Lecture 9 of
GSR Open Class
In-situ remediation of soil and groundwater: Physical-chemical
technologies
Speaker :Dr. Johan Gemoets, Vito Institute, Belgium
（February 16,2022）
Dr. Johan Gemoets, graduated from University of Southern California, Los Angeles, soil and groundwater remediation expert. He has been working in VITO (Vlaamse Instelling voor Technologisch Onderzoek), RMA (water management & technology, digital water services) since 1996. Dr. Ir. J. Gemoets has over twenty six years of practical experience in contaminated site remediation, including soil and sediment washing, biopile treatment, thermal desorption (ex-situ), air sparging, soil vapor extraction, bioventing, chemical oxidation, in-situ bioremediation and monitored natural attenuation. He develops and applies performance treatability testing methods on laboratory and pilot scale for the technologies mentioned. He works on behalf of the Flemish authorities in writing technology performance guidances, evaluating site cleanup projects and performing field inspections of cleanup contractors and soil recycling centers. He has been acting as calamity assessment expert (Ajka, HU) on behalf of the European Commission and he is a member of the working group Environmental Technology of the Flemish Engineering Society (KVIV/ie-Net). He is a lecturer on Environmental Technology at the University of Antwerp and has been a guest lecturer at the universities of Ghent and Hasselt.
Since 2015 he is a part time team member of the Flemisch Industrial Symbiosis project which facilitates valorization of industrial residual streams as secondary resources
This lecture provides an overview of in situ remediation techniques based on physical and chemical processes. For each technique, the working principle is described, and the boundary conditions related to soil conditions and pollutant properties are given. Examples of site application, pilot test and small scale test are introduced. The technologies discussed include extraction-based technologies such as purification, extraction treatment, Surfactant and solvent leaching, soil vapor phase extraction, multi-phase extraction, aeration, in situ thermal desorption, and in situ contaminant degradation or immobilization, such as in-situ chemical oxidation and reduction, in-situ incineration, permeable reaction walls and in-situ adsorption. Finally, several injection techniques are discussed.
It's important to construct a pollution conceptual site model of soil and groundwater before the remediation,which including the identification of three key factors of contamination ,the pollution sources,pathways and receptors.
Different pollution types may present distinct pathways from the ground surface to the water table,what were usually complicated. For example,the LNAPL(light non aqueous phase liquid)Floating pure product &source/plume,when there’s an oil spill,the LNAPL has the distribution of
volatilization,biodegradation,dissolution,dispersed and diluted by groundwater or trapped in pores between soil and sediment particles,While the DNAPL(dense non-aqueous phase liquids)&sinking pure product,like tetrachloroethene, trichloroethene and so on.Due to its gravity,except the vapours and residual parts the other DNAPL mainly go the pathway from the leak pool to the low permeability lens and then to the aquitard.
Before choosing a soil remediation technology,it’s important to know the total mass of the pollutants,not only concentrations in soil and groundwater,but also pure product and pollutants adsorbed to soil below the groundwater table,In the meantime,it’s necessary to master the 3D volume and location of pollutants versus location of receptors(human),as well as physical and chemical properties of pollutants.the following aspects you also need to consider.first and foremost，site-specific conditions,such as soil texture,stratification with permeable and less permeable soil layers,and limitations such as existing infrastructure and so on.Second,distinction source versus plume is essential,source area,where soil with pure product,often limited volume with large pollutant mass,while the plume area were mostly polluted volume under groundwater table,with dissolved and adsorbed pollutants.In addition, remediation in different stages is option,first source area（largest contaminant mass）,later on plume area（water saturated soil）.
The class discuss two kinds of association remediation technologies in situ for soil and groundwater.one called extraction technologies, which are based on construction of pollution so you try to take out of the contaminant from soil and groundwater ,like Pure product removal, Pump & treat, Surfactant & (co)solvent flush, Soil vapour extraction, and multiphase extraction,air sparging and in-situ thermal desorption. And so on .Otherwise, you may have a number of techniques where you want to degrade the contaminant of soil or make them immobile in the environment .including technologies like in-situ chemical oxidation, in-situ chemical reduction, in-situ incineration, permeable reactive barrier(PRB), in-situ adsorption; At last Dr. Johan Gemoets discuss a number of technologies of method to injection of reagents, including permanent injection well, direct push injection, MIP-in target injection.
