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1.
In situ bioremediation is an innovative technique for the remediation of contaminated aquifers that involves the use of microorganisms to remediate soils and groundwaters polluted by hazardous substances. During its application, this process may require the addition of nutrients and/or electron acceptors to stimulate appropriate biological activity. Hydrogen peroxide has been commonly used as an oxygen source because of the limited concentrations of oxygen that can be transferred into the groundwater using above-ground aeration followed by reinjection of the oxygenated groundwater into the aquifer or subsurface air sparging of the aquifer. Because of several potential interactions of H2O2 with various aquifer material constituents, its decomposition may be too rapid, making effective introduction of the H2O2 into targeted treatment zones extremely difficult and costly. Therefore, a bench-scale study was conducted to determine the fate of H2O2 within subsurface aquifer environments. The purpose of this investigation was to identify those aquifer constituents, both biotic and abiotic, that are most active in controlling the fate of H2O2. The decomposition rates of H2O2 were determined using both equilibrated water samples and soil slurries. Results showed H2O2 decomposition to be effected by several commonly found inorganic soil components; however, biologically mediated catalytic reactions were determined to be the most substantial. 相似文献
2.
The in situ bioremediation of aquifers contaminated with petroleum hydrocarbons is commonly based on the infiltration of groundwater supplemented with oxidants (e.g., O 2, NO 3−) and nutrients (e.g., NH 4+, PO 43−). These additions stimulate the microbial activity in the aquifer and several field studies describing the resulting processes have been published. However, due to the heterogeneity of the subsurface and due to the limited number of observation wells usually available, these field data do not offer a sufficient spatial and temporal resolution. In this study, flow-through columns of 47-cm length equipped with 17 sampling ports were filled with homogeneously contaminated aquifer material from a diesel fuel contaminated in situ bioremediation site. The columns were operated over 96 days at 12°C with artificial groundwater supplemented with O 2, NO 3− and PO 43−. Concentration profiles of O 2, NO 3−, NO 2−, dissolved inorganic and organic carbon (DIC and DOC, respectively), protein, microbial cells and total residual hydrocarbons were measured. Within the first 12 cm, corresponding to a mean groundwater residence time of < 3.6 h, a steep O 2 decrease from 4.6 to < 0.3 mg l −1, denitrification, a production of DIC and DOC, high microbial cell numbers and a high removal of hydrocarbons were observed. Within a distance of 24 to 40.5 cm from the infiltration, O 2 was below 0.1 mg l −1 and a denitrifying activity was found. In the presence and in the absence of O 2, n-alkanes were preferentially degraded compared to branched alkanes. The results demonstrate that: (1) infiltration of aerobic groundwater into columns filled with aquifer material contaminated with hydrocarbons leads to a rapid depletion of O 2; (2) O 2 and NO 3− can serve as oxidants for the mineralization of hydrocarbons; and (3) the modelling of redox processes in aquifers has to consider denitrifying activity in presence of O 2. 相似文献
3.
An anaerobic plume of process-affected groundwater was characterized in a shallow sand aquifer adjacent to an oil sands tailings impoundment. Based on biological oxygen demand measurements, the reductive capacity of the plume is considered minimal. Major dissolved components associated with the plume include HCO 3, Na, Cl, SO 4, and naphthenic acids (NAs). Quantitative and qualitative NA analyses were performed on groundwater samples to investigate NA fate and transport in the subsurface. Despite subsurface residence times exceeding 20 years, significant attenuation of NAs by biodegradation was not observed based on screening techniques developed at the time of the investigation. Relative to conservative tracers (i.e., Cl), overall NA attenuation in the subsurface is limited, which is consistent with batch sorption and microcosm studies performed by other authors. Insignificant biological oxygen demand and low concentrations of dissolved As (< 10 µg L − 1) in the plume suggest that the potential for secondary trace metal release, specifically As, via reductive dissolution reactions driven by ingress of process-affected water is minimal. It is also possible that readily leachable As is not present in significant quantities within the sediments of the study area. Thus, for similar plumes of process-affected groundwater in shallow sand aquifers which may occur as oil sands mining expands, a reasonable expectation is for NA persistence, but minimal trace metal mobilization. 相似文献
4.
