during AS remediation process because soil medium surface and organic matter on the surface have adsorption for the pollutants.(4) Simulation on remediation of NAPLs polluted groundwater by ASTMVOC is a numerical simulator for three-phase non-isothermal flow of water, soil gas, and a multicomponent mixture of hydrocarbons in multidimensional heterogeneous porous media. It is an extension of the TOUGH2 general-purpose simulation program developed at the Lawrence Berkeley National Laboratory. It has been strongly recommended by the China Geological Survey because of its good accuracy and reliability. It can simulate the pollutants behavioral patterns under the "natural" environmental conditions, and explain the water-soluble and volatile differences fir different VOCs that may occur in the NAPLs. It can simulate the hot remediation approach, such as steam injection or resistance heat up and the associated phase transitions and flow effects. A simple model for biodegradation is provided as well.The comparison results between the two-dimensional experiments and mathematical simulation of AS show that the error of simulation results is in an acceptable range. The reliability of the AS remediation model established by TMVOC is good. It can be well predicted pollutants decay law of toluene polluted groundwater during AS remediation process. Numerical model calculation results can meet the variety needs for analysis; especially for study phase change of NAPLs polluted groundwater during the process of AS remediation, micro process of mass transfer and provides an effective means to study the micro change of equilibrium in the polluted area. Numerical simulation plays an important guiding role and can act as reference for the design and implementation of AS system used in the remediation of NAPLs polluted groundwater. What’s more, it is also beneficial to cost savings as well as the AS technology standardization and large-scale promotion.(5) Example of AS program designThe drilling data on site indicate that the quaternary phreatic water of the polluted area in Jilin oilfield Kanxiatun occur in the sub-sand, sand, and gravel sand layer. Saturated zone has the thickness of 16.6 m and underlain by a 2.4 m thick layer which is composed of sub-sand clay. The surface layer is mainly composed of the fine sand formed by weathering with the thickness of about 1 m. The soil permeability varies from 10-13 m2 to 10-11 m2. Groundwater recharges by meteoric water infiltration and groundwater lateral runoff supply; groundwater discharge by evaporation of phreatic aquifer, underground runoff (discharge to the river) and artificial exploitation, etc. Underground runoff direction is from southeast to northwest. The average groundwater depth is 3.52 m. The average hydraulic gradient is 1.7%. Polluted area is on the groundwater flow direction that passes through the petroleum wells. The polluted area is typically moderate temperate continental monsoon climate. The average temperature is 4.7℃for the past years. Average annual rainfall is about 435.9 mm. Interannual variations of rainfall varies from 150 mm to 350 mm. Annual evaporation is 1694 mm with the maximum amount of 318.5 mm in May. Drilling data indicate that the chemical characteristics of the pore phreatic water are dominated by heavy carbonate calcium-sodium type, containing heavy carbonate chloride calcium-sodium type in part. The groundwater in aquifer is contaminated by hydrocarbons pollution in various degrees, with the over-limit radio of 82%, and the maximum over-limit radio up to 48.6 times. The pollution plume reached as far as 10 m on the vertical direction below the groundwater table. Field data indicate that the polluted area is suitable for remediation by AS technology. The key parameters AS program required is determined by combined the AS technical integration research method with the reliability of AS remediation model as TMVOC showed. Results show that it is suitable to inject the air at the rate of 12 m3/h for the AS system, and as a result, the effective radius is about 7 m and the remediation range can spread the whole aquifer below the downstream of AS point. According to the equilateral triangle method to design AS wells distribution, the air injection wells distance is 12 m. It is more suitable to start the AS system in the spring as the weather turns warm and the effective remediation time throughout the year is up to 8 months in such a case. LNAPLs are the main pollutants in petroleum oilfield. By simulating the migration laws at unsaturated-saturated zone of BTEX after the leakage in the unsaturated zone, the results indicate partition wall and long-term AS system are good methods to prevent new pollution caused by ground falling oil after complete remediation. AS remediation of NAPLs polluted groundwater is a long-term process, requiring at least 8 months or more to complete. Therefore, it is necessary to periodically monitor the water samples during remediation period and constantly optimize the AS system in order to insure the stable operation and good remediation efficiency of the AS system.更多还原