Treatability of nonylphenol ethoxylate surfactants in on-site wastewater disposal systems.

The fate of nine-mole nonylphenol ethoxylate (NPE9) discharged to an on-site wastewater disposal (septic) system was the focus of a 2-year investigation. Known amounts of NPE9-based detergent were metered daily into the plumbing at a single-family household. The ethoxylate-containing wastewater was discharged to the highly anoxic environment of a 4500-L septic tank before distribution to the oxic subsurface via 100 m of leach line. After 180 days of injecting detergent to the septic system, periodic soil pore water and/or groundwater samples were collected and analyzed for nonylphenol ethoxylates (NPEs), nonylphenol ether carboxylates, and nonylphenol. The NPE9 and degradation intermediates that were measured were reduced by 99.99% on a molar basis. An 18% reduction in molar concentration within the septic tank was observed. This was followed by a further 96.7% reduction of molar concentration within the leach lines. As the pore water migrated through the vadose zone, an additional 99.69% reduction in molar concentration was measured between the bottom of the leach lines (leach line effluent) and the lowest vadose zone monitoring location. The results obtained from these analyses indicate that degradation of the surfactant occurs within the anoxic portion of the disposal system with continued rapid biodegradation in the oxic unsaturated zone. Only trace amounts of degradation residuals were detected in soil pore water. The concentration and distribution of various degradation intermediates with respect to location, time, and ambient physical conditions were evaluated. Rapid and systematic degradation of NPE in on-site wastewater disposal systems was documented.     

Geotechnical engineering properties of incinerator ash mixes

The incineration of solid waste produces large quantities of bottom and fly ash. Landfilling has been the primary mode of disposal of these waste materials. Shortage in landfill space and the high cost of treatment have, however, prompted the search for alternative uses of these waste materials. This study presents an experimental program that was conducted to determine the engineering properties of incinerator ash mixes for use as construction materials. Incinerator ash mixes were tested as received and around optimum compacted conditions. Compaction curves, shear strength, and permeability values of fly ash, bottom ash, and their various blends were investigated. Bottom ash tends to achieve maximum dry density at much lower water content than does fly ash. The mixes displayed a change in their cohesion and friction angle values when one of the two mix components was altered or as a result of the addition of water. The permeability of bottom ash is quite comparable to that of sand. The permeability of fly ash lies in the range of those values obtained for silts and clays. A 100% bottom ash compacted at the optimum water content has a lower density value and yields a higher friction angle and cohesion values than most construction fills. This would encourage the use of bottom ash as a fill or embankment material because free drainage of water will prevent the buildup of pore water pressures.     

Analysis of a mesoscale infiltration and water seepage test in unsaturated fractured rock: Spatial variabilities and discrete fracture patterns

A mesoscale (21 m in flow distance) infiltration and seepage test was recently conducted in a deep, unsaturated fractured rock system at the crossover point of two underground tunnels. Water was released from a 3 mx4 m infiltration plot on the floor of an alcove in the upper tunnel, and seepage was collected from the ceiling of a niche in the lower tunnel. Significant temporal and (particularly) spatial variabilities were observed in both measured infiltration and seepage rates. To analyze the test results, a three-dimensional unsaturated flow model was used. A column-based scheme was developed to capture heterogeneous hydraulic properties reflected by these spatial variabilities observed. Fracture permeability and van Genuchten alpha parameter [van Genuchten, M.T., 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44, 892-898] were calibrated for each rock column in the upper and lower hydrogeologic units in the test bed. The calibrated fracture properties for the infiltration and seepage zone enabled a good match between simulated and measured (spatially varying) seepage rates. The numerical model was also able to capture the general trend of the highly transient seepage processes through a discrete fracture network. The calibrated properties and measured infiltration/seepage rates were further compared with mapped discrete fracture patterns at the top and bottom boundaries. The measured infiltration rates and calibrated fracture permeability of the upper unit were found to be partially controlled by the fracture patterns on the infiltration plot (as indicated by their positive correlations with fracture density). However, no correlation could be established between measured seepage rates and density of fractures mapped on the niche ceiling. This lack of correlation indicates the complexity of (preferential) unsaturated flow within the discrete fracture network. This also indicates that continuum-based modeling of unsaturated flow in fractured rock at mesoscale or a larger scale is not necessarily conditional explicitly on discrete fracture patterns.     