Chemical leak was numerically simulated for four chemical substances: benzene (light non-aqueous phase liquid (NAPL)), tetrachloroethylene (dense NAPL), phenol (soluble in water), and pentachlorophenol (white crystalline solid) in a hypothetical subsurface leak situation using a multiphase compositional transport model. One metric ton of chemical substances was assumed to leak at a point 3.51 m above the water table in a homogeneous unconfined aquifer which had the depth to water table of 7.135 m, the hydraulic gradient of 0.00097, the recharge rate of 0.7 mm/day, and the permeability of 2.92?×?10?10 m2. For comparison, surface spill scenarios, which had a long pathway from source to the water table, were simulated. Using the model results, point-source pollutant loadings to soil and groundwater were calculated by multiplying mass, impact area, and duration above and below the water table respectively. Their sensitivity to subsurface properties (depth to water table, recharge rate, porosity, organic carbon content, decay rate, hydraulic gradient, capillary pressure, relative permeability, permeability) was analyzed, with changing each parameter within acceptable ranges. The study result showed that the pollutant loading to groundwater was more sensitive to the subsurface properties than the pollutant loading to soil. Decay rate, groundwater depth, hydraulic gradient and porosity were influential to pollutant loadings. The impact of influential parameters on pollutant loadings was nonlinear. The dominant subsurface properties of pollution loadings (e.g., decay rate, groundwater depth, hydraulic gradient, and porosity for groundwater) also affect the vulnerability, and the subsurface pollutant loadings defined in this study are dependent on chemical properties as well, which indicates that the influential hydrogeological and physicochemical parameters to pollutant loadings can be used for pollution potential assessment. The contribution of this work is the suggestion that the sensitivity of pollutant loadings can be used for pollution potential assessment. Soil and groundwater pollution potential of chemicals are discussed altogether for leak scenarios. A physics-based model is used to understand the impact of subsurface properties on the fate and transport of chemicals above and below the water table, and consequently their impact on the pollutant loading to soil and groundwater. 相似文献
5.
Purpose The major aromatic constituents of petroleum products viz. benzene, toluene, and mixture of xylenes (BTX) are responsible for environmental pollution and inflict serious public concern. Therefore, BTX biodegradation potential of individual as well as formulated bacterial consortium was evaluated. This study highlighted the role of hydrogen peroxide (H 2O 2), nitrate, and phosphate in stimulating the biodegradation of BTX compounds under hypoxic condition. Materials and methods The individual bacterium viz. Bacillus subtilis DM-04 and Pseudomonas aeruginosa M and NM strains and a consortium comprising of the above bacteria were inoculated to BTX-containing liquid medium and in soil. The bioremediation experiment was carried out for 120?h in BTX-containing liquid culture and for 90?days in BTX-contaminated soil. The kinetics of BTX degradation either in presence or absence of H 2O 2, nitrate, and phosphate was analyzed using biochemical and gas chromatographic (GC) technique. Results Bacterial consortium was found to be superior in degrading BTX either in soil or in liquid medium as compared to degradation of same compounds by individual strains of the consortium. The rate of BTX biodegradation was further enhanced when the liquid medium/soil was exogenously supplemented with 0.01?% ( v/ v) H 2O 2, phosphate, and nitrate . The GC analysis of BTX biodegradation (90?days post-inoculation) in soil by bacterial consortium confirmed the preferential degradation of benzene compared to m-xylene and toluene. Conclusions It may be concluded that the bacterial consortium in the present study can degrade BTX compounds at a significantly higher rate as compared to the degradation of the same compounds by individual members of the consortium. Further, addition of H 2O 2 in the culture medium as an additional source of oxygen, and nitrate and phosphate as an alternative electron acceptor and macronutrient, respectively, significantly enhanced the rate of BTX biodegradation under oxygen-limited condition. 相似文献
6.
