978 resultados para SEDIMENT REMEDIATION


Relevância:

100.00% 100.00%

Publicador:

Resumo:

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared spectroscopy have been used to study the mineral pharmacolite Ca(HAsO4)•2H2O. The mineral is characterised by an intense Raman band at 865 cm-1 assigned to the (AsO4)3- symmetric stretching mode. The equivalent infrared band is found at 864 cm-1. The low intensity Raman band at 886 cm-1 provides evidence for (AsO3OH)2-. A series of overlapping bands in the 300 to 450 cm-1 are attributed to ν2 and ν4 bending modes. Prominent Raman bands at around 3187 cm-1 are assigned to water OH stretching vibrations and the two sharp bands at 3425 and 3526 cm-1 to the OH stretching vibrations of (HOAsO3) units.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

The main objective of this study was to perform laboratory experiments on calcium nitrate addition to sediments of a tropical eutrophic urban reservoir (Ibirite reservoir, SE Brazil) to immobilize the reactive soluble phosphorus (RSP) and to evaluate possible geochemical changes and toxic effects caused by this treatment. Reductions of 75 and 89% in the concentration of RSP were observed in the water column and interstitial water, respectively, after 145 days of nitrate addition. The nitrate application increased the rate of autotrophic denitrification, causing a consumption of 98% of the added nitrate and oxidation of 99% of the acid volatile sulfide. As a consequence, there were increases in the sulfate and iron (II) concentrations in the sediment interstitial water and water column, as well as changes in the copper speciation in the sediments. Toxicity tests initially indicated that the high concentrations of nitrate and nitrite in the sediment interstitial water (up to 2300 mg L-1 and 260 mg L-1, respectively) were the major cause of mortality of Ceriodaphnia silvestrii and Chironomus xanthus. However, at the end of the experiment, the sediment toxicity was completely removed and a reduction in the 48 h-EC50 of the water was also observed. Based on these results we can say that calcium nitrate treatment proved to be a valuable tool in remediation of eutrophic aquatic ecosystems leading to conditions that can support a great diversity of organisms after a restoration period. (C) 2012 Elsevier Ltd. All rights reserved.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

The time course of lake recovery after a reduction in external loading of nutrients is often controlled by conditions in the sediment. Remediation of eutrophication is hindered by the presence of legacy organic carbon deposits, that exert a demand on the terminal electron acceptors of the lake and contribute to problems such as internal nutrient recycling, absence of sediment macrofauna, and flux of toxic metal species into the water column. Being able to quantify the timing of a lake’s response requires determination of the magnitude and lability, i.e., the susceptibility to biodegradation, of the organic carbon within the legacy deposit. This characterization is problematic for organic carbon in sediments because of the presence of different fractions of carbon, which vary from highly labile to refractory. The lability of carbon under varied conditions was tested with a bioassay approach. It was found that the majority of the organic material found in the sediments is conditionally-labile, where mineralization potential is dependent on prevailing conditions. High labilities were noted under oxygenated conditions and a favorable temperature of 30 °C. Lability decreased when oxygen was removed, and was further reduced when the temperature was dropped to the hypolimnetic average of 8° C . These results indicate that reversible preservation mechanisms exist in the sediment, and are able to protect otherwise labile material from being mineralized under in situ conditions. The concept of an active sediment layer, a region in the sediments in which diagenetic reactions occur (with nothing occurring below it), was examined through three lines of evidence. Initially, porewater profiles of oxygen, nitrate, sulfate/total sulfide, ETSA (Electron Transport System Activity- the activity of oxygen, nitrate, iron/manganese, and sulfate), and methane were considered. It was found through examination of the porewater profiles that the edge of diagenesis occurred around 15-20 cm. Secondly, historical and contemporary TOC profiles were compared to find the point at which the profiles were coincident, indicating the depth at which no change has occurred over the (13 year) interval between core collections. This analysis suggested that no diagenesis has occurred in Onondaga Lake sediment below a depth of 15 cm. Finally, the time to 99% mineralization, the t99, was viewed by using a literature estimate of the kinetic rate constant for diagenesis. A t99 of 34 years, or approximately 30 cm of sediment depth, resulted for the slowly decaying carbon fraction. Based on these three lines of evidence , an active sediment layer of 15-20 cm is proposed for Onondaga Lake, corresponding to a time since deposition of 15-20 years. While a large legacy deposit of conditionally-labile organic material remains in the sediments of Onondaga Lake, it becomes clear that preservation, mechanisms that act to shield labile organic carbon from being degraded, protects this material from being mineralized and exerting a demand on the terminal electron acceptors of the lake. This has major implications for management of the lake, as it defines the time course of lake recovery following a reduction in nutrient loading.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

