Influence of residual surfactants on DNAPL characterization using partitioning tracers

The partitioning tracer technique is among the DNAPL source-zone characterization methods being evaluated, while surfactant in-situ flushing is receiving attention as an innovative technology for enhanced source-zone cleanup. Here, we examine in batch and column experiments the magnitude of artifacts introduced in estimating DNAPL content when residual surfactants are present. The batch equilibrium tests, using residual surfactants ranging from 0.05 to 0.5 wt.%, showed that as the surfactant concentrations increased, the tracer partition coefficients decreased linearly for sodium hexadecyl diphenyl oxide disulfonate (DowFax 8390), increased linearly for polyoxyethylene (10) oleyl ether (Brij 97), and decreased slightly or exhibited no observable trend for sodium dihexyl sulfosuccinate (AMA 80). Results from column tests using clean sand with residual DowFax 8390 and Tetrachloroethylene (PCE) were consistent with those of batch tests. In the presence of DowFax 8390 (less than 0.5 wt.%), the PCE saturations were underestimated by up to 20%. Adsorbed surfactants on a loamy sand with positively charged oxides showed false indications of PCE saturation based on partitioning tracers in the absence of PCE. Using no surfactant (background soil) gave a false PCE saturation of 0.0004, while soil contacted by AMA 80, Brij 97, and DowFax 8390 gave false PCE saturations of 0.0024, 0.043, and 0.23, respectively.     

Soil- and surfactant-enhanced reductive dechlorination of carbon tetrachloride in the presence of Shewanella putrefaciens 200

Sorption of organic contaminants to soils has been shown to limit bioavailability and biodegradation in some systems. Use of surfactants has been proposed to reverse this effect. In this study, the effects of a high organic carbon content soil and a nonionic surfactant (Triton X-100) on the reductive dechlorination of carbon tetrachloride (CCl₄) were examined in anaerobic systems containing Shewanella putrefaciens. Although more than 70% of the added CCl₄ was sorbed to the soil phase in these systems, the reductive dechlorination of CCl₄ was not diminished. Rather, rates of CCl₄ dechlorination in systems containing soil were enhanced relative to systems containing non-sorptive sand slurries. This enhancement was also observed in sterile soil slurries to which a chemical reductant, dithiothreitol was added. It appears that the organic soil used in these experiments contains some catalytic factor capable of transforming CCl₄ in the presence of an appropriate chemical or microbial reductant. The addition of Triton X-100 to sand and soil slurries containing S. putrefaciens resulted in increased CCl₄ degradation in both systems. The effect of Triton could not be explained by: (i) surfactant induced changes in the distribution of CCl₄, (i.e. decreased sorption) or the rate of CCl₄ desorption; (ii) a direct reaction between Triton and CCl₄; or (iii) increased cell numbers resulting from use of the surfactant as a substrate. Rather, it appears that Triton X-100 addition resulted in lysis of bacterial cells, a release of biochemical reductant, and enhanced reductive transformation of CCl₄. These results provide insights to guide the development of more effective direct or indirect bioremediation strategies.     

A controlled field experiment on groundwater contamination by a multicomponent DNAPL: creation of the emplaced-source and overview of dissolved plume development

