Comparison of Primary and Secondary Surfactant Flushing to Enhance LNAPL Recovery

Column experiments were conducted to compare the use of surfactants as a part of primary pumping to remove free phase NAPL to the use of surfactants to reduce or recover residual LNAPL in secondary treatment. Eight surfactant blends were tested, for a total of 48 column experiments. The column experiments show that the use of surfactants during primary pumping: (1) can potentially increase the amount of free product recovered; (2) can potentially reduce the amount of residual NAPL remaining after primary pumping; and (3) performs better than the use of surfactants to mobilize trapped residual NAPL.     

污染底泥原位覆盖技术综述

从污染底泥的危害入手,提出简单、有效且低成本的底泥原位覆盖技术.该技术将无污染的清洁材料铺盖到污染底泥上,通过覆盖材料对污染物的阻隔、稳固和吸附作用来有效控制底泥污染物.覆盖材料的粒径、比表面积和孔隙率、密度等特性关系到材料的吸附能力和对底泥污染物的阻隔和稳固作用,从而决定覆盖效果.选取覆盖材料及确定最佳覆盖厚度需要依据材料的这些特性.本文分析了原位覆盖技术的优缺点及适用条件和适用范围.介绍了几种常用的原位覆盖工程的施工方式及每种方式的优缺点,列举了大量的国内外覆盖工程实例,并就覆盖技术在我国良好的应用前景进行了分析.     

Feasibility of in situ implementation of vibrations to mobilize NAPL ganglia

A growing number of incidents of nonaqueous phase liquid (NAPL) spills in the recent past have warranted development of innovative and cost‐effective remediation technologies. Of particular concern is the entrapment of LNAPL (NAPL lighter than water) in the form of ganglia or blobs near the water table by virtue of strong capillary forces. The residual ganglia are the leftover component after pumping of free product and typically occupy 20 to 60% of the pore space. Mobilization of these ganglia would require unrealistically high hydraulic gradients and is often beyond the scope of pump‐and‐treat processes. This paper deals with the feasibility of in situ implementation of localized vibrations for controlled mobilization and collection of LNAPL ganglia. Specifically, the paper covers three components. First, the principles involved in soil‐water‐NAPL interactions under the influence of vibrations are discussed. The effects of vibrations on a soil‐NAPL‐water medium are postulated in terms of pore structure and relative density changes, changes in the permeability of the medium as a result of the changes in pore structure, and development of cyclic pore pressures. Second, results from bench‐scale experiments are presented that involved vibrating contaminated soils under the simultaneous influence of hydraulic gradients. A bench‐scale model consisting of a vibrator integrated with an injection and pumping system was found to be successful in these experiments. The results from the tests showed that up to 85% removal of ganglia can be achieved using this process. Third, the principles involved in the vibratory mobilization were applied to in situ conditions to develop a methodology to estimate the zone of influence of the process. The analogy between this process and an existing geotechnical process known as vibroflotation is exploited to demonstrate the methodology.     

Electronic (EK) remediation of a contaminated soil at several Pb concentrations and applied voltages

The in situ remediation of a lead‐contaminated silt loam by electrokinetic (EK) soil flushing was studied. Two initial soil Pb concentrations (150 and 1000 mg/kg of Pb) and applied voltages (30 and 60 V) were investigated. The EK soil flushing process was less efficient for the 150 mg/kg of Pb soils despite these tests being operated for longer durations, having larger EO flows and energy inputs, and lower soil pHs. The decrease in effectiveness was attributed to a larger average metal‐soil binding energy for the lower contaminated soil. Increasing the voltage increased the EO flow, current, energy input (kW‐hr/kg of soil), and provided a more evolved low pH front, resulting in more soil being remediated. There appeared to be a correlation between the amount of EO flow and the desorption and transport of soil‐bound lead. Because complete soil remediation did not occur in any of the tests, the final energy input per kilogram of soil could not be calculated.     