释氧材料经济有效的释氧是地下水原位生物修复的关键因素。实验通过在释氧材料中加入膨润土、磷酸二氢钾和硫酸铵等,改进释氧材料的性能。柱实验结果显示,该释氧材料释氧速率缓慢,释氧时间长,可以使溶液中DO长期保持在5 mg/L以上;另外,释氧材料中添加的缓冲剂及天然含水层介质对pH值有较好的缓冲作用,可以使pH值达到后续生物修复的要求。 相似文献
7.
This is the first study describing the chemical oxidation of hexachlorocyclohexanes (HCHs) in contaminated soil under water saturated and unsaturated flow through conditions. Soil contaminated with β-HCH (45 mg kg ?1) and γ-HCH (lindane, 25 mg kg ?1) was sampled from former lindane waste storage site. Efficiency of following treatments was tested at circumneutral pH: H 2O 2 alone, H 2O 2/Fe II, Na 2S 2O 8 alone, Na 2S 2O 8/Fe II, and KMnO 4. Experimental conditions (oxidant dose, liquid/solid ratio, and soil granulometry) were first optimized in batch experiments. Obtained results revealed that increasing dose of H 2O 2 improved the oxidation efficiency while in Na 2S 2O 8 system, maximum HCHs were removed at 300 mM. However, oxidation efficiency was slightly improved by Fe II-activation. Increasing the solid/liquid ratio decreased HCH removal in soil samples crushed to 500 μm while an opposite trend was observed for 2-mm samples. Dynamic column experiments showed that oxidation efficiency followed the order KMnO 4 > Na 2S 2O 8/Fe II > Na 2S 2O 8 whatever the flow condition, whereas the removal extent declined at higher flow rate (e.g., ~50% by KMnO 4 at 0.5 mL/min as compared to ~30% at 2 mL/min). Both HCH removal and oxidant decomposition extents were found higher in saturated columns than the unsaturated ones. While no significant change in relative abundance of soil mineral constituents was observed before and after chemical oxidation, more than 60% of extractable organic matter was lost after chemical oxidation, thereby underscoring the non-selective behavior of chemical oxidation in soil. Due to the complexity of soil system, chemical oxidation has rarely been reported under flow through conditions, and therefore our findings will have promising implications in developing remediation techniques under dynamic conditions closer to field applications. 相似文献
8.
The potential for aerobic biodegradation of MTBE in a fractured chalk aquifer is assessed in microcosm experiments over 450 days, under in situ conditions for a groundwater temperature of 10 °C, MTBE concentration between 0.1 and 1.0 mg/L and dissolved O 2 concentration between 2 and 10 mg/L. Following a lag period of up to 120 days, MTBE was biodegraded in uncontaminated aquifer microcosms at concentrations up to 1.2 mg/L, demonstrating that the aquifer has an intrinsic potential to biodegrade MTBE aerobically. The MTBE biodegradation rate increased three-fold from a mean of 6.6 ± 1.6 μg/L/day in uncontaminated aquifer microcosms for subsequent additions of MTBE, suggesting an increasing biodegradation capability, due to microbial cell growth and increased biomass after repeated exposure to MTBE. In contaminated aquifer microcosms which also contained TAME, MTBE biodegradation occurred after a shorter lag of 15 or 33 days and MTBE biodegradation rates were higher (max. 27.5 μg/L/day), probably resulting from an acclimated microbial population due to previous exposure to MTBE in situ. The initial MTBE concentration did not affect the lag period but the biodegradation rate increased with the initial MTBE concentration, indicating that there was no inhibition of MTBE biodegradation related to MTBE concentration up to 1.2 mg/L. No minimum substrate concentration for MTBE biodegradation was observed, indicating that in the presence of dissolved O 2 (and absence of inhibitory factors) MTBE biodegradation would occur in the aquifer at MTBE concentrations (ca. 0.1 mg/L) found at the front of the ether oxygenate plume. MTBE biodegradation occurred with concomitant O 2 consumption but no other electron acceptor utilisation, indicating biodegradation by aerobic processes only. However, O 2 consumption was less than the stoichiometric requirement for complete MTBE mineralization, suggesting that only partial biodegradation of MTBE to intermediate organic metabolites occurred. The availability of dissolved O 2 did not affect MTBE biodegradation significantly, with similar MTBE biodegradation behaviour and rates down to ca. 0.7 mg/L dissolved O 2 concentration. The results indicate that aerobic MTBE biodegradation could be significant in the plume fringe, during mixing of the contaminant plume and uncontaminated groundwater and that, relative to the plume migration, aerobic biodegradation is important for MTBE attenuation. Moreover, should the groundwater dissolved O 2 concentration fall to zero such that MTBE biodegradation was inhibited, an engineered approach to enhance in situ bioremediation could supply O 2 at relatively low levels (e.g. 2–3 mg/L) to effectively stimulate MTBE biodegradation, which has significant practical advantages. The study shows that aerobic MTBE biodegradation can occur at environmentally significant rates in this aquifer, and that long-term microcosm experiments (100s days) may be necessary to correctly interpret contaminant biodegradation potential in aquifers to support site management decisions. 相似文献
9.