We can removal of pure floating product - LNAPLE by meas of excavation and in-situ removal. For excavation of floating pure product,you need to choose the right position and put the extraction pump where floating pure product existing ,pump it up to an oil-water separator and then for further water treatment.if the pure product is not really moved,you can remove your products as much as possible.while In-situ removal of LNAPL often have two forms,Dual phase extraction(Water/oil) and Dual phase extraction (Water/oil/soil gas/water).
Removal of pure floating product - LNAPL is often used before application of other in-situ techniques.Two of the above methods of removal have their own advantages and disadvantages.for the excavation it may at risk of emissions of VOC, odour and explosion,LNAPL can be removed to large extent,and typically limited for shallow, non-volatile LNAPL.while by in-situ removal,you need to consider the reasonable permeability of soil, LNAPL viscosity should not be high,and always residual product.what’s more,for two-phase extraction,you need to avoid emulsions,and for dual pump system,by lowering of groundwater table to avoid smearing is needed.
DNAPLis heavier than LNAPL . It’s difficult to removal of sunken pure product for the reason that it’s difficult to find it ,you need to understand soil profile,and extract from low areas in less permeable soil layers, if you can find it ,you can just put some exceptional wealth and your black and suck it up and its difficult bother treatment so that is not that difficult, difficulties to find it and to take a lot of soil.
Pump and treat of groundwater has the main process of building pumping well in the downstream area of groundwater pollution plume, pumping polluted groundwater out to storage tank, cleaning the polluted water in the water treatment system.During the process of pumping,the groundwater can flush water saturated zone to refresh polluted pore water and desorb pollutants form soil at the same time.concentration of pollutants decreases exponentially (tailing),the time for remediation is correlating with the factors of retardation,contaminated volume,extraction flow,porosity,soil density.And during the water treatment process,there is little difficult to waste water treatment for the reason that Iron may cause clogging of activated coal filter or air stripper,and high water hardness (Ca++) may clog air stripper.
If you started applying pumping treat,concentration will decline in time,but some solutions will be short to clean up,while other solutions may take longer time to clean up or can get only a fraction of contaminant with respect to the initial concentration.
The relationship between concentration and extraction time is dependent,in ideal case,when you start pumping and concentration of the water that take out of the soil decline and eventually it will decline.but sometimes the concentration’s downtrend get stuck at a certain level which is above the remediation target and make it even worse if the pumping is stopped.so there are some requirements for pump and treat as the follows:
n Soil must be permeable for water (not for clay soil)
n Only for pollutants with good aqueous solubility (polar; eg MTBE)
n Not for apolar pollutants that adsorb strongly (PAH, mineral oil)
n High content of organic matter reduces effectiveness (sorption)
n Presence of pure product causes failure (NAPL, precipitate)
n Usually fails for chlorinated solvents (PER, TRI, TCA)
n Risk of damage to buildings if soil stability problems (re-infiltration?)
Groundwater recirculation well is a kind of in-situ groundwater treatment technology. Which has the characters of that groundwater level is not lowered,and no need to discharge groundwater,but you need beware of horizontal control.The recirculation well is often coordinated with air injection blower ,air extraction blower and upper recharge screen,lower intake screen.which make it possible of in well air stripping and more visual.It’s kind of groundwater well under vacuum,air bubbles entry into the atmospheric passively.This system can strip VOC from groundwater in-situ,and aerobic biodegradation of SVOC by dissolving oxygen in groundwater.
Because Pump & treat is often limits by the sort of contaminant in the soil ,you may try to improve the ability by using some chemicals suggested like surfactant and cosolvent to solve the goals.the surfactant and cosolvent flushing can increase solubility of pollutant,and decrease surface tension at the same time.It is an expensive technology and for this reason is not pretty much used.It’s water treatment is complicated in consequence of foaming with surfactants ans solvent recovery expensive.the common Surfactant are nonionic/anionic, foodgrade,and Cosolvents like ethanol, iPrOH, n-hexanol.It can also combine extraction with in-situ biodegredation.