Geotechnical Engineering Properties of Incinerator Ash Mixes

Abstract

The incineration of solid waste produces large quantities of bottom and fly ash. Landfilling has been the primary mode of disposal of these waste materials. Shortage in landfill space and the high cost of treatment have, however, prompted the search for alternative uses of these waste materials. This study presents an experimental program that was conducted to determine the engineering properties of incinerator ash mixes for use as construction materials. Incinerator ash mixes were tested as received and around optimum compacted conditions. Compaction curves, shear strength, and permeability values of fly ash, bottom ash, and their various blends were investigated. Bottom ash tends to achieve maximum dry density at much lower water content than does fly ash. The mixes displayed a change in their cohesion and friction angle values when one of the two mix components was altered or as a result of the addition of water. The permeability of bottom ash is quite comparable to that of sand. The permeability of fly ash lies in the range of those values obtained for silts and clays. A 100% bottom ash compacted at the optimum water content has a lower density value and yields a higher friction angle and cohesion values than most construction fills. This would encourage the use of bottom ash as a fill or embankment material because free drainage of water will prevent the buildup of pore water pressures.     

Removal of hydrogen sulfide gas and landfill leachate treatment using coal bottom ash.

Coal bottom ashes produced from three thermal power plants were used in column and batch experiments to investigate the adsorption capacity of the coal ash. Hydrogen sulfide and leachates collected from three sanitary landfill sites were used as adsorbate gas and solutions, respectively. Experimental results showed that coal bottom ash could remove H2S from waste gas or reduce the concentrations of various pollutants in the leachate. Each gram of bottom ash could remove up to 10.5 mg of H2S. In treating the landfill leachate, increasing ash dosage increased the removal efficiency but decreased the adsorption amount per unit mass of ash. For these tested ashes, the removal efficiencies of chemical oxygen demand (COD), NH3-N, total Kjeldhal nitrogen (TKN), P, Fe3+, Mn2+, and Zn2+ were 36.4-50, 24.2-39.4, 27.0-31.1, 82.2-92.9, 93.8-96.5, 93.7-95.4, and 80.5-82.2%, respectively; the highest adsorption capacities for those parameters were 3.5-5.6, 0.22-0.63, 0.36-0.45, 0.027-0.034, 0.050-0.053, 0.029-0.032, and 0.006 mg/g of bottom ash, respectively. The adsorption of pollutants in the leachate conformed to Freundlich's adsorption model.     

Impact of chemical leaching on permeability and cadmium removal from fine-grained soils

The aim of this study was to investigate the influence of chemical leaching on permeability and Cd removal from fine-grained polluted soils. Column leaching experiments were conducted using two types of soils (i.e., artificially Cd-polluted loam and historically polluted silty loam). Chemical agents of CaCl₂, FeCl₃, citric acid, EDTA, rhamnolipid, and deionized water were used to leach Cd from the soils. Results showed that organic agents reduced permeability of both soils, and FeCl₃ reduced permeability of loam soil, compared with inorganic agents and deionized water. Entrapment and deposition of colloids generated from the organic agents and FeCl₃ treatments reduced the soil permeability. The peak Cd effluence from the artificially polluted loam columns was retarded. For the artificially polluted soils treated with EDTA and the historically polluted soils with FeCl₃, Cd precipitates were observed at the bottom after chemical leaching. When Cd was associated with large colloid particles, the reduction of soil permeability caused Cd accumulation in deeper soil. In addition, the slow process of disintegration of soil clay during chemical leaching might result in the retardation of peak Cd effluence. These results suggest the need for caution when using chemical-leaching agents for Cd removal in fine-grained soils.