In the 1970s, acid sulfate soils (ASS) distributed within about 720 ha of predominantly mangrove and salt pan wetlands at East Trinity in north Queensland were developed after the area was isolated from tidal flooding by a surrounding seawall and the installation of tidal gates on major drainage creeks. Following drainage and oxidation of these estuarine acidic sediments, resultant acid leachate caused considerable, ongoing environmental problems including regular fish kills. A rehabilitation program covering much of these former tidal wetlands commenced in 2000 using a lime-assisted tidal exchange management regime. Changes in the established populations of estuarine fish and crustaceans were monitored in the two creeks (Firewood and Hills Creeks) where tidal flows were reinstated. In Firewood Creek between 2001 and 2005, there was a progressive increase in fish species richness, diversity and abundance. The penaeid prawn Fenneropenaeus merguiensis was a major component of the cast net catches in the lower sections of both Firewood and Hills Creeks but its relative abundance decreased upstream of the tidal gates on the seawall. Well established stocks of predominantly juvenile, male Scylla serrata resident upstream of the tidal gates indicated suitable habitats with acceptable water and sediment quality and adequate availability of food. The regular fish kills that occurred prior to the management regime abated and, overall, the implementation of the rehabilitation program is yielding positive benefits for the local fisheries.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

In Finland one of the most important current issues in the environmental management is the quality of surface waters. The increasing social importance of lakes and water systems has generated wide-ranging interest in lake restoration and management, concerning especially lakes suffering from eutrophication, but also from other environmental impacts. Most of the factors deteriorating the water quality in Finnish lakes are connected to human activities. Especially since the 1940's, the intensified farming practices and conduction of sewage waters from scattered settlements, cottages and industry have affected the lakes, which simultaneously have developed in to recreational areas for a growing number of people. Therefore, this study was focused on small lakes, which are human impacted, located close to settlement areas and have a significant value for local population. The aim of this thesis was to obtain information from lake sediment records for on-going lake restoration activities and to prove that a well planned, properly focused lake sediment study is an essential part of the work related to evaluation, target consideration and restoration of Finnish lakes. Altogether 11 lakes were studied. The study of Lake Kaljasjärvi was related to the gradual eutrophication of the lake. In lakes Ormajärvi, Suolijärvi, Lehee, Pyhäjärvi and Iso-Roine the main focus was on sediment mapping, as well as on the long term changes of the sedimentation, which were compared to Lake Pääjärvi. In Lake Hormajärvi the role of different kind of sedimentation environments in the eutrophication development of the lake's two basins were compared. Lake Orijärvi has not been eutrophied, but the ore exploitation and related acid main drainage from the catchment area have influenced the lake drastically and the changes caused by metal load were investigated. The twin lakes Etujärvi and Takajärvi are slightly eutrophied, but also suffer problems associated with the erosion of the substantial peat accumulations covering the fringe areas of the lakes. These peat accumulations are related to Holocene water level changes, which were investigated. The methods used were chosen case-specifically for each lake. In general, acoustic soundings of the lakes, detailed description of the nature of the sediment and determinations of the physical properties of the sediment, such as water content, loss on ignition and magnetic susceptibility were used, as was grain size analysis. A wide set of chemical analyses was also used. Diatom and chrysophycean cyst analyses were applied, and the diatom inferred total phosphorus content was reconstructed. The results of these studies prove, that the ideal lake sediment study, as a part of a lake management project, should be two-phased. In the first phase, thoroughgoing mapping of sedimentation patterns should be carried out by soundings and adequate corings. The actual sampling, based on the preliminary results, must include at least one long core from the main sedimentation basin for the determining the natural background state of the lake. The recent, artificially impacted development of the lake can then be determined by short-core and surface sediment studies. The sampling must be focused on the basis of the sediment mapping again, and it should represent all different sedimentation environments and bottom dynamic zones, considering the inlets and outlets, as well as the effects of possible point loaders of the lake. In practice, the budget of the lake management projects of is usually limited and only the most essential work and analyses can be carried out. The set of chemical and biological analyses and dating methods must therefore been thoroughly considered and adapted to the specific management problem. The results show also, that information obtained from a properly performed sediment study enhances the planning of the restoration, makes possible to define the target of the remediation activities and improves the cost-efficiency of the project.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The efficient remediation of heavy metal-bearing sediment has been one of top priorities of ecosystem protection. Cement-based solidification/stabilization (s/s) is an option for reducing the mobility of heavy metals in the sediment and the subsequent hazard for human beings and animals. This work uses sodium carbonate as an internal carbon source of accelerated carbonation and gaseous CO2 as an external carbon source to overcome deleterious effects of heavy metals on strength development and improve the effectiveness of s/s of heavy metal-bearing sediment. In addition to the compressive strength and porosity measurements, leaching tests followed the Chinese solid waste extraction procedure for leaching toxicity - sulfuric acid and nitric acid method (HJ/T299-2007), German leaching procedure (DIN38414-S4) and US toxicity characteristic leaching procedures (TCLP) have been conducted. The experimental results indicated that the solidified sediment by accelerated carbonation was capable of reaching all performance criteria for the disposal at a Portland cement dosage of 10 wt.