Soil vapour extraction basically use the principle of soxhlet extraction, with Extraction of soil gas with vertical filters and Extraction of groundwater to lower groundwater table (optional).Conditions to be satisfied by Soil vapour extraction technology are as follows:
n For volatile pollutants: Pv > 1 mm Hg BTEX, C6-C10 alkanes, PER, TRI, TCA,
n minimal thickness of unsaturated soil needed
n Air treatment required
n Soil needs to be permeable for air
n Limited effectiveness if:high moisture content (air permeability);high organic matter content (adsorption VOC);Soil layers with low permeability (storage of VOC).
n Discontinuous, alternating extraction (when tailing)
n Pilot test:Radius of influence for extraction filters;Air flow and pollutant flux to air treatment
Multi-phase extraction can used not only for LNAPL, but also for treating soil and groundwater,it can Not only for LNAPL, also for treating soil and groundwater, and Increase water extraction rates in medium permeability soil by application of high vacuum.Conditions to be satisfied by Multi-phase extraction technology are as follows:
n For VOC in unsaturated zone and shallow groundwater
n Also extracts LNAPL
n For medium permeability soil (10-3 à 10-5 cm/s)
n If too permeable: well is flooded with water
n If permeability too low: only partial effect with preferential flow paths
The air sparging technique is based on take compressed air into ground water,it’s a kind of extraction of air above groundwater table or injection of air below contamination.Air sparging technique is often used to remove volatile pollutants in soil and groundwater,especially for the pollutants that whose vapor pressure > 1 mm Hg,Henri-coëfficiënt > 0,01,like BTEX, PER, TRI, TCA and so on.
The technology is mainly applicable to sites with good permeability of aquifers.It can also used combing with SVE.and has the following characters:
n minimal thickness of unsaturated zone for SVE needed
n Not for heterogeneous soils : uncontrolled migration VOC
n Faster than pump & treat
n preferential flows ? minimize by discontinuous sparging
A pilot test was conducted for air sparging,and the objectives are as follows:
n Technical problems to inject air in soil/groundwater?
n Can stripped pollutants be captured? Mass pollutant?
n Identify safety issues (eg. vapour intrusion in building?)
n Can sufficient air flow be realized at reasonable pressure?
n Measure radius of influence of air injection points
n (design information for SVE if applied)
n Some of the settings are as follows:
n Seal surrounding wells to avoid short circuits for air
n Use short screen length for injection wells (eg. 0,5 m)
n SVE flow rate 2 – 5 x air injection flow rate
When to set the location of Air sparging pilot test ,something should be taken into consideration,for example,avoid hot-spot with NAPL,Risk of pushing VOC,and better in moderately contaminated area.
For pilot test air sparging and monitoring, the following should be paid attention to:
n Groundwater mounding (level diver probe)
n Groundwater pressure (PI-datalogger)
n Dissolved oxygen in groundwater
n VOC and oxygen in soil gas from vadose zone wells
n SVE blower unit monitor gas in and gas out
n Optional: conservative tracer test (He, SF6)
n Gas concentrations in ambient air and in buildings
n Field observations (odour, bubbling in groundwater wells, air bubbles in standing water at soil surface)
Another pilot test was conducted:air sparging pilot study for groundwater with vinyl chloride.In this study,the key settings are as follows:
n Vinyl chloride from 15 - 16 mbg
n spargepoints at 19 mbg
n Pulsed air injection
n 1,8 Nm³/h for each injection point
n Influence zone for each of 3 IF?
n Influence zone with 3 IF activated?
n Measure GWE, DO, SF6-tracer
In the same sites,we also conducted Air sparging pilot SF6 - tracer test(Inj well 1 only active),Nowadays use helium to measure in vadose zone as SF6 is greenhouse gas.and conducted Air sparging piloot :effect on dissolved oxygen.
The permeable reactive barriers involves a variety of reaction processes including Chemical reduction(Zerovalent iron),Adsorption (GAC, zeolite,…),pH-manipulation (precipitation),Biodegradation (biobarrier) and Mutifunctional (multibarrier).
But this technology is used only for plume controlling,and is usually limited depth up to 10mbg(depth of sealing clay layer?),it’s hard to find a kind of Lifetime of reagents.Problems also exist at the aspects of its Degradation rates,Inactivation over time (passivation of ZVI, clogging by precipitates such as calcium carbonate or hydrogen gas bubbles?)
A lab test was conducted:PRB: lab feasibility test.we concluded that CAH degradation rates specific for ZVI and groundwater chemistry.
Mainly have a brief introduction the principles and techniques of In-situ thermal desorption of VOC & SVOC.