     

Impact of nonaqueous phase liquid (NAPL) source zone architecture on mass removal mechanisms in strongly layered heterogeneous porous media during soil vapor extraction

An existing multiphase flow simulator was modified in order to determine the effects of four mechanisms on NAPL mass removal in a strongly layered heterogeneous vadose zone during soil vapor extraction (SVE): a) NAPL flow, b) diffusion and dispersion from low permeability zones, c) slow desorption from sediment grains, and d) rate-limited dissolution of trapped NAPL. The impacts of water and NAPL saturation distribution, NAPL-type (i.e., free, residual, or trapped) distribution, and spatial heterogeneity of the permeability field on these mechanisms were evaluated. Two different initial source zone architectures (one with and one without trapped NAPL) were considered and these architectures were used to evaluate seven different SVE scenarios. For all runs, slow diffusion from low permeability zones that gas flow bypassed was a dominant factor for diminished SVE effectiveness at later times. This effect was more significant at high water saturation due to the decrease of gas-phase relative permeability. Transverse dispersion contributed to fast NAPL mass removal from the low permeability layer in both source zone architectures, but longitudinal dispersion did not affect overall mass removal time. Both slow desorption from sediment grains and rate-limited mass transfer from trapped NAPL only marginally affected removal times. However, mass transfer from trapped NAPL did affect mass removal at later time, as well as the NAPL distribution. NAPL flow from low to high permeability zones contributed to faster mass removal from the low permeability layer, and this effect increased when water infiltration was eliminated. These simulations indicate that if trapped NAPL exists in heterogeneous porous media, mass transfer can be improved by delivering gas directly to zones with trapped NAPL and by lowering the water content, which increases the gas relative permeability and changes trapped NAPL to free NAPL.     

Oxidation of gas mixtures containing dimethyl sulfide, hydrogen sulfide, and methanethiol using a two-stage biotrickling filter

A biofiltration technique was developed for removing a mixture of hydrogen sulfide (H2S), methanethiol (MeSH), and dimethyl sulfide (Me2S) from waste gases. Since H2S, especially at high concentrations, disturbs the removal of Me2S, two biotrickling filters with different microbes and operating pH levels were connected in series to create a two-stage system. Different loads of these gases were studied in order to determine their impact on the removal capacity of the system. The microbial consortia for these filters were enriched from the sludge of a Finnish refinery with bubbling H2S or Me2S. Acclimation for Me2S took 2 weeks, though no acclimation time was needed for the other gases. The first filter, at a pH of 2, removed most of the H2S and some of the MeSH and Me2S. The second filter, at a pH of approximately 6.5, removed the rest of the MeSH and most of the Me2S. The total maximum loads of the whole two-stage biotrickling filter were 1150 g/m3/day for H2S-S (suffix S indicates the results are counted as sulfur amounts), 879 g/m3/day for Me2S-S, and 66 g/m3/day for MeSH-S treated in a gas mixture. The average removal efficiencies for all gases tested were 99% or higher.     

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.     

Single- and dual-porosity modelling of flow in reclaimed mine soil cores with embedded lignitic fragments