A unique field experiment has been undertaken at the CFB Borden research site to investigate the development of dissolved chlorinated solvent plumes from a residual dense non-aqueous phase liquid (DNAPL) source. The "emplaced-source" tracer test methodology involved a controlled emplacement of a block-shaped source of sand containing chlorinated solvents below the water table. The gradual dissolution of this residual DNAPL solvent source under natural aquifer conditions caused dissolved solvent plumes of trichloromethane (TCM), trichloroethene (TCE) and perchloroethene (PCE) to continuously develop down gradient. Source dissolution and 3-D plume development were successfully monitored via 173 multilevel samplers over a 475-day tracer test period prior to site remediation research being initiated. Detailed groundwater level and hydraulic conductivity data were collected. Development of plumes with concentrations spanning 1-700,000 micrograms/1 is described and key processes controlling their migration identified. Plumes were observed to be narrow due to the weakness of transverse dispersion processes and long due to advection and significant longitudinal dispersion, very limited sorptive retardation and negligible, if any, attenuation due to biodegradation or abiotic reaction. TCM was shown to be essentially conservative, TCE very nearly conservative and PCE, consistent with its greater hydrophobicity, more retarded yet having a greater mobility than observed in previous Borden field tests. The absence of biodegradation was ascribed to the prevailing aerobic conditions and lack of any additional biodegradable carbon substrates. The transient groundwater flow regime caused significant transverse lateral plume movement, plume asymmetry and was likely responsible for most of the, albeit limited, transverse horizontal plume spreading. In agreement with the widespread incidence of extensive TCE and PCE plumes throughout the industrialized world, the experiment indicates such solvent plumes are likely to be highly mobile and persistent, at least in aquifers that are aerobic and have low sorption potential (low foc content).     

Influence of cation type, ionic strength, and pH on solubilization and mobilization of residual hydrocarbon by a biosurfactant

This study investigated the effect of cation type, ionic strength, and pH on the performance of an anionic monorhamnolipid biosurfactant for solubilization and removal of residual hexadecane from sand. Three common soil cations, Na⁺, Mg²⁺, and Ca²⁺, were used in these experiments and hexadecane was chosen to represent a nonaqueous phase liquid (NAPL) less dense than water. Results showed that hexadecane solubility in rhamnolipid solution was significantly increased by the addition of Na⁺ and Mg²⁺. Addition of up to 0.2 mM Ca²⁺ also increased hexadecane solubility. For Ca²⁺ concentrations greater than 0.2 mM there was little effect on hexadecane solubility due to competing effects of calcium-induced rhamnolipid precipitation and enhanced hexadecane solubilization. Efficiency of NAPL solubilization can be expressed in terms of molar solubilization ratios (MSR). The results showed that MSR values for hexadecane in rhamnolipid solutions increased 7.5-fold in the presence of 500 mM Na⁺, and 25-fold in the presence of 1 mM Mg²⁺. The presence of cations also reduced the interfacial tension between rhamnolipid solutions and hexadecane. For example, an increase in Na⁺ from 0 to 800 mM caused a decrease in interfacial tension from 2.2 to 0.89 dyn cm⁻¹. Similarly, decreasing pH caused a reduction in interfacial tension. The lowest interfacial tension value observed in this study was 0.02 dyn cm⁻¹ at pH 6 in the presence of 320 mM Na⁺. These conditions were also found to be optimal for removal of hexadecane residual from sand columns, with 58% of residual removed within three pore volumes. The removal of residual NAPL from the packed columns was primarily by mobilization, even though solubilization was significantly increased in the presence of Na⁺.     

Removal of DNAPL contamination from the saturated zone by the combined effect of vertical upward flushing and density reduction

A common aspect of innovative remediation techniques is that they tend to reduce the interfacial tension between the aqueous and non-aqueous phase liquids, resulting in mobilization of the organic contaminant. This complicates the remediation of aquifers, contaminated with Dense Non-Aqueous Phase Liquids (DNAPLs), as they are likely to migrate downwards, deeper into the aquifer and into finer layers. A possible solution is the use of swelling alcohols, which tend to reduce the density difference between the aqueous phase and the DNAPL. To avoid premature mobilization upon the initial contact between the DNAPL and the alcohol, several researchers have proposed the use of vertical upward flow of the alcohol. In this paper, we present an equation, which describes the upward mobilization of both continuous and discontinuous DNAPLs and so the important parameters governing the upward controlled mobilization of the DNAPL. The need and required magnitude of this specific discharge was investigated by conducting four column experiments in which the initial density of the DNAPL and the permeability was varied. It was shown that the required flow velocities increase with the permeability of the porous medium and the initial density difference between the aqueous phase and the DNAPL. Whenever the specific discharge falls below the critical value, the DNAPL moves downward. A second set of column experiments looked at the impact of permeability of porous medium on the solubilization and mobilization of DNAPL during alcohol flooding. Columns, packed with coarse or fine sand, containing a residual trichloroethylene (TCE) or perchloroethylene (PCE) saturation were flushed with the alcohol mixture at a fixed specific discharge rate. The induced pressure gradients in the aqueous phase, which were higher in the fine sand, resulted for this porous medium in extensive mobilization of the DNAPL against the direction of the buoyancy force. The density of the first NAPL coming out of the top of the fine sand was close to that of the pure DNAPL. In the coarser sand, the pressure gradients were sufficient to prevent downward migration of the DNAPL, but upward mobilization was minimal. The predominant removal mechanism in this case was the much slower solubilization.     