Principles:
n Increase vapour pressure of pollutant (T> Tb) → Volatilization
n Lower viscosity of pure product to enhance flow (NAPL)
n Reduce surface tension of pollutant
n Increase water solubility of pollutant
n Techniques:
n Inject steam
n Inject electrical current
n Conductive soil heating
There are different heating methods for in-situ thermal desorption,for example,Injection of steam,In-situ thermal conduction heating,Soil heating with electrical alternating current,Injection of electric current and so on.Their main features are as follows.
Injection of steam（蒸汽注射）:The principles of injection of steam are if you steam, steam is over hundred degrees so deeply injected into the soil through an injection well.Have the following characteristics.
n Extraction needed of soil vapours and of condensed steam.
n Pyrolytic oxidation of hydrocarbons when also injecting air with steam (?)
n Economical if steam is available on - site from industrial production process.
In-situ thermal conduction heating（原位热传导加热）:
n Thermal conduction heating of soil with heated metal rods
n SVE（土壤蒸汽抽提） of volatilized VOC
Soil heating with electrical alternating current（交流电加热土壤）
n Apply alternating current with electrodes to heat soil and groundwater
n Six phase heating
n Heat groundwater
n to boiling point of contaminants (less than 100 ℃)
Injection of electric current-Creosote site (PAH , phenols)（电流注射﹣多环芳烃、酚类）
Taking the restoration of a creosote site as an example.
（1）Creosote site characteristics（杂酚油场地特征）
n Contamination :30000 kg creosote
l BTEX , PAH , phenols , mineral oil
l LNAPL & DNAPL
n Laer of peat between 6 and 8 mbg
n Peat layer should not become dry to prevent colapse of soil
n Aquifer below peat to be treated up to depth of 15 mbg
n Appy AC in soil to heat soil and groundwater
n Electro - thermal Dynamic Stripping
n Injection of water along electrodes for cooling electrodes and improved heat transfer by convection (steam generated)
n Injected water should keep peat layer moist
（2）Creosote site - Concept technical（杂酚油场地修复技术参数）
n Target temperature : just below 100 ℃
n Concrete vapour cap
n 170 electrodes at 84 locations
n Average power per electrode: 6,1kW
n 117 vertical and 38 horizontal multi-phase extraction filters
n 325 temperature sensors at 25 locations
n Total electricity consumption :4.474 MWh
n Cost :5 mio €
（3）Creosote site - premature termination（杂酚油场地﹣提前终止）
n Remediation targets not achieved
n pure product remained
n Dispute about underestimation of contaminant mass during site investigation
n (attracted creosote from outside treatment area?)
n Temperature increased above 100 ℃
n Soil collapsed by 50 cm → vapour cap damaged
n Soil gas extraction wells damaged
E.g. Creosote site in-situ thermal desorption premature termination due to physical damages.
n In situ combustion of LNAPL (coal tar , oil)
n Extraction and treatment of combustion gas
n Inject oxygen and ignite initially → autonomous combustion
n Low consumption of energy (exothermal process)
n In-situ destruction of pollutants by strong oxidants Tetrachloro-ethene (PER) with permanganate:
4 KMnO4+3 C2Cl4+4 H2O →6 CO2 +4 MnO2 +4 K++12 Cl- +8 H+
l Hydrogen peroxide
l Permanganate
- good for chlorinated ethenes, not for ethanes/benzene
l Persulfate
l Persulfate + catalyst = SO4·- (Fe2+, heat)
l Fentons Reagent (pH3-4)
- H2O2 +Fe2+ → Fe3++ OH- + OH·
l Percarbonate H2O2.Na2CO3 + Fe (II)) alkaline pH
l Ozone (O3) & perozone (H2O2 + O3) sparging
n Oxidant properties （氧化剂特性）
n Oxidant selection criteria（氧化剂选择标准）
n In-situ chemical oxidation （原位化学氧化）
l Soil oxidant demand (SOD)
may exceed pollutant oxidant demand!