Lignitic mine soils represent a typical two-scale dual-porosity medium consisting of a technogenic mixture of overburden sediments that include lignitic components as dust and as porous fragments embedded within a mostly coarse-textured matrix. Flow and transport processes in such soils are not sufficiently understood to predict the course of soil reclamation or of mine drainage. The objective of this contribution is to identify the most appropriate conceptual model for describing small-scale heterogeneity effects on flow on the basis of the physical structure of the system. Multistep flow experiments on soil cores are analyzed using either mobile–immobile or mobile–mobile type 1D dual-porosity models, and a 3D numerical model that considers a local-scale distribution of fragments. Simulations are compared with time series' of upward infiltration and matric potential heads measured at two depths using miniature tensiometers. The 3D and the 1D dual-permeability models yielded comparable results as long as pressure heads are in local equilibrium; however, could describe either the upward infiltration or the matric potential curves but not both at the same time. The mobile–immobile type dual-porosity model failed to describe the data. A simultaneous match with pressure heads and upward infiltration data could only be obtained with the 1D dual-permeability model (i.e., mobile–mobile) by assuming an additional restriction of the inter-domain water transfer. These results indicate that for unsaturated flow conditions at higher matric potential heads (i.e., here >− 40 hPa), water in a restricted part of the fragment domain must be more mobile as compared to water in the sandy matrix domain. Closer inspections of the pore system and first neutron radiographic imaging support the hypothesis that a more continuous pore region exists at these pressure heads in the vicinity of the lignitic fragments possibly formed by fragment contacts and a lignitic dust interface-region between the two domains. The results suggest that the small-scale structure is too complex as to be represented by weighted contributions of individual components alone.     

Improving phosphate removal of sand infiltration system using alkaline fly ash

Septic tank effluent is customarily disposed of by soil infiltration. Coarse, sandy soil such as those found in Perth, Western Australia, exhibit low attenuation capabilities for phosphate (PO4(3-)) during effluent infiltration. Amendment of such soil with different amounts of alkaline precipitator and lagoon fly ashes was investigated as a means of reducing phosphorus (P) leakage to ground water. Alkaline precipitator fly ash possessed the highest P sorption capacity in terms of its Langmuir and Freundlich isotherm parameters during initial batch tests. The test materials were repeatedly contacted with fresh PO4(3-) solutions over 90 contacting cycles to gain a better indication of long-term P sorption capability. Again, precipitator fly ash exhibited higher P sorption capacity than lagoon fly ash and Spearwood sand. Column studies assessed the influence of various application rates of alkaline precipitator and lagoon fly ashes on the P removal of septic tank effluent. Septic tank effluent was applied at the rate of 4 cm/day to the column for 12 weeks. Concentrations of P were monitored in the column effluent. All the fly ash columns were more efficient in reducing P migration compared to the sand column. Increased levels of fly ash in the soil columns resulted in increased P attenuation. Lagoon fly ash was inferior to precipitator fly ash for P removal; high application rates of fly ash caused clogging of the infiltration bed apparently due to their lower permeability. It is reasoned that 5-15% precipitator fly ash, and less than 30% lagoon fly ash could be added to coarse sands to produce an infiltration bed, which would result in a better quality effluent than can be obtained with untreated sand alone.     

Removal of carbonyl sulfide using activated carbon adsorption

Wastewater treatment plant odors are caused by compounds such as hydrogen sulfide (H2S), methyl mercaptans, and carbonyl sulfide (COS). One of the most efficient odor control processes is activated carbon adsorption; however, very few studies have been conducted on COS adsorption. COS is not only an odor causing compound but is also listed in the Clean Air Act as a hazardous air pollutant. Objectives of this study were to determine the following: (1) the adsorption capacity of 3 different carbons for COS removal; (2) the impact of relative humidity (RH) on COS adsorption; (3) the extent of competitive adsorption of COS in the presence of H2S; and (4) whether ammonia injection would increase COS adsorption capacity. Vapor phase react (VPR; reactivated), BPL (bituminous coal-based), and Centaur (physically modified to enhance H2S adsorption) carbons manufactured by Calgon Carbon Corp. were tested in three laboratory-scale columns, 6 in. in depth and 1 in. in diameter. Inlet COS concentrations varied from 35 to 49 ppmv (86-120 mg/m3). RHs of 17%, 30%, 50%, and 90% were tested. For competitive adsorption studies, H2S was tested at 60 ppmv, with COS at 30 ppmv. COS, RH, H2S, and ammonia concentrations were measured using an International Sensor Technology Model IQ-350 solid state sensor, Cole-Parmer humidity stick, Interscan Corp. 1000 series portable analyzer, and Drager Accuro ammonia sensor, respectively. It was found that the adsorption capacity of Centaur carbon for COS was higher than the other two carbons, regardless of RH. As humidity increased, the percentage of decrease in adsorption capacity of Centaur carbon, however, was greater than the other two carbons. The carbon adsorption capacity for COS decreased in proportion to the percentage of H2S in the gas stream. More adsorption sites appear to be available to H2S, a smaller molecule. Ammonia, which has been found to increase H2S adsorption capacity, did not increase the capacity for COS.     