Radon as a naturally occurring tracer for the assessment of residual NAPL contamination of aquifers

The noble gas radon has a strong affinity to non-aqueous phase-liquids (NAPLs). That property makes it applicable as naturally occurring partitioning tracer for assessing residual NAPL contamination of aquifers. In a NAPL contaminated aquifer, radon dissolved in the groundwater partitions preferably into the NAPL. The magnitude of the resulting radon deficit in the groundwater depends on the NAPL-specific radon partition coefficient and on the NAPL saturation of the pore space. Hence, if the partition coefficient is known, the NAPL saturation is attainable by determination of the radon deficit. After a concise discussion of theoretical aspects regarding radon partitioning into NAPL, related experimental data and results of a field investigation are presented. Aim of the laboratory experiments was the determination of radon partition coefficients of multi-component NAPLs of environmental concern. The on-site activities were carried out in order to confirm the applicability of the "radon method" under field conditions.     

Effect of cationic and anionic surfactants on the sorption and desorption of perfluorooctane sulfonate (PFOS) on natural sediments

Sorption and desorption of PFOS at water-sediment interfaces were investigated in the presence of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), and an anionic surfactant, sodium dodecylbenzene sulfonate (SDBS). CTAB remarkably enhanced the sorption of PFOS on the sediment. In contrast, the influence of SDBS to the sorption of PFOS was concentration dependent. Two contrasting factors were responsible for the phenomenon. One was the sorption of the surfactant itself to the sediment, which enhanced the sorption of PFOS. The other was the increase in solubility of PFOS caused by the adding of surfactants, which decreased the sorption of PFOS. SDBS had a much lower sorption capacity, but rather strong ability to increase the solubility of PFOS. High levels of SDBS remarkably reduced the sorption of PFOS on the sediment. These results imply that cationic and anionic surfactants may have contrast impacts on the distribution and transport of PFOS in the environment.     

The effects of scale and spatial heterogeneities on diffusion in volcanic breccias and basalts: Amchitka Island, Alaska

Knowledge of the factors that influence the diffusion of contaminants, such as the diffusivity and the connected porosity, is crucial to modeling the long-term fate and transport of contaminants in subsurface systems with small or negligible advective flow, such as in fractured crystalline rock. Fractured rock is naturally heterogeneous, and hence, understanding the diffusivity of a molecule through this material (or the formation factor of the medium) becomes a complex problem, with critical concerns about the scale of laboratory measurements and about the spatial variability of these measurements relative to the scale needed for fate and transport modeling. This study employed both electrical and tracer-based laboratory methods to investigate the effects of scale and pore system connectivity on the diffusivity for volcanic matrix rock derived from the study site, a former underground nuclear test site at Amchitka Island, Alaska. The results of these investigations indicate a relatively well-connected pore system with scale effects generally limited to approximately 6 cm lengths and well-correlated to observed heterogeneous features. An important conclusion resulting from this study, however, is that there is a potential for the estimated diffusivity to be misrepresented by an order of magnitude if multiple samples or longer sample lengths are not used. Given the relatively large number of measurements resulting from these investigations, an analysis of the probability density function (PDF) of the diffusivity was possible. The PDF of the diffusivity was shown to generally follow a normal distribution for individual geologic layers. However, when all of the geologic layers are considered together, the distribution of the subsurface as a whole was shown to follow a lognormal distribution due to the order of magnitude differences amongst the layers. An understanding of these distributions is essential for future stochastic modeling efforts.     