Laboratory feasibility testing is recommended
l Permanganate: MnO2 precipitates formed, coloured groundwater.
l Fentons reagent (pH 4): exothermal reaction & release of gas → risk of emissions of VOC and even explosion! Determine acid buffering capacity of soil
l Modfied Fentons reagent: hydrogen peroxide and chelated ferrous iron catalyst
l Free radical oxidants (Fentons , catalyzed persulfate , ozone) are short living → limited radius of influence ?
l Permanganate and persulfate have longer lifetimes in groundwater
l Oxidants can push plume forward → high concentrations at plume edge
l (in) effective for NAPL ??
n Chemical reductive degradation with reduced iron （还原铁化学还原降解）
l Metallic iron (ZVI)(nano-or micro-particles )
l Injected as slurry in groundwater
Fe (0) → Fe (Il)+2e- & 2H++2e → H2
l large specific surface area → reactive particles
l Good distribution in soil not that easy ( oating with hydrophylic biopolymers)
l Iron - sulfide particles (Fe2S)
n Zerovalent iron & Soil mixing pilot test （零价铁和土壤混合中试）
l Site: production of textiles , contaminated with CAH
l Source = sink pit for solvent disposal
l DNAPL at 7,0-8,0 mbg
l TCEmax in soil : 43700 mg / kg TCE
Groundwater:
-426 mg/ l TCE
-Minor 1,2-DCE & VC
l Soil type: low permeability sandy clay
n Lab test for determination of dose of ZVI （零价铁剂量测定小试）
n Pilot test soil mixing ZVI set-up （零价铁和土壤混合中试设置）
l 14 soil mix pillars up to 8,4 mbg
l 3000 kg of micro-iron ZVI -H4(10 pilars)+500 kg ZVI-H20(2 pilars)
l Guar gum to suspend ZV1-particles during injection
l GG also stimulates anaerobe biodegradation
l Stability reasons (road): pillars with grid
l Challenges
-ZVI suspension
-homogeneous distribution ZVI
n Samples of soil with ZVI from soil mixing pilot area evolution of CAH and degradation products in lab test （中试区混有零价铁的土壤样品在小试中 CAH 和降解产物的演变）
l TCE degraded tot cDCE, ethene & ethane
l after 36 weeks: end products free of chlorine
l ZVI & Soil mixing pilot – monitoring （零价铁和土壤混合中试﹣监测）
n Chemical reduction of Cr (VI) with dithionite （连二亚硫酸钠化学还原六价铬）
l Sodium ditionite (Na2S2O4) reduces toxic Cr ( VI ) ot insoluble Cr ( IIl ) mediated by Fe ( Il ) Generates sulfate, sulfite & smels
Fe3++Na2S2O4 → Fe2+ (+ Na2SO4)
3 Fe2++ CrO42-H0 → 3 Fe3++Cr3++8 OH-
l pH optimal at 6-8
l If soil has little available Fe then add iron sulfate to groundwater
（1）PlumeStop TM (Regenesis)
n “Liquid” activated carbon suspension
n Act carbon particles treated to prevent clustering and reduce adsorption to soil
n “may be regenerated by microbial biodegradation”
（2）TRAP & TREAT (BOS -100 TM)
n Activated carbon impregnated with zerovalent ijzer
n CAH adsorbed on GAC are degraded by chemical reduction with ZVI
n Inject suspension in groundwater or mix in soil during excavation
n Repeated injections possible
n Injection with pressure may give better product distribution than gravity injection
n Direct push injection - lost injection tip（直推注射）
l Botom-up injection (from deep to shallow)
n Direct push - horizontal injection （直推注射﹣水平注射）
l Better product distribution
n Pressure Injection & daylighting （压力注射与采光）
n MIP-IN TECHNOLOGY TM - TARGETED PRECISION INJECTIONS （MIP - IN 靶向精密注射）
l Detection part = MIP – part
Membrane interphase probe
l Injection part = IN - part
Direct push injection
l Detectors:
FID: aromatics, aliphatic
PID: BTEX, Some chlorinated
XSD: Halogens
n MIP-IN DEVICE（MIP-IN设备）
n MIP-IN: injection with real-time control by MIP-signal （MIP-IN: MIP 信号实时控制的注射）
n MIP-IN TECHNOLOGY DEVELOPED AND LICENSED BY EJLSKOV AND VITO （由EJLSKoV 和 VITO 开发许可的 MIP-IN 技术）
l Targeted injection
• Only where contamination
• Injection vol./ conc. contamination level
l Flexible system
• Different products. - “ mixtures ”
• Flow rate / pressure
• Concentration variability
l Combination of site investigation & remediation
l Real time data / logging
• Updating SCM while injecting
• Decision making in the field
• Documentation
• Visualisation of contamination
l Cost effective
• Reduced consumption of product
• Optimized effect of product injected
• Faster from site investigation to site remediation
• Minimize required mobilizations
l Environmental sustainable
• Minimized consumption of energy / product
• Minimize disturbance of uncontaminated soil / GW