Effect of Flush Water Temperature and Type on Commercial Shoreline Cleaning Agent Efficiency

A research team at the University of Alaska Fairbanks Water and Environment Research Center conducted a series of column experiments to investigate the effect of flush water temperature and type (salt vs. fresh) on shoreline cleaning agent (SCA) efficiency. Results confirmed that the use of SCAs can enhance oil removal from porous media but showed that at the colder temperatures common in Alaska the efficiency of shoreline cleaners is significantly reduced. Using salt water also tends to decrease the efficiency of flushing. The data also show that the majority of the removal attributable to the shoreline cleaning agent occurs within the first one to three pore volume flushes. After that time, the effectiveness of the flushing procedure drops off to that of pure water for all three SCAs tested.     

Evaluation of health risks from a buried mass of diesel fuel before and after bioremediation

Plans are being formulated for in situ bioremediation of a subsurface plume of diesel fuel No. 2 that resulted from an accidental fuel release. Raoult's law and the aqueous solubilities of the toxic components were used to estimate organic contaminant concentrations in leachate from the untreated fuel mass. Carcinogenic risks and noncarcinogenic hazard indices were calculated for undiluted leachate. An 80% decrease in hydrocarbon mass and increases in the average molecular weights of the component fractions were assumed to result from the treatment. Sample calculations are provided to show how to evaluate results of analyses for petroleum hydrocarbons after bioremediation.     

Vacuum‐enhanced recovery of water and NAPL: Concept and field test

Many hydrocarbon‐contaminated soils contain nonaqueous phase liquid (NAPL) following releases from facilities such as underground storage tanks and pipelines. The recovery of free product by pumping from extraction wells or trenches is often an essential prerequisite step prior to further remedial actions. Vacuum‐enhanced NAPL recovery (sometimes referred to as dual‐phase extraction or bioslurping) has attracted recent attention because it offers a means to increase NAPL recovery rates compared with conventional methods, and to accomplish dewatering, while also facilitating vapor‐based unsaturated zone cleanup. A conceptual model is presented that recognizes the effects that vacuum‐enhanced recovery has on soil water and NAPL, with a focus on liquid residing at negative gage pressures and therefore lacking sufficient potential energy to flow into a conventional recovery well or trench. The imposition during vacuum‐enhanced recovery of subatmospheric pressures within the subsurface can reduce the required potential energy (i.e., the entry suction), allowing liquid to be extracted that hitherto had not been able to flow into the well; moreover, it induces both pneumatic and hydraulic gradients toward the vacuum source that increase the rate of water and NAPL recovery. This conceptual model was tested during a 3‐week‐long pilot study at a South Carolina industrial site at which diesel fuel had been discovered in a saprolite formation. During Phase 1 of the pilot study, conventional recovery (liquid only) was carried out from a well screened at the water table, while during Phase 2 dual‐phase extraction was performed at the same well. The application of 27 kPa vacuum resulted in an increase in NAPL recovery from negligible (Phase 1) to approximately 6.6 l/d (Phase 2), with a concurrent increase in water recovery from approximately 190 to 760 l/ d. Neutron moisture probe observations revealed that vadose‐zone liquids underwent redistribution toward the extraction well in response to the onset of Phase 2, also in accordance with the conceptual model. An understanding of soil physical relationships is crucial to the successful application of these and other in situ soil remediation technologies.     

A feasibility study for the in situ remediation of a former tank farm

A feasibility study of the in situ remediation of a former tank farm (on a petrol station) was made over a period of 150 days at 10 °C. The natural attenuation (which is a sum of the abiotic losses and the natural biodegradation by the indigenous soil microorganisms) and the effect of biostimulation by inorganic nutrient supply were investigated. The contamination was not homogeneously distributed in the seven soil samples investigated. Nutrient addition had no statistically significant effect on hydrocarbon decontamination. A remarkable part of the decontamination had to be attributed to natural attenuation. Soil microbial counts and CO₂ evolution indicated a negative effect of nutrition on the number of microbial hydrocarbon degraders and on soil microbial activity.     