Effect of cropping and tillage on the dissipation of PAH contamination in soil

This study examined the effect of regular tillage and cropping on the dissipation rate of PAHs in contaminated soil. Lysimeters were placed under natural climatic conditions for 2 years and designed to measure the concentration of PAHs in soil and leachates and their toxicity. The soil initially contained 2077 microg PAHs g(-1). The largest decrease in PAHs concentration occurred during the first 6 months. No further significant decrease was observed after this time. The surface soil layer always contained significantly less PAHs than the deeper layer, regardless of the treatments. Less than 8.4 x 10(-8)% of the PAH initially present in the soil (e.g. less or equal to 33 microg PAHs per lysimeter) were leached from the soils during the experiment and the leachates presented no toxicity (as measured by the Microtox test). The toxicity of the soils decreased with time and was significantly lower on the cropped soil compared to the other treatments, despite the residual concentration of PAHs being the highest in this soil. This study demonstrated that the dissipation rates of PAHs were slow after using natural attenuation even when tillage and cropping were performed at the soil surface.     

The influence of the scale of mining activity and mine site remediation on the contamination legacy of historical metal mining activity

Globally, thousands of kilometres of rivers are degraded due to the presence of elevated concentrations of potentially harmful elements (PHEs) sourced from historical metal mining activity. In many countries, the presence of contaminated water and river sediment creates a legal requirement to address such problems. Remediation of mining-associated point sources has often been focused upon improving river water quality; however, this study evaluates the contaminant legacy present within river sediments and attempts to assess the influence of the scale of mining activity and post-mining remediation upon the magnitude of PHE contamination found within contemporary river sediments. Data collected from four exemplar catchments indicates a strong relationship between the scale of historical mining, as measured by ore output, and maximum PHE enrichment factors, calculated versus environmental quality guidelines. The use of channel slope as a proxy measure for the degree of channel-floodplain coupling indicates that enrichment factors for PHEs in contemporary river sediments may also be the highest where channel-floodplain coupling is the greatest. Calculation of a metric score for mine remediation activity indicates no clear influence of the scale of remediation activity and PHE enrichment factors for river sediments. It is suggested that whilst exemplars of significant successes at improving post-remediation river water quality can be identified; river sediment quality is a much more long-lasting environmental problem. In addition, it is suggested that improvements to river sediment quality do not occur quickly or easily as a result of remediation actions focused a specific mining point sources. Data indicate that PHEs continue to be episodically dispersed through river catchments hundreds of years after the cessation of mining activity, especially during flood flows. The high PHE loads of flood sediments in mining-affected river catchments and the predicted changes to flood frequency, especially, in many river catchments, provides further evidence of the need to enact effective mine remediation strategies and to fully consider the role of river sediments in prolonging the environmental legacy of historical mine sites.     

Influence of synthetic surfactants on the uptake of Pd, Cd and Pb by the marine macroalga, Ulva lactuca

Uptake of Pd, Cd and Pb by the marine macroalga, Ulva lactuca, has been studied in the presence of an anionic (sodium dodecyl sulphate, SDS), cationic (hexadecyltrimethylammonium bromide; HDTMA) and non-ionic (Triton X-100; TX) surfactant. Compared with the surfactant-free system, metal sorption was reduced in the presence of SDS or TX. Neither surfactant, however, had any measurable impact on cell membrane permeability, determined by leakage of dissolved free amino acids (DFAA), or on metal internalisation. We attribute these observations to the stabilisation of aqueous Cd and Pb by SDS and the shielding of otherwise amenable sorption sites by TX. Presence of HDTMA resulted in a reduction in the extent of both sorption and internalisation of all metals and a significant increase in the leakage of DFAA. Thus, by enhancing membrane permeability, HDTMA exerts the greatest influence on metal behaviour in the presence of U. lactuca.     