Presence of microbial and chemical source tracking markers in roof-harvested rainwater and catchment systems for the detection of fecal contamination

Microbial source tracking (MST) and chemical source tracking (CST) markers were utilized to identify fecal contamination in harvested rainwater and gutter debris samples. Throughout the sampling period, Bacteroides HF183 was detected in 57.5 % of the tank water samples and 95 % of the gutter debris samples, while adenovirus was detected in 42.5 and 52.5 % of the tank water and gutter debris samples, respectively. Human adenovirus was then detected at levels ranging from below the detection limit to 316 and 1253 genome copies/μL in the tank water and debris samples, respectively. Results for the CST markers showed that salicylic acid (average 4.62 μg/L) was the most prevalent marker (100 %) in the gutter debris samples, caffeine (average 18.0 μg/L) was the most prevalent in the tank water samples (100 %) and acetaminophen was detected sporadically throughout the study period. Bacteroides HF183 and salicylic acid (95 %) and Bacteroides HF183 and caffeine (80 %) yielded high concurrence frequencies in the gutter debris samples. In addition, the highest concurrence frequency in the tank water samples was observed for Bacteroides HF183 and caffeine (60 %). The current study thus indicates that Bacteroides HF183, salicylic acid and caffeine may potentially be applied as source tracking markers in rainwater catchment systems in order to supplement fecal indicator analyses.     

Full-scale biofilter reduction efficiencies assessed using portable 24-hour sampling units

Portable 24-hr sampling units were used to collect air samples from eight biofilters on four animal feeding operations. The biofilters were located on a dairy, a swine nursery, and two swine finishing farms. Biofilter media characteristics (age, porosity, density, particle size, water absorption capacity, pressure drop) and ammonia (NH3), hydrogen sulfide (H2S), sulfur dioxide (SO2), methane (CH4), and nitrous oxide (N2O) reduction efficiencies of the biofilters were assessed. The deep bed biofilters at the dairy farm, which were in use for a few months, had the most porous media and lowest unit pressure drops. The average media porosity and density were 75% and 180 kg/m3, respectively. Reduction efficiencies of H2S and NH3 (biofilter 1: 64% NH3, 76% H2S; biofilter 2: 53% NH3, 85% H2S) were close to those reported for pilot-scale biofilters. No N2O production was measured at the dairy farm. The highest H2S, SO2, NH3, and CH4 reduction efficiencies were measured from a flat-bed biofilter at the swine nursery farm. However, the highest N2O generation (29.2%) was also measured from this biofilter. This flat-bed biofilter media was dense and had the lowest porosity. A garden sprinkler was used to add water to this biofilter, which may have filled media pores and caused N2O production under anaerobic conditions. Concentrations of H2S and NH3 were determined using the portable 24-hr sampling units and compared to ones measured with a semicontinuous gas sampling system at one farm. Flat-bed biofilters at the swine finishing farms also produced low amounts of N2O. The N2O production rate of the newer media (2 years old) with higher porosity was lower than that of older media (3 years old) (P = 0.042).     