Optimization of 2-D Electrode Configuration for Electrokinetic Remediation

A practical evaluation of one- and two-dimensional applications of electric fields for in situ extraction of contaminants is provided. The evaluation is based on contaminant transport by electroosmosis and ion migration. Parameters evaluated include electrode requirements, effectiveness of electric field distribution, remediation time, and energy expenditure. Formulation is provided for calculating cost components of the process, including electrode, energy, chemicals, posttreatment, fixed, and variable costs. Equations are also provided for evaluating optimum electrode spacings based on energy and time requirements. The derivations show that spacing between same-polarity electrodes is as significant in cost calculations and in process effectiveness as that between anodes and cathodes. Decreasing the same-polarity electrode spacing to half the anode-cathode spacing will result in a 100% increase in electrode requirements, but will decrease the area of the ineffective electric field by one half. Selection of the voltage gradient impacts the optimum electrode spacing. The analysis show that a minimum exists in the cost versus electrode spacings relationship.     

Importance of Different Volatile Petroleum Hydrocarbon Fractions in Human Health Risk Assessment

Soil vapor data for benzene and four aliphatic and aromatic hydrocarbon fractions from five volatile petroleum hydrocarbon (VPH)-contaminated sites in western Canada were used together with the Canadian Council of Ministers of the Environment (CCME) Canada-Wide Standard for petroleum hydrocarbons to investigate the relative importance of benzene and the different fractions in human health risk assessment. VPH concentrations in soil vapor samples ranged from 4.0 to 4200?mg/m³, of which 0 to 4.6% was BTEX and 90 to 95% was hydrocarbons of the C_5–8 aliphatic fraction. VPH inhalation exposure by an adult receptor in a hypothetical, commercial building was modelled deterministically assuming 16- and 70 year occupational tenures. The magnitude of hazard quotients varied widely between sites, but their hydrocarbon fraction signatures were consistent, and characterized by higher hazard quotients in the C_5–8 and C_9–10 aliphatic and C_9–10 aromatic fractions relative to benzene and the TEX aromatic fraction. This work has shown that the C_5– and C_9–10 aliphatic fractions yield greater relative risk than the commonlyregulated TEX compounds, and that benzene becomes the primary chemical of potential concern only when an occupational tenure approaching 70 years is assumed.     

Speciation and bioavailability of zinc in amended sediments

Abstract

The speciation and bioavailability of zinc (Zn) in smelter-contaminated sediments were investigated as a function of phosphate (apatite) and organic amendment loading rate. Zinc species identified in preamendment sediment were zinc hydroxide-like phases, sphalerite, and zinc sorbed to an iron oxide via X-ray adsorption near edge structure (XANES) spectroscopy. Four months after adding the amendments to the contaminated sediment, hopeite, a Zn phosphate mineral, was identified indicating phosphate was binding and sequestering available Zn and Zn pore water concentrations were decreased at levels of 90% or more. Laboratory experiments indicate organic amendments exhibit a limited effect and may hinder sequestration of pore water Zn when mixed with apatite. The acute toxicity of the sediment Zn was evaluated with Hyalella azteca, and bioaccumulation of Zn with Lumbriculus variegates. The survivability of H. azteca increased as a function of phosphate (apatite) loading rate. In contaminated sediment without apatite, no specimens of H. azteca survived. The bioaccumulation of Zn in L. variegates also followed a trend of decreased bioaccumulation with increased phosphate loading in the contaminated sediment. The research supports an association between Zn speciation and bioavailability.     