Effect of nonionic surfactant partitioning on the dissolution kinetics of residual perchloroethylene in a model porous medium

At concentrations above the critical micelle concentration, surfactants can significantly enhance the solubilization of residual nonaqueous phase liquids (NAPL) and, for this reason, are the focus of research on surfactant-enhanced aquifer remediation (SEAR). As a consequence of their amphiphilic nature, surfactants may also partition to various extents between the organic and aqueous phases, thereby affecting SEAR performance. We report here on the observation and analysis of the effect of surfactant partitioning on the dissolution kinetics of residual perchloroethylene (PCE) by aqueous solutions (1000 mg/L) of the non-ionic surfactant Triton X-100 in a model porous medium. For this fluid system, batch equilibration experiments showed that the surfactant partitions strongly into the NAPL (NAPL-water partition coefficient equal to 12.5). Dynamic interfacial tension (IFT) measurements were employed to study surfactant diffusion and interfacial adsorption. The dynamic IFT measurements were consistent with partitioning of the surfactant between the two liquid phases. PCE dissolution experiments, conducted in a transparent glass micromodel using an aqueous surfactant solution, were contrasted to experiments using clean water. Surfactant partitioning was observed to delay significantly the onset of micellar solubilization of PCE, an observation reproduced by a numerical model. This effect is attributed to the reduction of surfactant concentration in the immediate vicinity of the NAPL-water interface, which accompanies transport of the surfactant into the NAPL. Accordingly, it is suggested that both the rate and the extent of diffusion of the surfactant into the NAPL affect the onset of and the driving force for micellar solubilization. While many surfactants do not readily partition in NAPL, this possibility must be considered when selecting non-ionic surfactants for the enhanced solubilization of residual chlorinated solvents in porous media.     

The influence of cosolvent and heat on the solubility and reactivity of organophosphorous pesticide DNAPL alkaline hydrolysis

The presented research concerned the compatibility of cosolvents with in situ alkaline hydrolysis (ISAH) for treatment of organophosphorous (OPP) pesticide contaminated sites. In addition, the influence of moderate temperature heat increments was studied as a possible enhancement method. A complex dense non-aqueous phase liquid (DNAPL) of primarily parathion (~50 %) and methyl parathion (~15 %) obtained from the Danish Groyne 42 site was used as a contaminant source, and ethanol and propan-2-ol (0, 25, and 50 v/v%) was used as cosolvents in tap water and 0.34 M NaOH. Both cosolvents showed OPP solubility enhancement at 50 v/v% cosolvent content, with slightly higher OPP concentrations reached with propan-2-ol. Data on hydrolysis products did not show a clear trend with respect to alkaline hydrolysis reactivity in the presence of cosolvents. Results indicated that the hydrolysis rate of methyl-parathion (MP3) decreased with addition of cosolvent, whereas the hydrolysis rate of ethyl-parathion (EP3) remained constant, and overall indications were that the hydrolysis reactions were limited by the rate of hydrolysis rather than NAPL dissolution. In addition to cosolvents, the influence of low-temperature heating on ISAH was studied. Increasing reaction temperature from 10 to 30 °C provided an average rate of hydrolysis enhancement by a factor of 1.4–4.8 dependent on the base of calculation. When combining 50 v/v% cosolvent addition and heating to 30 °C, EP3 solubility was significantly enhanced and results for O,O-diethyl-thiophosphoric acid (EP2 acid) showed a significant enhancement of hydrolysis as well. However, this could not be supported by para-nitrophenol (PNP) data indicating the instability of this product in the presence of cosolvent.

