Question

Explain the slurry-phase treatment, including the pretreatment, desorption, mixer deign, soil particle and specific surface.

Answer 1

Solution:

Slurry-phase treatment:

In slurry treatment, soil is excavated and conditioned and loaded into bioreactors. A main feature of slurry treatment is that soil inside reactor is kept in aqueous suspension by some type of mixing in a way that biological treatment is carried out under saturated conditions and nearly homogeneous suspension.There are several bioreactor configurations. At full scale, low cost bioreactors may consist of large lined lagoons (24 m × 15 m). Manufactured bioreactors can range 3 to 25 m diameter and 4.5 to 8 m height, with capacities between 60 to 1000 m3. Bioreactors are usually fitted with mixing devices, and aerobic slurry treatment are equipped with spargers or diffusers. Ancillary equipment may include gas emissions conduits and treatment, vessels for nutrient and pH conditioning of slurry, etc.

Mixer deign

Mixing intensity is a critical factor in slurry treatment design and performance. Its main role is to keep solid particles in suspension and provide slurry homogeneization, to help achieving a satisfactory aeration in aerobic slurry treatments, and to increase several mass transfer rates such as desorption of pollutants from soil, among others. This, in turn, usually translates in higher rates of contaminant biodegradation, in particular when difficult-to-degrade xenobiotic compounds such as PCBs have to be removed. Mixing selection and sizing mainly depends on slurry characteristics and kinetic requirements. Pilot studies and semi-empirical methods are usually required. Independently of the type of mixer selected, mixing power is of major concern because of its influence on the operating costs.

Pretreatment

The coarser fractions of soils (pebbles and sands, 0.85 to 4 mm) are discarded and sent to direct disposal, whereas fine fractions (clay and organic matter, < 0.85 mm) are retained and loaded into bioreactors. It is generally recognized that pollutants concentrate in fine particles of soil.