We investigated groundwaters in the vicinity of a coal ash site near an electric generating station in the western U.S.A. The purpose of the study was to ascertain why fine particles or colloids appear in some subsurface water samples there. If such fine particles are merely introduced during bailing or pumping operations which suspend otherwise immobile soil colloids, we should exclude these particulate materials from the water samples before analysis intended to quantify what is moving through the aquifer. However, if the colloids were truly suspended and moving with the groundwater flow in situ, then we should includes their contribution to our assessment of the mobile loads.Application of very careful sampling techniques (slow pumping rates, no atmospheric exposure) did not cause the large quantities of colloids observed previously to disappear from well water in which they occured. Additionally, the same sampling procedures did not cause similar abundances of colloids to appear in waters collected from neighboring wells installed and developed in the same manner and in the same geologic strata. Thus we believe sampling artifacts do not explain the colloids' presence in the groundwater samples.On the other hand, the groundwater chemistry and the nature of the suspended colloids (size, composition) strongly suggest these fine particles were suspended and therefore moving with the groundwater flow. At wells exhibiting large amounts of suspended colloids (≈10–100 mg L −1), the water was enriched in CO 2 and depleted in O 2 relative to nearby locations. The colloids were typically between 0.1 and 2 μm in size and were primarily silicates. These results suggest to us that, where infiltrating water is percolating through a site that has been mixed with coal ash, the secondary carbonate mineral in the soils are being dissolved; removal of this cementing carbonate phase may consequently release soil silicate colloids to be carried in the flowing water.Such processes may enhance contaminant transport in groundwater by augmenting the pollutant load moving in the groundwater, and increasing the permeability of the porous medium to pollutant infiltration with water water and/or rainwater. 相似文献
10.
Direct decomposition of N 2O by perovskite-structure catalysts including La 2NiO 4, LaSrNiO 4, and La 0.7Ce 0.3SrNiO 4 was investigated. The catalysts were prepared by the Pechini method and characterized by x-ray diffraction (XRD), BET, scanning electron microscopy (SEM), and O 2-TPD. Experimental results indicate that the properties of La 2NiO 4 are significantly improved by partially substituting La with Sr and Ce. N 2O decomposition efficiencies achieved with LaSrNiO 4 and La 0.7Ce 0.3SrNiO 4 are 44 and 36%, respectively, at 400ºC. As the temperature was increased to 600ºC, N 2O decomposition efficiency achieved with LaSrNiO 4 and La 0.7Ce 0.3SrNiO 4 reached 100% at an inlet N 2O concentration of 1,000 ppm, while the space velocity was fixed at 8,000 hr ?1. In addition, effects of various parameters including oxygen, water vapor, and space velocity were also explored. The results indicate that N 2O decomposition efficiencies achieved with LaSrNiO 4 and La 0.7Ce 0.3SrNiO 4 are not significantly affected as space velocity is increased from 8,000 to 20,000 hr ?1, while La 0.7Ce 0.3SrNiO 4 shows better tolerance for O 2 and H 2O (g). On the other hand, N 2 yield with LaSrNiO 4 as catalyst can be significantly improved by doping Ce. At a gas hour space velocity of 8,000 hr ?1, and a temperature of 600ºC, high N 2O decomposition efficiency and N 2 yield were maintained throughout the durability test of 60 hr, indicating the long-term stability of La 0.7Ce 0.3SrNiO 4 for N 2O decomposition. Implications:Nitrous oxide (N 2O) not only has a high global warming potential (GWP 100 = 310), but also potentially destroys ozone in the stratosphere. Pervoskite-type catalysts including La 2NiO 4, LaSrNiO 4, and La 0.7Ce 0.3SrNiO 4 are applied for direct N 2O decomposition. The results show that N 2O decomposition can be enhanced as Sr and Ce are doped into La 2NiO 4. At 600ºC, N 2O decomposition efficiencies achieved with LaSrNiO 4 and La 0.7Ce 0.3SrNiO 4 reach 100%, demonstrating high activity and good potential for direct N 2O decomposition. Effects of O 2 and H 2O (g) contents on catalytic activities are also evaluated and discussed. 相似文献
11.