     

A functional perspective on the analysis of land use and land cover data in ecology

Assessments of large-scale changes in habitat are a priority for management and conservation. Traditional approaches use land use and land cover data (LULC) that focus mostly on “structural” properties of landscapes, rather than “functional” properties related to specific ecological processes. Here, we contend that designing functional analyses of LULC can provide important and complementary information to traditional, structural analyses. We substantiate this perspective with an example of functional changes in habitat due to industrial anthropogenic footprints in Alberta’s boreal forest, where there has been little overall forest loss (~ 6% structural change), but high levels of functional change (up to 93% functional change) for species’ habitat, biodiversity, and wildfire ignition. We discuss the methods needed to achieve functional LULC analyses, when they are most appropriate to add to structural assessments, and conclude by providing recommendations for analyses of LULC in a future of increasingly high-resolution, dynamic remote sensing data.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01434-5) contains supplementary material, which is available to authorized users.     

The organic contamination level based on the total soil mass is not a proper index of the soil contamination intensity

Concentrations of organic contaminants in common productive soils based on the total soil mass give a misleading account of actual contamination effects. This is attributed to the fact that productive soils are essentially water-saturated, with the result that the soil uptake of organic compounds occurs principally by partition into the soil organic matter (SOM). This report illustrates that the soil contamination intensity of a compound is governed by the concentration in the SOM (C_om) rather than by the concentration in whole soil (C_s). Supporting data consist of the measured levels and toxicities of many pesticides in soils of widely differing SOM contents and the related levels in in-situ crops that defy explanation by the C_s values. This SOM-based index is timely needed for evaluating the contamination effects of food crops grown in different soils and for establishing a dependable priority ranking for intended remediation of numerous contamination sites.     

Sources, transport and reactivity of anionic and non-ionic surfactants in several aquatic ecosystems in SW Spain: a comparative study

Presence, distribution and transport mechanisms of the four major synthetic surfactants -linear alkylbenzene sulfonates (LAS), alkyl ethoxysulfates (AES), nonylphenol ethoxylates (NPEOs) and alcohol ethoxylates (AEOs)- have been simultaneously studied in different aquatic ecosystems. Urban wastewater discharges and industrial activities were identified as the main sources for these compounds and their metabolites. LAS, AES and carboxylic metabolites remained in the dissolved form (87–99%). However, NPEOs and AEOs were mostly associated with particulate matter (65–86%), so their degradation in the water column was limited due to their lower bioavailability. It was also observed that sorption to the particulate phase was more intense for longer homologs/ethoxymers for all surfactants. With respect to surface sediments, AES levels were considerably below (<0.25 mg/kg) the values detected for LAS and NPEOs. Concentrations of AEOs, however, were occasionally higher (several tens of ppm) than those found for the rest of the target compounds in several sampling stations.     

废水营养比对固定化藻菌去除污染物的影响及动力学研究

海藻酸钙作载体的固定化藻菌小球,经壳聚糖覆膜后,用于模拟废水的处理。通过研究废水初始氨氮浓度及碳氮比对固定化藻菌小球处理效果的影响,发现初始氨氮浓度为50 mg/L时,氨氮的去除率达最高值74.4%;碳氮比为35∶1时,COD去除率达最高值77.7%。系统最佳氮磷比与碳氮比分别为5∶1和35∶1。固定化藻菌降解有机物的动力学过程为一级不可逆生化反应过程,其降解速率常数约为0.099 h-1。     

Effect of soil moisture dynamics on dense nonaqueous phase liquid (DNAPL) spill zone architecture in heterogeneous porous media