The impact of methanogenesis on flow and transport in coarse sand

The effects of biofilm growth and methane gas generation on water flow in porous media were investigated in an anaerobic two-dimensional sand-filled cell. Inoculation of the lower portion of the cell with a methanogenic culture and addition of methanol to the bottom of the cell led to biomass growth and formation of a gas phase. Biomass distributions in the water and on the sand in the cell were measured by protein analysis. The biofilm distribution on sand was observed by confocal laser scanning microscopy. The formation, migration, distribution and saturation of gases in the cell were visualized by the charge-coupled device (CCD) camera. The effects of biofilm and gas generation on water flow were separated by performing one tracer test in the presence of both biofilm and a gas phase and a second tracer test after removal of the gas phase through water flushing. The results of tracer tests demonstrated that flow and transport in the two-dimensional cell were significantly affected by both gas generation and biofilm growth. Gas generated at the bottom of the cell in the biologically active zone moved upwards in discrete fingers, so that gas phase saturations (gas-filled fraction of void space) in the biologically active zone at the bottom of the cell did not exceed 40-50%, while gas accumulation at the top of the cell produced gas phase saturations as high as 80%. The greatest reductions in water phase permeability, based on measurements of reductions in water phase saturations, occurred near the top of the box as a result of the gas accumulation. In contrast the greatest reductions in permeability due to biofilm growth, based on measurements of biofilm thickness, occurred in the most biologically active zone at the bottom of the cell, where gas phase saturations were approximately 40-50%, but permeability reductions due to biofilm growth were estimated to be 80-95%.     

A multi-flowpath model for the interpretation of immiscible displacement experiments in heterogeneous soil columns

This work focuses on the phenomenon of the immiscible two-phase flow of water and oil in saturated heterogeneous soil columns. The goal is to develop a fast and reliable method for quantifying soil heterogeneities for incorporation into the relevant capillary pressure and relative permeability functions. Such data are commonly used as input data in simulators of contaminant transport in the subsurface. Rate-controlled drainage experiments are performed on undisturbed soil columns and the transient response of the axial distribution of water saturation is determined from electrical measurements. The transient responses of the axial distribution of water saturation and total pressure drop are fitted with the multi-flowpath model (MFPM) where the pore space is regarded as a system of parallel paths of different permeability. The MFPM enables us to quantify soil heterogeneity at two scales: the micro-scale parameters describe on average the effects of pore network heterogeneities on the two-phase flow pattern; the macro-scale parameters indicate the variability of permeability at the scale of interconnected pore networks. The capillary pressure curve is consistent with that measured with mercury intrusion porosimetry over the low pressure range. The oil relative permeability increases sharply at a very low oil saturation (< 10^− 3) and tends to a high end value. The water relative permeability decreases abruptly at a low oil saturation (~ 0.1), whereas the irreducible wetting phase saturation is quite high. The foregoing characteristics of the two-phase flow properties are associated with critical (preferential) flowpaths that comprise a very small percentage of the total pore volume, control the overall hydraulic conductivity, and are consistent with the very broad range of pore-length scales usually probed in soil porous matrix.     

Impact of chemical oxidation on soil quality

Oxidation treatment helps to reduce the polycyclic aromatic hydrocarbon (PAH) load in contaminated soils but it may also have an effect on the soil quality. The impact of permanganate and Fenton oxidation on soil quality is investigated. Soil quality is restricted here to the potential for plant growth. Soil samples were collected from an agricultural field (S1) and a former coking plant (S4). Agricultural soil was spiked with phenanthrene (PHE) and pyrene (PYR) at two concentrations (S2: 700 mg PHE kg⁻¹, S3: 700 mg PHE kg⁻¹ and 2100 mg PYR kg⁻¹). Soils were treated with both oxidation processes, and analyzed for PAHs and a set of agronomic parameters. A plant germination and growth test was run with rye-grass on treated soils. Results showed that both treatments produced the expected reduction of PAH concentration (from 64% to 97%). Besides, a significant loss of organic C and N, and strong changes in available nutrients were observed. Permanganate treatment increased the specific surface area and the cation exchange capacity in relation to manganese dioxide precipitation, and produced a rise in pH. Fenton oxidation decreased soil pH and increased the water retention capacity. Plant growth was negatively affected by permanganate, related to lower soil permeability and aeration. Both treatments had an effect on soil properties but Fenton oxidation appeared to be more compatible with revegetation.     