Abstract The traditional technologies for odor removal of thiol usually create either secondary pollution for scrubbing, adsorption, and absorption processes, or sulfur (S) poisoning for catalytic incineration. This study applied a laboratory-scale radio-frequency plasma reactor to destructive percentage-grade concentrations of odorous dimethyl sulfide (CH 3SCH 3, or DMS). Odor was diminished effectively via reforming DMS into mainly carbon disulfide (CS 2) or sulfur dioxide (SO 2). The removal efficiencies of DMS elevated significantly with a lower feeding concentration of DMS or a higher applied rf power. A greater inlet oxygen (O 2)/DMS molar ratio slightly improved the removal efficiency. In an O 2-free environment, DMS was converted primarily to CS 2, methane (CH 4), acetylene (C 2H 2), ethylene (C 2H 4), and hydrogen (H 2), with traces of hydrogen sulfide (H 2S), methyl mercaptan (CH 3SH), and dimethyl disulfide. In an O 2-containing environment, the species detected were SO 2, CS 2, carbonyl sulfide, carbon dioxide (CO 2), CH 4, C 2H 4, C 2H 2, H 2, formal-dehyde, and methanol. Differences in yield of products were functions of the amounts of added O 2 and the applied power. This study provided useful information for gaining insight into the reaction pathways for the DMS dissociation and the formation of products in the plasmolysis and conversion processes. 相似文献
12.
AbstractChlorinated volatile organic compounds are common constituents observed at many contaminated groundwater sites. Common industry practice has been to measure these constituents in groundwater on a weight concentration basis (e.g. µg/l, mg/l). This paper highlights the use of molar-based concentrations, especially in the case of parent-daughter degradation sequences commonly observed with the chloroethene, chloroethane, and chloromethane families of compounds. Converting to molar-based concentrations provides the practitioner greater insight into groundwater plume behavior including better evaluation of degradation processes, remedial progress, possible commingling, and/or sourcing. For example, this paper provides a tank analogy to evaluate whether the commonly misinterpreted observation of “DCE-stall” may be occurring at a site. Multiple examples of the benefits of using molar-based concentration data are also summarized in a project case study presented herein. As demonstrated in this paper, molarity does provide better clarity and can be a powerful evaluation tool in the groundwater practitioner’s toolbox. 相似文献
13.
Hydrogen peroxide is a widely used in situ chemical oxidation reagent which relies on catalysts to generate the suite of reactive species that are required to aggressively remediate contaminated soils and groundwater. In the subsurface environment these catalysts are usually transition metals that are added to the injected solution, or are naturally occurring. Chelating agents are widely used to maintain an adequate dissolved transition metal concentration in near-neutral pH conditions; however, they can also be used to improve the persistence of H(2)O(2) in situations when the aquifer solids have sufficient transition metal content. Ethylenediamine tetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) have been considered to be the most effective chelants and therefore are the most widely used. While previous research efforts have focused on the chelating agent efficiency, the long-term fate of these chelants in the natural subsurface environment is a concern since both EDTA and NTA are non-readily biodegradable. The focus of this investigation was to evaluate the potential of using the environmentally friendly or green chelating agent ethylenediaminedisuccinate (EDDS) as an alternative to EDTA or NTA to suppress the catalytic activity of naturally-occurring transition metals. A series of batch reactor and column experiments were performed using five different aquifer materials and the results demonstrate that EDDS has a comparative chelating efficiency to that of EDTA. The addition of EDDS was able to reduce the H(2)O(2) decomposition rates in the presence of the aquifer materials used in this investigation by 24-97% in well-mixed batch systems, and by 20% and 38% in the column trials where H(2)O(2) was detected in the effluent. 相似文献
14.