The amount, location, and form of NAPL in contaminated vadose zones are controlled by the spatial distribution of water saturation and soil permeability, the NAPL spill scenario, water infiltration events, and vapor transport. To evaluate the effects of these processes, we used the three-phase flow simulator STOMP, which includes a new permeability-liquid saturation-capillary pressure (k-S-P) constitutive model. This new constitutive model considers three NAPL forms: free, residual, and trapped. A 2-D vertical cross-section with five stratigraphic layers was assumed, and simulations were performed for seven cases. The conceptual model of the soil heterogeneity was based upon the stratigraphy at the Hanford carbon tetrachloride (CT) spill site. Some cases considered co-disposal of NAPL with large volumes of wastewater, as also occurred at the Hanford CT site. In these cases, the form and location of NAPL were most strongly influenced by high water discharge rates and NAPL evaporation to the atmosphere. In order to investigate the impact of heterogeneity, the hydraulic conductivity within the lower permeability layer was modeled as a realization of a random field having three different classes. For six extreme cases of 100 realizations, the CT mass that reached the water table varied by a factor of two, and was primarily controlled by the degree of lateral connectivity of the low conductivity class within the lowest permeability layer. The grid size at the top boundary had a dramatic impact on NAPL diffusive flux just after the spill event when the NAPL was present near the ground surface. NAPL evaporation with a fine grid spacing at the top boundary decreased CT mass that reached the water table by 74%, compared to the case with a coarse grid spacing, while barometric pumping had a marginal effect for the case of a continuous NAPL spill scenario considered in this work. For low water infiltration rate scenarios, the distribution of water content prior to a NAPL spill event decreased CT mass that reached the water table by 98% and had a significant impact on the formation of trapped NAPL. For all cases simulated, use of the new constitutive model that allows the formation of residual NAPL increased the amount of NAPL retained in the vadose zone. Density-driven advective gas flow from the ground surface controlled vapor migration in strongly anisotropic layers, causing NAPL mass flux to the lower layer to be reduced. These simulations indicate that consideration of the formation of residual and trapped NAPLs and dynamic boundary conditions (e.g., areas, rates, and periods of different NAPL and water discharge and fluctuations of atmospheric pressure) in the context of full three-phase flow are needed, especially for NAPL spill events at the ground surface. In addition, NAPL evaporation, density-driven gas advection, and NAPL vertical movement enhanced by water flow must be considered in order to predict NAPL distribution and migration in the vadose zone.     

Manipulation of density and viscosity for the optimization of DNAPL recovery by alcohol flooding

Laboratory experiments demonstrate that in situ recovery of pooled tetrachloroethene (PCE) from porous media may be accomplished more efficiently using multiple-step alcohol floods than with single alcohol floods. To optimize flooding efficiency while maintaining a low risk of downward DNAPL mobilization, a three-step flooding process is developed employing an isobutanol preflood, a composite alcohol mainflood, and a polymer solution postflood. The density and viscosity of these solutions are manipulated to prevent the onset and propagation of viscous and gravitational fingers, while maintaining phase behavior critical for efficient miscible NAPL displacement. An aqueous partitioning preflood solution of 10% by volume (10% v) isobutanol reduces the NAPL density in situ to approximately 1.00 g/ml by swelling the NAPL prior to miscible displacement induced by the mainflood. The composite alcohol mainflood, containing 65% v ethylene glycol and 35% v 1-propanol maintains miscibility while achieving neutral buoyancy and near stable displacement of the NAPL. Aqueous solutions of xanthan gum polymer efficiently displace the mainflood, reducing viscous fingering associated with waterfloods. Two-dimensional experiments using the multiple-step technique achieve 99.8% DNAPL mass recovery using a total of 0.45 pore volumes of alcohol, illustrating greater recovery efficiency than previous alcohol flooding formulations under comparable conditions.     

双酶协同水解剩余污泥条件优化

在碱性蛋白酶：中性蛋白为3：1的最优酶配比下,对剩余活性污泥进行水解提取蛋白质实验研究。实验以蛋白质提取率、SCOD/TCOD和有机质减少量三个指标来表现水解效果,探究温度、时间、pH以及加酶量对水解效果的影响。结果表明,蛋白质提取率、SCOD/TCOD和有机质含量变化三者存在较强的相关性,最佳水解条件是pH为9.0,反应时间4 h,加酶量5%和反应温度55℃。最佳水解条件下,污泥蛋白质提取率为65.89%,SCOD/TCOD为61.43%,有机质减少量81.05%。