% and a solid/water ratio of 1: 1. The concentrations of mercury and other heavy metals in the leachates were below 0.10 mg/L and 5 mg/L, respectively, complying with Chinese regulatory level (GB5085-2007). Compared to the hydration, accelerated carbonation improved the compressive strength of the solidified sediment by more than 100% and reduced leaching concentrations of heavy metals significantly. It is considered that accelerated carbonation technology with a combination of Na2CO3 and CO2 may practically apply to cement-based s/s of heavy metal-bearing sediment. (C) 2008 Elsevier B.V. All rights reserved.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Remediation of soil pollution is one of the many current environmental challenges. Anthropogenic activity has resulted in the contamination of extended areas of land, the remediation of which is both invasive and expensive by conventional means. Phytoextraction of heavy metals from contaminated soils has the prospect of being a more economic in situ alternative. In addition, phytoextraction targets ecotoxicologically the most relevant soil fraction of these metals, i.e. the bioavailable fraction. Greenhouse experiments were carried out to evaluate the potential of four high biomass crop species in their potential for phytoextraction of heavy metals, with or without with the use of soil amendments (EDTA or EDDS). A calcareous dredged sediment derived surface soil, with high organic matter and clay content and moderate levels of heavy metal pollution, was used in the experiments. No growth depression was observed in EDTA or EDDS treated pots in comparison to untreated controls. Metal accumulation was considered to be low for phytoextraction purposes, despite the use of chelating agents. The low observed shoot concentrations of heavy metals were attributed to the low phytoavailability of heavy metals in this particular soil substrate. The mobilising effects induced by EDTA in the soil were found to be too long-lived for application as a soil amendment in phytoextraction. Although EDDS was found to be more biodegradable, higher effect half lives were observed than reported in literature or observed in previous experiments. These findings caution against the use of any amendment, biodegradable or otherwise, without proper investigation of its effects and the longevity thereof. (C) 2005 Elsevier Ltd. All rights reserved.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The South Florida Water Management District (SFWMD) manages and operates numerous water control structures that are subject to scour. In an effort to reduce scour downstream of these gated structures, laboratory experiments were performed to investigate the effect of active air-injection downstream of the terminal structure of a gated spillway on the depth of the scour hole. A literature review involving similar research revealed significant variables such as the ratio of headwater-to-tailwater depths, the diffuser angle, sediment uniformity, and the ratio of air-to-water volumetric discharge values. The experimental design was based on the analysis of several of these non-dimensional parameters. Bed scouring at stilling basins downstream of gated spillways has been identified as posing a serious risk to the spillway’s structural stability. Although this type of scour has been studied in the past, it continues to represent a real threat to water control structures and requires additional attention. A hydraulic scour channel comprised of a head tank, flow straightening section, gated spillway, stilling basin, scour section, sediment trap, and tail-tank was used to further this analysis. Experiments were performed in a laboratory channel consisting of a 1:30 scale model of the SFWMD S65E spillway structure. To ascertain the feasibility of air injection for scour reduction a proof-of-concept study was performed. Experiments were conducted without air entrainment and with high, medium, and low air entrainment rates for high and low headwater conditions. For the cases with no air entrainment it was found that there was excessive scour downstream of the structure due to a downward roller formed upon exiting the downstream sill of the stilling basin. When air was introduced vertically just downstream of, and at the same level as, the stilling basin sill, it was found that air entrainment does reduce scour depth by up to 58% depending on the air flow rate, but shifts the deepest scour location to the sides of the channel bed instead of the center. Various hydraulic flow conditions were tested without air injection to verify which scenario caused more scour. That scenario, uncontrolled free, in which water does not contact the gate and the water elevation in the stilling basin is lower than the spillway crest, would be used for the remainder of experiments testing air injection. Various air flow rates, diffuser elevations, air hole diameters, air hole spacings, diffuser angles and widths were tested in over 120 experiments. Optimal parameters include air injection at a rate that results in a water-to-air ratio of 0.28, air holes 1.016mm in diameter the entire width of the stilling basin, and a vertically orientated injection pattern. Detailed flow measurements were collected for one case using air injection and one without. An identical flow scenario was used for each experiment, namely that of a high flow rate and upstream headwater depth and a low tailwater depth. Equilibrium bed scour and velocity measurements were taken using an Acoustic Doppler Velocimeter at nearly 3000 points. Velocity data was used to construct a vector plot in order to identify which flow components contribute to the scour hole. Additionally, turbulence parameters were calculated in an effort to help understand why air-injection reduced bed scour. Turbulence intensities, normalized mean flow, normalized kinetic energy, and anisotropy of turbulence plots were constructed. A clear trend emerged that showed air-injection reduces turbulence near the bed and therefore reduces scour potential.