Sediment Treatment Options

Techniques for in situ sediment treatment are still in an early stage of development, and the very few methods currently commercially available are usually restricted to situations where the low water levels allow for water flow diversion. Potential in situ treatment methods include biological, chemical, and stabilization processes. The main advantage relies upon avoiding sediment removal and, therefore, the related risk of spreading the contamination. However, technical limitations to the application of in situ treatments still exist, mainly because the effective delivery of such process reagents as substrates, nutrients, and chemicals, as well as mixing with the contaminated material, may be problematic. 

ELECTRO KINETIC TREATMENT OF CONTAMINATED MARINE SEDIMENTS 

Biological treatments have been applied on either slurry or solid phase. Since the remediation performance can be reduced by the presence of chloride and high heavy metal contents, a pretreatment (e.g. mechanical or chemical washing) may be necessary. 

In the framework of a land reclamation project, electrokinetics was applied in combination with preloading and prefabricated vertical drains to improve the mechanical strength of marine sediments intermittent current and noninsulated electrodes were adopted (Lo et al, 2000). The results showed that the mechanical properties of sediment were signiflcantly improved in the vicinity of the electrodes after 22-34 days, by applying voltage gradients ranging between 9.5 and 28.2V/m. 

Electrokinetics has also been tested as a means to increase the free settling velocity and the solids concentration of river sediments (Buckland, Shang, and Mohamedelhassan, 2000). The best results were obtained through a combination of electrokinetics and conditioning with FeCb. It was concluded that electrokinetic sedimentation is more effective than chemical coagulation. 

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Biological effects-based assessment of the ex situ quality of dredged sediments (ex situ BEBA) in order to select sediment management options (e.g. free or confined disposal or treatment options). 

Pretreatment is necessary for the treatment of the food industry wastewater. Pretreatment options such as flow equalization and neutralization, screening, FOG separation, acidification, coagulation-flocculation, sedimentation, and DAF are available. Selecting the appropriate technology depends on the wastewater characteristics. 

In this framework, electrokinetic treatment/remediation can be considered as a promising technique, since it is able to treat fine and low-permeability materials, can also be applied in situ (although detrimental influence of specific site conditions on system performance should be carefully considered), and may represent a possible single-stage option to achieve dewatering, consolidation, and removal of organic and inorganic pollutants as well as (for marine sediments) salts. 

Alternative 2 can be further broken down into active decontamination techniques and into more passive techniques, such as composting and phytoremediation. Table 32.1 presents the typical sediment remediation techniques used. In situ treatment, however, is another option. 

Membrane bioreactors are an option for municipal wastewater treatment when high effluent water quality is required, for example, bathing water quality, or when the receiving water body is very sensitive or when the water is to be treated for reuse. As mentioned before (see Section 9.2.5.1), the effluent quality is superior to that of secondary sedimentation. To attain a similar effluent quality by conventional treatment, effluent filtration and disinfection would be required in addition. This needs to be taken into account when comparing the cost of MBR and conventional activated sludge treatment. 

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