This study evaluated the feasibility of supplementing groundwater monitoring protocols by assessing the vadose zone for the extent of residual subsurface contamination. The study also characterized the response of the soil gas signatures with respect to different soil types and degrees of contamination.A field study was conducted at a former gasoline vending station located in Ottawa, Canada. The current state of contamination was determined by analysis of soil samples taken from boreholes. A series of 10 nested soil gas wells with monitoring depths of 0.75, 1.5, 2.25 and 3.0 m were then installed. Using these wells, soil gas surveys were performed at regular intervals over an extended period to quantify Gaseous TPH (TPH g), oxygen and carbon dioxide concentrations in the soil gas.Results indicate that soil gas wells located near the source term exhibited characteristic soil gas signatures and significant fluctuations in TPH g, oxygen, and carbon dioxide concentrations with time. Soil gas wells located beyond the soil contamination demonstrated limited correlation between TPH g, oxygen and carbon dioxide concentrations and decreased seasonal variability. 相似文献
15.
Dairy manure, acidified using organic acids (acetic, oxalic, and citric acid) were treated with microwave enhanced advanced oxidation process (MW/H 2O 2-AOP). The effect of a mixture of oxalic acid and commonly used mineral acids (sulfuric and hydrochloric acid) on MW/H 2O 2-AOP was also examined. Substantial amounts of phosphorus were released under MW/H 2O 2-AOP, regardless of organic acid or mineral acid used. All three organic acids were good acidifying reagents; however, only oxalic acid could remove free calcium ion in the solution, and improve settleability of dairy manure. The MW/H 2O 2-AOP and calcium removal process could be combined into a single-stage process, which could release phosphate, solubilize solids and remove calcium from dairy manure at the same time. A mixture of oxalic acid and mineral acid produced the maximum volume of clear supernatant and had an ideal molar ratio of calcium to magnesium for effective struvite (magnesium ammonium phosphate) crystallization process. A single-stage MW/H 2O 2-AOP would simplify the process and reduce mineral acid consumption compared to a two-stage operation. The results of a pilot scale study demonstrate that MW/H 2O 2-AOP is effective in treating manure and recovering resource from dairy farms. 相似文献
16.
This article reports on a field modelling study to investigate the processes controlling the plume evolution of para-toluenesulfonamide (p-TSA) in anoxic groundwater in Berlin, Germany. The organic contaminant p-TSA originates from the industrial production process of plasticisers, pesticides, antiseptics and drugs and is of general environmental concern for urban water management. Previous laboratory studies revealed that p-TSA is degradable under oxic conditions, whereas it appears to behave conservatively in the absence of oxygen (O 2). p-TSA is ubiquitous in the aquatic environment of Berlin and present in high concentrations (up to 38 μg L ?1) in an anoxic aquifer downgradient of a former sewage farm, where groundwater is partly used for drinking water production. To obtain refined knowledge of p-TSA transport and degradation in an aquifer at field scale, measurements of p-TSA were carried out at 11 locations (at different depths) between 2005 and 2010. Comparison of chloride (Cl ?) and p-TSA field data showed that p-TSA has been retarded in the same manner as Cl ?. To verify the transport behaviour under field conditions, a two-dimensional transport model was setup, applying the dual-domain mass transfer approach in the model sector corresponding to an area of high aquifer heterogeneity. The distribution of Cl ? and p-TSA concentrations from the site was reproduced well, confirming that both compounds behave conservatively and are subjected to retardation due to back diffusion from water stagnant zones. Predictive simulations showed that without any remediation measures, the groundwater quality near the drinking water well galleries will be affected by high p-TSA loads for about a hundred years. 相似文献
17.