Survey of States' 2000 Soils Cleanup Standards for Petroleum Contamination

The establishment of cleanup standards for petroleum-contaminated soils (PCS) at the state level in the U.S. has had a fairly recent history beginning in the mid-1980s. Kostecki et al. (1988) surveyed the 50 states in 1985 and found of the 22 states that reported having established levels of cleanup for PCS, only five states considered the levels formal. The remaining 18 states considered the levels informal with 8 states considering establishing formal levels. Only 1 state had a formal numerical cleanup standard, and 3 had informal numerical standards. One state directly applied federal groundwater standards directly to soils. A follow-up survey in 1987 (Bell et al., 1989) indicated the rapid development of myriad different cleanup standards between and within states, including action levels, remediation goals, cleanup levels, etc. With the implementation of EPA's Office of Underground Storage Tanks final rules for regulating underground storage tanks in 1988 and the existing state of confusion regarding policies, rules and regulations for the cleanup of PCS at the state level, the Association for the Environmental Health of Soils (AEHS) began conducting state-by-state surveys of environmental regulatory agencies in 1990 to determine cleanup standards for PCS for use by the regulated community. The following tables represent AEHS' compilation of state data for PCS cleanup standards for 2000. The Survey was conducted by telephone interviews and submission of written information by the appropriate listed agencies. Many of the states' programs have changed to or are in the process of changing to Risk Based Corrective Action (RBCA) approaches. Thus, the format of the summaries are less standardized than past surveys in order to accurately reflect the states' program. Every attempt has been made to accurately represent states' cleanup standards, however, users should be cautioned to the limitations of compiling complex regulatory information into tabular form. The information should only be used as a reference guide and legal, economic or technical decisions should be based on specific information obtained directly from the appropriate agency in each state for each specific site.     

脱脂棉固定化脂肪酶的非水活性与稳定性

脂肪酶具有非水催化作用,但其非水催化活性和稳定性需进一步提高,这是非水酶学的瓶颈问题之一。理想的策略是模拟脂肪酶的界面活化机制,以大分子代替水,优化、稳定化和有效分散酶蛋白,阻止其在有机相中变性。因此,选用多羟基、比表面积大、惰性、且与酶蛋白能兼容的大分子--脱脂棉纤维,作为固定化载体,以1∶0.9的质量比,通过物理吸附,将假单胞菌脂肪酶(Pseudomonas cepacia lipase)固定在脱脂棉纤维上。在催化己醇与乙酸乙烯酯的转酯反应中,反应1 h,脱脂棉固定化脂肪酶转化底物的能力是酶粉的3.7倍。在每次6 h共6次的循环催化中,固定化酶和酶粉转化底物的能力分别平均每次降低约0.3%和2.4%。表明脱脂棉固定化脂肪酶的非水活性,尤其是稳定性明显提高。这为通过固定化有效提高脂肪酶的非水催化作用,以满足工业应用的需要,提供了一种有效的途径和重要参考。     

In Situ emulsification and mobilization of gasoline range hydrocarbons using surfactants

In this article the conditions that govern surfactant‐enhanced emulsification and mobilization of petroleum hydrocarbons in soil are reviewed. The effect of soil properties, groundwater constituents, and differing surfactant solutions on the emulsification process is discussed. A constant head soil flushing apparatus used to characterize surfactant‐enhanced mobilization of m‐xylene is described. Data showing the effect of surfactant‐enhanced mobilization on m‐xylene removal efficiency in washed sand is presented. Flushing solutions were used at concentrations from below to well above the critical micelle concentration (CMC) of the surfactants used. Removal efficiencies are shown to vary with surfactant concentration and with surfactant type. Flushing solutions of anionic, nonionic, and anionic/nonionic surfactant mixtures were evaluated.     