Potential sensitivity of mires to drought,acidification and mobilisation of heavy metals: the sediment s/(Ca + Mg) ratio as diagnostic tool

In recent decades sulphate concentrations in the ground water in many parts of The Netherlands have increased dramatically resulting in increased production of iron-(di)sulphides in sediments of ecosystems fed by this water. A sediment survey was carried out to study the potential sensitivity of wetlands to drought and subsequent acidification as a consequence of iron-(di)sulphide oxidation. Dessication led to severe acidification and mobilisation of heavy metals when the sediment S/(Ca + Mg) ratio exceeded 2/ 3. A total of 47% of the investigated locations contained S/(Ca + Mg) ratios higher than 2/3 and in 100, 75 and 50% of the locations mobilisation of Zn, Cd and Ni exceeded the Dutch signal value for ground water. Consistent with the sediment survey, lime addition experiments confirmed that increasing the buffer capacity, down to a S/(Ca + Mg) ratio 2/3, led to a drastic inhibition of the acidification and heavy metal percolation from dredged sediments. The performance of the same processes under drained field conditions demonstrates the relevance of these processes during dry summers.     

油页岩循环流化床锅炉底渣和飞灰中重金属元素浸出毒性研究

为了研究我国桦甸油页岩65 t/h循环流化床锅炉的底渣和飞灰中重金属元素Cr、Cu、Pb和Zn的赋存状态及不同酸度条件下的浸出特性,分别进行了逐级提取实验和分批浸出的淋滤实验。逐级提取实验结果表明,这4种元素在底渣和飞灰中具有基本相当的赋存状态。硫化物结合态和稳定的残渣态是各元素的主要赋存状态,元素的潜在浸出能力大小表现为:PbCrCuZn,飞灰中各元素的潜在浸出能力大于底渣中的。浸出实验结果表明,元素的赋存状态决定了其浸提能力,浸提液的pH值对各元素浸出能力的影响不尽相同,各元素的浸出能力随浸提时间的延长都会趋于平衡,Cr和Pb的浸出浓度都高于地表水和饮用水的国家标准。     

Atrazine distribution measured in soil and leachate following infiltration conditions

Atrazine transport through packed 10 cm soil columns representative of the 0-10 cm soil horizon was observed by measuring the atrazine recovery in the total leachate volume, and upper and lower soil layers following infiltration of 7.5 cm water using a mechanical vacuum extractor (MVE). Measured recoveries were analyzed to understand the influence of infiltration rate and delay time on atrazine transport and distribution in the column. Four time periods (0.28, 0.8, 1.8, and 5.5 h) representing very high to moderate infiltration rates (26.8, 9.4, 4.2, and 1.4 cm/h) were used. Replicate soil columns were tested immediately and following a 2-d delay after atrazine application. Results indicate atrazine recovery in leachate was independent of infiltration rate, but significantly lower for infiltration following a 2-d delay. Atrazine distribution in the 0-1 and 9-10 cm soil layers was affected by both infiltration rate and delay. These results are in contrast with previous field and laboratory studies that suggest that atrazine recovery in the leachate increases with increasing infiltration rate. It appears that the difference in atrazine recovery measured using the MVE and other leaching experiments using intact soil cores from this field site and the rain simulation equipment probably illustrates the effect of infiltrating water interacting with the atrazine present on the soil surface. This work suggests that atrazine mobilization from the soil surface is also dependent on interactions of the infiltrating water with the soil surface, in addition to the rate of infiltration through the surface soil.