The microwave enhanced advanced oxidation process (MW/H 2O 2-AOP) was used to treat separated solid dairy manure for nutrient release and solids reduction. The MW/H 2O 2-AOP was conducted at a microwave temperature of 120°C for 10 minutes, and at three pH conditions of 3.5, 7.3 and 12. The hydrogen peroxide dosage at approximately 2 mL per 1% TS for a 30 mL sample was used in this study, reflecting a range of 0.53–0.75 g H 2O 2/g dry sludge. The results indicated that substantial quantities of nutrients could be released into the solution at pH of 3.5. However, at neutral and basic conditions only volatile fatty acids and soluble chemical oxygen demand could be released. The analyses on orthophosphate, soluble chemical oxygen demands and volatile fatty acids were re-examined for dairy manure. It was found that the orthophosphate concentration for untreated samples at a higher % total solids (TS) was suppressed and lesser than actual. To overcome this difficulty, the initial orthophosphate concentration had to be measured at 0.5% TS. 相似文献
18.
A newly designed continuous-flow 915 MHz microwave wastewater treatment system was used to demonstrate the effectiveness of the microwave enhanced advanced oxidation process (MW/H 2O 2-AOP) for treating dairy manure. After the treatment, about 84% of total phosphorus and 45% of total chemical oxygen demand were solubilized with the highest H 2O 2 dosage (0.4% H 2O 2 per %TS). The reaction kinetics of soluble chemical oxygen demand revealed activation energy to be in the range of 5–22 kJ mole ?1. The energy required by the processes was approximately 0.16 kWh per liter of dairy manure heated. A higher H 2O 2 dosage used in the system had a better process performance in terms of solids solubilization, reaction kinetics, and energy consumption. Cost-benefit analysis for a farm-scale MW/H 2O 2-AOP treatment system was also presented. The results obtained from this study would provide the basic knowledge for designing an effective farm-scale dairy manure treatment system. 相似文献
19.
ABSTRACT Nonthermal plasma chemical decomposition of bromomethane (CH 3Br) was investigated with a coaxial type packed-bed plasma reactor. It has been demonstrated that plasma chemical processing is an effective approach to decompose CH 3Br in a wide concentration range. It has been shown that CH 3Br decomposition reactivity depends on reactor operating factors such as background gas, O 2 concentration, and humidification. Higher decomposition efficiencies can be obtained in dry N 2. However, organic byproducts such as BrCN are concurrently produced under deaerated conditions. Water suppresses CH 3Br decomposition and also affects the yields of CO x (CO and CO 2) and organic byproducts due to the involvement of some active species generated from water. The presence of O 2 retards CH 3Br decomposition by quenching high-energy electrons, while it suppresses organic byproducts and improves CO x yield. The reacted carbons in CH 3Br are recovered as CO x almost quantitatively in air. Higher CO 2 selectivities cannot be achieved by increasing O 2 concentration. NO x formation, which is accompanied by CH 3Br decomposition, can be effectively suppressed by decreasing O 2 concentration down to 2%. Furthermore, reaction mechanisms are discussed by comparing the reactivities of CH 3Br and its congeners. 相似文献
20.
The aerobic biodegradation of oxygen and nitrogen heterocycles and o-cresol by subsurface bacteria in groundwater from an oil contaminated site at Zealand, Denmark, was compared to the biodegradation of these compounds in laboratory adapted suspended and fixed-film cultures. The aquifer at the abstraction site had a relatively high redox potential, since it contained nitrate. The groundwater (i.e. without the soil phase) had a high biodegradation potential for dibenzofuran, indole, quinoline, flourenone and o-cresol. All the compounds were degraded in groundwater within 5–15 days from an initial concentration of about 0.5 mg L −1 in both mixed substrate and single substrate experiments with an initial ATP concentration of 0.2 ng mL −1. Pyrrole, however, was not degraded in groundwater within 55 days in the mixed substrate experiment and very slowly, after a lag period of 20 days, in the single substrate experiment. The biodegadability picture found for groundwater in the mixed substrate experiment was similar to the results found with laboratory adapted suspended and fixed-film cultures. None of the compounds had any inhibitory effect on the biodegradation of naphthalene. 相似文献
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