Effect of CPC,Brij-35, and SDBS Surfactants on the Adsorption and Movement of Carbofuran in Indian Soils

Laboratory studies were conducted to determine adsorption and movement of carbofuran in aqueous surfactant-free and surfactant [(cationic, cetyl pyridinium chloride (CPC), non-ionic, polyoxyethylene lauryl ether (Brij-35) and anionic, sodium dodecyl benezene sulphonate (SDBS)] solutions of different critical micellar concentrations (1/2 × CMC, 1.0 × CMC, and 2 × CMC) in four different Indian soils using batch shake and soil thin layer chromatography (soil TLC) techniques. The measured equilibrium adsorption isotherms were in agreement with the Freundlich equation. Higher adsorption of carbofuran in both systems was observed on FRI silt loam (FSL) soil followed by Alampur silt loam (ASL), Kalai loam (KL), and Bhoran sandy loam (BSL) soils, as anticipated from Freundlich constant K_F and distribution coefficient K_D, in surfactant-free systems and K_F* and K_D* in surfactant-soil-water systems. The adsorption of carbofuran in surfactant-soil-water systems followed the order cationic > anionic > non-ionic at all CMCs studied. The R_f values obtained from soil TLC studies confirmed the above order of adsorption. The K_D and K_D* values were used to evaluate remediation efficiency (K_D*/K_D) of surfactants. Non-ionic surfactant, Brij-35, and anionic surfactant, SDBS, are favorable for remediating soil contaminated with carbofuran as K_D*/K_D ratio is less than 1.     

Fenton's Reagent-Based In Situ Chemical Oxidation Treatment of Saturated and Unsaturated Soils at a Historic Railroad Site

A targeted treatment program utilizing in situ chemical oxidation was used to remediate diesel fuel-derived petroleum compounds in unsaturated and saturated soils at a historic railroad facility. This program consisted of multiple injections at varying depths within temporary Geoprobe® injection points. The actual treatment time was less than 3 months. Overall concentrations of volatile and semivolatile organic petroleum compounds were reduced by approximately 70%, while the total petroleum hydrocarbon concentration was reduced by nearly 50%. Treatment efficiency in unsaturated soil was similar to that in saturated soil. The results of the remedial program indicate that the effect of grain size of the subsurface materials on treatment efficacy is significant. The project has shown that the use of this technology can be as effective as other in situ treatment technologies used for treating subsurface diesel fuel contamination.     

Selection of a remediation scenario for a diesel-contaminated site using LCA

Goal and Scope A comparison of in situ and ex situ treatment scenarios for a diesel-contaminated site was performed using an evolutive LCA. Treatment time along with primary (residual contamination left in soil or groundwater after treatment) and secondary (impacts due to remediation) environmental impacts were considered. The site under study had a light Non Aqueous Phase Liquid (LNAPL) thickness of up to 1 m, a diesel soil concentration of 10,500 mg/kg and a residual contamination in groundwater. Methods Four treatment scenarios to remove LNAPL and to treat soil and groundwater were compared: 1) pump and treat 2) bioslurping, bioventing and biosparging 3) bioslurping, bioventing and chemical oxidation and 4) ex situ treatment using biopiles. The technologies’ design was performed using simulation tools and analytical equations. The LCA was evaluated for each year of treatment. Environmental impacts were assessed using the U.S. EPA Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) method. Results and Discussion The biological in situ scenario (2) showed the least primary and secondary impacts but its treatment time was more than 4 times longer than that obtained for the ex situ scenario (4). The ex situ scenario showed the best treatment time but its secondary impacts were significantly higher than those found for the biological in situ scenario due to the pavement of the treatment area. The combined biological and chemical in situ scenario (3) was the worst in terms of secondary impacts while the pump and treat scenario (1) was the worst in terms of primary impacts. Two scenarios were selected: one based upon low environmental impacts and the other on the fastest treatment time. Conclusions Even without excavation, an in situ treatment can generate more secondary impacts than an ex situ treatment. Low environmental impact scenarios require time while rapid treatment scenarios generate high environmental impacts. The selection of the best remediation scenario will depend on the site owner’s priority. Recommendations Better characterization factors for aggregated substances are required. This paper is openly accessible!