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Eutrophication is a persistent problem in many fresh water lakes. Delay in lake recovery following reductions in external loading of phosphorus, the limiting nutrient in fresh water ecosystems, is often observed. Models have been created to assist with lake remediation efforts, however, the application of management tools to sediment diagenesis is often neglected due to conceptual and mathematical complexity. SED2K (Chapra et al. 2012) is proposed as a "middle way", offering engineering rigor while being accessible to users. An objective of this research is to further support the development and application SED2K for sediment phosphorus diagenesis and release to the water column of Onondaga Lake. Application of SED2K has been made to eutrophic Lake Alice in Minnesota. The more homogenous sediment characteristics of Lake Alice, compared with the industrially polluted sediment layers of Onondaga Lake, allowed for an invariant rate coefficient to be applied to describe first order decay kinetics of phosphorus. When a similar approach was attempted on Onondaga Lake an invariant rate coefficient failed to simulate the sediment phosphorus profile. Therefore, labile P was accounted for by progressive preservation after burial and a rate coefficient which gradual decreased with depth was applied. In this study, profile sediment samples were chemically extracted into five operationally-defined fractions: CaCO3-P, Fe/Al-P, Biogenic-P, Ca Mineral-P and Residual-P. Chemical fractionation data, from this study, showed that preservation is not the only mechanism by which phosphorus may be maintained in a non-reactive state in the profile. Sorption has been shown to contribute substantially to P burial within the profile. A new kinetic approach involving partitioning of P into process based fractions is applied here. Results from this approach indicate that labile P (Ca Mineral and Organic P) is contributing to internal P loading to Onondaga Lake, through diagenesis and diffusion to the water column, while the sorbed P fraction (Fe/Al-P and CaCO3-P) is remaining consistent. Sediment profile concentrations of labile and total phosphorus at time of deposition were also modeled and compared with current labile and total phosphorus, to quantify the extent to which remaining phosphorus which will continue to contribute to internal P loading and influence the trophic status of Onondaga Lake. Results presented here also allowed for estimation of the depth of the active sediment layer and the attendant response time as well as the sediment burden of labile P and associated efflux.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Mode of access: Internet.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The South Florida Water Management District (SFWMD) is responsible for managing over 2500 miles of waterways and hundreds of water control structures. Many of these control structures are experiencing erosion, known as scour, of the sediment downstream of the structure. Laboratory experiments were conducted in order to investigate the effectiveness of two-dimensional air diffusers and plate extensions (without air injection) on a 1/30 scale model of one of SFWMD gated spillway structures, the S65E gated spillway. A literature review examining the results of similar studies was conducted. The experimental design for this research was based off of previous work done on the same model. Scour of the riverbed downstream of gated spillway structures has the potential to cause serious damage, as it can expose the foundation of the structure, which can lead to collapse. This type of scour has been studied previously, but it continues to pose a risk to water control structures and needs to be studied further. The hydraulic scour channel used to conduct experiments contains a head tank, flow straighteners, gated spillway, stilling basin, scour chamber, sediment trap, and tailwater tank. Experiments were performed with two types of air diffusers. The first was a hollow, acrylic, triangular end sill with air injection holes on the upstream face, allowing for air injection upstream. The second diffuser was a hollow, acrylic rectangle that extended from the triangular end sill with air injection holes in the top face, allowing for vertical air injection, perpendicular to flow. Detailed flow and bed measurements were taken for six trials for each diffuser ranging from no air injection to 5 rows of 70 holes of 0.04" diameter. It was found that with both diffusers, the maximum amount of air injection reduced scour the most. Detailed velocity measurements were taken for each case and turbulence statistics were analyzed to determine why air injection reduces scour. It was determined that air injection reduces streamwise velocity and turbulence. Another set of experiments was performed using an acrylic extension plate with no air injection to minimize energy costs. Ten different plate lengths were tested. It was found that the location of deepest scour moved further downstream with each plate length. The 32-cm plate is recommended here. Detailed velocity measurements were taken after the cases with the 32-cm plate and no plate had reached equilibrium. This was done to better understand the flow patterns in order to determine what causes the scour reduction with the extension plates. The extension plate reduces the volume of scour, but more importantly translates the deepest point of scour downstream from the structure, lessening the risk of damage.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The application of spectroscopy to the study of contaminants in soils is important. Among the many contaminants is arsenic, which is highly labile and may leach to non-contaminated areas. Minerals of arsenate may form depending upon the availability of specific cations for example calcium and iron. Such minerals include carminite, pharmacosiderite and talmessite. Each of these arsenate minerals can be identified by its characteristic Raman spectrum enabling identification.

Relevância:

20.00% 20.00%

Publicador: